Round Trip to Orbit: Human Spaceflight

Alternatives

August 1989

NTIS order #PB89-224661
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Round Trip to Orbit: Human Spaceflight

Alternatives Special Report, OTA-ISC-419 (Washington, DC: U.S. Government Printing

Office, August 1989).

Library of Congress Catalog Card Number 89-600744

For sale by the Superintendent of Documents

U.S. Government Printing Office, Washington, DC 20402-9325

(order form can be found in the back of this special report)
Forewor d

In the 20 years since the first Apollo moon landing, the Nation has moved well beyond

the Saturn 5 expendable launch vehicle that put men on the moon. First launched in 1981, the

Space Shuttle, the world’s first partially reusable launch system, has made possible an array

of space achievements, including the recovery and repair of ailing satellites, and shirtsleeve

research in Spacelab. However, the tragic loss of the orbiter Challenger and its crew three and

a half years ago reminded us that space travel also carries with it a high element of risk-both

to spacecraft and to people.

Continued human exploration and exploitation of space will depend on a fleet of versatile

and reliable launch vehicles. As this special report points out, the United States can look

forward to continued improvements in safety, reliability, and performance of the Shuttle

system. Yet, early in the next century, the Nation will need a replacement for the Shuttle. To

prepare for that eventuality, NASA and the Air Force have begun to explore the potential for

advanced launch systems, such as the Advanced Manned Launch System and the National

Aerospace Plane, which could revolutionize human access to space. Decisions taken now will

affect the future of spaceflight in the 21st century.

This special report examines a wide range of potential improvements to the Space Shuttle,

explores the future of space transportation for humans, and presents policy options for

congressional consideration. It is one of a series of products from abroad assessment of space

transportation technologies undertaken by OTA, requested by the Senate Committee on

Commerce, Science, and Transportation, and the House Committee on Science, Space, and

Technology. In the past year, OTA has published a special report, Launch Options for the

Future: A Buyer’s Guide, a technical memorandum, Reducing Launch Operations Costs: New

Technologies and Practices, and a background paper, Big Dumb Boosters: A Low-Cost Space

Transportation Option?

In undertaking this effort, OTA sought the contributions of a wide spectrum of

knowledgeable individuals and organizations. Some provided information, others reviewed

drafts. OTA gratefully acknowledges their contributions of time and intellectual effort. OTA

also appreciates the help and cooperation of NASA and the Air Force. As with all OTA reports,

the content of this special report is the sole responsibility of the Office of Technology

Assessment and does not necessarily represent the views of our advisors or reviewers.

- Directo r
Advisory Panel on Round Trip to Orbit:

Human Spaceflight Alternatives

M. Granger Morgan, Chairman

Head, Department of Engineering and Public Policy

Camegie-Mellon University

I.M. Bernstein

Provost and Academic Vice President

Illinois Institute of Technology

Michael A. Berta

Assistant Division Manager

Space and Communications Group

Hughes Aircraft Company

Richard E. Brackeen

President & CEO

Matra Aero Space, Inc.

Preston Craig

Chief Scientist

United Technologies Space Flight Systems

Edward T. Gerry

President

W. J. Schafer Associates, Inc.

Jerry Grey

Director, Science and Technology Policy

American Institute of Aeronautics and Astronautics

William H. Heiser

Consultant

Otto W. Hoemig, Jr.

Vice President

Contel/American Satellite Corporation

Donald B. Jacobs

Vice President, Space Systems Division

Boeing Aerospace Company

John Logsdon

Director, Graduate Program in Science,

Technology and Public Policy

George Washington University

Hugh F. Loweth

Consultant

Anthony J. Macina

Program Manager

IBM Federal Systems Division

George B. Merrick

Vice President

North American Space Operations

Rockwell International Corporation

Alan Parker

Consultant

Gerard Piel

Chairman Emeritus

Scientific American

Bryce Poe, II

General, USAF (retired)

Consultant

Ben R. Rich

Vice President and General Manager

Lockheed Corporation

Sally K. Ride

Professor, Center for International Security

and Arms Control

Stanford University

Tom Rogers

President

The Sophron Foundation

Richard G. Smith

Senior Vice President

JLC Aerospace Corporation

William Zersen

Consultant

NOTE: OTA appreciates the valuable assistance and thoughtful critiques provided by the advisory panel members. The views

expressed in this OTA report, however, are the sole responsibility of the Office of Technology Assessment. Participation on

the advisory panel does not imply endorsement of the report.
OTA Project Staff on Round Trip to Orbit:

Alternatives for Human Spaceflight

Lionel S. Johns, Assistant Director, OTA

Energy, Materials, and International Security Division

Alan Shaw, International Security and Commerce Program Manager (from March 1989)

Peter Sharfman, International Security and Commerce Program Manager (through February 1989)

Ray A. Williamson, Project Director (from January 1989)

Richard DalBello, Project Director (until January 1989)

Eric O. Basques

Michael B. Callaham

Arthur Charo

Gordon Law

Contractor

Leonard David

Administrative Staff

Jannie Home (through November 1988)

Cecile Parker (through March 1989)

Jackie Robinson

Louise Staley
Acknowledgments

The following organizations generously provided OTA with information and suggestions:

Boeing Aerospace Company National Aero-Space Plane Joint Program Office

General Dynamics National Aero-Space Plane Interagency Office

McDonnell Douglas Pratt & Whitney

Morton Thiokol Rocketdyne Division of Rockwell International

NASA Headquarters Corporation

NASA Johnson Space Center Rockwell International Corporation

NASA Kennedy Space Center United Technologies Corporation

NASA Langley Research Center U.S. Air Force Cape Canaveral Air Force Station

NASA Marshall Space Flight Center U.S. Air Force Directorate of Space Systems

This report has also benefited from the advice of many space transportation experts from the Government and the

private sector. OTA especially would like to thank the following individuals for their assistance and support. The views

expressed in this report, however, are the sole responsibility of the Office of Technology Assessment.

James Bain

NASA

Paul Bialla

General Dynamics

Robert Barthelemy

NASP Joint Program Office

Darrell Branscome

NASA

Benjamin Buchbinder

NASA

Wallace Burnett

Rockwell International

Jerry Craig

NASA

Charles Darwin

NASA

John Gaines

General Dynamics

Daniel Gregory

Boeing Aerospace Company

Charles Gunn

NASA

Ron Harris

NASA

Capt. David Hart

US. Navy

NASP Interagency Office

Daniel Herman

NASA

Clay Hicks

Rockwell International

William J. Huffstetler

NASA

Ned Hughes

NASA

Robert A. Jones

NASA

David Kennison

Pratt & Whitney

Jack Kerrebrock

Massachusetts Institute of Technology

C. V. Lewis

Rockwell International

David Moore

Congressional Budget Office

Wally McClure

Rockwell International Corporation

Scott Pace

The Rand Corporation

Maj. Robert Preston

U.S. Air Force

Bill Rock

NASA

Robert Rosen

NASA

Thaddeus Shore

Strategic Defense Initiative

Organization

W. H. Siegfried

McDonnell Douglas

Maj. Jess Sponable

U.S. Air Force

NASP Joint Program

William Strobl

General Dynamics

Ted Talay

NASA

Charles Teixeira

NASA

Lowell Zoeller

NASA

Office
Related OTA Reports

Civilian Space

Advanced Space Transportation Technologies Assessment

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NOTE: Reports are available through the U.S. Government Writing Office, Superintendent of Documents, Washington, DC 20401

(202) 783-3238; and the National Technic~ Information Sewice, 5285 POII Royal Road, Spriwfieki, VA 22161, (703 )

487-4650.

vii
Congressional Alternatives for Crew-Carrying Launch Systems

If Congress wishes to continue to improve the safety, reliability, performance, and/or

economy of crew-carrying launch systems, it has a number of alternatives from which to choose.

Several are listed below; they are not mutually exclusive, nor is the list exhaustive. Congress

could decide to proceed with one or more from each list of options.

Because of the long lead times for the development of space transportation systems, some

decisions will have to be made in the next year or two. Others can wait until the middle of the

next decade or later.

Near-Term Decisions

If Congress wishes to: Then it could:

Improve Shuttle system safety ● Fund development of Liquid-fueled Rocket Boosters (LRBs).

and reliability: . Fund continued development and improvement of Advanced Solid Rocket Motors (ASRMs) and alternate

(See ch. 3.) turbopumps for the Space Shuttle Main Engines

● Fund continued gradual improvement of Redesigned Solid

Rocket Motors (RSRMs).

● Fund installation of built-in test equipment in the Shuttle

and more automated test equipment in launch facilities.

High confidence in the safety or reliability of LRBs,

ASRMs or other new systems would require many flight

tests.

Improve Shuttle system ● Fund development of LRBs.

performance (payload carried ● Fund continued development of ASRMs.

per flight): ● Fund improvement of RSRM thrust.

● Fund development of lighter External Tanks.

(See ch. 3.) ● Fund procurement of a new orbiter made of new,

lightweight materials,

● Fund procurement of a new orbiter capable of flying

unpiloted.

LRBs offer the greatest performance increase. In

principle they could lead to improved mission safety.

Maintain a sustainable

Shuttle launch rate of 9 to

11 launches per year:

(See ch. 3.)

. . . VIII

● Fund the purchase of at least one additional orbiter to be

delivered as soon as possible (1996), and direct NASA to

minimize the number of Shuttle flights flown per year.

NASA could reduce Shuttle flights by:

a. postponing or canceling some planned Shuttle launches;

or

b. relying more on expendable launch vehicles, such as Titan

IVs.
Reduce risks to fleet

capabilities during

Space Station

assembly:

A four-orbiter fleet is required to sustain a Shuttle launch

rate of 9-11 launches per year. Shuttle reliability is uncertain

but may lie between 97% and 9990. If it is 98%, there is a 50%

probability of losing one orbiter about every three years

assuming a launch rate of 11 per year. Higher launch rates

would require additional launch facilities.

Purchasing an additional orbiter would provide a hedge

against attrition. Minimizing the number of flights per year

would reduce the probability of attrition before Endeavour

enters service.

● Direct NASA to buy and use Titan IV launch vehicles, or

develop and use Shuttle-C launch vehicles, to carry some

Space Station elements to orbit.

● Fund immediate procurement of one or more additional

orbiters.

(See ch. 3.)

The first option would reduce the number of Shuttle flights

required for assembly (from 21 to 10, if Shuttle-C is used)

and the risk to the Shuttle and Shuttle crews. The second

option would hedge against the effects of attrition.

Reduce risks to successful Space

Station assembly:

(See ch. 3.)

Develop the

for building

ing

technology base

new crew-carrylaunch systems:

(See chs. 4 & 5.)

Provide for emergency crew

return from the Space Station:

(See ch. 6.)

Direct NASA to develop and use Shuttle-C to carry some

Space Station elements to orbit. (This would reduce the

total number of flights required and might reduce the risk

of losing an element.)

Continue to fund technology development and test efforts

such as:

a. the National Aero-Space Plane program; or

b. the Advanced Launch System program.

ALS or NASP technology could be used in the Personnel

Launch System or the Advanced

proposed by

● Fund a program to develop:

a. a capsule for Space Station

Manned Launch System

escape; or

b. a glider for Space Station escape.

However, the improvement to Space Station crew safety

that a crew emergency return vehicle might provide is highly

uncertain. ix
Far-Term Decisions

If Congress wishes to: Then it could:

Build safer, more reliable crew; ● Fund development of safer, more reliable launch systems

carrying launch systems: to augment or succeed the Shuttle. These might include:

a. a Personnel launch system (PLS), or

(See chs. 4 & 5) b. an Advanced Manned Launch System (AMLS), or

c. vehicles derived from the National Aero-Space Plane

program.

These systems are being designed to survive some types

of engine failure and could have crew escape systems.

However, designs have not been chosen, nor have detailed

safety assessments been performed.

Improve launch system

reliability:

(See chs. 3,4, 5)

Lower launch cost:

(See chs. 4&5)

● Fund development of launch vehicles or systems (e.g.

Space Transportation Main Engines) that could be

manufactured, integrated, and launched by highly automated methods with improved process control. Faulttolerant system design may be useful if critical components are not sufficiently reliable.

● Fund development of vehicles designed for quick turnaround, such as those being considered for an Advanced

Manned Launch System or as possible successors to the

proposed National Aero-Space Plane test vehicle (X-30).

Vehicles derived from the NASP X-30 may have greater

potential to reduce launch costs compared with two-stage

AMLS configurations. However, they would be more risky

to develop and would likely be available later.

x
Selected Options for Improving the Space Shuttle System

The following options were selected from a wide range of possible improvements to the Space Shuttle

System. The effectiveness of each option represents OTA’S considered judgement. However, each may be

more or less effective depending upon other improvements chosen and the pace at which they are implemented.

ObjectIves

Options

Major investment

1.

2.

3.

4.

5.

6.

Continue to develop the Advanced Solid

Rocket Motors (ASRMs)

Fund development of Liquid Rocket Boosters (LRBs)

Develop Shuttle-C

Fund purchase of one or more additional

orbiters

Fund development of capsule or glider for

Space Station escape

Institute integrated long-term program to

improve reliability, safety, and performance of Space Shuttle system

Supporting improvements

1.

2.

3.

4,

5.

6.

7.

Continue to improve the Redesigned Solid

Rocket Motors (RSRMs)

Incorporate built-in test equipment in existing launch vehicles and develop additional automated test equipment for

launch facilities

Develop lighter weight External Tank

(ET)

Develop lightweight structures for Shuttle

orbiter

Modify orbiter for automatic flight capability

Fund technology development and test

efforts

Shift all payloads not requiring crews from

Shuttle to expendable launch vehicles to

reduce Shuttle flight rate

KEY: *** . Very effectwe

** . Moderately effective

* . Somewhat effectw xi
Contents

Page

Chapter 1. Executive Summary.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 2. Issues and Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Chapter 3. Space Shuttle Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Chapter 4. Advanced Rockets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Chapter 5. The National Aero-Space Plant, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Chapter 6. Escape and Rescue Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Appendix A: Benefits and Drawbacks of Liquid Rocket Boosters for the Space Shuttle . . . . . . 105

Appendix B: From Take-Off to Orbit-The X-30 propulsion System. . . . . . . . . . . . . . . . . . . . . . . 109

Appendix C: NASP Materials and the X-30 Materials Consortium. . . . . . . . . . . . . . . . . . . . . . . . . 111

Appendix D: The Defense Science Board Report on NASP............,.., ............... 114

Appendix E: Recent Accomplishments of the NASP Program-An Abbreviated List

Supplied by The NASP Interagency Office.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

xii

CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

People in Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. .. ... .. O.. .O....

Space Transportation Options for the Next Decade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Purchasing Additional Space Shuttle Orbiters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Improving the Space Shuttle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Rescue or Escape Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Options for the Next Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Personnel Carrier Launched on Automated Launch Vehicles . . . . . . . . . . . . . . . . . . . . . . . .

Advanced Manned Launch System (AILS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Building an Aerospace Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Space Transportation and the Space Station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Technology Base for Piloted Spaceflight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Government Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Private Sector Role. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Internationa lCompetition and Cooperation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Boxes

3

3

4

4

5

10

11

11

12

12

15

16

16

17

18

18

18

Box Page

l-A. Maintaining and Improving the Current Shuttle System. . . . . . . . . . . . . . . . . . . . . . . . . . 7

I-B. Escape Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

l-C. Advanced Manned Launch Systems (AILS)... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

l-D. What Is the National Aero-Space Plane Program?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

l-E. Government Space Technology Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure

Figure Page

l-1. Shuttle Fleet Attrition if Orbiter Reliability is 98 Percent. . . . . . . . . . . . . . . . . . . . . . . . . 6
Chapter 1

Executive Summary

INTRODUCTION

In the early part of the next century, the

National Aeronautics and Space Administration

(NASA) and the Department of Defense (DoD)

intend to build new, advanced launch systems to

carry crews to space. In the interim, NASA

hopes to make Space Shuttle launches more

routine. Between now and the end of the century

NASA expects to employ the Space Shuttle to

conduct scientific and engineering research, to

launch space probes and satellites, and—in

partnership with Canada, the European Space

Agency, and Japan—to establish a permanent

human presence in space on the planned international Space Station.

This special report examines technologies

and systems for transporting astronauts and

scientists to and from low-Earth orbit, and

explores some of the policy choices that Congress faces in this critical aspect of the U.S.

Government’s space program. The report analyzes a variety of ways to make the Space

Shuttle system safer and more reliable. It also

explores several proposed systems to replace the

Shuttle early in the next century, and examines

proposals for a Space Station crew escape

system. Finally, the report discusses the most

advanced proposed launch system, the National

Aero-Space Plane, and compares it with other

potential future launch systems. The report does

not examine cargo-only launch vehicles except

insofar as their use may affect the need for

crew-carrying launchers.

OTA prepared this special report as part of an

assessment of advanced space transportation

technologies requested by the Senate Committee on Commerce, Science, and Transportation

and the House Committee on Science, Space,

and Technology. For this assessment, OTA has

previously published a special report, Launch

Options for the Future: A Buyer’s Guide; l 

a

technical memorandum, Reducing Launch Operations Costs: New Technologies and Practices,2 and a background paper, Big Dumb

Boosters: A Low-Cost, Transportation Option?3 A final report will summarize the findings

of these interim documents.

PEOPLE IN SPACE

Since 1961, when President Kennedy called

for a program to send men to the moon and back,

NASA’s “manned”4 space efforts have determined much of the direction and spending of the

government’s civilian space program. Today,

NASA’s projects involving humans in space,

primarily the existing Space Shuttle and the

planned Space Station, consume between 65 and

70 percent of NASA’s space budget, or between

$6.8 billion and $7.3 billion in fiscal year 1989.5

From the early days of the U.S. space

program, experts have argued over the appropriate mix of crew and automated civilian space

activities. Although employing people in space

to conduct most science research and exploration dramatically raises the costs compared to

automated approaches, the perceived national

and international benefits of having U.S. and

foreign citizens live and work in space have

nevertheless sustained the human component of

the civilian space program.

Assessing the most appropriate mix of spending on automated and crew-dependent activities

IU.S, Congess, of~ce of ~ttno109 Assessment, OTA-ISC-383 (Washington, DC: U.S. Government F’tktkg OffiCC, July 1988).

Zu.s. Congess, Office of RCtUIOIO~ Assessment, OTA-TM-ISC-28 (Washington, DC: U.S. Government Printing Office, September 1988).

31-J.s. Conmss, office of Technology Assessment (Washington, DC: Office of ‘Rxhnology Assessment, Februq 1989).

4~c tcms pi]ol~ or Crew-cqing are used in this report in heu Of ‘manned.”

s~e= fiws exclude w mi[jlon for ~ronautics. me fiscal year 1990 civilian space budget request of $12.8 billion (which excludes $463 million

for aeronautics) allocates about 71 percent to programs supporting crews in space. Most of President Bush’s 20 percent requested budget increase for

NASA for fiscal year 1990 derives from scheduled increases in the request for the Space Station.

– 3 –
4 ● Round Trip to orbit: Human Spaceflight Alternatives

is beyond the scope of this report. However,

existing U.S. policy calls for expanding 66human

presence and activity beyond Earth orbit into

the solar system."6 Pursuing this policy ‘n

earnest would eventually require markedly

increased funding of the government’s civilian activities involving people in space, and

therefore additional space transportation capability. Major projects requiring crews in space

could include the construction of a permanent

base on the Moon, or the exploration of Mars.

These, or other projects in the early part of the

next century, would require the support of

substantial in-orbit infrastructure, such as a

space station, orbital maneuvering vehicles, and

fuel storage depots. The pace and timing of such

expansion will depend on the willingness of

Congress, on behalf of U.S. taxpayers, to

support such activities in competition with other

uses of public monies.

In contrast to the civilian space program, the

DoD has not identified a firm requirement for

placing people in space.7 However, if military

needs were eventually to dictate a requirement

for the procurement of a fleet of aerospace

planes, as is contemplated by supporters of the

National Aero-Space Plane program, this development could lead to a major commitment by

the DoD to crews in space.

Expanded commitment to placing crews in

space for the civilian and/or military space

programs would eventually entail developing

new launchers and other space vehicles capable of transporting people. It would also

require increased yearly outlays for space

transportation.

Spaceflight is inherently risky. As America’s

reaction to the Challenger disaster suggested,

the loss of another Shuttle orbiter and its crew

would likely result in another long standdown of

the Space Shuttle, with attendent loss of momentum in the civilian space program. It would

most certainly lead to a painful reexamination of

the space program’s purpose and direction. Yet,

as the following section makes clear, the United

States should expect the loss of another orbiter

(though not necessarily with loss of life) at some

time in the next decade. If the United States

wishes to send people into space on a routine

basis, the Nation will have to come to grips

with the risks of human spaceflight. In

particular, it will have to accept the likelihood that loss of life will occur. If such risks

are perceived to be too high, the Nation may

decide to reduce its emphasis on placing

humans in space.

SPACE TRANSPORTATION OPTIONS

FOR THE NEXT DECADE

NASA and the aerospace community have

begun to consider how best to maintain or

enhance crew-carrying capacity for the next

decade, as well as for the beginning of the next

century. Decisions concerning systems that

would be developed for use in the next decade

must be made in the immediate future because

of the lead times required for these highly

complex systems. Cost and schedule will constrain the decisions on these systems.

Purchasing Additional Space Shuttle Orbiters

To reduce the risk of costly delay in

constructing or operating the Space Station,

or meeting other NASA and DoD missions,

NASA will have to add one or more orbiters

to its existing Shuttle fleet by the mid-1990s

and restrict the use of Shuttle to essential

payloads. Current plans call for reaching 14

Shuttle flights per year by 1993, one year after

NASA expects to add orbiter OV-105 (Endeavor), now under construction, to the fleet to

replace Challenger. If the existing three orbiters

8 are still operating at that time, the Shuttle

~e White House, “National Space Policy,” Fact Sheet, Feb. 11, 1988, p. 1.

71~~, tic Secre[q of Defense recently decided to cut spending on the National Aero-Space Plane program dramaticdly.

g~e flint now consists of Columbia, Dticovery, and Atlantis.
Chapter 1--Executive Summary ● 5

fleet will then consist of four orbiters. However,

continued dependence on only four orbiters

could be risky (figure 1-l). Launching each

orbiter three or four times every year creates a

growing cumulative risk of accidents or “wear

out; ‘ ‘ supporting the Space Station in addition to

other crew-related missions would be difficult if

not impossible with fewer than four orbiters. In

addition to adding resilience to Space Station

operations, building one or more additional

orbiters would also help preserve existing expertise and manufacturing ability.

If major structural spares9 were in the inventory, construction of an additional orbiter would

take about 5 years and cost about $2.5 billion,

including the cost of replacing the spares. In the

absence of structural spares to draw on, construction would take about 6 years. Therefore,

should Congress decide that it is important to

have another orbiter as soon as possible (1996),

it could either:

. fund NASA to build an additional orbiter

starting in fiscal year 1990; or

. fund NASA to order structural spares in

fiscal year 1990 and defer a final decision

on whether to build the orbiter until the

fiscal year 1991 budget is decided.

Some structural spares are needed for the

existing fleet in any case, so a decision in 1990

to purchase structural spares would not commit

Congress to fund construction of an additional

orbiter, but could provide necessary backup to

the four-orbiter fleet.

Improving the Space Shuttle

NASA is considering ways to extend the

useful lifetime of the Shuttle fleet by replacing

or enhancing Shuttle subsystems, such as avionics, structural components, and computers, and

by improving launch operations procedures

(box 1-A). Improvements, some of which have

Photo credit: National Aeronautics and Space Administration

Drawing of Space Shuttle orbiter, showing payload bay

doors open.

been made or are under way, might keep the

Shuttle fleet flying until 2010 or beyond.10

Minor improvements to the existing orbiter,

external tank, solid rocket boosters, and facilities could be accomplished during the regularly

scheduled structural inspection program (every

3 years). Major improvements to orbiters would

take a substantial commitment of NASA’s

energies, and a major funding commitment from

Congress. Improvements in the form of weight

reduction modifications or performance increases could boost the Shuttles carrying capacity or provide the opportunity to construct an

enhanced crew escape capability.

There is no way to know with certainty when

it is wiser to improve existing technology (the

evolutionary approach) or to leap to a new

generation of technology (the revolutionary

approach). Historically, the Nation has followed

a revolutionary path of technology development

when the perceived important future needs

could not be met by improving the existing

system, or when breakthroughs in technology

made dramatic new systems possible. Neither

of these conditions exist today with respect to

the Shuttle system. Evolutionary improve-

%uch as the aft fuselage module, crew comp~ent modde, or w@F

l~5uma(e5 of ~]Ife[lme of tie Shutfle flwt VW from about 2~5 to 2020,” depending on the flight rate, proposed upgrades, and number of orbiters

purchased.
6 ● Round Trip to Orbit: Human Spaceflight Alternatives

Figure l-l-Shuttle Fleet Attrition if Orbiter Recovery Reliability is 98 percent.

1

0.5

n .

Probability of having at least three or four orbiters

after flight 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

begin

I

Endeavour complete

Space station assembly

(OV=1O5)

on line

Shuttle reliability is uncertain, but has been estimated to range between 97 and 99 percent.’ If the Shuttle reliability is 98 percent, there

would be a 50-50 chance of losing an orbiter within 34 flights. At a rate of 11 flights per year, there would be a 50 percent probability of losing

an orbiter in a period of just over three years. The probability of maintaining at least three orbiters in the Shuttle fleet declines to less than

50 percent after flight 113.

Although loss of an orbiter would not necessarily result in loss of life, it would severely impede the progress of the civilian space program,

as it would likely lead to a long standdown of the orbiter fleet while the cause of the failure was determined and repaired. Seen in terms

of Space Station construction, if the probability of recovering an orbiter were 98 percent, the probability of retaining four operational orbiters

would be only 28 percent when Space Station construction begins on flight 92 and only 12 percent when the Phase I Space Station is

completed 42 flights later. IL.s@~~S, Ire., s~/u#wuff~.c @wstjofls, IWrks, and GM Adywss, LSYS48a8 (El %N*. CA: 1-).

SOURCE: Oft&x of Technokqy Assessment, 1989.

ments would allow NASA to increase human

spaceflight capabilities incrementally for lower

cost and technical risk than would be the case

for a whole new generation of vehicles.

However, if the Nation were to decide to pursue

major programs for people in space, such as a

lunar base or a mission to Mars, revolutionary

technological advances would be needed to

increase capabilities and reduce operating costs.

Congress is faced with several options for

enhancing the capabilities of the Shuttle system

or improving its safety and reliability:

Enhance the Performance of the Redesigned

Solid Rocket Motors (RSRMs)

Following the Challenger disaster, NASA

redesigned the Shuttle’s solid rocket boosters to

increase their safety and reliability. At that time,

it did not attempt to enhance booster performance. The payload capacity of the Shuttle could

be increased by 6,000 to 8,000 pounds by

substituting more energetic propellant, changing the motor’s thrust profile, and redesigning
Chapter 1—Executive Summary ● 7

Box l-A—Maintaining and Improving the Current Shuttle System

Buying Additional orbiters ● Automatic Orbiter Kit—An existing Shuttle orThree basic options are available: biter could be given the capability to fly an entire

● Build a copy of OV-105 mission automatically.

The Challenger replacement (C)V-105), already

. Operations Improvernents—Introducing a

being built, includes several important improve- number of new technologies and management

strategies to make Shuttle launch operations more

ments: efficient and cheaper, e.g., improved Shuttle tile —-addition of an escape hatch and pole; inspection and repair, and expert systems for —improved heat shielding tiles, strengthened

landing gear, wing structure, and engine pod; control.

—more than 200 internal changes, including Major Changes

electrical rewiring and improvements in the Some candidates include:

braking and steering systems.

. Advanced Solid Rocket Motors (ASRMs)-These

● Implement additional improvements would replace the existing RSRMs. Compared to

—Safety/Reliability; the RSRMs, they offer:

--Cost Reduction; and —up to 12,000 pounds additional lift capacity

—Performance. —better manufacturing reproducibility

(Some of’ these upgrades may involve structural —reduced stress on the Space Shuttle Main

changes, and therefore could not be made in Engines

existing vehicles. ) —potentially higher reliability

. Reduce airframe weight-Orbiter airframe —potential for enhancing competition

weight reduction of 8,000 to 10,000 pounds could ● Improve Redesigned Solid Rocket Motors--The

be achieved through the use of existing RSRMs could be improved further by

-composite materials; redesigning them to increase their thrust. The

—alloys; Shuttle’s payload capacity could be increased by

—intermetallics; and 6,000 to 8,000 pounds by substituting a more

—high temperature metallics. energetic solid propellant and by making other

Incremental Changes requisite changes to the motors.

Some alterations to the Space Shuttle system have . Liquid Rocket Boosters (LRBs)—They would

already been accomplished, or are already under way: replace the solid boosters on the Shuttle. Com-

● Redesigned Solid Rocket Motors (RSRM’s) pared to RSRMs, LRBs offer:

● Space Shuttle Main Engine Improvements- —--safer abort modes

Specific efforts directed at longer life and higher —up to 20,000 pounds additional lift capacity

—long history, potentially greater mission reli- reliability include improved: ability —welds; -capability of changing mission profiles more —manufacturing techniques;

—nondestructive testing; easily

—heat exchangers;

—safer Shuttle processing flow

—potential application as an independent launch

-controllers; system

-engine health monitoring; and —better environmental compatibility —turbopumps.

. Materials improvements-The emphasis on im-

● On-Board Computer Upgrades—Specific efforts proved materials has focused particularly on include: saving weight. For example, using aluminum- —identical computer modules ‘‘mass-produced’ lithium (Al-Li) for the external tank instead of the

for economy present aluminum alloy could provide a 20 to 30

-connection by optical fibers percent weight savings. Using composit e —a high degree of fault-tolerance

Other improvements NASA has considered or is

materials in the orbiter wings and other parts

could save an additional 10,000 pounds.

now working on:

● Crew Escape Module--This would allow for safe

● Extended Duration Orbiter (EDO)--NASA is

building in the capacity to extend on-orbit stays escape over a larger portion of the liftoff regime

from the current 7 days to 16-28 days. than now possible. It would replace the escape

pole system presently in place, but would be

heavier and much more costly.
8 ● Round Trip to Orbit: Human Spaceflight Alternatives

its nozzle. NASA estimates such changes would

require at least two years of development,

testing, and qualification. However, adding a

more energetic propellant might make the RSRM

less reliable than it now is.

Continue To Develop the Advanced

Solid Rocket Motor (ASRM)

NASA expects the ASRM to enhance Shuttle

reliability and performance, and plans to use it

starting in 1995 to replace the current, redesigned solid rocket motor. A 1987 National

Research Council Report recommended development of the ASRM on grounds that it would

‘‘enhance both the performance and reliability

of the post-Challenger Shuttle.’’11 According to

NASA, the ASRM would improve flight safety

margins, system reliability, and payload capability. However, a recent report by NASA’s

Aerospace Safety Advisory Panel questioned

whether the ASRM would provide sufficient

additional safety and reliability when compared

to the current RSRM.12

Using ASRMs might provide up to 12,000

pounds extra lift capacity and possibly reduce

the number of Shuttle flights required to assemble the Space Station from about 21 to about

16.13 NASA estimates that ASRMs would cost

$1 billion for development and testing, and $300

million for facilities construction, and could be

developed and tested in about 5 years. The

report of the Aerospace Safety Advisory Panel

suggested that NASA explore using this money

instead for added safety improvements to other

elements of the Shuttle system and said that

“NASA has not thoroughly evaluated other

alternative choices to the ASRM such as liquid

rocket boosters. ’ ’14

Develop a Liquid Rocket Booster (LRB)

Compared to solid rocket motors, LRBs offer

improved performance, simpler launch operations, fewer environmental hazards, and, potentially, improved mission safety. They could

provide from 12,000 to 20,000 pounds of extra

payload capacity for the Shuttle. The development of the necessary new liquid-fueled engines

for LRBs could be assisted by the research and

development already underway in the joint Air

Force/NASA Advanced Launch System program. However, LRBs offer greater development risk than the ASRMs and would likely cost

more to develop. They might also take from 2 to

3 years longer to develop and test than the

ASRMS.

15 NASA estimates that development,

demonstration, test and evaluation for the liquid

booster alone would cost $3 billion. It estimates

that orbiter and pad modifications, which would

be required to use the LRBs, might cost as much

as $500 million. However, if an LRB could be

powered by an engine requiring less ambitious

development than that envisioned by NASA, the

cost of the LRBs might be brought close to that

of the ASRMs and might be available about the

same time.l6

Develop the Shuttle-C

Alternatively, NASA could obtain extra space

transportation capability by building an expendable, unpiloted heavy-lift booster using Shuttle

1 IN~on~ Rese~ch co~cil, Report of the Cowwrdttee on the Space Station (Washington, DC: National Academy Press, September 1987). P. 23.

12NASA’s &row=c Stiety ~viwv Pine] que~ion~ the “wisdom of proc~ing wi~ he Procmment of a new solid rocket motor. . .” at this

time. See National Aeronautics and Space Administration, Aerospace Safety Advisory Panel Annual Report, March 1989, p. iii, and p.3.

13s~e Prqulsion exw~, including ~me wi~in NASA, have expressed concerns to OTA hat he ASRM may not meet its performance goal. They

base these concerns on ex~rience with other space systems that have suffered unavoidable weight growth. However, NASA officials familiar with the

ASRM program counter that even if the ASRMS do not filly achieve their expected performance, their development will eventually lead to more reliable

solid rocket motors for the Shuttle.

~d~roswce S@ety Advisory Panel Annual Report, op. cit., footnote 12.

15NASA*5 LRB ~udies ~ve es~im~ed hat &velopment ~d te~ing of LRBs would t&e unti] 1997. However, recent studies by Rocketdyne ad

by General Dynamics suggest that LRBs could be purchased more cheaply and developed in less time.

16Rocke~yne briefing to OTA, May 3, 1989.
Chapter l-Executive Summary ● 9

technology .17 This ‘‘Shuttle-C’ (for cargo)

would use the recoverable solid rocket boosters,

the same expendable external tank, and two

refurbished main engines (SSMEs) from the

Shuttle system. A large expendable cargo cannister, capable of transporting some 85,000 to

100,000 pounds of payload to low-Earth orbit

would substitute for the Shuttle orbiter.

Although Shuttle-C could not carry people, it

would be capable of flying some missions that

would otherwise require Shuttle flights and

could therefore substitute for purchasing an

additional orbiter. For example, if Shuttle-C

were used to ship major subassemblies of the

space station to orbit, one Shuttle-C flight would

replace two to three Shuttle missions. According

to NASA, four Shuttle-C flights could reduce

the number of Shuttle flights necessary to

assemble the Phase I Space Station from about

21 to about 10.

Shuttle-C would have the advantage of using

much of the same technology and parts that have

already proved successful in 28 Shuttle flights.

It would use the same launch pads, vertical

integration facilities, and launch support crews

now used for the Shuttle. It carries the disadvantage that because so many of the proposed

Shuttle-C’s components are common to the

Shuttle, an interruption of Shuttle operations as

a result of an accident or technical problem

might well lead to delays of Shuttle-C flights for

the same reasons. Conversely, a failure of the

Shuttle-C would probably ground the Shuttle

fleet.

Choosing among these alternatives is very

difficult because the choices are constrained by

budget limitations as well as competing technical capabilities. If Congress determines that

NASA should maintain a Space Station construction schedule offering full operational capability of its first phase by 1998, then any of

these options except perhaps LRBs would assist

that effort. Improved RSRMs could provide a

modest increase in Shuttle payload capability.

ASRMs and LRBs may both achieve greater

payload weight enhancements for servicing, but

LRBs might not be ready in time to be of help

in constructing the Space Station on the existing

schedule. However, LRBs may offer safer

Shuttle launch processing and improvements in

safety for Space Station operation, any additional Space Station construction, and for other

Space Shuttle missions. NASA officials estimate that the costs of developing the Shuttle-C

or the ASRM are roughly equivalent, and that

either system could be available by 1995.

Shuttle-C would provide the greatest payload

improvement, and would reduce much of the

pressure of depending on the Shuttle for building the Space Station. However, NASA has

identified few payloads for a Shuttle-C beyond

the Space Station components.

If Congress decides that the advantages of

having the heavy-lift capacity potentially provided by the Shuttle-C, and/or the extra margin

of safety and reliability provided by the LRBs

outweigh the advantages of developing the

ASRMs by 1995, it might wish to reconsider its

decision to proceed with ASRMs.

Making major Shuttle enhancements on a

project-by-project basis may not be the most

efficient way to improve the Shuttle system. To

choose one improvement may mean not pursuing another, worthwhile improvement. However, having a versatile, capable launch fleet that

provides reliable human access to space will be

important if Congress desires to maintain a

policy of supporting a human presence in space.

Hence, Congress may wish to consider a more

integrated approach to strengthening the

Nation’s space transportation capability by

funding a Shuttle Improvement Program

lasting, for example, 10 years. Such a program

could include development of advanced solid

rocket boosters, liquid rocket boosters, and the

17u.s. Conwess, Office of ~hn~jogy As~s~cnt, La~ch OpriOKT for the FU~re: A ll~er’s Guide, OTA-lSC-3fi3 (Washington, DC: U.S.

Government Printing Office, July 1988).
10 ● Round Trip to Orbit: Human Spaceflight Alternatives

Shuttle-C, as well as additional, more modest,

improvements summarized in box l-A. To

support this sort of program, which could cost as

much as $850 million per year for 10 years,

would require finding extra space program

funding, scaling down the Space Station program, or deferring other programs.

RESCUE OR ESCAPE VEHICLES

Crews living and working in the planned

Space Station could be exposed to substantial

risk from major failures of the Station or the

Space Shuttle that transports the crew. NASA is

attempting to reduce such risk by building safety

features into the Space Station and improving

the Shuttle’s design. Nevertheless, many analysts in NASA and the broader U.S. space

community believe that the United States may

need some means independent of the Shuttle to

rescue crews from the Space Station. Several

options have been suggested (box 1-B); these

could be based at the Space Station or on Earth.

To decide whether a risk-reducing effort is

worth the investment required, Congress

must be advised about how much the investment would reduce the risk. Even if an

alternate crew return capability were provided and worked as planned, it would not

eliminate all risks to station crewmembers. A

risk assessment of the Space Station should take

into account all phases of the crews’ experience

in space. For example, if the greatest risk to

Space Station crew members were experienced

in the flight to orbit, it may be more costeffective to improve the safety of the Shuttle or

any later crew-carrying space transportation

systems than to build a crew escape craft.

A rescue system, if built, would be needed for

the life of the Space Station. Therefore, its total

operating costs could easily exceed its development costs. Before committing to a specific

rescue strategy, system designers will have to

address the costs of developing the necessary

support infrastructure, which might include

Box I-B—Escape Vehicles

Several contingencies could require emergency

escape of personnel in space. These include medical

emergencies of Space Station crew members, major

equipment failures, damage from orbital debris, etc.

Escape could also be necessary if the Shuttle failed

to meet its scheduled launch date by so long a time

that the Station risked running out of critical

supplies.

Crew Emergency Return Vehicles (CERV)

NASA is considering two types of vehicles for

emergency return from space to Earth:

. Capsule—This simple vehicle would have an

ablative heat shield reminiscent of reentry

capsules from the early days of spaceflight,

and still used routinely by the Soviet Union. A

capsule, which could closely resemble the

Apollo capsule, would descend by parachute

and land in the ocean. Its advantages include

simplicity, relatively low cost, and proven

technology. In addition, capsules need little or

no piloting, which could be a major consideration if pilots are unavailable because they are

unable to function as a result of injury or a long

stay in orbit. Depending on its capability, a

capsule could cost $0.75 billion to $1.0 billion

to develop,

. Small Glider—A small, aerodynamically stable vehicle whose shape would provide lift,

and could land by parachute or at low speed on

a runway. A glider would provide a wider

range of landing sites and more frequent

opportunities for reentry and recovery (particularly for a version with landing gear), and

a softer ride than capsules (important if an

injured crew member is returning). However,

a glider would cost 20 to 50 percent more than

the simplest parachute version of a capsule.

ground operations hardware and personnel

at the mission control site, landing site crews,

and the necessary subsystems and logistics

support to resupply, replenish, and repair a

rescue vehicle on orbit. Each of these factors

can seriously influence the operational characteristics and costs of the system.
Chapter I-Executive Summary ● 11

NASA is also studying the possibility of

building a specialized glider that could be

launched into space atop an expendable launch

vehicle as well as return from the Space Station.

Such a glider could be used to provide 1) crew

emergency rescue, 2) assured access to space by

crews, 3) small logistics transport, and 4)

on-orbit maneuver. Whether capsules or gliders,

emergency rescue vehicles could be launched by

Titan III and Titan IV by 1995. Alternatively, a

Shuttle could launch two at a time, to be docked

at the Space Station.

OPTIONS FOR THE NEXT

CENTURY

Sometime in the early years of the next

century our existing launch systems will wear

out or become operationally obsolete. At that

point the United States will want to replace them

with more advanced systems. NASA and the

DoD are considering a variety of options for

advanced, crew-carrying launch systems.

Personnel Carrier Launched on

Automated Launch Vehicles

NASA is beginning to explore the possibility

of developing a personnel launch system (PLS)

that would use a small glider launched atop an

expendable launch vehicle, rated to carry people.18 Candidate launchers could include a Titan

III or Titan IV, or perhaps a new, as-yet

undeveloped launcher such as the Advanced

Launch System (ALS).

The ALS Joint Program Office has recognized the potential benefit of having a flexible

launch vehicle rated for launching crews. It has

therefore required that contractor proposals for

an ALS provide for a launch vehicle capable of

meeting both the design and quality assurance

criteria for crew-rating. Designing an ALS

launch vehicle at the outset to provide the

additional structural strength for crew-rating

Photo credit: National Aeronautics and Space Administration

Artist’s conception of an Apollo-type emergency rescue

vehicle entering the Earth’s atmosphere after leaving the

Space Station.

would be much less expensive than redesigning,

rebuilding, and retesting it after it is developed.

Having a crew-rated automated launcher in

addition to a Shuttle has three strong advantages: 1 ) the crew-rated vehicle could launch

new orbiters designed for launch with other

boosters; 2) it could enhance crew safety (if the

crew-rated launch vehicle carried an Apollo-like

capsule, crew escape could be easier than with

the Shuttle, and escape would be possible during

more of the trajectory than with the Shuttle); and

3) there maybe cases where it will be necessary

only to deliver personnel and cargo to the Space

Station, but not return cargo on the same trip. In

that case, there is no need to risk a Shuttle

orbiter. In view of the concerns over Shuttle

fleet attrition, it maybe important for NASA

to investigate the potential for using a crewISA NASA or AU Force launch vehicle is said to be crew, or ‘‘man-rated, ’ if it has been cetifkd as meeting certain Stifety Criteria. ‘HWSC inchJ&

design criteria as well as quality assurance criteria.
12 ● Round Trip to Orbit: Human Spaceflight Alternatives

rated ALS or other expendable launcher to

reduce the risk of losing crew-carrying capacity early in the next century.

Advanced Manned Launch System (AMLS)

NASA is studying several advanced concepts

for vehicles to replace the Shuttle. The Advanced Manned Launch System (AMLS—

previously called Shuttle II) program is studying

new designs with the goal of achieving an

improved U.S. piloted spaceflight capability

early in the next century. A vehicle significantly

different from the existing Shuttle would result

(box l-C). If activities involving crews in space

increase markedly in the next decade, and the

Shuttle proves unable to perform its missions,

an AMLS using advanced technology19 might

be needed. It could offer significant improvements in operational flexibility and reduced

operations costs over the existing Shuttle. However, development, thorough testing, and procurement of an AMLS fleet could cost $20

billion to $30 billion (1989 dollars).

The timing of the development phase for

an AMLS would depend on NASA’S need to

replace the Shuttle fleet. It will also depend in

part on progress reached with technologies

being explored in the Advanced Launch

System and National Aero-Space Plane (NASP)

programs. In any event, a decision on AMLS

will not have to be made for several more years.

For example, if Congress decided that an

operational AMLS was needed by 2010, the

decision to start the early phases of development

would have to be made by about 1995. By that

time, Congress should have had adequate opportunity to assess the progress made in the NASP

program (see below), which could be competitive with an AMLS.

Box 1-C—Advanced Manned Launch System

(AMLS)

The goal of the NASA AMLS program is to

define advanced manned launch system concepts,

including their development, system and operational characteristics, and technology requirements.

A vehicle significantly different from the existing

Shuttle would result. NASA is presently evaluating

five concepts:

• an expendable in-line two-stage booster with a

reusable piloted glider;

. a partially reusable vehicle with a glider atop

a core stage;

. a partially reusable drop-tank vehicle similar

to the fully reusable concept below but with

expendable side-mounted drop tanks;

. a fully reusable rocket with a piloted orbiter

parallel-mounted (side-by-side) to an unpiloted glideback booster;

● a two-stage horizontal takeoff and landing

air-breather/rocket, which would be fully reusable.

Critical technology needs for all AMLS concepts

include:

. light-weight primary structures

. reusable cryogenic propellant tanks

. low-maintenance thermal protection systems

. reusable, low-cost hydrogen propulsion

• electromechanical actuators

. fault tolerant/self-test subsystems

• autonomous flight operations

Building an Aerospace Plane

Developing a reusable vehicle that could be

operated like an airplane from conventional

runways, but fly to Earth orbit powered by a

single propulsion stage would provide a

radically different approach to space launch

and a major step in U.S. launch capability.

However, building such a vehicle poses a

much larger technical challenge than building a two-stage, rocket-based AMLS. An

aerospace plane could spur the development of

l~e c~KteroftW~oloW u~ in an AMLS would depend on NASA’s goats for this launch system and the epoch in which its design WtiS SCkZtd.

For example, if technologies used for the AMLS were frozen at 1992 levels, they would be considered “near term. ” However, if a decision to build

an AMLS were not reached until the middle of the 1990s, the technologies designers would usc to create an AMLS could be far more advanced.
Chapter l--Executive Summary ● 13

two new classes of military aircraft--one that

would combine quick response, global ranges,

and hypersonic20 speed with take-off or landing

in any part of the world, and another that would

combine access to space with quick response

from conventional runways.

The Department of Defense and NASA are

jointly funding the NASP program to build the

X-30 (box 1-D),21 a research vehicle intended to

demonstrate both single-stage access to space

and endo-atmospheric hypersonic cruise capabilities. NASP is a high-risk technology development program. Building the X-30 and

achieving orbit with a single stage would

require major technological advances in materials and structures, propulsion systems,

and computer simulation of aerodynamic

and aerothermal effects from Mach 1 to

Mach 25.22 The uncertainties in meeting design

goals are compounded because the successful

operation of the X-30 would require all of the

key enabling technologies to work in concert

with one another. In addition, ground test

facilities cannot replicate all of the conditions

that would be encountered in ascent to orbit.

Therefore, it is impossible to predict precisely

how the X-30 would perform when pilots make

the first attempts to push it far into the hypersonic realm.

As the NASP program is presently structured,

it is organized to meet a series of technical and

programmatic milestones, rather than a given

schedule. However, there is some danger that in

the current fiscally constrained environment, the

program office might relax some of its own

technical criteria in order to meet a schedule.

The next major milestone will occur when the

NASP program reports on its progress in

meeting the Phase H technology development

goals. If the NASP program were funded at the

Box l-D-What Is the National Aero-Space

Plane Program?

NASP is a program to build the X-30, an

experimental, hydrogen-fueled, piloted aerospace

plane capable of taking off and landing horizontally

and reaching Earth orbit with a single propulsion

stage. The design of the X-30 would incorporate

advanced propulsion, materials, avionics, and control systems, and make unprecedented use of

supercomputers as a design aid and complement to

ground test facilities. NASP is a technically risky

program that could spur the development of a

revolutionary class of reusable, rapid turn-around

hypersonic flight vehicles, that would be propelled

primarily by air-breathing “scramjet” engines,

Operational follow-ons to the X-30: An aerospace plane derived from NASP technology offers

the promise of dramatically reduced launch costs if

the vehicle can truly be operated like an airplane

using standard runways, with minimum refurbishing and maintenance between flights.

level requested in the 1990 budget submission

($427 million), NASP officials estimate they

would be ready to decide on development of an

X-30 at the end of fiscal year 1990. Program

officials estimate that if the program experiences no delays as a result of unanticipated

technical problems or of budgetary cuts, an

X-30 begun in fiscal year 1991 could achieve

orbital spaceflight by October 1996.

The X-30 would be a research vehicle, not a

prototype of an operational vehicle. To develop

an operational vehicle would require an additional, costly program beyond NASP. A development cycle that took full advantage of lessons

learned in the X-30’S planned test program

could not commence until the late 1990s at the

earliest. An operational vehicle derived from the

zoMWh J ;s the@ ~fWMd. ~ypez~ow’c USMI]y refers to flight at speeds of at ]east Mach s—k thM the SpCed of sound, or about 4,~miles

per hour.

zlHowev~r, ~ rWent @lslon @ cut ~e pro- DoD con~bution to NASp f~ding by two-~irds for fisc~ yem 1~ md to terminate funding for

it in subsquent years puts the program in doubt, See later discussion in this section.

22MXh M (25 tjmes MWh 1), is the speed necessary to reach Earth orbit.
14 ● Round Trip to Orbit: Human Spaceflight Alternatives

Photo credit: McDonnell Douglas

Artist’s conception of an X-30 aerospace plane.

proposed X-30 would therefore be unlikely until

approximately 2005 or even later unless it were

closely modeled on the X-30.

If the X-30 proved successful, the first

operational vehicles that employ NASP technologies are likely to be built for military use,

possibly followed by civilian space vehicles.

Commercial hypersonic transports (the “Orient

Express’ are a more distant possibility. Recent

studies have shown that from an economic

standpoint, commercial hypersonic transports

compare unfavorably with proposals for slower

Mach 3 supersonic transports based on less

exotic technology and conventional fuels. Therefore, the most economic route to commercial

high-speed air transport is unlikely to be

through the X-30 development program.

However, the X-30 program could provide

technical spin-offs to aerospace and other

high-technology industries through its development of advanced materials and structures

and through advances in computation and

numerical simulation techniques. It is too

early to judge the economic importance of such

spinoffs.

Operational hypersonic aircraft and spaceplanes may raise concerns about their effect on

Earth’s atmosphere. Designers are hopeful that

vehicles that cruise well above the stratospheric

ozone layer, and whose combustion products are

mostly water vapor, will not affect the environment significantly. The NASP program office is

sponsoring research on the potential atmospheric effects of a fleet of follow-on vehicles to

give a preliminary assessment of the major

environmental questions.

Even assuming a rapid resolution of the

myriad of technical issues facing the creation

of an X-30 capable of reaching orbit with a

single propulsion stage, translating this technology into an operational spaceplane might

come late in the period when an AMLS could

be ready, and perhaps after the time when

replacements for the Shuttle will be necessary. With their less exotic technologies, rocketpropelled AMLS vehicles could probably be

funded in the mid to late 1990s and still be

developed in time to replace aging Shuttles. An

AMLS program begun in this period would also

benefit from the technical base being developed

in the NASP program. However, the technical

uncertainties of both programs suggest that

Congress would benefit from monitoring

their progress and comparing the probability

of success of each before committing development funds for operational vehicles in the

mid-1990s. The costs of each program, as well

as other competing budget priorities, will

play a major role in such a decision.

The revised DoD budget of April 1989 would

cut DoD fiscal year 1990 funding for NASP

from $300 million to $100 million. DoD would

contribute no funds in subsequent years. DoD

has also proposed transferring responsibility for

managing NASP from DoD to NASA and

allowing NASA to obligate the $100 million of

fiscal year 1990 DoD funds.

The proposed cuts and change of management have raised the concerns of NASP propo-
Chapter l-Executive Summary ● 15

nents and accelerated a review of the NASP

program. Many of the ongoing research efforts

on materials, structures, and propulsion design,

which would be needed to support an informed

decision on the technical feasibility of building

an X-30, are scheduled for completion in fiscal

year 1990, the last year of Phase II. Furthermore,

critical applications and cost studies are not yet

complete.

Congress has three broad options on NASP

funding:

●

●

Continue to fund the program at or near

the original requested rate ($427 million). Funding of this level would allow the

NASP program to continue its Phase II

research program and to complete its

application and cost studies by the end of

fiscal year 1990. At that point, the Administration and Congress could then decide

whether or not to build two X-30 test

vehicles, as planned.

If the NASP program receives a budget

cut, and the joint management arrangement

is maintained, the Phase III decision would

likely slip by a year or more, depending on

the size of the cut. Although the program

would then risk losing momentum and

industry support, stretching Phase II out

but retaining total funding of roughly $427

million would still allow the program to

reduce many of the current uncertainties in

the technology.

Accept the current DoD proposal for

program cuts and transfer the-program

to NASA. Under this option, the NASP

program would still be able to pursue

useful technology studies. However, the

focus of the program would change to

emphasize the maturation of critical technologies in lieu of building a flight vehicle. In

addition, a decision whether or not to

construct a flight vehicle might be delayed

●

two or more years. If managed by NASA,

the program would compete with funding

for alternative launch systems such as the

AMLS and also with the Space Station

program, which, along with Space Shuttle,

will command most of NASAs resources

for the next decade and more.23

Moreover, a decision to transfer the

program to NASA with only limited funding would delay a decision on whether to

build a flight vehicle by several years. In

the interim, the Nation might risk losing the

substantial technology base that the NASP

program has built for hypersonic flight.

Recreating this technological base would

be both costly and time consuming.

Close out the NASP program. If Congress feels that the long-term goals of the

NASP Program are less important than

other pressing priorities in the Federal

budget, it could terminate funding entirely.

However, much of the progress made in the

program would be lost because contractors

would not be able to continue their research

to a logical conclusion.

SPACE TRANSPORTATION AND

THE SPACE STATION

NASA’s planned Space Station will make

permanent demands on space transportation—

for construction, servicing, supply, and possibly

emergency crew return. Uncertainty about the

adequacy of the current Shuttle fleet for

constructing and servicing the Space Station

makes station planning itself both uncertain

and risky. Deployment, servicing, and resupply of the Space Station face both the risks of

delayed launch schedules and loss of one or

more orbiters. In addition, losing a critical

element of the Space Station in transit to

orbit as a result of a Shuttle failure could lead

21J.s. Cqress, Congression~ Budget Office, The NASA Progrtvn in fhe 1990s and Beyond (Washingon, DC: Contgessional Budget Office. May

1988).
16 ● Round Trip to Orbit: Human Space flight Alternatives

to severe delays in Space Station construction

or even loss of the Space Station.24

A previous section outlined options for reducing the space transportation risk to Space Station

construction and operation. However, most of

these options would require additional funding

beyond NASA’s projected budget for Space

Station or for space transportation. Congress

may wish to postpone Space Station construction and operation and focus on improving the Nation’s ability to place crews in orbit

safely and reliably. Alternatively, Congress

could direct NASA to fly fewer non-Space

Station-related Shuttle missions in order to

reduce the risk that a Shuttle would be lost

before Space Station construction is completed. NASA might, for example, plan to use

Titan IVs to carry some Space Station elements

into orbit rather than risking the Shuttle to do so.

Furthermore, if appropriately designed, many

science payloads now tentatively manifested for

the Shuttle could be flown on ELVs purchased

competitively from the private sector.25

THE TECHNOLOGY BASE FOR

PILOTED SPACEFLIGHT

Building a new, advanced launch system, or

even making substantial modifications to existing launchers, requires a capable aerospace

industry, well-supported government research

programs, a cadre of well-trained engineers, and

an institutional structure capable of putting a

vast variety of technologies to innovative use.

Yet, according to several recent studies, our

existing space technology base has become

inadequate in recent years.26

Government Programs

Several of these studies have recommended

improving the Nation’s space transportation

technology base. Though specific proposals

differ in detail, they cite propulsion, space

power, materials, structures, and information

systems as areas in need of special attention.

In response to these and other concerns,

NASA and the Air Force have initiated four

major programs to improve the Nation’s launch

system technology base (box l-E). As currently

organized, these programs are directed primarily toward developing new, advanced capabilities. In the existing budget climate, it may be

more realistic to redirect some funding toward technologies that could be used to

improve existing launch systems and make

them cheaper to operate. Several launch vehicle manufacturers have already instituted programs to improve their launch vehicles, based

on technologies developed for the Advanced

Launch System program.

As noted in Reducing Launch Operations

Costs: New Technologies and Practices, launch

operations and logistics, especially for systems

that carry people, are labor-intensive and comprise a significant percentage of the cost of a

launch. Yet launch system designers have invested relatively little in technologies that would

reduce these costs. NASA’s technology programs are addressing issues in automation and

robotics, two technology areas that could significantly reduce launch operations costs. However, NASA could do much more to apply these

technologies to launch operations for the Shuttle. Funding basic and focused research for

space transportation technologies would help

241f a SpKe station C]ement for which Mere was no spare were lost, replacing that elcment would lake many months.

zs~ent s~e policy requires NASA, 4 ‘to the maximum extent feasible, 10 purchw expendable launch vehicle services competitively from private

launch companies—The White House, Office of the Press Stxretary, “Presidential Directive on National Space Policy,” Fact Sheet, February 11, 1988,

p. 9.

USW, for Cxmple, Nation~ Re~~ch Council, Aeronautics and Space Engineering Board, SPtlCe Technofofl @ Meef F’Umre ~ee~.$ (W@@m

DC: National Academy Press, December 1987); National Commission on Space, Pioneering the Spuce F’rontier(New York: Bantam Books, May 1986);

National Aeronautics and Space Administration, Leadership and America’s Furure in Space (Washington, DC: NASA, August 1987).
Chapter I-Executive Summary ● 17

Box I-E-Government Space Technology Programs

● Advanced Launch System (ALS) Focused Technology Program—a joint program between NASA and the Air

Force, carried out as an integral part of the ALS Demonstration/Validation Program. Its aim is to pursue research

on specific technologies of interest to the development of an ALS. The program’s contribution to crew-carrying

capabilities will be limited, but important. As much as possible, ALS program managers have deliberately

targeted their research at generic space transportation issues, in order to develop a broad technology base for

designing an ALS. The ALS program plans to spend $81.4 million on focused technology R&D in fiscal year

’89, out of a total budget of $153 million.

● Civil Space Technology Initiative—a NASA program designed to revitalize ‘the Nation’s civil space technology

capabilities and enable more efficient, reliable, and less costly space transportation and Earth orbit operations.”1

Funding for fiscal year ’89 is $121.8 million (’90 request—$144.5 million).

● National Aero-Space Plane—a DoD/NASA program to develop an aerospace plane capable of reaching orbit

with a single propulsion stage. Although this program does not have the specific focus of improving the Nation

technology base, some of the technology under development necessary for building the NASP, particularly new

materials and structures, new propulsion techniques, new computational techniques, and methods of handling

liquid and slush hydrogen, will find application elsewhere. The NASP Joint Program Office is spending $150

million over a 30-month period on materials development alone.

. Pathfinder-a NASA program especially directed at technologies for future human space exploration. Funding

for fiscal year ’89 is $40 million (fiscal year ’90 request $47.3 million). Very few of this program’s technologies

will be useful for Earth-to-orbit transportation, as it is directed primarily toward on-orbit and interplanetary

transportation and life-support issues.

INa[lOn~ Aeronautics Mid SpWe~stration, Office of Aeronautics and Space Twtmology, ‘‘CSTI Overview, ’ April 1988.

the United States prepare to meet future systems are still in the early stages of developspace transportation needs.

The Private Sector Role

In providing space transportation for people,

private firms now serve primarily as contractors

for government-defined needs. Reaching orbit

and working in space requires so large an

investment compared to the expected return that

private firms are unlikely to take the initiative in

developing crew-related space systems unless

Congress and the Administration set a high

priority on involving them more directly in such

development. 27 Because the government controls both access to space and most of the

technology, it will continue to determine launch

specifications and provide most of the funding.

This is especially true for systems involving

crews in space, in large part because such

ment, but also because they represent a major

national commitment and are funded solely by

public money.

By promoting private sector innovation toward improving the design, manufacture, and

operations of launch systems, the government

could reduce the cost of government launches.

Yet relatively few incentives to involve private

firms exist today.

If technology for crew-related systems eventually becomes an important arena for private

investment, commercial pressures will themselves provide the incentives for launch system

innovation. For the near term, however, such

incentives must come from the government

because projected future demand for crew27~e NASP ~rogm, for ~xnple, hm set a high Pfiorlty cm due~tly lnvo]ving private firSIISaduniversities in materials research and other ildViUICd

research on the X-30,
18 ● Round Trip to Orbit: Human Spaceflight Alternatives

carrying space transportation is small and depends entirely on government specifications.28

Incentives provided by the government could

include:

●

●

●

direct grants to develop new technology for

launch systems specifically directed toward saving costs rather than increasing

performance;

cash incentives to firms for reducing the

manufacturing costs of specific items procured by the government;29

encouragement of industrial teaming arrangements such as the NASP Materials Consortium.

INTERNATIONAL COMPETITION

AND COOPERATION

Competition

This decade has seen the rise of international

competition in space transportation. The development of space transportation systems is the

major achievement that signals a nation’s or

region’s status as a space power, able to develop

and control the use of advanced technology. In

addition to the Soviet Union, Europe, Japan, and

China now operate systems capable of launching sizable payloads.

At present, only the United States and the

Soviet Union are able to send humans to and

from space. However, the European Space

Agency (ESA), the Federal Republic of Germany, Japan, and the United Kingdom are all

developing their own reusable or partially reusable launch systems, which, if successful, would

be capable of transporting human crews. The

progress other countries are making in space

transportation for human crews is likely to

present technological and political challenges

to the United States by the end of the century.

Photo credit: Novosti

Soviet Shuttle Buran on the launchpad at the Soviet launch

complex.

Cooperation

The United States has always maintained a

vigorous program of international cooperation

in space science and applications in order to

support U.S. political and economic goals.

However, it has cooperated very little with other

countries in space transportation, in part because

most launch technology has direct military

applications and is therefore tightly controlled.

Nevertheless, because other countries have

2sRjch~d Br~k~n, s~ce challenge ’88: Fourth Annual Space Sy~osium Proceedings Report (Colorado Springs, ~: U.S. SpXe Foundtion,

1988), pp. 76-79.

29FW cx~plc, R~kWell hmtitjn~ mm 20 pereent of every dollar it saves NASA on building Shuttle OIbittX OV-105.
Chapter l-Executive Summary ● 19

developed their own launch capability, reducing much of the technological lead the

United States once held, and because progress in space will continue to be expensive,

cooperating on new space transportation

systems could benefit the United States.

For example, the United States has a strong

need to reduce the number of Shuttle flights

needed to construct and resupply the Space

Station. It could benefit by sharing responsibility for resupply of the Space Station with its

Space Station partners. ESA and NASA have

now established a working committee to discuss

appropriate standards for packaging, docking,

and safety. If such cooperation proves successful, it could be extended to include more

sensitive aspects of space transportation. In

particular, because ESA and Japan have developed and now operate their own launch systems,

they may have specific technologies or methods

to share with the United States in return for

access to some U.S. technology.

The United States could even be more innovative in cooperating with other countries. For

instance, the United States may decide to

provide an emergency crew escape or return

vehicle for the Space Station. NASA estimates

that the development of such a vehicle would

cost between $0.75 billion and $1.50 billion,

depending on its level of sophistication. If

properly redesigned and outfitted, the European spaceplane, Hermes, might be used as an

emergency return vehicle. Hermes could even

complement the Shuttle in Space Station crew

rotation. However, this option would require

radical change in U.S. thinking about Space

Station crew rescue and a similiar change in

Hermes planning as well. Specifically, it would

require partial redesign of Hermes to carry more

than the three crew members now planned for

Photo credit: British Aerospace

Artist’s conception of British Aerospace’s Hotol

aerospace plane taking off. If successful, this

space plane would reach Earth orbit with a single

propulsion stage.

this space plane. It would also require a degree

of international cooperation for which the United States has little precedent.

Because of the proprietary and military nature

of space transportation technology, cooperation

in this area can be expected to be more difficult

than cooperation in space science. Yet the

United States engages in a variety of cooperative

projects for the development of military systems. A deeper commitment to international

cooperation would assist the United States in

achieving much more in space than it can afford

to attempt on its own. To do this will require that

NASA and the U.S. aerospace industry do much

more to tap the technologies and expertise

available in other industrialized countries.
Chapter 2

Issues and Options

98-133

Photo credit: National Aeronautics and Space Administration

Space Shuttle Challenger lifts off from Kennedy Space Center on its second flight, June 18, 1983.

0 - 89 - 2
CONTENTS

Page

Launching Humans to Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Dependence on the Space Shuttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Inflexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Attrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wearout and Obsolescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Imminent Decisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Order More Orbiters?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Improve Existing Orbiters?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Improve Other Shuttle Elements and Facilities?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Develop Capsules or Gliders for Escape or Rescue?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Future Decisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Develop the Advanced Manned Launch System or a Different Advanced Rocket?. . . .

Develop a Single-Stage-to-Orbit Spaceplane?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table

2 3

25

25

25

26

26

26

26

26

27

27

27

28

Table Page

2-1. National Aeronautics and Space Administration Fiscal Year 1990

Budget Summary for Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Chapter 2

Issues and Options

The United States today depends entirely on the

Space Shuttle for transporting crews to and from

space. Not only does the Shuttle function as a

vehicle for launching spacecraft, it also serves as a

platform for experiments in science and engineering.

In the future, NASA intends to use the Space Shuttle

to deploy and service the planned Space Station. As

the Nation looks toward the future of piloted

spaceflight, it may wish to improve the Shuttle’s

reliability, performance, and operational efficiency.

Eventually, additions to the Shuttle fleet or replacement Shuttles will likely be desirable. This chapter

summarizes the major issues of maintaining and

improving the Space Shuttle and developing advanced crew-carrying launchers. It also presents a

range of congressional options for responding to

these issues.

LAUNCHING HUMANS TO SPACE

One of the distinguishing characteristics of the

U.S. civilian space program is its emphasis on

people in space, to demonstrate U.S. leadership in

the development and application of high technology.

Since the early days of the Apollo program, the

‘‘manned’ space effort.. of the National Aeronautics

and Space Administration (NASA) have served as a

major driver of the direction and spending of its

space activities. Today, NASA’s projects involving

people in space, primarily the Space Shuttle and

Space Station programs, consume between 65 and

70 percent of NASA’s budget (table 2-l).

Critics of NASA’s emphasis on humans in space,

especially critics in the space science community,

have questioned the wisdom of continuing to emphasize these activities because of the heavy explicit

and implicit demands they place on the civilian

space budget. In particular, critics note that using the

Shuttle to launch the Hubble Space Telescope and

large solar system probes, like Galileo and Ulysses,

subjects space science to unnecessary reliance on the

Shuttle’s ability to meet a launch schedule. ] These

critics point out that Europe and Japan, while

spending considerably less on space than the United

States, have nevertheless achieved noteworthy scientific and technological results. However, supporters of maintaining the human presence in space

argue that such activities provide essential visibility

for the U.S. space program and underscore America’s international technological leadership:

The [manned] space[flight] program is a visible

symbol of U.S. world leadership; its challenges and

accomplishments motivate scientific and technical

excellence among U.S. students; and it provides for

a diverse American population a sense of common

national accomplishment and shared pride in American achievement.2

Current space policy calls for demonstrating U.S.

leadership by expanding “human presence and

activity beyond Earth orbit into the solar system, ’

and “continuing our national commitment to a

permanently manned Space Station.”3 U.S. space

policy directs NASA to improve the Space Shuttle

system and start the Space Station by the mid- 1990s.

It also directs NASA to establish sustainable Shuttle

flight rates for use in planning and budgeting

Government space programs, and to pursue appropriate enhancements to Shuttle operational capabilities, upper stages, and systems for deploying,

servicing, and retrieving spacecraft as national

requirements are defined.4

Achieving all of these goals would be expensive.

In the Apollo era, the Nation had the well-defined

political goal to land a man on the Moon within a

decade and return him, a goal that carried the rest of

the space program and a large budget commitment

with it. If the budget for space activities were

unlimited and if the needs of the various space

interests could all be met equally well, then many

space program goals might be usefully pursued at

the same time. The United States could maintain its

IRO~fl B1ess, ‘‘Sp=e Science: What Wrong at NASA,” Issues in Science and Technology, winter 1988-89, pp. 67-73; Bruce Murray, “Civili~

Space: Ln Search of Presidential Goals, “ Issues in Science ami??chnology, spring 1986, pp. 25-37.

zJohn M. Imgsdon, “A Sustainable Rationale for Manned Space Flight,” Space Policy, vol. 5, 1989, pp. 3-6.

gThe whim HOUW, Office of the Press hmetmyl ‘‘The Resident’s Space Policy and Commercial Space Initiative to Begin the Next Century,’ Fact

Sheet, Feb. 11, 1989.

41bid.

-23-
24 . Round Trip to Orbit: Human Space flight Alternatives

Table 2-l-National Aeronautics and Space Administration

Fiscal Year 1990 Budget Summary for Spacea

(millions of current-year dollars)

Budget Plan

1988 1989 1990

Research and Development . . . . . . . . . . . . . . . . . . . . . 2,922.0 3,862.4 5,288.8

Space Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392.3 900.0 2,050.2

Space transportation capability development . . . . . . . . . 593.4 681.0 639.0

Space science and applications . . . . . . . . . . . . . . . . . . . . 1,581.8 1,830.2 1,995.3

Technology utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.0 16.5 22.7

Commercial use of space . . . . . . . . . . . . . . . . . . . . . . . . . 29.7 28.2 38.3

Transatmospheric research and technology . . . . . . . . . . 52.5 69.4 127.0

Space research and technology . . . . . . . . . . . . . . . . . . . 221.3 295.9 338.1

Safety, reliability, and quality assurance . . . . . . . . . . . . . 14.1 22.4 23.3

University space science and technology

academic program . . . . . . . . . . . . . . . . . . . . . . . . . . . . (21.6) (22.3) 35.0

Tracking and data advanced systems . . . . . . . . . . . . . . . 17.9 18.8 19.9

Space Flight, Control, and

Data Communications . . . . . . . . . . . . . . . . . . . . . . . . . 3,805.7 4,484.2 5,139.6

Shuttle production and capability . . . . . . . . . . . . . . . . . . . 1,092.7 1,128.2 1,305.3

Space transportation operations . . . . . . . . . . . . . . . . . . . 1,833.6 2,390.7 2,732.2

Space and ground networks

communications and data systems . . . . . . . . . . . . . . . 879.4 945.3 1,102.1

Construction of Facilities . . . . . . . . . . . . . . . . . . . . . . . . 178.3 275.1 341.8

Research and Program Management . . . . . . . . . . . . . 1,762.2 1,891.6 2,032.2

Total Budget Summary . . . . . . . . . . . . . . . . . . . . . . 9,001.1 10,493.3 12,804.4

aTotal NASA bu~t lass aeronautical reaaarch & technology

SOURCE: NatioMl Aaromutics and Space Administration.

preeminence in space transportation as well as in

other space activities. However, as a result of the

current budget stringency, Congress must choose

among competing ideas for the United States to

demonstrate its leadership rather than attempting to

demonstrate leadership across the board.

In contrast to U.S. civilian activities, the military

space program has spent relatively little on crews in

space, despite numerous efforts over the years by

some to identify military missions that would

require crews. Indeed, DoD has recently reaffirmed

that it has no requirements for crews in space.

Production of a piloted aerospace plane for military

use, such as is contemplated for a follow-on to the

current National Aero-Space Plane Program, would

reverse this historical stance.

An assessment of the appropriate mix of crewcarrying and robotic efforts for space science and

exploration, or for military activities, is beyond the

scope of this study. Expanded commitment to crews

in space, as contemplated by NASA and the Air

Force, would require increasing budgetary outlays

and would likely require the development of new

and costly crew-carrying space vehicles.

To illustrate the problem Congress faces, the

Space Shuttle system and the Space Station, both of

which require crews, dominate NASA’s budget for

the 1990s.5 As noted in a 1988 Congressional

Budget Office report, simply to maintain NASA’s

‘‘core program, ’ which includes these major programs, but no large additional ones, will require

NASA’s overall budget to grow from $10.5 billion

in fiscal year 1989 to about $14.4 billion in fiscal

year 1995.16 NASA plans to spend about $2.5 billion

per year for investment in its space transportation

system, including improvements to the Shuttle, an

advanced solid rocket motor, and in-orbit transportation vehicles. Operating the Shuttle will cost an

additional $2.0 billion. Anything new, such as an

SMOW of ~esident Bush’s 20 percen[ suggested budget increase for NASA for fiscal year 1990 derives from increases to buiid the Space Station,

which is scheduled for pemtanent occupation in 1996.

61J.s. Cmmss, con~ession~ Budget Office, The NASA Program in the )990s and Beyond (Washington, DC: May 1988), PP. x-xiv.
Chapter 2-Issues and Options ● 2 5

additional orbiter beyond OV-105, major modifications to the Shuttle, a Shuttle-C, a Personnel Launch

System, or a crew return vehicle, will add to these

costs.

Spaceflight is inherently risky. As noted in the

next section and in chapter 3, the exact reliability of

the Shuttle system is uncertain, but experts suggest

it ranges between 97 and 99 percent. Therefore, the

United States may expect to lose or severely damage

one or more orbiters within the next decade, perhaps

with loss of life, As America’s reaction to the

Challenger disaster demonstrated, the loss of another Shuttle crew in addition to an orbiter would

likely result in another long standdown of the Space

Shuttle system and could sharply reduce the productivity of the civilian space program. Loss of an

orbiter would also certainly lead to a painful

reexamination of the space program’s purpose and

direction.

One of the major challenges for the U.S. civilian

space program will be to learn how to reconcile

America’s goals for the expansion of human presence in space with the ever present potential for loss

of life. In particular, if the United States wishes to

send people into space on a routine basis, the

Nation will have to accept the risks these activities

entail. If such risks are perceived to be too high,

the Nation may wish to reduce its emphasis on

placing humans in space.

DEPENDENCE ON THE SPACE

SHUTTLE

U.S. dependence on the Space Shuttle for carrying

crews to space raises questions concerning the

longevity of the Shuttle fleet and the risks that

orbiters might be unavailable when needed. These

involve the inflexibility of the Shuttle system,

especially when scheduled to fly at rates close to the

maximum projected sustainable flight rate, and

possible attrition of the Shuttle fleet.

Inflexibility

Although NASA has estimated that Kennedy

Space Center can launch at most 14 Shuttles per year

with existing facilities, 7 NASA has scheduled 14

Shuttle flights in 1993,8 and plans to launch approximately 14 per year through the end of the century.

Scheduling launches at the maximum sustainable

launch rate leaves no margin to accommodate a

sudden change in launch plans or to fly any missions

that may be delayed by a future accident.

Attrition

Whatever the launch rate, the fleet will be subject

to a growing cumulative risk of attrition.9 In 1988, a

NASA contractor predicted post-Challenger Shuttle reliability would be between 97 and 98.6 percent

and used 98 percent as a representative estimate.10 A

more recent NASA study estimated the chance of

success on the Galileo mission would probably be

between 1 in 36 (97.2 percent) and 1 in 168 (99.4

percent). 11 The probability of orbiter recovery after

the Galileo mission would be comparable, because

the most likely causes of a mission failure would

probably destroy the orbiter. If reliability is and

remains 98 percent, there would be a 50 percent

chance of losing an orbiter on the next 34 flights,

a 72 percent chance of losing an orbiter before the

first Space Station assembly flight (if scheduled for

flight 92), and an 88 percent chance of losing an

orbiter before Space Station assembly is completed

42 flights later.

Because the construction of additional orbiters

requires about 6 years, in the early 1990s the only

way to increase the margin in the Shuttle launch

schedule is to delay some missions already scheduled or launch them on expendable launchers. To

increase the probability that the Nation will have

four operational orbiters in the mid-1990s, when

NASA expects to start construction of the Space

Station, some missions now scheduled could be

7Enc[oswe 10 Ictkr from D~ell R. Br~scorne, NASA HQ, to Richard DalBcllo, OTA, Mar. 31, 1988. A National Research Council panel estimated

that only 11 to 13 launches per year codd be sustained. see p~.$t-c~llwer As.~fssment of Swe sh~tle Fllgti Rates and utilization (Washington,

DC: National Academy Press, October 1986), p. 15.

8NASA He~qu~ers, Tr~\Wflation Services Office, Payfoad Flight Assignments, NASA Mixed Fleet, June 1989.

9VIZ, of not rWovenng ~ orbl[er in refurbishab]c condition, This may differ from tie risk faced by the crew, becau..e the crew might escape in some

situations in which the orbiter would be lost.

1~.sysmms, ~c,, S~~/e/Shu~/c.C operations, f/isks, and COS( Analyses, LSYS-88-008 (El Segundo, CA: L-systems, Inc. ) 1988).

I INASA, Ctie Q, l~epe~ent A~sess~n[ of s~ttle A~~l&nt s~enarlo prob~llltjes for the Galileo Mission, VO1. 1, April 1989.
26 ● Round Trip to Orbit: Human Spaceflight Alternatives

cancelled, delayed, or flown on expendable launchers. Ordering one or more orbiters now would

increase the probability of having four operational orbiters after the mid-1990s. Unless additional orbiters are added to the fleet, attrition is likely

to decrease fleet size, perhaps much more rapidly

than NASA expected originally or now plans for (see

ch. 3).

Wearout and Obsolescence

As time goes on, structural fatigue, wearout, and

obsolescence will become more important. Existing

Shuttle orbiters will be at least 15 years old in the

mid-1990s, when Space Station operations are

scheduled to begin. By that time, the designs of

many Shuttle systems will be 25 years old. It will be

economical to replace some systems, such as the

Shuttle computers, before they wear out, because

redesigned systems may be so much less expensive

to maintain and operate that the cost of upgrading

would be justified.12

Eventually, it will be economical to replace the

entire orbiter fleet with a fleet of newly designed

vehicles. As discussed in more detail in chapter 3,

NASA is now estimating the costs of operating

improved Shuttle orbiters and newly designed vehicles that would be used in an Advanced Manned

Launch System (AMLS).

NASA, the Air Force, and their contractors are

also estimating the costs of operating spaceplanes

that could be built using technology to be demonstrated by the experimental X-30 spaceplane now

being designed in the National Aero-Space Plane

program. When these estimates are completed,

comparisons of cost-effectiveness must be made to

forecast economic dates for phasing out orbiters of

existing design and introducing improved orbiters,

an Advanced Manned Launch System, and/or operational spaceplanes incorporating X-30 technology.

IMMINENT DECISIONS

If the United States wishes to continue its strong

dependence on the Space Shuttle, decisions about

whether or not to purchase a new orbiter or to

improve the Space Shuttle system should be be made

in the next year or two. These issues are discussed in

greater detail in chapter 3.

Order More Orbiters?

The United States must decide soon whether to

order one or more Shuttle orbiters in addition to the

one (OV-105) now under construction. Buying more

orbiters would provide increased fleet capacity and

flexibility and compensate for attrition. A new

orbiter could be a copy of OV-105, or could be

upgraded to improve safety, payload capability,

endurance in orbit, or ease or economy of operation.

It could be given a capability to fly automatically,

with or without a crew aboard, like the Soviet space

shuttle.

The longer a decision to order a “ship set” of

spare parts or another orbiter is delayed, the greater

will be the risk that the tooling or expertise needed

to manufacture some parts will be lost, thereby

leading to even longer lead times and greater cost.

Improve Existing Orbiters?

Existing Shuttle orbiters and OV-105 could be

modified to have some, but not all, of the improvements of safety, payload capacity, endurance, economy, and operability that a new orbiter could have.

This option could be chosen whether or not a new

orbiter (beyond OV-105) is ordered. It would

temporarily reduce the Shuttle flight rate, as making

modifications to orbiters effectively removes them

from the fleet for several months at a time.

Improve Other Shuttle Elements and

Facilities?

Shuttle elements other than orbiters could also be

upgraded. NASA and industry are considering many

options, with several goals. Some options, for

example, would increase the payload a Shuttle could

carry to orbit. This would allow the Space Station to

be assembled with fewer Shuttle flights and with less

extra-vehicular activity (EVA) by astronauts; EVA

is risky. It would also allow other payloads to be

carried with fewer Shuttle flights, and it would allow

heavier payloads to be carried on Shuttle flights.

IZNASA hw embmk~ on a program to fcpl~e the orbiters ’computers. However, because of the pace of improvements in computer technology, by

the time tiy are installed in the early 1990s, these computers will not be state-of-the-art.
Chapter 2--issues and Options ● 27

These options include:

●

●

●

●

continued development of Advanced Solid

Rocket Motors (ASRMs),

modification of Redesigned Solid Rocket Motors (RSRMs) to increase their thrust,

development of Liquid-fuel Rocket Boosters

(LRBs), and

development of lightweight External Tanks

(ETs).

These would increase Shuttle payload capability by

different amounts, and their other benefits and dates

of availability would differ (see ch. 3). Therefore,

two or more options might be pursued.

Alternatively, or in addition, NASA could develop complementary vehicles (e.g., Shuttle-C) to

carry large payloads to orbit and reduce the Shuttle

flight rate, thereby reducing the risk of Shuttle fleet

attrition. The United States need not decide this year

whether to proceed with one or more of these

options. However, if such improvements are desired,

more benefit will be reaped if they are begun sooner

rather than later.

Develop Capsules or Gliders for Escape or

Rescue?

Space Station crewmembers might become ill or

be injured and need to return to Earth before a

Shuttle could be prepared to rescue them. Although

NASA’s Aerospace Safety Advisory Panel has

recommended that ‘‘a single-purpose crew rescue

vehicle or lifeboat should be an essential part of the

Space Station’s design,”13 and although NASA’s

guidelines for “man-rating” space systems require

the Space Station to have some sort of escape system

(not necessarily single-purpose),14 NASA has not

yet decided to provide an escape system for the

Space Station. NASA has not estimated the risk

Station crewmembers will face, nor how much it

could be reduced by the various escape systems

NASA has considered developing.15 Whatever the

risk, it could be reduced to some degree, but not

eliminated, by providing an escape system for the

Space Station to complement safety measures already being pursued by NASA. ’G

NASA has considered several options for Space

Station “lifeboats” (see ch. 6):

● a dedicated Shuttle orbiter docked to the

Station;

. Apollo-like capsules; or

. gliders.

After the year 2000, NASA might rely on

spacecraft being developed by foreign partners in the

Space Station program (Hermes, HOPE, Saenger, or

possibly Hotol), or on “NASP-derived” spaceplanes for crew rescue or escape. But these would

not be available for the first years of Space Station

operation, unless Space Station construction is

delayed.

FUTURE DECISIONS

The United States need not decide now whether to

develop an Advanced Manned Launch System along

the lines now envisioned by NASA, or some other

version, and whether to develop a single-stage-toorbit aerospace plane. NASA and the Air Force have

programs to develop technologies for such vehicles

and to estimate their operational capabilities and

costs. Industry is also advancing proposals. More

technology development, design, and cost/benefit

estimation must be done before an informed rational

choice can be made in the early to mid-1990s.

Develop the Advanced Manned Launch

System or a Different Advanced Rocket?

In its AMLS program, NASA is studying concepts for an advanced reusable crew-carrying orbiter

(previously called Shuttle II) to succeed the Shuttle

in 2005 or later. NASA is evaluating five concepts:

. an expendable two-stage rocket;

. a partially reusable rocket;

. a partially reusable ‘‘drop-tank’ rocket;

. a fully reusable rocket; or

● a fully reusable two-stage vehicle that uses

airbreathing engines for the first stage.

13~zospxe safety MVISOV Pmei, Annuaf Report (Washington, DC: NASA Headquarters, Code Q-1. Mwch 1989), p. 7.

ldNation~ ~ronaulics and Spxe ,A&ninisMation, Guidelines for Man-Rating Space System, JSC-2321 1, prcliminiuy, September 1988.

15NASA h~ not ~outine]y ~fi~out qumti~tive risk ~~xssments of its sys~cms. SW T~dy E. Be]] and Karl EsCh, “The Space Shuttle: A Ca$e of

Subjective Engineering,” IEEE Specfrwn, June 1989, pp. 42-46.

16u.s. Cmgess, Congesslona] Budget Office, The NASA Program in the 1990s and Beyond (Washington, DC: May 1988)! PP. x-xiv.
28 ● Round Trip to Orbit: Human Spaceflight Alternatives

The airbreathing vehicle would take off from a

runway like art airplane, and both the unpiloted first

stage and the piloted orbiter would land on a runway.

The program will compare the costs and benefits

of an AMLS with the Shuttle evolution option under

study by the Johnson Space Center. It would be

prudent to defer a decision until NASA has completed preliminary designs of alternative vehicles in

sufficient detail to estimate technological risk and

life-cycle cost.

Develop a Single-Stage-to-Orbit Spaceplane?

The National Aero-Space Plane (NASP) program

is designing and developing technology for an

experimental single-stage-to-orbit air-breathing jet/

rocket aerospace plane, the X-30. Two X-30s are to

be built; they are intended to demonstrate the

feasibility of taking off from a runway, entering

orbit, reentering the atmosphere, landing on a

runway, and being prepared for another sortie within

24 hours. If the X-30 is successful, the government

will have a basis for greater confidence that operational aerospace planes (“NASP-derived vehicles,”

or NDVs) of similar design could be built to perform

civilian and military missions, including space

transportation. An NDV might serve as a space taxi

between Earth and low orbit.

The value of NDVs for space transportation will

depend in part on the importance of their unique

capabilities (e.g., rapid turnaround17) and in part on

the average cost per flight and per pound of payload.

NDVs might be very economical compared to

existing launch vehicles, and may compete in cost

with the proposed Advanced Launch System (ALS).

The NASP Joint Program Office is assessing the

ability of NDVs to satisfy some of the Air Force

needs18 that the ALS is being developed to satisfy.

However, in contrast to the ALS, a practical NDV

would not be able to carry extremely heavy payloads

(100,000 to 160,000 pounds to a low-altitude polar

orbit).

Average cost would likely depend sensitively on

maintenance man-hours per sortie (which is related

to turnaround time) and useful life. Aircraft that push

technology to the limit to increase speed and altitude

to perform novel missions often have greater-thanpredicted operating cost and shorter-than-predicted

useful life (see ch. 5). The A-11, SR-71, and the

Space Shuttle programs illustrated that maintenance

man-hours per sortie for such aircraft cannot be

estimated with confidence before considerable operational experience has been obtained, and useful

life cannot be estimated with confidence before

several vehicles have been retired or lost by attrition.

Even if NDVs were more costly than ALS for

space transportation, they could be judged worthwhile if they are necessary or uniquely economical

for military missions, such as surveillance from

orbit. The NASP Joint Program is assessing the

ability of NDVs to satisfy needs for a military

aerospace vehicle for the Air Force Space Command

and a military space flight capability for the Strategic Air Command.

The value and urgency of meeting these needs is

difficult to quantify; earlier stated needs for military

spaceplanes have gone unmet, with debatable but

not catastrophic effect on national security. For

example, in 1958 the Air Force proposed development of a rocket-powered spaceplane, the DynaSoar. It was to include ‘a manned capsule with glide

interceptor and satellite interceptor, together with

global reconnaissance and global bombardment

subsystems. The global bombardment capability

was to augment the Atlas, Titan, and Thor missiles

then in development. The Air Force Deputy Chief of

Staff for Development wrote that the Dyna-Soar and

four other proposed space programs, including a

Lunar Base System and an Advanced Reconnaissance System with a crew-carrying space station,

were “essential to the maintenance of our national

position and prestige.’ ’20 Development of the DynaSoar was approved, but in 1963, halfway through the

program, Secretary of Defense Robert McNamara

canceled the program, arguing that its objectives

‘7’’llrnaround time” is the time between a landing and the next take-off of the same vehicle.

18A~ Force ~Pxe Comad, ~SpACECOML~tate~nt of OperatW~lNeed (.TO/v) 00S- aaforanttdvamedhuch System (AILS), Aug. 12, 1988.

lgln foficmlng ~~y=s of tie po~n~~ ~onomic ~nefi~~ of NDVs ~d (he ALS, it will b @XXMIM to note whether, in estimating the savings

achievable by using NDVS or the ALS instead of existing launch vehicles, the same payloads are assumed to be launched on both systems.

20M,E. J)avieS ad WOR, Hfis, RAND’S Role in the EvO@lOn of Balloon ad Satellite Observation Systems and Related US. Space Technology,

R-3692-RC (Santa Monica, CA: The RAND Corp., September 1988), p. 96.
Chapter 2-issues and Options ● 2 9

could be met with the Manned Orbital Laboratory, weighed against the ability of other systems to

which was then just beginning and was later accomplish the Nation’s requirements for space

canceled.

21 The value of NDVs will have to be transportation.

Zlclwence J. Geiger, “The Strangled Infant: The Boeing X-20A Dyna-Soar, ‘‘ in Richard P. Hallion, The Hypersonic Revolution, vol. 2 (Wright

Patterson Air Force Base, OH: ASD Spcciat Staff Office, 1987),
Chapter 3

Space Shuttle Evolution

Photo credit: Nationalk Aeronautics and Spa ce Administration

The Space Shuttle Columbia begins its roll up the ramp to pad 39A after completing the 31⁄2 mile journey from the Vehicle Assembly Building

(September 1982)
CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

The Space Shuttle System Today. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Shortcomings of the Space Shuttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

NASA’s Flight Schedule. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Inflexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Risk of Attrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Obsolescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Near-Term Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Option 1: Buy Additional Orbiters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Option 2: Improve Existing Orbiters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Option 3: Improve Other Space Shuttle Elements or Facilities . . . . . . . . . . . . . . . . . . . . . . . 45

A Possible Shuttle Improvement Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Boxes

Box Page

3-A. Shuttle Attrition and Space Station Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3-B. Alternate Turbopump Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3-C. Shuttle Tile Automation System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Figures

Figure Page

3-1. Space Shuttle Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3-2. Kennedy Space Center Payload Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3-3. Kennedy Space Center Space Shuttle System Ground Flow. . . . . . . . . . . . . . . . . . . . . . . 36

3-4. Orbiter Ground Turnaround Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3-5. Effect of Flight Rate on Shuttle Orbiter Attrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

. . . . .

3-6

3-7

3-8

Shuttle Attrition if Orbiter Recovery Reliability is 98 Percent. . . . . . . . . . . . . . . . . . . . . 42

Expected Shuttle Payload Capability With Proposed Boosters.. . . . . . . . . . . . . . . . . . . . 46

Space Shuttle With Proposed Liquid-Fuel Rocket Boosters.. . . . . . . . . . . . . . . . . . . . . . 47

Tables

Table Page

3-1. Selected Possible Upgrades for New Orbiters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

3-2. Abort Mode Comparison of Shuttle/Booster Configurations . . . . . . . . . . . . . . . . . . . . . . 48

3-3. Materials Improvements for Shuttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

3-6. A Possible Shuttle Improvement Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Chapter 3

Space Shuttle Evolution

INTRODUCTION

At some point early in the next century, Shuttle

wearout, attrition, or a combination of advances in

technology and the emergence of missions beyond

the capacity of the Shuttle fleet will necessitate its

replacement. New crew-carrying vehicles would

incorporate advances in design, materials, and operations with the goal of attaining safe, reliable,

cost-effective transport of humans to space. In the

meantime, improvements to the current fleet may be

cost-effective.

THE SPACE SHUTTLE SYSTEM

TODAY

The Space Shuttle was the world’s first partially

reusable Earth-to-orbit launch vehicle (figure 3-1 ).

Begun in 1972, the Space Shuttle was first launched

in April 1981. It is capable of transporting both

humans and heavy, large payloads into low-Earth

orbit. Originally designed to carry payloads of

65,000 pounds to a reference orbit 110 nautical miles

high, inclined by 28.5 degrees, Shuttles are now

capable of carrying payloads of 52,000 pounds to the

same orbit. As of May 1989, the National Aeronautics and Space Administration had successfully

launched the Shuttle 28 times but experienced one

tragic failure when one of the Challenger’s Solid

Rocket Boosters (SRBs) failed in January 1986.

At launch, the liquid-fueled Space Shuttle Main

Engines (SSMEs) are ignited. If main engine operation appears normal, the SRBs are ignited 7 seconds

later; otherwise the main engines can be shut down

and the launch aborted. Once ignited, the SRBs

cannot be shut down before they bum out, 1 nor can

the Shuttle be safely held on the pad until the SRBs

bum out should a malfunction occur. Two and

one-half minutes into the flight, explosive bolts

separate the orbiter from the SRBs, which parachute

into the Atlantic Ocean and are recovered. After

about 8 minutes of flight, the SSMEs shut down and

the external tank separates from the orbiter, breaks

up as it reenters the atmosphere, and falls into the

Indian Ocean. In space, the Orbiter Maneuvering

System (OMS) engines, fueled by hyperbolic proFigure 3-1-Space Shuttle Elements

.

●

●

●

the orbiter,1 with the crew compartment and payload bay, which

also contains the three Space Shuttle main engines (SSMEs).

About the size of a DC-9, the orbiter weighs about 215,000 Ibs.

without its payload and has a 15 by 60 foot cylindrical payload

bay.

the external tank, which holds the liquid hydrogen fuel for the

SSMEs, and the liquid oxygen used to burn it.

two segmented solid-fuel rocket boosters (SRBs). Each is

made up of five Redesigned Solid Rocket Motor (RSRM)

segments. 1 T~ro are now ~r~ OrbitarS-~/Urn6ia, kawary, acd Atlantis. A fOurlh Ofilt9r,

Endeww will pm tha *et in 1992.

SOURCE: National Aeronautics and Space )klmtmstrat~on.

pellants, 2 propel the craft into the orbit desired for

the mission.

After the Shuttle crew completes its mission, the

orbiter fires its OMS engines to leave orbit, reenters

the atmosphere, glides to a runway, and lands. For

safety reasons, especially after the loss of Challenger, Shuttle orbiters will normally land at Edwards Air Force Base, California. However, in an

emergency, an orbiter could land at Cape Kennedy,

‘The SRBS can be destroyed in flight by the Range Safety Officer if, for example, the Shuttle veers out of control toward a populated area. Destroying

the SRBS in fligh[ would atso destroy the Shuttle orbiter.

2,4 fuel and ~ oxjdi~cr ~a[ ignile spontmeous]y when they come into contact. The OMS uses monomethyl hydmzine and mt.rogen tctroxide.

–33–
34 ● Round Trip to Orbit: Human Space flight Alternatives

Photo credit: National Aeronautics and Space Administration

The Shuttle orbiter in the Orbiter Processing Facility,

Kennedy Space Center. Visible are the orbiter’s three

Shuttle main engines and the two orbital maneuvering

system engines to the right and left of the

upper main engine.

Florida; White Sands Missile Range, New Mexico;

Zarogosa, Spain; Casablanca, Morocco; Rota, Spain;

or Guam. At the landing site, any remaining fuels are

removed from the orbiter, and the orbiter is ferried

atop a Boeing 747 aircraft to Kennedy Space Center,

where it is refurbished for the next launch.

Many systems and facilities are required to

process and launch a Shuttle and to communicate

with and advise its crew during a flight. NASA refers

to these systems and facilities, together with the fleet

of Shuttle orbiters, as the National Space Transportation System (NSTS, or STS).

Figure 3-2 shows the main facilities at Kennedy

Space Center (KSC) used for payload preparation

and for Shuttle launch preparation, launch, and

landing. The figure shows the Shuttle Landing

Facility (runway), the Operations and Control Building, the Vehicle Assembly Building (VAB), the

Orbiter Processing Facility, the Vertical Processing

Facility, the Launch Control Center, and launch pads

A and B of Launch Complex 39. Not shown are the

SRB Disassembly Facility, the SRB Rotational

Processing and Surge Facility, and the Mobile

Launch Platform, on which the Shuttle is erected in

the VAB. Facilities located elsewhere include the

Michoud Assembly Facility near New Orleans,

where external tanks are manufactured and shipped

to KSC by barge, and the Lyndon B. Johnson Space

Center (JSC) in Houston, Texas, where NASA plans

the missions, trains crews, develops flight software,

and controls missions via the Tracking and Data

Relay Satellite System and communications and

tracking stations located around the world. NASA

also maintains the Shuttle Landing Facility at

Edwards Air Force Base, California, where it uses a

dry lake bed as a runway, and the emergency landing

sites.

Launch operations include all the activities performed to maintain and launch Shuttles, including

refurbishment of orbiters and solid rocket boosters

after each flight. Figure 3-3 illustrates the operations

performed at Kennedy Space Center.3 The processing concept used at KSC is called integrate——transfa—

launch,” or ITL. The vehicle is assembled on a

Mobile Launch Platform in the Vehicle Assembly

Building and carried to the launch pad. This

minimizes orbiter time on the launch pad and

permits higher launch rates than could be achieved

with ‘‘integrate on pad’ processing.

As soon as the Shuttle lifts off the launch pad, the

mission is controlled from Johnson Space Center.

Payloads (experiments) may be controlled from

JSC, the Jet Propulsion Laboratory in Pasadena,

California, or the Goddard Space Flight Center in

Greenbelt, Maryland. But mission control is only

one part of the operations requirements. Mission

operations also include mission planning, training of

the flight crew and ground crews, development of

flight software, and the tasks performed by the flight

qFor f~er det~]s, w ch. 3 of U.S. Congress, Office of Ikchnology Assessment, Reducing Launch operariow Costs: New Technologies and

Practices, OTA-TM-ISC-28 (Washington, DC: U.S. Government Printing Office, September 1988).
Chupter 3-Space Shuttle Evolution ● 35
36 ● Round Trip to Orbit: Human Spaceflight Alternatives

I

-1
Chapter 3-Space Shuttle Evolution ● 37

crew in orbit. These activities may span 2 years or

more for a specific flight.

SHORTCOMINGS OF

THE SPACE SHUTTLE

U.S. dependence on the Space Shuttle for

carrying crews to space raises questions concerning

the longevity of the Shuttle fleet and the risk that

orbiters might be unavailable when needed. These

involve:

. the relative inflexibility of the Shuttle System,

especially when scheduled to fly at rates close

to the maximum sustainable flight rate;

● possible attrition of the Shuttle fleet as a result

of unreliability; and

. eventual obsolescence.

NASA’s Flight Schedule

NASA has estimated that 14 Shuttles can be

launched per year from the Kennedy Space Center

with existing facilities,4

and NASA has scheduled

14 Shuttle flights per year in 1993. However, NASA

has never launched more than 9 Shuttle flights per

year, and many experts doubt that 14 launches per

year can be sustained with a 4-orbiter fleet.5

The total number of workdays, or shifts, required

to prepare an orbiter for launch is called the

‘‘turnaround time. Keeping it short is essential for

reducing the cost per flight and increasing the

sustainable flight rate; turnaround time limits the

flight rate now. NASA’s goal of 20 shifts has never

been achieved. Actual turnaround time exceeded

200 three-shift workdays for the qualification (first)

flights of each of the first three orbiters, but had been

reduced to 55 three-shift days before the 25th flight,

on which the Challenger was lost (figure 3-4). After

that accident, NASA changed launch preparation

procedures; NASA estimates the turnaround time for

the first and second post-Challenger flights as 322

and 236 days respectively.6 NASA expects that in 4

years, turnaround time will decrease to 75 days,

which would allow 12 to 14 flights per year when a

fourth orbiter is added to the fleet. NASA expects

that a flight rate higher than 14 per year could not be

attained merely by buying more orbiters; with four

orbiters and a turnaround time of 75 three-shift days,

the flight rate would be limited by current facilities.

Additional orbiter processing facilities would be

needed to achieve a flight rate higher than 14 per

year.

In fact, NASA will have difficulty reaching a rate

of 14 flights per year unless it is able to find ways of

sharply reducing its current turnaround time. Its goal

of 14 flights per year assumes a ‘‘success-oriented

processing schedule’ and no margin for contingencies. Yet NASA is not achieving the reductions of

turnaround time it had anticipated. In addition, some

NASA officials have expressed concern that the 90

days planned for structural inspections and orbiter

modifications every three years may not be long

enough to accomplish all potential necessary work.7

Inflexibility

If NASA does eventually prove capable of launching 14 Shuttle flights per year, scheduling launches

at the maximum sustainable launch rate estimated by

NASA leaves no margin to accommodate a sudden

change in launch plans or to fly any missions that

may be delayed by a future accident. If a Shuttle

mission is changed, payloads and equipment for the

original mission may have to be removed before

equipment for the new mission can be installed.

If more margin were reserved in Shuttle launch

schedules, an orbiter could be on hand to be outfitted

quickly for an unplanned mission. This margin could

be provided by scheduling fewer missions per year

or by buying more orbiters—and more orbiter

processing facilities, if they become a bottleneck.

However, even with more margin, it could take as

long as a few months to prepare an orbiter for an

unscheduled mission, because of the lead time

required for mission planning+ orbiter processing,

4En~]os~e [0 lener from D~el] R. Brwcome, NASA HQ, to Richard DaJBello, OT’A. Mu. 31.1988.

sNatlon~ Re~eUch Comcil, Commltti on NASA Scientific and ‘fkchnological program Reviews, Posr-Challenger Assessment of Space Shurde

Flight Rates and Utilization (Washington, DC: Nationat Academy press, October 1986), p. 1S: krospace Safely Advisory %ncl, Annual Report

(Washington, DC: NASA Headquarters, Code Q-1, March 1989), p. iv.

~hcse estimates exclude the time spent improving the orbiters after the Chulfenger accident.

7NASA Kenn~y Space Center briefing, Apr. 26, 1989.
38 ● Round Trip to Orbit: Human Spaceflight Alternatives

700

600

600

400

300

200

100

0

Figure 34-Orbiter Ground Turnaround Experience

3-shift workday s

—

El Workdays on launch Pad

Workdays in vehicle assembly building

Workdays in orbiter processing faciIity

m

6 16 26

Shuttle flight sequence number

SOURCE: Office of Technology Assessment, 1989.

and crew training.8 There would still be insufficient of its crew-carrying space flight program while

flexibility to, say, rescue a Space Station crewmember who has a critical illness or injury. For this,

specially designed escape or rescue vehicles (discussed in ch. 6) might be needed.

Eventually, flexibility to schedule unplanned

Shuttle missions may decrease because of Shuttle

fleet attrition. Scheduling fewer missions per year

would compensate for this erosion of flexibility by

slowing the attrition of orbiters—but also at the cost

of foregoing opportunities for transporting people to

space. If the Nation wishes to improve the safety

increasing its flexibility, NASA and the Defense

Department will have to allow more margin in

Shuttle launch vehicle schedules.

Risk of Attrition

NASA intended each orbiter to last 100 flights

with a probability of at least 97 percent.9 If average

Shuttle “life” were limited primarily by attrition,

this design specification would require a 99.97

percent probability of recovering the orbiter in

refurbishable condition after each launch;10 if faSN~~ly, Shutie crews, pay]o~, and s~cific orbiter are chosen up to 2 years prior to a flight, in order to provide enough ttie for paylo~

integration and crew training.

9SP= Shun]e ~h~ C/D work slatemcnt design s~ifications.

IOA f~lm t. mover ~c orbl~r in ~f~bl,~able condition titer a la~ch could ~ cau~ by a failure of the orbiter, a failure of some other system,

human error, or unexpected conditions (e.g., lightning at launch).
Chapter 3-Space Shuttle Evolution . 39

tigue or wearout were significant, the probability

would have to be even higher. Orbiter recovery

reliability was probably lower during the first 25

flights; if it had been 99.97 percent, the odds against

losing an orbiter in the first 25 flights would have

been greater than 130 to 1. The reliability that would

have made the observed success rate most likely is

96 percent; the actual reliability is uncertain. ’l

NASA officials believe that Shuttle reliability

was improved after the loss of Challenger because

some failure modes were eliminated.12 However,

NASA has not estimated how much reliability has

been improved, because NASA does not routinely

estimate Shuttle reliability quantitatively,13 although

it has done so for planned missions that will employ

nuclear power systems.14

Estimates based partly on judgment vary widely.

For example, the late Richard Feynman, a member

of the Presidential Commission appointed to investigate the Challenger accident, called the Shuttle”. . .

relatively unsafe ..., with a chance of failure on the

order of a percent, ’ adding ‘It is difficult to be more

accurateo15 A NASA contractor estimated that

post-Challenger Shuttle reliability would be between 97 and 98.6 percent, with most failures caused

by propulsion failures during ascent.16 And while

one NASA division estimated that on the Galileo

mission the orbiter will have a 99.361 percent

probability of remaining intact until deployment of

the Jupiter-bound Galileo space probe begins,17

another NASA division estimated the probability

would likely lie between 1 in 36 (97.2 percent) and

1 in 168 (99.4 percent). *g

The uncertainty in Shuttle reliability on past

missions may be expressed in terms of statistical

confidence bounds. In essence, for each of several

possible values of reliability (called a lower confidence bound), one calculates a confidence level on

the probability that more failures would have

occurred than the number that did occur.19 If the

confidence level for a lower confidence bound

exceeds 50 percent, it is improbable that the

observed number of successes would have occurred

unless the reliability exceeded the lower confidence

bound, This approach is objective20 and takes into

account all factors, including human factors, that

may not affect the reliabilities of engines or other

components during ground tests. On occasion,

NASA has used confidence bounds.21

The method of confidence bounds possesses the

shortcoming that, even if reliability is high, many

launches are required to provide high statistical

confidence that it is. The 29 Shuttle launches to

date provide only 50 percent statistical confidence that Shuttle reliability has been at least

94.3 percent. If the reliability is now actually 94.3

1 IThe ~robabllity of s~ely r~overing he crew may differ from orbiter recovery reliabih!y, because the Crew might Survive Situations in which the

orbiter wouId be lost (e.g., main engine shutdown followed by crew bail-out and ditching of the orbiter at sea).

]zHowever, ~tentid new fallue modes were intr~uced. For ex~ple, radial bolts have been added to [he nozlle-to-c~~ Joint in tic SRBS) creat~g

new possibihties for blow-by or crack propagation. See Richard DeMeis, “Shuttte SRB: NASA’s Comeback Bid,” Aerospace America, April 1987,

p. 32 ff.

lsJ~es H. fletcher, ‘ ‘Risk Maagemcnt Policy for M~cd ~ ight prOgrlUllS, ’ NASA Management Instruction NMI 8070.4, effective Feb. 3, 1988;

Trudy E. Bell and Karl Esch, “The Space Shuttle: A Case of Subjective Engineering, “ IEEE $X?L’tW??I, June 1989, pp. 4246.

l~ener~ Elec~c As~o SpWe Division, F’lW/ &#e~ A~/ysis Report //for the Galileo Mission, doc. 87 SDS4213 (%lley Forge, PA: General

Electric Astro Space Division, August 1988).

i5Reporf of t~ pr~~ide~&/ co~ission on the Space Shuttle Challenger Accident, App. F. (WaSh@tOn, DC: U.S. Government printing Office,

1986); R.P. Feynman, What Do You Care What Other People Think? (New York, NY: W.W. Norton& Co., 1988), p. 236.

16L-Sys[cm~, In~., S~nle/L~hu~le.C oper~io~, Risks, and cost Analyses, LSYS-88-008 (El Segundo, CA: 1988).

17Gener~ Elatnc Aswo Sp=e Division, op. cit., NASA supplid no rationale for its estimates Of fdUre probabilities from which General Electric

calculated this probability, and NASA specifications had the effect of masking the overall uncertainty.

18NASA, Code @, clt~ in chapter 2, The probability of orbiter recovery after the Galiko mission would be comparable to the mission success

probability, bcxause the most likely causes of a mission failure would probably destroy the orbiter.

19Y. Fujino, “Approximate Binomial Confidence Limits, ” Biometrika, vol. 67, No. 3, 1980, pp. 677-681; see also C.R. Blyth and H.A. Still,

“Binomial Confidence Intervals, “ Journal of the American Statistlcul Association, vol. 78, No. 381, March 1983, pp. 108-116.

ZfJsubjative me~~s, if]ogic~ly Consistcnl, cm ~so be Valuable see M.G. Morgan imd M. Hem”on, Uncerfai~ ((!\arcn&m, b&nd: Cambridg e

University Press, in press).

21sW, e.g,, Jerry J. Fit~, NASA Transportation SerVICes Office, ‘‘Payload Backlog, Flight Rate Capability, Reliability and Downtime-Briefmg for

Dale Meyers, ” Nov. 5, 1987, rev. Dec. 9, 1987.
40 . Round Trip to Orbit: Human Spaceflight Alternatives

percent, there would be a better than even chance

of losing at least one orbiter on the next 12 flights

(figure 3-5).22

If reliability is, or becomes, higher, additional

flights will eventually provide greater statistical

confidence that is. But if it is judged more important

to have four orbiters in the mid-1990s than to have

high launch rates now, conservative planning would

allow for the possibility that reliability might be

lower than 94.3 percent by ordering one or more

additional orbiters as soon as possible and limiting

Shuttle launch rates until the first one becomes

operational. Even if reliability is 98 percent, launching Shuttles at the rates now planned would make it

unlikely that Space Station assembly could begin

before another orbiter is lost (see box 3-A and figure

3-6).

Obsolescence

After sufficiently many flights, an orbiter’s airframe could be so weakened by fatigue as to be

unsafe. Replaceable parts may also wear out; when

they do, replacement parts may no longer be

available from manufacturers. The manufacturers

that built them originally may have stopped making

such parts, the tooling used to build them may have

been destroyed, and the skilled workers who made

them may have left or retired. If sufficient spare parts

have not been stockpiled, replacement parts may

have to be custom-made, and this may require new

tooling, training of workers, extra expense, and

delay.

Existing Shuttle orbiters will be at least 15 years

old in the mid-1990s, when Space Station operations

are scheduled to begin. By that time, the designs of

most Shuttle systems will be 25 years old, On

occasion, it will be economical to replace some

systems before they wear out, because redesigned

systems would be so much less expensive to operate

that the cost of upgrading would be justified.

Eventually, it will be economical to replace the

entire orbiter fleet with a fleet of newly designed

vehicles that can be operated at lower life-cycle cost.

NASA is now estimating the costs of operating

improved Shuttle orbiters and newly designed vehicles that would be used in an Advanced Manned

Figure 3-5-Effect of Flight Rate on

Shuttle Orbiter Attrition

Cumulative probability of orbiter loss

1 00% -------

-----------

----

90%

.--

..-

~.-

80%/ / ,,” I

.

70% /

/

/

60% /

/

10% / ‘ --- 94 %

— 84 % I

I o% 1 1 I I 1 1 1 I 1 I

Flight 30 35 40 45 50 55 60 65 70 75 80 85 90 95100

7/year: 1990 1991 19921993

“Compare expected attrition at a launch rate of seven per y r

These graphs show the cumulative probability that at least one

orbiter will not be recovered after a flight, starting with flight 30, for

four possible values of orbiter recovery reliability: 84%, 94.3%,

98°/0, and 99%. The actual value of orbiter recovery reliability is

uncertain. 84% is the lower confidence bound on post-Challenger

reliability at a confidence level of 50%. 94.3% is the lower

confidence bound on reliability at a confidence level of 50%,

based on all flights to date. 98% is the nominal post-Challenger

reliability estimated by L Systems, Inc., and 99% is consistent with

a NASA estimate of Shuttle reliability on the Galileo mission (see

text).

Reducing the flight rate would slow the growth of the cumulative

probability of orbiter loss. For example, reducing the flight rate

from that scheduled by NASA in June 1989 to a rate of five flights

per year beginning 1990 would reduce the probability of orbiter

loss by 1995 from about 70 percent to about 44 percent, if the

orbiter recovery reliability were 98 percent.

SOURCE: Office of Technology Assessment, 1989.

Launch System. NASA, the Air Force, and their

contractors are also estimating the costs of operating

spaceplanes that could be built using technology to

be demonstrated by the experimental X-30 spaceplane. When these estimates are completed, comparisons of cost-effectiveness can be made to

forecast economically optimal dates for phasing out

orbiters of existing design and introducing improved

Shuttle orbiters, a Personnel Launch System, an

Advanced Manned Launch System, and/or operational spaceplanes incorporating X-30 technology.

22T~ fou ~st-c~ffenger launches to date, afl successful, provide only 50 percent confidence that post-Chulfenger reliability has been at kast 84

percent. If the reliability is 84 percent, there would be a better than even chance of losing an orbiter on the next four flights.
Chapter 3-Space Shuttle Evolution ● 41

NEAR-TERM OPTIONS

In the near-term the Nation could choose one or

more of the following options:

●

●

●

●

The

purchase additional orbiters--either copies of

the orbiter (OV-105) now being built, or

improved orbiters;

improve existing orbiters;

improve other Space Shuttle elements or facilities; or

develop Space Station escape capsules or a

Personnel Launch System to complement the

Shuttle fleet.

following sections discuss the first three options. The last one is discussed in chapter 6.

Option 1: Buy Additional Orbiters

Buying more orbiters would increase the resiliency of the Space Shuttle system, i.e., its ability to

recover rapidly from loss of an orbiter or any other

event that delays launches. As noted in earlier

sections, the Shuttle orbiter fleet is likely to continue

to suffer occasional attrition.23 Loss or prolonged

unavailability of one orbiter would throw NASA’s

plans for Space Station assembly and servicing into

disarray and could lead to loss of life.24

The Shuttle prime contractor, Rockwell International, argues that the Shuttle system could still be

flying in 2020. Although this is theoretically possible, it may not be desirable, primarily because of

obsolescence. The Shuttle will remain the crewcarrying workhorse well into the next century, but

other more cost-effective options will also be

pursued.

The company also believes that even in the

absence of attrition, the percentage of time the

orbiters are likely to spend being inspected, modified, or refurbished requires NASA to maintain five

orbiters in order to assure use of four.25 Rockwell

Box 3-A-Shuttle Attrition and

Space Station Assembly

The Shuttle fleet now consists of three orbiters;

a fourth is to become operational in 1992. All 4

orbiters will be needed to fly the missions now

scheduled for 1992-95 and planned for 1995-97,

when NASA plans (but has not yet scheduled) 21

Space Station assembly flights. Figure 3-6 shows

the probabilities that all 4, or at least 3, orbiters will

survive flights 30 to 200, if post-Challenger Shuttle

reliability is 98 percent. ’ If NASA adheres to its

current schedule through 1994 and flies 14 flights

per year thereafter, Space Station assembly would

begin by about flight 92 and be completed by about

flight 134. There is little statistical confidence that

orbiter recovery reliability is at least 98 percent—

only 7.8 percent confidence based on the four

post-Challenger flights, or 11.4 percent confidence

based on all flights to date. (See text for a discussion

of statistical confidence. )

1 L-Systems, Inc., Muttlel.Vhuttle-C Operations, Rtsb, and Cost

Analyses, LSYS-88-008 (El Segundo, CA: L-Systems, tnc., 1988).

officials similarly argue that having a slightly larger

fleet, or ‘fleet margin’ would allow for unexpected

contingencies and unscheduled downtime, ‘

Rockwell estimates that, starting from scratch, an

orbiter could be built in about 6 years. If some

structural spares are available, the time could be

reduced by about a year. Thus, if a new orbiter

(OV-106) were needed by, say, 1996, the decision to

build spares would have to be made in 1990. A

decision to purchase OV-106 could be delayed until

fiscal year 1991. Major structural components for

the Shuttle can take 4 to 5 years to produce. Space

Shuttle Main Engines (SSMEs) now require 4 years.

Orbiter OV-105,26 ordered to replace the Challenger, was begun in 1987 and is scheduled for

completion late in 1991.27 It will be ready in such a

relatively short time because major components

zspo~t-c~ffenger Asscssmenl of sp~e shut~e might Rates and Utilization, National Research Council (WiIShington DC, Nationat Academy Press,

October 1986); Report of the Committee on the Space Station of fic Nation~ Resewch co~cil (Wmhington DC: National Academy Press, September

1987). See atso L-Systems, Inc., “Shuttle/Shuttle-C Operations, Risks and Cost Analyses,” El Segundo, CA, LSYS-88-(XN, July 21, 1988, which

anatyses the probability of supporting Shuttle commitments under differing assumptions of fleet size, flight rates, and reliability.

24~M of ]jfe codd occu if resupply to the SlatIon is late.

ZsRockwel] prewn~tlon t. OTA, Nov. 15, 1988, p. 20. The L-Systems report also makes a Compelling case for repktcement ~d sP~e orbiters.

~ln May 1989, President Bush n~ed this ncw space shut~e orbiter ~’~eav~~~, titer the first shp comm~ded by James Cwk, the British explorer

who was the first European to discover Hawaii.

27F1rq flight is expected early in 1W2.
42 ● Round Trip to Orbit: Human Space flight Alternatives

Figure 3-6--Shuttle Attrition if Orbiter Recovery Reliability is 98 Percent

Probability of having at least three or four orbiters

1

0.5

0

after flight 30 40 50 60 70 80 90 100 110 120130140150160170180 190200

I

Endevour begin complete

Space station assembly

(OV=1O5)

on line

SOURCE: Office of Technology Assessment, 1989

already existed as spares. If too long a period passes

between major component buys, some of the expertise and physical plant required for manufacture

could be lost, leading to even longer lead times.

If Congress decided to proceed with building a

new orbiter, it has three basic options. Congress

could direct NASA to construct an orbiter:

● that is a copy of OV-105;

. designed for increased safety, performance

(e.g., endurance), and economy; or

. with reduced weight to increase payload capability or with other improvements (e.g., an improved escape system).

Build a Copy of OV-105 (Endeavour)

OV-105 is itself a greatly upgraded vehicle

compared with its predecessors and includes:

. addition of an escape hatch, with an extended

pole to allow crew members to slide down and

parachute to safety;

●

●

external changes including improved heat absorbing tiles, changes to the landing gear,

strengthening of the wing structure and engine

pod; and

more than 200 internal changes including

electrical rewiring and changes in the braking

and steering systems. Because of these improvements, building OV-106 identical to OV105 would still represent considerable modernization of the fleet.

Improve Safety, Performance, and Economy

For the second option, a large number of potential

new upgrades have been identified by the orbiter

prime contractor, Rockwell, and are shown in table

3-1. These have been categorized into the three basic

areas of safety and reliability, cost reduction, and

performance, although each change has benefits in

several categories. Orbiter upgrades are being continually defined and evaluated so that the list itself

is dynamic. NASA/JSC is studying the costs and
Chapter 3-Space Shuttle Evolution ● 43

benefits of possible improvements with a view to

identifying the most important improvements.

The orbiter cockpit could be made into a crew

escape module to allow the crew to escape in some

situations in which the existing escape pole system28

is unusable. However, a crew escape module would

be heavier and more costly; 29 developing it would be

a very difficult project and its utility is the subject of

considerable debate.

Space Shuttle main engine improvements that

would increase engine life and reliability are already

under way. They include improved welds, improved

manufacturing techniques, improved nondestructive

testing, improved heat exchangers, improved controllers, improved power head, engine health monitoring,30 alternate turbopump development (see box

3-B), and a technology test bed.31

The on-board computers of future launch vehicles, or existing orbiters, could consist of identical

computer modules “mass-produced” for economy

(possibly even commercial modules) and connected

by optical fibers for reduced susceptibility to electromagnetic interference. 32 Computers with a high

degree of fault-tolerance would also allow the

launch of a vehicle with a known fault rather than

holding the launch to replace a failed module and

retest the system.

The length of time an orbiter can remain in orbit

could be extended.33 NASA states that “extended

duration orbiters’ will allow NASA to fly missions

lasting 16 to 28 days (current orbiters are limited to

7 days). This would be useful for SpaceLab and for

tending the Space Station in the crew-tended phase,

or servicing commercially developed space facilities.34 It would also provide experience in technology areas beneficial for future space operations.

A Shuttle orbiter could be given the capability to

fly an entire mission automatically, as the Soviet

Table 3-l-Selected Possible Upgrades

for New Orbiters

Safety & reliability:

. Assured crew return

. Simplified hydraulics

. Increased strength skins

• Improved attitude control

● Suppressed helium overpressure

Cost reductionms:

● Simplified cooling

. Modernized crew displays

● improved tile durability

. Modernized telemetry

Performance:

● Extended duration orbiter

. Weight reduction

● Local structure strengthening

. Global Positioning Satellite (GPS) receiver-computer for

navigation

SOURCE: Rockwell International Corp.

shuttle Buran did on its first flight. Without a crew,

an automatic orbiter could carry extra payload. With

a crew, such an automatic orbiter could land even if

Shuttle pilots were incapacitated (e.g., by a depressurization accident).

Reduce Weight

The third option would involve significant weight

reduction of the airframe. Orbiter airframe weight

reductions of 8,000 to 10,000 pounds for both

retrofittable and nonretrofittable structures could be

achieved through the use of composite materials,

alloys, intermetallics, and high-temperature metallies. This would allow payload capability to be

increased by the amount orbiter weight is reduced

(i.e., up to 10,000 pounds) or allow an improved

escape system or other systems to be installed

without sacrificing payload capability. About 10$000

pounds of weight reduction would provide the

equivalent of one extra launch of 60,000 pounds of

payload in one and one-half year of OV-106 flights

(approximately six launches). The choice of specific

airframe structural modifications would depend on

cost-benefit analyses.

28~e ~=av @e ~~tem is o~y good ~der s~b]e flight conditions al re]ative]y ]OW Sp(XdS.

29George Marsh, ‘‘Eject, Eject, Eject,’ Space, January-February 1988, pp. 4-8.

301n ~~r wwd~, ~~g able t. diagnose engine operation when it IS firing. Thk ki(k tO il’tlprOVd pWfOITIUUICC and POtentid]y can signal if engine

shutdown is necessary to avoid catastrophic failure.

SIJ.W. SmelXr, MSFC, pre~ntation to OTA, Sept. 21, 1988.

szReducing tinch operations Costs, op. cit., footnote 3, p. 63.

ggDwayne WeW, JSC, presentation to OTA, Sept. 22) 1988.

341t Wou]d gener~ly & U=ful for a Who]e Cl=q of expefimen~$ s~ OTA’s sp~c Station study: Civi/hn !@ce ,$@fio~ and h? U.S. Furure in Space

(Washington, DC: U.S. Congress, Office of 7kchnology Assessment, OTA-ST1-241, November 1984).
44 ● Round Trip to Orbit: Human Space flight Alternatives

Box 3-B—Alternate turbopump Development

Improving the lifetime of the SSME is a good example of a significant incremental improvement. NASA has

a $228 million contract with Pratt and Whitney to build an alternate fuel and oxidizer turbopump that will be more

durable and reliable than the existing ones.1

 Pratt and Whitney will attempt to bring the engines closer to their

intended 55 missions (approximately 7.5 operating hours), between costly teardowns.2 NASA’s design goals call

for 30 missions before removal for minor seal and bearing replacements, and another 30 missions before major

overhaul. This would cut SSME refurbishment time and operational costs. These turbopumps are designed to be

completely interchangeable with the existing Rocketdyne pumps, have more benign failure modes for greater safety,

and will have only 4 welds compared to the present 297. The table below lists some of the ATD enhancements and

advantages to date. The new turbopump borrows heavily from Pratt and Whitney’s experience building the T800

helicopter engine; additional development is required for withstanding the harsh operating environment of

ultra-high pressures, cryogenic temperatures, and possible hydrogen embrittlement.

Benefits of Alternate turbopump Development

Principle: Benefits:

. Design for producibility utilizes precision cast- . Improved turbomachinery quality

ings and new processes and materials, thereby

minimizing number of welds, parts, and coatings. . Improved part-to-part repeatability

. Improved durability

Results to Date:

. Reduced machining requirements

. Number of welds reduced from 297 to 4. . Reduced manufacturing lead time by 20 months

. Rotor stack details reduced from 80 to 39 . Reduced turbomachinery cost ($3 million per

. No coatings in hot turbopump sections pump set)

IFrantc Cohtcci, “Space Power From Ftonda,” Sptwe, Nov-Dec 19S8, pp. 10-12; Edward H. Kolcum, “Pratt and Whimey Engine Thrbopumps Could Fly

on Space Shuttte in 1992,” Aviation Week and Space Techtw!ogy, Feb. 27, 1989.

2up,0 ~ ~=t, M ~gims have had complete turbine blade inspectmrt-s aft= evev mission.

Some of these upgrades could not be retrofitted —funding that is often difficult to obtain, particuinto existing vehicles because they would require larly when the overall U.S. budget is so constrained.

extensive and expensive structural changes. Major upgrades to the existing fleet could be

accomplished during the regularly scheduled strucOption 2: Improve Existing Orbiters35 tural inspection program (every 3 years), bringing

Redesign and improvement for all Shuttle sys- the entire fleet up to improved levels. However,

NASA would have to reduce its expectations for the terns is a continuing process.36 However, NASA,

through the Johnson Space Center, has begun to Shuttle schedule in order to have enough time to

examine how best to improve the existing Space make these modifications. As noted above, meeting

Shuttle system by making incremental changes. The the manifested launch rate of 14 flights per year

first effort studies major evolutionary modifications presents a major challenge to NASA, even in the

that could be applied to the existing Shuttle fleet. absence of major modifications to the Shuttle

This evolutionary path is becoming increasingly system.

attractive to NASA because it would allow a phased Improved Space Shuttle main engines and comimplementation of improvements, is relatively low- puters, discussed above, could be installed on

risk, and would not require “new program” funding existing orbiters.

35s= ~W Gene Austin, MSFC, “Shuttle Evolution/Follow-On,” Sept. 21, 1988, and C. ‘Ikixeira, JSC, Sept. 22, 1988.

36B~au~ of tic m~ulti nature of lhe Spwe shuttle system, some ch~ges can take place outside of orbiter changes.
Chapter 3-Space Shuttle Evolution ● 45

Reduce Airframe Weight

The airframe weight of existing orbiters (or

OV-105) could be reduced, but not by as much as the

airframe weight of a new orbiter could be reduced.

This would allow payload capability to be increased

by the amount orbiter weight is reduced, or allow an

improved escape system or other systems to be

installed without sacrificing payload capability.

Crew Escape Module

The cockpit of an existing orbiter could be made

into a crew escape module to allow the crew to

escape in some situations in which the existing

escape pole system would be unusable. A crew

escape module would be heavier and more costly;

installation on an existing orbiter would be more

costly, in terms of payload capacity sacrificed, than

would installation on a new orbiter, because the

airframe weight of a new orbiter could be reduced by

a greater amount.

Automatic Orbiter Kit

An existing Shuttle orbiter could be given a

capability to fly an entire mission automatically.

This would require installation of a kit consisting of

additional automatic control equipment (in the

orbiter galley) and cables. Rockwell International

estimates that it would take 2 years and cost $200

million to automate a first orbiter and $30 million to

$40 million each for successive orbiters. Rockwell

designers estimate the most difficult problem will be

steering and braking after landing.

Extending Duration in Orbit

An existing Shuttle orbiter could also be made an

Extended Duration Orbiter by installing fuel cell

pallets in the payload bay, and additional life support

supplies.

Option 3: Improve Other Space Shuttle

Elements or Facilities

Space Shuttle elements other than the orbiter

could also be improved, or replaced by newly

designed elements.

Continue Development of Advanced

Solid Rocket Motors 37

The Challenger accident was caused by a failure

in a solid rocket motor.38 After the accident, NASA

redesigned the solid rocket motors (SRMs) to

improve reliability; these redesigned solid rocket

motors (RSRMs) have been used on all subsequent

Shuttle flights. Seeking even higher reliability, as

well as higher performance, NASA has also initiated

development of Advanced Solid Rocket Motors

(ASRMs). They are to weigh less than RSRMs but

produce more thrust, allowing Shuttles to carry up to

12,000 pounds of additional payload to orbit. Figure

3-7 illustrates the expected improvement in ASRM

payload capability with respect to the present

RSRM. Some NASA officials have expressed concern over whether the full additional lift capability

of 12,000 pounds will be achieved. Their concerns

are the result of past experience with launch

systems. 39 Program officials at Marshall are confident that the 12,000 pound lift increase for the

ASRMs can be achieved, as they have incorporated

a lift margin to allow for weight growth of the solids.

Many also feel that even if the lift increase goal is not

completely met, that the other advantages of the

ASRMs such as increased reliability, reproducibility,

and a second supplier for of solids will make them

worthwhile. NASA expects that the ASRM program

will promote a competitive solid rocket motor

industry and encourage commercial initiatives.40

NASA has estimated the cost of the ASRM program

at $1.3 billion, of which $1 billion would be for

ASRM design, development, testing, and evaluation, and the rest for facility construction.

37s= ~W, U.S. Congess, office of WhIKIIOgy Assessment, Luunch (lptions for the Future: A Buyer’s Guide, pp. 27-28.

313c~lenger ~U lawch~ ~ wea~er much colder than the solid rocket motors were cetiificd to tolerate.

s~For exmple, ~ noted Cwller, tie origti~ Shuttle performance god ww 65,000 po~ds to 110 nmi, 28.5 degrees. But the existing Shuttle only

achieves 52,000 pounds to ttis orbit. Ttis d=e= in lifi capability mose from we%ht ~o~h of tie Shuttle i~lf ~d lower tian expected performance

from the propulsion systems.

40 NASA, *’SpXe Shutdc Advanced Solicl Rocket Motor—Acquisition Plan,” Mu. 31, 1988, P. 3.

ql~rospwe Sticty Advisory Panel, op. cit., p. 3, and press briefing, Mar. 28.1989.

d?-Ibid., IN. Cit. S* ~W, E]iot Marshall, ‘‘Shuttle Rocket Plan Under Fire, Science, VOI. 244, PP. 1 A5- 136.
46 ● Round Trip to Orbit: Human Spaceflight Alternatives

Figure 3-7--Expected Shuttle Payload Capability

With Proposed Boosters

1 ‘ ‘: 14 . .

I

I

SOURCE: Office of Technology Assessment,1989.

In March 1989, NASA’s Aerospace Safety

Advisory Panel (ASAP) announced its finding that

“on the basis of safety and reliability alone it is

questionable whether the ASRM would be superior

to the RSRM . . . until the ASRM has a similar

background of testing and flight experience. This

may take as long as 10 years. . .”41 The ASAP

recommended “that NASA review its decision to

procure the Advanced Solid Rocket Motor and

postpone any action until other alternatives. . . have

been thoroughly evaluated. ”42 NASA disagreed

with the ASAP findings and, in late April 1989, it

awarded two contracts to a partnership formed

between Aerojet and Lockheed.43 One contract is for

design and development of the ASRM; the other is

for the design, construction, and operation of an

automated solid rocket motor production facility.

NASA has designated Yellow Creek, Mississippi as

its preferred GOCO (government-owned/contractoroperated) ASRM production site and the Stennis

Space Center in Mississippi as the motor test

location. ASRMs could be ready for a first launch in

1994 or 1995.

Improve Redesigned Solid Rocket Motors

The Challenger disaster was attributed to a failure

of one of the Solid Rocket Motors.44 This prompted

a program that redesigned the motor’s joints and

made other improvements, some of which were in

process even before the Shuttle explosion. Many of

the improvements in the RSRMs relate to ablative

and insulation materials processing and nondestructive testing techniques. As of May 1989, the RSRMs

have now performed successfully on four Shuttle

flights. 45

The thrust of the RSRMs could be improved by

6,000 to 8,000 pounds by substituting a more

energetic solid propellant and by performing other

requisite changes to the motors.46 The additional

thrust would increase the Shuttle’s payload capacity

by the same amount but might decrease unreliability.

NASA has not estimated the cost of such improvements, but qualification testing alone would require

about 10 rocket firings at $10 million to $12 million

per test. These improved thrust RSRMs would be

ready for flight before 1995, which is when ASRMs

are scheduled to replace the existing RSRMs. More

extensive changes could give a payload increase of

13,000 pounds.47

Develop Liquid Rocket Boosters (LRBs)48

At the same time that NASA was planning its

ASRM work, propulsion experts inside NASA and

in the aerospace community began to reconsider the

practicality of replacing the current SRMs with

ql~row= s~ety Advis,Ov panel, op. cit., p. 3, and press briefing, Mu. 28, 1989.

qzIbld., ]Wo ~il. S= ~so, E1iot M~sh~l, “Shut~e Rocket plan Under Fire, ’ ‘ Science, vol. 24, pp. 135.136.

431mm~ia[e]y ~~er he ASAp ~U~ review on M~, 28, 1$)8$), NASA Administrator James Fletcher iIIUIOUIKCd to the pKSS that NASA would award

the ASRM Phase C/D contracts as planned, despite the ASAP concerns. One rea~n w~- hat tie f~ds had ~adY ~n au~ori~~.

44RePon of the Presldentid co~ls$lon on the Space Shuttle Challenger Accident, oP. cit.

d5D~coveV: Sepl, 29, ]988; Atlu~~: ~c. 2, 1988; Discoveq: M~. 13, 1989; Atlantis: May 4, 1989.

46s= resPnw by Mo~n Thioko], Inc, to NA!jA Marshall Space Flight Center request to provide candidate NS~ PaYlo~ Perfo~~Ce

improvements directly related to RSRM changes. Memo L060-FY89-170, Apr. 3.1989.

47[bidm

48~wh OptioM for t~ Future: A Buyer’s G~’&, op. cit., foomote 38, pp. 28-29.
Chapter 3-Space Shuttle Evolution ● 47

Figure 3-8-Space Shuttle With Proposed

Liquid-Fuel Rocket Boosters (LRBs)

(artist’s conception)

Photo credit: National Aeronautics and Space Administration

One of the Shuttle’s redesigned solid rocket motors being

attached to the mobile launch platform, Kennedy Space

Center.

Liquid Rocket Boosters.49 Initial studies indicate

that LRBs could replace or complement the RSRMs

or the ASRMs on the Shuttle, but would require

some redesign of Shuttle and launch pad systems.50

NASA estimates that development and testing for

the liquid booster alone would cost $3 billion spread

over 8 years.51 Pad modifications would cost $500

million. A conceptual drawing of the Shuttle atop

LRB rockets (two pods of four liquid engines each)

is shown in figure 3-8.

49LRBS ~ereo~~n~ly st~i~ at he ~wptlon of the shuttle program bul were rejected in favor of solids when h WiM estimated that LRB development

would cost $w10 million more and would take at least 1 year longer thm solids. (U.S. Congf=% HOUSC Committee on Science, Space and ~hnology,

Subcommittee on Space Science and Applications, Space Shuttle Rwovery HeWings. Apr. 29-30.1987, VO1. L P. 64; also Larty Wear, MSFC). Some

cite this as another case where a decision based on a constrained budget led to a less than optimal choice of technology for the long-term.

s~~~ SF= @rations Co. rep to KSC: Liquid Rctckct Booster Integration Study, LSO-~-286-1410, Novem~r 1988.

51’I’hi5 includes tie first flight article and operations costs for the first flight.
48 ● Round Trip to Orbit: Human Space flight Alternatives

pared to developing each separately .52 The Rocketdyne Division of Rockwell International has also

worked on modifying some of their existing engine

hardware into an “RSX” configuration (liquid

oxygen/kerosene fueled) for use on art LRB.53 Both

firms feel that LRBs could be developed for

substantially less than $3 billion.

LRBs could provide significant benefits in safety,

performance, reliability, operations, environmental

impacts, and the payload’s physical environment,

and offer important synergisms with other programs

(table 3-2). However, they would also present higher

risks, resulting from greater technical uncertainty,

longer development times, potentially higher initial

cost, and the need for launch pad modifications.

Appendix A discusses the benefits and drawbacks of

LRB development in more detail.

Develop Lightweight External Tank (ET)54

The emphasis on using improved materials in the

Shuttle system has focused particularly on saving

weight. For example, a 20 to 30 percent weight

savings in the weight of the external tank could

accrue from using aluminum-lithium (A1-Li)55 alloy

instead of the present aluminum alloy. If the external

tanks were made of Al-Li and the intertanks (which

hold the cryogenics) were made of graphite epoxy

composite, the Shuttle would weigh 12,000 pounds

less at lift-off. Because the external tank is carried

nearly all the way to orbit, reducing the weight of the

ET by 12,000 pounds would translate into almost

12,000 pounds of increased payload capability.

Additional ET options, which could improve reliability and reduce costs, would involve increased

use of robotics in manufacturing, nondestructive

evaluation techniques, and thermal protection system improvements. Table 3-3 lists some typical

materials improvements.

Table 3-2-Abort Mode Comparison of Shuttle/

Booster Configurations

Engine

failure a

Abort mode

Booster + SSME SRB ASRM LRB

o 1 RTLS RTLS TAL

o 2 Split-S or ditch Split-S or ditch Loft-return

o 3 Split-S or ditch Split-S or ditch Loft-return

1 0 None None ATO

1 1 None None RTLS

1 2 None None Loft-return

1 3 None None Loft-return

2 0 None None TAL

2 1 None None RTLS

2 2 None None Loft-return

2 3 None None Loft-return

aAaaumes engines tail at iiftoff.

KEY: ASRM=advanoed solid rooket motor; ATO=abort to orbit; LRB=liquid rodcet

booster; RTLS=Retum to launch site; Split-S.aircraft landing maneuwrr tha!

utihzes banidng to dissipate energy and siow down; SRB.soiid rocket booster;

SSME=Spa- Shuttte mam engine; TAL=tranaatiantic abort.

SOURCE: Generai Dynamics

Improve Operations56

Introducing a number of new technologies and

management strategies into Shuttle operations could

make these operations more efficient, faster, and

perhaps less expensive.57 An excellent example of

this is the Shuttle tile automation system described

in box 3-C. NASA is also exploring the use of expert

systems in Shuttle operations and making other

efforts to ‘‘take people out of the loop’ in order to

reduce the number of human operations and decisions. 58 Its goals are to speed up shuttle turnaround

and reduce costs.

A POSSIBLE SHUTTLE

IMPROVEMENT PROGRAM

To recapitulate, there are several options for

conserving, maintaining, and improving the existing

Shuttle fleet. The fleet could be conserved by flying

fewer Shuttle flights to reduce the expected attrition

521 ‘me c~e for a FJation~ Liquid Rocket Booster, ” General Dynanws Space Systems Division, March 1989.

53’’u.s. La~ch Vehicle=p]artnhtg for the Future, ” Roeketdyne, May 3, 1989.

sAhmch Optiom for the Future: A Buyer’s Gw”de, footnote 38, p. 29.

ss~m has ~n ~ome ~oncem ~$ t. tie impwt resistmce of A]-Li, but as wi~ any new candidate materials, extensive testing and certification would

be done before any actual use.

56~wch Optiom for the F#ure: A B~er’s Gw”de, footnote 38, p. Z$l; Redwing Launch Operatiom costs: New Technologies and Practices, op.

cit., footnote 3,

s~~wch optio~ for the Future, footnote 38, p. 29.

58cm must & exerciL~, of co~se, t. not t~e his too far since many cri[i~~ d~isions require h~an judgment, bd on the the b&st information

available to the person at that time.
Chapter 3--Space Shuttle Evolution . 49

Photo credit: National Aeronautics and Space Administration

The external tank is lowered into place between the solid

rocket motors in the Vehicle Assembly Building, Kennedy

Space Center.

rate. To do this without reducing service, Shuttles

could be modified to carry more payload, or

complementary vehicles could be developed to fly

missions that would otherwise require Shuttle

flights, Shuttle fleet size could also be maintained,

despite attrition, by ordering one or more additional

orbiters now, as a hedge against attrition. If NASA

waits until it loses an orbiter to order a replacement,

the replacement might cost more and take longer to

build than one ordered in the near future.

Table 3-3-Materials Improvements for Shuttle

External Tank:

● Use of robotics

● Nondestructive evaluation techniques

● Thermal protection system (TPS)

Improvements/composite applications

Rocket Boosters:

● TPS development

. High temperature sealant development

. Process improvements

. Advanced Thrust Vector Control (TVC)

System evaluation development

solid Rocket Motors:

. Ablative and insulation process

development and Nondestructive

Evacuation techniques

Space Shuttle Main Engines (SSMEs):

● Use of robotics

. Weld improvements

. Producibility

SOURCE: Rockwell International Corp.

Table 3-4 lists several improvements discussed

above, and some discussed in the OTA technical

memorandum Reducing Launch Operations Costs,

which could be elected to increase payload, safety,

economy, or utility. The list is illustrative, not

exhaustive, and contains entries (e.g., improved

RSRMs, ASRMs, and LRBs) with redundant benefits, because having a variety of booster options may

improve resiliency, and it may be desirable to have

both an early improvement in payload capability and

a larger improvement later.

A program of this magnitude could cost as much

as $8.5 billion. A 10-year program would therefore

require average funding of $850 million per year,

some of which (e.g., for ASRMs) NASA has already

planned to spend. However, to fund such a program

at a level that would make a marked improvement in

Shuttle system safety and performance would require finding extra space program funding, scaling

down the Space Station program, or deferring other

programs.
50 ● Round Trip to Orbit: Human Spaceflight Alternatives

Box 3-C-Shuttle Tile Automation System

Inspecting the some 31,000 thermal protection system (TPS) tiles on the Shuttle orbiters and repairing damaged

ones is highly labor intensive. Automating the inspection procedures could reduce overall labor costs, and increase

inspection speed and accuracy. In 1986 NASA began the Space Systems Integration and Operations Research

Applications (SIORA) Program as a cooperative applications research venture among NASA-KSC, Stanford

University, and Lockheed Space Operations Company. One of its initial tasks is to apply automation and robotics

technology to all aspects of the Shuttle tile processing and inspection system.

The team is developing an automated work authorization document system (AWADS) that will enable the

technicians to document the condition of each tile, determine any necessary repairs or replacement, and generate

work instructions. With the automated system, the computer, which is programmed to recognize each technician’s

voice, prompts the technician to find the correct tile, enter its number, and report on its condition in a systematic

way. The TPS quality control technician first inspects the tiles after each flight and enters the part number, location,

and condition of each tile into a computer database by voice. The computer’s central database automatically

generates a problem report in electronic format, which a TPS engineer uses to identify and recommend proper repair

procedures for the tile. The problem report proceeds through an electronic signature loop until final approval for

the repair. Finally, the TPS technician uses the voice data entry method to indicate tile status as repair procedures

are completed.

The AWADS system and other automated systems developed in the SIORA program use the Ada

programming language,1 the software environment that will be used in the Space Station and other large NASA

programs in the future. It offers the advantages of excellent portability from one hardware system to another, a rich

set of programming functions and tools, and a uniform code documentation.

Table 3-4-A Possible Shuttle Improvement Program

Options cost Benefit

Orbiter Improvements:

Develop alternate turbopumps for Space Shuttle main engines . . . . . . . $228 milliona

Safety and economy

Automate orbiter for unpiloted flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $200 millionb Safety

Extend orbiter fight duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $120 million Utility

Built-in test equipmentC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [?]C

Safety and economy

Boostsr Improvements:

Increase thrust of redesigned solid rocket motor. . . . . . . . . . . . . . . . . . . . $50 to $60 million More payload

Continue to develop advanced solid rocket motor. . . . . . . . . . . . . . . . . . . . $1.3 to $1.8 billion Safety and more payload

Develop liquid rocket booster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $3.5 billion Safety and more payload

Other elements:

Develop lightweight external tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [7] More payload

complementary Vehicles:

Develop Shuttle-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $1.5 billion For cargo

Develop capsule or lifting body for Space Station escape. . . . . . . . . . . . . . $0.7 to $2 billion Safety

Wraady funded by NASA.

kmly S30M to S40M Ior each additional OMW.

CSaa OTA-TM-ISC-28, Raduchg launch Operatkwm Costs.

NOTE: Most of thasa optkma would inomasa Shuttle payload capability, but by differant amounts; rhair other banafks and thair datas of availability would differ (saa fig. 3-9). Tharefora,

two or more qmons m@rt be purswd, for exampla, ASRMS to increase Shuttle payload capabdity and LRBs for increasad safety and racked environmental impact. On the

otir hand, NASA could develop complementary vahides (e.g. Shuttia-C) to carry large payloads to orbit and raducs the Shutfk flight rote, reducing Shuttle fleet attrftion. Tha

Unitad States naad not dada imminantiy whather to prooaad with one or mom of these options. However, if such improvements ara desired, more benafit will be raapad if thay

am begun earfter.

SOURCE: Offica of Tachnofogy Asaasament, 1989.
Chapter 4
CONTENTS

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Advanced Manned Launch System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Personnel Launch System (PLS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Crew-Rated Advanced Launch System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Stand-Alone LRB System.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

Foreign Crew- and Passenger-Carrying Vehicle Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Soviet Space Shuttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Soviet Spaceplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

European Space Agency Hermes Spaceplane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Japanese HOPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

German Saenger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

United Kingdom Hotol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Figures

Figure Page

4-1. Advanced Manned Launch System Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4-2. Role of Technology in Advanced Manned Launch System... . . . . . . . . . . . . . . . . . . . . . 55

4-3. Crew Emergency Rescue Vehicle (CERV)/Space Taxi and Return (STAR)... . . . . . 57

4-4. Soviet Space Shuttle Buran and Mir Space Station.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4-5. Soviet Spaceplane. ..... . . . . . . . . . . . . . . . . . . . . . . . . 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4-6. European Space Agency Hermes Spaceplane.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4-7. Japanese HOPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4-8. Federal Republic of Germany Saenger II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4-9. United Kingdom Hotol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Chapter 4

Advanced Rockets

INTRODUCTION

NASA is currently studying several proposed

advanced crew-carrying launch systems that would

help augment or supplant the current Shuttle fleet as

it ages. They include the NASA Advanced Manned

Launch System (AMLS-previously called Shuttle

II), a Personnel Launch System (PLS), a crewcarrying version of the joint DoD/NASA Advanced

Launch System (ALS), and a crew-carrying standalone Liquid Rocket Booster (LRB) system. NASA

expects the AMLS to supplant the current Shuttle,

but provide less payload capacity. The PLS or

crew-carrying ALS could help augment the Shuttle

if either is introduced before the Shuttle is retired.

The intent of each concept is to provide for more

cost-effective, reliable human access to space.

ADVANCED MANNED LAUNCH

SYSTEM

NASA’s Langley Research Center is leading the

AMLS program, which will define advanced crewcarrying launch system concepts, including their

development, system and operational characteristics, and technology requirements. The AMLS

program could by the year 20051 lead to a vehicle

significantly different than the Shuttle. NASA will

compare the AMLS and the PLS with the option for

an improved Shuttle, under study by the Johnson

Space Center (JSC), and decide how best to proceed.

NASA is evaluating five AMLS concepts (figure

4-1) listed below in order of increasing technological risk:2

●

●

●

●

An expendable in-line two-stage booster with

a reusable piloted glider.3 This configuration at

first appears similar to the U.S. Dyna-Soar4

concept of the early 1960s, which would have

been launched atop a Titan III, but would carry

a larger crew. Dyna-Soar would have carried

one or two pilots.5 The European Space Agency

and the Japanese NASDA have selected this

approach for their spaceplanes Hermes and

HOPE, respectively (see below). It might be

possible to use an ALS to launch an AMLS

orbiter.

A partially reusable drop-tank vehicle similar

to the fully reusable rocket concept described

below, except that hydrogen propellants for the

piloted orbiter are carried in expendable sidemounted drop tanks and the payload is carried

in an internal canister. This configuration

eliminates the need for a separate propulsion

and avionics module seen in the next option,

thus reducing its relative development and

operations costs.

A partially reusable vehicle with a glider atop

a core stage, which has expendable tanks but

recoverable engines and avionics. The core

stage would be side-mounted on a reusable

glideback booster. This partially reusable configuration may be economical at moderate

launch rates.

A fully reusable rocket with a piloted orbiter

parallel-mounted (side-by-side) to an unpiloted

glideback booster. This vehicle would be

shorter than the in-line or glider atop a core

stage version, making launch preparation easier. To facilitate payload integration or swapIThl~ ~wl~y ~mes hat he Prewnt Shutfle system, even with improvements and possible fkt ildditions, Will kIleMhg the end of its useful life

(as a result of wearout and/or attrition or cost reduction potential of new crew-cmying systems) titween 2005 ad 2010. Some argue that the present

Shuttle system, having made its first flight in 1981, is still a relatively new aerosp~e system. md wi~ well-consider~ improvements and additions to

the fleet could serve effectively until the yew 2020. In ei~er LWSC, ~ d~-ision to pr~=d wi~ m *S would not ~ rwuire-d until at least 1995.

2~d thus roug~y in order of incre~~g initial development cost. Total Iifc-cy]e COSL’3 would WUY ~eally, however, depending primarily on

reusability and flight rate.

3Thjs Vehjc]e could be Vev t~l, m~~g la~Ch preparation difficult. Its design would depend on the booster selected and on the mission requirements

of the orbiter. In addition, the orbiter engines could not b @itCd On the launch @ Pfior to liftoff md must ~ fired in flight after stage separation, which

would eliminate an abort mode on the ground. (An alternative mat would rcmovc ~is con~cm wo~d be to require only an orbltat maneuvering system

in the orbiter, as in the Soviet shuttle and rely on the booster to place the orbiter in orbit.) Another obvious disadvantage is that this cancept takes a step

back from reusability.

413W Ch. 5 of this rew, or for a much more det~]~ description sw ‘ ‘The Hypersonic Revolution—Eight C= Studies ~ tie Histow of HYPCmOI’IiC

Twhnology, ” vol. 1, case 11, Richard P. Hallion (cd.), WPAFB, Ohio, 1987.

SThe PLS concep[ could resemble the Dyna-Soar.

-53-

98-133 0 - 89 - 3
54 ● Round Trip to Orbit: Human space flight Alternatives

Figure 4-1-Advanced Manned Launch System Concepts

Fully reusable

Glider

All vehicles designed to same

reference mission (polar, 12 Klb)

and same 1992 technology level

(A/B ATR system more advanced)

Airbreather/rocket

Partially reusable Expendable stages (Horizontal takeoff)

KEY: A/B = airbreather; ATR = air-turbo-rocket.

SOURCE: National Aeronautics Space Administration, Langley Research Center.

●

ping, the orbiter would have a payload pod atop

its fuselage, rather than an internal payload bay.

The second-stage engines would be on the

orbiter. Fully reusable configurations such as

this are believed (but not proven) to minimize

cost per launch at high launch rates. The fully

reusable cryogenic tanks on both booster and

orbiter are a critical technology requirement for

this option.

A horizontal takeoff and landing air-breather/

rocket, which would resemble the German

two-stage Saenger spaceplane (see later discussion in this chapter). This configuration would

utilize the same technologies as for the AMLS

rocket concepts summarized above, except that

it would use an advanced air-turbo-rocket

(ATR) air-breathing engine for the first stage.

This vehicle would be fully reusable.

These alternate configurations also span a wide

range of reusability. The higher the anticipated

launch rate, the more attractive reusability becomes

from the standpoint of cost.

Because development of an AMLS vehicle need

not begin until the mid to late 1990s, NASA could

defer a decision on whether to start AMLS development until it has completed preliminary designs of

alternative vehicles in sufficient detail to estimate

technological risk and life-cycle cost.

Critical technology needs for all AMLS concepts

include:

light-weight primary structures,

reusable cryogenic propellant tanks,

low-maintenance thermal protection systems,

reusable, low-cost propulsion,

electromechanical actuators,

fault-tolerant/self-test subsystems, and

autonomous flight operations.

Figure 4-2 illustrates typical technology needs for

a fully reusable version of the AMLS. Although

meeting these advanced technology requirements

would be challenging, none is considered a “showstopper.” Thus, most experts feel that this technol-
Chapter 4--Advanced Rockets ● 55

Figure 4-2--Role of Technology in Advanced Manned Launch System (reusable version)

KEY:

Reusable

tanks

Smaller payload

(compared to shuttle)

Appropriate

crew size

Advanced avionics and endurance

Common propellant

OMS/RCS

(no hypergolics)

Light-weight

durable thermal

protection

system (TPS)

Reusable,

* low-cost engines

Light-weight

structures

OMS = Orbital maneuvering system; RCS . Reentry control system. design (tip fins)

SOURCE: National Aeronautics and Space Administration, Langley Research Center.

ogy could be available in time for an AMLS, since

the AMLS would not be needed until after 2005.

PERSONNEL LAUNCH SYSTEM

(PLS)

The Personnel Launch System is a new concept

that stems from “The Next Manned Transportation

System” (TNMTS) study organized by NASA

Headquarters. The TNMTS, a 2-year effort that

began in spring 1989, is now analyzing five primary

approaches:

1. purchase additional orbiters,

2. improve the current Space Shuttle system

(Shuttle evolution),

3. develop a Personnel Launch System (PLS),

4. develop advanced rocket-powered launch vehicles (AMLS), and

5. develop advanced launchers based on airbreather technology,

JSC was named the lead center for the PLS option

as well as for Shuttle evolution work. NASA’S

Langley Research Center will examine a lifting body

option6 for the PLS. The NASA centers, Marshall

and Kennedy, would have major roles in developing

a PLS but responsibilities for various tasks are still

to be determined.

As the PLS concept is so new, little can be said

about it, including its potential cost. It was prompted

by the desire for a crew-carrying vehicle that could

be available sooner than an AMLS and would also

be cheaper and simpler. It could range from a small

three- or four-person transport (similar to the space

taxi and return concept described in ch. 6) to a

vehicle sized to carry as many crewmembers as the

present Shuttle.

A PLS vehicle could in principle be designed to

be highly flexible and might also be configured to

carry cargo as well as people. For example: it might

be designed to carry small logistics payloads for the

6SU ~h, b for de~tiptions of lifting bodies.
56 ● Round Trip to Orbit: Human Spaceflight Alternatives

Space Station. It could also be designed to launch

capsules capable of providing emergency rescue

from the Space Station.

CREW-RATED ADVANCED

LAUNCH SYSTEM

Several aerospace experts have suggested that

should the United States decide to build the ALS, it

would be prudent to give this vehicle the capability

to launch people as well as cargo. If affordable,

resilience in human access to space is a desirable

feature, since today people can only be launched on

the Shuttle, which continues to be susceptible to

major delays or loss from attrition.

The ALS Civil Mission Needs Statement requires

that the ALS “provide a highly reliable (above 99

percent), fault-tolerant launch system capable of

having a man-rated variant.”8 ALS stages or components could be used in an AMLS, and a crew-rated

ALS launch vehicle could be used to launch a crew

rescue vehicle (CERV-discussed in ch. 6) or

alternatives to AMLS that have been proposed by

industry (figure 4-3). Finally, it might be used to

launch a PLS.

Current crew-rating procedures require the use of

greater strength margins in structural components,

additional redundancy in subsystems, and added

oversight and paperwork in the design, manufacturing, and operation of a launch vehicle compared to

non-crew-rated vehicles. ’” Some officials in the

ALS program, however, feel that the ALS would be

so highly reliable and robust that the additional

development cost or time required for crew-rating

the ALS would be small. As proposed, the ALS,

which could use all-liquid propulsion, would be

designed for high reliability and would include such

features as “engine out” capability (the ability to

complete the mission even if an engine fails to

operate), redundant electronics, and other high

reliability features; and thus is intrinsically designed

much like a crew-rated version.11 At present, there

no “ALS crew-rating program” per se. Although

the work statement for the ALS contractors does

state that the ALS must “be capable of flying

manned cargos,’ none of the contractors have yet

found a need to identify different cargo or crewcarrying configurations. ’2

Along with improved resiliency, a crew-rated

ALS would have three additional advantages:

1.

2.

3.

if the crew-rated ALS were designed to carry

a capsule like Apollo, crew escape could be

easier than with the Shuttle, and escape could

be possible during the whole trajectory, unlike

the Shuttle from which escape is impossible

during most phases of liftoff;

the crew-rated ALS could launch a crewcarrying PLS; and

there may be cases where it will be necessary

to take personnel and cargo up to the Space

Station but not down on the same mission. In

that case, there is no need to risk an orbiter.

Redundancy in crew-rated launchers has many

benefits, including improved resilience. But it would

come at a cost. Policymakers would have to decide

whether to saddle the ALS with the additional

development and operating costs for crew-rating or

7Having ~und~t luch systcms (usually of difl~nt technological heritages) capable of accomplishing the desired mission so that if one launch

system has to standdown, another can rapidly be used in its place.

‘Thomaa M. Irby, “Status of the ALS Program,” Proceedings of the Space Systems Productivity and Man@cturing Conference-V, Aug. 16-17,

1988, El Segundo, CA. Another ALS Systems Requirement Document states that the ALS design ‘will not preclude human cargo’ (Thaddeus Shore,

SDIO).

‘WhiU makea a launch system “man-rated” is open to variott.. interpretations. NASA is working on a consistent set of guidelines for crew-rating

space systems. This document, still undergoing review, defines crew-rating as follows:

A man-rated space system inewporates those design features and requirements necessary to accommodate human participmts. This provides the capability to safely

conduct InamEd operations, including safe rucovery from any credible enmgwxy situation Man-rating is the process of evaluating and aastuing that the hardware

and software can rmet prescribed, safety tiented design and operational criteria. 1[ is an integral pan of the design, developmeztt, verification, management and cam-cd

-.It c~u~ tighOU[ the operational life of the system.

(Guidelines for Man-Rating Space Systems-preliminary, Advanced Programs Office, NASA Johnson Space Center, JSC-23211, September 1988,

p. 5.)

l~swo~d ~SO m&e it mm difficult to reach the ALS goal of reducing vehicle and operations C05C8.

1 l~r Vw ~~.v~w paylo~s, rn~y argue that a vehicle should ~ CreW-rti ~YWaY.

1--cmof ALS ~iWen is that g Iot@s for the ALS may reach as high as 6 or 7, which is survivable by humans but not ve~ comfortable.

In contrast, the Shuttle is deaigned for a maximum of 3 g’s.
Chapter 4--Advanced Rockets ● 57

Figure 4-3--Crew Emergency Rescue Vehicle (CERV)/Space Taxi and Return (STAR)

Titan Ill Titan IV

1995

Core

Stage

1998

SOURCE: National Aeronautics and Space Administration, Langley Research Center.

whether resilience would be better served by a PLS

or a stand-alone LRB system.

STAND-ALONE LRB SYSTEM

If LRBs were developed as part of a Shuttle solid

rocket booster replacement program, or in conjunction with an ALS engine program, these boosters

could be used to propel a stand-alone system capable

of carrying people to orbit. Because the engines

would have already been developed, a launch system

built around an LRB could be cheaper to develop

than an entirely new launch system.

FOREIGN CREW- AND PASSENGERCARRYING VEHICLE

PROGRAMS

The United States and the Soviet Union are

currently the only nations capable of sending people

Single-stage

to orbit

Mach 6 staging

I

Air turbo rocket/rocket

horizontal

take-off

2005

to and from space. The Soviet Union has recently

developed a reusable space shuttle orbiter that is

launched on its heavy-lift launcher, Energia.

The European Space Agency (ESA), Japan, the

Federal Republic of Germany, and the United

Kingdom are all in various stages of developing their

own reusable launch systems, some of which, if

successful, would be capable of transporting humans

to orbit. The designs for these launch systems still

exist largely on paper. Nevertheless, these countries

possess a high level of technological capability and

could develop crew-carrying vehicles if they wished

to make the necessary investment, For these countries, building launch systems has become an

important part of decreasing their dependence on the

United States and the Soviet Union for reaching

space. Developing crew-carrying capability would

be a national achievement signaling their status as
58 ● Round Trip to Orbit: Human Space flight Alternatives

major space powers, able to develop and use a

broader range of advanced technology.

Non-U.S. concepts differ widely as to configuration, reusability, crew size, and payload capability,

and their project status ranges from preliminary

design, like the Hermes, to the Soviet Buran, which

has already completed its first test flight. Except for

the Soviet shuttle, none of these systems yet pose a

competitive challenge to the United States. The

United States should monitor the progress of these

programs both for competitive concerns and cooperative opportunities in order to respond appropriate y.

Soviet Space Shuttle

The Soviet counterpart to the U.S. Space Shuttle

made its maiden flight on November 15, 1988.

Lifted into space by an Energia booster (presently

the world’s largest booster), the 100-ton shuttle

named Buran (Snowstorm) remained aloft for two

orbits of the Earth, some 3 hours and 25 minutes. The

spacecraft is nearly identical in physical shape to

that of its American cousin (see figure 4-4), but it

does exhibit several key differences. The primary

difference is that Buran lacks its own main engines,

relying instead on propulsion provided by the

Energia to place the shuttle craft into orbit. Buran

also uses a set of small maneuvering thrusters to

reach orbit and later deorbit.

Similarities between the U.S. and Soviet designs

are striking. The delta wing, vertical tail structure,

payload bay, window placement, as well as thermal

protection patterns are common to both vehicles.

Initial reaction from Western experts held that the

identical profile of the two spacecraft had saved the

Soviets years of development time and expense by

copying U.S. plans. Soviet space engineers claim the

similarity derives from the same mission objectives

of both craft: ferrying people and payloads into Earth

orbit and maneuvering from space to a runway

landing. Soviet reports state the Buran can place

66,000 pounds of payload into orbit and return from

space with 44,000 pounds. ’s The Soviets claim that

special-purpose missions using Buran can last up to

30 days. Eventually, four flights per year are

envisioned using these shuttle vehicles.

Figure 4-4--Soviet Space Shuttle Buran and

Mir Space Station

35

30 . 30

25

15

I meter

SOURCE: Teledyne Brown Engineering.

In some respects, the Energia-Buran is more

versatile than the U.S. Shuttle. For example, the

Energia rocket can launch an orbiter, or it can be

launched without an orbiter, in which case it can

carry a payload weighing more than 220,000

pounds. It has four reusable first-stage boosters

clustered around an expendable second (“core”)

stage, which has four engines. First- and secondstage engines are ignited on the launch pad, and,

because all engines use liquid fuel, they can be shut

down on the pad or in flight to abort a launch if one

or more fails to achieve sufficient thrust. In some

cases the orbiter may still reach orbit, even if an

engine has been shutdown during flight. In any

event, the vehicle is expected to maintain controlled

flight-to an emergency landing site if carrying

crew, or to a place where it can ditch or crash without

endangering people or structures.14

Perhaps the most interesting feature of the Soviet

approach to winged space flight is the Soviet ability

to use automated landing systems. Buran’s first

flight was unpiloted and relied on ground controllers

for on-orbit maneuvering, Buran then used onboard

computers to carry out an automatic approach and

13T’ a 100.~i high orbit; sw U.S. Department of Defense, Soviet hlifilu~ power, 1988.

Iq_j. Gubanov, Prmda, July 30, 1988, M cd., p. 4. [in Russian]
Chapter 4-Advanced Rockets ● 59

landing at a special shuttle runway at Baikonur. 15

Three parachutes slowed the shuttle vehicle to a

stop.

By contrast, although the U.S. Shuttle fleet does

carry some automated landing equipment,l6 astronauts to date have vetoed its use below a certain

altitude. The Soviet technology used for Buran’s

automatic flight ability appears to be coupled to the

hardware developed for the Tu-204, a new Soviet

medium-range twin turbofan aircraft.

Reports remain sketchy as to overall capabilities

of the Soviet shuttle design. Six Soviet shuttlecraft

are believed to be in various stages of construction.

Another shuttle, named Ptichka (little bird) is

expected to be launched next. As many as 10

individuals can be accommodated in the Buran

shuttle, Soviet experts have stated.

The Soviets have modified MiG 25 ejection seats

for use in its space shuttle when it makes a piloted

flight, Soviet engineers state that the ejection seats

can even be used when the shuttle is on the launch

pad. The maximum speed at which they can be used

is Mach 3.17

Soviet Spaceplane 18

Still an enigma to the United States is the Soviet

Union’s subscale prototype spaceplane and what

part it plays in their space program. This l-ton

winged mini-spaceplane (see figure 4-5) in its first

four flights between 1982 and 1984 orbited Earth

only once and touched down in water. It has by now

possibly made a dozen flights.

The Soviet mini-spaceplane program resembles

the effort undertaken in the 1960s in the U.S.

Dyna-Soar program, and the European Hermes

project presently underway. Some U.S. experts

speculate that it was designed to evaluate the

aerodynamic and reentry characteristics of the much

larger Soviet shuttle. Others theorize that the plane

could be built for quick launch and turnaround, as

well as for occasional reconnaissance. A full-scale

spaceplane, capable of runway landings, is expected

Figure 4-5-Soviet Spaceplane

SOURCE: Royal Australian Air Fore@.

to fly with two to three cosmonauts, launched by the

SL-16 booster. Some experts have hypothesized that

the spaceplane could serve as a crew escape vehicle

attached to the Soviet Mir space station.

European Space Agency Hermes Spaceplane

This piloted shuttle has been championed by

France as an effort to provide an independent,

European, crew-carrying launcher. As a small,

winged spaceplane 15 meters long with a wingspan

of 10 meters, Hermes could carry a crew of three and

slightly over 2 tons of payload to a 500-km orbit. The

spaceplane itself originally was meant to be completely reusable but as now envisaged, the vehicle

will have an expendable adapter called the Hermes

Resource Module that will separate from the space15Rw-n~y, *C SovletS have exwes~ concerns about their automatic systems, and cite this m one reason for delaying the next flight (which will

carry no crew) until 1991. The first crew-carrying flight may not occur before 1992.

l~e U.S. Shuttie is not fully automatic as pilots must brake artd steer it on landing. Automating these tasks has been proposed, however--- Ch. 2.

17L$wCe, jMuq.Febmq 198$I! P. 5~.

Inpeter M. Banks and Sally K, Ride, “Soviets in SpWe, ” Scientific American, February 1989.
60 ● Round Trip to Orbit: Human Space flight Alternatives

plane and burn up during reentry. Current mission

planning calls for an initial unpiloted test launch on

an Ariane 5 in early 1998, crew-carrying flights

beginning in late 1998 or early 1999, and regular

operational flights twice annually starting in 1999 or

2000. Total development cost for the Hermes project

is estimated at over $4.5 billion,19 with most of the

financing coming from France and the Federal

Republic of Germany. Two vehicles would initially

be built, leading to an eventual fleet of four. Each

Hermes could make two to three flights per year.

One recent Hermes concept is shown in figure 4-6.

Japanese HOPE

The Japanese National Space Development

Agency (NASDA) is studying a concept called

“HOPE” (H-II Orbiting Plane), an unpiloted

winged mini-shuttle. HOPE would be launched atop

the Japanese H-II launch vehicle, an indigenously

designed and built expendable rocket, expected to

fly in 1992 (see figure 4-7).

Japan is considering HOPE for several missions,

such as delivery and return of materials from the

Japanese Experiment Module (JEM) of the international Space Station, polar-orbital missions, and

what the Japanese call “space technology experiments. The HOPE design still is emerging but

current plans call for it to land horizontally. NASDA

suggests a first flight date in late 1996.20

HOPE actually may be Japan’s first step toward

an autonomous piloted spaceflight capability early

in the 21st century. A national “Advisory Committee on Space Plane’ recommended a broad research

and development plan for a fully reusable aerospace

plane. The committee urged that the Space Plane

“be promoted as an important national R&D project,” but promised that the program would be

opened to international cooperation in its early

stages.

German Saenger

The Federal Republic of Germany is studying this

two-stage launch vehicle (figure 4-8), which would

be a piloted craft carrying a cargo plane piggyback

into space. Stage 1 would be a large hypersonic

aircraft propelled by six hybrid turbo-ramjets and

would be designed to take-off and land horizontally

at several large European airports. For flights

without a crew, the second stage would be of an

expendable cargo upper stage (“ Cargos”), capable

of placing 33,000 pounds into LEO or 5,500 pounds

into GEO. Cargus would use a single LOX/LH2

engine, the same powerplant being developed for the

Ariane 5 core. For piloted flights, a spaceplane

called “Horus” (Hypersonic Orbital Upper Stage)

would serve as Saenger’s second stage. Its present

configuration gives it the same basic shape as

Hermes with twice as much volume. Designers plan

for Saenger to operate as a ferry craft with limited

orbital duration—perhaps not more than 1 day.

Horus could lift 4,000 to 6,000 pounds of cargo, plus

two pilots and four passengers to a 270-mile orbit at

a 28.5-degree inclination. Horus would use two

LOX/LH2 engines similar in size to the U.S.

Shuttle’s SSMEs.

A major incentive for developing Saenger is the

potential reduction in space transportation costs.

The West German Research Minister states that, in

theory, Saenger has the potential of reducing the

costs of placing payloads into orbit from about

$3,500 per pound to $500 per pound. Recently, the

19’(cm~a Joins Hermes program, “ Avktion Week and Space Technology, Mar. 13, 1989, p. 30.

mst~eyw.K~debo,‘‘Jw~e~ f@fining u~~~ HOPE ~biter for pl~cd 1996 Lalmch, ’ Avi~iOn Weekati Space Technology, Apr. 3, 1989,

pp. 57-58.
Chapter 4-Advanced Rockets ● 61

Figure 4-7— Japanese HOPE Figure 4-8--Federal Republic of Germany Saenger II

SOURCE: Japanese National Space Development Agency.

German Government agreed to fund the initial

development work for Saenger with a first demonstration of components between 1993 and 1999. The

prototype could be finished by the turn of the

century. Development work carried out through the

European Space Agency (ESA) could begin as early

as 2004. For the first phase, which will run to the end

of 1992, the West German Research Ministry is

providing $122 million, 7 percent of its total budget

for space activities. The German Aerospace Research establishment is contributing $48 million,

and the German Research Society $17 million. A

further $22 million is being invested by the West

German aeronautics and space industry for a total

initial commitment of $209 million.21

SOURCE: Messer schmitt-Bolkow-Blohm GmbH, Space Systems Group.

United Kingdom Hotol

As early as 1978, British Aerospace Corp. began

studying the prospects for lowering the cost of

satellite launchings by 80 percent. Out of these

studies, and revolving around a new engine proposed by Rolls-Royce, British Aerospace drafted

plans to develop Hotol, a fully recoverable and

reusable unpiloted launcher capable of taking off

and landing from a runway and reaching orbit with

a single stage (figure 4-9).

The heart of the project is Hotol’s propulsive

power, the still-secret Rolls-Royce RB-545, called

the Swallow engine. This radically new hybrid

rocket engine is designed as a dual-rotor motor, first

burning onboard liquid hydrogen while liquefying

oxygen as the vehicle moves through the Earth’s

atmosphere. Above the atmosphere and on into orbit,

the engine then uses onboard liquid oxygen to bum

the fuel. This engine concept would halve the

amount of liquid oxygen required to be carried at

takeoff thus dramatically reducing the weight of the

craft compared to one using a conventional booster.

Hotol is designed to reach orbital velocity at a

height of 90 km. The craft would then coast into a

stable operational orbit of about 300 km. The design

goal is to deliver 7 to 11 tons into low-Earth orbit at

a cost of $300 per pound. Hotol is designed to

operate without human crews aboard for most

missions, although a pressurized habitable module

could be situated in the payload bay to support

astronauts, not as pilots, but in an “executive role. ”

2Jw Kirk, ‘ ‘Germany Enters l-ly~rsonic, Race, ’ Science, VO1. 243, Mar. 10, p. 1284, 1989.
62 ● Round Trip to Orbit: Human Spaceflight Alternatives

Hotol mission scenarios call for the vehicle to launch

and recover satellites, service space stations and

platforms, conduct microgravity and scientific experiments, and carry out military operations. A fleet

of 5 vehicles was planned, each with a 120-mission

design life. Hotol’s recurring launch cost was

estimated at just $5 million.

Hotol design teams completed a 2-year, $4

million proof-of-concept study in late 1987. They

outlined a follow-on “enabling technology” program that would lead to a development start in 1994

and a first flight by Hotol near the year 2000. Despite

the momentum built up by British Aerospace and

Rolls-Royce, the U.K. Government, in July 1988,

refused to provide a requested $9 million per year for

3 years to continue Hotol’s research and development. The two firms were to match the government

funding made available through the British National

Space Centre. Hotol’s future may depend on international participation but this would require declassification of the Swallow engine, something that the

British have been loath to do.

Figure 4-9-United Kingdom Hotol

SOURCE: British Aerospace.
Chapter 5

The National Aero-Space Plane

!

Photo credit Ahmkmal Aaro-Sv Ram Joint_ 017km+

Conceptual design for the X-30 National Aero-Space Plane.
CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operational Vehicles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X-30 Design Goals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Funding and Schedule. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NASP Technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .

Materials and Thermal Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Computational Fluid Dynamics and X-30 Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-A. NASP, the Orient Express, and High-Speed Commercial Transports . . . . . . . . . . . . . .

5-B. The Origins of NASP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-C. Limits of Computational Fluid Dynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figures

65

66

66

68

71

74

78

79

80

69

72

82

Figure Page

5-1. System Integration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

5-2. Typical NASP Flight Trajectories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

5-3. NASP Program Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

5-4. High Speed Propulsion System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

5-5. Engine Isp

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

Tables

Table Page

5-1. NASP Funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Chapter 5

The National Aero-Space Plane

INTRODUCTION

The National Aero-Space Plane (NASP) program

is a research effort funded by the Department of

Defense (DoD), the National Aeronautics and Space

Administration (NASA), and industry to develop

and demonstrate the technologies of hypersonic

flight in a revolutionary, piloted research vehicle

designated the X-30. If successful, the X-30 would

demonstrate the capability to reach outer space using

a single propulsion stage that would make unprecedented use of air-breathing engines.2 In a launch

demonstration that program officials hope to complete by October 1996, the X-30 would take off

horizontally from a conventional 10,000-foot-long

runway, accelerate to Mach 25 in the upper atmosphere, enter orbit, and return to Earth, landing on a

conventional runway. In contrast, a typical rocket

launcher ascends vertically from special launch

facilities and jettisons one or more propulsion stages

during flight.

The NASP program is currently developing the

technology to build the X-30. Although the X-30 is

meant to serve as a technology test-bed and not as a

prototype, it is being designed as a demonstration

vehicle that could resemble prospective operational

launch vehicles. Proponents of the X-30 believe it

could herald a new era in flight, spawning military

and civilian aircraft capable of global range at

hypersonic speeds, or low-cost and routine access to

space.

OTA included NASP in its assessment of advanced space transportation technologies because of

the possibility that operational vehicles of utility for

both the civilian and military space programs may

evolve from the X-30. These ‘‘NASP-derived vehicles” (NDVs) would offer a radically different

approach to space launch and might eventually

become important elements of a future space transportation system, ferrying people or cargo into

low-Earth orbit with rapid turn-around and low cost.

Depending on its eventual configuration and payloadcarrying capability, it is conceivable that a NASPderived vehicle might also supplement or replace the

Space Shuttle when the Shuttle fleet reaches the end

of its useful lifetime.

Program officials believe that an aerospace plane

could lower the cost to reach orbit because its design

would allow:

●

●

●

●

●

Not

rapid turn-around;

manpower support at commercial aircraft levels

(in contrast to Shuttle operations);

complete reusability of the system with minimal refurbishment between flights;

operations from conventional runways; and

greater payload fractions,3 the result of using

air-breathing, rather than rocket engines.

all of these potential economies would be

unique to NASP-derived launch vehicles; some

could also be realized in other advanced launch

systems.

Although this chapter refers often to vehicles

derived from technologies developed in the NASP

program, neither the construction of an X-30 vehicle

nor a follow-on program to build an operational

vehicle has been funded yet. A decision by a

DoD/NASA Steering Group on the feasibility of

moving beyond the current technology development

phase to construct a flight vehicle is now scheduled

for September 1990. As the later section, Policy and

Options explains, recent revisions in the DoD budget

submission for fiscal year 1990, if adopted by

Congress, would have a dramatic effect on the

direction of even the research portion of the NASP

program.

OTA did not perform a detailed evaluation of the

economic benefits of the NASP program or NASPderived vehicles, nor did it attempt to evaluate the

potential contribution of the NASP program to the

Nation’s defense or its defense technology base.

However, NASP officials believe that these contributions would be among the most important benefits

IH~rWnic USu~Iy refers t. flight at S-S of at lemt Mach S—five times the speed of sound, or about 4,000 miles Per ho~. Thes@ of so~d

in dry air is 331.4 meters per second (742.5 miles per hour) at a temperature of O degrees Celsius (273 degrees Kelvin).

ZAir.breathin~ en~nes b~ atmospheric oxygen d~ing combustion instead of c~ing ~ oxid~t in(ermd]y m is typical on rockets. All COllVel’ltlOnd

aircraft engines are air-breathers.

3Paylo~ fr~tlon is he weight of the pay]o~ expres~ ~ a fr~tion of tie launch vehicle’s gTOSS lift-off weight, including fuel.

-65-
66 ● Round Trip to Orbit: Human Space flight Alternatives

of their program. The broader implications of the

NASP program are beyond the scope of this report

and are considered only in so far as they affect the

support, schedule, cost, and likelihood of achieving

an operational launch capability. This report presents an overview of the NASP program, a short

introduction to the technologies of hypersonic flight,

and a guide to the issues likely to be faced by

Congress as the program nears the point where it

could move beyond its current research stage.

BACKGROUND

The X-30 requires the synergism of several major

technology advances for success. The propulsion

system is based on experimental hydrogen-fueled,

supersonic combustion ramjet (“scramjet”) engines. A scramjet is designed to allow combustion to

occur without slowing the incoming air to subsonic

speeds, as is typical in all other air-breathing

engines. Ground tests of scramjet engines indicate

that they could propel an aircraft to hypersonic

speeds, but the X-30 would be the first aircraft to

explore fully their potential in flight.

The X-30 airframe would require extremely

lightweight and strong structures, some capable of

withstanding temperatures thousands of degrees

hotter than materials currently used in aircraft

construction. In contrast to the thermal protection

tiles used on the Space Shuttle, some of the X-30’S

high-temperature tolerant materials would be

formed into load-bearing structures. In addition,

while some of the X-30’S materials, such as carboncarbon composites, have been used before (although

not as load bearing structures), others are still in a

laboratory stage of development. Furthermore, even

with special materials and coatings, novel cooling

techniques would be necessary to keep some leading

edges and internal engine parts at tolerable temperatures. The active cooling system would also be used

to recover fuel energy that would otherwise be lost

as heat. The use of “regenerative’ cooling techniques has never been attempted in an aircraft,

although the technique is commonly employed in

liquid rocket engines. Developing the instrumentation and control system of the X-30 also presents

unique technical challenges.

The X-30 would make unprecedented use of

numerical aerodynamic simulation as a design aid

and as a complement to ground-test facilities that are

unable to reproduce the full range of conditions the

X-30 would encounter in hypersonic flight. The

NASP program is currently utilizing a substantial

fraction of the U.S. supercomputer capability in

what officials describe as a massive effort to advance

the state-of-the-art in the computational techniques

needed to design the X-30. In fact, the dependence

on supercomputers and numerical simulation models of hypersonic flight is so great they constitute a

key “enabling” technology for the X-30, rivaling

propulsion systems and materials in importance.4

The requirement that aircraft structures be lightweight, reusable, and able to withstand thermal

cycling (heating and cooling) over multiple flights

stresses all aspects of vehicle design. In addition, the

engine, airframe, cooling systems, and control

systems would all be melded together in the X-30,

thus creating unusual challenges for both vehicle

designers and program managers (figure 5-l). For

example, the airframe and engine cannot be developed independently; instead, they must be designed

from the outset as a single package. The heat load on

the X-30 will be a sensitive function of both the

vehicle’s aerodynamics and of the heat generated by

engine combustion. In turn, the thermal requirements affect materials and structural requirements.

Finally, aircraft instrumentation and control systems

must be matched to airframe designs, which are

coupled to propulsion and thermal control systems.

OPERATIONAL VEHICLES

Even if the NASP program proves completely

successful, an additional program would still be

necessary to develop operational vehicles. The

extent of such a program would depend on how well

technology issues are resolved by the X-30 and how

much modification would be necessary for firstgeneration follow-on vehicles. Safety, crew escape,

environmental compatibility (pollution and noise),

1$’IIK embling t~hnologies of NASP were critically reviewed in Hypersonic Technology For Military Application, committee on HypeMiC

lkchnology for Milit~ Application, Air Force Studies Board, National Research Council (Washington DC: National Academy Press, 1989) and Report

of the D@wse Science Board Ti-.ask Force on tk Natiorud Aerospace Plane (NASP) (Washington DC: OffIce of the Under Secretary of Defense for

Acquisition, September 1988). See also National Aero-Space Plane: A Technology Development and Demonstration Program to Build the X-30 (US.

General Accounting Gffke Report GAO/NSIAD-88-122, April 1988),
Chapter 5--The National Aero-Space Plane ● 67

Figure 5-1--System Integration

Lift

Thrust

Forebody/inlet

integration

Aerodynamics

Lift/Drag/Control Moments

Thermal Control

Active Cooling/Bluntness Coatings

SOURCE: McDonnell Douglas.

●

●X*

Afterbody/exhaust

integration

Propulsion

lnlet/Combustor/Nozzle

Structure

Tankage/Fuselage Tail/Materials

production costs, maintenance costs, and the capability for rapid turn-around on a routine basis would

all have to be addressed in engineering an operational vehicle. A true operational capability also

presumes that the problems of pilot training, maintenance, logistics, and support for the vehicle (including hydrogen handling and storage capability) have

been solved. For a military vehicle there is the

additional issue of integrating the vehicle into the

existing military force structure.

The detailed characteristics of operational launch

vehicles that might follow the X-30 are classified.

According to program officials, the first-generation

of vehicles would not be expected to carry Shuttleclass payloads, although later variants might. How

much of the vehicle’s gross take-off weight could be

devoted to payload would depend on the success of

the NASP material and structures development

program and the actual engine performance.

The NASP Joint Program Office (JPO) is evaluating a concept for a vehicle about the size of a

McDonnell Douglas DC-10 that would be able to

carry 20,000 pounds to the low-Earth orbit of the

proposed Space Station. In general, a vehicle designed with a larger wingspan, more fuel, and more

powerful engines can carry a heavier payload, but

there are practical limits. As vehicle weight rises,

propulsion requirements become more difficult to

meet. Heavier vehicles also place more stress on

landing gear and brakes. In addition, take-off and

landing from conventional-length runways becomes

difficult as vehicle weights rise. Finally, vehicle

costs rise, especially if the vehicle is constructed

with expensive specialized materials.5 NASP designers have announced that they are striving for NDV

vehicle weights close to 400,000 pounds.6

In contrast to a launch vehicle, which would fly

directly to low-Earth orbit in about 30 minutes, a

hypersonic cruiser might fly for several hours at

speeds and altitudes of, for example, Mach 5-14 and

80,000 to 150,000 feet. Using hydrogen as fuel, its

range would extend to intercontinental distances.

Figure 5-2 compares the trajectory of the Space

Shuttle with representative trajectories for an aerospace plane carrying out orbital or hypersonic cruise

missions. 7 The NASP effort to develop hypersonic

cruise vehicles has sometimes been confused with

proposals to develop a commercial hypersonic

transport. At present, the vehicles being studied by

the NASP JPO do not include a commercial hypersonic transport or “Orient Express. ” Moreover, the

least costly path to the development of such a vehicle

would not be via the development of a Mach 25

aerospace plane (see box 5-A).

The relaxed speed requirement makes the

design of a hypersonic cruiser less challenging than

a Mach 25 orbital vehicle, but extended hypersonic

flight within the atmosphere would place a much

larger demand on thermal cooling systems (the

orbital vehicle experiences a higher peak thermal

load than the cruiser but it is for a much shorter

duration). Thus the optimum airframe for a hypersonic cruiser would differ in design from a single-stageto-orbit (SSTO) vehicle, and it is likely that operational versions of these vehicles would each require

a separate development program.

Preliminary projections by NASP contractors of

the operating and support costs of an NDV with a

5However, ~Wding to me NASp JPO, tie e~imat~ cost to increase the X-30’S baseline payload by even a factor Of four would sti!] be only a small

fraction of the total development cost for the vehicle.

6Doughls isbeii, ‘‘NASP, International Space Trade Highlight Symposium,” Washington Technology, Apr. 20-May 10, 1989, p. 20.

7~euvenng al h~r~nic sps has s~e su~sing con,q~nces, For cx~ple, a t~ at hypersonic s@ cart t&e an akrtlfl OVCl a SIZ~le

portion of the United States. A pilot in the X-30 making a 2g (one g is the acceleration due to gravity) turn at Mach 10 would travel over a track that

would take him from Edwards AFB, California to Denver, Colorado. A Mach 15 turn at 2 g would take the pilot over a ground track from Edwards to

Chicago.
68 ● Round Trip to Orbit: Human Spaceflight Alternatives

1000 ft

Figure 5-2--typical NASP Flight Trajectories

Space launch vehicle

350

Shuttle exit

300 -

.’

, “

.’

250 -

.’

:

:

.’ 200 -

150 -

-

Velocity 1,000ft/sec

SOURCE: McDonnell Douglas.

Hypersonic cruise

Cruise

Descend

o 5 10

Velocity 1,000ft/sec

payload capability to low-Earth orbit of 65,000

pounds (likely to be a second-generation NDV)

range from $1 million to $9 million per flight,

exclusive of development or production costs. In

terms of mass to orbit, the maximum cost of placing

payloads into low-Earth orbit was estimated at $140

per pound. Achieving these remarkably low costs

(one to two orders of magnitude improvement over

the Space Shuttle)8 would, among other things,

require rapid turn-around and fill reusability.

Rapid turn-around would allow high-rate operation and lower unit launch costs, in part because

nonrecurring costs could be spread over a larger

number of missions. However, to realize these

economies of scale presupposes that sufficient

missions exist to support the higher volume operations. In addition, maintenance costs between flights

costs would have to prove to be as low as predicted.9

A rough extrapolation from the projected X-30

costs indicates that potential unit costs of an

operational launch vehicle could be on the order of

$1 billion in addition to the costs of research,

development, testing, and evaluation.10 Predictions

of the development costs for an operational vehicle

are very uncertain at present because they extrapolate from preliminary cost estimates for the X-30.

Research and development costs for Shuttle components through 1984 totaled approximately $15

billion*’ ($18 billion in current dollars), however,

NASP officials believe development costs for operational vehicles derived from the X-30 would be less.

Whatever the actual costs, it is clear that a substantial commitment from DoD or NASA would be

necessary to build a fleet of launch vehicles.

X-30 DESIGN GOALS

As an experimental vehicle, the most important

function of the X-30 would be to serve as a flying

test bed where synergistic technologies—

propulsion, materials, structures, thermal control,

guidance, and flight instrumentation--could be

combined and proved. In particular, the X-30 would

effectively function as a “flying wind tunnel” for

high-Mach scramjet propulsion that cannot be completely validated using only ground-based facilities

and computer-based simulation.

Many important characteristics for the X-30 have

not been made public. These include size, weight,

and vehicle payload. However, NASP officials have

stated that the X-30’S size would be between that of

a Boeing 727 and a McDonnell Douglas DC-10, and

it would carry at least several thousand pounds of

instrumentation. The actual size and weight of the

X-30 would depend on many factors, including the

final airframe and engine design and the required

oFor a detai]ed di~ussion of Shuttle costs see ch. 7 and app. A of U.S. Congress, Office of ‘IM.rtology Assessment, bunch @tiomfor the FwMe:

Buyer’s Guide, OTA-ISC-383 (Washington, DC: U.S. Government Printing Office, July 1988).

9Achieving r~id turn-around would demonwti that little maintenance is required, provided maintenance is not simply Shifted from the flight line

to the depot, and provided the maintenance man-hours per sortie remains low over the life of each vehicle. Moreover, average vehicle service life must

meet or exceed the design service life of 150 sorties (to orbit) if the average cost per launch is to be as low as prdicted by estimates based on this

assumption. Note too that should payload costs come to exceed mission expendimres, the importance of reducing laurteh costs wotdd be diminished.

l~sfi~ is me~t to be illustradve—it is not based on any cost estimation model. Reliable cost estimates for an NDV cannot be made until an

X-30 is built and flight tested. Even then there would be uncertainties in life-cycle costs. The cost to deliver the new Space Shuttle orbiter Endeavour

(OV 105) in 1991 is expczted to be more @an $2 billion. However, this increase in cost over previous orbiters represents the expense of incorporating

new safety and other improvements, and restarting production lines.

I IA ~m~~lve ~omt~g of ShuMe ~ve]opment and procurement costs, based on Shuttle dtit obligations ss pre~nt~ in NASA budget

estimates, was performed in 1984 by David Smart, now with TRW Corp. The figure of $15 billion is a rounded estimate that appears in R.H. Miller,

D.G. Stuart, and A. Azarbayejani, “Factors Influencing Selection of Space Transpomttion Options,” paper presented at the 37th Congress of the

lntematiortal Astronautical Federation, ref. No. IAF 86-108, Innsbruck, Austria, Oct. 4-11,1986.

lz~. Robert Bfielemy, briefing on NASP to members of U.S. Senate, Russell Office Building, Apr. 20, 1989.
Chapter 5-The National Aero-Space Plane ● 69

Box 5-A--NASP, the Orient Express, and High-Speed Commercial Transports

In his January 1986 State of the Union Message, then President Ronald Reagan proclaimed, “We are going

forward with research on a new ‘Orient Express’ that could, by the end of the next decade, take off from Dunes

Airport [near Washington, DC] and accelerate up to 25 times the speed of sound, attaining low-Earth orbit, or flying

to Tokyo within two hours. ” The President’s speech placed NASP on the national agenda, but it also led to

considerable confusion over the objectives of the program. At present, the NASP program has no plan to develop

an Orient Express.

The principal objective of the NASP program is to build a Mach 25 experiment vehicle, the X-30, that would

develop, and subsequently demonstrate, the technologies for single-stage access to space. In contrast, the Orient

Express is a concept for a commercial hypersonic passenger transport. In addition, the maximum speed of the Orient

Express (roughly Mach 5 to Mach 10) would be far less than the Mach 25 orbital Speed required for the X-30.

NASA is studying the feasibility of a commercial supersonic transport in its High-Speed Civil Transport

Program (HSCT), an effort distinct from NASP. HSCT design objectives include a range of 7,500 statute miles

(6,500 nautical miles) with a full payload of 300 passengers (based on Pacific region markets) and a maximum

weight of not more than 1,000,000 pounds to maintain compatibility with existing airports. Environmental

compatibility and economic viability are the two most important parameters governing HSCT designs. These factors

in turn depend on airport noise, sonic booml, effects on atmospheric ozone, aircraft productivity, and operating and

production costs.

Initial HSCT studies have shown Mach 6 and above to be commercially noncompetitive with supersonic

transports in the Mach 2-3 range as a result of the slowing of aircraft productivity with increasing Mach number

and the relatively high cost of using hydrogen fuel to achieve the higher speeds. Mach 2-5 supersonic transports

could burn conventional petroleum-based fuels or cryogenic methane.

Some HSCT studies suggest that Mach 3.2, the practical speed limit for a kerosene-burning transport would

be the optimum choice in the near-term (year 2000+). Using kerosene eliminates the need for the exotic engines,

materials, and cryogenic fuel transfer and storage facilities that are necessary for Mach 5+ flight. Studies also show

that a Mach 3.2 vehicle could weigh some 450,000 pounds less than a Mach 5 transport, thus lowering vehicle size,

cost, and, indirectly, sonic boom. However, an important factor that could undercut the commercial viability of a

Mach 3 transport after the year 2,000 is the anticipated improvement in the next generation of sub-sonic transports.

Although there is some overlap in the technical development necessary to realize these aircraft, a Mach 3

supersonic transport would have essentially no value as a stepping stone to building the X-30, and a Mach 5+ Orient

Express would have only a limited value. Conversely, while the development of the X-30 could spur the

development of the Orient Express, some X-30 materials, propulsion concepts, cooling techniques, etc. would be

either unnecessary or too costly for a commercial transport. The NASP program would not provide a direct route

to supersonic commercial transport, nor is it likely to be the most economical route to commercial hypersonic

transport.

IAsurnirtg similar wing loading (a functim of aircraft weight), b sonic boom of a hyperaom“c aircraft could be similar to a supersonic aircraft. Hypersonic

tramporta would cruise at higher altitudes wheze them are W?e tm~a~ LTSdi~tS ~inve~i-.s- ~@of- h= a temperature dependence, these

temperature variations brak up an ammtft’s shock wave and reduce its effect on e p8rtIcufar ground kmtkm.
70 ● Round Trip to Orbit: Human Space flight Alternatives

payload (some of which would be devoted to

‘‘margin’ for items such as extra fuel). The required

orbital trajectory (polar or low inclination) would

also affect vehicle size, weight, and payloadcarrying capability. The NASP Joint Program Office

(JPO) has studied designs that range in weight from

less than 200,000 pounds to over 300,000 pounds.

The objectives of the NASP program as currently

structured include the following:

. Single-Stage-To-Orbit (SSTO): The foremost

objective of the X-30 would be to achieve orbit

using a single propulsion stage in a fully

reusable flight vehicle. An SSTO vehicle would

reach low-Earth orbit without carrying expendable booster rockets or external fuel tanks. In

principle, a fully reusable SSTO design may

have a greater potential to reduce the cost for a

vehicle to reach orbit than a multi-stage air-breathing/

rocket combination. However, achieving SSTO

with a reusable vehicle is also more challenging

technically than alternative methods for reaching orbit such as the two-stage vehicles being

studied by NASA (see ch. 4).*3

To achieve orbit in a single-stage would

require both efficient scramjet performance at

high Mach numbers and extremely high propellant fuel fractions. Scramjets must retain their

theoretical advantages in performance over

conventional rocket engines to high Mach

numbers if the X-30 is to achieve SSTO. High

propellant fuel fractions can only be accomplished in a design with very low structural

weight fractions because the payload is expected to be only a small fraction (on the order

of 5 percent) of the vehicle gross weight. Thus,

payload could not be reduced to compensate for

excessive structural weight. Attaining very low

structural weight fractions poses particular

challenges in the X-30 because it must contain

a large volume of low-density liquid hydrogen

(or hydrogen slush) fuel, and its structures must

●

●

●

●

be able to withstand high aerodynamic and

aerothermal loads.

Air-Breathing Propulsion to Hypersonic

Speeds: The speed necessary to enter low-Earth

orbit is approximately Mach 25. As originally

conceived, the X-30 would have attempted to

reach this speed using only air-breathing propulsion. However, all of the X-30 designs now

under consideration by the NASP JPO include

options to carry liquid oxygen (LOX) on-board

for thrust augmentation. LOX would either be

combined with hydrogen in separate reusable

rockets, or it could be added directly to the

scramjet engines. Some form of rocket assist

would also be necessary for propulsion when

the vehicle rises above the sensible atmosphere,

that is, for final insertion into orbit,14 maneuvering in space, and de-orbiting.

Hypersonic Cruise: Although the prime focus

of the X-30 program is on demonstrating the

ability to reach orbit with a single propulsion

stage, it would also demonstrate the capability

for prolonged flight at hypersonic speeds within the atmosphere.

Horizontal Tale-Off and Landing From ConventionalLength Runways: The X-30 is being designed

to enable take-off and landing from 10,000-footlong runways as part of a plan to demonstrate

the potential for responsive and economical

operations in military and civilian follow-on

vehicles.

Powered Approach to Landing and Go-Around

Capability: The X-30 and operational followons could use their low-speed propulsion systems to allow a landing under power. At a

penalty of carrying an extra several thousand

pounds of fuel to orbit, this propulsion capability would allow a launch vehicle returning to

Earth to have go-around capability—the ability

to abort a landing, circle an airfieid, and retry

the landing. Go-around is viewed as a desirable,

but far from essential, capability in an operaIZm. Robcrt B@elemy, briefing on NASP to members of U.S. Senate, Russell Office Building, Apr. 20, 1989.

13~ere we a ~m~r of complex ~~mffs tit wo~d have to ~ ev~~t~ to determine whe~r SST() vehicles would, in fact, k more cost effective

than TSTO (two-stage-to-orbit) vehicles. TSTO vehicles could use lower-risk technology than SSTO vehicles and they could have larger performance

“margins.” On the other hand, TSTO vehicles cotdd require more complicated and expensive ground operations. Safety would be of paramount

importance for a launch vehicle that would be used to transport humans. Therefore, the costs to certify a launch vehicle as flight ready would also have

an important effect in determining which design would be most cost effective.

14~ x.so wo~d follow a s~p ~aj~tw d~ng is f~~ ~ent to orbit. A .sm~] mount of rocket Power is nexxss~ to CUCUkhC the fmtd Orbit

and to place the vehicle at the desired altitude.
Chapter .5-The National Aero-Space Plane ● 71

tional vehicle. It could be traded for larger

payloads or used as ‘margin’ against performance shortfalls. In that case the vehicle would

make a gliding re-entry like the Shuttle.

● “Aircraft-like” Operability: The X-30 would

attempt to demonstrate the potential for operating future hypersonic cruise and launch vehicles in a manner that more closely resembles

today’s airline industry than the civilian space

program. This may be the most challenging

objective of the NASP program, for although

the X-30 may resemble an aircraft, it would be

a radical departure from all previous aircraft

designs.

In particular, the X-30 would attempt to

demonstrate the potential for service and maintenance turn-around times of 1 day or less,

safety and reliability factors similar to those of

aircraft, 150 flights without major refurbishing,

and the elimination of the complex launch and

support facilities and large ‘standing army’ of

technicians that have typified rocket launches.

According to the NASP JPO, rapid turn-around

is essential for many military applications and

it is the key factor in reducing operation and

support costs.

Flight tests of two X-30S would be conducted

from Edwards AFB, California over a 2-year test

program scheduled to begin in October 1994. The

flight control system, the pilot-instrumentation interface, crew escape systems, and solutions to the

potential for communication disturbances or blackout (by air heated so hot it forms a plasma around the

vehicle) would all be tested in this period. The flight

control system for a hypersonic vehicle poses

particular challenges, in part because of the coupling

between the propulsion system and the vehicle’s

aerodynamics.

FUNDING AND SCHEDULE

NASP grew out of a $5.5 million 1984 Defense

Advanced Research Project Agency (DARPA) study

called ‘Copper Canyon’ that revived interest in the

potential for hypersonic propulsion (see box 5-B).

At the time of the Copper Canyon study, some 300

people were engaged in research in what is now

called NASP. Today that number has risen to over

5,000.15

Federal funding for NASP has come mostly from

the Department of Defense (Air Force, Navy,

Strategic Defense Initiative organization, DARPA)

with smaller contributions from NASA. Beginning

in fiscal year 1988, all DoD funding was consolidated within the Air Force.16 The Air Force and

NASA are managing NASP in a Joint Program

Office at Wright-Patterson Air Force Base, Ohio.

Industry is also making a major contribution to

NASP funding.17 Total industry contributions to the

program, now over $500 million, could amount to

$700 million by September 1990. Most funding is

occurring in the current technology maturation and

concept validation phase of the progam. Some of

these investments include items of major capital

investment such as wind tunnels, supercomputers,

and materials research facilities that have applications in projects other than NASP. Figure 5-3 shows

the NASP schedule currently envisioned by the

NASP Joint program Office.

Table 5-1 gives a breakdown of NASP’s funding

by NASA and the Department of Defense. Congressional concern that NASA’s civilian role in the

program was too limited was expressed in the DoD

Appropriations Act for fiscal year 1987 and is

reflected in subsequent budgets. 18

The NASP program would undergo dramatic

change if the revised budget proposals submitted by

Secretary of Defense Cheney, in April 1989, were

15h. Ro&fl B~elemy, NASP Rogmrn Director, at OTA briefing, ~. 13.1988.

16s~ Ge~r~ ~co~ting Office Narwnal Aero-Space Plane. p 19.

]TConuUtor~ have expre~ concern abut tie b~den being imposed on them w a condition to ptuticipate in NASp. Dr. J=ph F. Shea, chtirman

of the 1987-88 Defense Science Board (DSB) study of NASP concurred in this concern, stating in a letter that accompanied the t.rtmsmission of the DSi?

report, ” I am compelled to point out that the concept of heavy cost sharing by the contractors is not realistic. The near-term business potential to be derived

is not large enough. . .“ Major industrial funding is scheduled to cease after NASP completes the ongoing demonstration, validation, and design

activities, and, if approved, enters Phase 111 development.

18sU GAO NatioMl Aero-Space Plane, P.29.
72 ● Rod Trip to Orbit: Human Space flight Alternatives

Box 5-B—The Origins of NASP1

Supersonic flight fist occurred in 1947 when Chuck Yeager, flying the Bell X-1 to a speed of 700 mph, became

the first person to break the sound barrier. The U.S. “X” plane (experimental research aircraft) program to develop

supersonic and hypersonic aircraft continued throughout the 1950s and 1960s, culminating in the creation of the

X-15, a rocket powered aircraft that set speed and altitude records of Mach 6.7 and 354,200 feet, respectively, before

the program was canceled in 1%8. The X-15 was essentially a flying fuel tank that could literally fly to the edge

of space, although it lacked the propulsive capabilities to achieve orbit. The program was cancelled in 1%8.

The X-20 “Dyna-Soar” program contributed substantially to the technical database on hypersonic flight, even

though a flight vehicle was never built. Before the X-20 program, hypersonic data had been derived primarily from

ballistic missile programs using blunt, nonlifting entry bodies. The X-20 was intended to be a piloted space glider

that would have been launched by a Titan III missile and its design would have allowed it to glide horizontally within

the atmosphere, and land horizontally on a runway. Among its proposed missions were reconnaissanace and satellite

inspection.

The X-20 was a costly program and some Administration officials, including Secretary of Defense McNamara,

questioned the necessity for a spaceplane to perform the missions proposed for the X-20. McNamara canceled

Dyna-Soar in December 1%3, citing the possibility of using a manned orbiting space laboratory for some of the

X-20 missions and noting that several hundred million dollars would be necessary to finish the program. At the time

of the cancellation government expenditures for the X-20 totaled over $400 million (roughly $1.5 billion in current

dollars).

Research on hypersonic vehicles and propulsion systems continued throughout the 1960s and 1970s, but was

given a relatively low priority. For example, a late 1970s cooperative effort between NASA and the Air Force to

develop a National Hypersonic Flight Research Facility never matured beyond the planning stage. Nevertheless,

research into hypersonic technologies never ceased. Research into advanced propulsion concepts led to the

fabrication of scramjet components that were tested in wind tunnels at speeds up to Mach 7.

Continued on next page

19 Under the revised DoD adopted by Congress. be completed in late 1990. A major part of Phase 11

budget, overall control of the program would be

transferred to NASA, and support in fiscal year 1990

would be cut by 66 percent to $100 million. DoD

funding of NASP in subsequent years would cease.

NASA’s contribution to NASP would also likely be

revised if the DoD revisions were enacted. The

potential effect of large revisions in the NASP

budget is discussed later in this report. In the

following discussion of the NASP schedule it is

assumed that control of the program is retained

within DoD and funding remains close to President

Reagan’s budget submission of February 9, 1989.

The Copper Canyon study, in effect, was Phase I,

‘‘concept feasibility,’ of NASP. Phase II, “concept

validation,” began in 1985 and is now scheduled to

is the “Technology Maturation Program,” an effort

to develop the requisite technologies and fabrication

techniques for the X-30. Currently, the prime NASP

contractors are Rockwell, General Dynamics, and

McDonnell Douglas (airframe); and Rocketdyne

and Pratt & Whitney (engines). The airframe companies are responsible for the design of the overall

system, including the airframe itself, the cryogenic

fuel tank, and structures such as leading edges and

nose tip.

Out of hundreds of initial airframe/engine configurations, six are presently under consideration (all

three airframe contractors have presented plans that

use either of the two engine designs). The five

contractors are scheduled to be combined into a

l~c ~vi~ b~~t ww submit~ by tie Secretary of Defense as part of a bipartisan budget agreement between president Bush md Conmstiond

leaders that cut some $10 billion of budget authority from President Reagan’s fiscal year 1990 DoD budget of $305.6 billion. (Molly Moore, ‘Pentagon

May Lose Weapons,” The Wurhingfon Post, Apr. 15, 19S9, p.1)
Chapter 5--The National Aero-Space Plane ● 73

The direct origins of NASP can be traced to Air Force support in the late 1970s and early 19802 for what became

known as the transatmospheric vehicle (TAV) concept. TAV may be viewed as a legacy of Dyna-Soar. It was seen

by the Air Force as a potential cargo-carrying successor to the Shuttle to carry defense payloads to orbit, and as a

military vehicle with the potential for global response. The Air Force studied many configurations of TAV, but in

contrast to the current NASP program, most envisioned a vehicle that would incorporate rocket propulsion, such

as advanced versions of the Space Shuttle’s main engines.

By 1984, TAV had grown into a major Air Force study effort. Support for TAV at the Air Force Space

Command came from its potential contribution to four key military space missions: Force Enhancement (including

global reconnaissance; surveillance; and command, control, and communications) Space Support (including

satellite insertion, rendezvous, inspection, servicing, repair, recovery, and support of Space Station) Space Control

(including protection of U.S. space assets) and Force Application.2 Support for TAV was also spurred by the

Strategic Defense Initiative, announced in March 1983, and by President Reagan’s commitment to NASA to build

a space station.

In early 1984, DARPA undertook a study to evaluate the possiblilites for hypersonic, air-breathing propulsion.

DARPA’s “Copper Canyon” study grew to embrace TAV concepts becoming, in effect, a TAV with air-breathing

propulsion. By the end of 1985, the Air Force, DARPA, NASA, SDIO, and the Navy were all studying concepts

for a TAV/Advanced Aerospace Vehicle (AAV), including single-stage-to-orbit concepts. NASP replaced the

TAV/AAV designation as of December 1, 1985. It became a national program following president Reagan’s 1986

State of the Union Address. Overall control of the program was transferred from DARPA to the Air Force in 1988.

l~e hl~[q of hw~~fli~t ~d the ~gi~ ~ NASP are discussed in a ~tibly rich ad &@kd histcxy ediLCd by AK Force his~~ RiCkd P.

Halliw The Hypersonic Revdutwn: Eight Case SrndKs in the History of Hypersonic Technology, VO11, 1924-1967; From Max Wier 10 Project Prime; vol 11

1%4-IM6, From Scramjet to the N&ional Aerospace Plane, (Special Staff Office-Aeronautical systems Division, Wright-Patterson Air Force Base: Dayton, OH

1987). Note: Distribution limited 10 DoD and DoD contractors. See also Seem Pace, National Aerospace Plane program” Principal Assumptwrw Findings, and

Policy Goafs, Rand Publication P-7288-RGS (Santa Monica, CA.: The RAND Corp., 1986), ‘IA. Heppmheimer, “cm H~ Science Save The Aezospace Phne?’

The Sciewis(, vol. 2, No. 19, Oct. 17, 1988, pp. 1-3, and John D. Moteff, The NarionalAerospace Pfane:A BriefHisfory, Congressional R eseuch Report fcr Congress

# 88-146 SPR (l%hington DC: Feb. 17, 1988).

ZHa]llm, T~ Hyperso~ Rewhdwn, Ibid., pp. 1~1~2.

single national team by 1990. The five engine and two X-30 vehicles sequentially and incorporate

airframe contractors have also been combined in a changes in the second vehicle based on flight data

novel cooperative materials consortium that began from the first. Assuming no delays, officials believe

in March 1988 and is budgeted at $150 million for the SSTO objective could be achieved by September

a 30-month period (see app. D). 1996.

NASP’s current schedule (see figure 5-3) calls for NASP officials project total costs through fiscal

a decision to be made in September 1990 on the year 1996 to be roughly $3.9 billion. Peak funding

feasibility of proceeding with Phase III of the levels are expected between fiscal year 1992 and

program, which would include advanced design, fiscal year 1994, when an estimated $550 million

fabrication, and flight tests of two X-30s. Portions of will be requested annually to build the two X-30

a third vehicle would also be built for tests on the vehicles. 20 NASP funding estimates are highly

ground. In addition to building the X-30s, Phase III uncertain because some of the full-scale materials

would also continue NASP’s Technology Matura- production techniques have not been completely

tion program. If the program is able to keep its developed, manufacturing and fabrication techcurrent schedule, a 2-year flight test program would niques are new, and designers have little or no

begin in October 1994. During the test program the experience with estimating costs for building a

X-30 could undergo some modification. A poten- hypersonic vehicle. Furthermore, Phase III budgets

tially more expensive option would be to build the are based on an extrapolation from an early DARPA

zost~ment by NAsp prqp~ heti Dr. Robert Barthclemy reported in Aerospace Daily, vol. 147, No. 58, Sept. *2, 1988, p. 457.
74 ● Round Trip to Orbit: Human Spaceflight Alternatives

Photo credit: General Dynamics Corp.

One conceptual design for the X-30 National

Aero-Space Plane.

Copper Canyon design for an X-30 whose empty

weight was only 50,000 pounds.21 Vehicle weights

have increased since then as designers have acquired

more test data and adopted more conservative

designs.

Designers believe that the empty weight of the

X-30 will be the key factor in determining procurement costs. This is because the structural weight of

an aircraft influences propulsion requirements and

material costs directly, and because it indirectly

affects the size and cost of many other aircraft

components. The JPO has established a cost estimation group for the X-30 in preparation for its Phase

III review.

In an admittedly highly optimistic scenario,

NASP officials told OTA that if the NASP program

were to make very rapid progress, a concurrent

program to build an operational vehicle could

commence while the X-30 was being flight-tested in

Phase 111. An ambitious schedule projects that an

operational vehicle program could be completed

before the year 2000. Achieving this goal presumes

a completely successful X-30 flight test program

without long delays from unexpected technical

problems, budgetary restrictions, or cost growth in

the program. It also presumes rapid progress in

translating X-30 technology into an operational

vehicle. Finally, it presupposes that an operational

vehicle would bear close similarity to the X-30 in

order to minimize new development efforts and

flight-testing.

A more conservative approach would wait for the

completion of Phase 111 before starting an operational program. If such a program began in the late

1990s, a first-generation operational vehicle would

not be expected until approximately the year 2005,

assuming the development cycle of the X-30 follows

previous development cycles for fighter aircraft

derived from experimental vehicles.22 Secondgeneration operational vehicles, which might possess increased performance, bear larger (Shuttleclass) payloads, or have better safety and operability

than fret-generation X-30 derivatives, would require a longer development cycle. Assuming firstgeneration follow-ons are available in 2005, a very

rough estimate for the date of Initial Operational

Capability (IOC) of these vehicles might be 2010 or

later,

NASP TECHNOLOGIES

There is an inherent risk in building a vehicle that

departs radically from all its predecessors and whose

design cannot be fully validated before flight testing.

Further complicating already challenging engineering problems are the complex interrelationships

between technologies caused by the necessity to

design the X-30 as an integrated package. The

following is a brief review of some of the challenges

21 t ‘ph= 111 ~~rn~ves: Contractor Findings, “ in National Aero-Space Plane Program Briefing to NASP Steering Committee, Nov. 7, 1988, p. 49.

Contractor concerns that Phase 111 costs could exceed preliminary Phase 111 budgets was also expressed.

n~on pWe, *’Nation~ ~rospue plme ~Wm: princip~ Assumptions, Findings, ~d Policy GptiOtM, ” Publication # P-T288-RGs, ‘r~ R~

Graduate School Santa Monica, CA, pp. 10-11. NASP ofllcials point to the rapid development cycle of the SR-71 to support their contention that an

operational vehicle could be built sooner than 2005. They also note that in some respects the propulsion and materials challenges that faced theSR-71

are analogous to those facing the X-30 and an NDV. However, the SR-71 suffered several years of troubled operation after the delivery of the first

production units. The SR-71 example holds lessons for both proponents and critics of accelerated development.
Chapter 5-The National Aero-Space Plane . 75

Figure 5-3--NASP Program Schedule

198 5

Phase 1

1990

1

i

I

I1

1

1

Design buiId &

mld -

1990 s

ground-test engin e

#

:

Air frame & component Design 8

FIight test

d eve I o P me n t build X-3 0

#

:

Applications 

studie s

Technology maturation

Spac e

~ Iaunc h

TechnoIog y

Hypersoni c

— cruis e

technolog y

` m

T I me now

SOURCE: National Aero-Space Plane Office.

Table 5-1--NASP Funding (in millions of dollars)

FY 86 FY 87 FY 88 FY 89 FY 90 FY 91

(PB )

a (RB )b

(PB) (RB)

DoD . . . . . . . . . . . . . . . 45 110 (149 )

c

183 (236) 228 (245 ) 300 100 390 0

NASA . . . . . . . . . . . . . 16 (62) 71 (104) 127 127d 119 ?

Total . . . . . . . . . . . . 61 172 (21 1) 254 (320) 316 (349) 427 227 509

Wn3sident FleqFYs budget submlsaion-Fetxuary 1989.

b~D MMIWICI budget-April 1989.

cNumbers in parwnthasis repserrt budget requests from previous fiscal years.

dNAsA outiap are expected to be radurxd if LhO twti50d DoD bU~l IS aP*.

SOURCES: For W 190$S8: “National Am-space Pfane Program Srbfirrg to NASP Steering Committee,” (NASP Joint Program Ofb, Nov. 7, 1988), p, 21

For W 1-1: NASP JPO and Rochwwtll Corporation.
76 ● Round Trip to Orbit: Human Spaceflight Alternatives

to be met in developing the key

gies of the X-30.23

Propulsion

enabling technoloThe X-30 would differ from all previous aircraft

in its use of air-breathing engines instead of rockets

to reach hypersonic speeds. One measure of fuel

efficiency is the specific impulse, Isp, which is

defined as the thrust delivered per unit mass of

propellant burning in one second.24 By avoiding the

necessity to carry an oxidizer, air-breathing engines

can achieve higher specific impulses than rockets,

although their advantage diminishes with increasing

speeds (figure 5-4). The higher Isp of air-breathing

engines makes a single-stage-to-orbit vehicle a

possibility despite the necessity to carry the weight

of wings and landing gear to orbit.

Jet engines generate thrust by admitting air

through an inlet, compressing a mixture of fuel and

air in a combustion chamber (combustor), igniting

the mixture, and letting the hot, compressed exhaust

products expand through a nozzle opening at high

speed. Compressing the fuel-air mixture before it is

ignited raises the temperature and pressure of the

mixture; this facilitates combustion and improves

the overall fuel efficiency of the engine.

Different configurations of air-breathing engines

would be needed to operate at subsonic, supersonic,

and hypersonic speeds within the atmosphere (see

app. C). Scramjets could, in principle, power an

aerospace plane from about Mach 5-6 to orbital

speeds (about Mach 25), assuming that theoretical

predictions of scramjet performance at high Mach

numbers prove accurate, and assuming that the

fraction of the spaceplane’s weight that was devoted

to structures could be made extremely small (the

Figure 5-4-High-Speed Propulsion System

Ramjet Engine

Flight Mach 2-6

Fuel

Shock Supersonic

SOURCE: Adapted from NASP Joint Program Office.

precise number is the subject of some debate). All

designs face the challenge of producing a propulsion

package that meets stringent aerodynamic and

weight constraints.

The X-30 would be the first vehicle to reach

hypersonic speeds propelled by scramjets. All designs envision the placement of a series of scramjet

modules side-to-side across the bottom of the aft

section of the vehicle (figure 5-5). In this way the

long forebody of the aircraft effectively becomes

part of the engine inlet, and with careful design it

will capture much of the air moving past the vehicle

and channel it into the engine inlets. The required air

compression in the combustor would be provided by

coupling the underside bow shock through the

engine inlets. The three airframe contractors have

proposed different configurations for the X-30. With

n’rhc djSCUS@OII hcm din the appendices is meant to senwas abricftutorial. More thorough, and technically more Sophisticated reviews, =Repon

of the Defeme Science Board Tizrk Force on the Nm”ond Aerospace Plane (NASP) (Washington DC: Offiec of the Under !lecremry of Defense for

Acquisition, 1988); and ~yper.ronic Technology For hfifitury Application, op. cit., footnote 4. NASP’S key technical challenges are also reviewed in

the GAO report Nationaf Aero-Spuce Plune, op. cit., foomote 4. Excellent popular introductions to NASP technologies are found in: T.A. Heppenheimer,

“Launching the Aeroepiw.e Plane,” High Technology, July 1986, pp. 46-51; and John Voelcker, “l%e iffy ‘Orient Express’,” fEEE Spectrum, August

1988, pp. 31-33.

~M~, ~ f-, js WXSIIy expr~ in units of pounds, and propellant mass flow rate is commonly expressed k “pouds’ Pr ~Ond. ~m~ ISP

is usually expressed in “seconds,’ Strictly speaking, the propellant mass flow rate should be measured in units of mass per second, not weight per second,

In that case, Isp would have units of velocity.
Chapter 5-The National Aero-Space Plane ● 77

12,000

10,000

‘SP 8,000

Thrust

P r 6,000

b

4,000

2,000

0

.

o 4 8 12 16 20 24

Mach number

SOURCE: McDonnell Douglas.

respect to the vehicle forebody, their designs reflect

compromises among aerodynamic drag, inlet compression efficiency, and structural considerations.

NASP officials have not yet chosen a final design.

All designs also envision making the airframe

afterbody part of the engine, in effect serving as a

nozzle and surface to expand the exhaust products.

This eliminates the weight of a nozzle and can also

help reduce the drag that results from the pressure

differential that develops between the front and rear

surfaces of the aircraft. The amount of forward thrust

generated by the scramjets is a sensitive function of

the intake airflow and the resultant exhaust expansion. Similarly, vehicle drag at high speeds is a

sensitive function of engine geometry. Again, this

illustrates the necessity to optimize performance by

designing airframe and engine together.

To reach orbit, the X-30 would rely on efficient

performance of scramjets at speeds in excess of

those that can be fully tested in ground facilities. In

addition, although scramjets can in principle produce positive thrust all the way to orbital speeds,

their propulsion efficiency as measured by engine

specific impulse declines as vehicle speed increases

(see figure 5-5). A plot similar to figure 5-5 that

included the effect of drag on the vehicle (effective

Isp) would show that as vehicle speed increases, the

net thrust decreases. Thus, a scramjet-driven hypersonic aircraft will be operating with very little

tolerance for unexpected thrust losses, or increases

Photo credit: Rocketdyne Corp.

Conceptual airframe and engine design for the X-30

National Aero-Space Plane.

in drag at the higher Mach numbers.25 The importance of this sensitivity could be lessened, at some

penalty in performance, by augmenting scramjet

propulsion with auxiliary rocket power. In addition,

the high-speed thrust sensitivity of a vehicle would

vary greatly with specific engine and airframe

designs.

As part of a risk reduction plan, propulsion

systems under consideration by the NASP JPO have

an option to augment the thrust of scramjet engines

with an auxiliary rocket-based propulsion system

before the vehicle reaches orbital speeds. In these

designs, liquid oxygen is carried on-board the X-30

and either added directly to the scramjet engines or

combined with hydrogen to power a separate rocket

propulsion system. Either approach involves design

tradeoffs. If separate rockets were chosen for thrust

augmentation they would be resuable and relatively

small, equivalent to the class of rockets needed to

~Stephen Korthals-Altes, ‘The Aerospace Plane: ‘IMnological Feasibility and Policy Implications” (S.M. thesis, Massachusetts Institute of

‘T&Imology, Cambridge, MA: 1986), pp. 50-55. The thrust sensitivity issue is also discussed in Bill Swectman, “Scramjet: ‘llIc NASP propulsion goal,”

Inreraviu, November 1987, p. 1208.
78 ● Round Trip to Orbit: Human Spaceflight Alternatives

propel an orbital transfer vehicle from low-Earth

orbit to geosynchronous orbit.

The speed at which auxiliary power might be used

during ascent is a complicated issue dependent on

many design factors. The disadvantages of early

rocket turn-on, or LOX augmentation of airbreathing engines, includes the need to carry heavy

liquid oxygen and tankage on-board. The resulting

heavier take-off weight of the vehicle increases the

required wing area, take-off speed, and overall size

and cost of the vehicle. On the other hand, additional

liquid oxygen is 50 percent more dense than jet fuel

and thus takes up relatively little space. Hydrogen

tankage is necessarily large because of the low

density of liquid hydrogen, roughly one tenth of jet

fuel. In fact, this is one of the reasons slush hydrogen

is being considered as a fuel (see Fuel discussion

below). Furthermore, at the very high speeds where

auxiliary power would be used, scramjets would be

operating in a mode that consumes extra amounts of

hydrogen. 26

Several other factors would affect the choice of

rocket transition point, including:

●

●

●

the X-30 will be subjected to higher drag while

in the atmosphere, but the drag would drop

substantially if the vehicle entered a low-drag

rocket trajectory;

the specific impulse of scramjet engines is

expected to drop off rapidly at higher Mach

numbers; and

scramjets tend to have less thrust available at

higher Mach numbers where rockets have no

such limitation.

According to NASP airframe contractors, the

X-30 could achieve SSTO even carrying the extra

weight associated with an auxiliary propulsion

system. However, SSTO performance could be

attained only if scramjets perform close to theoretical expectations, and only if extremely low structural weight fractions were achieved. A disputed

point among some propulsion and materials/

structures experts is whether near-term technology is

sufficiently mature to meet both these requirements.

The program management implications of this issue

are discussed in the Policy and Options section of

this chapter.

Fuel

Ordinary hydrocarbon fuels like kerosene, or the

more specialized derivatives used on some highperformance aircraft, would not be suitable for the

X-30’S scramjets. The amount of thrust that could be

derived from the combustion of these fuels is too low

compared with their weight, and they could not be

mixed or burned efficiently in the hypersonic airflow

of an X-30-sized combustor. As the X-30 accelerates

towards Mach 25, air will sweep fuel through the

combustion chamber in times on the order of 1

millisecond. Sustaining combustion and avoiding

flameout in these fast flow situations presents

complex problems.

One part of the solution to these problems will be

the use of hydrogen as fuel, Hydrogen has the

highest energy content per unit of mass of any fuel.

It also provides a burning velocity improvement of

a factor of five relative to conventional hydrocarbonfuels, and should allow the burning process to be

completed without unreasonably long combustion

chambers.27 By itself, however, hydrogen would not

solve all of the problems of igniting and burning fuel

traveling at hypersonic speeds. For example, engine

designers must also incorporate special “flameholding” techniques to stabilize the flame in scramjet

combustors without compromising engine aerodynamics or adversely affecting combustor conditions.

Hydrogen fuel offers several other advantages

over conventional fuels:

The large heat capacity of hydrogen provides a

possible heat sink for the enormous thermal

loads to which the X-30 would be exposed;

Its exhaust products are predominantly water

vapor, which is expected to prove environmenMA1 “c, him _a sl~~cmt ~wtlon of tie ~rmjet)5 thrust would be derived from hydro~n that was tidd to tie combustor, but did not

undergo a chemical reaction with oxygen. As hot hydrogen is expanded from the higher pressure combustor to the lower pressure nozzle, it cools,

converting heat into kinetic energy and adding to the thruw

zTHOWeVer, wdiq 10 ~ Air Force studies Board Report on Hypersonic ‘fkchrtdogy, the reaction btwwn hydrogen ~oxY8en ~ ~combustm

would not be complete before the mixture reached the engine nozzle. Unless the reaction was substantially completed during the expansion process some

of the energy available from the propellant would not be used to produce thrust.
Chapter S--The National Aero-Space Plane ● 79

tally safe when produced at the very high

altitude flight paths of hypersonic vehicles28;

. It does not produce noxious fumes, and there is

less danger from spreading flame than there

would be from conventional fuels because it is

less dense than air; and

. It could be combined with oxygen in a fuel cell

to generate electrical power for the X-30.

Hydrogen gas would be derived from tanks of

liquid hydrogen in order to permit enough fuel to be

stored in a reasonably sized container. However,

despite its higher energy content, liquid hydrogen’s

low density will result in fuel tanks some five times

larger than equivalent hydrocarbon fuel tanks.29 As

a result, NASP engineers are exploring the feasibility of using slush hydrogen-a mixture of 50 percent

solid and 50 percent liquid hydrogen that is roughly

15 percent more dense than liquid hydrogen. The

slush would have a greater density and greater

cooling power than liquid alone. The other major

concern with hydrogen is the potential problem of

hydrogen embrittlement in materials (see below).

Hydrogen would also be circulated through the

engine, and in some designs through the airframe, as

a coolant and as a means to increase combustion

efficiency. Regenerative cooling is a technique

typically employed by designers of liquid rocket

engines to recover waste heat. By cooling the engine

with fuel, the energy of the propellant is increased

before it is injected into the combustion chamber.

The addition of thermal energy to the propellant

results in an increase in the velocity of the exhaust

gases. If the exhaust nozzle is designed properly, the

extra energy of the expanding gases will produce

more thrust. The use of regenerative cooling techniques in the X-30 would allow waste engine heat,

or heat generated by aerodynamic heating (friction),

to be recovered and used to increase engine specific

impulse. The recovery of fuel energy would be

especially important for hypersonic cruise vehicles.

Materials and Thermal Management

Success in the materials and structures program

will have a pivotal effect on the pace at which the

X-30 can be developed, the X-30’S ability to achieve

its design goals, and the extent to which the

promised economies of future operational vehicles

may be realized (app. D). The projected structural

designs for all areas of the vehicle call for highstiffness, thin-gauge product forms that can be

fabricated into efficient load-bearing components.

These in turn require high-strength, low-density

materials that can retain their characteristics beyond

those tolerated by present-day, commercially available materials.

Current challenges center around scaling Up

laboratory production processes of advanced materials; developing fabrication and joining techniques to

form lightweight sandwich and honeycomb structures; and forming materials and coatings that can

withstand thermal cycling of the sort that would be

seen in a flight vehicle. The potential for material

failure under thermal cycling is a particular concern

for the X-30 and its possible derivatives because

vehicle structures will be exceptionally light, and

therefore thin, and temperature differences between

inner and outer layers of airframe and engine

structures will be unusually large.30

Even if their weight could be tolerated, most

metals lose their structural integrity above about

1,800 ‘F. Without cooling, leading edges of the

wings, tail, engine, and nose cap of the X-30 could

reach temperatures above 4,000 ‘F. Shock-heated

portions of the vehicle could reach temperatures in

excess of 5,000 ‘F, and large areas of the aircraft

28~~Pxlof hy~rsonlcVehicles On tieOme layeris tie largest concern. The NASP JPO @ let contracts for preliminary environmental

assessments to evaluate the potential effects of water emissions from X-30 f~llow-on vehi~lest ad ~ ev~u- he imp~t of wondw chemical reactions.

Note that the ascending flight profile of a orbital vehicle takes it quickly ~rough tie ~~sphefic b~d where ozone is concentrated (60,(XD75,000

feet),

Z’ljtephen Korthals-A1tes, ‘‘The Aerospace Plane: Ik.chnological Feasibility and Policy Implications,” p.43.

3~omider a thin ~rme Pmel or ~ion of WI engine wall that develops a ltugc temperature grti~t dtig flight because one side k exposed to

tzigher lwa~ or cold. Evety time the vehicle is flown, the matcrki would flex slightly became of differential expmion. Under repeated thermal cycles,

the continual flexing could eventually lead topennanent deformation or even fracture. Notice that it is the peak, or transient, thermal gradients that govern

the scale of this problem, The effects are most worrisome on thin gauge materials since they would fail before thicker materials, The plan to use thin

gauge, relatively brittle composite materials for portions of the X-30, and their potential to be exposed to large thermal gradients, is the source of some

concern among materials researchers.
80 ● Round Trip to Orbit: Human Spaceflight Alternatives

could be heated to temperatures above 2,500 °F.31

The greatest stress is within the engine where

materials are subjected to the largest simultaneous

aerodynamic and aerothermal load.

The Space Shuttle uses thermal protection tiles to

insulate the interior of the vehicle from the high

temperatures encountered on reentry. Covering most

of the X-30 with thermal tiles would increase vehicle

weight and, in addition, would defeat regenerative

cooling schemes to increase fuel efficiency unless

the tiles could be actively cooled. Instead, the X-30

will cool the hottest airframe structures by circulating hydrogen gas or by employing specially designed “heat pipes.”32

Using hydrogen cooling raises the potential for

hydrogen embrittlement.33 As hydrogen fuel is

transported to the engine it will turn from a liquid to

a hot gas, which can diffuse into most materials

without difficulty and can form brittle compounds

within those materials. The NASP JPO considers the

development of hydrogen barrier coatings a critical

challenge. The X-30 will require coatings that are

thin, lightweight, resistant to damage, and can be

applied to complex shapes, including internal passages. Embrittlement could make materials prone to

cracking and, in addition, it could affect operations

costs and turn-around times if increased maintenance and inspection are required. It could also

shorten the useful life of a structural component.

The materials problem is especially difficult in

structures that are exposed to both large thermal and

mechanical stresses. Perhaps the outstanding example of such a structure is the scramjet fuel injector.

To facilitate mixing of hydrogen fuel with air it is

necessary to place fuel injectors directly within the

very hot engine combustor instead of along the

cooler combustor walls. The injectors will experience large mechanical forces. In addition, to keep

temperatures from rising beyond material limits,

relatively cold hydrogen must be circulated at high

pressure within the injector. Even small changes in

injector placement and shape could have large

effects on the resultant airflow and engine performance.

34

Computational Fluid Dynamics (CFD)

and X-30 Design

The design of the X-30 will require unparalleled

use of computer simulation to model the vehicle’s

aerodynamic behavior at high Mach numbers. Wind

tunnels can provide only limited data, as existing

facilities can replicate flight conditions only to about

Mach 8. Computer modeling performed on the

fastest supercomputers is playing a key role in

designing and optimizing the X-30’S airframe and

propulsion system, and predicting the them-ml loads

that would be encountered by the vehicle.

Computational fluid dynamics (CFD) simulates

the behavior of fluids (both gases and liquids) by

solving numerically the fundamental equations of

fluid motion on a high-speed digital computer. The

process of simulating the airflow around an aircraft

begins by mathematically generating a picture of the

vehicle. Mathematical algorithms calculate airflows

over the simulated body at a number of points that

are spread out on a mathematical grid. Finer grids

and more sophisticated algorithms simulate the

resultant airflows with greater fidelity at the cost of

increased demands on computer memory and speed.

Furthermore, calculations must extend beyond the

surface of the vehicle’s body to account for important aerodynamic effects, and they must also include

flows through engines to evaluate propulsion performance. The critical areas where CFD is being

used on the X-30’S design are the calculation of

airflows around the forebody and engine inlets;

inside the engine’s combustion chamber (the most

difficult set of calculations); around the afterbody

31X.30 temperatures b, “National Am-space Plane,” briefing booklet supplied by Director of NASP Program Ikveloprnent, McDomell

Douglas, St. Louis, MO.

32A ~at piPi.s a clodsy5~m who=Wofing p~ciplcs ~~rnb]c ~~ of ~ or&n~ refi~rator. Heti applied to OIW end of a kt pipe v~fks

a fluid and causes it to travel to the other end which, for example, might be in thermal contact with a large structure that acmes as a heat sink. At the

cooler end, the fluid condenses giving up its latent heat of vaporization. The fluid then circulates back to the hotter end of the pipe by capillary action

along a wick. In the X-30, the working fluid could be lithium.

n-~ M.F. Ro~d, ** Mt@itds (%alien~s For The National kro-sp= phtte,’ Review qf Progress in Quantitative Non-Destructive

Evafuu$wn (New York, NY: Plenum Press), May 1989, p.13.

MS, A, ~xm et ~., 44s~tm ~d MMri~S ~~olo~ lgs~ for Reu~ble Launch Vehicles,” NASA ‘Mtrtical Memorandum 87626 (ti~,

VA: NASA LRC, October 1985), p. 15, cited in Richard Hallion, The ~ypersonic Revolution, vol. II, p.1357.
Chapter S-The National Aero-Space Plane . 81

and nozzle area; and around the entire integrated

engine/airframe. 35

The end result of a CFD simulation of X-30 flight

might be a set of pressure contours or temperature

profiles around the vehicle. Such a calculation might

take many hours or even days depending on the level

of approximation, even when performed on the

fastest supercomputers using state-of-the-art algorithms. Moreover, these calculations may be limited

in their ability to model turbulent airflows (see box

5-C) a critical issue in NASP airframe and propulsion design.

Because turbulence is characterized by extremely

small and rapidly changing eddies, a very detailed

simulation would be needed to model turbulence

faithfully over large volumes or long time spans.

CFD simulations typically include turbulent flow

only in a semi-empirical way, adding its effects to

theoretical models of smooth flow by the ad hoc

inclusion of terms based on experimental data.

While the resultant models may be valid over some

narrow range of conditions, their application at the

extreme conditions that would be encountered in

reaching orbit introduces uncertainties. Validating

CFD models is thus a critical issue for NASP.

Unfortunately, no existing or planned ground test

facility could simulate simultaneously the equivalent temperatures, pressures, air speeds, and turbulent effects that a spaceplane would encounter in its

ascent to orbit.

Wind tunnels, the primary means to acquire

experimental data, cannot produce long-duration air

flows with true temperature simulation over Mach 8

in volumes large enough to hold full-size engine and

airframe structures. For example, “blowdown”

facilities produce gas flows above Mach 8 by gas

expansion, but the process also results in very low

gas temperatures. However, because the Mach

number in the combustor is roughly one-third of free

stream, 36 even Mach 8 wind tunnel facilities can

provide some engine aerodynamics data over most

of the X-30’S speed range. Still, its quality decreases

at higher Mach numbers. Other challenges for wind

tunnels include simulation of “real gas” effects—

effects that are the result of the formation of

chemically reactive and excited-state atomic and

molecular species as a vehicle moves through the

upper atmosphere at hypersonic speeds. It is particularly important to develop models that include real

gas effects when describing conditions within the

X-30’S engine.

Pulse facilities (“shock tunnels”) can simulate

the heat content and pressure of air at speeds as high

as Mach 20, but the short duration of their flows

(typically 10 milliseconds or less) prevents full

steady-state conditions from being achieved and

makes instrumentation difficult. Moreover, the size

of test models is usually restricted in shock experiments. NASP is funding refurbishment and upgrading of several pulse facilities. Anew Rocketdyne test

facility that may open in 1990 promises to allow

full-scale engine component testing up to Mach 24.37

Hypersonic data gathered by the Space Shuttle

would be of limited use in designing the X-30

because the Shuttle’s shape and trajectory differ too

much from prospective NASP vehicles and flight

paths (the data would be of some use in validating

numerical simulation models of hypersonic flight).

Currently, NASP has no plans to gather hypersonic

data experimentally by deploying test vehicles from

the Shuttle, dropping projectiles from high-altitude

balloons, or by using ground or aircraft-carried

rockets. The position of the JPO is that such a

program would be a significant experimental undertaking that would consume large amounts of time

35~ ~ ~ment ~Pfi, ~e chief scientist ~ k Air Force’s Arnold Engi.mxxing Development Center stated that it took a year to set up the grid and solve

the flow field for the F-16 fighter. Another project to model tie F-15 fighter t~k four engin~rs work~g pw-time six months. However, automated

processes are reducing the time to setup vehicle grids. NASp offici~s P~ct~ hat it will SOOII ~possible to retie changes in airframe configurations

and re-grid the model in times on the order of 6 weeks. John Rhea, “The Electronic Wind lhnnel,” Air Force Magazine, vol. 72, No, 2, February 1989,

pp. 62-66. This article gives an overview of CFD efforts at tiold Eng~~ring Development Cen@r md other Air Force laboratories.

36The fluld M~h nm~r is ~v~~ly propofi~~ to the ratio of the square root of the tempt?rature of the gas in the combustor divided by the

temperature of the gas in the free stream (the temperature of the gas far out in front of the vehicle).

37wi]lim B. s-t, ‘61@ke~~e ~velopingFxility for Hypersonic propulsion ‘ksts, “ Aviation Week and Space Technology, Jan. 30, 1989, p. 65.

mis facility will be a refleeted shock tunnel and shouJd be able to Simuhue some of the temperature, pressure, and real gas effects that would be

encountered by the X-30 in an ascent to orbit. However, there will still be some limitations in testing. For example, reflected shock tunnels are limited

in their ability to perform combustion tests above the Mach 12-14 region because they produce higher levels of oxygen dissociation (50% at Mtwh 16)

than would be expected during actual flight conditions.
82 ● Round Trip to Orbit: Human Spaceflight Alternatives

Box 5-C—Limits of Computational Fluid Dynamics

Turbulent phenomena present a sometimes intractable problem for researchers attempting to model gas flows

using numerical techniques. While the time evolution of some types of gas motion is predictable, turbulent flows

are chaotic and only their gross behavior is amenable to computational analysis. A hallmark of turbulent flow is the

presence of disordered motion at all scales. For example, the swirls and eddies of a rising column of smoke contain

smaller-scale disturbances, and these enclose smaller ones, and so on. Unfortunately, to understand the large-scale

behavior of turbulent motion, it is sometimes necessary to include the effect of the small-scale disturbances.

A faster computer can simulate turbulence at smaller scales, but the practical limits set by storage and speed

limit how well any computer can predict flow patterns. For example, if the numerical simulation of a turbulent flow

requires calculations every one tenth of a millimeter, then enormous requirements would be made on computer

storage. ’ To make their calculations more tractable, computer models of airflows that include turbulence can resort

to simplifying assumptions, such as assuming two-dimensional instead of three-dimensional flow. Another

simplifying assumption is to neglect the “real gas” effects of chemically reactive species formed in hypersonic

airflows. Unfortunately, full three dimensional models that include real gas effects are necessary to predict the

aerodynamics and aerothermal loads that a particular airframe and engine configuration will experience in

hypersonic flight.

Outside the engine, the most important limitation of CFD is in its ability to characterize the “boundary layer

transition. ’ The location and length of the transition from laminar (smooth) to turbulent flow-the boundary layer

transition--has a significant impact on all aspects of engine and vehicle performance. For example, it affects the

lift and drag on the vehicle, the airflow into the engine, and heat transfer rates. Assumptions about the location of

the boundary layer transition therefore have a profound effect on design requirements for the propulsion system and

the cooling system.

Although CFD researchers report progress in predicting the location of the boundary layer transition, complete

validation of computer models is not possible using only ground-test facilities. NASP designers are making what

they describe as conservative assumptions regarding the flow patterns over the X-30 to minimize the effect of

boundary layer uncertainties in the performance of prospective vehicles. The boundary layer problem is another

illustration of the difficulties engineers have in designing a vehicle meant to explore the outermost regions of the

atmospheric flight envelope. It has also fueled disputes over whether the NASP philosophy of attempting to reach

orbit without first building an intermediate vehicle(s) is excessively risky.

l~w~ G~ca, “.%*8 (M the SCC=B of Fk,” New Scientist, July 7, 1988, p. 46. See also Edwin Gales, ‘‘Supercornput~s and the Need for Speed,”

New Scicntbt, Nov. 12, 1988, pp. 50-55.

and resources. Instead of a subscale hypersonic test Proponents of the NASP program argue that it

program, the JPO envisions using the X-30 as a would maintain U.S. leadership in competitive

flying test-bed to validate scramjet performance at technologies critical to the aerospace industry.

high Mach numbers. Furthermore, they assert that the NASP program will

POLICY CONSIDERATIONS lead to hypersonic aircraft and space launch vehicles

that would have revolutionary capabilities. HowAs summarized in earlier sections, the NASP ever, the Secretary of Defense and other DoD

program is currently developing the technology to officials have suggested that because the NASP

build an X-30 research vehicle. When this work is program is a high-risk program whose applications

complete, the NASP joint program office will report are long-term, it can be deferred in an era of stringent

to the Administration and to Congress on the budgets. 38 This section presents several important feasibility, timetable, and costs of proceeding with

development. considerations for Congress as it deliberates the

sSCraig Mault, ‘‘White House Acts to Reverse Aero-Space Plane Cancellation, “ Aviation Week and Space Ildtnology, Apr. 24, 1989, pp. 20-21.
Chapter 5-The National Aero-Space Plane ● 83

future of the NASP program in relation to other

civilian and military space priorities.

What future vehicles and mission capabilities

could the NASP program lead to, and how

would these compare with other alternatives?

The NASP program is designed to demonstrate

technologies that could lead to operational launch

systems for both military and civilian use in the early

part of the next century. Assuming the X-30 were to

complete its test program successfully, the first

operational vehicles derived from NASP technology

would likely be military launch vehicles, or perhaps

military hypersonic cruise vehicles. An aerospace

plane designed for military use could also be used

for a variety of civilian applications, including

transporting people to and from the proposed space

station.

Even if the X-30 proves successful, launch

vehicles or hypersonic aircraft derived from

NASP technology would have to compete for

funding and attention with other means of accomplishing the same military and civilian missions. If Congress believes that the NASP program should proceed only if it would lead to

cost-effective operational vehicles, it may wish to

examine the results of applications studies before

funding Phase III of NASP. Alternatives to piloted

NDVs would include expendable launch vehicles,

other reusable concepts that include two-stage-toorbit vehicles, and supersonic aircraft. An unmanned

version of a NASP-derived vehicle is still another

possibility. Because of their projected high unit

costs, NDVs could not be procurred in large

numbers. The NASP program office is comparing

the utility of a military aerospace plane against

alternative systems for carrying out the same missions. In addition to evaluating how well a small

fleet of NDVs might perform versus a larger number

of less costly systems, it will also be important for

these studies to include both the effect of the long

lead time for development of an NDV (operational

vehicles are unlikely before 2005) and the effects of

probable countermeasures.

Three classes of NASP-derived vehicles are

possible:

Option 1: A Military Aerospace Plane

Endo-atmospheric hypersonic aircraft based on

NASP technology could perform a variety of global

military missions requiring rapid response, including reconnaissance,39 interdiction, air defense,40 and

air strike. The NASP program has developed preliminary designs for hypersonic military aircraft

with ranges from 12,(K)0 to 17,000 nautical miles at

speeds of between Mach 7 and 12.41 Similarly, the

second type of military vehicle that could be

developed-a survivable, quick-response Mach 25

vehicle with access to space—would also have

unique military capabilities.

The relative importance of these capabilities rests

on a number of factors, including the comparative

costs and capabilities of alternative systems. For

example, small launch vehicles developed for DARPA’s

Lightsat program, which could provide responsive

surveillance by placing small dedicated satellites in

orbit to be used by field commanders, might

compete directly with the capability of launch

vehicles developed from NASP technology .42

Other potential missions for a NASP-derived

vehicle (NDV) may depend on the continuation of a

Strategic Defense Initiative with a space-based

component. For example, although an operational

spaceplane could not substitute for the Advanced

Launch System heavy-lift vehicle being sought for

some Strategic Defense System (SDS) payloads, it

might be capable of economically launching smaller

SDS payloads, such as space-based interceptor

satellites, on demand. In addition, a spaceplane

WA hWrW~c vehicle &velo@ from x.30 Mklogy might extend the speed and altitude hrnita of the Mach 3+ SR-71 “Blackbird,” and could

enable operation from more locations with faster response snd improved turn-around times.

40~ effofl ~ deveiop hy~rsonic wea~sfor Ar defense is being conducted as part of the Air Defense Initiative (ADI), a DoD/DARPA program

to counter the threat from low-observable bombers ~d cmi= missiles. @e application king s~d~ is tie feasibility of combining new surveilhmce

methods with hypersonic, long-range surface-to-air misiles to att~k ~rcr~t cqing ~r-launc~ cmi= missiles at long distances. Current air defense

interceptors could not travel fast enough to reach such cmiw missile cfie~ ~fore they were wi~ rmge of ti United States, even if they were detected

at the maximum range of new over-the-horizon radars.

dlN~p Joint Ro~~ Clffice, pc~ttd COItlmUIliCdOlt, A@ 1989.

42u,s. ~mss, office of ~~olom A-merit, Alrer~tive Spacecraft f)esign and LUMCh @hs, OTA B~k~urtd P~r, (Washington, ~:

U.S. Government Printing Office).
84 ● Round Trip to Orbit: Human Space flight Alternatives

could be valuable for on-orbit maintenance of SDS

Satellites.

Option 2: Civilian Aerospace Plane

A launch vehicle derived from NASP technology

is one of several concepts being considered for

low-cost piloted space transportation to and from

low-Earth orbit. As part of its Advanced Manned

Launch System (AMLS) Studies, NASA is studying

reusable rocket-powered vertically launched vehicles and air breathinghcket horizontal takeoff systems as Shuttle replacements (see ch. 4). In part

because of its simplified launch operations, a vehicle

requiring only a single stage to reach orbit may have

a greater potential to lower operating costs than

two-stage AMLS vehicles. However, a single-stage

vehicle would also require use of more advanced

technology (e.g., scramjet propulsion and new

materials), and its development would be inherently

more risky.

NASP shares some similarities with concepts for

an AMLS, but it has important differences as well.

Even though both programs will use new technology

in areas like materials and structures, and both plan

to incorporate autonomous vehicle operations to

reduce launch and operation costs, building an

aerospace plane requires a much larger technical

leap than building rocket-powered launch vehicles.

Even assuming a rapid resolution of the myriad

of technical issues facing the construction of an

X-30, translating this technology into an operational spaceplane might come late in the period

when an AMLS could be ready, and perhaps

after the time when replacements for the shuttle

will be necessary. Presumably, an AMLS program

that began in the late 1990s would still allow for

completion of an operational vehicle by the year

2010. An AMLS program begun in that time might

also benefit from matured NASP technologies,

especially in the area of materials and structures.

Prospective first-generation operational followons to the X-30 would almost certainly have less

payload capacity than the present Shuttle.43 They

would compare favorably with possible AMLS

vehicles (roughly 20,000 to 40,000 pounds into

low-Earth orbit). An NDV might be used for civilian

applications even without large payload capacity.

These could include satellite launch, responsive

satellite replenishment, on-orbit maintenance and

repair, ferrying of astronauts and cargo to the

proposed space station, and serving as a space rescue

vehicle.

The cost-effectiveness of these missions should

be evaluated in comprehensive applications studies

that evaluate the feasibility of using alternative

launch vehicles and assess future civilian launch

needs. For example, the feasibility of on-orbit

maintenance would depend on the operation and

support costs of a NASP-derived vehicle and on

satellite design. At present, the costs of on-orbit

retrieval or repair generally far outweigh the costs of

building new spacecraft.

Option 3: Orient Express

Perhaps mindful of the popularity of NASA’s

piloted space-flight program with the public, some

proponents of NASP have made exaggerated claims

regarding the civilian benefits of the X-30 program,

especially those pertaining to the commercial transport dubbed the Orient Express. Such claims have

abated and program managers now appear to be

sensitive to the dangers of overselling their program.

NASP officials were forthright in explaining to OTA

that their program has little to do with creating an

Orient Express.

If a Mach 5+ commercial transport is developed,

it will likely evolve from NASA’s High-Speed

Commercial Transport Program. Such a vehicle,

currently thought to compare unfavorably in cost

and environmental acceptability44 with slower supersonic transports that would fly between Mach 2 and

3, would benefit from the advanced technology

being developed for the X-30. However, as emphasized earlier, the X-30 program is neither the most

cost effective nor the most direct route towards

facilitating hypersonic civilian aircraft.

In the mid to late 1990s, Congress will have to

choose among the competing claims of proponents

of a variety of new launch systems, including

t3Rou@y 55,~ ~mds w~n l~ch~ Eat into a circular orbit 110 nautictd miles hit?h.

44 However, ~ n~ ewlla, hy-nic ~~~s wwld fly at very high altitudes and theN eXhaUSt products might not endmger he owe laYer.

Sonic boom effects might also be reduced by high altitude flight.
Chapter 5--The National Aero-Space Plane ● 85

NASP-derived vehicles. If the NASP program

achieves its technical goals and can demonstrate the

potential for low operational costs, launch systems

derived from NASP technology may well replace

other prospective launch systems. However, the

life-cycle costs, which include development, acquisition, and operations costs of each system, will have

to be examined and compared in order to choose the

best launch system mix.

What Auxiliary Benefits Could the NASP

Program Provide?

By providing a focus for defense research and

development on the technologies of hypersonic

flight, NASP and follow-on programs could make

important contributions to defense programs seeking long-range, fast weapons delivery. For example,

an obvious area for coordination in weapons development is the very long-range hypersonic surface-toair missile being sought by DARPA and the Air

Force for applications such as air defense, fleet

defense, and long-range targeting of mobile and

relocatable assets .45

Proponents of the NASP program maintain that it

would contribute important new technology to the

defense technology base.

46 Although it is clear that

the NASP program has contributed to the Nation’s

ability to manufacture new lightweight materials

capable of enduring high thermal and mechanical

stresses, has improved computational fluid dynamics techniques, and has advanced the theory and

application of hypersonic propulsion, it is too early

to assess how much these technologies will benefit

defense programs outside of NASP.

The long-term benefits of the NASP program to

civilian industry may also be substantial, but they

too are uncertain. Proponents of the NASP program

believe it would have important benefits in many of

the high-technology industries of the next century.

In particular, they believe that the program would

have great benefit for the civilian aerospace industry. However, other programs, such as a high-speed

commercial transport program, would also have the

potential to enhance the U.S. competitive position in

the civilian aerospace industry, and might do so

more directly than the NASP program.

Is the NASP Program Technically Sound?

OTA did not conduct a detailed assessment of the

technical soundness of the NASP program. Two

advisory bodies, the Defense Science Board (DSB)

and the Air Force Studies Board (AFSB) of the

National Research Council, have conducted recent

technical reviews.

The DSB report. In 1987, the DSB performed a

comprehensive technical review of NASP. Members

of a special task force said they were impressed by

the progress the NASP program had made. However, they were cautious in their outlook and warned

that they were “even more impressed by what has

yet to be done to reduce the remaining uncertainties

to a reasonably manageable level.”47 The DSB

study was conducted early in the technology development phase of the NASP program (Phase II) and

overlapped internal reviews by project management

that also concluded that some redirection of program

efforts was desirable. Appendix E presents an

overview of the DSB report and its impact on the

NASP program.

In response to the DSB report, officials in the

NASP program adopted a‘ ‘Risk Closure Program,’

a plan to remove uncertainties in the X-30’S component technologies systematically by mapping out in

advance a series of technical achievements that must

be attained to achieve program objectives. NASP

officials have stated that they will not recommend a

transition out of the current Phase II research stage

unless the risk closure effort is substantially complete. 48 At that time, they believe the technical risks

in moving to Phase 111 will center primarily around

technology supporting high-Mach scramjet propulsion.

Program managers assert that they have made

rapid progress in developing the key enabling

technologies for propulsion systems, materials and

45’ HOwcver, t. ~&e he= mi5sions pr~tical there is also the necessity to develop near reld-time SUIVeihUICe or Other intelligence methods to guide

long-range weapons close to targets, At present this is an unsolved problem.

WTA did not assess in detail the potential benefits of the NASP program to the Nation’s defense technology base.

dT&feM sci~~ Board Report on the National Aerospace Phtte, P.4.

dsst~ment by NA!jP JPO direetor Dr. Robert Barthelemy at OTA briefing, ~. 13, 1988.

98-1330 -89 - 4
86 ● Round Trip to Orbit: Human Spaceflight Alternatives

structures, and computational fluid dynamics since

the DSB report (app. E). They have also revised

designs for the X-30 to use technology possessing

lower risk, albeit at penalties such as an increase in

vehicle gross take-off weight.

The AFSB report. The Committee on Hypersonic

Technology for Military Application of the Air

Force Studies Board was formed to evaluate the

potential military applications of hypersonic aircraft

and assess the status of technologies critical to the

feasibility of such vehicles. Part of the Committee’s

task was to advise the Commander of the Air Force

Systems Command on the research and development

strategy of the National Aero-Space Plane. The

AFSB report followed the DSB report, and there was

some overlap in membership of the two committees.

Full committee meetings were held from April 1987

through March 1988.

The Committee recommended that the NASP

program office retain the ultimate goal of demonstrating the technical feasibility of reaching orbit

with a single propulsion stage, but, like the DSB,

expressed many concerns about the maturity of the

technologies that would be necessary to meet this

goal. In particular, the Committee felt that progress

in materials and structures would be a probable

limiting factor in meeting the JPO’s primary objective of demonstrating single-stage access to orbit.

The Committee also made a number of recommendations that would aid in the development of a

broad and aggressive research program into the

enabling technologies of hypersonic flight. For

example, it found an urgent need for the construction

of a new hypersonic wind tunnel that would permit

testing of hypersonic configurations at close to

full-scale conditions through Mach 10. A “quiet”

wind tunnel was recommended because of its

capability to simulate with good fidelity crucial

phenomena such as the boundary layer transition.49

The Committee agreed that a flight-test vehicle

was both desirable and necessary to complement

ground-test facilities. However, uncertainties in the

enabling technologies of the X-30 were sufficiently

great in the Committee’s view that they recommended that the NASP JPO retain an option to build

a research vehicle that would not be designed to

reach orbit. This recommendation is discussed later

in Issue 4.

The decision to recommend a move into Phase III,

the construction of the X-30, must be approved by

the NASP Steering Committee, chaired by the

Undersecretary of Defense for Acquisition. NASA’s

Office of Aeronautics and Space Technology Administrator serves as vice-chair of the Steering

Committee. If approved, the final decision on

whether or not to fund development of a flight

vehicle would then be made by the Administration

and the Congress.

How risky is the NASP development strategy?

This discussion assumes that the NASP program

will continue to exist as a development program,

leading to an X-30 research vehicle. Recent decisions within DoD cast doubt on that assumption.50

The potential effects of a range of budget options are

discussed below in Issue 6.

Option 1: Go Slow In Phase II?

NASP officials plan to use the X-30 as a flying

test-bed that will first explore the hypersonic flight

regime and then attempt to reach orbit. NASP

program managers face the fundamental choice

between attempting to design and build the X-30 as

soon as possible, or going slower in Phase II with the

expectation that more advanced technologies would

lower the risk of subsequent performance shortfalls.

Both paths have advantages and risks.

If the X-30 is able to reach orbit with a single

stage, it will have achieved a remarkable goal, one

that could revolutionize launch concepts. However,

if engineers are forced to design a vehicle with little

flexibility or little performance margin in order to

meet the objective of SSTO, they would face severe

cost restrictions should subsequent design modifications prove necessary. Modifying sub-scale models

in ground facilities would be much easier and

Cheaper than attempting to make modifications in a

flight vehicle. A longer ground test program could

fg~or~gto IIIC AFSB, aqujet wind tunnel would minimize disturbances to gas flow that emanate fhn wind tunnel settling ch~~ md mml.ic

radiation from nozzle wall boundary layers.

50~ @.il 1989, ~c ~R~ of ~f~ &;&d to cut wing of tie NMp pro- dramatically ancI recommended that tk program be transferred

to NASA. However, other dccisionmakers, including members of Congress, will also shape the future of the NASP program.
Chapter S-The National Aero-Space Plane ● 87

reduce the risk of failing to meet program goals and

might also allow the incorporation of more advanced

technology. Yet, stretching out the Phase II program

could raise the costs of technology development and

lead to loss of interest in the goal of building an X-30

test vehicle.

NASP officials have chosen to use the Phase 111

decision points 51 to decide whether or not to build the

X-30. The possibility of stretching out Phase II, or

moving to some intermediate developmental phase

that might allow some full-scale component construction and testing without actual assembly of an

X-30, is not a formal option in current plans.

Officials believe that slowing the pace of the

program at this time is unnecessary and would prove

to be wasteful. In a fiscally constrained environment

they may also be responding to the perception that

research and development programs that have

mostly a long-term payoff are especially vulnerable

to budget cuts.

Option 2: Build A Series of Vehicles?

The NASP JPO plans to use the X-30 as both a

research vehicle, which would acquire test data at

hypersonic speeds, and as a demonstration vehicle,

which would fly to orbit and cruise within the

atmosphere at hypersonic speeds. In some respects,

these goals may conflict with one another.

The AFSB report expressed concerns over the

performance of the scramjet propulsion system at

high Mach numbers. In order to ensure that the X-30

is able to reach the high Mach numbers critical to

testing scramjet designs, it recommended that the

X-30 incorporate auxiliary rocket propulsion to

enable controlled flight with some independence

from the air-breathing propulsion system. In addition, the AFSB recommended that JPO consider

fabricating a series of flight research vehicles that

would incrementally explore the flight regimes of a

SSTO vehicle.

This strategy could have at least two advantages.

First, it could lower the risk of “failure.” Some

analysts believe that an X-30 that could not meet its

promised objectives, especially single-stage access

to space, would risk reducing, or even ending,

government interest and investment in hypersonic

technologies. Second, it might aid researchers by

allowing them to design a better test vehicle. For

example, a vehicle that was not designed to reach

orbit could use the relaxed materials and propulsion

system requirements to fabricate a less expensive

vehicle that might be easier and cheaper to instrument and reconfigure during testing. Fabricating a

series of aircraft that would culminate in a SSTO

spaceplane might be more costly than building the

X-30 directly. However, it might also spare the

necessity of a costly modification program if the

X-30 failed to achieve its design objectives. In

summary, a program management strategy that built

a series of test vehicles might allow researchers to

“learn to crawl before they learn to walk.”

NASP officials have rejected the idea of an

intermediate vehicle on a variety of technical

grounds, including the difficulty in extrapolating

data acquired at lower Mach numbers to design a

single-stage-to-orbit, Mach 25, vehicle.52 Furthermore, they dispute the contention that an X-30

designed to achieve orbit conflicts with its role as a

technology test bed. For example, they note that the

X-30 would carry sufficient payload capacity to

carry a full complement of instrumentation.

Officials also believe that the X-30 would have

ample margin to reach orbit and serve as a research

vehicle, especially if an option to build an X-30 with

additional payload capacity is exercised. They also

believe that an X-30 designed with rocket thrust

augmentation would be almost certain to reach the

high Mach numbers desired for scramjet tests.

NASP contractors also disputed the claim that the

X-30 is excessively risky. For example, Pratt &

Whitney and Rocketdyne officials claim their engine designs allow considerable flexibility in engine

geometry without an excessive number of moving

parts.

While not explicitly acknowledged by NASP

officials, the decision over which development

strategy to pursue also affects future support for the

program. NASP officials report that a survey of

potential military users for a Mach 8 to 24 hyperSIU~ c-tPIW ad funding profiles, this would likely occur in September lm.

52~ ~~~ti “~cle mi@ sW~ a twms~e &~W wi~ ~~r.~~~ng~~mqe,but two-stage vehicles arE not being Cotidd in

the NASP program. Two-stage vehicles are being considered in NASA’s AMLS studies,
88 . Round Trip to Orbit: Human Spaceflight Alternatives

sonic cruiser found relatively little interest in this

vehicle compared to one that could demonstrate an

ability to reach orbit. In a limited funding environment, NASP officials may well fear that a multistage program to step up to Mach 25 incrementally

would not be funded, regardless of the technical risk.

In addition, the cost of building a series of flight

vehicles would be higher than building an X-30, if,

as implicitly assumed, the X-30 is able to meet

program objectives without costly modifications to

its original design.

NASP program managers have a delicate task as

they balance the advantages of deciding to move into

Phase 111, in order to maintain DoD and NASA

support, against the risks of selecting an X-30 design

that might later fall short of expectations and even

impede future hypersonic technology development.

Congress may well wish to explore the advantages

and shortfalls of both approaches as it debates

whether or not to fund development of the X-30

when the current Phase II program is completed.

How much will Phase III of the NASP program

cost?

The NASP program has already cost about $800

million in Federal funds and $500 million contributed by industry, exclusive of “infrastructure”

costs, such as Air Force and NASA salaries, and

overhead costs for facilities. NASP officials have

stated that a continuation of funding close to the

Phase 11 requests ($427 million for fiscal year 1990)

will be sufficient to both meet the technology goals

set out in the Risk Closure Plan and to support a

Phase 111 decision in late 1990.53 Current estimates

for Phase III costs are very uncertain because they

are based on extrapolations from designs now

viewed as overly optimistic.54 This uncertainty is

compounded by the inherent difficulty in projecting

costs for an aircraft as novel as the X-30. Recent

experiences with high-technology programs, such as

the B-2 bomber, suggest cost growth in Phase 111 is

a very real possibility. The NASP JPO is preparing

detailed cost estimates for their Phase 111 review, but

preliminary figures will not be available until the fall

of 1989.

Whatever the estimates, the fabrication and testing of a flight vehicle in Phase III of the NASP

program would require substantial increases in

funding over current expenditures. Even without

unforeseen cost growth, the NASP budget, as

currently projected, will rise from the current level

of approximately $320 million to about $500 million

in fiscal year 1991. Peak expenditures are expected

in fiscal years 1992-1994, when spending is projected to rise to approximately $550 million per year.

As a practical matter, funding for Phase III will

depend on convincing the Administration and Congress that operational follow-on launch systems

show sufficient promise to continue the program. In

all likelihood, Air Force support will be essential.

What would be the options for the NASP

program if its budget were cut?

As the NASP program nears the end of its

technology maturation and concept validation phase,

it is coming under increasing scrutiny by lawmakers

and defense officials already struggling with steady

or declining defense budgets. The revised DoD

budget submitted by Secretary of Defense Cheney in

April 1989 cut DOD funding for NASP from $300

million to $100 million. DoD would contribute no

funds in subsequent years. In addition, the Secretary

proposed to transfer responsibility for managing

NASP from DoD to NASA and allow NASA to

obligate the $100 million of fiscal year 1990 DoD

funds.

The proposed cuts and change of management has

accelerated a review of the NASP program. Yet,

many of the important tests that would be needed to

support an informed decision on the technical

feasibility of the program are scheduled to be

performed in fiscal year 1990, the last year of Phase

II. Furthermore, the critical applications and cost

studies are not yet complete.

Congress has three broad options on funding for

NASP:

531x, Ro&n B~ejemy,citi in “One Ch One, ” Defense News, Oct. 24, 1988, p. 46.

54Ewly ~I~c NNp vehicles envisioned a SO,(MO pound take-off gross weight vehicle (’ ‘Phase III Alternatives: Contractor Findings,’ National

Aero-Space Pfane Program Briefing to NASP Sreering Commiaee, Nov. 7,1988, p. 49) and only air-breaihing propulsion from a standing start to Mach

25, Current NASP designs plan to use less exotic materials; the vehicle is much larger and heavier; and, as noted earlier, designs include options to carry

on-board liquid oxygen to augment air-breathing engines or fuel a separate rocket ppulsion system.
Chapter 5-The National Aero-Space Plane ● 89

Option 1: Continue to fund the program at or near

the original requested rate.

Under this option, NASP would receive $300

million from DoD and $127 million from NASA in

fiscal year 1990. Funding of this level ($427 million)

would allow the NASP program to continue its

Phase II research program and to complete its

application and cost studies by the end of the fiscal

year. At that point, the Administration and Congress

could then decide whether or not to build two X-30

test vehicles.

A decision to continue planned funding of the

program would ensure that the contractor teams and

the materials consortium were maintained for another year. Even if the Administration and the

Congress decided to delay development of an X-30

for several years, the Phase II findings and technologies would be available for a later effort. In addition,

the technologies developed in Phase II would be

available for other purposes.

If Congress were to restore funding of NASP to a

level of roughly 75 percent of its original request,

and if the current management arrangement were

retained, the Phase III decision would likely slip by

a year or so, depending on the size of the cut.

Although the program would then risk losing

momentum and industry support, testing and evaluation could proceed in an orderly fashion, and, in

addition, the extra time might allow for the maturation of more advanced materials, and the refinement

of computational fluid dynamics simulations.

Option 2: Accept the current DoD proposal for

program cuts.

The DoD proposal would cut the DoD contribution by two-thirds in fiscal year 1990 and turn the

program over to NASA. DoD would contribute

nothing in subsequent years. Under this option, the

NASP program would still be able to pursue

important technology studies; however, the program

would not focus on the development of a flight

vehicle.

With only $100 million of DoD support, and

assuming NASA funding did not rise (in fact, a cut

in funding would be likely), a decision on whether

or not to construct a flight vehicle might be delayed

3 to 4 years. The program would probably need to be

transfered back to DoD in the mid-1990s in order to

proceed with a test aerospace plane, because NASA

has little incentive to build an X-30 on its own. If

managed by NASA, the program would compete

directly with funding for alternative launch systems

such as AMLS and also with the Space Station

program, which, along with the Space Shuttle, will

command most of NASA’s resources for at least the

next decade.55

The NASP program currently enjoys broad

support and financial commitment from industry because it is focused on building a flight-test

vehicle that could lead to the production of

operational vehicles. If the program is restructured

into a technology maturation program only, as

would likely occur if the program is transferred to

NASA and DoD funding is ended, much of what has

become a national technology base could be lost.

Moreover, there is the risk that a future decision to

develop a hypersonic flight-test vehicle would not

be supported by industry. The importance of industry support for NASP should not be minimized. In

fact, NASP officials believe their greatest accomplishment to date has been the marshaling of the talents

of thousands of the Nation’s most talented scientists

and engineers, and the creation of innovative industry teaming arrangements. Recreating this base of

expertise would be both costly and time consuming.

Option 3: Cut funding entirely.

If Congress feels that the long-term goals of the

NASP program are less important than other pressing priorities in the Federal budget, it could decide

to terminate funding entirely and close the NASP

program out. However, some funding would have to

be supplied to complete contractual obligations

already made. In addition, unless contractors were

able to continue their work to a logical conclusion,

much of the progress made in the program would be

lost.

The diversity of its potential benefits has given

NASP a broad base of support; however, a decision

to move beyond the concept validation phase of the

program will require a demonstration that the

55u.s0 ~nw.~, con~esslon~ Budget Office, me N~A ~o~~ in tie l~s~d Beyond (w@ington, Dc: Congressional Budget Office, May

1988).

98- 133 0 - 89 - 5
90 ● Round Trip to Orbit: Human Space flight Alternatives

program is technically sound and that it has adopted vehicle imply that Service support, most likely from

a prudent management strategy. As a practical the Air Force, will be necessary.

matter, the high costs to build and test a flight
Chapter 6

Escape and Rescue Vehicles

Photo credit National Aeronautics and Space Administration

Artist’s conception of a capsule-type escape vehicle after it has just left the international Space Station.
CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Space Station Crew Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Crew Emergency Return. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Docking Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Operations Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

Other Rescue Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Cooperation Issues Related to Station Supply or Rescue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Figures

Figure Page

6-1. Space Station Emergency Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

6-2. Design Reference Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

6-3. CERV Glider Configured for Water Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

6-4. Assured Crew Return Capability/Space Taxi and Return Vehicle Options . . . . . . . . . . 97
Chapter 6

Escape and Rescue Vehicles

INTRODUCTION

Several contingencies could arise that would

require the emergency escape or rescue of personnel

in space. These include medical emergencies of

Space Station crewmembers, major equipment failures, or damage from orbital debris. Rescue might

also be necessary if the Shuttle failed to meet its

scheduled launch date by so long that the Station was

in danger of running out of critical supplies.

The U.S. space community is investigating the

need for a means of crew rescue or escape1 from the

Space Station, independent of the Space Shuttle. As

noted in chapter 3, the existing Space Shuttle

system is neither robust enough nor reliable

enough to support continuously, at low risk, the

needs of Space Station crew during deployment

and operations. The Space Station may need a

‘‘lifeboat,’ a capsule kept at the Space Station for

emergency escape to Earth, or a rescue vehicle kept

ready on a launch pad on Earth.

SPACE STATION CREW SAFETY

The National Aeronautics and Space Administration (NASA) has studied several Space Station

safety and emergency management options, including building ‘‘safe havens, ” with limited on-board

medical support, and resupply/rescue by the Shuttle

(see figure 6-l). Because a rescue by the Shuttle

could take several weeks, NASA has also investigated options for an assured crew return capability

(ACRC). 2

The Space Station itself will be designed to

provide Station crew with safe havens during

emergencies. Methods for assuring maximum possible safety include: providing the means to seal off

modules or systems experiencing failures, frees, or

breaches; providing all modules with at least two

exits; and placing emergency supplies in each

section to sustain any trapped or isolated crew. The

safe haven approach could also be extended to

include an ability to leave a crippled Space Station

and seek temporary refuge in an independent orbiting facility until rescue could be initiated from Earth.

NASA is assessing two categories of ACRC

options: 1) escape vehicles based at the Space

Station that could respond within hours, and 2)

ground-based rescue vehicles that would be independent of the Shuttle and potentially more responsive than the Shuttle to an emergency. These ACRC

options include:

●

●

●

●

●

●

anew ground- or space-based emergency return

vehicle;

aground-based Shuttle ready to be launched on

demand;

an orbiter, modified as necessary, for extended

on-orbit stay time to be docked at the Space

Station;

unpiloted Shuttle launch with automated or

remote control capability for rendezvous operations;

ELVs to resupply Station crew for an indefinite

period, possibly in conjunction with an orbital

manuevering vehicle (OMV);

modifications to the Station safe havens, which

may enhance the other five options.

NASA has characterized the need for an escape or

rescue capability by defining three possible scenarios (’‘design reference missions’ that would require some or all Station crew to return to Earth

before a Shuttle could be dispatched to rescue them.3

NASA has estimated some of the probabilities that

these or other emergencies might occur. However, it

has not characterized the probabilities of other

scenarios in which a rescue capability would not

help-for example, loss of an orbiter carrying

crewmembers for the Station during ascent on a

I AS ~~ ~ ~1~ rcpfl, crew exar imp]les retm from tie Space Station in a capsule or vehicle dockd at tie station, while rescue implies sending

up an Earth-based vehicle (piloted or unpiloted) to retrieve crew members.

2A]s0 bow ~ &W ~ergency Rescue vehicle (CERV) options. NASA completed Phase A work on the CERV concept in December, 1988. NASA

expected to issue an RFP in April 1989 for further studies of CERV for the Space Station, which would focus on more specific concepts. After this study,

a follow-on contract was supposed to be awarded for Phase B work. These plans have been placed on hold, however, until after the NASA FY90 budget

request is acted upon,

3SW ‘l ACRC.CERV ph~ A Repo~, ’ NASA Johnson Space Center, JSC-23321, Dec. 23, 1988, sec. 1.4.1, Space Station Crew Safety Mternatives

Study, p. 4-7.

-93-
94 ● Round Trip to Orbit: Human Spaceflight Alternatives

Figure 6-l-Space Station Emergency Management

Space Station

/

• 45 day crew resources

● Space station

redundant systems

● Oual retreat/command

areas

● In flight repair/spares

Safe Haven (2 locations)

● Routine class I medical support

● Minimal class II

illness support

● Limited class Ill stabilization

HMF medical compartment

Trash management Communication equipment

Personal hygiene Tools

Towels

● Resupply

First aid kit •Up to 45-day turnaround

emergency flight

KEY: HMF = health maintenance facility; NSTS = national space transportation system.

SOURCE: National Aeronautics and Space Administration, Johnson Space Center.

crew-rotation mission and its affect on total mission alternate crew return capability would reduce the

risk.4

risks of reaching and living on the Space Station

It may be, for example, that the risks Station only marginally. To decide whether a risk-reducing

crewmembers face are dominated by the risk of effort is worth the substantial investment required,

ascent on the Shuttle, in which case investment in an Congress must be advised on how much the invest4NASA d~~ n~ ~tlnely Cw out ~obabilistic fi~ ~~ysis of its space systems. Trudy E. Bell iind K~l E~h, “’I%e Space Shuttle: A Case of

Subjective Engineering, “ IEEE Specrrwn, June 1989, pp. 4246.
Chapter 6--Escape and Rescue Vehicles ● 95

ment would reduce the risk.5 Even if an alternate

crew return capability were provided and worked as

planned, it would not eliminate all risks to station

crewmembers. In deciding whether or not to fund

development of a crew escape vehicle, Congress

may wish to ask NASA to conduct an analysis

comparing the risks faced by crews living on the

Space Station to those of reaching the Space Station

and returning to Earth.

CREW EMERGENCY RETURN

If, in the judgment of NASA officials and

Congress, a risk assessment demonstrates the need

for emergency crew escape, two basic options

present themselves:

1. Simple capsule designs with an ablative heat

shield reminiscent of the “Viking” and “Discoverer” reentry capsules from the early days

of spaceflight. Also included in the capsule

category, although it has a more extended

‘‘loiter time ”6

than those described above, is

an Apollo derivative capsule that would also

include an ablative heat shield (figure 6-2).

Advantages of capsules include simplicity,

relatively low cost, and proven technology.

Capsule designs also need little or no piloting,

which would be a major advantage. Requiring

that a pilot be available at all times on the

Space Station would be expensive and a

questionable use of resources. In addition,

pilots might become too weak to function as

pilots after a stay in space of 20 or more days,

making capsule designs desirable.

2. Small, aerodynamically stable gliders (medium lift/drag lifting bodies)7 that can land by

parachute or at low speed on a runway. A Crew

Emergency Rescue Vehicle (CERV) configured for water recovery (figure 6-3) would

provide a wider range of landing sites and

greater time margins for reentry and recovery

and a softer ride than capsules (important if an

injured crew member is returning).8 However,

a glider would cost at least 20 to 30 percent

more than the simplest chute version of a

capsule. 9

NASA has also considered a Space Taxi and

Return (STAR) vehicle, which could serve several

missions:

. crew emergency rescue or escape;

● assured crew access (an ‘‘up-CERV,’ which

could complement the Shuttle);

. small logistics transport; and

. use as an on-orbit maneuver vehicle as shown

in figure 6-4.

CERV or STAR spacecraft could be launched by

Titan III or Titan IV launchers, an Advanced Launch

System, or a booster based on a Shuttle liquid rocket

booster. A Shuttle could put two crew rescue

vehicles up at one time for docking at the Space

Station. Which alternative is chosen depends on

which options NASA chooses for the Personnel

Launch System.

Swhat is “acceptable” crew risk is, of course, an emotional issue. Those doing hazardous work on Earth, such as construction and mining,

acknowledge risk and expxt a certain number of fatalities on a project such as abridge, *yscw=t of t~el. some f=l that a hard look must be given

at spending a few billion dollars to rescue (assuming it is even a survivable emergency) a few Pple at tie Space Station. Any appropriations would

have to compete with efforts that maybe seen as saving more lives, such as research on cancer and infant mortality. (Tom Rogers, quoted in “Fleeing

[Space Station] Freedom,’ by Richard DeMeis, Aerospace America, May 1989, pp. 3841.)

Others believe that no matter what the cost-benefit analyses say, that a rescue craft is a naessity -

The proapwt of all the world seeing the ordesl of a smanded crew or a dying crew rnemkr nightly on [elaisi~ is chilling. W natimal nightmsre of a crew in trouble

wnh no tunely wty home, no matter what the chances of occurrence, is reason enough for many both within and outside of NASA to push for a rescue vehicle as a political

ne.cesslty.

(Richard DeMeis, Ibid.)

6~1~r gives ~ ~dic~on of how rapi~y a vehicle p]wmet.s towards Earth. Extended loiter idlOWS more flexibility fOr kding during certain

advantageous “windows”and greater crossrange, allowing for landings at more desirable locations.

7Some ~xWn5 dist~~ish &tw=n gli~rs, which have true wings and provide a relatively high lift-to-drag ratio, and lifting bodies, which have no

wings, and a lower lift-to-drag ratio.

8A gli~r w~ld Cxwnence one t. two g’s while Cqsuies wo~d ex~ricrtce ~rnos~ fo~ g’s for tie Discoverer or @oi10 ship,Or SeVetl g’S fOr tk

Viking shape.

!JEng~&m ~ NASA Lmgley &lleve he differenti~ t. ~ 20 to so ~rcent, However, o~er engin~rs that OTA consdted believe the differential

could be even greater, perhaps 50 percent.
96 ● Round Trip to Orbit: Human Space flight Alternatives

Figure 6-2--Design Reference Missions (DRMs)

Viking shape Discoverer shape

•ORM: 1, 2 only ● llRM: 1, 2, 3

● ’Space ejection seat’ ● Capable space vehicle

● Minimal loiter with limited loiter

● implest subsystems ● Simpie subsystems

● Water landing ● Water landing

good boat good targeting

Apollo shape

ŽDRM : 1, 2, 3

● Capable space

vehicle with

extended loiter

● Apollo-based

subsystems

● Water landing

good targeting

Viking Discoverer Apollo

shape shape derivative

Design Reference Missions(DRMs)

Proven shape

● DRM: 1, 2, 3

● Capable space

vehicle with

limited loiter

● Simpie

subsystems

● Water/land

landing good

targeting

● Growth

capability

LaRC

lifting body

● DRM1 —Some problem makes shuttle not ● DRM2—Propagation of failure exceeds safe ● DRM3—Medical emergency exceeds health

available in timeframe needed. Crew leaves haven capability. Shuttle turnaround time maintenance facility capability. Shuttle

when convenient. exceeds need. Crew leaves immediate. turnaround time exceeds need. Crew leaves

SOURCE: National Aearonautics and Space Administration.

as soon as possible for desired landing

zone.

Figure 6-3--CERV Glider Configured for Water Recovery

Jump

J

*

>

Fiash Aft thrusters >

evaporator

SOURCE: National Aeronautics and Space Administration, Langley Research Center.
Chapter Escape and Rescue Vehicles ● 9 7

Figure 6-4--Assured Crew Return Capability (ACRC)/Space Taxi and Return (STAR) Vehicle Options

Cargo transport

SOURCE: National Aeronautics and Space Administration, Langley Research Center.

If the United States wants to develop an escape or

rescue capability independent of the Shuttle, and if

Space Station deployment remains on schedule, a

decision should be made within the next 2 years

concerning whether to pursue capsules or gliders.

The fastest, cheapest way to allow crew escape

from the Space Station would be to dock reentry

capsules of proven capability--shaped like NASA’s

Apollo or Viking capsules or the Department of

Defense’s Discoverer capsules-to the Space Station for emergency use. Development costs could

run between $300 million and $500 million. NASA

estimates that development and testing of a capsule

On-orbit maneuver vehicle

would take about 5 years. However, capsules have

less development potential than gliders since gliders

could be eventually upgraded to perform tasks other

than crew escape.

As noted, glider development would cost more

and would probably take longer (although it could

still be ready in time for Space Station use). At even

greater cost, NASA could procure extra Shuttle

orbiters and keep one docked to the Space Station.10

Other options might be available in the next century.

For example, NASA could rely on “NASPderived” spaceplanes11 for crew rescue.

IOHowever, l~ving ~e shu~lc at ~e Spu station would ~ expnsive ad have a major impact on the Station’s operations and )ogistics. For

example, there would be increased station drag and inertia changes thal would require use of more attitude control fuel. The Shuttle itself would probably

rquire major modifications to achieve long stays in orbit.

11~~ wo~d probtily not be available until X)10. See ch. 5.
98 ● Round Trip to Orbit: Human Spaceflight Alternatives

Photo credit: National Aeronautics and Administration

Artist’s conception of a glider-type escape vehicle about to

touch down at sea after reentry.

DOCKING ISSUES

As noted above, one or two escape vehicles could

be docked at the Space Station or a rescue vehicle

could wait on a launch pad12 on Earth. Both basing

modes have their proponents. An escape vehicle

docked at the Station could be used rapidly. NASA

estimates that emergency response times would

range from 17 minutes in the best case to 48 minutes

if an accident occurred while crew was involved in

extra vehicular activity. *3 Once the escape vehicle is

freed, it could be launched towards Earth as soon as

a landing window is available. However, an escape

vehicle might be sitting idle in the space environment for long periods of time-up to 2 to 4

years-which could adversely affect its reliability.15

Basing a rescue vehicle on a launch pad could

provide added flexibility for rescue, for example, to

send personnel or supplies to the Space Station, to

provide medical assistance, maintenance, or to

dispatch a replacement crew. Maintenance and

replacement of critical systems is also easier when a

rescue vehicle is based on Earth, but it could not be

used for emergencies requiring quick response. The

rescue spacecraft and its launcher would need a

dedicated launch pad and would take a relatively

long time to reach the Station and return. Under

existing launch operations conditions, a launch

vehicle would also take weeks to prepare, even if it

were ready and able to use a dedicated launch pad.

NASA has not estimated comparative costs or safety

benefits for all of these options. However, pad

basing does not meet NASA’s medical requirement

of returning a sick or injured crew member to

Earth-bound medical care within 24 hours. Thus,

NASA has decided not to pursue pad-basing concepts, although others believe that this option should

remain open for further study.

OPERATIONS SUPPORT

Before committing to a rescue strategy, system

designers will have to address the costs of developing the necessary support infrastructure and operating the chosen system. Because a rescue system, if

built, would be needed for the life of the Space

Station, its total recurring costs could easily exceed

its development costs. Support infrastructure might

include ground operations hardware and personnel

at the mission control site, landing site crews located

around the world, and the necessary subsystems and

logistics support to resupply, replenish, and possibly

repair a CERV on orbit. Depending on the detailed

design of the CERV, each of these factors can

seriously influence the operational characteristics

and costs of the system.

As illustrated by the Space Shuttle, operating

costs can constitute a major component of the

life-cycle costs of a system.16 Decisions made early

121 ‘p~ b~ng’ ~ ~hem mews having a launch Vehicle smred on-site with a launch pad suitable for it available on demand. In practice, a vehicle

would not be routinely sitting on a launch pad for long periods because the environment at existing launch sites is corrosive.

13+ OAcRC~RV Ph= A Studie5, B~k 1,“ NASA Johnson Space Center, JSC- 23265, Nov. 15, 1988, p. 4.18. See sec. 4.0 Reference

Conjuration Operations Studies/4.l Emergency Timelines for Use of CERV.

lq~id. S, 5, G~r~ (operational Studies/ 5,3 CERV Daylight baling Study.

IsFor i~u~ wofi ~ this ace, ibid, sec. 2.8, CERV Mtin@nme.

16Life-cycle ~~ inclu~ ~tie nom~g co~s of development ~d proc~ment md the ~urring CMS of maintenance ad operations.
Chapter 6-Escape and Rescue Vehicles ● 99

in the development of the Shuttle to minimize

‘‘up-front” costs led to greatly increased operating

costs. 17 In order to avoid mortgaging future genera-

.

tions, any rescue system should be designed from the

outset to minimize operational costs.

OTHER RESCUE EXAMPLES

The need to provide means for rescuing crews

working in isolated, hostile environments is not new.

Other experiences with designing and using rescue

capability might provide useful data for examining

the risks and benefits of providing alternative crew

rescue vehicles for the international Space Station.

● U.S. Skylab: During the Skylab space station

missions, the United States maintained the

ability to launch a rescue Apollo craft and

outfitted it with a prepared “kit’ kept in

readiness at Kennedy Space Center. However,

this rescue mission probably could not have

been launched in less than 2 weeks under the

best of circumstances. Also the Apollo vehicle

that transported the crew to Skylab was kept

attached to the space station during each

mission, providing the crew with the means to

reach Earth independent of ground launched

systems.

● U.S.S.R. Soyuz: The Soviet Union keeps a

Soyuz capsule attached to its space station Mir

at all times when there is a crew on board.

When a visiting crew reaches Mir, the older

Soyuz, already at the space station, is used to

return crew members to Earth. The Soviets

have used their emergency return capability

several times to return ailing crew.

● Antarctic Research Stations.- Antarctic stations

provide interesting analogues of the Space

Station. Each research station typically maintains a backup station, kept physically separate

from the main station. Usually, an old research

building (some dating from the early 1950s) is

kept supplied and operational in case of fire or

other disaster that would cause the research

crew to abandon the operational station. These

older stations are physically separated to avoid

the spread of fire and only maintained well

enough to provide a backup capability. During

the winter months, the stations are very isolated, but a few emergency rescue missions

have been performed and supply drops are

possible.18 The various countries that maintain

Antarctic research stations have also cooperated to rescue research parties in emergencies.

COOPERATION ISSUES RELATED

TO STATION SUPPLY OR RESCUE

The United States has always maintained a

vigorous program of international cooperation in

space. As noted in an earlier OTA report:

“U.S. cooperative space projects continue to serve

important political goals of supporting global economic growth and open access to information, and

increasing U.S. prestige by expanding the visibility

of U.S. technological accomplishments. ’

The Space Station is a major cooperative program in

which the United States will provide the basic ‘core

station, ’ and Canada, ESA, and Japan will contribute sizable subsystems.20

Today, because other countries have developed

their own indigenous launch capability, and because

progress in space will continue to be expensive,

cooperating on space transportation could be highly

beneficial to the United States. For example, the

United States could share responsibility for resupply

of the international Space Station with its Space

Station partners, and it could begin to share launch

technology in a variety of areas where such sharing

could be mutually beneficial.

ESA has proposed using the Ariane 4 and 5

launchers as alternative means for carrying cargo to

the Space Station. The United States would gain

additional assurance that critical cargo could reach

the Space Station in the event the Shuttle or U.S.

expendable launchers are for any reason unable to do

17u.s, con~ss, ~fice of ~~ology Assessment, Reducing Launch Operations Costs: New Technologies and Practices, C)TA-TM-ISC-28

(Washington, DC: U.S. Government Printing Office, September 1988).

lg~lays of up ~ z WA SE not uncommon as a result of weather and equipment problems.

l~$s. Con==, office of ~~olo~As==ent, /tiermtiO& Cooperation ad co~etit~n in Civilian sp~e Activities, C)TA-lSC-239

(Washington, DC: Jtdy 1985).

Wanada will contribute a servicing module and ESA and Japan will contribute pressurized laboratory modules.
100 ● Round Trip to Orbit: Human Spaceflight Alternatives

so, which could save money and make the Space

Station more effective. Europe would gain experience in automated docking systems and be able to

use Ariane to make inkind contributions for Space

Station operations, a much more attractive arrangement for European governments than one in which

they contribute funding alone.

In order for other countries to use their launch

systems to supply the Space Station, or to dock with

it, these countries will have to reach agreement with

the United States on appropriate standards for

packaging, docking, and safety. ESA and NASA

have established a working committee to discuss

these matters. If discussions prove successful, the

experience of the committee could eventually be

used as a basis for extending cooperative agreements

to include cooperation on more sensitive aspects of

space transportation.

In addition, Europe has proposed using the

Hermes to carry crews to the Space Station and to

service its Columbus module. Japan is also interested in using its H-II launcher for supplying the

Space Station, and would eventually wish to employ

its proposed spaceplane, HOPE, for the same

purpose.

Cooperation could assist U.S. efforts in other

ways. NASA estimates that developing a crew

emergency return capability would cost between $1

billion and $2 billion, depending on its level of

sophistication. NASA could potentially rely on

space vehicles being developed by foreign partners

for crew rescue. These include Hermes, HOPE,

Saenger, or possibly Hotol (ch. 4). Several factors

must be remembered, however. The Hermes crew

would nominally be only three or four people,

limiting its CERV capabilities in case the full Space

Station contingent (8 crew) had to return.21 Also, the

scheduled date for permanently manning the Space

Station is 1996 (although this date could slip).

Hermes operational flights would start in 1999 or

2000 and its nominal orbit would be at 2 degrees

inclination, far from the 28.5 degree Space Station

orbit-making rescue more difficult and time consuming. The initial Japanese HOPE vehicle will not

carry crew; a crew-carrying version may be developed early in the 21st century. A prototype Saenger

could be finished by 2000 with an operational

vehicle coming several years later. Hotol for most

missions would be launched in an automated configuration and would not be ready until at least 2000.

Use of an off-the-shelf Soviet spacecraft for rescue

has been suggested as another international approach, although NASA has no plans to pursue this

option.

21~me have su=s~&We uni~d St- ~ldf~d ~ of the European Heroes in order to speed up its devebpment and to incorporate StiNiOn

reseue provisions in the design. This could cost the United States less than developing its own rescue vehicle.
Appendixes
Appendix A

Benefits and Drawbacks of Liquid Rocket

Boosters for the Space Shuttle

Potential Benefits

Safer Abort Modes

Figure A-1 and table A-1 give abort mode comparisons

for different Shuttle/booster configurations. The Liquid

Rocket Boosters (LRBs) allow a variety of safe abort

modes, that is, several engines could fail on lift-off and

still not cause a catastrophic mission failure.1 A Solid

Rocket Booster (SRB) or Advanced Solid Rocket Motor

(ASRM) failure, however, is generally catastrophic because solids cannot be turned off after they are ignited.

The LRB configuration consists of two boosters, each

with four liquid-fueled engines. The ASRM and SRB

configurations each consist of two solid booster rockets.

All configurations rely on three Space Shuttle Main

Engines (SSMEs) on the orbiter.

Long History, Potentially Greater Mission Reliability

All major launch systems use liquid engines for part or

all of the first stage; there is an extensive data base on their

performance and use and fuel handling needs. LRBs can

be test fired before launch. If the engine monitoring

instruments indicate a problem, the engines can be shut

down and the flight aborted on the pad. This is presently

done with the SSMEs for a very short period before the

solids are ignited.3 Once a solid rocket is ignited it cannot

be shut off-it burns through all of its fuel.4

The LRBs can also be tightly monitored during flight

and can be shutdown if a problem arises-perhaps before

a catastrophic engine failure occurs. If the system were

designed with sufficient margin, the thrust of the remaining engines could be increased to compensate for the

shut-down engine, and the mission completed without

requiring an abort mode.

Shutting down a liquid engine would present some

problems of vehicle control in part because the control

system would have to balance the thrust of a the remaining

engines. Because the remaining engines can be throttled

(unlike solids) it is possible to compensate for changed

moments of force about the vehicle’s center of gravity to

reduce airframe stress and prevent cartwheeling. The

failure of more than one engine would be even more

difficult to compensate for. Control of these types of

potential failures have not been thoroughly investigated.

Increased Lift Capability

The LRB performance improvement for the Shuttle

could be an additional 20,000 pounds5 to low-Earth orbit

as shown in figures 3-7 and A-2.

Mission Profiles Can Be Changed Relatively Easily

As noted above, LRBs can be throttled while solid

boosters cannot. Once a solid is poured to a predetermined

configuration, its burn and hence thrust characteristics are

set, fixing the direction and speed of the Shuttle on ascent.

(Some flexibility is allowed by throttling the three SSMEs

but this entails several potential problems and is avoided

if possible.) These solid booster thrust characteristics

sometimes change unpredictably when the solids age. In

contrast, throttling LRBs within reasonable thrust ranges

is relatively easy and can be used to compensate for

different payloads, atmospheric conditions, desired trajectories or orbits, etc. This can lead to more “efficient”

launches and perhaps slightly heavier payloads.

IAII of ~= ~ue that a sir@e ~g~ (CW motor) fadure does na affect the OpeTiitIOIt of arty other engti (OX tllOtOl). A C41taSlrOphtC faihm2 Of One t%lgti (Or motor)

could of course destroy the Shuttle (no abort mode).

% reliability of liquid engines versus solid rockets is the subject of heated debate and incwsing study. NASA is creating a thttabase that covers evety U.S. launch and

full -scale engine test--ov er 1,300 liquid or solid propulsion events. h will include date, vehicle, engine type, top three anomalies (iftherc wereprobkxns) with comective action

taken, comments, documentation, and location of documentatmn. This database should be available -.NASA intends to keep it updated with future latmcha and cngtne

tests. Study of tlus database could help resolve smne of the pr=enl Um=Wmty in hquid V. wkfs reliabiW statidcs. (’l’he Aemwce Corp. also has a sitilcant datiaae

on engine successes and failures and the American fnstitute of Aeronautics and Astronautics has working groups analyzing these solids V. Iiqulds reliability issues).

Some LKB proponents feel that arguing about solid versus liquid engine reliabdity IS not german e; they believe that the probability of mission success, or the ability to

abort a missmrt safely, are the critical points. They argue mat even if a given L~ engine w=e slishtfy l@s refiable ~~ a given did rocket motor, *aUse of the ability

to shut down the liquid engine in flight, the mission reliability for tk vehicle using LMs would be W= hm * for a vehicle using sohd rocket motors.

3~me Shuttie ~=lm, me of the~ss~’s wu ~U[ down after the Shuttle was akMfy We]] into its flight, and the mission Was not affected. Shutting down an

SSME takea about 30 seconds. The proposed LRBs are simpler enginea and can be shut down essentially instarttamous Iy (“unmediate !kel cutoff) thus making catastrophic

engtrte faihwe emer to avoid “in ca9e engine monitors detect ast anomaly.

4~ ~q,if ● solid is afready ignited, one could provide a means to blow out r-he opposite end of the motor and ignite it also, yielding esacmially zero thrust. Howevcs,

the other solid (evut if functioning properly) would also havelobe‘‘shutdown” in the same manner in cmier [o prevestt vehicle cartwheelirtg. With both solids emerttially

shut-down the Shuttle would have to be well into ita tmjectmy to affect any roaaonable ● bort. The joha to the Shuttle aystem ad G(mnec t points would also be revere and the

Shuttle would probably break ● part. Thus this is not a viable option.

%s perfotmanc.e increase, wluch is nearly double that planned for the ASRMS, would be possible in part because the LRBs would be longer and of greater diarnem

than the ASRMS. NASA held the diametm and length of the ASRM design to dimensions that would necessitate little or no alteration of the mobile launch platform. Becauae

liquid estginea would require fuel tanks that are larger than the ASRM dimensions to reach even 12,000 pounds additional thrust, NASA relaxed the gcmne trical ccmstrainta

in the LRB desigm

-105-
106 ● Round Trip to Orbit: Human Spaceflight Alternatives

Figure A-1-Intact Abort Modes for Space Shuttle Missions

<

Intact abort crew and orbiter safely recovered at Ianding Site

A Shuttle orbiter is not expected to survive a ditching at sea, although the crew might escape and survive if controlled gliding flight is established before ditching.

SOURCE: General Dynamics.

Safer Shuttle Processing Flow Lighter Structure Would Allow Horizontal Assembly

LRBs are fueled just before launch. SRMs, on the other Empty LRB tanks are lighter than assembled solid

hand, carry explosive fuel at all times and must be handled rocket segments, which are stacked vertically, For examcarefully. Safety considerations are a critical, and expen- ple, the Soviet Energia heavy-lift launch vehicle is

sive, part of SRM use—from manufacture, to transport, to assembled horizontally and then raised to the vertical only

launch vehicle mating, to liftoff. At some points in the shortly before launch. Horizontal assembly and transport

Shuttle processing flow, entire buildings must be evacu- is much easier than vertical processing.

ated while a handful of people cater to the solid rockets.6

Liquid cryogenic fuels are well understood and have a

good safety record.7

6Five w more days are lost during this procedure. Twenty to thirty people are idled.

7H~o~= ~~~~po@ti~Iy -cn~[O theenvironmm[, but these are not being proposed forLRBs. LRBs would w -C fWM of @uid oxygetiiquid

hyckogcn fuels or perhaps liquid oxygen/hydrocubon fuels. Hydrocarbons such as methane or korossrw arc relatively benign snv iromnul[ally,

- hut of ths exhaust of any of these rockets may produce small amounts of nitric and Ntrous oxide ti’om the nitrogen in the air, just as automotive and jet engines do.
Appendix A-Benefits and Drawbacks of Liquid Rocket Boosters for the Space Shuttle ● 107

LRBs Are More Environmentally Sound

The exhaust of an LRB fueled by liquid hydrogen

would consist solely of steam. The exhaust of an LRB

fueled by RP-1 (kerosene) or some other hydrocarbon

would contain both steam and carbon dioxide, along with

small amounts of other gases. In contrast, the exhaust of

atypical solid-propellant rocket contains large amounts of

hydrochloric acid.8

Synergisms With Other Programs

The proposed ALS launcher could use the same

engines developed for the LRB, or vice-versa. The LRB,

if developed, could be used as a stand-alone launch

vehicle.

Potential Drawbacks

Technical Uncertainties

The engine technology is known but the engines do not

yet exist. Other uncertainties exist as to whether LRBs

should be pump-fed or pressure-fed,9 what fuel combinations (LOX/LOH, LOX/HC)10 to use and for which stages

or even whether to look at different cycle concepts.11

Earlier, NASA expressed a concern that the larger LRBs

would place unacceptable loads on the Shuttle wings.

Subsequent wind tunnel tests have shown that the wing

loads are acceptable.

Long Development Times

NASA has estimated that if an LRB program started

today, liquid boosters might not be available until at least

1997.12 This long time period results from the stringent

development and testing requirements inherent for a new

engine, particularly one that must be “crew-rated.”

ASRMs themselves could not be on-line until 1994, and

they represent less development risk than do the LRBs.

High Initial Cost

NASA estimates that LRBs would cost $3 billion. Pad

modifications would cost about $0.5 billion. A new flight

dynamics data base would also have to be generated. By

Table A-1—Abort Mode Comparison of Shuttle/

Booster Configurations

Engine

failure a Abort mode

Booster + SSME SRB ASRM LRB

o 1 RTLS RTLS TAL

o 2 Split-S or ditch Split-S or ditch Loft-return

o 3 Split-S or ditch Split-S or ditch Loft-return

1 0 None None ATO

1 None None RTLS

1 2 None None Loft-return

3 None None Loft-return

2 o None None TAL

2 None None RTLS

2 2 None None Loft-return

2 3 None None Loft-return

%3sumes errginaa fail at liftoff.

KEY: ASRM.atfvati sofid roeftat motor; ATG-abwi to orbit; LRB=lquld rocket

Imostar; RTLS=Retum to launch she; Spiit-S=aircraft Iandmg maneuver mvetvrng

a rawraa of diraetion and rapid baa of attitude; SRB=sofid rocket booster;

SBME=SpwxI 3hutUa main engine; TAL=transaUantic abort,

SOURCE: Gerwral Dynamics.

comparison, the cost for the ASRMs is estimated at $1

billion DDT&E and $300 million for construction of

facilities. At this point it is hard to know how accurate

these estimates really are. Rocketdyne Corp. has suggested that it would be possible to build a much cheaper

engine, based on its engine used on the Atlas 11 and Delta

II expendable launchers.13 If LRBs cost significantly

more to develop than ASRMs, they could strain an

already tight NASA budget.14 However, developing

LRBs in consort with ALS propulsion needs could

actually be a cost-effective path and could help both the

Shuttle and ALS programs.

Unique Operational Requirements

The same pad could in theory accommodate both solids

and liquids, but as a practical matter NASA would need

to dedicate a unique pad to each during the transition from

solids to liquids because fuel handling, launch tower

needs, component logistics, etc. would differ from those

on the current Shuttle system.15 It may be too expensive

to keep both forever just to increase resiliency-but this

could be explored. For example, Pad B at KSC could

%rnp-fed appears to have the edvantagc sirw, for one thing, pressure-fed would take 5 yeatx longer to develop thm pump-fed,

loL4u1d Cky@iquid Hydrogen w Liquid Oxygd~*

1 ls~h as rhe Pratt and WMney split+xpander CYCIC.

12K ~= Bm~ 1~ wl~ ~vwal ~~ti ~mwt~g, one winmr could be chosen in 1991 for full-scale development. The LRBs would be ready for flight irt

1997. However, in the Rocketdyne ccnxept, the engines could be available earlier since much hardware already exists and is proven.

13Rw~,W ~efmg to OTA, May 1989.

l~s ~xti-t~~d -m s~l, howev=, if a ~lid ~e[ agfi des~y~ a shuttle, LOSS of the c~fenger cost & Natim between $7 billion ad $13.5 bil[ion,

dqmndmg on how the accounting is &me for the cost of failure, Ye;, a new engine, like that neorkd for an LRB, would have ita own signifkam risks of failure.

15~~ -tiy~ql~ a ~mdy of optimal c@@ w~~h wo~d & qu~ at KSC in order ~ uw LRB’.s on ~ Shutdc, “Liquid Rocket kter integration

Study,” Final Report, Vets. 1-5, Ixrckheed Space OperaticmsCanpany rep to NASA-KSC Advmced Projats and Technology Office, LS04X)0-286- 1410, NAS 10-11475,

Nuvernber 1988.
108 ● Round Trip to Orbit: Human Spaceflight Alternatives

Figure A-2--Options for Increasing Shuttle Payload Capability v. Date of Availability

Payload Capability+

(thousands of Ibs.)

I

40 -

20 -

0

 198 9 199 5 199 6 199 7

* To 110 n.mi. 28.5-degree orbit,

KEY: A1-Li ET = Aluminum-lithium external tank; ASRMs = Advanced Solid Rocket Motors; LRS6 = Liquid Rocket Soo6ter6; RSRM. Redesigned Solid Rocket

Motor; RRSRME = Redesigned RSRhk

SOURCE: O#lOe Of TOOhndogy AMe8mem, IfBe.

remain a solids facility while the presently unused Pad A building (VAB) would be faster and less dangerous with

could be converted to accommodate LRBs. One opera- liquid boosters.l6

tional advantage is that processing in the vehicle assembly

16Howcvm, Shuule Mnamundlinlc iscmmmimd by orbita promasing, hcace fester VAE processing does no[ necessarily mean faster STS turnaround times.
Appendix B

From Take-Off to Orbit—The X-30 Propulsion Systeml

For take-off, the X-30 will need an engine that can

produce thrust from a standing-start. An example of such

an engine is the turbojet. Air flowing into a turbojet is

diffused and compressed before it is combined with fuel

and ignited. The compressor is similar to a fan and is

powered by a turbine driven by exhaust products. A

limiting factor in the ability of turbojets to propel aircraft

to high speeds is the ability of the turbine to withstand the

high temperatures caused by combustion and compression processes. In practice, these problems prevent

turbojets from propelling aircraft to speeds above approximately Mach 3. Even when aircraft speeds are

supersonic, however, air speeds within the engine combustor remain subsonic as air is slowed during its passage

through the turbomachinery.

An aircraft traveling faster than the speed of sound

causes a shock wave as pressure builds up ahead of

leading edges of the moving body. In effect, pressure

disturbances that travel at the speed of sound build up

faster than they can dissipate. In the ramjet, the compressor and turbine are eliminated, and instead, air entering

the combustor is compressed by the compression wave

(“ram action”) generated by air entering a suitably

shaped engine inlet. Ramjets thus require auxiliary

propulsion to boost the velocity to a point where they can

sustain combustion and generate thrust. In practice,

supersonic speeds are usually necessary before ramjet

propulsion becomes practical.

In order to facilitate mixing and burning of the fuel in

the combustion chamber (combustor) of a ramjet, air is

slowed to subsonic speeds by passage through a diffuser.

The heating inside the engine that results from the

transition to subsonic air speed and from fuel combustion

places a practical limit to ramjet propulsion by hydrocarbonbased fuels, such as kerosene. Even with special materials

and cooling to solve the material creep problem at high

temperatures, 2 if the temperature rises too high the

efficiency of the combustion process decreases because

fuel is no longer burned completely.3 For conventional

ramjets this translates into upper limits on speeds of about

Mach 5 to 6. However, the engine I of ramjets falls off

rapidly above about Mach 4 (figure 5.5 . )

For speeds up to approximately Mach 6 there are

concepts for propulsion systems that combine turbo and

ramjet operation. To propel vehicles faster than this with

air-breathing engines requires a scramjet (supersonic

combustion ramjet); an engine where compression, fuel

mixing, and combustion all occur at supersonic speeds,

This allows, in theory, an engine that could start to work

at about Mach 5 and continue to produce positive thrust

all the way to Mach 25. Hydrogen gas derived from liquid

or slush hydrogen is planned as the fuel source for the

scramjets. Its primary drawback to hydrogen is that its low

mass density results in large containment structures.

There are several concepts for combining scramjets

with lower-speed propulsion systems. However, as a

result of several factors, the optimum engine design

changes dramatically at the low- and high-speed extremes. A key challenge for X-30 designers is to

maximize the performance of low- and high-speed

propulsion cycles over their speed range. As the X-30

accelerates from takeoff to hypersonic speeds, designers

plan to change the shape of engine air inlets by using

variable panels and control internal engine geometry with

movable structures. Still there are fundamental tradeoffs

in design that are unavoidable.

Drag forces on an aircraft moving through the atmosphere increase as the square of the vehicle’s airspeed and

the power expended in overcoming drag increases as the

cube of the airspeed. However, drag is also proportional

to air density, which decreases with altitude. To minimize

drag and aerodynamic heating, the X-30 will accelerate to

high speed in the uppermost parts of the atmosphere

where the air density is very low. However, generating

thrust at near-orbital speeds requires an engine with large

and efficient air intakes to capture enormous quantities of

air-both because of the thin air at high altitudes and

because air entering the engine is expelled after combustion at a relatively small increase in speed (although the

mass flow is much higher at the higher speeds). In

contrast, at low speeds, engines take in a relatively small

amount of air and accelerate it (in the combustion process)

to high speeds.

While a subsonic jet might have an inlet covering 15

percent of frontal area, to capture sufficient air at Mach 6

an inlet covering 70 percent of frontal area would be

desirable. However, at orbital speeds (Mach 25) an inlet

covering some 95 percent of frontal area would be

needed. 4 The geometric cross section of the engine inlet

is too small to achieve these figures. In practice, to capture

Isme ~f~e h.~ ~f~e NASp ~W]Sion ~c]e ~cl=s~l~ However, the following discussion is illustrative of ti propulsion ~nw~ king exPlor~ @ c~act~

waling in the NASP program. A final engb design has not been chosen yet by the NASP Joint Program Office.

%recp describes the &forma tion of a mamrial thermally cycled at high temperatures.

3At hj@ m~s~-~of c~bustion dis~ja~ in~ mo]~ular fra~~fg, ~c di~~iation -a~h energy (most fragMClltS fail IO recombine in the

nozzle) reducing fhe total kintiic energy of the fhel fragments, and thus lowering the thrust. See ‘‘The Pocket Ramjet Reader, ” Chemical Sys[ems Division, United

‘khnologies, Sunnyvale, CA, p. 12.

4EWtie Ma Am fiB. Ro&rI J-S Of NASA L~gleY.

-l09 –
110 ● Round Trip to Orbit: Human Spaceflight Alternatives

the large amounts of air required for scramjets requires

engine inlets where, in effect, the entire front of the

aircraft functions as part of the engine inlet. This

necessitates an integrated engine and airframe designs

On the other hand, a smaller engine inlet would be

desirable to minimize drag for flight at low speeds and

low altitudes. The size of the engine inlet is one design

tradeoff. Another would arise if, as currently anticipated,

auxiliary rocket-based power6 were used to supplement

the X-30’S air-breathing propulsion system. Igniting

rockets at relatively low hypersonic speeds might allow

smaller scramjet engines and inlets but only at the penalty

of decreased payload. Alternatively, if designers opt to

keep payload constant the increased weight associated

with rocket propulsion could be compensated by, for

example, designing the X- 30 to have greater lift. Larger

wings would provide more lift, but vehicle size, weight,

and cost would increase too.

5Pod mounted scramjct cosxcpts were explored in the 1%0s but macarchcrs found that air inlets could not capture enough air and, in additicm, there was excessive drag

from support Suuta.

~hc auxiliary proptdsiat system would usc liquid oxygen carried on-board the X-30 to supply either ksaarnjct engines or a small, separate rocket. The tam

“rocket-based power” is used here to refer to either approach.
Appendix C

NASP Materials and the X-30 Materials Consortium

Materials Consortium

The five prime National Aerospace Plane (NASP)

engine and airframe contractors have joined into a

uniquely funded contract arrangement to demonstrate the

production readiness of advanced materials critical to the

success of the X-30. The Materials Consortium (officially

designated as the NASP Materials and Structures Augmentation Program) places contractors, in competition for

Phase III of the NASP program itself, in a cooperative

arrangement. Each of the five contractors has lead

responsibility for the development of one material type,

including the fabrication processes to produce structures,

but each also participates in the efforts of the others. All

data developed by the contractors are shared equally on a

nonproprietary basis, including industrial research and

development (IRAD) that was completed or ongoing prior

to the contract awards. In addition, a large portion of the

funding is being transferred to subcontractors, universities, and research institutes directly supporting the prime

contractors in advanced development work.

The Consortium members and their area of principal

investigation are: General Dynamics-refractory composites (including carbon-carbon and ceramic matrix

composites), Rockwell-titanium aluminide alloy development (Ti3

l and TiAl) and scale-up effort, McDonnell

Douglas-titanium metal matrix composites (including

SiC fiber reinforced Ti3Al), Rocketdyne-high conductivity materials (including copper matrix composites),

and Pratt & Whitney-high creep strength materials

(including monolithic and reinforced TiAl, using fibers

composed of titanium diboride and alumina).

The consortium was funded in March 1988 at a budget

of $150 million for a 30-month period. Recently, a

subsystems consortium was formed to develop some 11

different systems including avionics and instrumentation,

crew escape, slush hydrogen technology, and turbomachinery. As in the Materials Consortium, work in the

subsystems consortium is being done on a nonproprietary

basis. Both the NASP JPO and contractors appear highly

satisfied with the consortium arrangement.

NASP Materialsl

The X-30 airframe will utilize noninsulated, loadbearing hot structures without the thermal protection tiles

of the shuttle. Where necessary, these hot structures will

be cooled with hydrogen using several active cooling

schemes. The projected structural designs for all areas of

the vehicle call for high-stiffness, thin-gauge product

forms that can be fabricated into efficient load-bearing

components. These in turn require high strength, low

density materials that can retain their properties up to

temperatures beyond the capabilities of present day

commercially available materials.

Current challenges center around scaling up laboratory

production processes of advanced materials; developing

fabrication and joining techniques to form lightweight

sandwich and honeycomb structures; and forming materials and coatings that can withstand thermal cycling of the

sort that would be seen in a flight vehicle. In addition,

concerns about the possibility of material fatigue must be

resolved (see discussion of transient thermal fatigue in

footnote 30).

The major classes of materials with promise for the

X-30 are rapid solidification technology titanium aluminide alloys (RST Ti), metal matrix composites based

on reinforced titanium aluminizes (Ti-Aluminide MMC),

high thermal conductivity materials, carbon-carbon (C-C)

composites, and ceramic matrix composites.

Titanium-based materials are candidates for large

portions of the X-30 external and internal structure.

Currently available titanium alloys are lightweight and

can withstand temperatures of 1,100 “F but in the X-30

even greater temperature tolerance is desirable to minimize active cooling requirements. Higher temperature,

titanium-based materials are possible using recently

developed rapid solidification technology. RST Tialuminide is produced when molten titanium and aluminum are dropped on a spinning disk that sprays small

droplets of the material into a region of cold helium gas.

The material cools at an extraordinary rate-up to one

thousand degrees in one millisecond-and is transformed

into a fine powder with unique properties. In particular,

RST materials are not contaminated with oxygen and the

sudden cooling produces a material without stratification

or other nonuniformities.

At room temperature, RST aluminum displays similar

strength to conventional aluminum. However, RST Tialuminides exhibit much higher strength and stiffness at

high temperatures compared to conventional titanium

alloys while having only one-half the weight of the

material previously used at these temperatures. Alloy

systems based on Ti3Al can withstand about 1,500 “F and

alloys based on TiAl can withstand about 1,800 “F. They

are also lighter than the currently available hightemperature nickel alloys.

TiA1-based alloys are the most desired of the Tialuminides because of their combination of high1~ ~at~~~ ~~=tim ~W* ~x~mlvc]y on Ter~e M, F, R~ald, “Ma~~s ch~lenges Fm The NatiO~ ~ro-spa~ plme, ” Rev&qf/’rogwss in Quanri@ve

Non-Destructive Ewdnation (New York, NY: Plenum Press, May 1989). See also: Ned Newman and Richard Pinckert, “Materials for NASP,” Aerospace America, May 1989

pp. 24-26, 31; Man S. Brown, “Taming Ceramic Fiber,” Aerospace America, May 1989, pp. 14-22 and Jay G. Baetz, “Metal Matrix Gmpim: ThekTuTw H= ~,”

Aerospace America, November 1988, pp. 14-16.

-111-
112 . Round Trip to Orbit: Human Space flight Alternatives

temperate tolerance, light weight, and greater resistance

to hydrogen embrittlement. Their drawback has been that

their brittleness makes it difficult to roll them into sheets,

a necessary step to fashion sandwich panels. Some recent

progress has been reported, but currently Ti3Al-based

alloys figure more prominently in near-term plans for the

X-30 because of their greater ductility. Use of Ti3Albased alloys instead of TiAl would cause some increase

in vehicle weight because their density is about 10 percent

higher than TiA1. In addition, Ti3Al is more susceptible to

hydrogen embrittlement and would therefore require

barrier coatings if actively cooled with hydrogen.

Metal matrix composites of titanium use embedded

silicon carbide fiber to produce a material that is much

stronger and stiffer than the unreinforced metal. Silicon

carbide reinforced titanium can reportedly withstand

temperatures of 1,500 “F and is a candidate material for

thin panel structures that will form parts of the X-30’S

skin. There are several technology challenges associated

with incorporation of the fibers into the matrix. Among

them is the thermal expansion mismatch between fiber

and matrix, leading to a propensity for cracks to appear in

the low ductility matrix during formation of the composite or on thermal cycling.

One solution being pursued is the development of

alternative reinforcing fibers that have a better thermal

match, such as titanium diboride and titanium carbide.

NASP is also setting up pilot plants to explore Ti-MMC

composites formed with rapid solidification plasma

deposition methods. Some success has been reported with

Ti3A1-matrix materials and work is underway to extend

this to TiA1-based composites. A challenge for all

Ti-MMC materials will be to develop methods for

evaluating the presence of cracks in the fiber/matrix bond

without compromising the integrity of the material. In

addition, there is a concern with all fiber reinforced

materials related to their reactivity at high temperatures

with the host material.

Carbon-carbon composites (carbon fibers embedded in

a carbon matrix) are candidate materials for heat shields

and large portions of the X-30’S skin. Carbon-carbon is

one-third lighter than aluminum, retains its strength to

very high temperatures, and has been used on the Space

Shuttle leading edges and nose. On the Shuttle, carboncarbon on the wing leading edge and the nose cap is

exposed to temperatures as high as approximately 2,750

‘F. Mission lifetimes of Shuttle C-C wing panels are

currently 65 to 85 flights, but new sealant coatings are

being introduced that will increase this figure to 100

flights. The challenge for NASP materials researchers is

to create a material that is able to withstand repeated

thermal cycling during the specified minimum of 150

X-30 flights.

At very high temperatures, untreated carbon-carbon

would react with oxygen and form carbon dioxide.

Researchers are testing a large number of protection

schemes for carbon-carbon, including the application of

special coatings that can form a barrier to oxygen, and the

addition of oxidation inhibitors to the carbon matrix. The

oxidation problem is exacerbated by the necessity on the

X-30 to make carbon-carbon structures and oxidation

coatings very thin to save weight. Although tests on

samples of carbon-carbon materials during simulated

NASP temperature-pressure cycles demonstrate increasing longevity, the durability of the composite is not yet

equal to the materials used on the Shuttle.* The advanced

carbon-carbon composites being developed for NASP are

expected to provide greater strength than the C-C used on

the Shuttle. With appropriate oxygen barrier coatings,

temperature resistance to over 3,000 “F should be

possible. 3

Some parts of the X-30, such as leading edges and the

nose cap, would exceed the temperature limits of carboncarbon. In addition, these sections of the vehicle would be

exposed to very high heat loads. Researchers are investigating the use of alternative composites that would be

actively cooled as one solution to this problem. Ablative

coatings of carbon-carbon are still another option; however, their use would increase maintenance and support

costs.

On the Shuttle, carbon-carbon is placed on top of a

metal load-bearing substructure. However, to save

weight, carbon-carbon would be used at some locations in

the X-30 as a load-bearing structure. Engineers have a

particular concern with the use of C- C as a load-bearing

structure because of the potential for cracks to form as a

result of thermal cycling. Finding coating materials

whose thermal expansion coefficient is close to that of the

carbon-carbon substrate will be necessary to prevent

cracks and subsequent oxidation of the substrate.

Joining of carbon-carbon is another area of concern.

Close fitting of parts and control of surface finish is

necessary because at hypersonic speeds small irregularities in surface smoothness, or gaps where materials are

joined, could generate hot spots that would be sufficient

to burn through surface materials. On the Shuttle,

dimensional tolerances of carbon-carbon can be now be

%cm tests with small samples of ~iSily prepuedcarbonurbcm have withstood some 200 hours (roughly equivalent to 100 flights) of simulated NASP tempmwe

and pseuure flight pmfilea, However, roaearchaa have not yet fabricated large structures with Ihia mucrial and there is some concern that the material will not retain its

characteristics whm fabricated in full-scale pieces. In additicm, the material is relatively heavy becauae of its thick coating. (MMX types of carbon-carbon do not suffer from

Utaae poblesns, but they have not denwnatrated ss hmg a lifetime under simulated NASP flight profilm.

%arlarxi B. Whisenbunt, Director Cartxm-Cubon lkchmlogy Applications, LTV Cap., brief~ to OTA, May 30, 1989.
Appendix C-NASP Materials and the X-30 Materials Consortium ● 1 1 3

controlled to 0.010 inches.4 Researchers expect similar

performance will be available on the advanced carboncarbon composites that would used on the X-30.

For operation above about 2,500 ‘F designers are also

investigating the possibility of ceramic-matrix composites. These materials could form lightweight structures

with better oxidation resistance than carbon-carbon.

Historically, a problem with ceramic materials has been

their brittleness and propensity to develop cracks. Researchers are attempting to find a reinforcement material

for the ceramic matrix that will help alleviate this

problem. Ceramic-composites are candidate materials for

selected airframe applications, such as surfaces adjacent

to the nose cap and leading edges of the X-30, and also for

engine components and panels.

Two classes of ceramic-matrix materials are being

studied. Glass-ceramic composites may be useful up to

about 2,200 “F and can be fashioned into honeycomb-core

panels and other complex shapes. They are a possible

alternative to some titanium aluminizes. Advanced ceramicmatrix composites, such as silicon carbide fiber inbedded

in a silicon carbide matrix (SiC-SiC), are not as well

developed as the glass-ceramics, but their resistance to

hydrogen embrittlement makes them an attractive material for actively cooled hot structures, Again, the potential

for cracking is a concern with all Ceramic-matrix materials.

Graphite reinforced copper matrix composites are

being studied for structures that will be actively cooled.

This material is expected to be durable and it exhibits

higher thermal conductivity (in the direction of the fiber),

lower density, and higher strength than pure copper.

NASP is exploring production methods for this material

and is also investigating the possibility for creating other

reinforced high thermal conductivity copper composites.
Appendix D

The Defense Science Board Report on NASP1

Among the most thorough outside technical reviews of

the X-30 program to date is that of the Defense Science

Board Task Force on NASP. The DSB task force,

composed of eminent aerospace experts, was asked to

evaluate the degree to which the technology base could

support a decision for NASP to advance to Phase III—the

design, fabrication, and flight test of a selected engine and

airframe configuration.

Most of DSB’s work was performed in the first half of

1987, although the study was not released publicly until

October 1988. NASP officials believe some parts of the

DSB study are now out of date and note that the DSB

report occurred while airframe and engine configurations

were still in a very preliminary design stage. In particular,

vehicle designs being examined by the DSB closely

resembled initial concepts that came from the Copper

Canyon study of 1986. These concepts have been

abandoned by NASP as overly demanding of near-term

technology.

The DSB found that NASP was a vitally important

national program and affirmed decisions to focus the

program around the objective of achieving single-stage-toorbit. However, the DSB also noted that, “early estimates

of vehicle size, performance, cost, and schedule were

extremely optimistic. “ The DSB concluded that NASP’s

Technology Maturation Program was inadequate to

support NASP’s schedule with an acceptable degree of

risk.

In response to the DSB report and internal evaluations,

NASP officials modified their schedule; focused their

program on a small number of vehicle and engine options;

established an elaborate risk-closure plan based on the

achievement of a specific series of technical objectives or

milestones; and combined the five major engine and

airframe contractors in a novel Materials Consortium.

NASP believes rapid progress has been made in the key

enabling technologies of the X-30 since the DSB performed their study. A brief review of some of the DSB's

conclusions and NASP’s response is given below. Space

allows only a cursory review of the many areas of

technical concern.

In aerodynamics DSB found the greatest uncertainty in

predicting the point at which air flowing smoothly over

the vehicle (laminar flow) becomes turbulent. Lift decreases, drag increases, and heat transfer rates change

when airflows become turbulent. Thus, predicting the

location of this “boundary layer transition” has a

profound effect on vehicle design. For example, the DSB

noted that location of the transition point could affect the

design vehicle take-off gross weight by a factor of two or

more

As noted earlier, progress has been made in the ability

of computational fluid dynamics to characterize the

boundary layer transition since the DSB report. Furthermore, X-30 designers believe that a vehicle designed with

‘‘conservative’ assumptions about the boundary transitionsuch as assuming laminar flow only between Mach 4 and

Mach 15, and only over part of the forebody-would still

allow a vehicle design that would meet the primary

objective of single-stage-to-orbit. Nevertheless, until an

X-30 undergoes flight testing there will be uncertainty

regarding the adequacy of computational predictions.

In propulsion DSB expressed a large number of

concerns including: the integration of a low-speed propulsion system with a ramjet/scramjet; the potential effect of

combustion instabilities, transients, or even flameout

during acceleration; engine performance at high Mach

numbers; and the adequacy of knowledge of thermal loads

(influenced by uncertainties in the boundary layer problem noted above). The DSB called for increased experimental verification to improve understanding of the

complex NASP design. In particular, they suggested

NASP consider performing fully integrated engine tests in

a variable Mach wind tunnel.

To address these concerns, NASP officials plan to

conduct over 20,000 hours of wind tunnel testing in Phase

II of the program. These tests would include near

full-scale wind tunnel tests at Mach 8, Additional Phase

III engine qualification and certification tests are also

being planned. Officials have rejected recommendations

to improve hypersonic test facilities beyond what is

already planned because of their cost (hundreds of

millions of dollars) and long developmental lead times,

Nevertheless, a recent National Research Council Air

Force Studies Report considered the development of new

hypersonic test facilities an urgent requirement.

NASP officials also believe that, based on their latest

analysis and ground tests, the problem of large engine

thrust changes or flameout (here collective y referred to as

‘‘unstarts”) will not occur outside the range of Mach 2 to

8. To control engine unstarts within this region, NASP

contractors are planning to implement engine designs that

could survive the unstart condition, control the unstart,
Appendix D-The Defense Science Board Report on NASP ● 115

and be relit.2 Safe mission aborts are also being designed.

However, not all experts appear satisfied that the issue of

combustion instabilities has been resolved.3

Some of the details of the NASP propulsion system are

classified, preventing a complete discussion here. NASP

has reduced the number of potential engine types to two

and will select one (along with one airframe) in late 1990.

At least in principle, the problem of designing a propulsion system that can accelerate a candidate X-30 airframe

from a standing start to Mach 25 has been solved. How

well theoretical expectations match up to experimental

performance would be demonstrated in a flight test

program.

In addition to its concern with the pace of materials

development, DSB was concerned with the lack of

knowledge characterizing the behavior of potential materials when fashioned into aircraft structures-some of

which would be subjected simultaneously to severe

aerodynamic and aerothermal stresses. The large uncertainties in theoretical predictions, and the lack of an

adequate experimental data base appeared especially

worrisome given the design requirement to minimize

structural weight. In fact, the DSB stated that the

knowledge base at the time of their report was such that

a decision to proceed to Phase 111 ‘‘is considered an

unacceptable risk to program success and in fact could

impose serious flight safety risks. ”

NASP officials have stated that if the technology is not

sufficiently mature to support a decision to begin Phase III

they will not do so, but will continue technology

development until a positive decision can be made.

Furthermore, there are contingency plans in most of the

technical risk areas identified by JPO. For example, in the

structures and materials program, a heavier material

closer to availability may be substituted for a less mature

material. The increased weight could be accommodated at

a cost in payload; an increase in vehicle size, weight, and

cost; or the substitute of rocket propulsion for scramjet

propulsion (which in turn will lower payload or increase

the vehicle’s gross weight). The tradeoff process is an

ongoing one. Since the time of the DSB report, several

higher risk materials have been eliminated from consideration for use in the X-30 and the Phase III decision has

been delayed 1 year to provide additional time to mature

key technologies.

2Betwm ~~ut MaCh 1 ~M=h z * hock WaVC m~t p-s ~ough the engine mkt withou[ causing the engb to fl ameouL ~anges in air flow patterns that cause a

sudden 10ss of thrust must also be avoided. In addition, st~y flOW md~tl~ mmt be mainmw * entie wr~on is Wmfm from ramjet 10 scramjct mode. Unstarts

can result in hamrdms asymmetrical thrust con~tions unless corrected quickly. They were a problem in early flights of the Au Free’s high-altitude, Mach 3+, SK-71

“Blackbird” reumnaiasance aircraft, but are now routinely controlled. In briefings and letters to OTA, Pratt & Whitney ad Rocketdyne offtcials prowled details of their

methods to avoid and cmttrd thrust instabilities. Both contractors supported the NASP JPO contention that instabilities would no[ be a seven problem deqnie the reservations

expressed irt the DSB repmt, and more recently by the Air Force Studies Board Report.

3FW exwle,w HY~rsOnic Technology for Military Apphcatiom. . . . op. ct(. foomote 4
Appendix E

Recent Accomplishments of the NASP Program—

An Abbreviated List Supplied By The NASP Interagency Office

The earlier discussion of NASP Technologies naturally

focused on the technical challenges for the NASP

program. This list, provided to OTA by NASP program

officials, is provided to complement that discussion.

Detailed SSTO Vehicle designs from three aerospace

companies:

. Polar orbit, fuel for powered landing with go-around.

● Design payload and 4X payload.

. Reusable air frame without refurbishment.

. Wind tunnel verification of subscale models to Mach

20.

. CFD verification of full scale design.

Detailed propulsion system designs from 2 engine

companies:

Mach 0-20 (airbreathing and rocket).

Wind tunnel test of sub scale engines to Mach 7.

Wind tunnel test of large combustor models to Mach

12.

Mixing and over 95 percent combustion with wall

injectors in 2-inch combustor.

Wind tunnel tests of inlets to Mach 14 to 16.

Demonstration of hydrogen film cooling for friction

reduction and heat transfer reduction in combustor.

completely new family of Full Navier-Stokes (FNS)

Parabolized Navier-Stokes (PNS) computer codes

that calculate airflow and reactions from nose to tail over

complex geometries:

. Integrated into these analysis tools are: air reactions,

combustion reactions, boundary layer characteristics, shock wave characteristics, flow interactions,

and algorithms to expedite conversions of solutions.

● A fast solving PNS code that can calculate the flow

characteristics from the nose, through the engine

with combustion, and out the nozzle, including

free-stream air interactions.

Greatly expanded hypersonic test capabilities:

Low turbulence wind tunnels for prediction of

boundary layer transition: Mach 6, Mach 20.

GASL/NASA free piston expansion tube pilot operating with velocity to 25,000 feet per second.

Rocketdyne large free piston shock tube (RHYFL)

under construction for 1990 completion.

Large engine test facilities (ETF) for test of large

engine models have been constructed at Marquardt

and Aerojet.

Active thermal control:

. Heat pipe cooling of nose and engine struts,

. Hydrogen cooling of inlet combustor and nozzle.

Structure:

● Integrated structure using fuel tank integrated with

vehicle skin,

. Fuel storage and handling systems,

. Integrated thermal control systems.

Materials Development Consortium:

Ž Titanium-aluminide sheet fabrication and advanced

carbon-carbon with new coating systems.

. Joints and fasteners of carbon-carbon and titaniumaluminide.

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