OCTOBER 2006

Alternatives for

Future

 U.S. Space-Launch 

Capabilities

CONGRESS OF THE UNITED STATES

CONGRESSIONAL BUDGET OFFICE

A

STUDY

CBO
Pub. No. 2568
The Congress of the United States O Congressional Budget Office

CBO

Alternatives for Future

U.S. Space-Launch Capabilities

October 2006

A

STUDY
Note

Unless otherwise indicated, all years referred to in this study are federal fiscal years, and all 

dollar amounts are expressed in 2006 dollars of budget authority.
Preface

Currently available launch vehicles have the capacity to lift payloads into low earth 

orbit that weigh up to about 25 metric tons, which is the requirement for almost all of the 

commercial and governmental payloads expected to be launched into orbit over the next 10 to 

15 years. However, the launch vehicles needed to support the return of humans to the moon, 

which has been called for under the Bush Administration’s Vision for Space Exploration, may 

be required to lift payloads into orbit that weigh in excess of 100 metric tons and, as a result, 

may constitute a unique demand for launch services.

What alternatives might be pursued to develop and procure the type of launch vehicles necessary for conducting manned lunar missions, and how much would those alternatives cost? 

This Congressional Budget Office (CBO) study—prepared at the request of the Ranking 

Member of the House Budget Committee—examines those questions. The analysis presents 

six alternative programs for developing launchers and estimates their costs under the assumption that manned lunar missions will commence in either 2018 or 2020. In keeping with 

CBO’s mandate to provide impartial analysis, the study makes no recommendations.

Paul B. Rehmus wrote the study under the supervision of J. Michael Gilmore. Raymond Hall 

prepared the cost estimates for the alternative launch vehicle programs considered in the 

study. Robert Dennis, Douglas Hamilton, David Moore, and Thomas Woodward of CBO 

provided comments on an earlier draft, as did representatives from several U.S. aerospace 

companies and the National Aeronautics and Space Administration. Marshall Kaplan of the 

Institute for Defense Analyses reviewed the study and provided insights. (The assistance of 

external reviewers implies no responsibility for the final product, which rests solely with 

CBO.) 

Loretta Lettner edited the study, and Christine Bogusz and Kate Kelly proofread it. Cynthia 

Cleveland and Allan Keaton formatted the tables, Maureen Costantino designed the cover, 

and Christian Howlett prepared the study for publication. Lenny Skutnik printed the initial 

copies, and Simone Thomas prepared the electronic version for CBO’s Web site 

(www.cbo.gov).

Donald B. Marron

Acting Director

October 2006

Contents

Introduction and Summary ix

1 Current Capabilities and Plans 1

Current Launch Capabilities and Projected Worldwide 

Demand Through 2020 1

Launch Requirements for the Vision for Space Exploration 4

2 Alternatives for Future NASA Manned Space-Exploration 

Capabilities 9

Existing Heavy-Lift Launch Systems 9

Close Derivatives of Existing Systems 12

New Super-Heavy Launch Vehicles 16

Program Cost Comparisons 20

A On-Orbit Assembly, Launch Vehicle Reliability, and

Overall Probability of Mission Success 27

B Human Safety on Launch Abort 31

C Considerations That Affect Lunar Missions Executed 

Using Multiple Launches 35
VI ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

D Schematic Depictions of Launch Vehicle Derivatives and 

Their Antecedents 39

E Cost Estimates for Alternative Launch Systems 47
CONTENTS VII

Tables

2-1. Characteristics of Existing U.S. Heavy-Lift Launch Vehicles 11

2-2. Selected Characteristics of the Close-Derivative Launchers Considered by CBO 14

2-3. Comparison of the Costs of the Close-Derivative Launchers Considered by CBO 15

2-4. Selected Characteristics of the Super-Heavy Launchers Considered by CBO 18

2-5. Comparison of the Costs of the Super-Heavy Launchers Considered by CBO 19

2-6. Cargo Launches Needed to Execute a Manned Lunar Mission with the Alternative 

Cargo Launchers Considered by CBO 21

C-1. Launch Cycles Needed to Ensure Mission Success 37

E-1. Comparison of Unit Recurring Costs for Selected Launchers 49

E-2. Summary of Costs for Space Exploration Alternatives from 2006 to 2017 51

Figures

S-1. Worldwide Capacity and Demand for Launch Services x

S-2. Costs Through 2017 of Using Close-Derivative Launchers to Conduct Manned 

Lunar Missions Under the More Ambitious Schedule xiv

S-3. Costs Through 2017 of Using Super-Heavy Launchers to Conduct Manned 

Lunar Missions Under the More Ambitious Schedule xv

1-1. Worldwide Capacity and Demand for Launch Services 3

1-2. Projections of U.S. Launch Capacity and Demand 5

2-1. Existing and Historical U.S. Heavy-Lift Launch Vehicles 10

2-2. Close-Derivative Launchers Considered by CBO and Their Antecedents 13

2-3. Super-Heavy Launchers Considered by CBO as Cargo Launch Vehicles and

Their Antecedents 17

2-4. NASA’s Projected Funding for VSE Launch Vehicles Through 2017 22

2-5. Costs Through 2017 of Using Close-Derivative Launchers to Conduct Manned 

Lunar Missions 23

2-6. Costs Through 2017 of Using Super-Heavy Launchers to Conduct Manned 

Lunar Missions 24

A-1. Historical Launch Reliability 28

A-2. Overall Probability of Mission Success 29
VIII ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

B-1. Acceleration on Launch Abort for Various Launch Vehicles 32

B-2. Acceleration on Launch Abort for Apollo 17 33

C-1. Historical Launch-Pad Delays for Selected Launch Systems 36

C-2. EELV Annual Launch Capacity and Potential Demand 38

D-1. Proposed Modifications to Generate the Shuttle Close Derivatives 40

D-2. Proposed Modifications to Generate the Atlas V Close Derivatives 41

D-3. Proposed Modifications to Generate the Delta IV Close Derivatives 42

D-4. Proposed Modifications to Generate the Shuttle-Derived Super-Heavy Launchers 43

D-5. Proposed Modifications to Generate the Atlas Super-Heavy Launcher 44

D-6. Proposed Modifications to Generate the Delta Super-Heavy Launcher 45

Boxes

1-1. Launch System Weight Classes and the Reference Orbit 4

2-1. Risks Associated with Developing and Producing NASA’s Launch Vehicle Choices 26

Figures (Continued)
Introduction and Summary

A Presidential directive issued on January 14, 

2004—called the new Vision for Space Exploration 

(VSE)—set out goals for future exploration of the solar 

system using manned spacecraft. Those goals included 

returning to the moon no later than 2020. Although sufficient capabilities exist to meet the projected needs of 

both the U.S. commercial sector and the government for 

launching unmanned payloads into space through 2020, 

that is not the case for manned space flight. The proposed return to the moon called for under the VSE and 

now planned by the National Aeronautics and Space 

Administration (NASA) could require the development 

of the capacity to launch payloads weighing more than 

100 metric tons (mt).1

 No launch vehicles currently exist 

that can handle payloads weighing more than about 25 

mt. Thus, NASA’s plans for manned space flight beyond 

low earth orbit (LEO) could require a significant increase 

in launch capability.2 How that capability could be provided and at what cost are the focal points of this study.

In considering manned lunar missions, the Congressional 

Budget Office (CBO) explored alternatives that would 

use existing launch vehicles; those that would require 

minor modifications to the designs of existing launchers 

(termed “close derivatives”); as well as those that would 

call for major modifications to existing vehicle designs to 

develop essentially new and much more capable launchers.3

 All of the alternatives would require multiple 

launches to assemble in LEO the fuel and hardware 

needed to fly to the moon. Under the alternatives, CBO 

estimates, the costs to develop and procure launch vehicles that could support a manned lunar mission in 2018 

(under a more ambitious schedule) would range from 

$26 billion to $38 billion. NASA’s projection of funding 

is $30 billion. The use of less capable existing or closederivative launchers could be less costly but would 

require up to eight launches to assemble a single lunar 

mission. Using the new and more capable launchers considered by CBO would be more costly but could reduce 

to two the number of launches needed per lunar mission. 

The greater the number of launches needed to assemble a 

mission, the greater the complexity of the mission—

including both the need to perform on-orbit assembly of 

the mission’s components and the risk that at least one 

launch would fail, putting the success of the mission at 

risk. Thus, there is a trade-off between the overall costs of 

launch vehicles and the risk of mission failure. 

Current Launch Capabilities and

Projected Worldwide Demand

Excluding manned flight beyond LEO, U.S. needs for 

launch vehicles involve putting into orbit payloads (both 

commercial and governmental in origin) that weigh less 

than 25 metric tons, with the majority weighing less than 

12 mt. Typical payloads consist of satellites (usually 

designed to track weather, facilitate communications, aid 

scientific research, or conduct surveillance) or mission

1. A metric ton is 1,000 kilograms, or about 1.1 short tons; a short 

ton is 2,000 pounds.

2. Low earth orbit is defined as one of a group of circular orbits that 

lies between the appreciable atmosphere (which is about 120 nautical miles, or nm, high) and the Van Allen radiation belt (which is 

about 1,000 nm high) and has an inclination to the equator of less 

than 60 degrees. A variety of other orbit classes are recognized. 

Those with inclinations of greater than 60 degrees are referred to 

as polar orbits. Geosynchronous orbits (GSOs), which are also 

known as geostationary orbits, are about 22,000 nm high and 

allow satellites to remain over a single point above the Earth. 

Another class of orbits is the set of elliptical geosynchronous transfer orbits (GTOs) that are often used for transitions between 

LEOs and GSOs.

3. CBO characterizes as close derivatives those new launch vehicles 

that are substantially similar to existing systems. The essentially 

new and much more capable launchers are termed “super-heavy” 

launchers.
X ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Summary Figure 1.

Worldwide Capacity and Demand for Launch Services

(Number of launch vehicles)

Source: Congressional Budget Office based on data provided by the Federal Aviation Administration and the Futron Corporation.

Note: Capacity is the number of launches that existing infrastructure and production facilities can support if fully manned and funded. 

Demand is either the number of launches required on historical launch manifests or current projections of future launch manifests.

For a variety of reasons, therefore (because of delays in the availability of payloads, for instance), the number of actual launches 

usually ends up being less than the demand reflected on manifests.

a. Excludes the National Aeronautics and Space Administration’s Vision for Space Exploration initiative.

support (such as consumables, parts, or manpower) for 

the International Space Station, or ISS. Current estimates 

from various sources of worldwide launch capacity for 

payloads weighing less than about 25 mt range from 

approximately 120 to 150 launches per year. According 

to projections obtained by CBO, worldwide demand for 

launching such payloads through 2020 ranges between 

70 and 80 launches a year (see Summary Figure 1). Projected capacity is an estimate of the maximum number of 

launches that existing launch pads and launch vehicle 

manufacturing facilities can support if fully manned and 

funded. Projected demand includes all launches now 

expected worldwide for either commercial or governmental purposes. The projections obtained by CBO indicate 

that maximum worldwide launch capacity for payloads of 

less than 25 mt will exceed demand by about 50 percent 

to as much as 100 percent.

Launch Needs for Manned 

Lunar Missions

The flights to the moon conducted during the Apollo 

program (from 1966 to 1972) required the capacity to 

launch about 140 mt into LEO. That capability was provided by a single, expendable launch vehicle, the Saturn 

V. The details of the lunar missions being planned by 

NASA under the VSE could be more ambitious than 

those conducted under the Apollo program. (One motivation for resuming lunar missions is to help enable eventual manned space flight beyond the moon—including to 

Mars.) NASA also plans to use the spacecraft that would 

be used to fly to and return from the moon—the crew 

exploration vehicle, or CEV—to service the ISS after the 

retirement of the space shuttle in 2010. NASA has estimated that the net effect of those changes relative to 

Saturn/Apollo might increase the weight of a manned 

lunar mission by about 10 percent. 

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

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120

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160

Governmental Demand Worldwidea

Commercial Demand Worldwide

Total Launch Capacity Worldwidea
INTRODUCTION AND SUMMARY XI

The alternatives considered by CBO for returning 

humans to the moon fall into two categories: those that 

would use existing heavy launchers and those that would 

require developing new launch systems. The new launch 

systems considered by CBO include close derivatives of 

existing systems—launchers that could lift somewhat 

heavier payloads than current systems—as well as new, 

larger launchers, referred to as super heavies, that could 

lift payloads weighing 100 mt or more. Generally, the 

alternatives considered by CBO have also been considered by NASA or its contractors, including Boeing, Lockheed Martin, and ATK Thiokol, as NASA continues to 

develop its plans for returning humans to the moon.

Existing Heavy-Lift Launch Vehicles

The existing U.S. heavy-lift launch systems considered by 

CBO include NASA’s space shuttle, Boeing’s Delta IV 

Heavy (D4H) variant of the U.S. Air Force’s set of 

evolved expendable launch vehicles (EELVs), and the 

most capable variant of Lockheed Martin’s Atlas V 

Medium (A5M) EELV.4

 The Delta IV Heavy has a lift 

capacity of 25 mt, the most capable variant of the Atlas V 

Medium has a lift capacity of 20.5 mt, and the space 

shuttle can lift a payload weighing 18 mt.5

 Therefore, 

using existing U.S. heavy-lift launch systems would 

require six to eight launches to propel into LEO all of the 

mass necessary to execute a manned lunar mission.

Although in the Apollo program the payload for lunar 

exploration was lifted into LEO with one launch, NASA 

considered options for the VSE program that require 

multiple launches. The use of multiple launches has 

wide-ranging implications for both safety and cost savings. In particular, such a strategy could theoretically permit the use of existing launchers rather than require the 

development of a new launch vehicle with lift capability 

exceeding 100 mt. (That would translate into less capable 

but individually cheaper launch vehicles.) Using multiple 

launches would also mean, again theoretically, that a 

single launch failure would not cause the failure of an 

entire mission. Further, multiple launches could permit 

the crew to be lifted on a launcher designed to be highly 

reliable, while less reliable launchers were used to lift the 

other, heavier elements of the payload, or cargo. 

There are, however, potential drawbacks associated with 

using multiple launches. Multiple launches could require 

time to execute (perhaps several months), during which 

subcomponents of the full payload, some likely containing cryogenic fuels, must remain in LEO. Notwithstanding improved techniques for insulating cryogenic fuels, 

on-orbit storage of such fuels for many months would be 

a challenge (because of leakage) and would require that 

fuel in excess of the amounts actually burned be lifted 

into LEO, thereby potentially increasing the total number of launches needed. The subcomponents would also 

have to be assembled into a complete spacecraft in orbit, 

potentially requiring the development of a capability for 

reliable and fully automated rendezvous, docking, and 

on-orbit assembly that the United States has never 

attempted. 

Relying on multiple launches could also complicate mission planning because the more launches that needed to 

be executed to complete a mission, the less the probability that all of those launches would succeed. A launch 

failure or failure of an on-orbit rendezvous and docking 

would render a payload subcomponent unusable, and 

which subcomponent might fail could not be predicted 

a priori. Thus, a complete set of additional payload subcomponents might be needed to ensure completion of a 

successful mission.

New Launch Vehicles: Close Derivatives of

Existing Systems

Although representative close derivatives selected by 

CBO have the capability to lift payloads two to four 

times heavier than existing launchers, that increase in 

payload weight would be achieved by making major 

modifications to just a few components of an existing 

launch system rather than major modifications to nearly 

all of its components. In this study, CBO analyzed the 

cost and performance of close-derivative launch vehicles 

4. The evolved expendable launch vehicles are the Air Force’s current 

fleet of launchers designed to take heavier payloads (weighing 

between 5 mt and 25 mt) into orbit.

5. The weight that a launch vehicle can lift into orbit varies depending on the orbit and launch location. The orbit referenced here is 

circular, 220 nautical miles high, and inclined 28.6 degrees to the 

equator with launch from the Kennedy Space Center. For this particular orbit, the shuttle’s performance is taken from S.J. Isakowitz 

and others, International Reference Guide to Space Launch Systems, 

4th ed. (Reston, Va.: American Institute of Aeronautics and Astronautics, 2004), p. 434.
XII ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

that could be used to execute a manned lunar mission 

similar to those considered by NASA and members of the 

U.S. space-launch industry. The close derivatives considered by CBO included modified versions of the space 

shuttle and its components, as well as modified versions 

of both the Atlas and Delta versions of the EELV. In all 

cases, the launch vehicles used to lift a spacecraft and its 

crew into LEO, called crew carriers, are distinct from 

cargo carriers, which are used to lift the remaining 

payload.

The specific close-derivative launch vehicles considered 

by CBO include the following:

B The Five-Segment “Stick” (crew carrier/lift capacity, 

26 mt). This launch vehicle’s antecedent is based on 

the four-segment solid rocket booster (SRB), a pair of 

which now help lift the shuttle into orbit. (The main 

propulsion system for the shuttle is composed of three 

“sticks,” two four-segment SRBs attached to the central external tank, or ET—the third stick.) The SRBs 

are composed of individual cylindrical sections, each 

of which contains a casting of solid fuel. The single 

five-segment stick considered here would consist of 

five such sections, which constitute the first stage of 

the rocket, as well as a new second stage (with an independent liquid-fuel propulsion system) mounted on 

top of the SRB. That additional stage is needed to 

provide the capability to lift 26 mt into LEO. 

B The Side-Mount (cargo carrier/lift capacity, 77 mt).

Also conceptually similar to the space shuttle, the 

Side-Mount would use the space shuttle propulsion 

system with a cargo canister replacing the airplane-like 

orbiter. The payload that the side-mount could lift 

into LEO would be about 77 mt.

B The Delta IV Heavy with Modifications, or D4H with 

Mods (crew carrier/lift capacity, 21 mt). Based on the 

existing Delta IV Heavy developed by Boeing, the 

D4H with mods would be able to lift about 21 mt 

into LEO.

B The Delta IV Medium Plus, or D4M+ (crew carrier/lift 

capacity, 18 mt). Relative to the single-stick Delta IV 

Medium (D4M) EELV, from which it is derived, the 

D4M+ would have an expanded first-stage central 

core with additional engines and an expanded second 

stage. Those modifications would enable the D4M+ 

to lift about 18 mt into LEO. 

B The Delta IV Heavy Plus, or D4H+ (cargo carrier/lift 

capacity, 40 mt). The three-stick D4H is built using 

three of the first-stage central cores used for the D4M. 

Similarly, the D4H+ would use three of the central 

cores of the D4M+, enabling it to lift about 40 mt of 

cargo into LEO.

B The Atlas V Medium Plus, or A5M+ (crew carrier/lift 

capacity, 24 mt). This single-stick vehicle is based on 

the Atlas V Medium (A5M) EELV, developed by 

Lockheed Martin. Relative to the existing A5M 

launcher, the A5M+ would have a larger first-stage 

central core and an upgraded second stage providing 

the capability to lift about 24 mt into LEO.

B The Atlas V Heavy Plus, or A5H+ (cargo carrier/lift 

capacity, 74 mt). This Atlas-derived cargo carrier 

would be based on the A5M+ crew carrier. The first 

stage of the A5M+ would serve as the basis for this 

three-stick vehicle. Relative to the A5M+, the A5H+ 

would also feature additional engines in its second 

stage. It would have the capability to lift about 74 mt 

into LEO.

New Launch Vehicles: Super Heavies

The super-heavy launch vehicles considered by CBO 

could lift payloads of 100 metric tons or more into low 

earth orbit. In general, those prospective launchers would 

require significant and relatively expensive upgrades to 

many—if not all—of the major systems that compose 

existing launchers. CBO considered super-heavy launch 

vehicles that would use components of the space shuttle, 

as well as launchers that would represent new and much 

more capable designs incorporating selected components—primarily engines—used on the current EELVs.

The specific super-heavy launchers considered by CBO 

include the following:

B The Top-Mounted, Shuttle-Derived Super Heavy 

(cargo carrier/lift capacity, 125 mt). In the January 

2006 release of the President’s 2007 budget, this cargo 

launch vehicle was identified as NASA’s recommended 

solution for supporting manned lunar missions.6

Because many of its major components would be 

drawn from the space shuttle, CBO refers to the 

vehicle as the shuttle-derived super heavy. It would be 

6. See Office of Management and Budget, Budget of the United States 

Government, Fiscal Year 2007 (January 2006).
INTRODUCTION AND SUMMARY XIII

about the size of the Saturn V rocket used for the 

Apollo flights to the moon, and its payload to LEO 

would be about 125 mt. It would use two fivesegment SRBs (as opposed to the shuttle’s two foursegment SRBs). The five-segment SRBs would be 

mounted on the sides of an elongated version of the 

shuttle’s existing external tank, which would be modified to house five expendable versions of the existing 

(reusable) space shuttle main engines (SSMEs).7 A 

large cargo canister, or “shroud,” would be mounted 

on top of the tank-SRB assembly.

B The Longfellow (cargo carrier/lift capacity, 108 mt).

This launch vehicle—proposed by an industry consortium that includes Boeing, Lockheed Martin, and 

ATK Thiokol—would resemble the shuttle-derived 

super heavy, but several aspects of its design would be 

different. In particular, it would use less expensive 

engines in its first stage and would be taller to accommodate a second stage. The Longfellow would be able 

to lift about 108 mt into LEO. 

B The Delta Super Heavy (cargo carrier/lift capacity, 

146 mt). The closest antecedent of this vehicle—proposed by Boeing—is the D4H. This launcher, however, would incorporate many changes relative to 

either the existing D4H or the prospective D4H+. 

Those changes include the use of three expanded firststage cores 8 meters in diameter. The largest of the 

super heavies considered by CBO, this launcher would 

be capable of lifting the largest payload into LEO—

about 146 mt. 

B The Atlas Super Heavy (cargo carrier/lift capacity,

135 mt). The closest antecedent of this vehicle—proposed by Lockheed Martin—would be the Atlas V 

Heavy Plus. Relative to that prospective launcher, the 

Atlas super heavy would have a substantially expanded 

8.4-meter first-stage central core powered by five 

engines. The expanded central core would be surrounded by four of the smaller first-stage cores used in 

the A5H+’s triple-stick configuration. Thus, the Atlas 

super-heavy launcher’s first stage would be a five-stick 

configuration with 13 engines. The launcher’s second 

stage would be similar to that of the A5H+ but would 

incorporate a lengthened payload shroud. Those 

changes would result in a vehicle capable of lifting 

135 mt into LEO.

Six Alternative Launch Programs

CBO has constructed projections of the budgetary 

resources needed through 2017 to develop and procure 

launch vehicles that would support the return to the 

moon called for under the VSE. The projections are built 

for a total of six alternative launch programs—three that 

would use close-derivative launchers and three that would 

use super-heavy launchers—as follows:

B The “pure Atlas-derived” alternative.8 This program 

would use the A5M+ launcher as the crew carrier and 

the A5H+ launcher as the cargo carrier.

B The “pure Delta-derived” alternative. This program 

would feature the D4M+ as the crew carrier and the 

D4H+ as the cargo carrier. 

B The “pure shuttle-derived” alternative. This program 

would use the five-segment stick as the crew carrier 

and the Side-Mount as the cargo carrier.

B The “pure Atlas-antecedent” alternative. This program would use the A5M+ launcher as the crew carrier 

and the Atlas super heavy launcher as the cargo carrier.

B The “pure Delta-antecedent” alternative. This program would use the D4M+ as the crew carrier and the 

Delta super heavy launcher as the cargo carrier.

B The “shuttle-derived super-heavy” alternative. This 

program would use the five-segment stick as the crew 

carrier and the top-mounted, shuttle-derived superheavy launcher as the cargo carrier. With the release of 

the President’s budget for fiscal year 2007, it was also 

NASA’s choice for VSE launch vehicles.

Programmatic Assumptions and Cost Comparisons

In order to construct budgetary projections for the alternatives described above, CBO needed to make a variety 

of “programmatic” assumptions, such as when launch 

vehicles would first be used, whether they would be used 

to lift cargo or a spacecraft and its crew, and how many 

test flights would be necessary before a launcher was 

7. Although recently, NASA has announced that, instead of the 

SSMEs, it will be using RS-68 engines like those currently used on 

the Delta IV first stage.

8. The term “pure” means that both the crew carrier and the cargo 

carrier are derived from vehicles in the same (Atlas-, Delta-, or 

shuttle-derived) family of launchers.
XIV ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Summary Figure 2.

Costs Through 2017 of Using CloseDerivative Launchers to Conduct 

Manned Lunar Missions Under the 

More Ambitious Schedule

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Notes: NASA = National Aeronautics and Space Administration.

The more ambitious schedule initiates International Space 

Station support in 2012 and the first lunar mission in 2018.

The term “pure” means that both the crew carrier and the 

cargo carrier are derived from vehicles in the same family of 

launchers.

The term “close derivative” describes new launchers that 

retain a close pedigree to existing systems.

deemed ready for use. CBO used two sources for making 

those assumptions. First, to the extent that NASA’s September 2005 Exploration Systems Architecture Study 

(ESAS) specified schedules and other program details, 

CBO used that study’s assumptions—unless they were 

supplanted by materials the agency prepared to support 

the submission of the President’s budget for 2007. In particular, justification materials supporting the 2007 budget indicate that NASA remains hopeful that it can meet 

the schedule outlined in the ESAS for conducting the 

first flight of the crew exploration vehicle, which is set for 

2012, and the first manned lunar mission, which is 

planned for 2018. However, the agency recognizes that 

budget constraints might delay those events until 2014 

and 2020, respectively. Therefore, CBO has constructed 

budgetary projections for the launch vehicle funding 

needed to execute both of those schedules. The programmatic assumptions that CBO made include the 

following:

B Certification of a launch vehicle—whether a crew carrier or a cargo carrier—for operational use would 

require three test or demonstration (test/demo) flights. 

B Appropriations for hardware production and launch 

services would precede a launch by two years.

B The first operational flight of the CEV (which would 

be lifted into LEO by the crew carrier) would occur in 

either 2012 (under the more ambitious schedule) or 

2014 (according to the less ambitious schedule). The 

first manned lunar mission would occur in either 

2018 (the more ambitious schedule) or 2020 (the less 

ambitious schedule). 

B Five ISS support flights per year would be conducted 

through 2016, beginning in either 2012 or 2014. 

Cumulative ISS support flights would therefore total 

25 or 15. The launch vehicle for those flights would 

be the CEV launcher, regardless of whether or not the 

payload to the ISS included a crew.

B Two manned lunar missions would occur annually, 

beginning in either 2018 or 2020.

B No budgetary allowances for launch failure are made. 

To execute the more ambitious schedule for returning 

humans to the moon, CBO estimates that total costs 

through 2017 for pursuing the three alternatives using 

close-derivative launch vehicles would range from about 

$26 billion for the pure Atlas-derived launch program to 

almost $31 billion for the pure shuttle-derived program 

(see Summary Figure 2). Executing the less ambitious 

schedule would cost $15 billion to $16 billion through 

2017, CBO projects. In that case, the costs of executing 

the more ambitious schedule would simply be deferred to 

later years.

To execute the more ambitious schedule using the three 

alternatives that incorporate super-heavy launchers, CBO 

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NASA's

Projection

Pure

AtlasDerived

Pure

DeltaDerived

Pure

ShuttleDerived

Close-Derivative Alternatives
INTRODUCTION AND SUMMARY XV

Summary Figure 3.

Costs Through 2017 of Using 

Super-Heavy Launchers to Conduct 

Manned Lunar Missions Under the 

More Ambitious Schedule

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Notes: NASA = National Aeronautics and Space Administration. 

The more ambitious schedule initiates International Space 

Station support in 2012 and the first lunar mission in 2018.

Each alternative includes the close-derivative crew carrier 

associated with the indicated family. The term “pure” means 

that both the crew carrier and the cargo carrier are derived 

from vehicles in the same family of launchers.

The term “close derivative” describes new launchers that 

retain a close pedigree to existing systems.

a. NASA’s choice of crew launch vehicle and cargo carrier as 

outlined in the President’s budget for 2007.

estimates that costs through 2017 would range from 

about $31 billion to $38 billion (see Summary Figure 3). 

To execute the less ambitious schedule using super-heavy 

launchers, CBO estimates that costs through 2017 would 

range from about $20 billion to $26 billion. Again, executing the less ambitious schedule would simply defer 

costs to later years.

Both schedules imply a period when NASA could not 

support manned space flight with the proposed VSE 

vehicles after the retirement of the space shuttle in 2010. 

With the earlier, more ambitious schedule, the hiatus 

would be two years, and with the less ambitious schedule, 

it would be four years. 

NASA’s funding projections through 2017 to support the 

development and purchase of VSE launch vehicles total 

$30.1 billion. Through 2010, the projected amounts are 

about $1.0 billion annually. After 2010, annual amounts 

are about $3.5 billion. NASA’s projection is constructed 

to support development and use of the shuttle-derived 

five-segment stick as the crew carrier and the similarly 

derived top-mounted super-heavy launcher as the cargo 

carrier—that is, the shuttle-derived super-heavy alternative considered by CBO. Through 2017, CBO’s estimate 

of the budgetary resources needed to execute that alternative on the more ambitious schedule totals about $32 billion; CBO’s estimate for executing the less ambitious 

schedule totals $20 billion.9

0

5

10

15

20

25

30

35

40

45

NASA's

Projection

Pure

Atlas

Antecedent

Pure

 ShuttleDerived

Pure

Delta

Antecedent

Super-Heavy Alternatives

a

9. In May 2006, NASA announced that its design for the cargo carrier had evolved and now featured RS-68 engines in an expanded 

first stage rather than SSMEs. Using that new design for the cargo 

carrier, CBO’s preliminary estimates of the total programmatic 

costs for the more aggressive schedule decreased to $30 billion 

and, on the less aggressive schedule, to $19 billion.

CHAPTER

1

Current Capabilities and Plans

With the exception of plans for manned space 

flight beyond low earth orbit (LEO)—which have been 

called for under the Bush Administration’s Vision for 

Space Exploration (VSE)—sufficient capabilities exist 

through 2020 to meet projected needs of both U.S. commercial and governmental launching of unmanned payloads into space.1 Those capabilities involve launching 

payloads that weigh less than 25 metric tons (mt), with 

the majority weighing less than 12 mt. Manned space 

flight beyond LEO, however, such as the return to the 

moon proposed under the VSE and now planned by the 

National Aeronautics and Space Administration (NASA), 

could require the development of the capability to launch 

payloads that weigh more than 100 mt. No launch vehicles presently exist that can handle payloads weighing 

more than about 25 mt. Thus, using current launch vehicles for a manned lunar mission would require that in 

excess of 100 mt of hardware and fuel be divided into 

multiple payloads that could be launched separately and 

then assembled into a functional whole in LEO before 

the mission departed for the moon.

The Vision for Space Exploration, which was issued as a 

Presidential directive on January 14, 2004, outlined goals 

for future exploration of the solar system using manned 

spacecraft. Among those goals was a proposal to return 

humans to the moon no later than 2020. The ultimate 

goal of resuming lunar missions would be to help enable 

eventual manned space flight beyond the moon—including to Mars. During the Apollo program (in effect from 

1966 to 1972), manned space flight to the moon 

required the capability to launch about 140 mt into 

LEO, which was provided by a single Saturn V launcher. 

The details of the lunar missions being planned by NASA 

under the VSE could be more ambitious than those conducted under the Apollo program. In addition, NASA 

plans to use the crew exploration vehicle (CEV), the 

spacecraft that will be used to fly to and return from the 

moon and to service the International Space Station (ISS) 

after the retirement of the space shuttle in 2010. As will 

be discussed later, NASA has estimated that the net effect 

of those changes relative to Saturn/Apollo would increase 

the weight of a manned lunar mission by about 10 percent. Manned missions to Mars would, at a minimum, 

require launching payloads into LEO many times the 

weight required for lunar missions.

In this section of its analysis, the Congressional Budget 

Office (CBO) discusses projections that the Federal Aviation Administration (FAA) has made for commercial and 

governmental launches of payloads weighing less than 

25 mt—that is, payloads not involving the VSE launch 

capabilities. Those projections indicate that currently 

existing launch capabilities should be sufficient to handle 

payloads weighing less than 25 mt through at least 2020. 

This chapter also discusses the issues that CBO considered in developing and assessing alternative launch systems that could potentially be used to execute the VSE. 

The specific alternatives that CBO developed are discussed in detail in Chapter 2.

Current Launch Capabilities and

Projected Worldwide Demand 

Through 2020

Current estimates of worldwide launch capacity for payloads that weigh less than about 25 metric tons range 

from about 120 to 150 launches per year. Current projections of worldwide demand for launching such payloads

1. Typical unmanned payloads consist of satellites designed to track 

weather or facilitate communications, conduct scientific research, 

or perform surveillance.
2 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

range between 70 and 80 launches a year (see Figure 1-

1).2 Projected capacity is an estimate of the maximum 

number of launches that existing launch pads and launch 

vehicle manufacturing facilities can support. Projected 

demand includes all launches now expected worldwide 

for either commercial or governmental purposes. Current 

projections indicate that maximum worldwide launch 

capacity for payloads of less than 25 mt will exceed 

demand by up to 100 percent for the foreseeable future.

Those projections of excess launch capacity may be 

underestimated, however. Data compiled by the FAA 

since 1993 indicate that actual launches of payloads—

such as communications satellites—into geosynchronous 

orbit (GSO) range from about 60 percent to 86 percent 

of what has been forecast.3 On average, actual launches 

conducted by the U.S. Air Force have been about 72 percent of its forecasts.4

 Projected launches exceed actual 

launches for a variety of reasons, including delays in the 

development and manufacture of the satellites scheduled 

for launch.

Worldwide demand for launches of payloads that weigh 

between 11.4 mt and 25 mt, referred to as heavy-launch 

demand by the FAA, is projected to be about 20 annually, 

much less than the estimated capacity (see Box 1-1 on 

page 4). Several current launch systems can accommodate 

the lifting of payloads at the upper end of that range (or 

beyond) into certain low earth orbits, including the space 

shuttle and the heavy-lift version of Boeing’s Delta IV 

launcher.5 Until its planned retirement in 2010, the space 

shuttle will be used almost exclusively to lift payloads 

associated with servicing and completing the construction of the ISS. Projected demand for Delta IV Heavy 

(D4H) launches is currently as high as two per year for 

U.S. governmental payloads. Launch vehicles with a maximum lift capability of between 11.4 mt and 20 mt 

include other versions of Boeing’s Delta IV, versions of 

Lockheed Martin’s Atlas V launcher, and a number of 

launchers manufactured abroad. The latter include the 

Ariane 5G used by the European Space Agency, the Chinese Long March 3B, and several variants of the Zenit 

and Proton launch systems now operated by the Single 

Economic Space.6 The projected maximum capacity of 

those foreign systems, the majority of which can lift payloads no greater than about 18 mt, is somewhat greater 

than 40 launches annually.

The majority of the projected future worldwide demand 

for launches (about 72 percent) is associated with plans 

by governments, such as those of Russia, China, the 

United States, and members of the European Union, to 

place into orbit environmental-sensing satellites, other 

remote-sensing satellites (for example, synthetic aperture 

radars), and military-application satellites. With the 

exception of the period spanning 1997 to 2001—when 

launches of communications satellites from companies 

such as Iridium and Globalstar caused commercial 

demand to rise to about 42 percent of worldwide 

launches—this projection of continued dominance by

2. These projections are based on reports published by the Federal 

Aviation Administration and studies by the Futron Corporation, a 

company that the FAA and NASA use to project launch capacity 

and demand. See Federal Aviation Administration, Office of 

Commercial Space Transportation (AST) and the Commercial 

Space Transportation Advisory Committee, 2005 Commercial 

Space Transportation Forecasts (May 2005); FAA and AST, Commercial Space Transportation Quarterly Launch Report, 4th Quarter, 

2004; and Futron Corporation, NASA ASCENT Study Final 

Report (January 31, 2003). On April 11, 2005, Futron also provided data on projected launch vehicle rates directly to CBO. The 

projections displayed in this report include both capacity and 

demand for launching any payload expected to achieve earth orbit 

and exclude suborbital payloads (that is, payloads that do not 

achieve earth orbit). The capacity for space shuttle launches is 

assumed to be 10 annually. The FAA and Futron have published a 

May 2006 forecast for commercial launch demand that increases 

the potential number of such launches by seven in 2007 relative to 

the 2005 forecast. Beyond 2007, the 2005 and 2006 commercial 

launch forecasts differ very little. 

3. Geosynchronous orbits, also known as geostationary orbits, are 

about 22,000 nautical miles (nm) high and allow satellites to 

hover over points on the equator. Other classes of orbits are also 

recognized. A low earth orbit is defined as one of a group of circular orbits that lies between the appreciable atmosphere (which is 

about 120 nm high) and the Van Allen radiation belt (which is 

about 1,000 nm high) and has an inclination to the equator of less 

than 60 degrees. Orbits with inclinations greater than 60 degrees 

are referred to as polar orbits. Also recognized are elliptical geosynchronous transfer orbits that are often used for transitions 

between LEOs and GSOs.

4. General T.S. Moorman (Ret.) and others, Enabling Assured Space 

Access Study, Booz Allen Hamilton (January 15, 2005), p. 17. 

5. The Delta IV Heavy has flown only once and failed to place its 

payload into the correct orbit. Versions of the Angara rocket under 

development by the Khrunichev State Research and Production 

Space Center in Russia are being designed to lift up to 23 mt. A 

version of the Russian Proton launch vehicle can lift 20 to 21 mt.

6. The Single Economic Space consists of Russia, the Ukraine, 

Kazakhstan, and Belarus, which announced in the third quarter 

of 2004 that they intended to merge their space enterprises.
CHAPTER ONE CURRENT CAPABILITIES AND PLANS 3

Figure 1-1.

Worldwide Capacity and Demand for Launch Services

(Number of launch vehicles) 

Source: Congressional Budget Office based on data provided by the Federal Aviation Administration and the Futron Corporation.

Note: Capacity is the number of launches that existing infrastructure and production facilities can support if fully funded and staffed. 

Demand is either the number of launches required on historical launch manifests or current projections of future launch manifests.

For a variety of reasons, therefore (because of delays in the availability of payloads, for instance), the number of actual launches 

usually ends up being less than the demand reflected on manifests.

a. Excludes the National Aeronautics and Space Administration’s Vision for Space Exploration initiative.

governments for launch services is consistent with historical experience. 

Although the number of satellites launched annually is 

projected to increase, the number of projected launches 

remains roughly constant.7 That is because advances in 

electronics and composite materials are assumed to continue to reduce satellite mass, thereby allowing multiple 

satellites to be lifted into orbit during a single launch 

(known as multi-manifesting). That assumption also 

underlies the projection of the need for fewer launches of 

payloads that exceed 20 mt. (About 75 percent of payloads are lifted by launch vehicles that are not classified as 

heavy. At the upper end of the heavy range—that is, 

about 21 mt—projected demand through 2020 amounts 

to less than 3 percent of total demand.)

If projections are restricted to payloads built by U.S. 

manufacturers and lifted into orbit using U.S. launch systems, supply exceeds demand through 2020, consistent 

with worldwide projections (see Figure 1-2 on page 5).8

Both U.S. supply and demand make up about 40 percent 

of the respective worldwide annual projections through 

2010. By 2020, however, U.S. demand is projected to fall 

to about 35 percent of worldwide launch demand. That 

occurs because the on-orbit lifetime of U.S. satellites is 

assumed to continue to improve, requiring fewer 

launches of replacement satellites. Demand for governmental and commercial launches in Asia is assumed to

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

0

20

40

60

80

100

120

140

160

Governmental Demand Worldwidea

Commercial Demand Worldwide

Total Launch Capacity Worldwidea

7. Futron has completed sensitivity analyses on assumptions that 

underlie these observations, but with the possible exception of a 

“breakout” of space tourism, the excess in space-launch capability 

is expected to continue.

8. Projections of U.S. launch capacity exclude the Sea Launch system 

operated by Boeing in partnership with RSC-Energia (based in 

Moscow), Kvaerner ASA (based in Oslo), and SDO Yuzhnoye/PO 

Yuzhmash (based in Dnepropetrovsk, Ukraine). Those projections 

also exclude the capacity provided using Proton and Angara 

launch vehicles at the Bakonur Cosmodrome in Kazakhstan of 

International Launch Services, a joint venture between Lockheed 

Martin and the Khrunichev State Research and Production Space 

Center in Russia.
4 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

increase as the economies of those countries, particularly 

China’s and India’s, continue to grow. 

U.S. governmental demand for unmanned launches 

accounts for about 50 percent of total U.S. demand 

through 2020. That demand—about 94 percent of 

which is for payloads weighing less than 11.3 mt and 

none of which is for payloads exceeding 25 mt—is dominated by missions for the Department of Defense (DoD), 

NASA’s unmanned earth and space science missions, and 

missions for the Department of Commerce, principally 

the launching of environmental-sensing satellites operated for weather forecasting and other purposes by the 

National Oceanic and Atmospheric Administration. 

DoD launches make up 63 percent of total governmental 

demand.

Launch Requirements for the Vision 

for Space Exploration

The only demand currently projected for launches into 

orbit of payloads that weigh more than 25 metric tons 

applies to the manned lunar missions now planned as 

part of the VSE program. The treatment here briefly 

compares and contrasts manned lunar missions conducted under the Apollo program and those planned 

under the VSE. The discussion also considers future missions to Mars.

Lunar Missions Under the Apollo Program

The Saturn V launcher was capable of lifting a payload of 

somewhat less than 140 mt into LEO.9

 That payload 

consisted of the Apollo three-man command-and-service 

module (CSM), the ascent and descent stages of the lunar 

module (LM), the lunar excursion module (LEM), and 

the third stage of the Saturn V, which was used both to 

reach orbit and to propel the CSM, LM, and LEM out of 

low earth orbit and into a lunar trajectory. The propellant 

used to travel to the moon, descend to and ascend from 

the moon’s surface, and return to Earth made up about 

75 percent of the 140 mt payload.

Box 1-1.

Launch System Weight Classes and the Reference Orbit

The Federal Aviation Administration (FAA) distinguishes among launch vehicles on the basis of the 

maximum weight of payload that a given vehicle can 

place into orbit. The distinctions are as follows:

B Light = less than 2.3 metric tons (mt);

B Medium = 2.3 mt to 5.5 mt;

B Intermediate = 5.5 mt to 11.4 mt; and

B Heavy = greater than 11.4 mt.

The maximum payload that a launch vehicle can lift 

depends on both the launch site and the intended 

orbit. Therefore, to determine whether a given 

launcher is capable of lifting a light, medium, intermediate, or heavy payload, both the launch site and 

the orbit into which the payload is to be lifted must 

be specified. The FAA typically specifies a launch 

from Cape Canaveral, Fla., into a circular orbit that is 

220 nautical miles (nm) in altitude at a 28.6 degree 

inclination to the equator. (A launch directly east 

from the Kennedy Space Center will result in an orbit 

inclined at the latitude of the center—28.6 degrees. 

The altitude of the orbit of the International Space 

Station, or ISS, is 220 nm.) Relative to that “reference” orbit, changes in altitude of plus or minus 

100 nm would reduce or increase a given launch 

vehicle’s maximum payload weight by about plus or 

minus 3 percent. Increasing the orbit’s inclination to 

56 degrees (the ISS’s inclination) would reduce the 

launcher’s maximum payload weight by about 8 

percent. 

9. The payload of 140 metric tons is derived from weight data provided in Richard W. Orloff, Apollo by the Numbers: A Statistical 

Reference, NASA SP-2000-4029 (National Aeronautics and Space 

Administration, updated September 27, 2005), available at http://

history.nasa.gov/SP-4029/SP-4029.htm. In that reference, 140 mt 

is the weight of the Apollo 17 command-and-service modules, the 

lunar module, the spacecraft/lunar module adapter, the instrument unit, and the S-IVB stage (the third stage of the Saturn V), 

including the fuel remaining in that stage needed to propel the 

Apollo command-and-service modules and lunar module from 

low earth orbit to the moon.
CHAPTER ONE CURRENT CAPABILITIES AND PLANS 5

Figure 1-2.

Projections of U.S. Launch Capacity and Demand

(Number of launch vehicles)

Source: Congressional Budget Office based on data provided in May 2005 by the Federal Aviation Administration, the Futron Corporation, 

the U.S. Air Force, and the National Aeronautics and Space Administration (NASA).

Note: Capacity is the number of launches that the infrastructure and production facilities can support if fully manned and funded. Demand is 

either the number of launches required on historical launch manifests or current projections of future launch manifests. For a variety 

of reasons, therefore (because of delays in the availability of payloads, for instance), the number of actual launches usually ends up 

being less than the demand reflected on manifests.

a. Excludes NASA’s Vision for Space Exploration initiative.

Lunar Missions Under the VSE

According to current estimates, implementing a return to 

the moon as NASA now plans to do under the VSE program would require that a payload of about 150 mt be 

lifted into LEO. NASA plans to use propellants similar to 

those used for the Saturn/Apollo program and engines 

with similar efficiencies. Thus, about the same amount of 

propellant per pound of payload that was lifted into LEO 

during the Saturn/Apollo missions would be necessary for 

NASA’s planned return to the moon. NASA’s current 

plans for the VSE indicate that it is considering an 

increase in the size of the crew relative to that of Apollo 

(six for the VSE versus three for Apollo)—implying the 

need for a larger spacecraft. NASA is also considering 

lunar landings farther from the moon’s equator and lunar 

missions that would last longer than a few days (as was 

typical during the Apollo program). Those changes 

would require more fuel for both the descent to and 

ascent from the moon and a greater mass of other consumables for life support. NASA is also planning to use 

the spacecraft that will transport humans to and from the 

moon—the CEV—to transport crew and limited 

amounts of cargo to and from the International Space 

Station after retirement of the space shuttle in 2010. 

However, NASA plans to use lightweight composites and 

state-of-the-art miniaturized electronics in constructing 

the VSE spacecraft, as well as improved techniques for 

insulating stored cryogenic fuel that are designed to 

reduce leakage during travel to and from the moon. 

NASA has estimated that the net effect of all those 

changes might increase the mass lifted into LEO for a 

return to the moon by approximately 10 percent to somewhat more than 150 mt.10

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

0

10

20

30

40

50

60

70

U.S. Governmental Demanda

U.S. Commercial Demand

Total Launch Capacitya

10. That estimate was made by NASA during the summer of 2005. As 

NASA and its contractors continue to work on the designs for the 

hardware that will be used to conduct manned lunar missions, 

such weight estimates are likely to change.
6 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Although in the Apollo program the payload for lunar 

exploration was lifted into LEO with one launch, NASA 

considered other options for the VSE program, most of 

which would require multiple launches. The use of multiple launches would mean that less-capable and individually cheaper launchers could be used. In particular, such a 

strategy could permit the use of existing launchers rather 

than require the development of a new launcher with lift 

capability exceeding 100 mt. Multiple launches also 

would mean that a single launch failure would not necessarily cause overall mission failure. Further, multiple 

launches could permit the crew to be lifted on a launcher 

designed to be highly reliable, while less reliable launchers 

were used to lift other elements of the payload (cargo) 

that would fly to the moon.

There are, however, potential drawbacks associated with 

using multiple launches. Multiple launches require time 

to execute (perhaps several months), during which subcomponents of the full payload, some likely containing 

cryogenic fuels, must remain in LEO. Notwithstanding 

improved techniques for insulating cryogenic fuels, onorbit storage of such fuels for many months would be a 

challenge and would require that fuel in excess of the 

amounts actually burned would need to be lifted, thereby 

potentially increasing the total number of launches 

needed.11 The subcomponents would also have to be 

assembled into a complete spacecraft on-orbit, potentially 

requiring the development of a capability for reliable and 

fully automated rendezvous and docking, which the 

United States has never demonstrated. Multiple launches 

could also complicate mission planning because a launch 

failure or the failure of on-orbit rendezvous and docking 

would render a payload subcomponent unusable, and 

which subcomponent might fail could not be predicted 

a priori. Thus, additional payload subcomponents might 

need to be kept ready for launch in order to ensure completion of a successful mission.

As will be discussed in Chapter 2, the program alternatives considered by CBO for meeting the launch needs of 

manned lunar missions would require two to four

launches. NASA is currently planning to use two 

launches into LEO to execute a single mission to the 

moon: one using the crew carrier to lift the crew and a 

small amount of cargo (which cumulatively weigh about 

26 mt) and a second using the cargo carrier to lift the rest 

of the cargo (including the lunar lander and the fuel 

needed to travel to and from the moon, which weigh 

about 125 mt).12 The reasons NASA cites for that choice 

include crew safety and the avoidance of complexities 

associated with on-orbit assembly in LEO of more than 

two payloads.13

Future Mars Missions

In nine NASA studies completed between 1988 and 

2000, estimates of the weight of the payload that would 

need to be lifted into LEO for a Mars mission ranged 

between 470 mt and 1,500 mt. The variation depended 

on the propulsion system used for the long journey

11. The use of noncryogenic propellants has also been proposed as a 

way to eliminate the problem of fuel leaking while it is stored in 

LEO. However, cryogenic propellants such as liquid hydrogen 

burned with liquid oxygen are the most efficient in terms of thrust 

produced per pound of fuel burned per unit of time. Although the 

use of noncryogenic propellants can reduce the weight of fuel 

tanks and engines, more of such propellants is needed to launch a 

given payload from LEO to the moon than is needed using cryogenic fuels. The latter effect usually dominates, implying that the 

use of noncryogenic propellants would require a heavier payload 

to be lifted from the Earth into LEO. For example, CBO estimates that the use of hydrazine and nitrogen tetroxide rather than 

liquid hydrogen and oxygen as the propellant for launching a mission to the moon from LEO would about double the weight of 

the propellant that must be lifted into LEO. The additional 

weight of cryogenic fuel that would need to be lifted to provide 

sufficient margin to accommodate leakage is less if the multiple 

launches needed to execute a mission can be achieved within 

approximately six-month periods of time. For instance, with passive cooling techniques, it is possible to limit leakage to under 

4 percent per month, or less than 30 percent in a six-month 

period, according to a 1982 study conducted for NASA. Modern 

insulation further limits losses. See National Aeronautics and 

Space Administration, Contractor Report 3536, Future Orbital 

Transfer Vehicle Technology Study, vol. 2 (1982). 

12. That choice was first presented with NASA’s release of the draft 

results of its Exploration Systems Architecture Study (ESAS) in 

September 2005 and finalized in the ESAS Final Report in 

November 2005.

13. Arguments favoring the separation of crew and payload are 

implicit in the recommendations contained in “Long-Term: 

Future Directions for the U.S. in Space,” Chapter 9.3 in Columbia 

Accident Investigation Board Report, vol. 1 (August 26, 2003). As 

discussed in Appendix B of this report, maximizing crew safety 

while maximizing launch vehicle lift capacity can be conflicting 

goals. 
CHAPTER ONE CURRENT CAPABILITIES AND PLANS 7

between LEO and Mars.14 Therefore, the lightest Mars 

mission would require that a minimum of three to four 

times the mass of a lunar mission be launched into LEO.

NASA’s plans for return missions to the moon avoid the 

complexities associated with on-orbit assembly that is 

dependent on more than two launches. However, such 

challenges for conducting a manned mission to Mars 

remain. Instead of developing a launch vehicle in at least 

the 400 mt class, which is not anticipated, capability for 

on-orbit assembly would be needed.15 Assembling inert 

components in space can be either human-assisted or 

completely automated. If human-assisted, crew members 

could perform such operations on-orbit or control the 

assembly remotely. The United States has not demonstrated successful autonomous or remotely assisted assembly. Russia has demonstrated remotely assisted docking 

with its Progress resupply vehicle. NASA, however, has 

demonstrated only human-assisted, on-site assembly (for 

example, during construction of the International Space 

Station).

Unlike the mandated return to the moon, which has been 

slated for no later than 2020, the VSE states no specific 

schedule for a manned mission to Mars. Moreover, 

NASA’s current planning through 2020 for manned space 

flight focuses on the funding and programs needed for 

returning humans to the moon. Consequently, this analysis, which examines launch needs through 2020, excludes 

consideration of launch capabilities and the associated 

technologies that may be needed to support human travel 

to Mars.

14. See National Aeronautics and Space Administration, Launch Vehicle Capability Trade Study (NASA briefing, 2003), which contains 

a comprehensive list of those nine studies. The lower-weight 

payloads correspond to the use of propulsion systems such as 

nuclear thermal rockets. Use of chemical propulsion of the same 

type that NASA now plans to use for the VSE lunar missions 

would require lifting payloads into LEO at the upper end of the 

range.

15. Assuming that the propulsion systems and design constraints are 

similar, CBO estimates that launching a payload three times larger 

than the maximum capacity of the Saturn V would require a 

launch vehicle about 1.4 times taller and wider than the Saturn V.

Even if all engineering issues were surmountable, the infrastructure to build, transport, and launch such a large vehicle does not 

exist. The costs for those new facilities, ignoring the costs of the 

large vehicles themselves, would be substantial.

CHAPTER

2

Alternatives for Future NASA Manned

Space-Exploration Capabilities

The Congressional Budget Office considered two 

sets of alternatives for resuming manned space flight to 

the moon: those that would use existing heavy-lift launch 

vehicles and those that would require developing new 

launch systems. The new launch systems assessed by 

CBO include close derivatives of existing systems as well 

as designs that represent major departures from existing 

launch vehicles. The close-derivative launch vehicles 

would require relatively modest changes to the designs of 

existing launch systems and, in the case of cargo carriers, 

would result in vehicles that could lift several times the 

weight of current payloads. The vehicles that would constitute major departures from existing vehicles—referred 

to as super heavies—would be able to lift payloads weighing 100 metric tons or more.

Existing Heavy-Lift Launch Systems

Existing U.S. heavy-lift launch systems considered by 

CBO include the following:

B The National Aeronautics and Space Administration’s 

space shuttle;

B Boeing’s Delta IV Heavy variant of the U.S. Air 

Force’s family of evolved expendable launch vehicles; 

and

B The most capable variant of Lockheed Martin’s 

Atlas V Medium EELV.1

Payload is an important factor in distinguishing among 

those systems. The D4H has a lift capacity of about 25 

metric tons, the most capable variant of the Atlas V has a 

lift capacity of 20.5 mt, and the space shuttle can lift a 

payload weighing 18 mt.2 The Saturn V rocket that was 

used for the original manned Apollo missions to the 

moon carried a much heavier payload than existing systems do, lifting about 140 mt into low earth orbit with a 

single launch (see Figure 2-1). Therefore, using today’s 

U.S. launch systems would require six to eight launches 

to lift into LEO all of the mass necessary to execute a 

manned lunar mission.

Challenges Using the Space Shuttle 

The challenges associated with ensuring safe and reliable 

operation of the space shuttle have led NASA to decide to 

retire the shuttle fleet in about 2010, after the International Space Station is completed. Therefore, using the 

shuttle to execute manned lunar missions would require 

that decision to be reversed. Based on its historical performance, the shuttle would be expected to have a launch 

failure rate of about 2 percent.3

 Because at least eight 

shuttle launches would be required to deliver about 140 

mt into LEO, the probability that all those launches 

would succeed is about 87 percent. Thus, there is a significant chance—13 percent—that at least one payload 

would fail to reach LEO.

1. At the inception of the EELV program, the plan was to develop 

both Delta IV Heavy and Atlas V Heavy launchers capable of 

lifting about 25 mt into low earth orbit. Subsequently, the 

Department of Defense and Lockheed Martin agreed to forgo 

production of the A5H. Although the most capable version of the 

Atlas V is not designated a “heavy” launcher, its lift capacity places 

it in the heavy-lift launch category as defined by the Federal Aviation Administration.

2. Those payloads are assumed to be lifted into an orbit of 220 

nautical miles in altitude inclined at 28.6 degrees. The combined 

weight of the space shuttle orbiter and the payload that is lifted 

into LEO is about 100 mt; however, the orbiter returns to Earth 

after delivering an 18 mt maximum payload into that reference 

orbit.

3. That rate attributes the loss of Columbia to launch failure because 

its breakup during reentry resulted from damage caused during 

liftoff by the shedding of foam insulation from the external tank. 
10 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure 2-1.

Existing and Historical U.S. Heavy-Lift Launch Vehicles

Source: Congressional Budget Office.

Note: Figures drawn to approximate scale; EELV = evolved expendable launch vehicle; mt = metric tons.

a. Metric tons of payload to a circular reference orbit of 220 nautical miles in altitude at a 28.6 degree inclination to the equator.

As has been noted previously, which launch might fail 

could not be predicted. Moreover, once a failure 

occurred, experience indicates that a long delay would 

ensue before shuttle operations resumed because of concerns regarding crew safety. As a result, it is likely that the 

failure of any of the eight space shuttle launches needed 

to assemble the 150 mt payload required for a manned 

lunar mission would mean overall mission failure.

Even if all of the launches were successful, simply executing eight space shuttle launches in rapid succession would 

be a challenge. During the quarter-century that the shuttle program has been in operation, its launch rate has 

reached eight missions annually only four times. Currently, NASA hopes to execute two lunar missions annually, which would require an unprecedented 16 shuttle 

launches per year. Moreover, as indicated previously, the 

need to limit on-orbit leakage of cryogenic fuels would 

most likely require that the lunar mission be assembled in

Saturn V

(1966 to 1972)

137 mta

Current Configurations 

Historical Configuration

(Apollo Program)

Space Shuttle

(1981 to today)

18 mta

EELV—Medium 

(2006 to today)

20 mta

EELV—Heavy 

(2004 to today)

25 mta
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 11

Table 2-1.

Characteristics of Existing U.S. Heavy-Lift Launch Vehicles

Source: Congressional Budget Office.

Note: LEO = low earth orbit. (For all launch systems, this orbit is a circular reference orbit 220 nautical miles in altitude at a 28.6 degree 

inclination to the equator.)

a. This statistic attributes the 2003 crash of the shuttle orbiter Columbia to launch failure.

b. The first figure is the cost per pound of the payload. The second is the cost per pound if the orbiter, whose inert mass is about 78 metric 

tons, is considered part of the payload.

c. The launch was not entirely successful because the test payload reached orbit but not the intended one. 

d. Includes contractor and government investment for the entire family of launchers, an entirely new RS-68 engine, and launch-pad

modifications at the Cape Kennedy and Vandenberg launch sites.

e. Includes contractor and government investment for the entire family of launchers and launch-pad modifications at the Cape Kennedy and 

Vandenberg launch sites.

f. The 13 launches consist of two unmanned flights, one manned mission to LEO, nine lunar-mission launches, and one Skylab launch. 

LEO over a maximum of about six months. That requirement suggests the need for monthly shuttle launch rates 

twice those that have been achieved historically to conduct a single lunar mission.

Finally, because the reusable space shuttle returns to 

Earth and has to be refurbished before each launch, it is 

relatively expensive to use. Therefore, using the shuttle to 

lift a pound of payload into orbit costs about four times 

more than did using the Saturn V (see Table 2-1). 

Challenges Using the Delta IV Heavy EELV

The launch reliability of systems such as the Delta IV 

class of vehicles should be similar to that of their Delta 

predecessors, as well as to that of the space shuttle (see 

Appendix A).4

 The number of launches required for the 

D4H to lift about 150 mt into LEO would be six, implying about a 10 percent chance that one payload would 

fail to reach orbit. Therefore, the use of the D4H to 

return humans to the moon would raise issues regarding 

overall mission success similar to those associated with 

using the space shuttle.

The Delta IV Heavy launch system was not designed for 

human space flight, however, which creates problems in 

complying with the safety standards that NASA has 

established for manned space flight. (At least one of the 

payloads lifted into LEO for a manned lunar mission 

would consist of the spacecraft that would travel to the 

moon with its crew.) Those problems include:

B A lack of redundant systems;

B Insufficient safety margins in the strength of the structures that compose the launcher;

Characteristic

Payload Capacity to LEO (Metric tons) 18 25 20 137

Operational Launch Success Rate (Percent) 98.28a c 100 100

Number of Launches 116 1 1 13 f

Design, Development, and Testing (Billions of 2006 dollars) ~40 3.5 d 2.0 e 31

Recurring Costs per Launch (Billions of 2006 dollars) 0.9 0.3 0.2 1.7

Recurring Costs per Pound of Payload (2006 dollars) 23,000/4,300 b 96 5,400 4,500 5,500 68 96% 76%

Space Shuttle Delta IV Heavy Atlas V Saturn V (1969)

4. When computed using a large sample of launches, there is no 

reason to expect the reliability of the Delta IV Heavy to be any 

better or worse than the demonstrated reliability of similar 

expendable launchers. However, the D4H has flown only once, 

and it failed to place its test payload into the intended orbit. The 

problem—cavitation in a fuel line, which could affect all Delta 

IVs—was discovered and fixed. The Delta IV Medium resumed 

flying on May 24, 2006.
12 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

B A lack of sensors and systems for monitoring the performance of the launch vehicle during flight—called 

health monitoring equipment—which could alert the 

crew to an impending failure and the need to execute a 

“launch escape”; and

B A need for modifications to the Delta launch pad to 

enable a crew to escape, if necessary, prior to launch.

A particular issue regarding the safety of manned space 

flight that is associated with the Delta IV Heavy launch 

vehicle is the trajectory it must follow as it lifts humans 

into orbit. The trajectory that enables the D4H to lift its 

full 25 mt payload tends to be especially steep, allowing 

the vehicle to ascend directly to high altitude. If the 

launcher developed a problem during ascent that required 

the crew to perform a launch escape by separating the 

crew from the booster, the ballistic trajectory on which 

the crew would descend to Earth would be similarly 

steep. The deceleration experienced by the crew during 

that steep descent into the atmosphere would exceed the 

safety limits specified by NASA, which are established to 

ensure that the crew does not suffer serious injury (see 

Appendix B). Therefore, using the D4H would require 

either that NASA’s safety standards be relaxed or that the 

launcher fly a less direct trajectory. Use of a more gradual, 

or so-called depressed, trajectory would require more fuel 

to be expended per pound of payload lifted, reducing to 

under 20 mt the maximum weight of payload that the 

D4H could lift.

Challenges Using the Atlas V Medium EELV

The most capable version of the Atlas V Medium that is 

currently available can lift a 20.5 mt payload into LEO, 

which would require at least seven launches to execute a 

manned lunar mission. Therefore, its use to return 

humans to the moon would raise issues regarding overall 

mission success similar to those posed by either the space 

shuttle or the Delta IV Heavy. With some reduction in 

payload mass, the trajectory that the Atlas V followed 

could also be tailored to avoid the potential for crew 

injury during a launch abort. However, using the Atlas V 

would require resolution of the same problems related to 

redundancy, safety margin, health monitoring, and crew 

escape that are associated with the Delta IV Heavy 

launcher. Use of the A5M would further require that its 

Russian-made RD-180 engine be certified as acceptable 

for manned space flight. According to NASA staff, such 

certification would require the development of the capability for a U.S. supplier to manufacture and test the 

RD-180.

Close Derivatives of Existing Systems

CBO characterizes as “close derivatives” those new launch 

vehicles that retain a close pedigree to existing systems. 

Although those close derivatives may have the capacity to 

lift payloads two to four times heavier than existing 

launch vehicles, that increase in payload weight could be 

achieved by making major modifications to just a few 

components of an existing launch system. In this study, 

CBO analyzes the cost and performance of closederivative launch vehicles that could be used to execute a 

manned lunar mission. The vehicles are similar to those 

considered by NASA and members of the U.S. spacelaunch industry, including Boeing, Lockheed Martin, 

and ATK Thiokol.5 The close derivatives considered by 

CBO include modified versions of the space shuttle and 

its components, as well as modified versions of both the 

Atlas and Delta versions of the EELV. In all cases, the 

launchers used to lift the spacecraft and crew (called crew 

carriers) into LEO are distinct from the launchers (called 

cargo carriers) used to lift the remaining payload, such as 

the lunar lander and fuel needed to support flight to and 

from the moon. 

Shuttle-Derived Launch Vehicles

B The Five-Segment “Stick” (crew carrier/lift capacity, 

26 mt). This launch vehicle is based on the foursegment solid rocket booster, a pair of which now help 

lift the space shuttle into orbit (see Figure 2-2). The 

main propulsion system for the shuttle is composed of 

three “sticks”: two four-segment SRBs attached to the 

central external tank, or ET (the third stick). The ET 

carries the liquid hydrogen and liquid oxygen that fuel 

the space shuttle main engines housed in the rear portion of the orbiter (which is also attached to the ET). 

The SRBs are composed of individual cylindrical sections, each containing a casting of solid fuel. The 

single five-segment stick considered here would consist of five such sections, all of which would constitute 

the first stage of the rocket. A new second stage (with 

an independent liquid-fuel propulsion system) would 

be mounted on top of the SRB. The additional stage is 

needed to provide the capability to lift into LEO 26 

5. The close-derivative launchers considered by CBO are based on 

information received from contractors and NASA from September 2004 through October 2005.
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 13

Figure 2-2.

Close-Derivative Launchers Considered by CBO and Their Antecedents

Source: Congressional Budget Office.

Note: Figures drawn to approximate scale; EELV = evolved expendable launch vehicle; SRB = solid rocket booster; NASA = National 

Aeronautics and Space Administration. The term “close derivative” describes those new launch vehicles that retain a close pedigree to 

existing systems. Figures may be family representatives. 

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment SRBs attached to the central external tank 

(the third stick).

b. A single five-segment stick based on a four-segment SRB.

c. With cargo canister on side.

d. The A5 551 is the largest of the Atlas V medium-lift launchers. A design for a triple-stick Atlas V heavy-lift vehicle has completed Air Force 

review, but no production is planned.

e. The “Medium Plus” refers to an upgraded version of the medium (single-stick) branch of the respective EELV family of launchers.

f. The “Heavy Plus” refers to the triple-stick version of the medium plus branch of the respective EELV family of launchers.

Proposed NASA Vehicles

Space-Shuttle-Derived Family EELV-Derived Family

Current NASA

Configuration

Four-Segment

SRBa

Atlas V Mediumd

Delta IV Family Atlas V Family

Crew Launch

Vehicle

Cargo Launch

Vehicle

Crew Launch

Vehicle

Cargo Launch

Vehicle

Single Stickb

Side-Mountc

Delta IV

Heavy with

Modifications

Delta IV

Medium

Pluse

Delta IV

Heavy

Plusf

or

Crew Launch

Vehicle

Cargo Launch

Vehicle

Current Air Force

Configurations

Delta IV Heavy

Atlas V

Medium

Pluse

Atlas V

Heavy

Plusf

or
14 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Table 2-2.

Selected Characteristics of the Close-Derivative Launchers Considered by CBO

Source: Congressional Budget Office based on data provided by the National Aeronautics and Space Administration, Boeing, 

Lockheed Martin, and ATK Thiokol.

Note: EELV = evolved expendable launch vehicle; LEO = low earth orbit (for all launch systems, this orbit is a circular reference orbit 220 

nautical miles in altitude at a 28.6 degree inclination to the equator); mt = metric tons. 

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment solid rocket boosters attached to the central 

external tank (the third stick). 

b. If a launch fails, the maximum acceleration—expressed in multiples of gravity’s acceleration—that a crew could experience in uncontrolled ballistic reentry.

c. Not a relevant characteristic for a cargo carrier. 

mt. (NASA refers to that spacecraft as the crew exploration vehicle, or CEV.) As of September 2005, 

NASA’s proposed solution for the crew carrier was a 

four-segment stick with a second stage propelled by 

modified versions of the space shuttle main engines. 

However, with the submission to the Congress of the 

President’s fiscal year 2007 budget request, NASA 

changed that proposal to a five-segment stick using a 

second stage equipped with a variant of the less powerful J-2S engine—a modified version of the J-2 engine 

used on the second and third stages of the Saturn V. 

That combination of engines and booster would 

require that the engines in the CEV provide propulsion to attain the needed circular low earth “parking” 

orbit.

B The Side-Mount (cargo carrier/lift capacity, 77 mt).

The Side-Mount would essentially consist of the space 

shuttle propulsion system with a cargo canister replacing the airplane-like orbiter. (Because it must house 

and protect a human crew and carry up to 18 mt of 

cargo to and from LEO, the 80-ton orbiter is relatively 

massive. Its structure, including its wings, must also 

withstand the heat and force of atmospheric reentry.) 

The cargo canister would be relatively light because it 

would be expendable. Therefore, the payload that the 

Side-Mount could lift into LEO would increase to 

about 77 mt (see Table 2-2).

EELV-Derived Launch Vehicles

B The Delta IV Heavy with Modifications, or D4H with 

Mods (crew carrier/lift capacity, 21 mt). The modifications that CBO considered would provide the component redundancy, structural safety margins, and 

health monitoring equipment required for manned 

flight. The D4H with mods, like the existing D4H, 

would be a three-stick launch vehicle with about three 

times the number of first-stage hardware components 

featured on the less capable, single-stick versions of the 

Delta IV. That additional hardware, however, also 

introduces additional opportunities for failure, making the D4H with mods less reliable than the shuttlederived, single-stick launchers discussed previously.6

The D4H with mods would be capable of lifting 

about 21 mt into a circular LEO.

Alternative

Five-Segment Sticka Crew Carrier 26 10.6

Side-Mount Cargo Carrier 77 c

Delta IV Heavy with Modifications (D4H with Mods) Crew Carrier 21 18

Delta IV Medium Plus (D4M+) Crew Carrier 18 18

Delta IV Heavy Plus (D4H+) Cargo Carrier 40 c

Atlas V Medium Plus (A5M+) Crew Carrier 24 16.5

Atlas V Heavy Plus (A5H+) Cargo Carrier 74 c 96 68 96%

EELV-Derived

Launch-Abort Accelerationb Payload to LEO (mt)

Shuttle-Derived

Primary Mission

6. That assessment is based on the contractor’s estimates of the 

vehicles’ reliability.
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 15

Table 2-3.

Comparison of the Costs of the Close-Derivative Launchers Considered by CBO

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Note: EELV = evolved expendable launch vehicle.

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment solid rocket boosters attached to the central 

external tank (the third stick).

B The Delta IV Medium Plus, or D4M+ (crew carrier/lift 

capacity, 18 mt). Relative to the single-stick Delta IV 

Medium (D4M) EELV—which was developed for the 

U.S. Air Force and has executed several successful 

launches—the D4M+ would feature an enhanced 

first-stage core with six solid rocket boosters and an 

expanded second stage with additional engines. Those 

modifications would enable the D4M+ to lift about 

18 mt into a circular LEO flying a depressed trajectory. Designed as a single-stick launcher, it would be 

more reliable than the D4H with mods.

B The Delta IV Heavy Plus, or D4H+ (cargo carrier/lift 

capacity, 40 mt). The Delta IV Heavy is built using 

three of the first-stage central cores featured on the 

Delta IV Medium. Similarly, the D4H+ would use 

three of the central cores of the D4M+, enabling it to 

lift roughly 40 mt of cargo into LEO.

B The Atlas V Medium Plus, or A5M+ (crew carrier/lift 

capacity, 24 mt). Developed for the Air Force, the 

Atlas V Medium has carried out several successful 

launches. Relative to the existing A5M launcher, the 

A5M+ would have a larger first-stage central core and 

an upgraded second stage providing the capability to 

lift about 20 mt into LEO. In addition, the A5M+ 

would incorporate the structural safety margins, component redundancy, and health monitoring equipment needed for manned space flight. Although the 

most capable version of the existing A5M can also lift 

20 mt, it requires the use of five strap-on SRBs 

(attached to the first-stage central core) to do so. 

Because of its expanded first stage, the A5M+ would 

not need to use strap-on boosters, and its first stage 

would serve as the building block for a heavy-lift cargo 

carrier. The A5M+ would be capable of lifting about 

24 mt into a circular LEO.

B The Atlas V Heavy Plus, or A5H+ (cargo carrier/lift 

capacity, 74 mt). The first stage of the Atlas V 

Medium Plus would serve as the basis for this threestick vehicle. Relative to the A5M+, the A5H+ would 

feature additional engines in its second stage. It would 

have the capability to lift about 74 mt into LEO.

Comparisons of the Costs of the Close-Derivative 

Launchers

CBO’s estimates for the costs of the launchers described 

above indicate the following (see Table 2-3):

B On a per-vehicle basis, recurring costs for the shuttlederived crew carrier and the EELV-derived crew carriers would be about the same, within 10 percent.

Alternative

Five-Segment Sticka Crew Carrier 4.8 0.45

Side-Mount Cargo Carrier 4.7 0.95

Delta IV Heavy with Modifications (D4H with Mods) Crew Carrier 2.9 0.47

Delta IV Medium Plus (D4M+) Crew Carrier 3.3 0.40

Delta IV Heavy Plus (D4H+) Cargo Carrier 5.2 0.60

Atlas V Medium Plus (A5M+) Crew Carrier 5.3 0.40

Atlas V Heavy Plus (A5H+) Cargo Carrier 4.0 0.60

Primary Mission

Shuttle-Derived

EELV-Derived

Cost

Development Unit Recurring Cost

Nonrecurring

(Five launchers per year)
16 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

B On a per-vehicle basis, recurring costs for the EELVderived cargo carriers would be about one-third less 

than those for the shuttle-derived Side-Mount. Those 

lower costs reflect, in part, the potential for the sharing of fixed costs (such as for launch pads and production facilities) that is possible between EELV-derived 

vehicles and DoD’s EELV program.7 Such sharing is 

not possible with shuttle-derived vehicles because only 

NASA uses them. EELV-derived cargo carriers also 

have less lift capacity than the shuttle-derived cargo 

carrier: reduced performance implies lower costs for 

each individual launch vehicle. But, in the case of the 

EELV-derived D4H+, that reduced performance also 

means that more cargo carriers would have to be 

launched to conduct a lunar mission. 

B Nonrecurring costs for the design, development, and 

testing of the EELV-derived launchers would be about 

the same, on average, as those for shuttle-derived 

launchers. 

The methodology and assumptions on which these 

results are based are discussed in detail in Appendix E.

New Super-Heavy Launch Vehicles

The super-heavy launch vehicles considered by CBO are 

designed to lift payloads of 100 mt or more. In general, 

those prospective launchers would require physically significant and relatively expensive upgrades to many—and, 

in some cases, nearly all—of the major systems that make 

up existing launchers. Thus, developing super-heavy 

launchers would more than likely entail greater risks of 

cost growth and schedule slippage than would be the case 

with the close-derivative launchers discussed previously. 

A primary consideration would be the need to accommodate a larger number of engines in the first stage and, 

when present, the second stage.8

 (For depictions of the 

super-heavy launchers considered by CBO and comparisons of those vehicles to closely related existing launchers, 

see Figure 2-3. For greater detail, see Appendix D.) CBO 

considers super-heavy launch vehicles that use components of the space shuttle, as well as launchers that would 

represent new and much more capable designs that incorporate selected components (primarily engines) used on 

the current EELVs. CBO does not consider as an alternative rebuilding the Saturn V. Duplicating the infrastructure and engineering expertise needed to rebuild and 

reconfigure the Saturn V would probably make such an 

alternative unattractive when compared with alternatives 

that rely, at least in part, on the infrastructure and expertise associated with currently operational launchers.9

Super-Heavy Launchers That Use Shuttle 

Components

B The Top-Mounted, Shuttle-Derived Super Heavy 

(cargo carrier/lift capacity, 125 mt). In the President’s 

budget for 2007, this cargo launch vehicle was identified as NASA’s recommended solution for supporting 

manned lunar missions.10 Because many of its major 

components would be drawn from the space shuttle, 

CBO refers to the vehicle as the shuttle-derived super 

heavy. Designed to be about the size of the Saturn V 

rocket, the vehicle would be able to lift a payload to 

LEO weighing about 125 mt (see Table 2-4). It would 

use five-segment solid rocket boosters (as opposed to 

the four-segment SRBs used on the shuttle). Two of 

those five-segment SRBs would be mounted on the 

sides of an elongated version of the shuttle’s existing 

external tank, which would be modified to house five 

expendable versions of the existing (reusable) SSMEs. 

Because the vehicle has no second stage, the payload 

engine designated to continue powering the assembled 

lunar mission from low earth orbit would need to be 

burned twice: once to establish the needed circular 

low earth parking orbit; and a second, subsequent 

time to propel the assembled mission on a trajectory 

to the moon. A large cargo canister or shroud would 

be mounted on top of the ET/SRB assembly to house 

the payload.

7. The U.S. Air Force formally projects in its future manifests that it 

will fly about nine EELV flights annually, split roughly equally 

between the Delta IV and Atlas V. The annual number of EELV 

flights conducted recently, however, has been less than one-third 

of that projection.

8. Builders of launch vehicles usually regard the development of new 

engines as the riskiest aspect of constructing new launchers. A 

risk-reduction step used by NASA and industry teams is to rely on 

proven engines (or only slight variations) but to build larger 

launchers to house more of them.

9. Ignoring the unavailability of parts and suppliers, reconfiguration 

might be necessary because the Saturn V does not meet 

current NASA safety standards (see Appendix B).

10. See Office of Management and Budget, Budget of the United States 

Government, Fiscal Year 2007 (January 2006).
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 17

Figure 2-3.

Super-Heavy Launchers Considered by CBO as Cargo Launch Vehicles and

Their Antecedents

Source: Congressional Budget Office.

Note: Figures drawn to approximate scale; EELV = evolved expendable launch vehicle; NASA = National Aeronautics and Space 

Administration; SRB = solid rocket booster.

a. The A5 551 is the largest of the Atlas V medium-lift launchers. A design for a triple-stick Atlas V heavy-lift vehicle has completed Air Force 

review, but no production is planned.

Proposed NASA Vehicles

Space-Shuttle-Derived Family EELV-Derived Family

Current NASA

Configuration

Four-Segment

SRB

Atlas V Mediuma

Delta IV Family Atlas V Family

Delta Super Heavy

or

or

Current Air Force

Configurations

Delta IV Heavy

Longfellow

Top-Mounted

Heavy-Lift Launcher,

or Super Heavy

Five-segment

SRB

Atlas Super Heavy
18 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Table 2-4.

Selected Characteristics of the SuperHeavy Launchers Considered by CBO

Source: Congressional Budget Office based on data provided by 

the National Aeronautics and Space Administration, 

Boeing, Lockheed Martin, and ATK Thiokol. 

Note: EELV = evolved expendable launch vehicle; LEO = low earth 

orbit (for all launch systems, this orbit is a circular reference 

orbit 220 nautical miles in altitude at a 28.6 degree inclination to the equator); mt = metric tons. 

B The Longfellow (cargo carrier/lift capacity, 108 mt).

This launcher—proposed by an industry consortium 

that includes Boeing, Lockheed Martin, and ATK 

Thiokol—would resemble the shuttle-derived super 

heavy but with several different design aspects. Rather 

than expendable versions of SSMEs, the first stage of 

this launcher would rely on four of the RS-68 engines 

currently used on the Delta IV EELVs. It would also 

have a second stage powered by a single J-2S engine, 

atop which would be mounted a cargo canister. 

Because the Longfellow would be able to lift about 

108 mt into LEO, overall its four RS-68 engines and 

single J-2S engine would provide less capability than 

the five SSMEs used on the shuttle-derived super 

heavy (see Table 2-4).11

Super-Heavy Launchers with EELV Antecedents

B The Delta Super Heavy (cargo carrier/lift capacity, 

146 mt). The closest antecedent of this vehicle—

proposed by Boeing—would be the existing Delta IV 

Heavy. The new launch vehicle, however, would 

incorporate many changes relative to the prospective 

Delta IV Heavy Plus. Those changes include the use 

of three expanded first-stage cores, each 8 meters in 

diameter and each equipped with four RS-68 engines. 

Thus, the three-core first stage of this launch vehicle 

would have 12 engines rather than the three-core, 

three-engine first stage of the existing D4H. The 

Delta super heavy would also have a larger second 

stage (8 meters in diameter) equipped with a single 

SSME. That SSME would be modified to start at high 

altitude (in contrast to the existing SSME, which is 

designed to start at sea level). In terms of physical 

dimensions, this launch vehicle would be the largest 

of the super heavies considered by CBO. It also would 

be capable of lifting the largest payload—about 146 

mt—into LEO (see Table 2-4). 

B The Atlas Super Heavy (cargo carrier/lift capacity, 

135 mt). The closest antecedent of this vehicle—proposed by Lockheed Martin—would be the Atlas V 

Heavy Plus. Relative to that prospective launcher, the 

Atlas super heavy would have a substantially expanded 

8.4-meter first-stage central core powered by five RD180 engines (as opposed to the two that power the 

A5H+). The expanded central core would be surrounded by four of the smaller first-stage cores used in 

the A5H+’s triple-stick configuration. Thus, the first 

stage of the Atlas super heavy would consist of a fivestick configuration with 13 engines (see Figure 2-3). 

The launcher’s second stage would be similar to that of 

the A5H+ but would incorporate a longer payload 

shroud. Those changes would result in a vehicle capable of lifting 135 mt into LEO (see Table 2-4). In 

physical dimensions, the Atlas super heavy would not 

need to be as large as the other super-heavy launchers 

considered by CBO. That difference is due primarily 

to the type of liquid fuel used for its first-stage 

engines: unlike the other prospective super-heavy 

launchers, which would use liquid oxygen and liquid 

hydrogen, the Atlas super heavy would consume liquid oxygen and a kerosene variant. The use of lessdense liquid hydrogen requires larger tanks, necessitating larger first-stage assemblages for the prospective 

super-heavy launchers that use space shuttle or Delta 

IV components. 

11. In May 2006, NASA announced that it was changing the design 

of its super heavy to incorporate key features of both the shuttlederived super heavy and the Longfellow. The new design for the 

130 mt cargo carrier replaces the five SSMEs powering the vehicle’s first stage with five of the RS-68 engines used on the first 

stage of the Longfellow. (Unlike the Longfellow, the newly 

designed cargo carrier would not have a powered second stage.) 

Five RS-68 engines would require more space under the tank, 

which in turn would require that the diameter of the first stage be 

larger than that of the existing ET. CBO lacks the information 

needed to prepare other than a preliminary estimate of the costs of 

this new cargo-carrier design.

Primary Mission

Shuttle-Derived

Longfellow Cargo Carrier 108

Super Heavy Cargo Carrier 125

EELV Antecedent

Delta Super Heavy Cargo Carrier 146

Atlas Super Heavy Cargo Carrier 135

Payload to

Alternative LEO (mt)
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 19

Table 2-5.

Comparison of the Costs of the Super-Heavy Launchers Considered by CBO

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Note: EELV = evolved expendable launch vehicle.

Comparisons of the Costs of Super-Heavy Launchers

The recurring launch costs of the super-heavy launchers 

considered by CBO range from $1.1 billion to $1.5 billion; their nonrecurring development costs range from 

$8 billion to nearly $17 billion (see Table 2-5).12 By 

comparison, historical data indicate that the recurring 

launch costs of the Saturn V were about $1.7 billion and 

that its nonrecurring development costs were about $30 

billion. The Saturn V’s greater nonrecurring costs were 

attributable to the development of its engines and other 

associated technology—work that would not have to be 

repeated for the super-heavy launchers considered by 

CBO.

Unlike the case for close-derivative cargo launchers, the 

super-heavy launchers based on shuttle components are 

not necessarily more expensive than super-heavy launchers with EELV antecedents. The Atlas and Delta superheavy launchers would be much larger than their EELV 

antecedents. Therefore, they could not as easily share the 

launch pads, manufacturing facilities, ground-support 

equipment, and other support facilities that the prospective close-derivative Atlas and Delta launchers would 

share with existing EELVs. The absence of the opportunity to share infrastructure is the primary reason that the 

Longfellow, Atlas, and shuttle-derived super-heavy 

launchers all have recurring and nonrecurring costs that 

are relatively similar.

Except for the Delta super heavy, nonrecurring costs for 

the super-heavy launchers would amount to about $9 billion. The Delta super heavy’s nonrecurring costs would 

be significantly higher, primarily because of its size (and 

larger payload). Building and assembling the large-volume, triple-stick configuration of the Delta super heavy 

would require substantial modifications to existing manufacturing, integration, fuel storage and handling, and 

launch facilities—even if the shuttle launch pad was used 

for the Delta super heavy.13 Accommodating those needs 

would cause nonrecurring costs for this launcher to be 

higher than corresponding costs for the other super-heavy 

launchers considered by CBO, which would make greater 

use of existing facilities that required fewer modifications 

(see Appendix E).

The Longfellow lifts the smallest payload into LEO of 

any of the prospective super-heavy launchers—108 mt. 

Thus, two Longfellow launchers would be needed to lift

Alternative

Longfellow 8.0 1.1 4,600

Super Heavy 8.9 1.3 4,700

Delta Super Heavy 16.7 1.5 4,700

Atlas Super Heavy 9.0 1.2 4,100

Recurring Cost per

Development

(Two launchers per year)

Nonrecurring

Cost (Dollars per pound)

Unit Recurring Cost Pound of Payload

EELV Antecedent

Shuttle-Derived

12. CBO’s preliminary estimates of the costs of NASA’s latest design 

for the shuttle-derived super-heavy cargo carrier using five RS-68 

engines indicate that the lower bound on those recurring costs 

could be about $1.0 billion and that the lower bound on nonrecurring costs could be about $7.4 billion.

13. Details of the infrastructure requirements and their relatively high 

expense were provided to CBO on August 5, 2005, during 

discussions with members of Boeing’s Launch Services Division in 

Huntington Beach, Calif.
20 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

the cargo associated with a single manned lunar mission, 

basically negating its lower per-launch cost.14

According to CBO’s estimates, the unit cost of the Atlas 

super heavy would be 10 percent less than that of the 

shuttle-derived super heavy.15 Nonetheless, some observers might argue that the shuttle-derived launcher would 

be more cost-effective than the Atlas. Relative to the shuttle-derived super heavy, the first stage of the Atlas super 

heavy would be more complex because of its larger number of engines (15 versus seven) and sticks (five versus 

three). Generally, greater complexity implies reduced reliability (because of greater opportunities for potential failure).16,17 If the Atlas failed more often than the shuttlederived super heavy, its use might be more expensive 

overall because of the need for additional launches to 

compensate for failures.

Program Cost Comparisons

In this section, CBO provides projections for the funding 

that NASA would need for launch vehicle development 

and procurement to execute manned lunar missions using 

the alternative crew and cargo launchers described previously. Those CBO projections are compared with NASA’s 

current projection of the funding it estimates will be 

needed through 2017 to develop and buy launch vehicles 

capable of supporting both flight to the International 

Space Station and manned lunar missions.

To generate those projections, CBO needed to make a 

variety of “programmatic” assumptions, such as when the 

vehicles would first be used to launch either cargo or a 

spacecraft and its crew and how many test flights would 

be necessary before a launch vehicle was deemed ready for 

use. CBO used two sources for building those assumptions. First, to the extent that the September 2005 Exploration Systems Architecture Study documented the 

programmatic assumptions NASA is using, CBO’s projections are built on those assumptions—unless they have 

been subsequently superseded by materials the agency 

prepared for the President’s budget. In particular, justification materials provided for the 2007 budget indicate 

that NASA remains hopeful it can meet the schedule outlined in the ESAS for conducting the first flight of the 

CEV in 2012 and the first manned lunar mission in 

2018. However, the agency recognizes that budget constraints might delay those events until 2014 and 2020, 

respectively. Therefore, CBO has constructed budgetary 

projections for launch vehicle funding needed to execute 

both of those schedules. The programmatic assumptions 

that CBO made include the following: 

B Certification of a launch vehicle—whether a crew carrier or a cargo carrier—for operational use requires 

three test or demonstration (test/demo) flights. 

B Appropriations for hardware production and launch 

services precede a launch by two years.

B The first operational flight of the CEV (carried aloft 

by the crew carrier) occurs in either 2012 (the more 

ambitious schedule) or 2014 (the less ambitious 

schedule). The first manned lunar mission occurs in 

either 2018 (the more ambitious schedule) or 2020 

(the less ambitious schedule). 

B Five ISS support flights per year are conducted 

through 2016 beginning in either 2012 or 2014.18

Regardless of whether the payload to the ISS includes 

a crew, the launcher for those flights will be the crew 

14. Based in part on the Columbia Accident Investigation Board Report

and NASA’s decision to separate cargo and crew launches, CBO 

did not consider a case in which one Longfellow would launch 

cargo and a second would launch the remaining cargo, as well as 

the lunar spacecraft and its crew.

15. CBO’s preliminary estimate of the costs of NASA’s latest design 

for the shuttle-derived super heavy, which would use five RS-68 

engines instead of SSMEs, suggests that this relationship could be 

reversed: rather than 10 percent lower, the unit cost of the Atlas 

super-heavy cargo carrier could be about 20 percent higher.

16. Reliability calculations are complex, involving a number of tradeoffs. On the one hand, more engines and sticks imply the need for 

more tanks, valves, sensors, and moving parts, all of which present 

more failure modes. On the other hand, with enough engines, if 

one failed to ignite (one of the most common failure modes for 

engines), the remaining engines might still be able to deliver a 

payload into its intended orbit.

17. The first stage of the Soviet N-1 moon rocket had 30 engines. All 

four test flights of that rocket ended in failure before separation of 

the first stage could be completed.

18. NASA also supports the ISS with funds in another account called 

the ISS Cargo and Crew Services (ISS CCS) project. This account 

funds both purchases of launches from foreign providers (in particular, Russia) and development of U.S. commercial launch services to LEO. In NASA’s budget projections through 2017, which 

were prepared earlier this year, the agency assumes that its crew 

carrier will be used for five ISS support flights annually, with the 

new ISS CCS project providing one additional support flight to 

the ISS annually.
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 21

Table 2-6.

Cargo Launches Needed to Execute a Manned Lunar Mission with the Alternative 

Cargo Launchers Considered by CBO 

Source: Congressional Budget Office based on data provided by Boeing, Lockheed Martin, and ATK Thiokol. 

Note: EELV = evolved expendable launch vehicle; LEO = low earth orbit (for all launch systems, this orbit is a circular reference orbit 220 

nautical miles in altitude at a 28.6 degree inclination to the equator); mt = metric tons. 

a. Does not include 18 to 28 mt delivered to LEO by a separate launch of the crew carrier. 

launch vehicle. With the retirement of the space shuttle projected to occur in 2010, this assumption implies 

a hiatus in manned space flight of two to four years.

B Two manned lunar missions occur annually, beginning in either 2018 or 2020.

B No budgetary allowances are made for launch failure.

The more ambitious schedule would require that 29 crew 

carriers be purchased to conduct operational launches 

through 2017.19 Twenty-five of those vehicles would support ISS missions, and four would be designated for lunar 

missions. Executing the more ambitious schedule would 

require purchasing four to 12 cargo carriers through 2017 

to conduct lunar missions starting in 2018. The range in 

the number of needed cargo carriers reflects the differing 

number of launches associated with each of the alternatives that CBO considered (see Table 2-6).

The less ambitious schedule implies that 15 crew carriers 

would be purchased through 2017 to conduct operational launches. All of those launchers would be used for 

ISS support missions. Executing the less ambitious schedule would not require cargo carriers to be purchased 

through 2017 to conduct operational launches, however. 

The Vision for Space Exploration Initiative: 

Projected Funding for Launch Vehicles

Through 2017, NASA has projected the funding that it 

anticipates will be needed to develop and purchase launch 

vehicles to conduct missions to the ISS and to the moon. 

Four accounts are directly related to VSE launch vehicles 

under what the agency calls its Constellation Systems 

Program, as follows:

B Crew Launch Vehicle. This account also supports the 

delivery of crew and cargo to the ISS using the fivesegment launcher.

B Heavy-Lift Launch Vehicle (the cargo carrier).

B Launch and Mission Systems (L&MS). This account 

covers processing, launch operations, and research and 

development of facilities, ground equipment, control 

systems, and communications networks for the crew 

launch vehicle, the cargo carrier, and the CEV. NASA 

Alternative

Side-Mount 77 2 154

Longfellow 108 2 216

Super Heavy 125 1 125

Delta IV Heavy Plus (D4H+) 40 3 120

Atlas V Heavy Plus (A5H+) 74 2 148

Delta Super Heavy 146 1 146

Atlas Super Heavy 135 1 135 96 68 96%

Cargo Launches per Maximum Cargo Payload

per Lunar Mission (mt)a Payload to LEO (mt) Lunar Mission

Shuttle-Derived

EELV Antecedent

19. An operational launch is executed in order to conduct a mission to 

the space station or to the moon. CBO distinguishes those 

launches from the test launches conducted in order to assure that a 

newly developed launcher is ready for operational use. The number of test launches conducted through 2017 under any given 

alternative is the same for either the more ambitious or less ambitious schedule.
22 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure 2-4.

NASA’s Projected Funding for VSE Launch Vehicles Through 2017

(Billions of 2006 dollars)

Source: Congressional Budget Office based on the President’s budget for fiscal year 2007.

Note: NASA = National Aeronautics and Space Administration; SEI = system engineering and integration; VSE = Vision for Space 

Exploration.

budget materials available to CBO do not specify how 

much L&MS funding will be allocated to the CEV 

and how much to the launchers. Therefore, CBO 

assumes that, through 2010, L&MS funding is solely 

associated with the CEV. After 2010, two-thirds of the 

funding is assumed to be associated with crew and 

cargo launchers.

B System Engineering and Integration (SEI). This 

account funds activities that support all aspects of the 

Constellation Systems Program. The NASA budgetmaterials available to CBO do not specify how much 

SEI funding will be allocated to support development 

and operational launches of the crew and cargo carriers. Therefore, CBO assumes that the fraction of SEI 

funding allocated to support launch vehicles will be 

equal to the fraction of funding for the Constellation 

Systems Program (less SEI) composed of the three 

launch vehicle accounts listed immediately above.

Through 2017, NASA’s projections for cumulative funding in those four accounts, which is slated to support the 

development and purchase of VSE launch vehicles, total 

$30.1 billion. Through 2010, the projected amounts are 

about $1.0 billion annually. After 2010, annual amounts 

are about $3.5 billion (see Figure 2-4). NASA’s projection 

is constructed to support the development and use of the 

five-segment stick as the crew carrier and the shuttlederived super-heavy launcher as the cargo carrier.

Comparisons of Program Costs Using 

Close-Derivative Launchers

CBO has constructed budgetary projections through 

2017 for three alternative launch programs that would 

use close-derivative launchers, as follows:

B The “pure Atlas-derived” alternative. This program 

would use the A5M+ launcher as the crew carrier and 

the A5H+ launcher as the cargo carrier.

B The “pure Delta-derived” alternative. This program 

would feature the D4M+ with mods as the crew carrier and the D4H+ as the cargo carrier.

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0

Crew Launch Vehicle

($13.4 billion)

Cargo Launch Vehicle

($9.0 billion)

Launch and Mission Systems

($5.4 billion)

SEI

($2.3 billion)

Total = $30.1 billion
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 23

Figure 2-5.

Costs Through 2017 of Using Close-Derivative Launchers to Conduct Manned 

Lunar Missions

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Notes: NASA = National Aeronautics and Space Administration.

The more ambitious schedule initiates International Space Station support in 2012 and the first lunar mission in 2018. The less ambitious schedule initiates International Space Station support in 2014 and the first lunar mission in 2020.

The term “pure” means that both the crew carrier and the cargo carrier are derived from vehicles in the same family of launchers. 

The term “close derivative” describes new launchers that retain a close pedigree to existing systems. 

B The “pure shuttle-derived” alternative. This program 

would use the five-segment stick as the crew carrier 

and the Side-Mount as the cargo carrier.

The above three alternative programs do not constitute a 

complete set of alternatives that could be pursued using 

the four close-derivative crew carriers and three closederivative cargo carriers described previously. CBO has 

chosen to analyze this subset in order to limit the number 

of budgetary projections it built to a manageable number 

while still illustrating the differences in costs associated 

with pursuing EELV-derived or shuttle-derived programs.

To execute the more ambitious schedule for returning 

humans to the moon, CBO estimates that total costs 

through 2017 for pursuing the three alternatives it considered using close-derivative launchers would range from 

about $26 billion for the pure Atlas-derived launch program to almost $31 billion for the pure shuttle-derived 

program (see Figure 2-5). Executing the less ambitious 

schedule would cost $15 billion for the pure Deltaderived program to $16 billion for the pure shuttlederived program through 2017, CBO estimates. 

Comparisons of Program Costs Using 

Super-Heavy Launchers

CBO has constructed budgetary projections through 

2017 for three alternative launch programs that would 

use new super-heavy launchers, as follows:

B The “pure Atlas-antecedent” alternative. This program would use the A5M+ launcher as the crew carrier 

and the Atlas super-heavy launcher as the cargo carrier.

0

5

10

15

20

25

30

35

40

NASA's

Projection

Pure

AtlasDerived

Pure

DeltaDerived

Pure

ShuttleDerived

Close-Derivative Alternatives

More Ambitious Schedule

0

5

10

15

20

25

30

35

40

Less Ambitious Schedule

NASA's

Projection

Pure

DeltaDerived

Pure

AtlasDerived

Pure

ShuttleDerived

Close-Derivative Alternatives
24 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure 2-6.

Costs Through 2017 of Using Super-Heavy Launchers to Conduct Manned 

Lunar Missions

(Billions of 2006 dollars)

Source: Congressional Budget Office.

Notes: NASA = National Aeronautics and Space Administration.

The more ambitious schedule initiates International Space Station support in 2012 and the first lunar mission in 2018. The less ambitious schedule initiates International Space Station support in 2014 and the first lunar mission in 2020.

Each alternative includes the close-derivative crew carrier associated with the indicated family. The term “pure” means that both the 

crew carrier and the cargo carrier are derived from vehicles in the same family of launchers.

The term “close derivative” describes new launchers that retain a close pedigree to existing systems. 

a. NASA’s choice of crew launch vehicle and cargo carrier as outlined in the President’s budget for 2007.

B The “pure Delta-antecedent” alternative. This program would use the D4M+ as the crew carrier and the 

Delta super-heavy launcher as the cargo carrier. 

B The “shuttle-derived super-heavy” alternative. This 

program would use the five-segment stick as the crew 

carrier and the top-mounted, shuttle-derived superheavy launcher as the cargo carrier. Upon submission 

of the 2007 budget, this was NASA’s choice for VSE 

launch vehicles.20

To implement the more ambitious schedule using 

super-heavy launchers, CBO estimates that costs through 

2017 would range from $31 billion to $38 billion (see 

Figure 2-6). CBO’s estimates indicate that using NASA’s 

choice of launch vehicles to execute the more ambitious 

schedule would cost about $2 billion more than the funding contained in NASA’s budget projection through 

2017.21

0

5

10

15

20

25

30

35

40

45

NASA's

Projection

Super-Heavy Alternatives

a

More Ambitious Schedule

0

5

10

15

20

25

30

35

40

45

Less Ambitious Schedule

Super-Heavy Alternatives

NASA's

Projection

Pure

 ShuttleDeriveda

Pure

Atlas

Antecedent

Pure

 ShuttleDerived

Pure

Delta

Antecedent

Pure

Atlas

Antecedent

Pure

Delta

Antecedent

20. See Office of Management and Budget, Budget of the United States 

Government, Fiscal Year 2007.

21. CBO’s preliminary estimate for the costs of NASA’s latest design 

for the shuttle-derived super-heavy cargo carrier, which uses five 

RS-68 engines, indicates that programmatic costs for the more 

ambitious schedule could be about $30 billion, essentially the 

same amount contained in NASA’s future funding projection.
CHAPTER TWO ALTERNATIVES FOR FUTURE NASA MANNED SPACE-EXPLORATION CAPABILITIES 25

To execute the less ambitious schedule using super-heavy 

launchers, CBO estimates that costs through 2017 would 

range from $20 billion to $26 billion. CBO’s estimates in 

this case indicate that using NASA’s choice of launch 

vehicles would cost about $10 billion less through 2017 

than the funding contained in NASA’s budget projections.22 (However, given the risks inherent in the designs 

of the crew and cargo launchers chosen by NASA, CBO’s 

estimates could be low; see Box 2-1.) That savings comes 

from reducing the number of ISS support missions from 

25 to 15 and delaying procurements for four lunar missions beyond 2017.

22. CBO’s preliminary estimate for the costs of NASA’s latest design 

for the shuttle-derived super-heavy cargo carrier, which uses five 

RS-68 engines, indicates that programmatic costs for the less 

ambitious schedule could be about $19 billion, which is about 

$11 billion less through 2017 than NASA’s future funding 

projection.
26 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Box 2-1.

Risks Associated with Developing and Producing NASA’s Launch

Vehicle Choices

The National Aeronautics and Space Administration 

(NASA) has acknowledged that its choice of launch 

vehicles, particularly the five-segment stick proposed 

by the agency as a crew carrier, presents a number of 

risks.1

 Such risks could cause actual costs to exceed, 

perhaps substantially, estimates made by the Congressional Budget Office (CBO). The risks cited by 

NASA personnel relate to the following functions:

B Stability control. A launch vehicle’s stability—that 

is, its resistance to deviation from its intended 

flight path—is related to its ratio of height to 

width; the higher the ratio, the greater the potential for problems with stability. Launcher designs 

usually attempt to maintain a height-to-width 

ratio that is no greater than 15:1; but, the fivesegment stick will have a height-to-width ratio of 

18:1. Thus, NASA expects that maintaining stability control of the five-segment stick will present 

a greater challenge than that posed by existing 

launch vehicles.

B A large second stage powered by a modified 

engine. Since the 1960s, the largest second stages 

have had dry weights (that is, weight that does not 

consist of fuel) of about 4 metric tons (mt) or less. 

By contrast, the second stage of the fivesegment stick will weigh about 10 mt. (That additional weight is a contributor to the five-segment 

stick’s relatively large height-to-width ratio.) The 

second stage will be powered by an updated version of the J-2S engine, which was developed at 

the end of the Apollo program.

B Structural integrity of the five-segment solid 

rocket booster. The crew carrier’s five-segment 

solid rocket booster must support the weight of 

both the second stage and the crew exploration 

vehicle during powered flight. NASA expects that 

the structural safety margins incorporated in the 

design of the four-segment sticks used for the 

space shuttle will suffice for the five-segment stick, 

even though the four-segment stick was designed 

for substantially different loads and stresses. However, the testing needed to verify that expectation 

remains to be done.

B Organizing and executing the construction of 

a launch vehicle rated for manned space flight.

NASA last oversaw such an effort more than 20 

years ago with the development and testing of the 

space shuttle.

Since NASA’s publication of the Exploration Systems 

Architecture Study (ESAS), the crew carrier has 

evolved from a four-segment stick with a second stage 

powered by a space shuttle main engine (SSME) to a 

five-segment stick with a variant of the J-2S engine, 

which has less lift capability.

Evolution of the cargo carrier design has also begun. 

Recently, NASA announced that the SSME powering 

the cargo carrier recommended in the ESAS report 

will be replaced with the RS-68.2 RS-68 engines offer 

lower cost and higher thrust; however, they also are 

less efficient (on a thrust-per-weight basis) than the 

SSMEs. That limitation could require the use of a 

powered second stage on the cargo carrier. (The 

Longfellow also features RS-68 engines in the first 

stage but adds a liquid-fueled second stage to overcome that limitation.) CBO lacks a detailed description of the evolving design of the cargo carrier and, 

therefore, has not considered that recent development among its alternatives. 1. See, for instance, comments from NASA’s manager of Constellation Systems Launch Vehicles Project at the Marshall 

Space Flight Center, cited by Frank Morring Jr. in “Tight 

Schedule; Crew Launch Vehicle Targets 2012 Human Mission; Challenges Abound,” Aviation Week & Space Technology, 

April 24, 2006, p. 32.

2. Frank Morring Jr. in “Bigger Prop Tank Was Key to NASA’s 

RS-68 Decision,” Aerospace Daily & Defense Report, May 22, 

2006.
APPENDIX

A

On-Orbit Assembly,

Launch Vehicle Reliability, and

Overall Probability of Mission Success

On-Orbit Assembly

Relying on multiple launches to execute a manned lunar 

mission requires the capability to assemble various hardware subcomponents into a functional whole in low earth 

orbit (LEO). Such assembly requires that the subcomponents be designed to rendezvous in space and dock with 

one another. Those operations can be accomplished by 

humans (either remotely from the ground or locally in 

LEO) or autonomously. In constructing the International 

Space Station (ISS), the National Aeronautics and Space 

Administration (NASA) has gained experience assembling a large mass in orbit using a crew on-site. (The 

space shuttle was used to lift into LEO subcomponents of 

the ISS that were later assembled by the shuttle’s crew.) 

During all of the Apollo lunar missions, the command 

and service module and the lunar module performed 

undocking and redocking maneuvers while in flight. 

Those operations were controlled locally by the crew in 

the command and lunar modules. 

The Russians have demonstrated the ability to rendezvous and dock in space using remote control. In particular, since 1989 their Progress program has flown the 

Progress M and the Progress M1 on 55 flights to the 

former Mir space station and to the ISS with only one 

failure. (In 1997, the Progress M collided with the MIR 

and damaged it, although not catastrophically.) Incapable 

of carrying a crew, the Progress vehicles delivered cargo to 

either the MIR or the ISS. 

The United States has not successfully demonstrated rendezvous and docking by remote control or autonomously. 

NASA launched a Demonstration of Autonomous Rendezvous Technology (DART) spacecraft in April 2005 to 

rendezvous with and conduct close-proximity maneuvering about a target spacecraft. However, the mission terminated early, and NASA reported that the DART spacecraft had experienced, among other problems, 

irregularities in its navigation system.1 The Department 

of Defense is pursuing initiatives similar to DART. One is 

the Orbital Express program, which is designed to demonstrate on-orbit satellite servicing; it is scheduled for 

launch in late 2006. Another is the XSS-11 mission, 

which successfully rendezvoused with its launch vehicle 

in April 2005 and is scheduled to spend a year rendezvousing (but not docking) with other objects in orbit. 

With no directly relevant experience, it is difficult to 

assign a probability of success to eventual assembly operations that might be conducted by the United States—

either remotely or autonomously—in an effort to return 

humans to the moon. Using the demonstrated success of 

the Russian Progress program—0.982—as a benchmark, 

CBO performed a parametric analysis of the likelihood of 

a manned lunar mission’s failing using probabilities of 

success for on-orbit assembly that ranged from 0.98 to 

0.99. In that analysis, the crew-assisted docking that 

would follow the launch of the crew carrier spacecraft is 

assumed to be successful. 

Launch Reliability

CBO’s parametric analysis uses probabilities of successful 

launch ranging from 0.959 to 0.998. The lower bound of 

that range is the 15-year average of successful launches of 

the Atlas, Delta, and Titan expendable launchers, as well 

1. NASA, Overview of the DART Mishap Investigation Results, available at www.nasa.gov/pdf/148072main_DART_mishap_

overview.pdf.
28 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure A-1.

Historical Launch Reliability

(Probability of successful launch)

Source: Congressional Budget Office.

a. The Delta IV heavy-lift launcher, included in these averages, accomplished test objectives but failed to place its dummy payload into the 

intended orbit.

as the space shuttle (see Figure A-1). The upper bound is 

the average of the probabilities of successful launches projected by Boeing, Lockheed Martin, NASA, and ATK 

Thiokol for the launch vehicle options that each organization considered during 2005 prior to completion of 

NASA’s Exploration Systems Architecture Study.

Overall Probability of Launch and 

Assembly Success

Not surprisingly, alternatives that require the least number of launches are least likely to experience a failure (see 

Figure A-2). The use of close-derivative launchers to 

execute a manned lunar mission would require three or 

four launches, with a probability of failure ranging from 

3 percent to 21 percent. The use of the super-heavy alternatives, which would require two launches, would have a 

probability of failure of 2 percent to 10 percent.

Shuttle Titan Atlas Deltaa NASA's and Contractors'

Predictions for

Launcher Reliability

0.850

0.875

0.900

0.925

0.950

0.975

1.000

1990–2004 1995–2004 2000–2004
APPENDIX A ON-ORBIT ASSEMBLY, LAUNCH VEHICLE RELIABILITY, AND OVERALL PROBABILITY OF MISSION SUCCESS 29

Figure A-2.

Overall Probability of Mission Success

(Probability of successful launch and assembly)

Source: Congressional Budget Office.

Notes: AR = assembly reliability; LVR = launch vehicle reliability.

From 1990 to 2004, the average overall LVR of the shuttle and the Atlas and Delta families is 0.959.

a. The number of launches is N-1 cargo launches plus 1 crew launch. Reliability for docking the crew exploration vehicle with its cargo is 

assumed to be 1.0.

b. Probability of mission success with the super-heavy launchers.

c. Probability of mission success with the shuttle-derived Side-Mount, Longfellow, or Atlas V Heavy Plus cargo vehicles.

d. Probability of mission success with the Delta IV Heavy Plus cargo vehicle.

12345678

0.75

0.80

0.85

0.90

0.95

1.00

LVR = 0.959, AR = 0.98

LVR = 0.959, AR = 0.99

LVR = 0.98, AR = 0.98

LVR = 0.98, AR = 0.99

LVR = 0.99, AR = 0.98

LVR = 0.99, AR = 0.99

LVR = 0.998, AR = 0.98

LVR = 0.998, AR = 0.99

b c d

Number of Launchesa

APPENDIX

B

Human Safety on Launch Abort

Human safety on launch abort is a primary consideration when distinguishing between the lift capacity 

of crew carriers and cargo carriers. As mentioned in 

Chapter 1, maximizing crew safety while maximizing 

launch vehicle lift capacity can be conflicting goals. No 

crew carrier considered in this Congressional Budget 

Office (CBO) report would fail to meet safety standards 

set by the National Aeronautics and Space Administration (NASA). However, trade-offs in design must occur 

to ensure crew safety, and those trade-offs affect the alternatives differently. Human safety during launch abort 

becomes an issue only if a mission has to be terminated 

because the launch has already failed to the degree that 

the crew must return to Earth safely before it reaches 

orbit.

Launch Trajectories and Launch Abort

The potential for death or injury during an aborted 

launch depends on the deceleration that the crew experiences as the spacecraft returns to Earth; that deceleration, 

in turn, depends on the launcher’s trajectory on ascent. A 

launch vehicle that lifts its payload to a high altitude 

quickly is said to fly a steep trajectory; a launcher that 

ascends to a high altitude more gradually is said to fly a 

shallow or depressed trajectory. In general, the more 

depressed the trajectory that a booster flies, the more 

work it has to do to lift its payload into orbit. Therefore, 

a given launcher will be able to deliver less payload to 

orbit if it flies a more depressed trajectory. However, more 

depressed trajectories are safer for crewmembers, if they 

must abort, because they fall less steeply back into the 

atmosphere. Hence, trajectories that tend to maximize 

payload delivery tend to reduce crew safety.

Both the magnitude of the deceleration that the crew 

experiences—measured in multiples of the acceleration of 

gravity at the Earth’s surface, or g’s—and the duration of 

the acceleration are relevant in determining whether a 

return trajectory might harm or kill the crew of a spacecraft. On the basis of data collected by the Air Force during tests of aircraft ejection seats, NASA has developed a 

standard for acceleration and its duration along the “eyeballs in” direction that should not be equaled or exceeded 

during a launch abort in order to ensure the survival of 

the spacecraft’s crew (see Figure B-1).1

A Comparison of the Alternatives

To be deemed safe, a launch vehicle must fly an ascent 

trajectory that, in the case of launch abort, would result 

in a return trajectory that satisfied NASA’s safety standard. (As illustrated in Figure B-1, the vehicle would fly 

trajectories with curves of acceleration versus duration 

that lie below the curve labeled “NASA Standard.”) 

Because the existing evolved expendable launch vehicles 

(EELV) lift their unmanned cargo payloads along relatively steep trajectories, the EELV-derived crew carriers 

considered by CBO generally reduce payload capability 

and adopt depressed trajectories to maintain a safe profile 

for manned flight. The space shuttle’s abort trajectory has 

substantial margin in meeting NASA’s safety standard, as 

would the five-segment, shuttle-derived crew carrier. 

Analogous calculations for the Saturn V launcher were 

performed for CBO by the staff of ATK Thiokol. Those 

calculations indicate that if a launch abort had occurred 

during the Apollo program, the Saturn V launcher’s trajectory on ascent could have subjected the Apollo command module’s crew to unsafe decelerations during its 

return to Earth (see Figure B-2). 

1. The “eyeballs in” direction assumes that the crewmembers reenter 

the atmosphere oriented so that their backs face the direction of 

motion. Other orientations also are important, but the eyeballs in 

direction is used here to make comparisons.
32 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure B-1.

Acceleration on Launch Abort for Various Launch Vehicles

(Acceleration, or g’s, in the +Gx “eyeballs in” direction)

Sources: Congressional Budget Office based on contractors’ estimates for launch vehicles. The NASA standard is from National Aeronautics 

and Space Administration, Man-Systems Integration Standards, NASA-STD-3000, vol. 8, Crew Exploration Vehicle Launch

Segment (2005).

Note: Force is expressed in multiples of terrestrial surface gravity (g’s). The direction of force is eyeballs in (with deceleration pressing on 

the astronauts’ chests and eyes as they lie on their backs while descending toward Earth). 

1

10

100

0.1 1 10 100 1000

NASA Standard

Shuttle-Derived

Crew Launch Vehicle Atlas V Medium Plus

Delta IV Heavy

with Modifications

Duration (Seconds)
APPENDIX B HUMAN SAFETY ON LAUNCH ABORT 33

Figure B-2.

Acceleration on Launch Abort for

Apollo 17

(Acceleration, or g’s, in the +Gx “eyeballs in” direction)

Sources: The NASA standard is from National Aeronautics and 

Space Administration, Man-Systems Integration Standards, NASA-STD-3000, vol. 8, Crew Exploration Vehicle 

Launch Segment (2005). The Apollo 17 calculations were 

done for the Congressional Budget Office by ATK Thiokol.

Note: Force is expressed in multiples of terrestrial surface gravity 

(g’s). The direction of force is eyeballs in (with deceleration 

pressing on the astronauts’ chests and eyes as they lie on 

their backs while descending toward Earth).

a. Apollo 17’s maximum abort acceleration slightly exceeds the 

NASA standard.

1

10

100

0.1 1 10 100 1000

NASA Standard a

Apollo 17

Duration (Seconds)

APPENDIX

C

Considerations That Affect Lunar Missions 

Executed Using Multiple Launches

A lunar mission that relied on multiple launches 

into low earth orbit (LEO) would be subject to constraints that would not affect missions conducted with a 

single Apollo-style launch. A primary constraint is the 

need to ensure that all the launches were executed in a 

short enough span of time to preclude substantial leakage 

of the cryogenic hydrogen fuel stored in orbit, which 

would be used to launch the assembled spacecraft from 

LEO to the moon. That constraint would make it necessary to account for potential launch delays and manage 

actual delays caused by problems related to weather, range 

safety issues, and launch vehicle performance. The potential need to launch other spacecraft from the same launch 

pad(s) used for launching manned lunar missions could 

cause scheduling constraints, which also must be 

considered.

Hydrogen Leaks

Hydrogen molecules are the lightest in existence and, 

therefore, are quite volatile. Consequently, anything containing hydrogen, even in the cold, near-vacuum conditions of space, leaks readily.1

 Assuming a predetermined 

mission length and launch schedule, launch vehicle 

designers plan for the excess hydrogen fuel needed to 

compensate for the leakage. (For example, about 34 percent of the mass of hydrogen fuel stored in LEO might 

leak from its on-orbit storage container during one year.)2

However, once a payload is placed into LEO with a given 

amount of cryogenic hydrogen fuel on board, other 

launches must proceed according to the assumed schedule or too much hydrogen will boil away, leaving insufficient amounts of fuel to propel the assembled lunar mission out of LEO and to the moon. 

Launch Cycle

A launch cycle generally consists of two phases: the time 

that is required at a launch complex to assemble and 

ready the launch vehicle and payload involved in a single 

launch, and the time required to both execute the launch 

and refurbish the complex for the next anticipated 

launch. Infrastructure at the shuttle launch complex and 

at the launch complex that serves the Atlas evolved 

expendable launch vehicle (EELV) can support one 

launch every 30 days. The launch cycle for the Delta 

EELV launch complex is 21 days. Therefore, as currently 

configured and if fully staffed, the shuttle and Atlas complexes could each support 12 launches annually, and the 

Delta complex, 18. 

Launch Delays

Most delays, or at least their duration, can be anticipated 

and accommodated within the launch cycle. Approximately one-third of Air Force launches occur on time. 

Another third of launches occur with a delay that can be 

accommodated within the launch cycle. And roughly 

one-third of launches are delayed until later launch 

cycles.3

 About 50 percent of those launch delays are 

1. Oxygen and other gases also leak but not as extensively, which is 

why hydrogen leakage usually dominates considerations.

2. Actual boil-off rates are complex functions of the material used to 

construct the storage container, its geometry, and whether and 

how passive and/or active cooling techniques are employed. A 

boil-off rate of 34 percent is typical for passive cooling techniques 

and traditional storage containers.

3. Data extracted from the U.S. Air Force’s Eastern Range Launch 

Performance, 1988 to 2002.
36 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure C-1.

Historical Launch-Pad Delays for Selected Launch Systems

(Number of launches)

Source: Congressional Budget Office based on data from shuttle-mission-delay records and from D.P. Thunnisen, Balancing Cost, Risk, and 

Performance Under Uncertainty in Preliminary Mission Design (Reston, Va.: American Institute of Aeronautics and Astronautics, 

2004).

caused by weather, 42 percent are caused by malfunctioning hardware (in the launch vehicle, payload, or sensing 

systems prior to launch), and 8 percent are caused by 

range problems (such as the failure of a tracking camera 

or other sensor used to monitor the launch downrange 

after the vehicle’s launch or prior to its reaching orbit).

The typical delay is usually of short duration. Simpler 

launchers like the Delta II have experienced an average 

launch delay of only 2.4 days, whereas more complex 

launch systems can suffer longer delays (see Figure C-1). 

The shuttle’s average delay has been 12 days. 

To accommodate such delays, launch cycle missions contain built-in margins. For instance, for the Atlas EELV, a 

four-day margin is built into the schedule. In addition, a 

typical launch cycle will assume that work is conducted 

five days per week, with no work performed on weekends. Therefore, a 30-day launch cycle may have a builtin allowance for delays of up to about 12 days.

Experience indicates, however, that some very long 

launch delays can occur, particularly for the more complex launchers (see Figure C-1). A less complex launcher 

like the Delta II experiences launch delays that exceed 

12 days about 4 percent of the time. The more complex 

space shuttle has experienced launch delays that last 

longer than 12 days about 20 percent of the time, but it 

also has experienced delays of longer than 30 days about 

10 percent of the time.

Launch Delays and Launch Cycles

Because there is some chance that complex launch vehicles will experience a long delay, the total number of 

launch cycles available to lift the components of a 

manned lunar mission can become a key consideration.

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

0

5

10

15

Shuttle Launch Delays, 1981 to 2000

Number of Days Delayed

Number of Days Delayed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

0

10

20

30

40

50

Weather

Problems

Range

Safety

Issues

Launch Vehicle

Performance

Payload

Hardware

Malfunction

Delta II Launch Delays, 1989 to 2001
APPENDIX C CONSIDERATIONS THAT AFFECT LUNAR MISSIONS EXECUTED USING MULTIPLE LAUNCHES 37

Table C-1.

Launch Cycles Needed to Ensure

Mission Success 

Source: Congressional Budget Office based on data provided by 

Boeing, Lockheed Martin, and ATK Thiokol.

Note: T = threshold of success (percent); L = required launches 

per mission; D = number of additional launch cycles 

planned for delays; L + D = number of launch cycles 

necessary for mission success to exceed T; p = probability 

of launch within a given launch cycle, which is assumed to 

be equal for all launches associated with a given mission. 

This is particularly true if the number of mission 

launches is large. In general, the number of launch cycles 

available for existing launchers would be sufficient to 

accommodate both manned lunar missions and other 

launches, providing the former occurred without appreciable delay. However, if delays became too long, then 

current launch capacity could be insufficient. The following calculation indicates the interplay between launch 

cycle capacity and launch delay. 

Let:

L = the number of launches required for a manned lunar 

mission (L ranges between 2 and 4 for the alternative 

launchers considered by the Congressional Budget 

Office);

B = the boil-off constraint in launch cycles (B is the number of launch cycles within which hydrogen boil-off is not 

a constraint. For instance, if the launch cycle is one 

month, and boil-off becomes a problem after eight 

months, then B = 8);

D = the number of additional launch cycles put into a 

mission’s launch schedule to accommodate the possibility 

of delays; 

p = the probability that a given launch will occur within 

one launch cycle (for example, the data for the shuttle 

and Delta II suggest that launches of manned lunar missions might occur within the planned launch cycle about 

90 percent of the time, or p = 0.9); and

T = the desired probability that all launches occur on 

schedule (for instance, T = 0.99 would reflect the desire 

that all L launches occur within L + D launch cycles at 

least 99 percent of the time). 

Using that framework, the minimum number of added 

launch cycles, D, that must be built into a launch schedule to ensure the desired probability, T, of executing all 

launches on schedule can be computed as a function of 

the number of launches needed, L, and the probability 

that a single launch occurs within one launch cycle, p.

In equation form, the relationship between these variables can be expressed by the inequality: 

If it is desired that T be 0.99 or greater, the total number 

of launch cycles that must be incorporated (L + D) in 

constructing a launch schedule for a manned lunar mission would be about twice, or more, the number of 

launches needed (L). (See Table C-1.) 

There are two additional constraints on D. One expresses 

the requirement that L + D not exceed B, or L + D <= B. 

The results displayed in Table C-1 indicate that planning 

to launch enough hydrogen fuel to accommodate six 

months of leakage (B = 6) might be an insufficient margin if the close-derivative launchers (L = 3 or 4) considered by CBO were used to execute a manned lunar mission from the same launch pad. That margin would 

probably be sufficient, however, if most of the superT L D L + D

0.99 4 3 7

0.99 2 2 4

0.999 4 4 8

0.999 2 3 5

0.99 4 4 8

0.99 2 3 5

0.999 4 5 9

0.999 2 4 6

p = 0.85

p = 0.9

T >pL

(1-p) ( )

D i

i=0

L+i-1

i
38 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure C-2.

EELV Annual Launch Capacity and Potential Demand

(Number of launch cycles)

Source: Congressional Budget Office.

Notes: EELV = evolved expendable launch vehicle; NASA = National Aeronautics and Space Administration. 

The “Average Demand” column displays the arithmetic average of the demand projected for the period spanning 2005 through 2020 

for Department of Defense and commercial launches; the arithmetic average of the demand projected by NASA for launches of other

than manned lunar missions for the period spanning 2005 to 2012; and CBO’s estimate of the launches needed to execute manned 

lunar missions through 2020 using the pure Delta-derived alternative. The term “pure” means that both the crew carrier and the cargo 

carrier are derived from vehicles in the same family of launchers.

The “Peak Demand” column displays the maximum annual demand projected for each mission over the time periods considered.

a. A potential surge capacity of up to about 35 launch cycles is possible.

heavy launchers considered by CBO were used (L = 2, 

which excludes the Longfellow).

A second constraint on D is that consecutive launch 

cycles not conflict with other launch demand. For all 

super-heavy alternatives and the shuttle-derived close 

derivatives, the launch pads and other facilities used 

would be dedicated exclusively to launching lunar missions; therefore, conflict would not be an issue. For the 

EELV close-derivative launchers considered by CBO, 

however, conflict would be an issue because those launchers would use the same launch pads and facilities now 

used for launching Atlas and Delta EELVs. In particular, 

during years in which demand peaks for EELV launches 

that support other than manned lunar missions, existing 

capacity would be barely sufficient to accommodate the 

demand for those launches as well as the EELV launches 

needed to conduct manned lunar missions (see Figure C2). In case a single launch vehicle proved unreliable, that 

near sufficiency could put the Air Force’s desire for 

assured access at risk.4

Existing EELV

Capacity

Average Demand Peak Demand

0

5

10

15

20

25

30

35

Department of Defense

Commercial

NASA—Other Missions

NASA—Manned Lunar Missions

Using EELV Close Derivatives

a

4. The Air Force’s policy of assured access is a justification for both 

the Atlas V and Delta IV lines of launchers. In the absence of 

Vision for Space Exploration missions, either one of those lines 

has the infrastructure in place to meet (or, in 2012, to nearly 

meet) the Air Force’s launch demands to place payloads of up to 

about 20 metric tons in orbit. Peak demands are taken from an 

Air Force manifest of projected launch demand through 2020. 

However, the recent flight history of the EELV program suggests 

that actual flights may be significantly lower than projections.
APPENDIX

D

Schematic Depictions of Launch Vehicle

Derivatives and Their Antecedents

The figures in this appendix—which, within a given 

figure, are drawn to scale—depict the crew and cargo 

launch vehicles considered by the Congressional Budget 

Office under various alternatives. Their antecedent 

launch systems are also included.
40 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure D-1.

Proposed Modifications to Generate the Shuttle Close Derivatives

Source: Congressional Budget Office based on information provided by Boeing, Lockheed Martin, and ATK Thiokol. 

Note: ET = external tank; SRB = solid rocket booster; SSMEs = space shuttle main engines.

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment SRBs attached to the ET (the third stick).

b. Modifications would include increasing the four-segment SRBs to five segments each, adding a new upper stage using a simplified version 

of the J-2 engine (J-2S) from Saturn V, and adding a new launch vehicle human monitoring system.

c. Modifications would include using the existing SRBs and ET, and developing a new, expendable payload carrier with three simplified 

SSMEs.

Current Shuttle Configuration

Crew Launch

Vehicle

Cargo Launch

Vehicle

Four-Segment

SRB

Three SSMEs

ETa

Proposed NASA Vehicles

Crew Launch Vehicle

Five-Segment

Stickb

Side-Mountc
APPENDIX D SCHEMATIC DEPICTIONS OF LAUNCH VEHICLE DERIVATIVES AND THEIR ANTECEDENTS 41

Figure D-2.

Proposed Modifications to Generate the Atlas V Close Derivatives

Source: Congressional Budget Office based on information provided by Lockheed Martin.

a. Modifications would include a new 5.4-meter first-stage booster tank and an upper-stage tank, two RD-180 engines for a booster, and four 

RL-10 engines for the upper stage. Reliability enhancements and a new launch vehicle human monitoring system would be added.

b. The Atlas V Heavy Plus would consist of a three-body version of the Atlas V Medium Plus, the same booster design, and the same upperstage design. An expanded cargo shroud would be included.

Crew Launch Vehicle Crew Launch Vehicle Cargo Launch Vehicle

Current Atlas V

500 Series

Proposed NASA Vehicles

Atlas V

Medium Plusa

Atlas V

Heavy Plusb
42 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure D-3.

Proposed Modifications to Generate the Delta IV Close Derivatives

Source: Congressional Budget Office based on information provided by Boeing.

a. Modifications would include increased redundancy and new launch vehicle human monitoring systems, but the same cores and second 

stage would be used.

b. Modifications would include increased redundancy, new launch vehicle human monitoring systems, an enhanced first stage and six 

graphite epoxy motors (GEMs), and an enhanced second stage with three RL-10 engines.

c. The Delta IV Heavy Plus would include six GEMs, the same upper stage as the Delta IV Medium Plus, and a larger payload shroud.

Proposed NASA Vehicles

Current Crew Launch Vehicles

Delta IV Heavy Delta IV Medium

Cargo Launch Vehicle

Delta IV

Heavy with

Modificationsa

Delta IV

Medium

Plusb

Delta IV

Heavy

Plusc

Crew Launch Vehicles
APPENDIX D SCHEMATIC DEPICTIONS OF LAUNCH VEHICLE DERIVATIVES AND THEIR ANTECEDENTS 43

Figure D-4.

Proposed Modifications to Generate the Shuttle-Derived Super-Heavy Launchers

Source: Congressional Budget Office based on information provided by NASA and Boeing, Lockheed Martin, and ATK Thiokol.

Note: EDS = earth departure stage; ET = external tank; SRB = solid rocket booster; and SSMEs = space shuttle main engines. 

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment SRBs attached to the ET (the third stick).

b. Modifications would include using five-segment SRBs, developing a new first stage from a modified and stretched ET, and four RS-68 

engines. A new second stage using one J-2S engine would be developed along with a new expendable payload carrier mounted above the 

new second stage. With its second stage, the Longfellow is about 393 feet high and about 15 feet taller than the super heavy.

c. Modifications would include using five-segment SRBs, developing a new first stage from a modified and stretched ET, and five SSMEs. The 

rocket would have no second stage (circular orbit requires a first burn of the EDS). A new expendable payload carrier mounted above a 

modified ET would also be developed.

Current Shuttle Configuration

Cargo Launch

Vehicle

Cargo Launch

Vehicle

Four-Segment

SRB

Three SSMEs

ETa

Proposed NASA Vehicles

Cargo Launch Vehicle

Super Heavyc Longfellowb

or
44 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Figure D-5.

Proposed Modifications to Generate the Atlas Super-Heavy Launcher

Source: Congressional Budget Office based on information provided by Lockheed Martin. 

a. Modifications to the first stage would include a new 8.4-meter central core with five RD-180 engines and four liquid rocket boosters 

(LRBs) that are similar to the Atlas V Heavy Plus’s LRBs. The second stage would include a Centaur second stage that is typical of the 

Atlas V Heavy Plus. A lengthened payload shroud would be added.

Cargo Launch Vehicle Cargo Launch Vehicle Cargo Launch Vehicle Cargo Launch Vehicle

Current Atlas V

500 Series

Proposed NASA Vehicles

Atlas V

Medium Plus

Atlas V

Heavy Plus

Atlas Super Heavya
APPENDIX D SCHEMATIC DEPICTIONS OF LAUNCH VEHICLE DERIVATIVES AND THEIR ANTECEDENTS 45

Figure D-6.

Proposed Modifications to Generate the Delta Super-Heavy Launcher

Source: Congressional Budget Office based on information provided by Boeing.

a. Modifications to the first stage would include three new 8-meter cores, each with four RS-68 engines. The second stage would consist of 

a new 8-meter stage with space shuttle main engines and a new, expanded 8-meter cargo shroud.

Cargo Launch Vehicle Cargo Launch Vehicle Cargo Launch Vehicle Cargo Launch Vehicle

Current Delta IV

Medium

Proposed NASA Vehicles

Delta IV

Medium Plus

Delta IV

Heavy Plus

Delta Super Heavya

APPENDIX

E

Cost Estimates for Alternative Launch Systems

In this study, the Congressional Budget Office 

(CBO) examined two time frames that would enable the 

National Aeronautics and Space Administration (NASA) 

to meet future space-launch needs designed to further 

both human exploration of the solar system and a return 

to the moon. Each schedule takes into account a Presidential directive issued in January 2004 that called for a 

return mission to the moon no later than 2020. Subsequent to that directive, NASA concluded that a lunar 

mission in 2018 was feasible and announced plans to 

launch two lunar missions a year from that point forward. In addition, NASA has stated publicly that the new 

launch system used for lunar missions would also be used 

to service the International Space Station (ISS). On the 

basis of information provided by NASA, CBO estimates 

that between 15 and 25 ISS support missions would be 

launched.

The first path considered by CBO would achieve the 

more ambitious goal of two lunar missions a year by 2018 

and would provide 25 ISS missions over the 2012-2016 

period. The second path assumes that the moon missions 

would not start until 2020 and that the number of ISS 

missions, starting in 2014, would total only 15. For both 

paths, CBO considered six program alternatives that 

would meet the specific mission goals. Each alternative 

would involve purchasing two types of launch vehicles—

one for transporting the crew and supporting the ISS, 

and a second, larger vehicle (called the cargo carrier) for 

lifting the rest of the lunar payload into orbit. 

This appendix details the basis for the cost estimates 

developed for each of the six program alternatives, assuming they would be implemented under the more ambitious schedule. (Tables, however, may include data for 

both schedules.) Under the more ambitious schedule, 

each alternative would call for the purchase of 29 crew 

launchers and from four to 12 cargo launchers, depending on the lift capability of each cargo launcher. Some of 

the cargo launchers represent new, larger systems that 

would be able to lift payloads weighing in excess of 

100 metric tons (mt). As a result, fewer of them would be 

required. Others are closer derivatives of existing systems 

that on a single launch lift between 40 and 77 mt into 

orbit. A description of the configuration and costs of the 

existing launchers is provided for clarity and because 

those existing systems form the basis for the estimates of 

the larger launch systems. 

CBO calculates that costs to execute the more ambitious 

schedule for each of the six alternatives would range from 

$26 billion to $38 billion. Those estimates include 

nonrecurring and recurring costs incurred over the 

2006-2017period. Nonrecurring costs include costs for 

modifying existing launch systems, designing and developing new launchers, and constructing or modifying 

launch pads for new launchers. Recurring costs include 

costs for purchasing launchers and launch services. All 

costs in this appendix are expressed in constant 2006 

dollars.

Existing Launch Systems

Delta IV and Atlas V Launchers

The Delta IV is a two-stage launch vehicle built by the 

Boeing Corporation. Boeing produces five configurations 

of the launcher to place a mix of medium or heavy payloads into space. The first stage uses a booster core powered by an RS-68 engine, and the second stage is powered 

by an RL-10 engine. Both engines burn liquid hydrogen 

and liquid oxygen to generate thrust. The payload is 

encapsulated in a fairing for protection. The four Delta 

IV configurations that launch payloads weighing up to 

13 mt into space use a single booster core that can be augmented with up to four solid rocket motors and a second 

stage that measures 4 or 5 meters in diameter. Those configurations are referred to as medium-lift launch vehicles. 
48 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

The configuration that launches payloads weighing up to 

25 mt uses three of the booster cores strapped together to 

provide greater lift and a 5-meter second stage. That configuration is called a heavy-lift launch vehicle. 

The Atlas V, built by Lockheed Martin, is also a two-stage 

launcher. Lockheed Martin currently produces several 

configurations of the launcher that can place a mix of 

payloads weighing up to 20.5 mt into space. Those configurations are called Atlas V Medium (A5M) launch 

vehicles. Another configuration, designed but not being 

built, would be able to place heavier payloads into space. 

The A5M’s first stage uses a booster core powered by an 

RD-180 engine, and the second stage is powered by one 

or two RL-10 engines. The RD-180 engine burns liquid 

oxygen and kerosene propellants to generate thrust, and 

the payload is encapsulated in a fairing for protection. All 

of the A5M configurations use a single booster core that 

can be augmented with up to five solid rocket motors and 

a second stage that measures slightly more than 3 meters 

in diameter. The configuration capable of launching 

heavier payloads would use three boosters strapped 

together to provide greater lift. 

According to CBO’s estimates, the cost to buy a mediumlift launch vehicle (defined in this appendix as a launcher 

capable of lifting fewer than about 20 mt) would be 

about $200 million: roughly $100 million to purchase 

the launcher and another $100 million to pay for launch 

services. The cost to buy a heavy-lift launch vehicle (capable of lifting about 25 mt) would total roughly $350 million: about $200 million to purchase the launcher and 

another $150 million to pay for launch services. The estimate for the medium-lift launch vehicle includes the cost 

of four solid rocket motors that would be strapped to the 

first-stage booster core. (For a breakdown of the estimates 

by cost category for each of the existing launchers, as well 

as estimates of the recurring costs for new launchers, see 

Table E-1.) 

Information provided by the Air Force in budget justification materials to the Congress served as the basis for 

CBO’s estimates. The Air Force calculates that the cost to 

buy 137 launch vehicles—125 medium and 12 heavy 

launchers—would total nearly $23 billion in 1995 dollars. After inflating that figure to 2006 dollars, CBO 

projects that the Air Force’s estimate would increase to 

$28 billion. The Air Force has indicated that its estimated 

costs are almost evenly split between launchers and 

launch services, with about $15 billion paying for the 

launchers and $13 billion paying for launch services. 

Although the Air Force budget justification materials did 

not distinguish between the heavy launcher and medium 

launcher when considering costs, CBO was able to calculate separate estimates by assuming that each heavy 

launcher would cost about twice as much as a medium 

one. The factor of two assumes that the recurring cost for 

the booster core is about the same as the cost for the second stage. Therefore, a heavy launcher consisting of three 

booster cores and one second stage (four components) 

would cost twice as much as a medium launcher consisting of one booster core and one second stage (two 

components). 

Similarly, CBO calculated the costs of placing a heavy 

launcher and a medium launcher into space. Based on 

information provided by the Air Force and Boeing, CBO 

developed a cost-estimating relationship that uses the 

weight of the launcher to determine costs for launch services. CBO concluded that launch service costs increase 

with launcher weight. Using that relationship, CBO estimates that the cost to place a heavy launcher (with a dry 

weight of about 85 mt) into space would be about 50 

percent more than the cost of placing a medium launcher 

(weighing about 50 mt).

Space Shuttle

The space shuttle is made up of three main components—an orbiter, two solid rocket boosters (SRBs), and 

an external tank (ET). The orbiter serves as the crew’s 

home in space and is powered by three space shuttle main 

engines (SSMEs) that burn liquid hydrogen and liquid 

oxygen to generate thrust. The cockpit is located in the 

forward fuselage, and the main engines are located in the 

aft fuselage. Mission payloads are carried in the midsection of the orbiter. The two SRBs are each powered by 

a solid rocket motor. The motors burn solid fuel mixed 

with oxygen and provide most of the thrust to launch the 

space shuttle. The external tank contains the propellants 

used by the three main engines on the orbiter. 

On the basis of information that NASA provided to the 

Congress in 2002 in budget justification materials, the 

cost to launch a space shuttle is about $900 million, 

assuming a launch rate of five missions per year. Unit 

costs would be higher with lower launch rates. Some 

components of the space shuttle, namely the orbiter and 

the SRB canisters, are reusable, and NASA refurbishes 

them after each launch. Although less than the cost of 
APPENDIX E COST ESTIMATES FOR ALTERNATIVE LAUNCH SYSTEMS 49

Table E-1.

Comparison of Unit Recurring Costs for Selected Launchers 

(Millions of constant 2006 dollars) 

Source: Congressional Budget Office. 

Notes: NASA = National Aeronautics and Space Administration. The estimates of recurring costs assume a purchase rate of four or five units 

per year for existing launchers and new crew launchers and a rate of two a year for the new cargo launchers. The estimate of overhead 

costs for new launchers is calculated by multiplying the launcher and launch-service costs by 30 percent. 

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment solid rocket boosters attached to the central 

external tank (the third stick).

b. Breakdowns of costs by category are not available. 

c. These launchers do not incur NASA overhead costs because they are used by the Air Force to launch military payloads into space. 

purchasing new components, the cost to refurbish the 

orbiter and SRBs is significant.

New Launch Systems

As noted earlier, this CBO study examined six alternatives for purchasing new launch systems to support missions both to the moon and to the ISS. Four alternatives 

would involve buying launchers that either are derivatives 

of or use components of the Delta IV and Atlas V launchers; two alternatives would call for purchasing launchers 

that either are derivatives of or use components of the 

space shuttle. (For a summary of costs for the six alternatives assuming the more ambitious schedule, see Table E2.) The costs vary from $26 billion to $38 billion. All the 

alternatives call for the purchase of 29 crew launchers—

25 for ISS missions and four for lunar missions. Appropriations for those purchases would start in 2010. 

Depending on the alternative, either four, eight, or 12 

cargo launchers would be purchased, starting in 2016.

The technical characteristics and costs for launchers that 

would be purchased for each alternative are provided 

below. In many cases, CBO employed cost-estimating 

relationships developed jointly by NASA and the Air 

Force that use the weight of a launcher’s components to 

estimate the cost of those components. (The costestimating relationships are contained in the NASA-Air 

Force Cost Model, or NAFCOM.)

Launcher

Delta IV Medium (D4M) 100 100 c 200

Atlas V Medium (A5M) 100 100 c 200

Delta IV Heavy (D4H) 200 150 c 350

Space Shuttle b b b 900

Delta IV Medium Plus (D4M+) 150 150 100 400

Atlas V Medium Plus (A5M+) 150 150 100 400

Delta IV Heavy with Modifications (D4H with Mods) 200 150 100 450

Five-Segment Single Sticka 200 150 100 450

Delta IV Heavy Plus (D4H+) 250 200 150 600

Atlas V Heavy Plus (A5H+) 250 200 150 600

Side-Mount 450 300 200 950

Longfellow 550 300 250 1,100

Delta Super Heavy 850 300 350 1,500

Atlas Super Heavy 600 300 300 1,200

Shuttle-Derived Super Heavy 700 300 300 1,300 96 68 96%

Hardware Overhead

Launch NASA

Services Total

Existing Launchers

Possible NASA Crew Launchers

Possible NASA Cargo Launchers
50 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Alternative 1

According to CBO’s estimates, 29 crew launchers and 

12 cargo launchers would be purchased under this alternative (see Table E-2). The cost to develop and purchase 

those launchers would total about $28 billion over the 

2006-2017 period, CBO estimates. 

CBO assumed that the crew launcher would be a variant 

of the Delta IV Medium launcher, known as the Delta IV 

Medium Plus (D4M+). The D4M+ would use the same 

first-stage booster core currently used by the Delta family 

of medium launchers with six solid-fuel rocket motors. 

The D4M+ would increase the length of the second stage 

on the medium launchers by about 20 percent, adding 

two RL-10 engines. Because the new launch system 

would be used as a crew launcher, state-of-the-art features 

would be incorporated to aid human flight. Also, more 

safety features would be added to conform with NASA’s 

standards for a manned launch.1

Allowing for about $3.5 billion in nonrecurring costs and 

roughly $12 billion in recurring costs, CBO estimates 

that the crew launcher would cost about $15 billion over 

all. The estimate of nonrecurring costs includes the 

following:

B about $1.4 billion for redesigning the current medium 

launcher to the D4M+ configuration, on the basis of 

information provided by the Delta IV contractor;

B about $1.1 billion for three test flights, using the recurring per-unit cost estimates that are discussed later 

in this appendix but increasing those estimates by 30 

percent (a factor of 1.3) consistent with NAFCOM 

methods for estimating the cost of test-flight assets;

B about $0.3 billion for modifying launch pads, based 

on information provided by the contractor on the 

nature of the needed modifications;

B about $0.8 billion for the costs of program management and systems engineering—overhead—associated 

with NASA launch activities, assuming a 30 percent 

burden rate.2

 (For all estimates, CBO assumes that 

costs would be increased by 30 percent to account for 

NASA’s overhead.)

The estimate of recurring costs of about $12 billion 

includes the cost of buying 29 D4M+ launchers, at an 

average cost of about $400 million each. As shown in 

Table E-1, the estimate of per-unit recurring costs 

includes about $150 million in launch vehicle costs, 

$150 million in launch service costs, and $100 million in 

overhead.

CBO assumed that the cargo launcher would be a variant 

of the Delta IV Heavy launcher, known as the Delta IV 

Heavy Plus (D4H+). The D4H+ would use the same 

first-stage booster cores and second stage currently featured on the Delta IV Heavy launcher but would add two 

solid-fuel rocket motors to each of the three booster cores 

and add two RL-10 engines to the second stage. Those 

changes would allow the new launch system to be used as 

a cargo launcher with a payload lift of about 40 mt. 

According to CBO’s estimates, the cargo launcher would 

cost about $12 billion—about $5 billion in nonrecurring costs and about $7 billion in recurring costs (see 

Table E-2). The estimated nonrecurring costs include the 

following:

B about $1.1 billion for redesigning the current heavylift launcher to the D4H+ configuration, on the basis 

of information provided by the Delta IV contractor;

B nearly $1.6 billion for conducting three test flights;

B about $0.3 billion for modifying the launch pads, on 

the basis of information provided by the contractor on 

the nature of the needed modifications;

B about $1 billion for “mothballing” many NASA 

launch facilities (as a result of not using Pad 39, now 

used by the space shuttle), on the basis of information 

provided by NASA; and

B about $1.2 billion for NASA overhead.

The estimate of recurring costs includes the cost of buying 12 D4H+ launchers, at an average cost of about $600 

million each (see Table E-1 for detailed information on 

the breakout of recurring costs). 

1. The safety and human aids collectively fall under NASA’s launch 

vehicle health management (LVHM) system.

2. The burden rate assumes full cost accounting and represents 

government overhead associated with the staffing and maintenance of NASA’s facilities.
APPENDIX E COST ESTIMATES FOR ALTERNATIVE LAUNCH SYSTEMS 51

Table E-2.

Summary of Costs for Space Exploration Alternatives from 2006 to 2017

(Billions of constant 2006 dollars) 

Source: Congressional Budget Office.

Note: The more ambitious schedule would involve purchasing 25 crew launchers to support the International Space Station (ISS) starting in 

2010 and purchasing cargo launchers to support two lunar missions a year starting in 2016. The less ambitious schedule would involve 

buying only 15 crew launchers for the ISS missions starting in 2012 and would delay the start of purchases for the lunar missions to 

beyond 2017. 

a. The main propulsion system for the shuttle is composed of three “sticks”: two four-segment solid rocket boosters attached to the central 

external tank (the third stick). 

Alternative

1 Crew: Delta IV Medium Plus (D4M+) 29 3.3 12.0 15.5

Cargo: Delta IV Heavy Plus (D4H+) 12 5.2 7.2 12.4

Total 8.7 19.2 27.9

2 Crew: Atlas V Medium Plus (A5M+) 29 5.3 12.0 17.4

Cargo: Atlas V Heavy Plus (A5H+) 8 4.0 4.8 8.8

Total 9.3 16.8 26.1

3 Crew: Five-Segment Sticka 29 4.8 13.5 18.3

Cargo: Side-Mount 8 4.7 7.6 12.3

Total 9.5 21.1 30.6

4 Crew: Delta IV Medium Plus (D4M+) 29 3.5 12.6 15.5

Cargo: Delta Super Heavy 4 16.7 6.0 22.7

Total 20.2 18.0 38.2

5 Crew: Atlas V Medium Plus (A5M+) 29 5.3 12.0 17.3

Cargo: Atlas Super Heavy 4 9.0 4.8 13.8

Total 14.3 16.8 31.1

6 Crew: Five-Segment Sticka 29 4.8 13.5 18.3

Cargo: Shuttle-Derived Super Heavy 4 8.9 5.2 14.1

Total 13.7 18.7 32.4

1 Crew: D4M+ 15 3.5 6.0 9.5

Cargo: D4H+ 0 5.2 0.0 5.2

Total 8.7 6.0 14.7

2 Crew: A5M+ 15 5.3 6.0 11.3

Cargo: A5H+ 0 4.0 0.0 4.0

Total 9.3 6.0 15.3

3 Crew: Five-Segment Stick 15 4.8 6.8 11.6

Cargo: Side-Mount 0 4.7 0 4.7

Total 9.5 6.8 16.3

4 Crew: D4M+ 15 3.5 6.0 9.5

Cargo: Delta Super Heavy 0 16.7 0.0 16.7

Total 20.2 6.0 26.2

5 Crew: A5M+ 15 5.3 6.0 11.3

Cargo: Atlas Super Heavy 0 9.0 0.0 9.0

Total 14.3 6.0 20.3

6 Crew: Five-Segment Stick 15 4.8 6.8 11.6

Cargo: Shuttle-Derived Super Heavy 0 8.9 0.0 8.9

Total 13.7 6.8 20.5 96 68 96%

Costs

More Ambitious Schedule

Set of Launchers

Less Ambitious Schedule

Purchase Quantity One-Time Recurring Total
52 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

Alternative 2

Under this alternative, 29 crew launchers and eight cargo 

launchers would be purchased, CBO estimates (see 

Table E-2). The cost to develop and purchase those 

launchers would total about $26 billion over the 2006- 

2017 period, CBO estimates.

CBO assumed that the crew launcher would be a variant 

of the Atlas V Medium launcher, known as the Atlas V 

Medium Plus (A5M+). The A5M+ would feature a redesign of the first-stage booster core and second stage currently used on the Atlas family of medium launchers. The 

width of those stages would increase from just over 4 

meters to slightly more than 5 meters, but the length of 

the booster core would decrease by about one-third. The 

first stage would be powered by two RD-180 engines, 

and the second stage would be powered by four RL-10 

engines. Because the new launch system would be used as 

a crew launcher, state-of-the-art features would be added 

to aid in human flight, and more safety features would be 

added to conform with NASA’s standards for manned 

launch. 

According to CBO’s estimates, the crew launcher would 

cost about $17 billion—roughly $5 billion in nonrecurring costs and about $12 billion in recurring costs (see 

Table E-2). The estimate of nonrecurring costs includes 

the following:

B about $2.2 billion for redesigning the current medium 

launcher to the A5M+ configuration, based on information from the Atlas V contractor;

B about $1.1 billion for conducting three test flights;

B about $0.3 billion for modifying launch pads;

B about $0.5 billion for equipping U.S. companies to 

manufacture all of the components of the Russian 

RD-180 engine; and

B about $1.2 billion for NASA overhead.

The estimate of recurring costs (about $12 billion) 

includes the cost of buying 29 A5M+ launchers, at an 

average price of about $400 million each, the same as the 

overall unit cost of the D4M+.

CBO assumed that the cargo launcher would be a variant 

of the Atlas V Medium launcher, known as the Atlas V 

Heavy Plus (A5H+). The A5H+ would use the same firststage booster cores and second stage as the A5M+ crew 

launcher but would strap together three boosters in a 

manner similar to that used for the Delta IV Heavy 

launcher. Also, two RL-10 engines would be added to the 

second stage, bringing the total number of engines on the 

second stage to six. Those changes would allow the new 

launch system to be used as a cargo launcher with a payload lift of about 74 mt. 

CBO estimates that the cargo launcher would cost about 

$9 billion—about $4 billion in nonrecurring costs and 

nearly $5 billion in recurring costs. The estimate of nonrecurring costs includes the following:

B about $0.2 billion to transition the A5M+ design to 

the A5H+ configuration, on the basis of information 

from the contractor regarding the needed redesign of 

the A5H+;

B about $1.6 billion for conducting three test flights;

B about $0.3 billion for modifying launch pads, on the 

basis of information provided by the contractor on the 

nature of the needed modifications;

B about $1 billion for deactivating NASA launch facilities; and

B about $0.9 billion for NASA overhead.

The estimate of recurring costs (about $5 billion) 

includes the cost of buying eight cargo launchers, at an 

average cost of about $600 million for each A5H+ (see 

Table E-1). 

Alternative 3

CBO estimates that 29 crew launchers and eight cargo 

launchers would be purchased under this alternative. The 

cost to develop and purchase those launchers would total 

about $31 billion over the 2006-2017 period, CBO 

estimates. 

CBO assumed that the crew launcher would use a variant 

of the space shuttle’s solid rocket booster, known as the 

five-segment single stick. The five-segment single stick 

would be a two-stage launch vehicle. The first stage 

would be comparable to the SRBs used on the space shuttle, except it would add an extra segment of solid fuel to 

increase lift capability. A second stage would be added to 
APPENDIX E COST ESTIMATES FOR ALTERNATIVE LAUNCH SYSTEMS 53

further increase lift capability. The second stage would be 

powered by a variant of the J-2S engine. 

According to CBO’s estimates, the crew launcher would 

cost about $18 billion—nearly $5 billion in nonrecurring costs and over $13 billion in recurring costs (see 

Table E-2). The estimate of nonrecurring costs includes 

the following:

B about $0.8 billion for redesigning the first-stage solid 

rocket boosters, based on NAFCOM estimates;

B about $2 billion for designing a second stage and 

the associated shroud, based on information from 

NAFCOM;

B about $1.3 billion for conducting three test flights; 

and

B about $1.1 billion for NASA overhead.

The estimate of recurring costs (more than $13 billion) 

includes the cost of buying 29 five-segment, single-stick 

launchers, at an average price of about $450 million each. 

CBO assumed that the cargo launcher would be a variant 

of the space shuttle, known as the Side-Mount. The SideMount would consist of three main components—two 

SRBs, an external tank, and a payload carrier. This variant would be most similar to the space shuttle, minus the 

orbiter and with a payload carrier replacing it. The payload carrier would be powered by three space shuttle 

engines that burn liquid hydrogen and liquid oxygen to 

generate thrust. The two SRBs would be identical to 

those used on the space shuttle, and each would be powered by a solid rocket motor. The external tank would 

contain the propellants used by the three main engines on 

the payload carrier. The payload carrier would be positioned on the side of the external tank.

CBO estimates that the cargo launcher would cost over 

$12 billion—nearly $5 billion in nonrecurring costs and 

nearly $8 billion in recurring costs. The estimate of nonrecurring costs includes the following:

B about $0.1 billion for redesigning the solid rocket 

boosters and external tank to allow them to interface 

with the payload carrier, on the basis of NAFCOM 

estimates;

B about $0.9 million to design the payload carrier, on 

the basis of NAFCOM estimates;

B about $2.6 billion for conducting three test flights; 

and

B about $1.1 billion for NASA overhead.

The overall cost of each Side-Mount launcher would total 

about $950 million, CBO estimates—about the same as 

the cost for each space shuttle. The cost for buying eight 

of the launchers would total nearly $8 billion, CBO 

estimates.

Alternative 4

According to CBO’s estimates, 29 crew launchers and 

four cargo launchers would be purchased under this alternative (see Table E-2). The cost to develop and purchase 

those launchers would total about $38 billion over the 

2006-2017 period, CBO projects. 

CBO assumed that the crew launcher would be the 

D4M+, the same launcher that would be used under 

Alternative 1. As mentioned earlier, CBO estimates that 

the nonrecurring costs would total about $3.5 billion and 

the recurring cost for buying 29 D4M+ launchers would 

total about $12 billion.

CBO assumed that the cargo launcher would use components of the Delta IV Heavy launcher but would represent a new design with much greater lift capability. The 

D4 super heavy would feature redesigned versions of the 

booster cores and second stage currently used on the 

Delta heavy launcher, allowing the super heavy to be used 

as a cargo carrier with a payload lift of nearly 150 metric 

tons—almost six times the lift capacity of the Delta IV 

Heavy launcher. The length of the boosters would 

increase by 50 percent and the width would increase by 

60 percent, resulting in a mass increase of about 150 percent. Like the Delta IV Heavy launcher, each D4 super 

heavy would use three booster cores strapped together, 

but each booster would be powered by four RS-68 

engines, an increase of three engines per core over the 

current Delta IV cores. The length of the second stage 

would increase by 100 percent, and the width would 

increase by 60 percent, resulting in a mass increase of 

about 220 percent. The second stage would be powered 

by one SSME that would be modified from its current 

configuration on the space shuttle.
54 ALTERNATIVES FOR FUTURE U.S. SPACE-LAUNCH CAPABILITIES

The cargo launcher would cost about $23 billion—about 

$17 billion in nonrecurring costs and about $6 billion in 

recurring costs, CBO estimates (see Table E-2). The estimate of nonrecurring costs includes the following:

B about $3.6 billion for redesigning the Delta IV Heavy 

launcher to the D4 super-heavy configuration, on the 

basis of information from the Delta IV contractor;

B about $4.3 billion for conducting three test flights;

B about $5 billion for modifying launch pads, on the 

basis of information provided by the contractor on the 

nature of the needed modifications to Pad 39; and

B about $3.9 billion for overhead.

The estimate of recurring costs of about $6 billion 

includes the cost of buying four of the cargo launchers, 

an average cost of about $1.5 billion for each launcher 

(see Table E-1 for detailed information on the breakout 

of the recurring costs). 

Alternative 5

CBO assumed that 29 crew launchers and four cargo 

launchers would be purchased under this alternative. The 

cost to develop and purchase the launchers, according to 

CBO’s estimates, would total about $31 billion over the 

2006-2017 period. 

CBO further assumed that the crew launcher would be a 

variant of the Atlas V Medium launcher, known as the 

A5M+—the same crew launcher considered under Alternative 2. As stated earlier, CBO estimates that the nonrecurring costs would total over $5 billion and that the 

recurring costs for buying 29 of those launchers would 

total about $12 billion. 

Under this scenario, CBO assumed that the cargo 

launcher would use components of the A5H+—the cargo 

launcher considered under Alternative 2—but, known as 

the A5 super heavy, it would have much greater lift capability. The A5 super heavy would use the same type of 

boosters as those featured on the A5H+ but would strap 

four of the boosters into a cluster. Each booster would be 

powered by two RD-180 engines. In the center of that 

cluster would be a fifth booster, slightly longer and wider 

than the other four boosters and powered by five RD-180 

engines. Thus, the first stage would be powered by a total 

of 13 RD-180 engines. (The second stage of the A5 super 

heavy would correspond to that of the A5H+.) Those 

changes would allow the vehicle to be used as a cargo carrier with a payload lift of about 134 mt. 

CBO estimates that the cargo launcher would cost nearly 

$14 billion—about $9 billion in nonrecurring costs and 

nearly $5 billion in recurring costs. The estimate of nonrecurring costs includes the following:

B about $1.4 billion to transition the A5H+ design to 

the A5 super-heavy configuration, based on information provided by the contractor about the design of 

the A5 super heavy;

B about $3.3 billion for conducting three test flights;

B about $1.2 billion for modifying the launch pads, 

based on information provided by the contractor and 

NASA analysts;

B about $1 billion for mothballing NASA launch facilities; and

B about $2.1 billion for NASA overhead.

The estimate of recurring costs of over $5 billion includes 

the cost of buying four cargo launches at an average of 

about $1.2 billion each—about twice the per-unit cost of 

an A5H+ launch.

Alternative 6

As with all the alternatives considered under the more 

ambitious schedule, CBO estimates that 29 crew launchers would be purchased under this scenario; four cargo 

launchers would be required (see Table E-2). The cost to 

develop and purchase those 33 launch vehicles would 

total about $32 billion over the 2006-2017 period, 

according to CBO’s projections. 

CBO assumed that the crew launcher would be the 

five-segment single stick, the same vehicle considered 

under Alternative 3. As discussed earlier, CBO estimates 

that the cost of this launcher would total about $18 billion—about $5 billion in nonrecurring costs and over 

$13 billion in recurring costs. 

CBO assumed that the cargo launcher would use components of the space shuttle but have much greater lift 

capability. The Shuttle-derived super heavy would be a 

one-stage launch vehicle consisting of three main compo-
APPENDIX E COST ESTIMATES FOR ALTERNATIVE LAUNCH SYSTEMS 55

nents—two SRBs, an external tank, and a payload carrier. 

The two rocket boosters and the external tank would be 

strapped together to form the first stage. The rocket 

boosters would be identical to the booster used on the 

five-segment single-stick launcher. The external tank 

would be comparable to the tank used on the space shuttle and it would be powered by five SSMEs. Because 

those engines burn liquid hydrogen and liquid oxygen to 

generate thrust, placing five of them on the cargo 

launcher would provide lift capability of about 125 mt. 

The payload carrier would be positioned on top of the 

external tank.

The cargo launcher would cost about $14 billion, consisting of about $9 billion in nonrecurring costs and 

about $5 billion in recurring costs, according to CBO’s 

estimates (see Table E-2). The projection of nonrecurring 

costs includes the following:

B about $1.1 billion for designing the external tank, on 

the basis of NAFCOM estimates;

B about $0.5 billion for designing the payload carrier, 

on the basis of NAFCOM estimates;

B about $3.5 billion for conducting three test flights;

B about $1.5 billion for modifying launch pads, on the 

basis of information provided by contractors about the 

nature of the needed modifications; and

B about $2 billion for NASA overhead.

The estimate of recurring costs of about $5 billion 

includes the cost of buying four cargo launchers, at an 

average of about $1.3 billion apiece (see Table E-1).