Space Propulsion Synergy Team

A Guide for the Design of Highly Reusable Space Transportation

August 29, 1997

Final Report

**Abstract**

A Guide for the Design of Highly Reusable Space Transportation was
developed to provide designers and decision makers a means for focusing
key factors and relationships so that the resulting product is highly
reusable, very responsive, safe, dependable, operable, reasonable in
acquisition costs, and definitely affordable. The intent is to aid in
strategic decision making. The guide deals with the many variables that
go into providing an affordable, highly reusable Space Transportation
System and brings an order of priority for improvement to each along
with a descriptive understanding of each factor. These factors are
called design and program features and benchmarks are provided where
possible from existing systems. The desirable features have been
developed from a combination of lessons learned in Shuttle, a bench
marking approach, previous studies, a rigorous top-down methodology, and
the experience and insights of team members. The consideration of these
actual design features is important in broad architectural studies to
produce operability and acceptable recurring costs when operating a
reusable space transportation system.

Contents

+----------------------------------------------------------------+-----+
| Introduction                                                   | 1   |
|                                                                |     |
| Critical Information for Decision Making                       | 4   |
|                                                                |     |
| Beyond QFD - Key Questions for Decision Making                 | 11  |
|                                                                |     |
| Margin Considerations                                          | 13  |
|                                                                |     |
| About This Guide - A Brief Description                         | 16  |
|                                                                |     |
| Document Format Description                                    | 18  |
|                                                                |     |
| Figures 1, 2 and 3: Prioritized Measurable Criteria - Design   | 19  |
| Features                                                       |     |
|                                                                | 22  |
| Guide - Part I - Design Features                               |     |
|                                                                | 22  |
| > \(1\) Number of toxic fluids (reduce):                       |     |
| >                                                              | 25  |
| > \(2\) System margin (increase):                              |     |
| >                                                              | 27  |
| > \(3\) Number of systems with BIT / BITE (increase):          |     |
| >                                                              | 30  |
| > \(4\) Number of confined spaces on vehicles (reduce):        |     |
| >                                                              | 32  |
| > \(5\) Number of hours for turnaround between launches        |     |
| > (reduce):                                                    | 34  |
| >                                                              |     |
| > \(6\) Number of different propulsion systems (reduce):       | 36  |
| >                                                              |     |
| > \(7\) Number of unique stages, flight and ground (reduce):   | 37  |
| >                                                              |     |
| > \(8\) Number of active ground systems required for servicing | 39  |
| > (reduce):                                                    |     |
| >                                                              | 41  |
| > \(9\) Number of purges required (reduce):                    |     |
| >                                                              | 44  |
| > \(10\) Number of components with demonstrated high           |     |
| > reliability (increase):                                      | 48  |
| >                                                              |     |
| > \(11\) Number of potential leakage / connection sources      | 49  |
| > (reduce):                                                    |     |
| >                                                              | 52  |
| > \(12\) Number of active systems to maintain a safe vehicle   |     |
| > (reduce):                                                    | 55  |
| >                                                              |     |
| > \(13\) Percent (%) of propulsion system automated            | 57  |
| > (increase):                                                  |     |
| >                                                              | 58  |
| > \(14\) Number of hands on activities required (reduce):      |     |
| >                                                              | 60  |
| > \(15\) Number of active components required to function      |     |
| > including flight ops (reduce):                               | 62  |
| >                                                              |     |
| > \(16\) Technology Readiness Level (TRL) (increase):          | 63  |
| >                                                              |     |
| > \(17\) Number of different fluids (reduce):                  | 65  |
| >                                                              |     |
| > \(18\) Mass fraction required (reduce):                      | 67  |
| >                                                              |     |
| > \(19\) Number of systems requiring monitoring due to hazards | 68  |
| > (reduce):                                                    |     |
| >                                                              | 69  |
| > \(20\) Number of parts (different, backup, complex)          |     |
| > (reduce):                                                    | 71  |
| >                                                              |     |
| > \(21\) Number of expendables (fluid, parts, software)        | 72  |
| > (reduce):                                                    |     |
| >                                                              | 74  |
| > \(22\) Number of checkouts required (reduce):                |     |
| >                                                              | 76  |
| > \(23\) Number of pollutive or toxic materials (reduce):      |     |
| >                                                              | 78  |
| > \(24\) Number of inspection points (reduce):                 |     |
| >                                                              | 79  |
| > \(25\) Number of propulsion sub-systems with fault tolerance |     |
| > (increase):                                                  |     |
| >                                                              |     |
| > \(26\) Number of engines (reduce):                           |     |
| >                                                              |     |
| > \(27\) Average Isp on the reference trajectory (increase):   |     |
| >                                                              |     |
| > \(28\) Number of manhours (c/o, handle, assemble, etc) on    |     |
| > sys. between LCF/HCF (reduce):                               |     |
| >                                                              |     |
| > \(29\) Number of criticality 1 failure modes (reduce):       |     |
| >                                                              |     |
| > Design Features (30 through 64)                              |     |
+================================================================+=====+
+----------------------------------------------------------------+-----+

Contents

> Continued

+----------------------------------------------------------------+-----+
| Figure 4: Prioritized Measurable Criteria - Programmatic       | 84  |
|                                                                |     |
| Guide - Part II - Programmatic Considerations                  | 85  |
|                                                                |     |
| Summary and Conclusions                                        | 93  |
|                                                                |     |
| Further Information                                            | 95  |
|                                                                |     |
| Background of the SPST                                         | 96  |
|                                                                |     |
| Overview of the SPST Approach                                  | 99  |
|                                                                |     |
| What is QFD?                                                   | 100 |
|                                                                |     |
| Verifying Functional Requirements - Performance                | 102 |
|                                                                |     |
| Notes and References                                           | 103 |
|                                                                |     |
| Acknowledgments                                                | 105 |
|                                                                |     |
| Acronyms and Abbreviations                                     | 106 |
+================================================================+=====+
+----------------------------------------------------------------+-----+

Introduction

About the Design and Programmatic Features, and the SPST

Customer demands for future space transportation systems include much
greater affordability, responsiveness, dependability and dramatically
lower life cycle costs including acquisition costs and research and
development costs and risks. The purpose of this "Guide" is to provide a
prioritized, high level set of design and programmatic features against
which future space transportation systems may be evaluated to determine
their degree of improvement over current systems and their ability to
satisfy these customer demands. The guide may be used by a concept
developer, a program manager, a technology developer or by designers at
a total vehicle architecture level.

This guide was developed by the Space Propulsion Synergy Team (SPST) as
part of its support to the Highly Reusable Space Transportation (HRST)
project activities. The Space Propulsion Synergy Team (SPST) is a broad
based group of diverse individuals from NASA, industry and academia,
which has addressed in past and current efforts the direction of future
space transportation systems and technology. The involvement of key
backgrounds and areas of insight in the SPST has been an integral part
of understanding and prioritizing areas for improvement.

During the past several years that the SPST, previously identified as
the SPSG, has been active, they have developed and applied an effective
process for comparative assessment of candidate space transportation
systems and technologies. The process utilizes the strengths inherent in
a team with diversified backgrounds and expertise; and the basic
principles of a highly credible approach known as Quality Function
Deployment (QFD). This approach assures that there is a direct link
between the space transportation system capability and
characteristics/attributes, and those required by the "customer".

Most important, this approach also includes the development and
definition of "measurable criteria" to be utilized in assessing the
degree to which a system concept or a technology enhances the system
characteristics/attributes desired by the customer. These "measurable
criteria" are presented in this guide and constitute the principle aid
in the definition and design of an HRST or any advanced space
transportation system.

However, it was realized that the system concept with the most
attractive attributes and hence the greatest long term payoffs can lose
support when programmatic constraints are tight. National space
policies, international agreements, schedule, budget, availability and
maturity of technology are a few of the examples of these "programmatic
constraints". Therefore, the SPSG devised a dual assessment and
prioritization system that balances these two driving forces. A graphic
visualization of the process is shown below. This approach enables
decision makers to make decisions based on knowledge of both the long
term strategic payoffs, "desired attributes" and the individual projects
"programmatic constraints". The later are subject to short term changes,
but once the long term strategic payoffs, "desired attributes" are
established, they remain quite stable.

![](media/image1.emf){width="5.490277777777778in" height="4.30625in"}

The stability of the "desired attributes" or long term benefits, in a
transportation system has been thoroughly demonstrated over the past
several years by the SPST and other organizations/groups. The SPST
(SPSG) has developed and prioritized the desired attributes in a space
transportation system several times, each time with a different group of
individuals with consistent results.

Also, these sessions were in support of several different advanced space
transportation programs. They included a follow-on exercise for the
Access to Space studies and support of the RLV project definition and
technology plan. Both of these activities utilized the process
previously developed and exercised by the SPSG. The definition and
prioritization of the required system attributes that resulted from each
of these exercises were very consistent with those previously developed
and were also consistent with those recently formulated for the HRST.

There have been other activities using the same basic process, notably
several initiated by the USAF, but including industry and NASA
participation. These activities also resulted in the identification and
prioritization of required/desired space transportation system
"attributes" that were very similar to those presented in this guide.

This dual prioritization approach is addressed in further detail in the
next section of this report as are the definitions of the programmatic
constraints.

Although the focus of the information provided in this guide has been
within the context of the Highly Reusable Space Transportation (HRST)
project, the applicability is to any future reusable systems seeking to
improve over a current system such as Shuttle.

The features or criteria around which this guide is organized must be
considered as a whole. If a future space transportation system improves
or not on any one particular feature is not as important in determining
merit as whether it improves or not on the majority of the significant
features. A full understanding of future systems in regards to this
guide is considered crucial to understanding a sense of direction for
improvement as well as an understanding of the relative merits of
systems competing for further development, acquisition and eventually
operation.

Critical Information for Decision Making

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In determining what information and data is most crucial to the
decisions involved in defining, designing, and providing a market driven
HRST system for the future we need to first identify that market, the
customers, and clearly understand what they want in, and demand of, a
space transportation system. However, in addition to the "customers" who
will eventually pay for the services of a space transportation system,
there are several other organizations / individuals who will be major
players or "stakeholders" who must be fully considered and satisfied if
a proposed space transportation system enterprise is to be successfully
marketed and profitably operated. Including the paying customers, the
stakeholders are:

1.  [The]{.underline} [financial investor]{.underline} who will provide
    the capital for the development, acquisition and initial operation
    of the transportation system. He will demand a reasonable return on
    investment. It is possible that the investment may be divided into
    these two parts:

-   Capital for the design, development, and marketing of the
    [transportation vehicles]{.underline} to be utilized in the
    operation of a space transportation system, for example a "United
    Spacelines".

-   Capital for the operator to acquire vehicles, facilities, and
    support infrastructure to start operations of a "United Spacelines."

1.  [The User or]{.underline} [Payload]{.underline}
    [Customer]{.underline} who will pay the operator for the
    transportation services of cargo and personnel in space.

2.  [The Developer and Producer]{.underline} of the space transportation
    vehicle which will be procured and utilized in the operation of a
    space transportation system. This includes the critical selection of
    the vehicle concepts which best satisfies all of the transportation
    system desired attributes and the design, development,
    certification, and production of the vehicle.

3.  [The Transportation System Operator]{.underline} of a "United
    Spacelines" who will acquire, establish and operate the
    transportation system as a profitable, business enterprise. This
    transportation system operator is a customer of the vehicle
    developer and producer.

4.  

5.  [The federal, state and local governments]{.underline} representing
    the general public, each play several important roles which must be
    addressed by both the system developer and operator.

-   The role to be played by the [federal government]{.underline} is
    still evolving; but it is expected to be patterned after the role
    the federal government has developed with the airline transportation
    industry. The major elements are:

-   National policies to foster affordable, safe, reliable space
    transportation.

-   Provide development and demonstration of advanced technologies.

-   Assure public safety which is manifested in "spaceport"
    certification, launch permits, reentry control, and eventually space
    vehicle certification.

-   Negotiate, ratify, and enforce international agreements and treaties
    of space transportation operations.

-   Environmental control - ground, air and space.

-   The state governments are interested in the potential economic
    benefits, development of new jobs, and the safety and environmental
    consequences of spaceport operations in their or neighboring states.
    They may be financial and political supporters or adversaries, and
    may be involved in support infrastructure, financing and development
    as needed.

-   The role of local governments, again using the model of airline
    transportation systems is expected to have the following elements:

-   Investment and operations for fees of a spaceport similar to the
    relationship of a municipal airport and airlines.

-   Tax structure and incentives.

-   Support infrastructure financing and development of roadways, power
    supply, communications, etc.

-   Motivated by economic growth.

-   Constrained by environmental and safety concerns. The general
    public, taxpayers, will be concerned with many of the issues and
    decisions involved in establishing and operating a spaceport and
    need to be brought into the decision process as early as possible.

The purpose of outlining the major organizations and the role they will
play in establishing and operating an HRST system of the future is to
help the reader understand how and why this design guide was developed
and how it may be helpful to designers and decision makers.

In developing this "Guide for the Design of HRST Systems" the "paying
customer" and each of the other four stakeholders needs and demands were
considered as requirements to be satisfied in the best manner possible.
Particularly, the Commercial Space Transportation Study^8^ has recently
examined potential markets and associated needs to spur these markets.
In the process used to accomplish this, the SPST divided the overall
requirements into three categories:

-   [Functional performance]{.underline} of the transportation system
    such as capability in terms of payload or destination.

-   [Desired attributes]{.underline} of the transportation system
    (essentially demands of the customers) such as safety,
    affordability, dependability, or flexibility.

-   [Programmatic constraints]{.underline} of the transportation system
    such as cost, schedule, or risks associated with the design,
    development and implementation of the system including
    infrastructure.

The following chart focused on affordability shows the relationship of
these categories and places them in two groups. The one group (desired
attributes & functional performance) is described here as *recurring
cost* or operational effectiveness and the other group (programmatic
constraints) is described as *non-recurring cost* or programmatics. This
group is further broken down into program acquisition (commitment) and
technology R&D (long lead investment). The technology cycle is required
when the technology readiness and risk from performance and operability
goals compliance are not satisfied. Therefore, the key to achieving the
objective of space transportation systems affordability is brought about
when and only when the program acquisition criteria are properly met
(technology margins, options, readiness, and full compliance of
performance and operability goals can be achieved).

![](media/image2.emf){width="5.999305555555556in"
height="5.436111111111111in"}

[FUNCTIONAL PERFORMANCE]{.underline}

The functional performance requirements used in the QFD process were
basically those defined in the HRST project guidelines. The performance
requirement was to deliver 30,000 lbs +/- 10,000 lbs to a 100 nm, 28.5
degree inclination orbit. A candidate transportation system (HRST) must
provide credible evidence, system design and performance data to prove
that it can satisfy the functional requirements.

In order to make a reasonable assessment of the potential of a candidate
transportation system meeting the functional performance requirements
there is a critical level of conceptual design data and performance
flyout trajectory data that must be available. Since the concepts
currently being considered for HRST include several variations and
combinations of air breathing and rocket propulsion systems the design
and performance analysis data must include critical parameters
appropriate to these concepts. This data should include key aerodynamic
characteristics of the vehicle such as the lift and drag coefficients as
a function of altitude and Mach number, engine maps giving thrust and
propellant flow rate as a function of altitude, Mach number and
equivalence ratio, detailed breakout of component weights and a
description of the force accounting system. The underlying data base for
the engine maps should also be included in the data. This would include
inlet compression efficiency, inlet air capture ratio, mixing combustion
and exhaust nozzle efficiencies where applicable.

The section in this guide "Verifying Functional Requirements -
Performance" further expands on information relevant to the performance
aspects of an HRST, such as an air breather. For purposes of this guide
and the initial work of the SPST, it should be noted, however, that the
focus has been principally on the desired attributes and programmatic
constraints of future concepts.

[DESIRED ATTRIBUTES]{.underline}

In addition to meeting functional or performance requirements a
candidate space transportation system must be evaluated in accordance
with the degree to which it provides the attributes or features most
desired by customers. These were identified by the QFD process as
follows:

+------------------------------------+---------------------------------+
| **Affordable / Low Life Cycle      | **Responsive**                  |
| Cost**                             |                                 |
|                                    | > Flexible                      |
| > Low Recurring Cost               | >                               |
| >                                  | > Capacity                      |
| > Low Cost Sensitivity to Flight   | >                               |
| > Growth                           | > Operable                      |
| >                                  | >                               |
| > Operation and Support            | > Vehicle Health Management     |
| >                                  | >                               |
| > Initial Acquisition              | > Ease of Vehicle/System        |
| >                                  | > Integration                   |
| > Vehicle/System Replacement       | >                               |
|                                    | > Maintainable                  |
| **Dependable**                     | >                               |
|                                    | > Simple                        |
| > Highly Reliable                  | >                               |
| >                                  | > Launch on Demand              |
| > Intact Vehicle Recovery          | >                               |
| >                                  | > Easily Supportable            |
| > Mission Success                  | >                               |
| >                                  | > Resiliency                    |
| > Launch on Time                   |                                 |
| >                                  | **Safety**                      |
| > Robustness                       |                                 |
|                                    | > Vehicle Safety                |
| **Environmental Compatibility**    | >                               |
|                                    | > Personnel and Public Safety   |
| > Minimum Effect on Atmosphere     | >                               |
| >                                  | > Equipment and Facility Safety |
| > Minimum Impact all Sites         |                                 |
|                                    |                                 |
| **Public Support**                 |                                 |
|                                    |                                 |
| > Benefit GNP                      |                                 |
| >                                  |                                 |
| > Social Perception                |                                 |
+------------------------------------+---------------------------------+

These transportation system attributes were prioritized according to a
combination of the importance to the customer, where we are today in
space transportation, and how much we need to improve. Note that the
lower level does not mean less important. Rather, it indicates that in
view of current transportation system characteristics the need for
improvement there is not as great.

![](media/image3.emf){width="6.740277777777778in"
height="5.047916666666667in"}

*Figure A. Attributes of a Reusable Space Transportation System*

However, it is very difficult for a transportation system decision maker
or designer to respond to desired attributes, such as highly reliable,
flexible or maintainable. Therefore, the next step in the process used
to develop this guide was to identify measurable criteria that correlate
with, such as have a positive impact on, the desired system attributes.
There were many measurable criteria (64) identified. To aid the system
definition and design decision process they have been prioritized in
accordance with the degree of impact they have on the desired
attributes. These are shown in Figures 1, 2 and 3. Each of these
measurable criteria is addressed individually in this guide. Each of the
highest criteria is a design feature that significantly impacts many of
the desired attributes, particularly affordability, safety,
dependability and operability.

In other words, the incorporation of design features, particularly those
in the top 20 will have a positive impact on many of the attributes that
the customer desires in a space transportation system. This relation of
the design criteria and the desired system attributes and sub-attributes
is shown on the following page.

Each of the systems major attributes and sub-attributes on the left have
been connected to a box or boxes containing those design features which
if incorporated in the system design would have a positive, beneficial
impact on the desired attributes.

It may be noted here that the design criteria are divided into two
groups. In the first group the desired direction is to minimize (minimum
number). For example a minimum "number of potential leakage / connection
sources" will have a significant positive impact on several of the
desired system attributes. In the second group the direction is to
maximize (maximum number). For example a maximum "number of components
with demonstrated high reliability" in an HRST system will have a major
impact on affordability (operations and support) and dependability
(intact vehicle recovery, mission success and launch on time).

The highest priority (top 20) criteria, if manifest in a design with the
desirable directions of improvement, will obviously have the greatest
positive influence on the desired attributes. Therefore, [information
and data on these top 20 criteria are most critical in any decision
making process]{.underline} that will define the most marketable
transportation systems and choose among alternative design concepts.

Unfortunately, in the initial phases of the decision making process
regarding future, next generation transportation systems, only top level
information or data is traditionally available. In exercising the QFD
process using the measurable criteria (Figures 1, 2 and 3) it was found
that information on many of the top 20 criteria was not available even
from transportation system studies that had been completed. In other
words a different type of system information was required by a large
number of measurable criteria. Referring to the description of levels
shown below many of the criteria required data at Level 2 and some at
Level 3.

Level 1 - Transportation System Concept Definition. This includes a
sketch of the system and a functional description, performance analysis,
preliminary mission trajectory and weight estimates.

Level 2 - Transportation System and Subsystem Description. This includes
sub-systems configuration and functional descriptions including weight
estimates. This includes propulsion, avionics, thermal protection and
power generation definition.

Level 3 - System Preliminary Design Review. Information and data
normally included in a PDR.

To correct this situation some level 2 subsystem description and data
must be developed in the initial phases of advanced system studies. This
is necessary in order to provide the critical information required by
the top 20 criteria. This requirement needs to be communicated to the
technical community involved in advanced transportation system studies
and analysis.

Again, to assess future operational scenarios it is necessary to answer
questions for which information is not often traditionally available
before decision making processes such as funding distribution. "How
often will it fly and for how much and why?" is a question the answer to
which begins by addressing the criteria in this guide. This is not
entirely a novel conclusion:

> *Only the direct hardware driven costs, about 32 percent of the Space
> Shuttle Program Budget, were addressed by the study. Current
> operations cost accounting methods were found to be inadequate for
> accurately determining the savings from subsystem improvements. The
> NASCOM was not designed for estimating modifications to existing
> systems and there are only limited tools available for estimating
> space flight operations costs.*
>
> From the NASA Access to Space Study, Summary Report^14^
>
> OSSD, NASA HQ, January 1994

[PROGRAMMATIC CONSTRAINTS]{.underline}

The identification of the transportation system design features that
will benefit (have a positive impact on) the desired system attributes
was addressed in the previous section. The other dimension that must be
addressed in any decision making process involved in the definition and
design of an advanced space transportation system is the programmatic
constraints. These are factors such as schedule, cost, risks and
investor incentive in a given market environment. Again, in the QFD
process that has supported this guide, measurable criteria were
developed and prioritized. These are shown in Figure 4. Adequate
information on these program criteria is as critical to strategy as the
design features based on desired system attributes.

Our ability to acquire the critical information and data on schedule,
costs, technical risks and so forth met with many of the same problems
as were addressed in the previous section on desired system attributes.
The necessary data is not readily available in the initial phases of
transportation system studies and conceptual designs. It will be
necessary to proceed to Level 2 in some cases to obtain it. For example,
the number of technology breakthroughs required for successful
development of a particular concept may require definition of major
sub-systems.

It should be noted that in contrast to the stability of the desired
attributes and the related design features in this guide that the
program constraints may be expected to vary far more over shorter
periods of time for several reasons. Global or national economic change,
international competition and political scenarios may all significantly
impact program considerations. This further emphasizes the need and
value in defining the desired attributes and related measurable criteria
or design features since they are the foundation of a technical strategy
that can be expected to focus improvement efforts for the long term.

Beyond QFD - Key Questions for Decision Making

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QFD (described further in "What is QFD?") is not all inclusive in it's
ability to aid the decision making processes associated with large,
complex technical projects. Sophisticated tool sets for analysis and
modeling of future options from a technical, programmatic, performance
and market perspective are required. One such project currently in work
is called OSAMS.

**Operations Simulation and Analysis Modeling System (OSAMS)**

A Decision Support System

In order to develop a future space transportation system that achieves
cost goals in the order of \$200 per pound to low earth orbit, a
systematic method needs to be developed to assess the impacts of various
concept alternatives on cost and mission effectiveness. Specifically, an
unbiased, user-friendly \"tool\" is required to allow program managers
and developers to quickly assess the most effective areas to invest
scarce resources and evaluate the potential impacts of these investments
to the \"life-cycle\" and per mission cost of the system.

The NASA Advisory Council, in a letter dated 31 August, 1995, states
that \"Much of the cost for current launch vehicles is in the
operations, launch rate, and support. For a reusable vehicle, this has
proven to be the major driver (e.g., Shuttle). We recommend that a
reasonably detailed economic model be developed that includes all the
acquisition and operations costs; that is total life cycle cost. Such a
model would be used to evaluate contending RLV concepts. This should be
maintained by an independent studies and analysis group to help guide
future RLV decisions.\" Further the NAC adds, \"From the outset, the RLV
of the future should be designed as a operational vehicle.\"

These recent statements by the NAC are equally applicable to HRST (and
other space programs) and strongly support the development of an
independent, NASA in-house capability for operations/life cycle cost
analysis. The development of a comprehensive operations simulator for
use in the very early concept evaluation phase, as well as extensible to
later phases, would be a major step in realizing this capability. This
tool would provide program managers and developers a method of
performing analysis on all elements of life-cycle costs. It would allow
a unbiased and consistent means to evaluate competing alternative launch
and operations concepts, evaluate the impact of proposed technologies,
and provide insight into life cycle, development and operations costs.

OSAMS will provide managers and developers with the needed analytical
capability described above. OSAMS will be a powerful, flexible decision
support system that will enable managers and developers to gain insight
to HRST (or other system) concepts and variations. OSAMS will provide
this support through a computer based environment for the analysis of
systems concepts and will aid the manager/engineer in both life and
flight cycle evaluations of concepts through the use of interactive
dialogues with the system engineer. These dialogues will be conducted
through a display screen using windows and pull down menus using a
variety of input devices that include keyboard, mouse, and function
keys. Using these completed dialogues in combination with pre-defined
OSAMS components, the system engineer will be able to describe HRST
concepts through a series of documentation activities that describe
mission models, flight vehicle concepts, vehicle ground processing
concepts, payload processing concepts, and maintenance and refurbishment
concepts. Using OSAMS tools the system engineer will transform these
HRST elements into a dynamic monte carlo simulation of these combined
elements and interactions.

OSAMS will support procedures for analyzing these statistically valid
simulations in terms of life-cycle cost, and system performance.
Life-cycle cost is composed of research and development costs,
acquisition costs, operations costs, maintenance and refurbishment
costs, disposal costs, and the associated cost of system failure. System
performance measures includes both system and schedule reliability,
facility utilization, payload delivery, and market competitiveness.

OSAMS will aid HRST developers in HRST program implementation planning.
OSAMS

analytical tools will include methods for calculating return on
investment, and technical and program risk. OSAMS will also aids HRST
developers by providing automated methods of performing sensitivity
analysis on key concept and mission model parameters. OSAMS will provide
a state-of-art environment where its modeling and simulation tools can
be used individually or as a set of highly integrated tools for
evaluating system concepts, aiding in the selection of alternative
investments in technology to reduce operations and life cycle costs, and
ultimately, in improving the operability of the resulting HRST system.

Margin Considerations

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The amounts and the types of margin present in a vehicle design strongly
impact the resulting transportation architecture. Two types of margin
will be discussed; growth and technology margins used (and used up)^2^
in design and development, and margins still present in the fielded
system.

Traditionally, margin is used during the early stages of program design
and acquisition as a contingency to allow for weight growth and growth
resulting from addressing design uncertainties during development. This
type of margin should always be present with the amount being dependent
on the maturity and definition of the subsystems technology and the
overall design. For example, in the Access to Space study^14^ and the
RLV studies which followed a weight margin of 15% was used on all
subsystems, both vehicle and propulsion. The studies represented a new
architecture (SSTO) using many unproved subsystems. Since the historical
weight growth of the SSME engine was 14% and the engine had relatively
low TRLÕs at the time the design concept was frozen, the use of 15%
appears to be Òin the ballparkÓ for experimental programs but
questionable for HRST goals. All HRST design concepts should have this
kind of margin included and defined. This type of margin should be
included when trajectories are run to determine performance closure. All
architectural concepts must include these margins to allow true concept
comparisons.

The type of margin discussed above should always be present in
preliminary concept designs but is not the type of margin that will
increase the probability of reaching the HRST goals - very affordable
space transportation, because this type of margin is, historically,
always used up simply to make the design a reality. Also, note that
historically past programs were focused on performance and not
economics. Indeed, the choice of an appropriate number to use for this
margin is based on finding what margin was needed in past designs.

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  **The type of margin useful to achieving the HRST goals is margin built
  into the system, or subsystems, and not used merely to achieve the
  minimum necessary system performance. It is essentially the ability to
  operate the system, at least before using the margin to improve
  affordability, in a de-rated condition and still achieve the minimum
  required system performance.**

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The type of margin useful to achieving the HRST goals is margin built
into the system, or subsystems, and not used merely to achieve the
minimum necessary system performance. It is essentially the ability to
operate the system, at least before using the margin to improve
affordability, in a de-rated condition and still achieve the minimum
required system performance. Margin of this type is available to improve
affordability and not merely to compensate for the uncertainties of
development. This type of margin is considered in aeronautical
transportation systems but up until now has not been adopted for
aerospace transportation systems.

Four measurable criteria were identified for this type of margin: mass
fraction margin, thrust (chamber pressure) margin, average specific
impulse margin, and payload margin. Because each of these criteria
correlated against a subset of the desired attributes, none of them
individually rated very high (40/63, 44/63, 50/63, and 59/63
respectively). A single criteria measuring overall system margin was
also considered and it rated very high. There are also many other
subsystem margins that could have been considered, such as thermal
management, fluid flow or current capacity, but they would have been too
detailed in relation to the other criteria.

Mass fraction and thrust (chamber pressure) margin are directed
specifically at the vehicle and the propulsion system respectively.
Margin designed in for the mass fraction allows use of more robust
components and structures, or higher safety factors on life limiting
structure and components. This margin would also allow the use of
heavier but more developed technologies in selected applications. All of
these are reflected in planned and unplanned maintenance and life, which
in turn affects inspections, logistics, facilities, and turnaround time,
responsiveness and safety.

Thrust margin is generally related to operating rocket engines below
their maximum design limit to increase operating life. This is thought
to increase mean time between failures of the propulsion systems. For
example, the theoretical mean time between failures of the Phase 2 SSME
improves more than ten times if operated at a power level of 100%
instead of 109%^19^. The improvement is related to decreased
temperature, speed, and pressure environments within the engine and
component operation away from the structural limits used when the engine
was designed. Low cycle thermal fatigue limits are particularly
impacted. In general, de-rating an engine significantly improves its
life which allows less inspection, better predictability of failure
(unusual conditions do not push internal environments beyond design
limits), and less maintenance. All of which lower logistic and facility
requirements and improve turnaround time. The cost of including a thrust
margin is an essentially linear reduction in engine thrust / weight.
Also in the area of the rocket engine start transition, the stresses
traditionally exceed the steady-state conditions resulting in large
operating life reductions and requirements for inspection and
maintenance. Margin must be included here to cover transition by
providing a softer start capability. For systems where performance is
the main goal or where the mission is barely possible with expected
engine weight, thrust margin may be a luxury; but for systems where
operating cost is the main goal, thrust margin may instead be a
necessity.

The criteria on average specific impulse margin is traditionally treated
as essentially a technology uncertainty margin. It is aimed at those
systems where a high specific impulse is predicted and is critical to
the design, where there is a tight coupling between details of vehicle
geometry and engine performance. Thus, this margin is more like the
margins discussed at the beginning of this section which should be
present in the preliminary design. The amount of margin should probably
be varied depending on the degree of database available for the vehicle
/ propulsion system being studied. To the degree that the specific
impulse margin is not consumed during development, it acts the same as a
payload margin and could be used to avoid operations such as abort
options like RTLS and TAL or other operations which increase
infrastructure and add considerable operating cost.

The last of the four margins considered is a payload margin. This is
essentially an overall system margin which can be traded to all
subsystems if necessary. To strongly affect affordability, this margin
must be maintained and not simply used as a weight growth margin during
development. Besides allowing propulsion subsystem de-rating (i.e.,
lower thrust for the nominal payload), payload margin is usable after
the system is developed for system additions targeted specifically to
improve operations based on operating experience (without this margin
this is not possible while still meeting the nominal payload).
Additionally, payload margin produces the flexibility to respond to new
demands and commercial opportunities.

In summary, any system with margins over and above the development
margins will be more operable than one without margins because of
subsystem operation at reduced design environments. This will in turn
lower maintenance, logistics, and facilities requirements, while
allowing targeted system additions to address remaining or newly
discovered operability problems while still performing the required
mission. The payload margin will provide flexibility to new business.
The specific impulse margin will reduce operational infrastructure
required for safe operation. These are the characteristics which produce
affordable space transportation systems.

About This Guide - A Brief Description

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The guidance contained in this document can be categorized as "design
features" or "program features". The design features are those which
bear directly on the technical aspects of a concept. Program features
relate to the management focus that brings about the implementation of
the concept.

-   Design Features: These are measurable criteria. A number may be
    assigned to these for current systems. For future systems a target
    may be set which is then the "design target". The more improvement
    is made in each criteria the greater the correlation to meeting more
    vague, qualitative goals such as affordability of operation or high
    flight rate. These capture the recurring aspects of reusable space
    transportation systems.

-   Program Features: These are measurable criteria. In general these
    present more of a challenge to baseline or set new targets for.
    These capture the non-recurring aspects of a reusable space
    transportation system.

Major characteristics of the guidelines are:

[Prioritized:]{.underline}

The first 29 of the design features and the first 9 program features
correlate very strongly to effectiveness and efficiency respectively.
Effectiveness refers to results such as being low cost to buy and
operate. Efficiency refers to how much was spent in time or money to get
to that final product. The higher the rank (1, 2, 3, ...) the more
strongly the features correlate to qualitative "wants" such as low life
cycle cost which includes low cost to develop, manufacture, buy and
operate.

[Numeric:]{.underline}

Numbers exist for where we are in many areas. Hence numbers may be
assigned for how much we wish to improve.

[Directional:]{.underline}

A sense of direction can result from assessing a future concept against
these features. Relative merit can be assessed among multiple concepts.
Assessing a set of design variables against these features will not
result in quantitative life cycle cost estimates, schedule timelines or
dollars per pound to orbit. The intent here is to assist in determining
strategic directions for improvement which may then be more
quantitatively assessed by implementing more detailed analysis, methods
or models. This communication of practical engineering information can
aid in focusing more formal requirements (Blair and Ryan 1992)^6^.

More detailed subsystem understanding and iteration on the implemented
results of QFD's, based on lessons learned, technology demonstration and
product experience, are required to fully exploit the QFD method. In
this way quality, meeting customer demands and growing markets, is built
into the technology across many levels. From this approach, detailed
relationships between features and costs in space transportation systems
can eventually mature.

Document Format Description

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-   The format that follows for each of the **design features** is:

+--------------------------+-------------------------------------------+
| \(#\) Number of          | States the design feature. Most of the    |
| [.]{.underline}          | measurable criteria can be directly       |
|                          | manifested in a design. For a minority of |
|                          | the measurable criteria the feature is    |
|                          | not directly a technical aspect of a      |
|                          | system but rather relates to areas        |
|                          | requiring emphasis.                       |
+--------------------------+-------------------------------------------+
| Shuttle Benchmark:       | An estimate for the Shuttle program.      |
| [.]{.underline}          |                                           |
+--------------------------+-------------------------------------------+
| Derivation:              | A brief description of the current        |
|                          | situation and definition.                 |
+--------------------------+-------------------------------------------+
| Level: 1, 2 or 3.        | For a new concept a number for comparison |
|                          | relative to Shuttle may not be available  |
|                          | until further definition is worked.       |
|                          | Decision makers must try and make as many |
|                          | of the criteria as possible into          |
|                          | information that is available early on in |
|                          | any decision making process. Ideally, all |
|                          | the criteria contained here would be      |
|                          | "Level 1" information.                    |
|                          |                                           |
|                          | 1 - Usually available early in the        |
|                          | concept development and evaluation.       |
|                          |                                           |
|                          | 2 - Available as the concept becomes more |
|                          | defined.                                  |
|                          |                                           |
|                          | 3 - More detailed information that is     |
|                          | available as the design matures to a      |
|                          | preliminary design phase.                 |
+--------------------------+-------------------------------------------+
| Visions of Improvement:  | A description of how to improve on the    |
|                          | criteria, what makes the criteria worse   |
|                          | and other considerations.                 |
+--------------------------+-------------------------------------------+
| Target for Improvement   | How the feature can be targeted or        |
|                          | interpreted for improvement.              |
+--------------------------+-------------------------------------------+

-   The format that follows for each of the **programmatic features**
    is:

  --------------------------- -------------------------------------------
  Program Feature             Definition / clarification.

  --------------------------- -------------------------------------------

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\(1\) Number of toxic fluids (reduce):

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**Shuttle Benchmark**: 10 (majors only)

**Derivation:**

This criteria includes toxic fluids for both flight and ground
operations. The number of different toxic fluids used in a space
transportation system relates very strongly to recurring costs, such as
operation of the system, and hence to life cycle cost and overall
affordability. The correlation is also very strong to initial
acquisition, the ability to launch on time, the degree of supportability
and personnel and public safety. Public environmental concerns are also
affected. Reductions in the number of different toxic fluids improves
significantly in all these prior areas.

For Shuttle the major toxic fluids include:

-   Hypergols (N2O4 and MMH) for OMS/RCS as well as hydrazine (N2H4) for
    auxiliary power units (APU's).

-   Hydraulic fluid for the actuation of aero-surfaces, landing gear and
    valves.

-   Waterproofing agents (DMES) for tile thermal protection systems.

-   Freons (3 types): R-21 for thermal management on board the vehicle
    (indirect and direct cooling of avionics, crew cabin, and fuel cells
    and warming/cooling of hydraulics on orbit); R-114 in the orbiter
    payload coolant loop as well as the ground coolant unit circulation
    module; and R-22 for the ground coolant refrigeration module after
    the ammonia boilers are turned off (pre-launch and post landing).

-   Ammonia (NH3) for thermal management (heat from the Freon-21 loops
    below 100,000 feet until ground cooling is turned on).

    Other:

-   CFC-113: Trichlorotrifluoroethane (Freon PCA, precision cleaning
    agent) for ground operations.

Toxic fluids such as the hypergols or waterproofing agents are
significant contributors to the number of keepout zones around a system.
This prevents other work. Costly infrastructure for SCAPE operations
(protective suits and gear) is required for hypergols. For all the toxic
fluids, including the hydraulic fluid or freon loops, operational
affordability is driven by manpower intensive system verifications,
mostly manual, such as leak checks, interface verifications, non
standard payload interfaces, or verifications for air intrusion into
hydraulic lines.

**Level:** 2 - Information is available on this criteria as the concept
becomes more defined. However, this should be considered critical
information required of any concept very early in decision making.

**Visions of Improvement:**

Basic improvements include the elimination of hypergolic fluids for
auxiliary propulsion (both OMS and RCS) such as through the use of O2/H2
based systems. Further basic improvement would build on the prior plus
address any toxic power sources such as hydrazine APU's. Candidates for
power sources such as batteries may simply replace one toxic fluid and
set of tasks for another. Higher density fuel cell type power sources
may improve on this criteria but must consider thermal management of the
power supply which relates to toxic fluids such as freons and ammonia
discussed ahead. A whole picture of thermal loads and management is
required in optimizing for power requirements, reducing toxic fluids and
providing cooling of avionics or other heat generating sources.

Another basic improvement would be the replacement of hydraulic fluid
actuation of aerosurfaces, landing gear and valves by the use of
electromechanical actuators (EMA's). This conversion from a fluid to an
electrical system is synergistic with the "number of systems with BIT /
BITE (increase)", a top ranked criteria.

Further improvement would also eliminate the use of toxic waterproofing
agents such as DMES for tile type thermal protection systems. Maximum
improvement here assumes *elimination of the waterproofing task* and not
just replacement of the toxic fluid DMES with a non-toxic.

Maximum improvement would address all the prior as well as thermal
management systems for (1) avionics (or electronic equipment generating
heat), (2) power sources (such as fuel cells on Shuttle) and (3)
environmental control systems (passengers, A/C). All of these currently
use freons which are either banned from production or are planned to be
banned. This area is synergistic with the "number of active components
required to function including flight (reduce)". Reductions in heat
loads from avionics or increases in power source efficiencies could
reduce some of the active (fluid) thermal management load requirements.
The remaining heat loads as well as increasing passenger heat loads
would have to be addressed via non-toxics to fully improve on this
criteria.

Finally, ideal levels of improvement would have addressed all the prior
as well as the use of toxic fluids in ground operations and recurring
manufacturing operations such as the use of freon PCA in field cleaning
or manufacturing processes.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established with relative ease. Improvement may be measured relative to
the number of toxic fluids for Shuttle.

For example, a design may target using only 2 toxic fluids, freon PCA
and one low toxicity HCFC coolant circuit, almost an order of magnitude
improvement over Shuttle.

![](media/image7.emf){width="5.99375in" height="2.2319444444444443in"}

*Table 1. Hazardous operations are one aspect of the major toxic fluids
on Shuttle. This example for the Shuttle Auxiliary Power Units
demonstrates high manpower requirements due to the use of hydrazine, a
hypergol. SCAPE operations require keepout zones, preventing or
displacing other work as well as making the operations themselves
difficult due to bulky protective suits and gear. Source: Electric
Actuation Technology Bridging Program^12^.*

\(2\) System margin (increase):

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**Shuttle Benchmark:** Zero to low - indeterminate as of this revision.

**Derivation:**

-   This criteria refers to that margin which is available in a fielded
    operating system. It is essentially the ability to operate a robust
    system in a de-rated condition while still achieving the minimum
    required system performance. This margin is not that which is used
    during development in expectation of weight growth due to
    uncertainties of design or technology.

This criteria correlates strongly to operation and support costs,
reliability, flexibility, capacity, maintainability, ease of support and
vehicle safety.

For Shuttle examples of lack of margin or negative margin (of this type,
in the fielded system) include:

-   Thrust levels at 109%, not 100% (or less)

-   Engine removals every launch, not every 55 starts

-   7-8 launches per year, not 40

-   50Klbs to due east orbit LEO, not 65Klbs

-   3 weeks to launch from VAB rollout, not 24 hours

Traditionally, margin is used during the early stages of design as a
contingency to allow for weight growth and growth resulting from
addressing design and actual weight uncertainties (component and
subsystem performance) during development and technology maturation.
This type of margin should always be present in studies and preliminary
designs with the amount of margin being dependent on the maturity of the
subsystems, overall design and technologies. Also reference the section
"Verifying Functional Requirements - Performance". The unique nature of
margin considerations is also clarified further in the section "Margin
Considerations".

**Level:** 1 - This type of margin, planned for a fielded operating
system, should be included during concept evaluation and development as
an early design requirement.

**Visions of Improvement:**

Basic improvement allocates extra margin early in the design at the
overall program level, not within subsystems where it will be used as
the traditional weight growth contingency. To the extent margin is then
preserved or inherent in the fielded system it not only results in a
more robust system but can be used for flexibility (higher payloads,
different altitudes, different inclinations). This assumes a concept
definition that intends to operate in a de-rated condition for all
technical disciplines resulting in a very robust transportation system.

The current Shuttle has no system margin in the sense used here. For
example, if it were decided to change a subsystem to improve the overall
operability of the Shuttle and that change increased the Shuttle weight
(a likely result), then other systems would also have to be modified to
decrease their weight to make up the difference (difficult and
expensive). Thrust would have to be somehow increased (either increasing
cost or decreasing the life of the engines), or the payload capability
on the nominal mission would have to be decreased. In other words, there
is no system margin left in the fielded system.

Ideal levels of improvement would target robust systems designs which
have more than adequate margin even after adjusting for uncertainties in
development with expected weight growth.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established. The amount of system margin over and above the weight
growth and development uncertainty margins needed to achieve various
levels of affordability and flexibility is not currently known. A target
of 5 to 10 percent appears reasonable but would need to be quantified
for each system since there is no previous history for this type of
margin in space transportation systems.

\(3\) Number of systems with BIT / BITE (increase):

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**Shuttle Benchmark:** Low - indeterminate as of this revision.

**Derivation:**

-   This criteria is intended to include the health management of
    *[fluid, mechanical and structural systems]{.underline}* as well as
    traditional electronics.

-   The objective is to determine the overall health of the space
    transportation system to speed turnaround with as little manpower as
    possible.

The percentage of systems with built in test capability (Vehicle Health
Management (VHM) or Health Management (HM) in general of flight and
ground systems) or equipment relates very strongly to recurring costs
such as operation of the system, and hence to life cycle cost and
overall affordability. The correlation is also very strong to the
ability to launch on time, launch on demand and the degree of
supportability. Increases in the percentage of systems with BIT / BITE
improves significantly in all these prior areas. This assumes the
development of such systems is toward highly reliable sensors, software,
hardware and computing capability.

Shuttle currently lacks true BIT / BITE for fluid, mechanical and
structural systems and the use in electronic systems is limited in the
ability to isolate problems to the lowest line replaceable unit (LRU)
possible. Manpower intensive fault isolation of fluid systems such as
propulsion contributes significantly to high turn-around times and low
flight rates. Assuming reliability increases (addressed in other
criteria) the criticality of space unique systems dictates that a
significant requirement of future systems is improvement in fault
isolation. For example, hazardous gas detection systems can indicate a
leak in the ET intertank but can not specifically tell where.

**Level:** 3 - More detailed information that is available as the design
matures to a preliminary design phase. However, all attempts should be
made to determine this information as early in the decision making as
possible especially in relation to evaluating one concept's merits
against another.

**Visions of Improvement:**

Basic improvements include electronic systems with power on go/no-go
capabilities taking maximum advantage of up to date computational
capability.

Further improvements incorporate smart systems into fluid, mechanical
and structural systems. This includes health indication capability for
valves such as timing or sticking without recurring to unreliable
microswitches or moving parts in general for sensing. Further
improvement includes fast, low manpower leak isolation capability during
turnaround such as for tankage. This means quickly being able to know if
and where a leak is, not just that one exists in a general area.

More advanced improvement begins to provide built in, non-intrusive leak
detection capability as part of health management for valves and
critical propulsion systems. Eliminating physical connections or
intrusions into the vehicle (such as flowmeters to test ports or
accessing joints for mass spectrometry) is envisioned. All this while
still being able to quickly assess as well as isolate any problems to
the lowest LRU.

Maximum improvement provides a "brilliant system" for the entire space
transportation system from landing to launch as well as in flight and
orbit.

![](media/image8.emf){width="4.489583333333333in" height="3.375in"}

*Figure B. The development of BIT / BITE capability for fluid,
mechanical, structural and electronic systems would directly address the
fault isolation which is 36% of when component failures are detected.
Currently Shuttle relies on very manpower intensive approaches (non-BIT
/ BITE) for this part of turnaround activity. The 54% of fault isolation
occurring during maintenance and servicing must also be addressed by
means of BIT / BITE given it's manpower intensive non-BIT / BITE nature
as well. Current remote health diagnostics emphasize the flight portion
of the system. Source: Shuttle CAPSS / GPSS.*

**Target for Improvement:**

This criteria is not a "pure" design feature a target for which can be
easily established. It is included here as a critical *direction* for
future systems to improve upon versus Shuttle. Two related issues are
reliability and criticality.

-   It is assumed reliability increases (another critical direction)
    result in BIT / BITE systems simplifying system turnarounds.

-   It is assumed critical systems, regardless of robustness or
    reliability increases, will still require checkout, test or
    verification in some way and hence fault detection.

BIT / BITE must be targeted to these critical remaining areas (for
example propulsion system leakage isolation) to avoid manpower intensive
turnaround operations.

\(4\) Number of confined spaces on vehicles (reduce):

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**Shuttle Benchmark:** 6 (majors only)

**Derivation:**

Confined spaces on a vehicle generally mean:

-   Purges which mean \...

-   Pneumatic systems and associated infrastructure (dedicated panels,
    supply facilities)

-   Hazardous gas detection systems (HGDS) and associated infrastructure
    (dedicated panels and instrumentation)

-   Potential hazards to personnel (O2 insufficiency)

This criteria includes compartments on the vehicle and associated
interfaces that correlate very strongly to operation and support costs
and hence to life cycle costs and overall affordability. The correlation
is also very strong to simplicity and maintainability. Safety in
particular is affected by this number for both the vehicle (explosive
hazards) and personnel (lethal environments). The related infrastructure
consists not only of the requisite high pressure pneumatic systems and
facilities but also the associated hazardous gas detection capabilities.
Criticality dictates high degrees of redundancy in the pneumatic systems
further complicating the system and increasing both acquisition and
operating costs. Hazardous gas detection capability, to the degree that
precision and accuracy requirements exist, further adds to pneumatic
system hardware and complexity to assure flowrate requirements.

*Major* Shuttle closed compartments include:

-   ET/Orbiter interface at the 17-inch disconnects (purged and
    instrumented)

-   External tank nose cone compartment (purged)

-   ET to H2 vent arm ground umbilical cover plate (GUCP) (purged and
    instrumented)

-   Orbiter to T-0 umbilicals (propellant servicing) (purged and
    instrumented)

-   Orbiter aft boat-tail (purged and instrumented)

-   External tank intertank (purged and instrumented)

**Level:** 3 - This criteria addresses more detailed information that is
available as the design matures to a preliminary design phase. However,
all attempts should be made to determine this information as early in
the decision making as possible especially in relation to evaluating one
concept's merits against another. Alternatively, a target or set of
approaches that can possibly reduce this number should be maintained as
a priority throughout concept development.

**Visions of Improvement:**

Basic improvements here are a challenge as SSTO type vehicles do not
eliminate, but rather integrate tankage. Associated confined spaces may
migrate as well. Aerodynamic considerations further exacerbate this
number by precluding options (open trusses) that would have more easily
applied to expendable vehicles. Access, also a criteria in this guide,
is consistent with the goal of eliminating confined spaces and
associated complexity if a third criteria, an increased number of
components with demonstrated reliability, is properly addressed in
development. This allows the selection of components for acquisition
which have a reduced probability of requiring any access at all.

Basic improvements are possible at the interfaces for any SSTO compared
to Shuttle. The use of an external, disposable tank with fuel and
oxidizer disconnect cavities (confined, purged spaces) is eliminated by
design.

Further improvements include precluding air intrusion into smaller
compartments (such as a forward LOX tank nose cone compartment) such as
through the use of foam or other material closeouts. This eliminates
purge requirements.

More advanced improvement would eliminate interface compartments for
servicing such as at a GUCP or T-0 umbilicals. Solutions such as an H2
vent line on board the vehicle routed to the servicing lines begin by
eliminating separate systems.

Maximum improvement would target no aeroshell requiring a purge and
instrumentation.

Ideal levels of improvement require maximum creativity to eliminate
compartments currently accepted as requirements for access such as aft
boat tails and propellant intertanks. This relates synergistically with
the criteria "number of components with demonstrated high reliability
(increase)". The effect of up front development leading to high
operational readiness and components with long life limits, high
reliability and reusability, and robust margins is evident in the
ability to dramatically improve, or not, on this confined spaces
criteria.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
easily established. It is also a critical *direction* for future systems
to improve upon versus Shuttle. A related issue to consider is
criticality which dictates compartments with potential hazardous gas
leakage should be purged and instrumented regardless of demonstrated
reliability for the seals, protrusions and penetrations in that
compartment.

\(5\) Number of hours for turnaround between launches (reduce):

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**Shuttle Benchmark:** 3-4 months (per individual vehicle, serial time,
not labor hours) between each launch, or 190,000 labor hours (direct
labor hours only, orbiter OPF only), or use 4 to 10:1 ratios for the sum
of direct and indirect labor hours (orbiter OPF only, launch site only,
actual expenditures higher).

**Derivation:**

This criteria correlates strongly to recurring costs, such as operation
of the system, and hence to life cycle cost and overall affordability.
The ability to launch on time, the ability to meet planned requirements
(capacity) such as time and number of launches, and the overall
supportability of the system all relate to this criteria.

For Shuttle this measure in serial time is measured in months. In
manhours the measure is in hundreds of thousands of manhours if counting
*only* direct labor charges.

**Level:** 3 - Reference "Target for Improvement".

**Visions of Improvement:**

Days not weeks. Hours not days.

**Target for Improvement:**

This criteria is not a "pure" design feature. It is included here as a
critical *direction* for future systems to improve upon versus Shuttle.
A reduced number of hours for turnaround is a [resultant of design
features]{.underline} that are included in this guide.

The high rank (4) for this criteria is an indication of the importance
of understanding the recurring work associated with a design, such as
for turnaround of one vehicle. This is a key question in decision making
including technologies to develop, which to acquire or implement, and
how to integrate them into a system as well as the final risk that
flight and cost rates will be achieved or not. Targeting should aim for
zero turnaround operations other than servicing of propellant and
expendables as a general ground rule for starting a design exercise.

The high rank also stresses the need for adequate models of vehicle or
fleet operations based on an understanding of the implications to
operations of certain designs and development and acquisition
strategies. The other design features and program features in this
document provide a sense of direction using significant criteria that
can aid in understanding future turnaround scenarios.

![](media/image9.emf){width="5.386805555555555in"
height="2.7868055555555555in"}

*Table 2. Turnaround times between launches are dictated by both planned
work and unplanned work. This data for Shuttle orbiter turnaround
manpower requirements does not include the integration activities in the
VAB, involving mating the orbiter to the External Tank (ET) and Solid
Rocket Boosters (SRB's). This adds another 7 days on average to
turnaround time. It also does not include time on the pad, on average
another 30 days to add to turnaround time. Source: Shuttle CAPSS.*

\(6\) Number of different propulsion systems (reduce):

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**Shuttle Benchmark:** 4 *plus*

**Derivation:**

This criteria relates very strongly to recurring costs, such as
operation of the system, and hence to life cycle cost and overall
affordability. The correlation is also very strong to the ease of
integration and the degree of supportability. The associated separate
infrastructures, organizations and manpower result in the high rank for
this criteria.

The Shuttle uses 4 completely independent propulsion systems:

-   LOX/LH2 main engines (3)

-   Solid Rocket Boosters (2)

-   Orbital Maneuvering System using hypergols (2 Pods plus aft RCS)

-   Forward Reaction Control System (RCS) using hypergols

**Level:** 1 - Usually available early in the concept development and
evaluation.

**Visions of Improvement:**

Basic improvements would be achieved in any SSTO concept over Shuttle by
virtue of deletion of the SRB's. Launch assist concepts would not change
this number assuming a Shuttle type configuration (MPS, Sled, and
separate OMS and RCS = 4).

Further improvement would combine more of the hardware for both main
propulsion as well as orbital maneuvering. Turbopump operating ranges
would likely require expansion. Common thrusters and or nozzles would be
consistent with this moderate level of improvement.

Further improvement would synergistically combine this criteria with top
ranked criteria such as reducing the number of different fluids or
reducing the number of toxic fluids. A combination OMS/MPS with a
separate RCS but all using common fluids would be an improvement.

Maximum improvement would continue to build on all of the prior by
adding further degrees of common hardware (such as tankage) for all
propulsive functions (MPS/OMS/RCS). The number of different propulsion
systems would then have reached a comparison value of between 1 and 2
(some common hardware).

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be set
with relative ease. Improvement may be measured relative to the 4
independent Shuttle systems.

\(7\) Number of unique stages, flight and ground (reduce):

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**Shuttle Benchmark:** 3

**Derivation:**

The Shuttle stages include solid rocket boosters, external tank and
orbiter. The number of stages used in a space transportation system
relates very strongly to recurring costs, such as operation of the
system, and hence to life cycle cost and overall affordability. The
correlation is also very strong to ease of integration and the degree of
supportability. Reductions in the number of stages improves
significantly in all these prior areas.

The relation of major interfaces to costs, both recurring (operational)
and non-recurring (acquisition), makes this a significant feature of a
design.

**Level:** 1 - Usually available early in concept development.

**Visions of Improvement:**

Basic improvements would be toward a single stage to orbit vehicle.

A ground assist concept, such as with a sled propelled by some means,
would count as two stages (negative impact on this criteria). A flight
second stage would have an equal number (two) as a sled concept;
however, other criteria would be affected differently according to the
particular traits of the sled or flight stage. For two stages versus
single stage operations the increased one time facility costs and
increased annual operations costs resulting from two stages can
significantly affect life cycle costs (Hamaker 1996)^11^.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established with relative ease. A particular two stage design is not
excluded over a single stage design. Consideration of the whole set of
design features, and especially the significant first 20 to 29, should
be weighed in determining if a particular set of design variables is an
improvement over another. Within the intent of this guide no one
criteria is a means for decision making; rather, the extent to which an
architecture optimizes on most of the top features can be an indicator
of connecting to higher level goals such as routine, affordable space
transportation.

\(8\) Number of active ground systems required for servicing (reduce):

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**Shuttle Benchmark:** Numerous. Exact value unknown as of this
revision.

**Derivation:**

-   Active ground systems required for servicing include not just
    propellants but other fluids or expendables.

-   Shuttle active ground systems required for servicing include:

-   LO2/GO2 and LH2/GH2 propellants storage and handling

-   GHe and GN2 facility systems

-   Fuel cells power reactants (LO2/LH2)

-   Hypergolics OMS/RCS (N204 and MMH)

-   Hypergolics APU's (Hydrazine)

-   Hydraulic systems

-   Environmental Control and Life Support Systems (ECLSS)

-   Freons

-   Ammonia

-   Water

The number of active ground systems required for servicing relates
strongly to the affordability of operations and support, the capacity of
the system (ability to meet multiple customers planned requirements such
as time, payload size, and weight, number of launches, launch rate and
payload destination), the ease of vehicle and system integration,
maintainability, the ability to launch on demand and supportability.

**Level:** 2 - Information is available on this criteria as the concept
becomes more defined. However, this should be considered critical
information required of any concept very early in decision making.

**Visions of Improvement:**

Basic improvement here begins with a common propellants ground rule
(NASA SGOES 1988)^18^. Servicing can then be integrated and ground
infrastructure simplified and reduced. Vehicle systems can also benefit
from greater integration. Examples include propellant grade fuel cells
and O2/H2 based auxiliary propulsion. Power supplies using non toxics
would begin to simplify servicing by eliminating bulky, hazardous scape
operations. Power supplies providing both on orbit requirements as well
as high horsepower ascent or landing requirements (TVC, aerosurfaces,
landing gear) would simplify vehicle systems servicing by eliminating
separate systems servicing.

Further improvement would address ECLSS and thermal management
requirements. Eliminating any need to violate system integrity would
begin to enable closed loop systems not requiring servicing during
turnaround. For example, hydraulic systems with the capability of
actuating, such as for checkout, without ground interfaces violating
system integrity are desirable.

More advanced improvement would make any remaining servicing
requirements low on manpower requirements such as through automated or
simplified umbilicals with rapid integrity checkout capability.

![](media/image10.emf){width="4.989583333333333in"
height="3.7395833333333335in"}

*Figure C. The "LRU PR's" (components actually removed and replaced) for
the Shuttle ground systems per flow are about 800 on average. Active
ground systems account for a significant portion of this turnover.
Source: Shuttle PRACA system.*

**Target for Improvement:**

This criteria is a "pure" design feature which represents actual
hardware that can be accounted for. Improvement may be measured relative
to complex Shuttle systems.

For example, a design may target one servicing operation - propellant
loading, although multiple liquids, gases or charging of electronic
(power) systems may be involved. Serial operations or servicing and
intrusive breakage of one system to support the checkout of another
should be avoided. Serial operations as a schedule risk reduction may be
indicative of unreliable hardware with potential hazards which relates
to other criteria that must be improved upon in future systems (for
example "number of components with demonstrated high reliability").

\(9\) Number of purges required (reduce):

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**Shuttle Benchmark:** Numerous. Exact value unknown as of this
revision.

**Derivation:**

The Shuttle system requires numerous purges for (1) closed compartment
inerting (reduce O2), conditioning (humidity) and temperature control as
well as (2) ice prevention external to the hardware and (3) protecting
hardware from the elements (salt spray, SRB dust, corrosion).

Also reference "Number of closed compartments".

*Major* purges on Shuttle include:

-   ET/Orbiter interface at the 17-inch disconnects (purged and
    instrumented)

-   SRB aft skirt GN2 purge

-   GO2/GH2 Pressline purge

-   LH2 vent shroud

-   External tank nose cone purge

-   ET to H2 vent arm ground umbilical cover plate (GUCP) (purged and
    instrumented)

-   Orbiter to T-0 umbilicals (propellant servicing) (purged and
    instrumented)

-   Orbiter aft boat-tail (purged and instrumented)

-   External tank intertank (purged and instrumented)

-   Assorted valve stem purges

-   TSM purge

-   Pneumatic panels (enclosure / boxes) purged

**Level:** 2 and 3 - This information is usually not expected in early
concept definition. The information becomes available as the concept
matures and goes toward a preliminary design phase.

**Visions of Improvement:**

Basic improvement is achieved as a concept reduces stages such as an
SSTO. Element interfaces and boosters are deleted.

For improvement beyond the prior a vehicle thermal protection system
would be required to be more robust so as to withstand ice impacts
should any form during loading. This is a driver of the GO2/GH2
pressline purge and the H2 vent shroud purge.

Further improvement would build on the prior and eliminate interface
purges as well such as for umbilicals.

Maximum improvement would delete the need for purges in major vehicle
compartments such as in engine aft compartments or intertank areas. The
relation of these is to costly infrastructure which is both critical to
being able to launch on time as well as to safety. This in turn
addresses purges for compartments such as ground infrastructure
pneumatic panels. The purge is desirable in pneumatic panels since
enclosures protect against the environment; however, the elimination of
functions reduces the baseline number of these panels.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can
established based on the following questions: (1) is the thermal
protection system targeted to be robust enough to withstand ice impact
with zero damage, (2) are interfaces for loading or venting targeted to
have closed compartments or not and (3) how much ground infrastructure
such as for gas supplies or valve actuation are targeted (how many
pneumatic systems?).

This criteria is extremely synergistic with the "number of potential
leakage sources" and the "number of closed compartments". Improvements
here generally improve in these other areas as well.

See "number of potential leakage / connection sources (reduce)".

\(10\) Number of components with demonstrated high reliability
(increase):

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**Shuttle Benchmark:** Low - Indeterminate as of this revision.

**Derivation:**

Mature technology is a cornerstone of reliable operations. Up front
development of systems to a high operational readiness reduces the risk
later that vehicle productivity goals will be met. A design for support
results. This criteria correlates strongly to initial acquisition costs,
to the affordability of eventual operations and support, to the
reliability of systems during turnaround and to the safety and mission
reliability of the design.

-   The term "reliability" as used here is comprehensive in scope. It
    includes reliability during turnaround (process reliability) as well
    as in flight operations. The link between (1) mission
    reliability, (2) the means by which this reliability is achieved
    ("designed in" *or* "inspected, tested, repaired and replaced in")
    and (3) the affordability of operating a system requires this broad
    view of the term.

**Level:** 3 - More detailed information that is available as the design
matures to a preliminary design phase. Particularly as the certification
practices, reusability, reliability and maintainability goals and
approaches are defined. Final definition is not obtained until actual
qualification tests, design iterations and further demonstrations of
life limits and analysis are complete.

**Visions of Improvement:**

Basic improvements in this criteria begin with an understanding of data,
such as from Shuttle, to adequately understand the reliability of
designs. These measures include but are not limited to:

-   Mean Time Between Failure (MTBF)

-   Mean Time to Repair (MTTR)

-   Logistics Down Time (LDT)

-   Availability, total system as well as subsystems (Ai)­

-   Life limits (both maximum/minimum on/off cycles as well as usage
    time). This encompasses low cycle fatigue problems as well as high
    cycle fatigue.

Basic implementation then takes these baseline data (such as for
Shuttle) and targets new goals. A basic improvement would be the
implementation of a development and qualification program framed to
achieve these goals for evolved hardware. Further improvement builds on
the prior through actual, extended flight history and the compilation of
data that allows further iteration as systems are upgraded individually.

Maximum improvement envisions low cycle time between product
developments that quickly build on previous product experience. One
reusable launch system builds on another in quick succession. Improved
computational techniques allow testing and design changes to be done
quickly and at minimal cost versus test stands and tests to failure of
actual hardware.

The high rank for this criteria stresses the need for rigorous test of
designs pre-acquisition in the qualification / certification phase so as
to have supportable, fast turnaround systems. This criteria is extremely
synergistic with the pre-operational program considerations contained in
this guide.

![](media/image11.emf){width="6.446527777777778in"
height="3.7395833333333335in"}

*Figure D. The "LRU PR's" (components actually removed and replaced) for
one orbiter per flow are over 100 on average. The chart does not include
SSME or tile. Post OMDP (marked with an "\*"), the LRU counts at KSC are
notably above average. The chart includes only work done in the OPF.
Ground systems would add over 700 more LRU PR's on average per flow. The
STS-49 flight was OV-105's first. Source: Shuttle PRACA system.*

-   **Certification and Life Cycles**

The development of long life limits has a major effect on the
certification of future transportation systems. At one extreme, aircraft
certification is done once and maintenance results in "maintaining
certification" of an aircraft. At another extreme, Shuttle certification
(a CoFR) is done every flight and processing, including maintenance,
test, checkout and repair is the means of achieving *certification each
and every flight*. High cycle life is key to true reusability, reducing
failures, increasing the time between scheduled maintenance and reducing
operating costs and hence greatly reducing life cycle costs of a
transportation system.

**Target for Improvement:**

This criteria is not a "pure" design feature even though targets for
subsystems may be established analytically. Reliability, Maintainability
and Supportability (RM&S) studies can gather data and set targets;
however, the [*implementation*]{.underline} of a program to achieve
these targets - the testing, design iteration, analysis, and
demonstration of designs - is not as easily defined as for other
criteria. Programmatic considerations are synergistic with this
criteria. Up front decisions such as which technologies to fund, which
to focus on extending life limits for, and which to iterate (improve on)
more in the design and technology cycle, are the programmatics that will
determine the degree to which this criteria is high or low on any system
eventually acquired.

This criteria is included here as a critical *direction* for future
systems to improve upon versus Shuttle. Shuttle may be considered the
implementation of a system with low levels of demonstrated reliability,
in particular process reliability, the reliability of components during
turnaround. Improvement may be measured relative to the degree to which
components, sub-systems and eventually whole systems measure in
demonstration compared to similar existing Shuttle systems or
approaches.

\(11\) Number of potential leakage / connection sources (reduce):

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**Shuttle Benchmark:** Fluids ≈ 10^3^-10^4^, Electrical ≈ 10^4^ - 10^5^
ROM. Precise value indeterminate as of this revision.

**Derivation:**

This includes electrical and fluid systems.

For fluid systems, manpower intensive operations are driven in Shuttle
processing by a combination of (1) high numbers of potential leakage
sources for fluid systems, (2) the use of manual methods in fluid
systems certification (hands on including over a dozen approaches), (3)
the criticality of systems dictating high numbers of required tests and
(4) the lack of reliability of components further dictating high numbers
of required tests for seals as well as components removed and replaced.

Electronic systems (all vehicle systems) require a separate computerized
database ("SCAN") for tracking all connectors that are disassembled,
reassembled and retested (\> 5000+ pins on average requiring
recertification per turnaround with an increase in this number by one
order of magnitude to \> 30,000 pins for the flow following depot
maintenance). Unfortunately, a similar computerized, central database
does not exist for fluid systems and the degree of de-configuration and
retest for fluids is unknown to any high certainty.

The number as a baseline can be considered in either of two ways. First,
potential sources, even if no requirements exist for verifying integrity
(unless broken into) and second, required verifications. Required fluid
verifications are estimated in the order of thousands of leak checks per
Shuttle flow.

Some examples:

-   LOX Facilities: \>1000 per flow (leak checks)

-   LH2 Facilities: \>1000 per flow (leak checks)

-   ET Processing: \> 20 per flow, much higher if hazardous gas
    detection requirements during loading are included.

-   MPS Processing: \> 40 per flow + \>30 interfaces

-   Shuttle Main Engines: \>80 per flow per engine + \>10 interfaces

To clarify, the prior in systems such as facilities, are driven by
infrastructure such as pneumatic panels. A requirement for a nosecone
purge brings with it a pneumatic panel, heater and controllers. Also,
the prior [does not include bulk leak checks]{.underline} done using
hazardous gas detection capabilities scanning whole engine blocks, ET
intertanks or aft compartments. This would increase the count into the
tens of thousands of joints. These integrated or functional fluid system
verifications are no less manpower intensive than individual joint tests
given the need for sophisticated equipment, purges, firing room
monitoring and GSE setups - most manual.

Other systems such as freon cooling loops (ECLSS) using high degrees of
brazing do not have periodic, individual leak checks. However, systems
which only check violated joints are not immune from numerous
verifications given high component failure rates such as thrusters for
OMS/RCS or required breakage into systems as part of processing such as
for hydraulic systems.

**Level:** 3 - More detailed information that is available as the design
matures to a preliminary design phase.

**Visions of Improvement:**

There are various levels of cumulative improvement possible for this
criteria.

-   Systems deletion / systems simplification

-   Systems reliability - seals and sealing techniques

-   Systems reliability - components (Also reference other criteria such
    as "number of components with demonstrated high reliability")

-   System robustness to leakage (design tolerance to wider variation in
    operating parameters)

Basic improvements begin with the simplification of systems. SSTO
concepts by definition reduce potential leakage and connection sources
by eliminating the integration of distinct stages or segments. Cabling
in SRB segments as well as fluid and electrical interfaces to disposable
tanks or SRB's are deleted. Further basic improvements would simplify
major fluid systems such as propulsion, eliminating purges and
associated ground infrastructure. The elimination of GHe inject systems,
POGO systems and turbopump interseal purges further provide basic levels
of improvement.

Sled launch assists could entail similar interfaces for fluid and
electrical systems negating a portion of the interface gains mentioned
previously. Further, the introduction of more cryogenics such as liquid
helium (LHe) for superconducting applications introduces potential
leakage sources. This area is synergistic with "number of (%) of
propulsion system automated (increase)". The automation of interface
checkouts such as leak checks would address the manpower factor
associated with leakage and connection points.

More significant improvement, assuming complex fluid systems will
continue to be associated with propulsion systems and servicing
requirements, would entail seals and sealing techniques dramatically
improved over current designs. Welding, brazing or otherwise eliminating
leak paths would eliminate the associated tasks and manpower. This
assumes much higher levels of component reliability as well as ease of
manufacture. It also assumes areas are not regularly accessed reducing
the probability of unintended personnel damage.

Maximum improvement builds on the prior (deletion, automation and new
seal techniques) and adds increased component reliability. This
precludes work in areas that are susceptible to damage. For example, a
new welding technique that is easy to use in manufacturing and to verify
and which eliminates periodic maintenance checks may not be implemented
due to high probabilities that intensive component refurbishment in the
area causes unintended damage to lines. This applies also to connectors
and cabling and electronic components. Notice the synergy here to
"number of components with demonstrated reliability (increase)".

Finally, ideal synergy would take one more step. The "number of
potential leakage / connection sources (reduce)" is synergistic with a
high number of the other criteria contained in these guidelines. Assume
advances in the area of "number of confined spaces on vehicles
(reduce)", which in turn allow improvement in the criteria "number of
purges required (reduce)", thus improving on the "number of active
systems to maintain a safe vehicle (reduce)". The prior assumptions
would greatly benefit through simplification the "number of potential
leakage / connection sources (reduce)"; however, a major component of
launch system infrastructure and cost would have gone without
addressing - pneumatic systems for valve actuation.

To complete building on the ideal target for improvement, the
introduction of electronic systems would be a highly promising approach.
Tank vent valves, as well as all vehicle valves and facility valves
could be motor driven (electromechanical valves). This adds electrical
connectors but drastically reduces fluid systems leakage sources and
massively eliminates infrastructure (GHe/LHe and GN2/LN2 facilities,
truck farms and tube banks). Electrical connectors can also more easily
include self test capabilities. These electrical systems in turn would
allow further improvement in areas of health management and automation
(such as "number of systems with BIT / BITE (increase)". Compatibility
and electrical concerns for areas such as LOX could be addressed through
design and materials selection as well as zero seal magnetic couplings.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established with relative ease as a design matures. It is also a
*direction* for future systems to improve upon versus Shuttle. Basic
reductions inherent to an SSTO or even a sled assisted concept do not
represent the limits of possible improvement.

The high rank here stresses the need to target seals and sealing
techniques as requiring much improvement in any next generation concept.
Improvement must also target component reliabilities to have maximum
effect. Pneumatic systems should be targets for virtual total
replacement with electronic systems of valves on the vehicle and the
ground.

![](media/image12.emf){width="5.0in" height="3.75in"}

*Figure E. Liquid propulsion systems on Shuttle have dominated launch
delays. The LH2 leak days of delay are primarily contributed by the
STS-35 and 37 flows in 1990. Note that the SRB delay contribution is
mostly 51-L. Leaks constitute not only a launch on time issue but a
recurring aspect of manpower intensive operations targeted at preventing
such incidents. Recurring operations, such as leak checks in fluids
systems, are directly linked to the reliability as well as criticality
of systems. To support recurring verifications of system integrity
multitudes of leak check methods are in use as shown. Source: LSOC
Database*

![](media/image13.emf){width="3.9972222222222222in"
height="2.8881944444444443in"}

\(12\) Number of active systems to maintain a safe vehicle (reduce):

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

This includes ground supplied purges, hazardous gas detection capability
during loading, turbopump interseal purges, GHe inject during loading,
LOX bleeds during loading, hydraulic heating in orbit, replenish valves
during loading, flow control valves during ascent and a host of other
systems.

This criteria has a strong synergistic relation with the "number of
purges" as well.

**Level:** 2 - Information is available on this criteria as the concept
becomes more defined.

**Visions of Improvement:**

Basic improvements begin with the deletion of the root causes requiring
these active systems for safe operation. This results in simplification
of systems. Shorter feedlines such as with a LOX tank aft must trade the
elimination of active systems such as GHe inject against any flight
concerns and active systems for stability of flight. Flow control valves
for in flight cryogenic tank pressurization can be replaced with fixed
orifice designs if system design goals target robust tanks and
structural margins. Reduced margins in cryogenic tank structures that
require higher pressure settings during loading are undesirable. Vent
valve cycles, an active system, increase and work against this criteria.

Further improvement would indicate active cooling systems for thermal
protection, such as with an airbreather at high Mach numbers, is
undesirable. The criteria "number of potential leakage and connection
sources" is also synergistically, adversely affected by active cooling.
Benefits (reference criteria "26 - Average Isp on reference trajectory")
of higher Mach number approaches requiring active cooling must be
weighed against these related negative acquisition and operation
aspects.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established based on an active accounting of current systems such as
Shuttle. A further determination of which systems may be deleted and
which, for a new system, are essential would also indicate the
*direction* in which a new system is heading. The high rank for this
criteria stresses the importance of improvement in this direction.

\(13\) Percent (%) of propulsion system automated (increase):

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**Shuttle Benchmark: ≈ 0**

**Derivation:**

-   Reference is to [turnaround]{.underline}, not flight.

This criteria is a subset of the criteria "number of systems with BIT /
BITE (increase)".

This criteria is synergistic with the criteria "average Isp on the
reference trajectory (increase)".

This criteria is re-addressed here specifically for propulsion given
that propulsion alone has a very strong correlation to the sensitivity
to flight growth costs, operation and support, the capacity of the
system, the maintainability of the system and even safety concerns.
Being able to increase flight rates (vehicle utilization) without
increasing overall costs results in a desirable sensitivity to costs per
flight, in a decreasing direction. Expenditures in automation up front
in development and acquisition relates to this ability to produce high
flight rates per vehicle.

Assumptions again include reliable, non-intrusive instrumentation. The
reliability assumption is synergistic with the criteria "number of
components with demonstrated reliability" and to development and
certification activity. The non-intrusive assumption is synergistic with
the "number of potential leakage / connection sources".

Currently, Shuttle has little of the previous characteristics. Manpower
intensive (manual) operations are the norm for the propulsion systems
turnaround (main propulsion, external tank, servicing facilities and
interfaces, orbital maneuvering systems and reaction control systems).
"Manual" describes assorted tasks. For example, (1) having to
individually perform mass spectrometer leak checks (passing detectors
slowly over and around individual joints and having to bag these in some
cases) or (2) having to install access kits to break into joints,
install plugs, and configure and connect flow meters and K-bottles for
one leak check and (3) having to do this repeatedly for multitudes of
joints and (4) having to remove access kits followed by meticulous
inspections of areas to be "closed out". Bulk leak checks (many joints
at one time) using hazardous gas detection capabilities and "cans" or
the existing compartments (such as the aft) result in knowledge of leaks
existing or not but not necessarily of where or which one of the many
joints. This causes the previous manual operations to go into effect.

**Level:** 2 and 3 - This information is usually not available early in
concept definition. The importance in early decision making and eventual
results exists nonetheless.

**Visions of Improvement:**

Reference "number of systems with BIT / BITE (increase)".

A list of propulsion operations in broad categories would be:

-   Leak checks

-   Valve checkout (including check valves and relief valves)

-   Electrical systems checkout (cabling, controllers, interfaces)

-   Hydraulic systems checkout

-   Servicing interfaces checkout

-   Engine checkout (inspections of turbopumps, purges, drying)

Basic targets for improvement would delete hydraulics (synergistic with
"number of toxic fluids (reduce)" and with "number of potential leakage
/ connection sources (reduce)"). Basic improvement would also extend
life limits on engine components by addressing low cycle fatigue
transients and duration or high cycle fatigue wear. These would be
addressed in startup sequencing development as well as new technology.
This would in turn begin to preclude the removal of engines from flight
to flight, hence reducing interface checkouts such as inspections,
connections and leak checks. The full benefits of automating turnaround
checkout can then begin to be exploited. For example, low cycle fatigue
life in turbopumps can be improved by controlling start transients to
minimize or eliminate those mixture ratio variations during the
transient that cause rates of temperature change such that the core and
the surface of the blades and nozzles can not track each other and thus
produce significant temperature differences and resulting thermal
strains; and by controlling the shutdown to reduce or eliminate the same
problem during the quench. High cycle fatigue can be addressed by
instrumentation and internal flow passage designs to minimize flow
induced vibration.

The synergy of turnaround automation with component reliability must be
stressed.

For those fluid areas remaining, such as interfaces for servicing
umbilicals, the automation of connection, checkout including leak
checks, and servicing would be a further improvement.

Eventual targets should include the prior and the transition to
electronic systems for broad application to valves and on board
instruments that are non-intrusive. Reference "number of potential
leakage / connection sources (reduce)".

One point to account for in sled launch assist concepts, which would be
part of the propulsion system, is all electrical systems versus systems
using a cryogenic commodity such as LHe (for superconductors such as in
some maglev concepts). Cryogenic commodities in addition to those in use
today would work against the direction of improvement for "number of
potential leakage / connection sources" and would add another system
that would require (1) intensive manpower similar to current cryogenic
propulsion systems or (2) add to the list of automation that this
criteria stresses is required in future propulsion systems. Improvements
in automation of servicing umbilicals could just as easily apply to a
sled with LHe requirements as to the actual vehicle interfaces.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established based on the total number of planned tasks and how many of
these tasks will be done via automation for any given concept. It is
also a *direction* for further improvement.

\(14\) Number of hands on activities required (reduce):

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

Reference "5-number of hours for turnaround between launches (reduce)".

This criteria correlates strongly to recurring costs, such as operation
of the system, and hence to life cycle cost and overall affordability.
The ability to launch on time as well as meeting planned requirements
all relate to this criteria.

**Level:** 3 - Reference "Target for Improvement". Information for a
concept relating to task requirements and the nature of these tasks,
manpower intensive or not, may not be available early in concept
development or decision making. An evaluation of features that are more
easily measurable (number of toxic fluids, number of stages, number of
propulsion systems) as well as the intended direction of development
(number of systems with BIT/BITE, number of confined spaces, number of
components with demonstrated reliability, number of leakage / connection
sources), can indirectly give a sense of positive or negative
improvement in this criteria.

**Visions of Improvement:**

Basic improvements would include interfaces (any number of stages or
ground support tasks) that are automatic to a degree that manpower is
counted in the dozens, not hundreds of "touch labor" personnel.

Further improvements assume concepts that land, are connected to
immediately, and only require refueling or servicing of expendables, to
launch again.

**Target for Improvement:**

This criteria is not a "pure" design feature a target for which can be
easily set. It is included here as a critical *direction* for future
systems to improve upon versus Shuttle. A reduced number of hands on
activities is a [resultant of design features]{.underline}, pure and
directional, that are included in this guide.

Tasks that exist for Shuttle are for the most part "hands on". Launch
control center remote activity is not "hands on" by definition but is
usually coupled to personnel in the field. As an example, securing a
launch pad following launch requires over 100 personnel in the immediate
hours after launch at that pad with about equal numbers of personnel at
remote sites such as the launch control center.

The high rank of this criteria stresses the need to adequately
understand the hands on activities associated with certain designs. A
model of vehicle processing and turnaround with associated manpower is a
parameter as important in a concept definition as a performance model
that verifies the thermodynamic closure of an engine cycle.

![](media/image14.emf)

*Table 3. Thermal Protection Systems, in the Shuttle case due to lack of
robustness and a need for waterproofing, are one principal component of
hands on activity. Laborhours on TPS account for 1/3 to 1/2 of all OPF
laborhours. Performance requirements combined with previous technology
limitations dictated this. New technologies and approaches must address
not only performance requirements as a given but also the need for
robust, zero-maintenance thermal protection systems. Source: Shuttle
CAPSS. TPS hours include backshop. Total OPF hours shown include TPS
hours.*

+---------------------------------------------------+------------------+
| Access to Space Report ^14^, Budget Baseline      | Labor, Head      |
| 1994, Shuttle                                     | Count            |
|                                                   |                  |
| > Thermal Protection System Operations,           | 153              |
| > Logistics, KSC                                  |                  |
| >                                                 | 250              |
| > Thermal Protection System Operations, KSC       |                  |
+---------------------------------------------------+------------------+
| Waterproofing Operations, Shuttle (NASA Ames,     | Labor, Hours per |
| 1994)^15^                                         | Flow             |
|                                                   |                  |
|                                                   | 2,268            |
+---------------------------------------------------+------------------+

*Table. 3a The example given here for Thermal Protection Systems, as
with any hands on activity, should not obscure the larger component of
indirect costs that associate with any activity directly tied to a space
transportation system. For example, head count for facility operations
and maintenance at KSC (Access to Space, 1994)*^14^ *is 1,298; for the
on-going production of expendable elements, external tanks at Michoud,
LA, it is 2,376.*

One particular area that must be a major target for future improvement
in the area of hands on activity is thermal protection systems. The
manpower intensive nature of Shuttle TPS is shown in Table 3 and 3a.
Robustness improvement here is very synergistic with other criteria such
as the need for purges (criteria 9) or active systems (criteria 8) that
prevent ice formation external on the vehicle (Shuttle pressline, GH2
vent shroud, GOX vent arm and associated purges), toxic fluids
(criteria 1) such as waterproofing agent and turnaround time (criteria
5).

Note that the increased use of an active vehicle thermal protection
system (active cooling via fluids) for aerosurfaces, forebody, leading
edges, or propulsion works against 2 major criteria, criteria 11 on
potential leakage sources and criteria 15 on active components required
to function. The same applies to active thermal management systems such
as for avionics or environmental control. These in turn are direct
relationships to hands on activities. Improvements reducing hands on
activities for any reusable vehicle must target this major component,
the thermal protection system, while providing solutions linked to the
other criteria as prioritized.

\(15\) Number of active components required to function including flight
operations (reduce):

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

Reference "number of active systems to maintain a safe vehicle".

This criteria emphasizes function versus safety. Shuttle requires
systems such as recirculation pumps for conditioning during loading or
ground pumps for supplying LOX. Dependability, the ability of hardware
to perform when needed the first time, every time, strongly correlates
to this criteria. The probability of intact vehicle recovery and mission
success correlate to this criteria. Simplicity, or if active systems are
numerous, complexity, also correlates strongly to this criteria.

Explosive charges for separating interfaces are an example of active
systems that must function and are dependable, yet are not supportable.
They are manpower intensive as well as safety concerns and operations
impacts (causing clears.)

Thermal management using fluid systems in active cooling loops (for
avionics, personnel, fuel cells, hydraulics) are another example of
active systems on Shuttle.

**Level:** 2 and 3 - Information on this criteria is usually not
available early in concept development. As the design matures this
information can be used to assess the likely supportability of a
concept.

**Visions of Improvement:**

Basic improvements would target rotating machinery such as ground pumps
or on board recirculation pumps. Further improvements would include
passive thermal management schemes for electronics as well as any other
heat generating devices. Low voltage electronics and forced convective
cooling (fans) could simplify systems overall.

For future systems possible additions and hence negative impacts include
active cooling during ascent, retractable engine fans and variable
geometry requiring active closure, opening or variation of flow paths.
These would also impact negatively criteria such as "number of potential
leakage / connection sources".

Maximum improvement would reduce Shuttle type systems while avoiding a
net increase due to the addition of entirely new functions to be
achieved.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
established based on an active accounting of current systems such as
Shuttle. A challenge is also accounting for potentially new active
systems in future concepts such as active cooling during ascent, active
engine components such as retractable fans, variable geometry requiring
active closure, opening or variation of flow paths and turbomachinery
count (or the "number of engines").

It is also included here as a *direction* for future systems to improve
upon versus Shuttle if qualitative improvements such as dramatically
higher affordability and individual vehicle flight rates are a goal.

\(16\) Technology Readiness Level (TRL) (increase):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** Low - indeterminate as of this revision.

**Derivation:**

Technology Readiness Levels (TRL) as defined by NASA require
reassessment focused on applications, operational costs and
demonstration in valid environments. Shuttle represents technology
implementation with low TRL ratings *if* an understanding of operational
implications is considered a part of the TRL definition. By functional
definition the TRL ratings are high. Operability assessments of
technologies are required if TRL rankings are to be used to focus on the
recurring costs aspects of technologies.

**Level:** 1 or 2 - These values may be determined early in concept
development and demonstration. More definition occurs as concepts
evolve.

**Visions of Improvement:**

A basic improvement in this criteria would be the redefinition of all
TRL requirements to fit the goals of future highly reusable space
transportation. Further improvement is implementation and is synergistic
with the criteria "number of components with demonstrated high
reliability (increase)". The research, technology and development phases
must define goals at subsystem levels that are consistent with the broad
goals of the entire transportation system. Testing and demonstration
should focus on support requirements such as (1) long life limit, high
reliability parts to preclude high levels of replacement costs including
manufacture, logistics, handling, dedicated design engineering and
launch site infrastructure and support, and (2) customer requirements
such as those of potential commercial operators or payload providers.

**Target for Improvement:**

This is a "pure" design feature targets for which can be established for
components and subsystems only *once TRL definitions focused on life
cycle costs can be agreed upon by the technical community.*

\(17\) Number of different fluids (reduce):

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**Shuttle Benchmark:** 16 (majors only)

**Derivation:**

High numbers of *different* fluids correlate strongly to operation and
support costs, the ability to launch on time, the simplicity of the
vehicle and to overall supportability, recurring costs and hence life
cycle costs.

The Shuttle \*uses:

-   LO2 and LH2 for main propulsion.

-   Fuel cell grade LOX

-   Hypergols (N2O4 and MMH) for auxiliary propulsion (OMS/RCS) as well
    as hydrazine for auxiliary power units (APU's).

-   Hydraulic fluid for the actuation of aero-surfaces, landing gear and
    valves.

-   Waterproofing agents (DMES) for tile thermal protection systems.

-   Freons (R-114, 21 and 22) for thermal management (indirect and
    direct cooling of avionics, other systems, crew cabin A/C, as well
    as ground operations).

-   Ammonia (NH3) for thermal management.

-   GHe and GN2 for inerting and purges.

-   Water for cooling loops (A/C environmental control).

-   Freon precision cleaning agent for ground operations.

Other examples include the National Aerospace Plane (NASP) planning
which included "liquid hydrogen, liquid oxygen, liquid helium, methanol,
silane, hydraulic fluid, polyalphaolefin and liquid nitrogen"^16^. This
list does not address NASP planning for thermal management (freons,
water) as well as other gases, however these would add to this list of
different major fluids to be counted as a concept matures to design and
through implementation.

Commonality provides opportunities to eliminate and or simplify separate
infrastructure and facility requirements. The integration of vehicle
systems required for this is also desirable.

This criteria is extremely synergistic with the "number of toxic fluids
(reduce)".

**Level:** 1 or 2 - This information is usually available early in
concept development; however, thermal management may not be defined till
later (affecting 5 of the fluids mentioned). This is critical
information to decision making that should be required as early in
concept development and decision making as possible.

**Visions of Improvement:**

Basic improvements first address the criteria "number of toxic fluids"
and then move on to this criteria. Additions of fluids such as RP1 to
LO2 and LH2 as main propellants have negative associated impacts. A
system consisting of only RP1, LO2, LH2, GHe, GN2, water, one freon,
ammonia and freon PCA would still have 9 of the 16 commodities, 4 of
which would be toxic.

**Target for Improvement:**

This criteria is a "pure" design feature a target for which can be
easily established. A target for improvement would be to have LO2, LH2,
GHe and GN2, water, one freon, and freon PCA - a total of 7 and less
than 1/2 of current Shuttle systems.

\*Manufacturing fluids would further increase this number.

\(18\) Mass fraction required (reduce):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** To avoid accounting for SRB comparisons the
benchmark used here is for an all rocket powered SSTO type vehicle
similar to the bipropellant Access to Space^14^ baseline Option 3. The
basic rocket equation, with Isp limitations and delta-V requirements as
constraints, places this number at ≈ 0.90 mass fraction required for an
all rocket SSTO.

+-----------------------------------+-----------------------------------+
| System                            | Propellant Mass Fraction          |
+-----------------------------------+-----------------------------------+
| Rocket                            | 0.88-0.89                         |
|                                   |                                   |
| > Single Stage                    | 0.85-0.86                         |
| >                                 |                                   |
| > Two Stage                       | 0.65-0.72                         |
|                                   |                                   |
| Combined Cycle Airbreather        | 0.57-0.64                         |
|                                   |                                   |
| > Single Stage                    |                                   |
| >                                 |                                   |
| > Two Stage                       |                                   |
+-----------------------------------+-----------------------------------+

*Table 4: These mass fraction comparisons are not gains of simply "0.2"
for airbreathers as possible improvements. Rather they represent a
potential [tripling]{.underline} of the design space available with
associated potential operability gains through more robust, reusable
systems. Source: Johns Hopkins University, Applied Physics Lab,
Briefing^5^, to Space Propulsion Synergy Team by Dr. Frederick S.
Billig^4^.*

**Derivation:**

Reference "2- System margin (increase)" and "27 - Average Isp on the
reference trajectory (increase)".

This criteria may be considered to be the inverse of the prior Isp
criteria. Two distinctions are required:

-   The criteria is focused on lower mass fractions as enabling more
    operable, robust systems. Lower mass fractions are only meaningful
    if they translate into payload and or robustness and operability.

-   The increase in Isp is one possible approach to reducing or meeting
    a mass fraction. A mass fraction criteria stressing reduction is
    more inclusive of these possibilities.

Higher mass fractions in the 0.90 range cause increased sensitivity to
vehicle size (gross lift off weight) in so far as low Isp and Isp
variations (such as less Isp resulting during development) are combined.
Solutions result in low margins and lack of robustness of the vehicle as
performance requirements must be met. This is operationally undesirable.

**Level:** 1 - Similar to Isp this is information available early in
concept development.

**Visions of Improvement:**

Mass fractions of 0.635 to 0.715 are desirable assuming the gains carry
as a side effect more robust, operable systems. The additional systems
such as active cooling or more engine modes which may be associated with
reductions in mass fraction must be traded against features such as
those contained in this guide.

Maximum improvement in mass fraction takes into account not only Isp
gains but also the efficiency with which the spaces of a vehicle are
designed. The synergy to component reliability is critical. This in turn
relates to confined spaces, which are undesirable, purges, which should
be eliminated, and the degree of difficulty in accessing areas, which
should be minimal. This is not the only criteria related to component
reliability in this guide. As with "number of components with
demonstrated reliability" or "technology readiness levels" the relation
to thorough test and demonstration of operable, long life, reusable and
robust characteristics is intrinsically tied to broad advances in
operability.

**Target for Improvement:**

No target has yet been determined here even though this is a "pure"
design feature. Optimal design would continue to reduce mass fraction
focused on payback and operability of the systems that result in these
gains.

\(19\) Number of systems requiring monitoring due to hazards (reduce):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

Shuttle system examples include:

-   Closed compartments (monitoring for hazardous gases such as leakage
    of O2 or H2 during loading as well as monitoring for O2 content
    during personnel access). This includes the orbiter aft, ET
    intertank, and, for leakage concerns only, interfaces such as the H2
    vent arm carrier plate.

-   LOX System temperatures during loading (for geysering effects).

-   Cryo tank pressures and intertank temperatures (for maintaining
    structural margins and load limits).

**Level:** 2 and 3 - This information is often unavailable in early
concept development.

**Visions of Improvement:**

Monitoring of confined spaces for O2 content can reduce requirements by
avoiding a need for access at all. This is synergistic with other
criteria such as "number of components with demonstrated high
reliability", "number of hands on activities required", "number of
systems with BIT / BITE" and others.

Basic improvements continue with reductions in loading requirements by
using more robust structures capable of safely being loaded at low
pressures with minimal vent cycling for cryogenics. For example, a
pressurized LOX loading with cycles between 8 and 12 psig could be
caused by low robustness requiring pressure to assist structural
margins. The system monitoring requirements for temperature and pressure
increase as does the degree of hazard associated with the operation. Low
pressures and robust tanks are improvements.

**Target for Improvement:**

This criteria is not a "pure" design feature a target for which can be
easily set. It is included here as a critical direction for future
systems to improve upon versus Shuttle.

\(20\) Number of parts (different, backup, complex) (reduce):

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**Shuttle Benchmark:** Indeterminate as of this revision (examples
below).

**Derivation:**

-   Complexity: One measure is parts count.

-   Commonality: Maintenance, test and checkout procedures and the
    logistics supply system are simplified.

For one system to be compared against another the level at which the
comparison is made must be specified. Levels of complexity may be
determined at the component, subsystem, system, element or architecture
level. Also, the purpose of the parts can not be separated from the
measure of complexity. Additional parts (complexity) may allow greater
affordability such as through systems automation or health monitoring,
requiring more sensors and lines of code, or it may entail more parts to
increase mission reliability, such as engine out return to launch site
capability through out ascent. The productivity of each part, it's
resulting benefit, is positive. An increase in parts count, meaning
increased complexity and opportunities for failures and turnaround
expense, is negative. Trades are required which establish these
relations across the life cycle of the product.

+-----------------------------------------------+----------------------+
|                                               | Major Component      |
|                                               | Parts                |
+-----------------------------------------------+----------------------+
| Space Shuttle Main Engine (SSME)              | 5,807 *^13^* / ≈     |
|                                               | 4,744\* by P/N's for |
| Total for Four (Low and High Pressure)        | Block 1 Engine 2036  |
| Turbopumps per SSME                           |                      |
|                                               | 2,700 *^13^*         |
| Piece Part Count per SSME                     |                      |
|                                               | 70,000 *^13^* /      |
| Number of Welds per SSME                      | ≈29,000\*            |
| *^13,\ and\ FMEA/CIL^*                        |                      |
|                                               | > for Block 1 Engine |
|                                               | > 2036               |
|                                               |                      |
|                                               | ≈3000, Phase II      |
|                                               | Engine               |
+-----------------------------------------------+----------------------+
| Shuttle Orbiter Thermal Protection System     | ≈27,000              |
| (Tiles and Blankets)                          |                      |
+-----------------------------------------------+----------------------+

*Table 5: (London 1994)^13^, \*Rocketdyne Parts List, and FMEA/CIL
Statistics.*

Shuttle systems are characterized by a high degree of complexity focused
on performance (function) and mission reliability (as through
redundancy). The effect of this resulting complexity on operations for
turnaround and launch (dependability) was not a design driver. Lack of
reliability of individual parts further dictated the addition of
processes (inspections, checkouts, tests) that result in low flight rate
and high recurring cost.

This criteria is synergistic with other criteria such as "number of
components with demonstrated high reliability (increase)", "number of
different propulsion systems (reduce)", "number of unique stages
(reduce)", "number of active ground systems required for servicing
(reduce)", "mass fraction required (reduce)", and the "number of
propulsion sub-systems with fault tolerance (increase)".

**Level:** 3 - Parts count and degree of complexity is information
usually developing as the design matures to a preliminary design phase.
Early on in decision making the "complexity factor" may not be as
clearly understood. However, this is still critical information that
should be determined as early as possible in decision making.

**Visions of Improvement:**

Basic improvement addresses the architecture of the total transportation
system incorporating many of the criteria already covered elsewhere in
this guide for other reasons. For example, reducing toxic fluids or
following a common propellant ground rule allows more commonality of
parts. This simplifies maintenance procedures as well as the logistics
system.

Further improvement increases reliability both for the flight as well as
the turnaround by reducing parts count. For example, the elimination of
a system through a creative approach inherently increases reliability
during processing (fewer opportunities for failures).

Ideal levels of improvement occur when the productivity of additional
systems far outweighs the increased complexity, such as in achieving
more valuable functions or qualities (such as loitering or faster
turnaround capability). This requires rigorous demonstration, evolution
and design iteration aimed at creating hardware with extremely high
levels of component reliability. The result is negative "opportunistic
failures" during turnaround operations are not as easily accumulated and
costly.

-   Shuttle replacement of parts on each orbiter per flow varies from
    100 to 200 parts per flow. Reference Figure "D" in design feature
    10, number of components with demonstrated high reliability.

**Target for Improvement:**

Two targets can be established here. One is to reduce parts count over
Shuttle. This begins to address extremely high operating expenses due to
complex systems and the resulting opportunities for failures.

The second, with likely more impact, targets component reliability. Data
for current systems (MTBF, Life Limits, Reliability) can be quantified
and high targets for demonstrating new designs established. Rigorous
qualification and certification in the pre-acquisition phase including
tests to failure enables the affordable operation of complex systems.

\(21\) Number of expendables (fluid, parts, software) (reduce):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

For Shuttle this includes numerous fluids. The distinction for this
criteria from others already discussed is primarily that it includes
"soft goods" such as seals and software. Software is here considered an
expendable for Shuttle given the unique flight to flight requirements of
parts of the Shuttle software set.

-   Softgoods (seals for example, even if not of the "soft" variety such
    as metallic seals, naflexes, washers). These include flight and
    ground (regulators, facility, interfaces).

-   Software

-   Propellants (LO2 and LH2)

-   Propellants (Hypergols)

-   GHe and GN2

-   Hydrazine (auxiliary power units)

-   Catalyst (auxiliary power units)

-   Hydraulic fluid (flight and ground)

-   Cleaning fluids (Freon PCA and others)

-   Freons (thermal management)

-   Ammonia (thermal management)

-   Propane (LH2 flare stack)

-   Conditioned air

-   DMES (waterproofing agent)

**Level:** 1 and 2: These values may be determined early in concept
development and demonstration. More definition occurs as concepts
evolve.

**Visions of Improvement:**

Assuming other higher priority criteria (such as criteria "1" - toxic
fluids, "17" - different fluids or "18" - mass fraction) are addressed
then the focus of this criteria becomes primarily softgoods and
software.

Basic improvement in the use of softgoods would address (1) component
reliability (criteria "10") and (2) interfaces (criteria "30").

Ideal levels of improvement would have been achieved when the servicing
of main propellants is the only expendable from flight to flight.

**Target for Improvement:**

This criteria is a "pure" design feature which represents actual
materials to account for.

Targets for improvement in this criteria are synergistic with
improvements in other areas such as "number of toxic fluids (reduce)",
"number of different fluids (reduce)" and "number of purges required
(reduce)". Improvement may target one servicing operation of main
propellants, limited use of gases such as GHe and GN2, no hydraulic
fluid servicing from flight to flight, no additional fluids for power,
no waterproofing or special coatings, and no highly unique software
loading or reconfiguring from flight to flight.

\(22\) Number of checkouts required (reduce):

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**Shuttle Benchmark:** High - indeterminate as of this revision.

**Derivation:**

-   The term "checkout" indicates functional, dynamic verification as
    distinct from inspections (criteria 23).

Where there is no automated VHM system available as on Shuttle the
functional verification must be performed to establish the reliability
of a component or system. This includes all redundant components and
systems which are required to provide fault tolerance of critical
functions. On Shuttle these include, but are not limited to:

-   Valves (for back flow if check valves, for actuation including
    timing, internal leakage, and flowrate verifications).

-   Electrical systems (using intrusive breakout boxes to perform
    checkouts given the high number of electronic systems with no BIT /
    BITE).

**Level:** 3 - Information on the checkouts that will be required
requires information that may not be available early in concept
definition.

**Visions of Improvement:**

As other criteria are improved upon, such as fewer toxic fluids, more
BIT / BITE, fewer highly critical conditions such as confined spaces
requiring purges, fewer active ground systems for servicing, and fewer
potential leakage and connection sources, then improvements will
accumulate in this criteria (fewer checkouts.)

Basic improvement requires that not only in flight reliability of
components be increased but that it be done without use of processing
intensive inspection or checkout to isolate, repair and replace faulty
components pre-flight. Rigorous certification focused on robust,
dependable, maintainable as well as reliable systems is required. High
reliability *and* reusability are both required to assure reductions in
the number of checkouts.

**Target for Improvement:**

This criteria is not a "pure" design feature that is easily targeted. It
is a resultant of features already listed such as the high ranking
criteria number 10 - number of components with demonstrated high
reliability. Targets may be set upon a full understanding of the
criticality, complexity and demonstrated reliability of components
especially the robustness of systems and the reliability demonstrated
during processing.

\(23\) Number of pollutive or toxic materials (reduce):

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

The distinction here from toxic fluids, a much higher ranked criteria,
is in the greater correlation to processing (safety and supportability)
and recurring costs associated with the fluids rather than the expended
materials. Both are related. Materials here represent primarily a
recurring cost impact due to regulated waste management and disposal of
hazardous materials.

These include contaminated fuels, cleaning solutions, primers, paint
strippers, lubricants, post launch waste water, hypergolic scrubber
fluids, as well as materials impregnated with any of these fluids.

**Level:** 2 and 3 - Information on this criteria is usually not
available early in concept development. As the design matures this
information can be used to assess the likely supportability of a
concept.

**Visions of Improvement:**

Basic improvement addresses cleaning requirements the processes for
which generate highly regulated waste. This in turn relates to the size
of infrastructure, the replacement of components on ground systems many
of which have stringent cleaning requirements and the degree of
intrusion into systems.

**Target for Improvement:**

This criteria is a pure design feature targets for which can be
established focusing on existing quantities of pollutants and setting
new levels as well as materials replacement schedules based on these
data.

\(24\) Number of inspection points (reduce):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

-   Inspection here is used to refer to establishing a level of
    accomplishment such as the degree to which a product has met
    objectives or acceptability to design specifications.

Shuttle inspection points include:

-   Orbiter TPS (Tile, carbon-carbon, after each flight)

-   SSME MCC / nozzle (step and gap for thermal damage)

-   SSME turbopumps (bearing degradation, torque checks, end travel
    check, nozzle burn through)

-   Orbiter structure (cracks, corrosion, OMDP only)

-   Orbiter windows (inspected and polished every flight)

-   Orbiter brake system (wheel and tire)

-   Orbiter payload bay radiators (every flight for space debris)

-   Orbiter cold plates (for degradation of surface finish or damage
    during component removal and replacement)

-   ET TPS debonds (foam, pre-flight)

-   Orbiter composite structure degradation

-   Internal corrosion in fluid systems (example: water flash
    evaporator, thermal management systems)

-   Interfaces for sealing surface finishes, damage and coatings (For
    example, ET to Orbiter 17-inch disconnects, SSME to MPS, every
    flight)

-   ET / Orbiter 17-inch disconnects (every flight, every ET set even
    though new, every Orbiter set even though reused)

-   Orbiter MPS screens for debris

-   OMS / RCS inspections for nitrate buildups

-   Hydraulic fluid filters

-   Inspect for hydraulic leaks visually

Multitudes of other requirements to visually inspect an area and verify
an acceptable condition exist for Shuttle.

**Level:** 3 - More detailed information that is available as the design
matures to a preliminary design phase and beyond.

**Visions of Improvement:**

Basic improvement on this criteria is synergistic with the "number of
components with demonstrated high reliability (increase)". While in
flight reliability for Shuttle systems may be relatively high (for space
systems) it is assured in part by inspections for critical systems
during turnaround. The more numerous the inspection requirements the
higher the manpower required to accomplish work within a given flight
rate. Process reliability, the reliability during turnaround, if low,
dictates high numbers of mandatory inspections to assure components are
ready for the next flight, or to assure that all failed components are
found and repaired, replaced or have problems adequately addressed.

Robust development, providing both high reliability in use as well as
high life limits for reusability, relates directly to this criteria.
Definition of a development plan including test, design iteration,
targeted reliability and life limits is required.

**Target for Improvement:**

This criteria is a "pure" design feature an adequate understanding of
which would be obtained upon quantifying inspection requirements on
Shuttle such as through the review of OMRS documents. It is also a
[resultant]{.underline} of the degree to which other features listed are
improved upon or not. The ideal target is to require no more than a
simple walk around of a future highly reusable space transportation
system, hence approaching aircraft type operations.

\(25\) Number of propulsion sub-systems with fault tolerance (increase):

  -----------------------------------------------------------------------

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**Shuttle Benchmark:** Indeterminate as of this revision.

**Derivation:**

Current Shuttle systems increase complexity for certain critical
functions in order to assure a higher reliability in flight.

For example, the Shuttle hydraulic system is triple redundant to avoid
loss of control of main engine functions such as thrust vector control.
For the SRB's double redundancy is used in hydraulics. Auxiliary
propulsion (OMS /RCS) is cross fed to provide certain backups. Power
systems (APU's ≈ 135 Hp each) are triple redundant under nominal
operation. A simple example is the use in many systems of quad redundant
check valves (series and parallel) or dual redundant filters (in
parallel) to assure proper flow and function. This is all desirable from
the perspective of fault tolerance; however, complexity increases if
defined by parts count and processing activity increases due to more
opportunities for failure.

**Level:** 2 - Information usually not available early on in concept
definition.

**Visions of Improvement:**

To assure fault tolerance increases without impacting operations a
demonstrated high reliability per component is required. Basic
improvements in fault tolerance must be coupled to the reliability of
components during turnaround, often called process reliability or
supportability. This criteria is synergistic with "number of components
with demonstrated high reliability (increase)". Basic improvements would
require (1) simplification of systems, (2) fault tolerance through
increased margins and robustness for operation, and (3) a thorough
research, development and demonstration focused on high component life
limits (millions of cycles, millions of minutes, component lifetimes
near to vehicle lifetimes) and (4) the iteration on designs, tests to
failure, improvements in reusability including ground and flight
operation.

**Target for Improvement:**

Targets for this criteria require a comparison by components to similar
components on a system such as Shuttle. Comparisons to commercially
similar equipment can also serve as targets. Further, for new components
in next generation systems the target can be established with a
comparison or "sanity check" to the operational goals and life cycle
cost goals for the system.

\(26\) Number of engines (reduce):

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**Shuttle Benchmark:** 3 SSME's, 2 OMS engines, 2 SRB's

**Derivation:**

-   An engine is defined as: The number of discrete propulsion sets that
    are individually delivered or installed or that are individually
    overhauled. Equals the number of engines for conventional bell
    nozzle rocket engines.

The number of engines is a multiplier of maintenance and test
requirements for any given configuration. Where more engines are used to
reduce power levels, enhancing life limitations on components and
increasing reusability, there is a benefit. Being able to achieve that
*same benefit with fewer engines* is always desirable. This is
synergistic with the criteria "number of components with demonstrated
high reliability (increase)".

+---------------------------------------------+-------------+----------+
|                                             | Engines     | Total    |
+---------------------------------------------+-------------+----------+
| *Atlas IIAR (Liquid\*, Centaur)*            | 1, 1        | 2        |
+---------------------------------------------+-------------+----------+
| *Access to Space Airbreather / Rocket*      | 2+2         | 4        |
+---------------------------------------------+-------------+----------+
| Shuttle (Main Propulsion, SRB's, OMS)       | 3, 2, 2     | 7        |
+---------------------------------------------+-------------+----------+
| Atlas IIAS (Liquid\*, Liquid, Solids,       | 1, 1, 4, 2  | 8        |
| Centaur)                                    |             |          |
+---------------------------------------------+-------------+----------+
| *Access to Space All Rocket Bipropellant    | 7, 2        | 9        |
| SSTO (Main and OMS)*                        |             |          |
+---------------------------------------------+-------------+----------+
| Saturn Apollo Moon Rocket (Stage 1, 2, 3,   | 5, 5, 1, 1  | 12       |
| 4)                                          |             |          |
+---------------------------------------------+-------------+----------+
| Soviet N-1 Moon Rocket^3^ (Stage 1, 2, 3,   | 30, 8, 4,   | 44       |
| 4, 5)                                       | 1, 1        |          |
+---------------------------------------------+-------------+----------+
| \*2 Thrust chambers per engine              |             |          |
|                                             |             |          |
| Note: Varying payload, launch rate          |             |          |
| capabilities, staging events.               |             |          |
|                                             |             |          |
| *Italics = Planned or conceptual, not       |             |          |
| flown.*                                     |             |          |
+---------------------------------------------+-------------+----------+

*Table 6: Various engine count examples. Note that a requirement for
"engine out" capability possibly increases the number of engines for a
vertical take-off rocket whereas with horizontal take-off, imposing the
same requirement, it is still possible to reduce engine count.*

The number of engines on a vehicle is strongly related to the ease of
integration and the maintainability of the propulsion system.

**Level:** 1 - This is information available early in the conceptual
phases of vehicle definition.

**Visions of Improvement:**

Basic improvement begins by altering the definition of an "engine". The
sharing of components, such as at the turbopump level should a failure
occur, begins to reduce parts count or to provide more fault tolerance.
Reduced power levels are required to enable this. Further, integration,
combined with increased throttle capability and control, could eliminate
separate systems for orbital maneuvering such as the 2 Shuttle OMS pods.
This is synergistic with reducing the number of different fluids which
also enables fewer active ground systems for servicing.

Ideal levels of improvement would be enabled by a few high reliability
engines. Similar to aircraft, the number of engines could be a targeted
architectural feature once highly reusable space transportation is
enabled similar to airline preferences for twin jet aircraft versus
aircraft with 3 or more engines.

**Target for Improvement:**

Targets for improvement over the current 3+2+2 configuration could (1)
target commonality (of fluids, hardware, tankage) and then (2) target
fewer remaining engines.

**(27) Average I~sp~** on the reference trajectory (increase):

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**Shuttle Benchmark:** To avoid accounting for SRB's the benchmark used
here is for an all rocket powered SSTO type vehicle similar to the
bipropellant Access to Space^14^ baseline Option 3. The value for an
SSME type performance is 430s (about 370s at sea level and 450s in
vacuum).

  ----------------------------------------------- -----------------------
                                                  I^\*^

  SSME type                                       375sec

  Ejector Scramjet type                           645sec
  ----------------------------------------------- -----------------------

*Table 7: Comparison of rocket versus rocket based combined cycle (RBCC)
systems using an I^\*^ method (Escher 1995)^10^.*

**Derivation:**

Shuttle or subsequent possible all rocket SSTO vehicles have low
effective Isp. This has various implications: (1) higher mass fractions
required (0.90), (2) increased sensitivity to vehicle size (gross lift
off weight) and (3) increased risk to payload targets not being met
during development. All of the prior can be considered as resulting
directly or indirectly in low robustness of a vehicle.

High Isp gains enable mass fraction requirements as low as 0.6 to 0.7.
Effective Isp of 700-800 s begins to enable these targets. Much enhanced
operability is a side effect through the allowance of more robust,
operable systems on the vehicle that may be enabled by the lower mass
fraction.

**Level:** 1 - Usually available as information very early in any
concept development.

**Visions of Improvement:**

The high rank here assumes dramatic Isp gains. Associated improvements
could include:

-   More robust thermal protection systems (assuming passive only)
    enabled by less weight sensitivity in development.

-   Powered approaches for landing and self ferry.

-   Higher margins in major subsystems such as propulsion down to the
    component level.

-   Operating ranges well below design tolerances eliminating the
    practice of running engines at \> 100% of rated thrust. This extends
    life limits resulting in more supportable, less manpower intensive
    systems.

**Target for Improvement:**

This criteria is a "pure" design feature; however, a technology
development effort that must assure closure of the performance aspects
must creatively integrate these with the guidelines contained here for
maximum operational and programmatic (pre-operational) benefit. Hence,
Isp gains consistent with these guidelines should be targeted.

\(28\) Number of manhours (c/o, handle, assemble, etc) on system between
LCF/HCF (reduce):

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**Shuttle Benchmark:** High - indeterminate as of this revision.

**Derivation:**

LCF (low cycle fatigue) and HCF (high cycle fatigue) are contributors to
component failures. Low values for life limits mean little reusability
and hence lack of affordability due to inspection, checkout, test,
repair or replacement of LRU's. On/off cycles create transients on high
pressure turbomachinery for example which limit reusability in the
propulsion system. Duration or wear due to extended use can also limit
reusability if high cycle life is low. Safety factors that are
relatively high (1.5, 2 or 4) do not always correlate to high
reusability and should not be taken as an indication of robustness (for
example use of a component to ½ of fleet leader failure experience).

Manhours and costs accumulate as components with low reusability require
attention on a system such as Shuttle. This criteria is a subset to "9 -
number of components with demonstrated high reliability (increase)"
given the limitation here to only LCF and HCF problems.

**Level:** 3 - More detailed information that is available as the design
matures to a preliminary design phase.

**Visions of Improvement:**

Improvement here includes:

-   Robustness and margin

-   Certification (qualification) practices

-   New technologies

Increased power level margins on engines begin to increase life limits
on propulsion systems, a major cost component of any space
transportation system. An example is design and development of an engine
at a 100% power / thrust level but using it at only 75% of this rating.
Preserving this margin during development is a priority for improvements
in this criteria.

Certification (qualification) practices require definition. A major
programmatic cost driver is the iteration of designs, tests to failure
and redesigns for increased life cycle limits addressing either LCF or
HCF. Programmatics dictate:

1.  Identifying those systems with life limits driven by LCF/HCF.

2.  Identifying costs associated with these systems.

3.  Focusing certification on extending life limits for those systems
    with the highest portion of life cycle costs.

More advanced improvement address LCF/HCF using new technologies.
Examples here include fluid film bearings or laser ignition for
turbomachinery, new materials and manufacturing techniques.

**Target for Improvement:**

This criteria is partially a resultant of other features contained in
this guide. It is also a "pure" design feature targets for which can be
established based on similar systems such as those on Shuttle. A
detailed breakdown of systems and components (by part) and an analysis
of design, repair and maintenance data for LCF/HCF causes is required.
Correlations of major cost elements to systems with low reusability are
required. Current accounting methods for Shuttle problem tracking do not
accomplish this. No comprehensive study has addressed this to date.

\(29\) Number of criticality 1 failure modes (reduce):

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**Shuttle Benchmark:** Shuttle criticality 1 failure modes are Orbiter ≈
1700, Solid Rocket Boosters ≈ 2200, External Tank ≈ 1100, Shuttle Main
Engines ≈ 800, and GSE ≈ 300. Criticality 1R failure modes are Orbiter ≈
6300, Solid Rocket Boosters ≈ 1300, External Tank ≈ 100, Shuttle Main
Engines ≈ 400,and GSE ≈ 400 (*from Critical Hardware Lists, JSC)*.

**Derivation:**

Criticality 1 failure modes are defined as "loss of life or vehicle".
Where redundancy exists but loss of both redundant items could cause
loss of life or vehicle the designation is 1R. Criticality 1 failure
modes correlate strongly to personnel and public safety. For Shuttle a
FMEA / CIL approach is used to manage risk by identifying and formally
documenting potential and critical failures.

**Level:** 2 and 3 - This information is usually not expected in early
concept definition.

**Visions of Improvement:**

A vision of improvement is sufficient redundancy or simplicity to reduce
criticality 1 failure modes to a fraction of current Shuttle levels
*while simultaneously improving on the total system reliability during
processing.* Functionality, the usefulness of the system to a payload
customer, being flexible or having generous capacity, would also be
simultaneously improved upon.

**Target for Improvement:**

This criteria is a "pure" design feature which represents actual
hardware that can be accounted for. Improvement here may be measured
against complex Shuttle systems. Improvement here must be synergistic
with top criteria such as "number of systems with BIT / BITE
(increase)", "number of active ground systems required for servicing
(decrease)", "number of components with demonstrated reliability
(increase)", and "number of parts (different, backup, complex)
(decrease)". Targeting reductions in criticality 1 failure modes without
addressing these other criteria would adversely affect process
reliability resulting in increased turnaround and operating costs.

Design Features (30 through 64)

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Further expansion on all the design features, such as with the
measurable criteria 1 through 29, will be done in future reports. The
SPST will continue to support efforts relating to space transportation
by exploring questions and answers key to future decision making. The
remaining criteria are:

30. \# of element to element interfaces requiring engineering control
    (-)

31. Hours to refurbish propulsion system (-)

32. \# of physically difficult to access areas (-)

33. \% of propulsion subsystems monitored to change from hazard to safe
    (+)

34. \# of hours to refurbish launch site between each launch (-)

35. Mean time between major overhaul (-)

36. Amount of energy release from unplanned reaction of propellant (-)

37. \# of manufacturing, test and operations facilities (recurring) (-)

38. \# of ground power systems (-)

39. \# of active engine systems required to function (-)

40. Margin, mass fraction (+)

41. Mean time between major overhaul as % of cost of system (+)

42. Amount of real time inspection or repair (-)

43. \# of hazardous processes (-)

44. Margin, thrust level / engine chamber pressure (+)

45. Hardware cost (-)

46. \# of major systems required to ferry or return to launch site (plus
    logistics support) (-)

47. \# of modes or cycles (-)

48. \# of alternate dedicated emergency abort sites required (-)

49. \# of engine restarts required (-)

50. Margin, average specific impulse (+)

51. \# of keepout zones (-)

52. \# of aero-control surfaces (-)

53. \# of cleanliness requirements (-)

54. Facility capitalization cost (-)

55. Cost of transportation / requirements (-)

56. \% of trajectory time available for abort (+)

57. Amount of response time to initiate safe abort (-)

58. \# of tools required (-)

59. Margin, % of payload (+)

60. \# of process steps to manufacture (-)

61. \# of attainable destinations (+)

62. Ideal delta-V on reference trajectory (-)

63. \# of acres permanently affected (-)

64. \# new unique approaches (+)

Design Features (30 through 64) - Definitions

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The following are brief definitions and clarifications of the prior
design features.

-   Note: (-) Indicates the desirable direction is to reduce.

> (+) Indicates the desirable direction is to increase.

30. \# of element to element interfaces requiring engineering control
    (-): This feature includes major interfaces between distinct
    organizations. On Shuttle for example, orbiter to SSME and orbiter
    to ET interfaces correspond to distinct centers and contracts.
    Internal but still formal interfaces incur the recurring costs of
    configuration control, documentation and organizational or customer
    interfaces.

31. Hours to refurbish propulsion system (-): Includes all systems, not
    just the engines. Propellant tanks and associated systems,
    feedlines, main propulsion, controllers and sensors are included.
    Also includes the interfaces from any facilities such as propellant
    feeds or vents, electrical interfaces and any other fluid
    requirements (such as purges). This criteria is a resultant of other
    features listed in this guide such as the high priority criteria on
    toxic fluid count, the degree of BIT / BITE, or the number of
    components with demonstrated high reliability.

32. \# of physically difficult to access areas (-): Any area requiring
    more than reasonable access. An example is the Shuttle orbiter aft,
    requiring access kit installation and great care accessing the area.
    Little space is provided for error such as a missed step. Crawling
    in uncomfortable positions is the norm.

33. \% of propulsion subsystems monitored to change from hazard to safe
    (+): Any potential hazards should be monitored in the propulsion
    system and in some way changed as required to a safe configuration.

34. \# of hours to refurbish launch site between each launch (-):
    Includes the facility as well as the interfaces to the vehicle
    (feeds, vents and electrical as well as other fluids). This criteria
    is a resultant of other features listed in this guide such as high
    priority criteria on toxic fluids count, the number of purges, the
    number of leakage or connection points and the degree of BIT / BITE.

35. Mean time between major overhaul (-): Depot maintenance operations
    reduce fleet productivity. The desirable direction is a high number
    of flights between any required major downtime.

36. Amount of energy release from unplanned reaction of propellant (-):
    Measured by quantity of propellant such as cryogens, hypergols or
    any others such as RP-1 or any propellants for auxiliary propulsion
    or station keeping.

37. \# of manufacturing, test and operations facilities (recurring) (-):
    For Shuttle this includes external tank (ET) production and SRB/SRM
    manufacture and continuing refurbishment. It also includes engine
    test facilities. Operations facilities include the launch site such
    as processing hangers, landing sites, and pads.

38. \# of ground power systems (-): For example a ground power
    transmission station or a dedicated electrical power generating
    facility.

39. \# of active engine systems required to function (-): Similar to the
    "number of active components required to function including flight
    operations (reduce)" except considering only the engine, a subset of
    the propulsion system.

40. Margin, mass fraction (+): Given a mass fraction requirement it is
    desirable both during development and into implementation to carry
    margin on the mass fraction. For the purposes of this guide the mass
    fractions are assumed to be low, a higher priority (reference
    criteria 17-Mass fraction required (reduce)). For example, a concept
    requiring 0.70 mass fraction but developed and implemented at a
    value of 0.72 would have margin. This would be similar to the use of
    15% weight growth margins in development so as to avoid the
    undesirable effects of inevitable weight growth. These undesirable
    effects in development and implementation include (1) loss of
    robustness, (2) increased thrust power levels on engines (3) loss of
    payload. The ability to implement with mass fraction margin allows
    greater flexibility (such as greater payload) at less cost for the
    transportation system at a later point if required.

41. Mean time between major overhaul as % of cost of system (+): For an
    expensive component, relative to the whole system, the mean time
    between major overhaul should be increased (as in more reusability).

42. Amount of real time inspection or repair (-): Measured in manhours.
    Robust systems requiring no inspection or which in some way reduce
    the processing tasks manpower intensive nature are desirable.
    Functional, in use verification is desirable where such use is truly
    indicative of the health of the system. This criteria is a resultant
    of other features listed in this guide.

43. \# of hazardous processes (-): This includes lifting operations,
    toxic fluids, complex loading scenarios and use of purges.

44. Margin, thrust level / engine chamber pressure (+): Given a GLOW the
    development and implementation of a system with thrust levels well
    below those designed, tested and certified to is desirable. For
    example, a design may be certified at 100% but used only at 75%
    power levels. Increased reusability of propulsion systems components
    and hence operability of the system results. Combined with other
    approaches reusability of the propulsion systems increases.

45. Hardware cost (-): The actual cost of a component such as a spare
    that is required to continue operations. Does not include the
    handling, tracking and analysis associated with that part, or the
    work to actually replace the component and verify a successful
    repair.

46. \# of major systems required to ferry or return to launch site (-)
    (plus logistics support): Includes any dedicated ferry craft (such
    as the Shuttle 747), all facilities such as a mate de-mate facility
    or any contingency equipment.

47. \# of modes or cycles (-): Air breathing rocket, ram, scram, pure
    rocket as well as any changes such as from RP-1 to LH2 constitute a
    mode or cycle.

48. \# of alternate dedicated emergency abort sites required (-): Does
    not include an alternate site if that site is not dedicated to the
    abort contingency.

49. \# of engine restarts required (-): Restarting of engines, to the
    extent it can be avoided, is not desirable; however, this is
    secondary to the higher priority criteria "5 - number of different
    propulsion systems (reduce)".

50. Margin, average specific impulse (+): Given an engine Isp the use at
    a lower Isp value is desirable allowing flexibility or capability
    for the transportation system. For the purposes of this guide the
    Isp is assumed to be high, a higher priority (reference criteria
    26-Average Isp on the reference trajectory (increase)).

51. \# of keepout zones (-): Hazardous loading operations, purged
    confined spaces and toxic propellant storage areas are included in
    this count. Keepout zones often interfere with other required
    operations.

52. \# of aero-control surfaces (-): Includes body flaps, rudders,
    ailerons, elevons and any other actuated or active surface.

53. \# of cleanliness requirements (-): Includes any requirements for
    handling, particulate, non-volatile residue, storage, component
    cleanliness, maintaining clean levels, blow downs, filters,
    analysis, manufacture, assembly and operations.

54. Facility capitalization cost (-): Dedicated facilities infer a high
    cost to operate a system and to maintain it on a recurring cost
    basis.

55. Cost of transportation / requirements (-): Any dedicated
    transportation requirements such as equipment, special handling or
    transportation of components for manufacture.

56. \% of trajectory time available for abort (+): The ideal is an abort
    capability from engine ignition through any part of the flight. An
    engine out capability from engine start with 100% of trajectory time
    available for abort is desirable.

57. Amount of response time to initiate safe abort (-): The time
    required to automatically respond to an abort condition and safe a
    vehicle should be reduced to the least time possible.

58. \# of tools required (-): For operation, dedicated tool requirements
    such as unique shop tools, wrenches and aids.

59. Margin, % of payload (+): Reference criteria "39" - margin, mass
    fraction, "43" - margin, thrust level and "49" - margin, average
    Isp. The establishment of margin in payload capability serves as a
    forcing function in development avoiding implementation of systems
    with payload preservation at the expense of robustness, reusability
    or operability. For example, a targeted 23,000 lbm payload to a
    given orbit may be used to initially develop and analyze a concept
    for closure (affecting implementation decisions) even though 20,000
    lbm is the eventual requirement. This is distinct from the 15%
    weight growth margin traditionally used in concept development.

60. \# of process steps to manufacture (-): Includes cleaning, welding,
    X-Rays or other NDE, assembly, coatings, materials manufacture such
    as autoclaves, hardening, and finishing and or any unique points in
    the manufacturing process.

61. \# of attainable destinations (+): References orbits and cross range
    capability.

62. Ideal delta-V on reference trajectory (-): Gains from air launches,
    speed as well as gravity, gains from nozzle underexpansion
    avoidance, and improved Isp, or speed gains from any launch assist
    provide a reduction here. This efficiency of configuration
    characteristic enables comparison of different concepts. A full
    analysis of the vehicle and it's forces while flying the reference
    trajectory is required.

63. \# of acres permanently affected (-): Includes operations as well as
    any dedicated manufacturing capability.

64. \# new unique approaches (+): This is from a public perspective
    only, the novelty of the approach or the public appeal.

![](media/image15.emf){width="9.340277777777779in" height="7.01875in"}

Programmatic Considerations

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As previously noted a comparative assessment of space transportation
system concepts or design choices within a system must address not only
measurable design criteria but also programmatic considerations. The
value of this approach has been discussed in the introduction to this
document. This section addresses the specific programmatic
considerations or factors (as shown on the previous page as well as
visualized on the X-axis of the figure on page 2). These programmatic
considerations impact the non-recurring cost portion of the life cycle
cost of a space transportation architecture. Further these non-recurring
costs may be divided into those involved in the R&D phase and those in
the program acquisition phase.

The programmatics outlined here cover the traditional categories of
program management activities such as cost, schedule, technical, risk,
and procurement.

[DEFINITIONS]{.underline}

**R&D - TECHNOLOGY:**

The technology "R&D" category of programmatic considerations is the
first major non-recurring cost step leading to "Program Acquisition". An
aircraft production analogy would be the technology R&D in composite
materials and structures, CRT flight instruments, and upgraded turbojet
engines required to enable a new state-of-the-art transport such as the
Boeing 777. Technology R&D must be identified and established as
possible "upfront" before a manufacturing decision (program acquisition)
is committed.

The following list of programmatic considerations include 11 related to
the R&D phase of a program.

**PROGRAM ACQUISITION:**

"Program Acquisition" is the final non-recurring-cost, major program
activity, leading to the fabrication and delivery of the desired
"affordable" space transportation system. This "system" includes the
delivered vehicles as well as required support infrastructure. An
aircraft production analogy would be the data gathering and
decision-making process leading to major capital (non-recurring)
investment in factory facilities, tooling, and operations-support
infrastructure necessary to support production and delivery of aircraft
to the customer.

The following list of programmatic considerations include 7 related to
this program acquisition phase of a program.

**The following describes and clarifies features of any program in an
order prioritized using previously described methodology.**

"Level" refers to the level or phase in the acquisition cycle at which
the desired programmatic information is available. Level 1 is concept
definition, 2 is system and subsystem description and 3 is at the
preliminary design review phase.

\(1\) PA - Number of major new technology development items (engines,
airframes, TPS...) (reduce):

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The system requiring the greatest quantity of new items to develop can
be expected to have a much higher risk to the schedule and cost of
eventual acquisition.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(2\) PA - Technology readiness at program acquisition milestone: TRL
6 + margin (increase)

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Assessment for the program acquisition phase includes evaluating all the
technologies that were researched, developed and demonstrated and then
determining if a particular technology will be part of the acquisition
or not. For example, a technology at TRL 8 at the time of preliminary
program acquisition decisions is more desirable than one at TRL 6 all
other factors being equal.

**Level:** 3 - This represents information that may not be available
until later in decision making, such as at a PDR phase.

\(3\) R&D - Time required to establish infrastructure (schedule of the
R&D phase) (reduce)

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Infrastructure here refers to major test facilities for R&D requirements
such as wind tunnels or test stands. Those concepts requiring a
relatively short period of time for the accomplishment of the R&D phase
are more attractive than those requiring many years to complete. The
measure is in years.

**Level:** 1 through 3: Partial information and estimates may be
available for this information early in concept development. More
information becomes available as the project proceeds into a preliminary
design phase.

\(4\) PA - Infrastructure cost: initial system implementation (capital
investment) (reduce)

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This cost represents a major non-recurring financial investment for
system support facilities, equipment and other amortized physical plant
properties.

**Level:** 1 - This represents information traditionally available early
in concept development.

![](media/image16.emf){width="5.061805555555556in" height="6.5875in"}

*Figure F. The relation of flight systems to eventual infrastructure
(NASA OEPSS 1992)^17^.*

\(5\) PA - Total system DDT&E concept development and implementation
cost (reduce)

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This is a prime cost estimate factor (not including infrastructure)
which will weigh heavily in go-no-go program acquisition decisions.
DDT&E and implementation refers to Design, Development, Test and
Engineering as well as the theoretical first unit (implementation) which
encompasses first vehicles as well as operating sites.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(6\) R&D - Number of technology breakthroughs required to develop and
demonstrate (reduce)

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How many basic physics, materials or performance technical breakthroughs
must be developed and demonstrated? Those technologies requiring a
greater quantity of "proof of concepts" can be expected to have a higher
schedule and program risk.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(7\) PA - Technology capability margin (performance as fraction of
ultimate) (increase)

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The resulting fraction can enable an adequate assessment of technical
performance margin deemed essential for a robust, affordable system. An
example is an engine that can perform the mission at 90% of the maximum
rated chamber pressure rather than 106%. The expectation of being able
to create, preserve and implement this margin is the program
consideration.

**Level:** 2 through 3: Information in this criteria is traditionally
available as the project matures to a PDR phase.

\(8\) R&D - Number of full scale ground or flight demonstrations
required (reduce)

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This refers to the development and demonstrations in full scale (system,
sub-systems, components) required during the technology R&D phase. The
cost of facilities, GSE, material, technical support and headcount
relate strongly to the number of demonstrations required.

**Level:** 2 - This represents information often available early on
before any PDR phase.

\(9\) R&D - Current TRL (increase)

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As with the design features (reference design feature 16-Technology
Readiness Level) the determination of where a technology is relative to
TRL descriptions is a key determinant of placing further emphasis on one
approach versus another. The programmatic applicability is generally
concerned with technologies at the low end of the TRL spectrum as
measured against each other for similar functions.

This criteria, while also used as a design feature, has a different
implication from a programmatic perspective. The programmatic concern is
the risk to the R&D schedule as well as cost containment.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(10\) R&D - Number of operational effectiveness attributes previously
demonstrated (increase)

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A determination of readiness from an operational perspective may not
always equal a determination of readiness from a purely functional
perspective. A functional perspective may involve only the mission or
performance aspect, such as a thermal protection system capable of
withstanding certain temperatures or of reliably protecting a vehicle
from either ascent or descent heating environments. An operational
perspective will go further and include the ability to perform at low or
zero levels of turnaround support, with true reusability and robustness.

A technology which has demonstrated operational systems effectiveness
would be more desirable than one having demonstrated fewer. Operational
systems effectiveness may be measured by having demonstrated attributes
such as affordability, reliability, dependability, simplicity, or
maintainability. A complete list of desirable attributes is contained in
"Overview of the SPST Approach" under "Benefits (Technical)".

**Level:** 1 through 2: This represents information often available
early before a PDR phase.

\(11\) PA - Number of other options available (increase)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

A particular technology may fulfill a function that may also be achieved
with a competing technology. For example, high density fuel cells and
batteries may both be available as a power source system at acquisition
yet only one may be needed. Having multiple options is desirable for any
functional need of a space transportation concept. Program acquisition
is enhanced by having varied choices possible to proceed into as well as
backups should later events require a redirection.

**Level:** 1 through 2: This represents information often available
early before a PDR phase.

\(12\) R&D - Number of applications beyond space transportation
(increase)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

The ability to gain support, private, public or otherwise sponsored for
a technology endeavor, increases as the number of possible secondary
applications increases. Can the technology be applied to aircraft,
trains, automobiles or other areas outside of space transportation
systems?

**Level:** 1 through 2: This represents information often available
early before a PDR phase.

\(13\) R&D - Time to reach TRL 6 from start of R&D (reduce)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

Overall program schedule requirements will be affected by upfront R&D
timelines. For any technology the ability to reach TRL 6 quickly is
desirable.

**Level:** 1 through 3: Partial information and estimates may be
available for this information early in concept development. More
information becomes available as the project proceeds into a preliminary
design phase.

\(14\) R&D - Number of related technology databases available (increase)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

In assessing levels of risk for budgets, performance, operability and
schedule those technologies reasonably well related to documented R&D
from previous work should encounter a minimum, predictable level of
program risk. "How good is the database?" and "has this been done before
or is it all new?" are key questions.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(15\) R&D - Number of new facilities required costing over \$2M
(reduce)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

This item serves as further quantifier of technology R&D that may likely
contribute to an unacceptable level of overall program affordability.
This includes test sites and manufacturing sites related to R&D.

**Level:** 3 - This represents information that may not be available
until later in decision making, such as at a PDR phase.

\(16\) PA - Number of items requiring major ground test articles and
demonstration (example: new engines) (reduce)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

Major ground test articles are extremely consuming of time and
resources. The technology meeting a majority of all other requirements
and possessing the least test requirements can be expected to have a
cost and schedule advantage.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(17\) R&D - Cost to reach TRL 6 (reduce)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

This measure is in cost. Assuming a set of options or technologies will
likely achieve an equal benefit, measured against the design features in
this guide for example, then the option which costs less to reach a TRL
at which a program acquisition point can be made is more desirable.

**Level:** 1 - This represents information traditionally available early
in concept development.

\(18\) R&D - Total annual funding by item at peak dollar requirements
(reduce)

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

The measure here is cost. The percent of a programs annual funds
required by a particular technology R&D effort is preferably low all
other factors being equal.

**Level:** 1 - This represents information traditionally available early
in concept development.

Summary and Conclusions

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

The intent of this report is a dynamic document providing a framework
which will be updated as more data is gathered, improvements are
implemented in current systems and new systems are developed and
demonstrated.

This document is focused on the HRST study - "to identify innovative new
systems concepts that can achieve Earth-to-orbit (ETO) transportation at
costs of \$100-\$200 per pound payload". These costs are now
approximately \$5,000-\$8,000. With few exceptions the features and the
priority order presented in this report are also very applicable to any
new space transportation system and to the Shuttle program and any
future upgrades it may implement. The identification of concepts and
associated technologies that hold the greatest promise of achieving very
low recurring costs in space transportation results in critical up front
investment decisions. Understanding how system choices relate to
eventual recurring costs is a critical part of any up front planning.

The SPST challenges the technical community developing new systems to
compare the features of their systems to the features, especially the
design features, contained in this guide. The same basic questions apply
to a system or an entire concept.

-   Are many of the first 10 design features being improved upon?

-   Are many of the first 20 design features being improved upon?

-   Is a design responsive to the most important programmatics but not
    the most important design features?

-   Is an effort focused on functional performance or is a balanced
    approach being used which addresses the design features as well as
    programmatics?

-   Have other disciplines been directly involved early on in
    determining the direction of a technology development - what should
    be developed and focused on? Has manufacturing been involved early
    on well before implementation? Have operators been involved in
    setting a development focus?

Even if the prior questions are not easily answered (such as assessing a
concepts improvement against the design features) is the general thrust
or direction of a concept responsive to many of the top design features?

This document may be used by designers or program managers in terms of
general thrust or direction even if a full assessment against the
recommended improvements in order of priority is not immediately
possible. The emphasis here is strategic.

Various conclusions are possible at this point:

1.  The questions contained in each of this guides design features (how
    many toxic fluids, how much potential for BIT/BITE and so forth)
    must be well understood and quantified. Being non-traditional
    information at early decision making stages does not alter this
    need. This information has been determined to be key to
    understanding the total costs of a space transportation system. It
    is important that any HRST, reusable being the focus, quantify and
    understand the relationship of certain design features to eventual
    life cycle costs - development, acquisition and especially
    operation.

2.  The need to quantify, predict and optimize recurring costs as well
    as other attributes of a concept such as launch on time or
    operability requires further efforts such as in modeling
    development. The ability to answer the question "how often can it
    launch and how many people are required" leads directly to "how much
    will it cost to operate". In order to enable successful decision
    making connected to long term goals information is required to
    formulate benchmarks that allow predicting the eventual operating
    costs of potential designs and architectures. This information which
    establishes a resource that is a result of a design would allow
    improvements focused on the costs of access to space to be well
    anchored and therefore more likely to actually succeed in achieving
    market growth through greater overall affordability.

3.  A significant few top features have been determined here based on
    diverse sets and levels of information and team member backgrounds.
    Tentatively, it can be derived that an understanding of the complex
    inter-relationships of these top criteria is key to any strategy for
    improvement in space transportation affordability. A "cascade"
    effect for these criteria should be sought for improvements at the
    component, subsystems, and architecture levels. The intent is to
    have a ripple through as many of the important, prioritized criteria
    as possible. This is similar to the approach used in cascading
    weights to achieve performance gains.

Further Information

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

**à**

Background of the SPST

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

The Space Propulsion Synergy Team traces it's origins to the Space
Propulsion Synergy Group. This group was formed in 1990 to address the
findings of the Space Propulsion Technology Symposium held at Penn State
University (Bray 1993 and Dankhoff and Hope 1993)^7,9^. These findings
included:

-   "The lack of a recognized national space propulsion strategy is
    detrimental to U.S. space programs and international posture"

-   "There exists major gaps between technology developers and users,
    and a means of correcting this is essential"

-   "Technology users (i.e. propulsion system developers, producers and
    operators) should provide their real requirements, and share in
    technology program planning and funding"

The SPSG eventually became involved in the Access to Space Study^14^,
and, as the Space Propulsion Synergy *Team*, the X-33 / RLV technology
development and demonstration programs.

Positive involvement of the SPST in the future direction of access to
space toward low cost, routine operations continues with support to the
Highly Reusable Space Transportation Study, the subject of this report.

Currently the membership involved in providing support and insight to
the Highly Reusable Space Transportation project includes a diverse
group of government, industry and academia. The membership that has been
or is currently involved in HRST support activity, such as the
development of this guide, includes:

Dana Andrews Boeing / D&SG T- 206-773-1137

Seattle, WA **F -6624**

Jim Berry McDonnell Douglas T- 714-896-3557

Huntington Beach, CA **F -5807**

Jim Bray LMMSS T- 504-257-5536

MAF, LA **F -1210**

Ray Byrd Boeing T- 407-783-0220 / ext. 309

Cocoa Beach, FL **F -2712**

Ed Cady McDonnell Douglas T- 714-896-5075

Huntington Beach, CA **F -6930**

George Cox P&W / UTC T- 407-796-2887

West Palm Beach, FL **F -5099**

Steve D'Alessio Johns Hopkins Univ., APL T- 301-953-6000 / ext. 7810

Laurel, MD **F -5937**

Bryan S. DeHoff Aerospace Technical Services T- 513-755-1360

West Chester, OH **F** -**1360**

Walt Dankhoff SPST Executive Secretary T- 410-257-0056

Wash. D.C., AIAA **F- 301-855-8332**

Bruce Farner USAF, Philips Lab T- 805-275-5206

Edwards AFB, CA **F -5852**

Tom Funicilli Aerojet T- 916-355-3249

CA **F -3015**

Dave Goracke Rocketdyne T- 818-586-0378

Canoga Park, CA **F -0579**

Jerry Grey AIAA T- 516-537-3942

Wash. D.C. **F- 212-595-3184**

Joe Hamaker NASA / MSFC T- 205-544-0602

**F -5861**

Joe Haney Rockwell T- 310-922-1057

Downey, CA **F -5358**

Ron Hankins Aerojet T- Retired

CA **F**

Robert Houston LMMSS T- 504-257-1510

MAF, LA **F -1210**

Larry Hunt NASA / LaRC T- 804-864-3732

**F -8545**

Lee Jones NASA / MSFC T- 205-544-7094

**F -3960**

Gary Lee Boeing / D&SG T- 206-773-8964

Seattle, WA (SATWG I/F) **F -9070**

Dan Levack Rocketdyne T- 818-586-0420

Canoga Park, CA **F -0579**

Scott May NASA / MSFC T- 205-544-9525

**F -5861**

Carey McCleskey NASA / KSC T- 407-861-3775

**F -0103**

Earl Pansano LMMSS T- 504-257-5302

MAF, LA **F -1210**

Russel Rhodes NASA / KSC T- 407-861-3874

**F -3036**

John Robinson Propellant Supply Tech. T- 303-979-8179

CO **F -1597**

Rick Vargo McDonnell Douglas T- 407-383-2827

FL **F -269-6202**

Gordon Woodcock Boeing T- Retired

Huntsville, AL **F**

Edgar Zapata NASA / KSC T- 407-861-3955

**F -3036**

Overview of the SPST Approach

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

**Benefits (Technical), Programmatics (Constraints) and Functions
(Performance)**

**[Benefits (Technical)]{.underline}**

+------------------------------------+---------------------------------+
| **Affordable / Low Life Cycle      | **Responsive**                  |
| Cost**                             |                                 |
|                                    | > Flexible                      |
| > Low Recurring Cost               | >                               |
| >                                  | > Capacity                      |
| > Low Cost Sensitivity to Flight   | >                               |
| > Growth                           | > Operable                      |
| >                                  | >                               |
| > Operation and Support            | > Vehicle Health Management     |
| >                                  | >                               |
| > Initial Acquisition              | > Ease of Vehicle/System        |
| >                                  | > Integration                   |
| > Vehicle/System Replacement       | >                               |
|                                    | > Maintainable                  |
| **Dependable**                     | >                               |
|                                    | > Simple                        |
| > Highly Reliable                  | >                               |
| >                                  | > Launch on Demand              |
| > Intact Vehicle Recovery          | >                               |
| >                                  | > Easily Supportable            |
| > Mission Success                  | >                               |
| >                                  | > Resiliency                    |
| > Launch on Time                   |                                 |
| >                                  | **Safety**                      |
| > Robustness                       |                                 |
|                                    | > Vehicle Safety                |
| **Environmental Compatibility**    | >                               |
|                                    | > Personnel and Public Safety   |
| > Minimum Effect on Atmosphere     | >                               |
| >                                  | > Equipment and Facility Safety |
| > Minimum Impact all Sites         |                                 |
|                                    |                                 |
| **Public Support**                 |                                 |
|                                    |                                 |
| > Benefit GNP                      |                                 |
| >                                  |                                 |
| > Social Perception                |                                 |
+------------------------------------+---------------------------------+

**[Programmatics (Constraints)]{.underline}**

+------------------------------------+---------------------------------+
| During the Technology R&D Phase:   | During the Program Acquisition  |
|                                    | Phase:                          |
+------------------------------------+---------------------------------+
| **Affordable / Low Life Cycle      | **Affordable / Low Life Cycle   |
| Cost**                             | Cost**                          |
|                                    |                                 |
| > Cost to Develop                  | > Cost to Acquire               |
|                                    |                                 |
| **Schedule**                       | **Schedule**                    |
|                                    |                                 |
| **Risk**                           | **Risk**                        |
|                                    |                                 |
| **Dual Use Potential**             | **Technology**                  |
|                                    |                                 |
|                                    | **Investor Incentive**          |
+------------------------------------+---------------------------------+

**[Functions (Performance)]{.underline}**

Payload of 30,000 lbm nominal (+/- 10,000 lbm), volume of 15 X 35 ft, to
28.5 degrees and 100 nautical miles nominal altitude. Multiple
customers.

What is QFD?

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

Quality Function Deployment (QFD) is a method pioneered by the Japanese
in the late 60's as a way of translating consumer demands into design
targets. To quote Yoji Akao (Akao 1988)^1^:

> *"With such fast paced change occurring these days, especially in our
> social and economic environment, many companies are facing rapid
> changes in industrial structure bought about by the technological
> innovation and changing consumer trends. These companies are finding
> that the effort to develop new products is crucial for their
> survival."*

![](media/image17.emf){width="5.99375in" height="4.095833333333333in"}

> ⇓ ⇓ \...⇒

*Part of the matrix for the QFD correlating* *attributes to measurable
criteria*

Immediately, one might conclude that the notion of consumers is, for the
most part, not relevant to the business of launching payloads to orbit,
or at least the situation is not at all similar to a person in the
market for a new VCR. This perception is entirely incorrect. In so far
as there are customers with demands for better or new products then QFD
is fully applicable. The business of translating these demands from the
vague and qualitative (and not very useful) to the more specific and
material is custom made for a method such as QFD.

A QFD has certain requirements. Customer definition must be given great
thought. Teams must be synergistic. The qualities of our systems,
attributes such as responsiveness or flexibility, must be fully
explored, defined and related. Possible measures of these qualities must
be determined. Finally, the relation of the specific measures to
qualitative attributes must be explored, reasoned out, and weighted. The
process is methodical and with relentless pressure yields the insights
leading to the all important design targets that eventually must guide
product development.

Besides countless information on the World Wide Web (searches on "QFD"
will yield a variety of papers, organizations and other information) one
book suggested here for further reading is the translation from the
Japanese of Yoji Akao's "[Quality Function Deployment - Integrating
Customer Requirements into Product Design]{.underline}"^1^.

Verifying Functional Requirements - Performance

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

The SPST approach to functional or performance requirements is a
simplified "gate". For purposes of developing the criteria contained in
this guide, which is strategic in nature, and understanding the
interrelationships and priorities, the specific details on the
performance of particular concepts and technologies is not required.
However, in determining the transportation system performance closure or
compliance there must be a growth or technology margin included at this
early stage. Further detailed steps in the technology evaluation process
requires that performance aspects of potential technologies, or whole
transportation systems built from these technologies, be one of the
basic building blocks in the decision making process.

One such example applies to rocket based combined cycle (RBCC) type
vehicles. The following is one possible approach to maintaining a
necessary tracking of the ability of a concept to reach closure and
satisfy functional requirements.

Possible spreadsheet, with entries listed at one second intervals along
the flight trajectory:

+-------------+--------------------------------------------------------+
| t           | time, s                                                |
|             |                                                        |
| u           | velocity, ft/s                                         |
|             |                                                        |
| Z           | altitude, ft                                           |
|             |                                                        |
| X           | downrange, ft                                          |
|             |                                                        |
| M           | Mach number                                            |
|             |                                                        |
| W           | weight, lbf                                            |
|             |                                                        |
| q           | dynamic pressure, lbf/ft^2^                            |
|             |                                                        |
| θ           | flight path angle, deg                                 |
|             |                                                        |
| α           | angle of attack, deg                                   |
|             |                                                        |
| T           | thrust, lbf                                            |
|             |                                                        |
| L           | lift, lbf                                              |
|             |                                                        |
| D~0~        | drag at zero lift, lbf                                 |
|             |                                                        |
| D~L~        | induced drag, lbf                                      |
|             |                                                        |
| D           | total vehicle drag, lbf                                |
|             |                                                        |
| I~f~        | engine specific impulse, s                             |
|             |                                                        |
| I~eff~      | vehicle specific impulse = I~f~(1-D/T)                 |
|             |                                                        |
| w~e~        | engine airflow rate, lbm/s                             |
|             |                                                        |
| w~H2~       | hydrogen flow rate, lbm/s                              |
|             |                                                        |
| w~O2~       | oxygen flow rate, lbm/s                                |
|             |                                                        |
| ER          | overall engine equivalence ratio                       |
|             |                                                        |
| a           | vehicle acceleration, ft/s^2^                          |
+-------------+--------------------------------------------------------+

Notes and References

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

Pg.

+-----+----------------------------------------------------------------+
| 1   | 1.  Akao, Yoji (1988) "Quality Function Deployment:            |
| 00, |     Integrating Customer Requirements into Product Design,"    |
|     |     \[Translation from "Hinshitsu tenkai katsuyo no jissai" by |
| 101 |     Glenn H. Mazur\], Productivity Press, Portland, OR.        |
+-----+----------------------------------------------------------------+
| 2.  | 3.  American National Standards Institute and American         |
|  13 |     Institute of Aeronautics and Astronautics (1992) "Guide    |
|     |     for Estimating and Budgeting Weight and Power              |
|     |     Contingencies for Spacecraft Systems," American Institute  |
|     |     of Aeronautics and Astronautics, Washington, D.C.          |
+-----+----------------------------------------------------------------+
| 4.  | 5.  Aviation Week & Space Technology (1991) "Soviet Union      |
|  72 |     Reveals Moon Rocket Design That Failed to Beat U.S. to     |
|     |     Lunar Landing," *in Issue of February 18, 1991,*           |
|     |     McGraw-Hill, Inc.                                          |
+-----+----------------------------------------------------------------+
| 6.  | 7.  Billig, Frederick S. (1990) "Design and Development of     |
|  60 |     Single-Stage-To-Orbit Vehicles," *in APL Technical Review, |
|     |     Volume 2, Number 1, 1990,* Johns Hopkins University.       |
+-----+----------------------------------------------------------------+
| 8.  | 9.  Billig, Frederick S. (1996) "Briefing to the Space         |
|  60 |     Propulsion Synergy Team," Washington D.C., March, 1996.    |
+-----+----------------------------------------------------------------+
| 10. | 11. Blair, J.C., and Ryan, R.S. (1992) "The Role of Criteria   |
|  17 |     in Design and Management of Space Systems," *AIAA paper    |
|     |     92-1585*, and in *MSFC Knowledge Capture Series,* NASA     |
|     |     Marshall Space Flight Center, Huntsville, Al.              |
+-----+----------------------------------------------------------------+
| 12. | 13. Bray, Jim (1993) "Payoffs for Applying QFD Techniques in   |
|  96 |     the SPSG Strategic Planning Support Effort for ETO         |
|     |     Transportation and Propulsion Systems," *in                |
|     |     AIAA/SAE/ASME/ASEE 29th Joint Propulsion Conference and    |
|     |     Exhibit, June 28-30, 1993*, Martin Marietta Manned Space   |
|     |     Systems, New Orleans, LA.                                  |
+-----+----------------------------------------------------------------+
| 14  | 15. CSTS Alliance, Boeing, General Dynamics, Lockheed, Martin  |
| . 5 |     Marietta, McDonnell Douglas, Rockwell (1994) "The          |
|     |     Commercial Space Transportation Study, Executive Summary   |
|     |     and Final Report," NASA Contract No.s NAS1-19247, 19242,   |
|     |     19241, 18230, 19244 and 19243.                             |
+-----+----------------------------------------------------------------+
| 16. | 17. Dankhoff, Walter F., and Hope, William P. (1993) "Overview |
|  96 |     of the Space Propulsion Synergy Group (SPSG) Strategic     |
|     |     Planning Support Efforts for Earth to Orbit                |
|     |     Transportation," *in AIAA/SAE/ASME/ASEE 29th Joint         |
|     |     Propulsion Conference and Exhibit, June 28-30, 1993*.      |
+-----+----------------------------------------------------------------+
| 18. | 19. Escher, William J.D. (1997) "The Synerjet Engine,          |
|  74 |     Airbreathing / Rocket Combined-Cycle Propulsion for        |
|     |     Tomorrow's Space Transports, Selected Papers, 1963-1996,"  |
|     |     Society of Automotive Engineers, Inc., Progress in         |
|     |     Technology Series, SAE PT-54, Paper "A User's Primer for   |
|     |     Comparative Assessments of All-Rocket and Rocket-Based     |
|     |     Combined-Cycle Propulsion Systems for Advanced             |
|     |     Earth-to-Orbit Space Transport Applications".              |
+-----+----------------------------------------------------------------+

Pg.

+-----+----------------------------------------------------------------+
| 36  | 11. Hamaker, Joseph (1996) "Single Stage to Orbit Versus Two   |
|     |     Stage to Orbit: A Cost Perspective," *in Space Technology  |
|     |     and Applications International Forum (STAIF-96), January   |
|     |     1996*, NASA Marshall Space Flight Center, Huntsville, Al.  |
+-----+----------------------------------------------------------------+
| 12. | 13. Lockheed Space Operations Company, NASA (1993) "1993       |
|  24 |     Orbiter Processing Study Phase I Final Report,             |
|     |     APU/Hydraulics Baseline Assessment," part of the           |
|     |     Electrical Actuation Technology Bridging Program,          |
|     |     December, 1993, NASA Contract No. NAS10-10900, CCBD        |
|     |     SSP-58754. \[Ref. used herein is to sections not covered   |
|     |     under information disclosure restriction\].                |
+-----+----------------------------------------------------------------+
| 14. | 15. London, John R. Lt Col, USAF, (1994) "LEO on the Cheap,    |
|  63 |     Methods for Achieving Drastic Reductions in Space Launch   |
|     |     Costs," Maxwell Air Force Base, Research Report No.        |
|     |     AU-ARI-93-8, Air University Press.                         |
+-----+----------------------------------------------------------------+
| 16. | 17. NASA (1994) "Access to Space Study," Summary Report,       |
|  10 |     Office of Space Systems Development, NASA Headquarters,    |
| ,13 |     Washington D.C.                                            |
|     |                                                                |
| 53, |                                                                |
| 60, |                                                                |
|     |                                                                |
| 74  |                                                                |
| ,96 |                                                                |
+-----+----------------------------------------------------------------+
| 18. | 19. NASA (1994) "A Survey of Waterproofing Procedures for      |
|  53 |     Shuttle," prepared for NASA, Ames Research Center by The   |
|     |     Hans W. Wynholds Company, NASA Purchase Order No. A39157DC |
|     |     (BCV).                                                     |
+-----+----------------------------------------------------------------+
| 20. | 21. NASA (1992) "Design Notice, Ground Operations Summary,     |
|  58 |     NASP," Langley Research Center, Systems Analysis Office,   |
|     |     Document X30NP92001 Unclassified.                          |
+-----+----------------------------------------------------------------+
| 22. | 23. NASA (1992) "Operationally Efficient Propulsion System     |
|  87 |     Study (OEPSS)," NASA Contract No. NAS10-11568.             |
+-----+----------------------------------------------------------------+
| 24. | 25. NASA (1988) "Shuttle Ground Operations Efficiencies /      |
|  37 |     Technologies Study (SGOES)," Volume 3, Space-vehicle       |
|     |     Operational Cost Drivers Handbook (SOCH), NASA Contract    |
|     |     No. NAS10-11344.                                           |
+-----+----------------------------------------------------------------+
| 26. | 27. Rocketdyne, NASA (1996) "Advanced Transportation System    |
|  14 |     Studies, Technical Area 3, Alternate Propulsion Subsystem  |
|     |     Concepts, Rocket Engine Life Analysis, Task Final Report," |
|     |     NASA Contract No. NAS8-39210, DCN 1-1-PP-02147, August     |
|     |     1996, Rockwell International, Rocketdyne Division.         |
+-----+----------------------------------------------------------------+

Acknowledgments

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

This work was enabled by the contributions of members of the Space
Propulsion Synergy Team (SPST / HRST Support Team) for both content and
guidance. A complete listing of members can be found in the section
"Background of the SPST" on page 97. The support of industry members to
the ongoing function of the SPST is specially noted as is the support of
the American Institute of Aeronautics and Astronautics (AIAA). This work
was performed as a product for the NASA HRST study.

Acronyms and Abbreviations

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

+----------------------+-----------------------------------------------+
| A/C                  | Air Conditioning                              |
|                      |                                               |
| Ai                   | Availability, Inherent                        |
|                      |                                               |
| APU                  | Auxiliary Power Unit                          |
|                      |                                               |
| BIT                  | Built in Test                                 |
|                      |                                               |
| BITE                 | Built in Test Equipment                       |
|                      |                                               |
| CAPSS                | Computer Aided Planning and Scheduling System |
|                      |                                               |
| CIL                  | Critical Items List                           |
|                      |                                               |
| c/o                  | Checkout                                      |
|                      |                                               |
| CoFR                 | Certificate of Flight Readiness               |
|                      |                                               |
| DDT&E                | Design, Development, Test and Engineering     |
|                      |                                               |
| DMES                 | Dimethylethoxysilane                          |
|                      |                                               |
| ECLSS                | Environmental Control and Life Support System |
|                      |                                               |
| EMA                  | Electromechanical Actuator                    |
|                      |                                               |
| ET                   | External Tank                                 |
|                      |                                               |
| FMEA                 | Failure Mode Effects Analysis                 |
|                      |                                               |
| GH2                  | Gaseous Hydrogen                              |
|                      |                                               |
| GHe                  | Gaseous Helium                                |
|                      |                                               |
| GLOW                 | Gross Lift Off Weight                         |
|                      |                                               |
| GN2                  | Gaseous Nitrogen                              |
|                      |                                               |
| GNP                  | Gross National Product                        |
|                      |                                               |
| GO2                  | Gaseous Oxygen                                |
|                      |                                               |
| GPSS                 | Ground Processing Scheduling System           |
|                      |                                               |
| GSE                  | Ground Support Equipment                      |
|                      |                                               |
| GUCP                 | Ground Umbilical Carrier Plate                |
|                      |                                               |
| H2                   | Hydrogen                                      |
|                      |                                               |
| HCF                  | High Cycle Fatigue                            |
|                      |                                               |
| HCFC                 | Hydrochlorofluorocarbons                      |
|                      |                                               |
| HGDS                 | Hazardous Gas Detection System                |
|                      |                                               |
| Hp                   | Horsepower                                    |
|                      |                                               |
| HRST                 | Highly Reusable Space Transportation          |
|                      |                                               |
| I/F                  | Interface                                     |
|                      |                                               |
| Isp                  | Specific Impulse                              |
|                      |                                               |
| LCC                  | Life Cycle Cost                               |
|                      |                                               |
| LCF                  | Low Cycle Fatigue                             |
|                      |                                               |
| LDT                  | Logistics Down Time                           |
|                      |                                               |
| LH2                  | Liquid Hydrogen                               |
|                      |                                               |
| LHe                  | Liquid Helium                                 |
|                      |                                               |
| LO2                  | Liquid Oxygen                                 |
|                      |                                               |
| LOX                  | Liquid Oxygen                                 |
|                      |                                               |
| LRU                  | Line Replaceable Unit                         |
|                      |                                               |
| MCC                  | Main Combustion Chamber                       |
|                      |                                               |
| MMH                  | Monomethylhydrazine                           |
|                      |                                               |
| MPS                  | Main Propulsion System                        |
|                      |                                               |
| MTBF                 | Mean Time Between Failure                     |
|                      |                                               |
| MTTR                 | Mean Time to Repair                           |
|                      |                                               |
| N2O4                 | Nitrogen Tetroxide                            |
|                      |                                               |
| NDE                  | Non-Destructive Test                          |
|                      |                                               |
| NH3                  | Ammonia                                       |
|                      |                                               |
| nm                   | Nautical mile                                 |
|                      |                                               |
| O2                   | Oxygen                                        |
|                      |                                               |
| OMRS                 | Operations Maintenance Requirement            |
|                      | Specification                                 |
| OMS                  |                                               |
|                      | Orbital Maneuvering System                    |
| OPF                  |                                               |
|                      | Orbiter Processing Facility                   |
| OSAMS                |                                               |
|                      | Operation Simulation and Analysis Modeling    |
| PA                   | System                                        |
|                      |                                               |
| PCA                  | Program Acquisition                           |
|                      |                                               |
| PDR                  | Precision Cleaning Agent                      |
|                      |                                               |
| PR                   | Preliminary Design Review                     |
|                      |                                               |
| PRACA                | Problem Report                                |
|                      |                                               |
| PVT                  | Problem Reporting and Corrective Action       |
|                      |                                               |
| QFD                  | Pressure, Volume, Temperature                 |
|                      |                                               |
| R&D                  | Quality Function Deployment                   |
|                      |                                               |
| RBCC                 | Research and Development                      |
|                      |                                               |
| RCS                  | Rocket Based Combined Cycle                   |
|                      |                                               |
| RLV                  | Reaction Control System                       |
|                      |                                               |
| RM&S                 | Reusable Launch Vehicle                       |
|                      |                                               |
| ROM                  | Reliability, Maintainability, and             |
|                      | Supportability                                |
| RP-1                 |                                               |
|                      | Rough Order of Magnitude                      |
| SCAN                 |                                               |
|                      | Rocket Propellant, Kerosene                   |
| SPST                 |                                               |
|                      | Shuttle Connector Analysis Network            |
| SRB                  |                                               |
|                      | Space Propulsion Synergy Team                 |
| SSME                 |                                               |
|                      | Solid Rocket Booster                          |
| SSTO                 |                                               |
|                      | Space Shuttle Main Engine                     |
| TRL                  |                                               |
|                      | Single Stage to Orbit                         |
| TSM                  |                                               |
|                      | Technology Readiness Level                    |
| TVC                  |                                               |
|                      | Tail Service Mast                             |
| VHM                  |                                               |
|                      | Thrust Vector Control                         |
|                      |                                               |
|                      | Vehicle Health Management                     |
+----------------------+-----------------------------------------------+