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1
Introduction
THE TASK
The National Research Council's Aeronautics and Space Engineering Board
established the Pane! on Small Spacecraft Technology to
review the National Aeronautics and Space Administration's (NASA) plans
for a new small spacecraft technology development program;
review NASA's current technology program and priorities for relevance
to small spacecraft, launch vehicles for small spacecraft, and small
spacecraft ground operations;
examine small spacecraft technology programs of other government
agencies;
assess technology efforts in industry that are relevant to small spacecraft,
launch vehicles, and ground operations; and
identify technology gaps and overlaps and prioritize areas in which greater
investments are likely to have high payoff, considering the current and
projected budgets, the NASA mission statement (see Appendix A), and the
needs of industries that utilize space.
Small spacecraft are variously defined within the aerospace industry as weighing
less than 1,000 pounds, as weighing less than 1,000 kilograms, or as allowing the
selection of a smaller launch vehicle. NASA uses the terms miniature spacecraft or
micro-spacecraj! to imply the reduction of mass, volume, and components to allow
downsizing by one or more launch vehicle classes over current practice (Hanks, 1993~.
However, for consistency in this report, small spacecraft will be defined as those
weighing approximately 600 kilograms or less.
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Introduction
BACKGROUND AND STATUS
In the past, NASA has focused a large percentage of its resources on the large
manned system programs: Apollo, Space Shuttle, and Space Station. These types of
programs not only have long duration and very expensive engineering and manufacturing
phases, but commit NASA to very high operational costs extending over a period of ten
to twenty years. Also, many of NASA's unmanned space programs such as the Tracking
and Data Relay Satellite System, Viking, and the large observatories (High Energy
Astronomy Observatory, Gamma Ray Observatory, and Hubble Space Telescope) cost
hundreds of millions to billions of dollars during development and manufacture, and up
to hundreds of millions of dollars in yearly operations costs. The national importance and
visibility of these programs resulted in an environment in which the consequences of
failure were so severe that any degree of technological risk to improve performance or
reduce cost was unacceptable. It also brought about a large bureaucracy that included
numerous levels of oversight review. in an effort to reverse this trend, NASA has
indicated its intent to emphasize the use of small spacecraft to conduct the majority of
its future space science and applications missions (Goiclin, 19931. This approach is
intended to result in a space program with more frequent flights at markedly lower cost
per flight. It is anticipated that such a program will engender a more aggressive approach
to the application of advanced technology in its flight programs because of the higher
tolerance for risk that will result from the much lower cost for each flight. NASA
believes that this approach will also enable much shorter times from program initiation
to flight (two to three years total), with the resultant greater versatility, improved
responsiveness to mission requirements, and enhanced efficiency. Another stated
objective is to develop technology and transfer it to industry, both in the aerospace and
nonaerospace sectors, in order to enhance national competitiveness and stimulate the
creation of jobs for Americans.
The high cost of NASA's large space programs has resulted in minimal spending
for advanced technology research and development, since most of the funds available to
NASA have been spent in support of the large programs. As a consequence, much of the
technology required to carry out future small spacecraft missions economically is not
available from the NASA technology program. Fortunately, the Department of Defense
(DoD), several of its agencies, and numerous industrial firms have had active small
spacecraft technology development programs in the past, and the results of these efforts
are now available for use by NASA. However, expenditures for national defense have
been severely curtailed in recent years, and additional cutbacks are projected for the
future. The United States is facing increasing international competition in the commercial
space areas of communications, remote sensing, and in the launch vehicle market (Mintz,
1994; NRC, 1992; Pelton et al., 19921. If NASA is going to provide the leadership for
itself and the commercial sector, it must maintain an evolving, long-term, continuous
technology program specifically aimed at enabling future, highly demanding space
missions at a reasonable cost.
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8
Technology for Small Spacecraft
Space Systems Costs
The overriding factor inhibiting access to space is cost. The cost drivers are the
development and construction of the spacecraft, the mission sensors, the launch vehicle,
launch and mission operations, and extensive testing and reviews to lower the perceived
risk to an acceptable level. Advanced technology that has been sufficiently developed by
NASA, other government agencies, and industry to permit incorporation in NASA small
spacecraft can contribute to the reduction in cost for each of these elements and is
addressed in this report.
An effective way to lower launch costs is to reduce the weight of the spacecraft,
including the mission payload sensors. For most spacecraft, the principal weight drivers
are (~) electrical power systems, (2) propulsion and propellant systems, (3) structures,
and (4) guidance and control systems. Payload instruments also can contribute
significantly to the overall spacecraft weight (Auclair, et al., 1993; Davis, 1993; Larson
and Wertz, 19921.
Although not directly a technology issue, it is worth noting that the cost of
developing and constructing the spacecraft can be influenced markedly by the customer
and contractor program management implementation. NASA, DoD, and industry have
demonstrated with recent small spacecraft technology development programs that
simplified technical requirements, coupled with a design-to-cost approach and closely
integrated engineering, operational, and manufacturing development activity, can reduce
the cost of space missions. Such programs include the Small Explorer spacecraft
program; the Miniature Sensor Technology Integration (MSTI) program; and the
Microsats program.1 The panel believes these techniques can be successfully extended
to future small spacecraft programs.
Small Spacecraft Applications
Technology has progressed so rapidly, particularly in the electronics arena, that
much can be accomplished now with the use of integrated circuits, high-capacity
computers, and small devices with large memory capability. In adclition, there have been
impressive advances in miniaturized instruments, lightweight materials and structures,
high-output and small power sources, and accurate position determination through use
of the Global Positioning System (GPS). These technologies, combined with the changes
in the approach to systems engineering, management, and operations processes, can
~ The Small Explorer program for science missions is sponsored by NASA's Goddard Space
Flight Center (GSFC); the MST} program is sponsored by the Ballistic Missile Defense
Organization (BMDO), the U.S. Air Force Phillips Laboratory, and the let Propulsion
Laboratory (IPL) to test miniature sensor technology; and the Microsals program is sponsored
by the Advanced Research Projects Agency (ARPA) to provide improvements to small spacecraft
communications technology.
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Introduction
permit small spacecraft to be far more efficient and cost effective, as well as to
accomplish missions with much greater capability than previously believed possible.
Using currently available technology augmented by a vigorous technology
development program, the pane! believes that:
.
.
.
.
For many missions, a small spacecraft can be used to achieve the mission
requirements with capability approaching that of today's large spacecraft.
The Small Explorer program is an example of a program that uses a small
spacecraft to achieve significant scientific objectives.
For many of the more demanding missions, small spacecraft can achieve
a significant percentage of the mission objectives at much lower cost. The
Mars Pathfinder program (formerly called the Mars Environmental Survey
(MESUR)/Pathfinder program) is an example of a current effort to apply
this philosophy to the unmanned exploration of Mars.
It is likely that some missions requiring simultaneous measurements by
multiple sensors can be accomplished with constellations of small
spacecraft.
Some missions that require larger, more complex spacecraft can be
accomplished at significantly lower cost through application of
technologies developed for small spacecraft.
Not all small spacecraft missions are both faster and less expensive than large
spacecraft, since technology research and development for miniaturization is costly. The
pane} further recognizes that the use of multiple spacecraft in constellations may not be
less expensive than large spacecraft. However, the use of small spacecraft in
constellations distributes the risk among several spacecraft and launch vehicles rather
than concentrating all the risk with one large spacecraft. This distribution of risk should
result in a less costly systems engineering approach. Because of the lower cost to build
and launch a small spacecraft replacement, the use of such constellations can enable a
much more economical replacement of an instrument that fails on orbit than if it were
one of several on a large spacecraft.
A more detailed description of current and potential small spacecraft applications
is given in Appendix B.
Current Small Spacecraft Programs
Although NASA's combined investments in large science missions (Voyager,
Hubble, Galileo) are greater than its total investment in the more numerous small
spacecraft missions, small spacecraft have served a long-standing role in NASA missions
that predates the current enthusiasm for small spacecraft. Numerous space physics and
astrophysics missions have been completed through the Explorer and Small Explorer
programs, and JPL has participated in a number of DoD small spacecraft programs that
sensed to advance component technology in several key areas.
9
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10
Terrestrial Probes.
Technology for Small Spacecrap
in order to transition from large, one-of-a-kind spacecraft to smaller spacecraft,
NASA has initiated several programs. For example, the NASA Office of Space Science
has initiated the Discovery program, which consists of a series of science missions that
are intended to proceed from development to flight in three years or less at a
development cost of less than $150 million each (FY 1992 dollars). The first mission,
known as the Near Earth Asteroid Rendezvous, led by the Johns Hopkins University's
Applied Physics Laboratory, is scheduled for launch in February 1996 (Leery, 19931.
JPL is the leac' center on the Mars Pathfinder mission, the second Discovery mission,
which is also projected for launch in 1996. JPL also has proposed the Pluto Fast Flyby
mission. The goal is to launch two small spacecraft of less than 140 kilograms each on
a direct trajectory to Pluto by 2001 (Staehie et al., 1993~.
in addition, NASA has proposed the Thermosphere Ionosphere Mesosphere
Energetics and Dynamics (TIMED) mission, which includes a system of probes to study
little-known aspects of the Earth's upper atmosphere. TIMED is to be the first of the
Office of Space Science's series of small spacecraft missions, known as the Solar
in support of the emphasis on small spacecraft, the Spacecraft and Remote
Sensing Division was created within the Office of Advanced Concepts and Technology
(OACT) at NASA Headquarters. This division is responsible for the development of
technology to reduce the cost and launch weight of spacecraft through miniaturized
components, advanced instrumentation, operations technology, and sensors integrated into
advanced design concepts. The Spacecraft and Remote Sensing Division is currently
working with the Office of Space Science to develop and infuse advanced technology into
three scientific small spacecraft missions: (~) the proposer! TIMED mission, (2) Mars
Pathfinder, and (3) the proposed Pluto Fast Flyby mission (NASA/OACT, 19931. In
addition to the technology infusion activities, OACT's Spacecraft and Remote Sensing
Division has established a Small Spacecraft Technology Initiative. This program will
demonstrate a new approach to technology integration. Two technology demonstration
flights are planned within three years; each is designed to envelop a range of mission
requirements and develop standard hardware and software interfaces for various
applications. A Request for Proposal for the Small Spacecraft Technology Initiative was
released February 28, 1994, with award dates scheduled for the second quarter of 1994.
Programmatic and budget details of the Small Spacecraft Technology Initiative and
current NASA programs are discussed further in Appendices C and D. The rate of
progress of this initiative is in question, since it received less than one-half of NASA's
requested budget for fiscal year 1994.
As noted previously, DoD and its agencies have active small spacecraft programs.
Appendix D gives a summary of those activities. In addition, a new small spacecraft
industry is emerging, based to a large extent on past and current government programs.
A listing of some commercial programs is given in Chapter 6 of this report.
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Introduction 11
APPROACH
The Panel on Small Spacecraft Technology was established in late 1992 and met
in January, April, May, June, September, and December, 1993. At the first three
meetings, the entire panel heard over 32 briefings by representatives from many
government agencies and industry and from other experts on small spacecraft technology
issues. In addition, the pane! formed subpanels in several technical areas: (1) power and
propulsion; (2) automation, robotics, and artificial intelligence; (3) materials and
structures; (4) communications, guidance and control; (5) sensors; (6) launch vehicles;
and (7) ground operations, infrastructure, and cost analysis. The subpanels conducted 23
site visits to various aerospace companies, NASA centers, and government laboratories.
Appendix E lists the industry and government participants in this study. The panel
membership is listed in the front of this report.
At the June meeting, the panel met and discussed each subpanel's preliminary
findings and recommendations. In December, the panel met to discuss and prioritize the
overall findings and recommendations. In September and November of 1993, and January
1994, a writing team composed of several panel members met to work on the draft
report.
The data obtained by the panel during its meetings and site visits form the basis
for this report. Detailed information on key, enabling technologies for small spacecraft
are discussed in the venous chapters of the report along with specific findings ant!
recommendations. Overall findings and prioritized recommendations on small spacecraft
technology and NASA's small spacecraft program are noted in the last chapter of this
report.
Representative terms from entire chapter:
launch vehicles
