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Introduction
The Space Station Freedom program has as its objective the
establishment of a permanently manned facility in low earth
orbit. The facility is intended to be used for a range of
activities and to accommodate a number of alternative
evolutionary growth paths. The Space Station also is
envisioned, by the National Aeronautics and Space
Administration (NASA) and others, as an essential element in
the recovery and maintenance of U.S. leadership in civil space
activities and as an opportunity for increased international
cooperation.
Table 1 lists the major intended attributes of the Space
Station Freedom manned base (the program also includes polar
orbiting platforms and a co-orbiting man-tended free-flyer).
The Phase 1 Space Station is planned to be a facility with the
potential to support activities in microgravity materials
research, fluid physics, crystal growth, biomedical studies,
human habituation studies, and astrophysical and earth
observations. The station would also support in-space
technology experiments and development efforts.
BACKGROUND
There have been a number of external reviews of the Space
Station Freedom program. The National Research Council (NRC),
at the request of the President's Assistant for National
Security Affairs, the Director of the Office of Management and
Budget, the President's Science Advisor, and the Administrator
of the National Aeronautics ant! Space Administration, undertook
a study of the Space Station program in 1987. Prior to that
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Table 1 Intended Attributes of Space Station Freedom Manned Base
A Permanently Occupied Spacecraft
A Research Laboratonr
An Observational Platform
Verv High User Power (45 kW)
Very Low Quasi-Stead~r Micro~ra~ritv
Accelerations
An Ontimized Spacecraft Attitude
High Data Rate f300 MbPs)
Weeklv Extravehicular Acti~ritv
(6 hours/week,
An Internal Environment of One
Standard Atmosphere
Clean External Environment (Gases.
Condensibles. EMI)
A Payload Pointing Svstem
Large Annual Unmass Capability
{50.000 k~r/`rr)
Accommodations for Suace Station
Evolution
The spacecraft would have 8 crew of eight and a
facility lifetime of 30 years; it is designed to
conduct the operational and medical research
required to support long-term manned space
exploration objectives.
More than 120 standard equipment racks would be
available to hold scientific research equipment.
The platfo...` could hold four ~ fi're large
experiment footprints of 10 m for long (up to 30
yeare) aberration times.
Such pourer levels are required to operate
experiments; they are especially necessary to pourer
furnaces, and so forth, for materials research.
Accelerations of 1 x 10 6 g (at f < 0.1 Hs) are
critical for materials research in order to force
diffusion-dominated process.
Designed to benefit both laboratory and
observational experiments (LVLH = +/- 5~; +/- 2.5
stability; < .02 /see stabilization rate), this
attitude keeps the residual microgra~rity
acceleration Rector in a near-constant direction
for materials rceearch. It also provides
sufficient pointing orientation for many obeenring
nstn~mente. It is accomplished without disturbing
thruster firings, by using control moment gyros.
This rate will support modern research needs for
high resolution and high-speed image transfer.
EVA would be available to users for external,
obeer~rational experiment resupply (cryogens, film,
etc.) as well as for servicing and repair.
This internal environment is critical, since it
allocate researchers to draw on decades of
ground-based life science data.
A clean environment is necessary for the conduct of
optical and plasma obeer~ratione.
It will handle large payloads (3 m in diameter by
m long, 6,000 kg mass), providing 30 arc set of
inertial pointing for precision obeenratione.
A large upmass capability is needed to provide
resupply and experiment change-out for research.
The Station is designed to allow more power, crew,
laboratory space, and attached payload space to be
added.
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activity, the Aeronautics and Space Engineering Board of the
NRC conducted examinations of various aspects of the Space
Station program during 1984 and 1985, including its
maintainability, program performance, onboard command and
control, solar thermodynamics research and technology, and
research and technology in space.
In early 1987, the NASA Associate Administrator for Space
Station indicated an interest in having the NRC examine the
Space Station program with a view toward identifying critical
engineering issues related to the stationts design and
operation. This activity was preempted by the aforementioned
study for the White House, et al. However, in early 1988 the
NASA Office Space Station submitted a formal request for an NRC
workshop to identify and prioritize Space Station engineering
issues. (See Appendix A) The workshop was held on November
7-11, 198S, at the Beckman Center in Irvine, California; this
report summarizes the main findings of that event, and reflects
the views and opinions of the workshop committee.
APPROACH
Following formal acceptance of NASA's request by the NRC's
Governing Board, an ad hoc committee was formed by the
Aeronautics and Space Engineering Board to conduct the
workshop. The members of the committee were chosen for their
expertise in the areas of space systems, space structures,
guidance and control, operations and management, space
transportation, power, communications, space medicine and life
sciences, robotics, software development and management,
utilization, and space applications. Prior to the workshop,
the committee was supplied with extensive background
materials. The workshop itself was an intensive,
four-and-a-half clay review of the engineering and operational
aspects of the planned Space Station, with some sessions
lasting until nearly midnight. Nonetheless, the magnitude of
the program under review coupled with the limited time
available to conduct the review, make several caveats
necessary:
· The workshop was not a technical audit. Most of the
committee's information was based on views of the Space Station
program and design plans as of November 198S, derived primarily
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from briefings presented at the workshop by Level I and Level
II personnel of the NASA Space Station program.
· Some areas of possible concern, such as materials and
the effect of the space environment thereon, were not
represented in the briefings or by the expertise of the
committee. Some thoughts of the committee concerning these
areas are included in the Supplementary Discussion section of
this report.
· The workshop report has not attempted to identify all
the good features of the Space Station program. The committee
has noted some of these aspects at various points in the
report, but most of its energies have been directed--in
accordance with its task statement (see Appendix B)--toward the
identification of issues.
· The limited time available to the committee made it
impossible to do a more detailed prioritization of the issues
identified in this report, especially across subsystems.
However, the committee does believe that all of the issues
identified in this report will require resolution for the Space
Station program to be successful.
Consequently, the issues identified in this report should not
be construed as an exhaustive set of concerns, but rather those
that appeared most important to the committee based on its
necessarily limited review of the Space Station program.
Furthermore, the committee was not asked to address the
desirability of developing a Space Station; President Reagan's
1984 decision was taken as the committee's point of departure.
In its deliberations the committee has searched for the
inconsistent, the overly optimistic, and for those areas that,
if they continue in the direction they are currently headed,
are likely to be troublesome later. The committee used two
basic principles in its evaluation: (1) early recognition and
correction of potential problems is the most efficient and
least costly approach, and (2) flexibility in design and
Insurance provided by alternative approaches can yield major
downstream dividends, especially when coping with unexpected or
unanticipated events.
The following sections of the report present the workshop
committee's major findings and recommendations. A number of
general design issues are discussed first. Next, issues
related to Space Station utilization and operations
requirements are identified' followed by issues concerning
specific Space Station systems and subsystems. Finally, a
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number of management issues that the committee believes could
have an important impact on Space Station design and operation
are discussed.
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Representative terms from entire chapter:
station program
