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Executive Summary
The International Space Station (ISS) is truly an inter-
national undertaking. The project is being led by the United
States, with the participation of Japan, the European Space
Agency, Canada, Italy, Russia, and Brazil (see Figure ES-1~.
Russia is participating in full partnership with the United
States in the fabrication of ISS modules, the assembly of ISS
elements on orbit, and, after assembly has been completed
(so-called "Assembly Complete"), the day-to-day operation
of the station. Construction of the ISS began with the launch
of the Russian Zarya module in November 1998 followed by
the launch of the U.S. Unity module in December 1998. The
two modules were mated and interconnected by the crew of
the Space Shuttle during the December flight, and the first
assembled element of the ISS was in place. Construction
will continue with the delivery of components and assembly
on orbit through a series of 46 planned flights. During the
study period, the Assembly Complete milestone was sched-
uled for November 2004 with the final ISS construction
flight delivering the U.S. Habitation Module.
This study of the engineering challenges posed by long-
term operation of the ISS shows that the National Aeronautics
and Space Administration (NASA) and the ISS developers
have focused almost totally on completing the design and
development of the station and completing its assembly in
orbit. After ISS Assembly Complete, the primary work on
orbit will shift to scientific and engineering research, ISS
operations, and the maintenance of ISS systems and experi-
ments. Therefore, many of the issues and opportunities
related to long-term operations have not yet been addressed
thoroughly by NASA except as they apply to the more
immediate tasks of ISS assembly.
Despite this near-term focus, the committee found no
major engineering problems with the design of the ISS that
would adversely affect long-term operations. Most of the
deficiencies can be corrected with procedural changes and
equipment or software upgrades in time for incorporation at
ISS Assembly Complete. Although funding for most of
these changes has not been committed because of the higher
1
priority of current program issues, funds are likely to be
available in the out years of the program as ISS assembly
proceeds toward completion.
In the first committee meeting in September 1998, the
committee reviewed the report of the Cost Assessment and
Validation (CAY) Task Force of the NASA Advisory
Council, which had been released several months earlier
(CAY, 1998~. The Terms of Reference for the CAV Task
Force were compiled by NASA on October 14, 1997, con-
current with, and in direct response to, the congressional
interest expressed in the Appropriations Act of October 17,
1997, which also chartered this study. The CAV report was
published in April 1998, just one month after the official
start date of this study. The report examined in detail the
cost and schedule risks in the ISS program, focusing on the
assembly phase of the program and predicting a one to three
year slip in schedule and a most likely date for Assembly
Complete of December 2005.
The committee found the CAV report to be a comprehen-
sive and timely study of the ISS budget risks and decided
that it need not be duplicated and that the study on the long
term operation of the ISS should be complementary to it.
Therefore, the committee decided to focus on the engineer-
ing challenges of long-term ISS operations and delve into
budget issues only if they were not covered in the CAV
report. However, the CAV report covered the budget issues
thoroughly and the recommendations in this report fit the
CAY's budget assumptions for the operational phase.
The committee made 36 recommendations, 17 of which
are highlighted in this Executive Summary. All of the
committee's recommendations are treated in detail in the
body of the report.
In the area of communications and data handling, the
committee concluded that increases in communications up-
link and downlink bandwidths, and an increase in the avail-
ability of communications links through the tracking and
data relay satellite system (i.e., increased antennae mutual
visibility time) will be critical to the efficiency of long-term
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ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION
operation of the ISS. Enhanced communications will be an
enabling innovation for long-term ISS missions by allowing
time for on-orbit training and for the introduction of inter-
active maintenance and repair tutorials that will facilitate
making detailed equipment diagnoses and evaluations and
will support direct interaction between the crew and the prin-
cipal investigators (PIs) of the experiments. Thus, operating
efficiency would be increased and the aggregate demands on
crew time for long-term operations would be eased. These
changes should be reflected in NASA's plans for the ISS.
This subject is discussed further in Chapter 5.
Recommendation. The National Aeronautics and Space
Administration should make increasing the uplink bandwidth
a high priority and should evaluate the importance of video
communications.
Recommendation. The International Space Station
antennae should be relocated in a configuration that allows
continuous communication through the tracking and data
relay satellite system.
NASA's control procedures for space flight operations
have evolved over many years of diligent attention to detail,
and they are excellent. These procedures are highly refined
and have been highly successful since the very first sub-
orbital Mercury flight some four decades ago. The
challenges associated with the long-term operation of the
ISS, however, will be very different from the challenges of
the short-term human space flights of the past 40 years.
The committee was concerned that the ISS operations and
maintenance workload might leave ISS flight crews little
time for research as happened in recent years on the Russian
space station, Mir. NASA has not done sufficient analyses
to alleviate this concern. The committee concluded that a
rigorous analysis will be necessary to determine if the crews
of the ISS will have enough time to conduct research. To
that end, NASA should prepare a long-term "design refer-
ence mission" showing projected clusters of crew activities
against a timeline. It would be useful, for example, to show
a typical 30-day timeline with the Space Shuttle docked
either at the beginning or the end of the 30-day period. This
would help determine if measures to increase onboard crew
efficiency and conserve the crew's working time will be nec-
essary. This subject is discussed further in Chapter 3.
Recommendation. The National Aeronautics and Space
Administration should reassess the crew's activities against
a more realistic timeline based on the Phase 1 Mir experi-
ence, as well as experience gained during assembly of the
International Space Station. If the crew could take on more
of the day-to-day mission operations, the aggregate require-
ments for ground crew personnel would be reduced.
The time on orbit of three to four months for an ISS crew
suggests a mode of operation different from the operational
mode appropriate, for example, for the much shorter dura-
tion Space Shuttle flights. This difference was noted by sev-
eral of the U.S. astronauts who lived and worked on Mir in
the Phase 1 program and who had had prior flight experience
on several Space Shuttle flights. The observation is also
included in the "Phase 1 Lessons Learned" documentation
of August 26, 1998 (NASA, 1998a). The flight crews who
will have months of accumulated experience with the equip-
ment and experiments on board the ISS, will be extremely
well qualified to participate in the planning of maintenance
tasks and to implement changes to experiment protocols
deemed necessary by the principal investigators (PIs). The
resourcefulness of flight crews is legendary in NASA' s his-
tory of space flight operations, and they should be delegated
the responsibility for a great deal of the day-to-day planning
of on-orbit operations. NASA should reassess its basic
philosophy of space flight operations to take advantage of
their expertise. This subject is discussed further in Chapter 3.
Recommendation. The National Aeronautics and Space
Administration should allow the International Space Station
(ISS) crew on orbit to contribute to the development and
optimization of the daily timeline. The time saved would
allow the crew to devote more time to scientific research.
Oversight of the accomplishment of crew tasks aboard the
ISS should be maintained by mission control through peri-
odic flight crew/ground controller progress reviews.
Recommendation. The National Aeronautics and Space
Administration should adopt the practice demonstrated dur-
ing the Mir program of direct communications between the
crew and principal investigators (PIs). Crew members and
PIs should be able to exchange data and instructions to enable
the crew to carry out experiments in the way that best fulfills
the goals of the experiment. Computer links should be
developed and communications systems upgraded to pro-
vide real-time assessments of the data and the capability of
responding to change.
Recommendation. The National Aeronautics and Space
Administration (NASA) should develop a new concept of
operations for the long-term operation of the International
Space Station that includes the integration of new informa-
tion technologies into mission control center processes.
NASA should consider adopting the Russian operational
practice used for Mir (i.e., maintaining a small team in the
mission control center and relying on experts on call with
remote access to the data and personnel in the mission con-
trol center).
Recommendation. The National Aeronautics and Space
Administration should reassess its crew requirements for the
International Space Station and consider including a pay-
load specialist in the seven-person crew.
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EXECUTIVE SUMMARY
All of the information provided to the committee shows
that the baseline extravehicular mobility unit (EMU) is a
mature system that can be expected to support the ISS opera-
tional phase. Nevertheless, many improvements could be
made, including reducing prebreathing requirements,
increasing the use of robotics for extravehicular activities
(EVAs), and using more autonomous robotics that demand
less crew time, skills, and training. Long-term operations
will also afford a unique opportunity to use the ISS as a test
bed for advances in EVA equipment and technology. This
subject is discussed further in Chapter 4.
Recommendation. The National Aeronautics and Space
Administration and its international partners should develop
a plan to incorporate improved control modes for the baseline
robotic systems on the International Space Station (i.e., the
space station remote manipulator system and the special
purpose dexterous manipulator) that would simplify their
operation and reduce astronaut training time (e.g., "flying
the end pointy. The plan should address cost and safety
considerations as well as teleoperation by ground-based
operators.
Recommendation. The National Aeronautics and Space
Administration should assess the potential improvements in
extravehicular activities from the introduction of new robotic
technology into human-robot systems. This assessment
should include a comparison of the cost for development and
implementation and the potential cost savings and risk
reduction associated with the use of these systems.
Recommendation. The National Aeronautics and Space
Administration should use the International Space Station
(ISS) as a technology test bed for advanced extravehicular
activity (EVA) systems, including robotic systems to sup-
port long-term ISS operations and future space missions.
Rather than introducing only incremental changes, revolu-
tionary approaches should be pursued to developing new
materials, achieving greater mobility, and incorporating new
technologies for both EVA suits and robotics systems in sup-
port of future exploration initiatives.
The committee found that the requirements for logistics
and resupply flights and for on-orbit maintenance could be
refined and probably reduced by applying more practical,
targeted failure analysis and logistics management
techniques based on current NASA and Air Force space
operations experience. The techniques NASA is currently
using for failure prediction and logistics management are
outdated. Overcompensating for the general nonspecific
nature of the analyses will lead to excessively large and
costly inventories of spare parts, maintenance depots, and
ISS resupply flights (Butina, 1998; NASA, 1998b). With
better planning, the ISS program could decrease logistics
and maintenance costs and reduce the number of resupply
3
flights required, thereby reducing the frequency of disturbances
to the ISS microgravity environment for critical experiments.
This subject is discussed further in Chapter 3.
Recommendation. The National Aeronautics and Space
Administration should greatly expand its focus on failure
detection, isolation, and recovery (FDIR) in conjunction with
the failure modes and effects analysis (FMEA). The follow-
ing issues should be addressed specifically:
· allocation of responsibility to automated/nonautomated
functions
· consistency of the FDIR with known failures
· integration with space and ground crew training and
logistics
Several models exist for logistics planning. NASA has
developed a computerized provision planning system for the
EMU that tracks current inventory and projects future
requirements based on a number of program parameters.
This system could be used as a model for improving logis-
tics planning. Lessons learned from the Hubble Space Tele-
scope Program could also be used to improve planning. This
subject is discussed further in Chapter 3.
Recommendation. The National Aeronautics and Space
Administration should reassess its current philosophy for
providing spare parts, as well as the depots and associated
personnel required to maintain them for the operational Inter-
national Space Station (ISS). The criticality of hardware,
wear-out factors, and the potential for subsystem upgrades
should be considered in the reassessment. The logistics,
reliability, and mission assurance personnel for the ISS
should establish an ongoing liaison with their counterparts
in the Hubble Space Telescope program to evaluate a new
philosophy for the ISS and the possibility of reducing asso-
ciated costs.
ISS management has expressed serious concerns about
the ability of the Russian partners to deliver on their com-
mitments. Nevertheless, NASA's options for reducing the
dependency of the ISS Program on Russia are limited.
NASA described three options:
Option 1. Provide funding to Russia as necessary to
complete and sustain all Russian contributions.
Option 2. Provide funding to Russia for items neces-
sary to continue the ISS Program in the near term while
funding the U.S. capabilities (e.g., U.S. propulsion
module) necessary to eliminate dependence on Rus-
sian participation, thereby establishing U.S. autonomy,
in the long term.
· Option 3. Provide no funding support to Russia and
adjust the schedule of the ISS Program, as necessary,
to accommodate late Russian deliveries.
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ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION
The committee believes that a more thorough analysis of
these options is required, particularly as they apply to the
long-term operation of the ISS after Assembly Complete.
This subject is discussed further in Chapter 2.
Recommendation. The National Aeronautics and Space
Administration should develop a concise comparison of
Options 1 and 2 to document the relative costs, as well as the
program risks and benefits, associated with implementing
Option 2 in order to reduce International Space Station (ISS)
dependence on Russia and achieve autonomy for the ISS
Program in the long term. The cost estimates should include
the following items:
· the incremental cost of operating the Space Shuttle to
replace Soyuz/Progress logistics flights
· the cost of developing a U.S. propulsion module and
delivering it to the ISS
· the cost and risk associated with integrating a U.S.
propulsion module with the ISS this late in the ISS
program
· other costs that may accrue in establishing U.S.
autonomy
· risks to the program schedule
The committee reviewed NASA's plans for using the in-
ternational launch vehicle fleet to ensure access to the ISS
assuming that over the long-term operation of the ISS one or
both of the primary launch vehicles supporting the ISS (i.e.,
the Space Shuttle and the Soyuz) would be in a stand-down.
NASA has not yet seriously considered this aspect of contin-
gency planning for operations in support of the ISS after
Assembly Complete. NASA has been operating on the
assumption that either the Space Shuttle or the Soyuz, or
both, will be available for crew launches.
If both the Space Shuttle and the Soyuz were concurrently
in a stand-down mode, however, support of ISS crew opera-
tions would no longer be possible. Other vehicles, particu-
larly the autonomous transfer vehicle (ATV) (propellant
logistics) launched by Ariane and the Japanese H-II transfer
vehicle (HTV) launched by the H-II launch vehicle, are part
of the ISS logistics support baseline and could be used for
noncrew-related logistics operations in case of a concurrent
stand-down of the two primary vehicles. In one scenario,
the ISS would be moved to a higher altitude to prolong its
life and reduce logistics flight requirements. The ISS can
survive without a crew, and, like the Soyuz/Progress logis-
tics resupply vehicle, the ATV can dock without a crew. In
this scenario, the contingency plan for the concurrent stand-
down mode, therefore, is to "mothball" the ISS by moving it
to a higher orbit and replenishing propellant via the ATV in
an automatic docking mode.
The committee believes that NASA should look more
carefully at its contingency plans for the operational phase
of the ISS and assess other options for ensuring its
survivability in case of a concurrent stand-down of the Space
Shuttle and the Soyuz launch vehicles, and the Soyuz/
Progress logistics resupply vehicle. This subject is discussed
further in Chapter 2.
Recommendation. The National Aeronautics and Space
Administration (NASA) should develop contingency plan-
ning for personnel transport and resupply during the opera-
tional phase of the International Space Station (ISS). The
assessment should identify viable options other than moving
the ISS into a high storage orbit in case of a concurrent stand-
down of the Space Shuttle, the Soyuz, and the Soyuz/
Progress vehicles. NASA's plan should accommodate new
launch vehicles that may become operational during the
operational lifetime of the ISS for both crew transport and
ISS resupply. The plan should address the relative costs of
the various options for ensuring access to the ISS.
NASA plans to deorbit the ISS with a controlled reentry
at the end of its useful operating lifetime on orbit. The com-
mittee believes that NASA should conduct a rigorous
reassessment of entry probability criteria and the risks
associated with ISS reentry to determine if the present
decommissioning/deorbiting plan should be changed.
NASA's plan should be consistent with the agency's objec-
tives of maximizing the safety of the operation and minimiz-
ing the potential risks associated with the reentry of such a
large object. This subject is discussed further in Chapter 6.
Recommendation. Because of the potential hazards asso-
ciated with the reentry of relatively large objects, the safety
requirement for International Space Station reentry should
be more stringent than the requirement for other National
Aeronautics and Space Administration operations (i.e., the
chance of casualties should be much less than 1 in 10,000~.
Recommendation. The National Aeronautics and Space
Administration should undertake a thorough analysis of
International Space Station reentry operations, including
ranges of uncertainty associated with the multiple variables
of reentry operations. The analysis could take the form of a
Monte Carlo simulation of reentry operations and projected
impact areas to characterize the hypothetical potential for
property damage or casualties. The analysis should include
the sequence of operations, possible failures, and conse-
quences of failures, from the initiation of reentry operations
to final impact. Uncertainty variables should include, but
should not be limited to, reliability characteristics, duration
of burn, atmospheric density, ballistic coefficients of frag-
ments, population densities, and the characterization of
acceptable impact areas.
Finally, NASA has an important ongoing program to
identify preplanned product improvements (P3I) for the ISS.
Under this program, ~ ~~ ~ ~
the staff of the ISS Program Office, and
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EXECUTIVE SUMMARY
the appropriate offices in the Engineering Directorate at the
NASA Johnson Space Center, recommend candidate items
for ISS system or component upgrades. Some of these up-
grades could significantly reduce maintenance and resupply
requirements for the long-term operation of the ISS thereby
increasing crew efficiency. Although the P3I program is
being conducted carefully and responsibly, its current
funding is grossly inadequate. NASA should assign high
priorities to the preplanned product improvements, and other
specific items that will contribute to the efficient operation
of the ISS after Assembly Complete and make the ISS less
dependent on Russian supplied hardware. NASA should pre-
pare a long-range budget plan for P3I to ensure that cost-
effective and operations-effective upgrades are developed in
time for ISS Assembly Complete. To ensure that NASA
does not defer the long-term needs of the ISS until they
become program critical, the committee recommends that
NASA designate a senior ISS staff person to oversee imple-
mentation plans for post-Assembly Complete ISS operations,
including the upgrades identified in the P3I activity. This
subject is discussed further in Chapter 5.
Recommendation. The National Aeronautics and Space
Administration should designate a senior member of the
International Space Station (ISS) staff to assemble, review,
and approve budgets and implementation plans for post
Assembly Complete, to facilitate improvements in ISS
systems, and ISS operations, and to maintain a high degree
of management visibility for this important activity.
The space station envisioned in the early 1960s could
have been built with technology available at that time. As
the committee noted in this report, the same is true of the
ISS, which relies on existing technology and well established
manufacturing techniques wherever possible. Therefore,
the committee believes that the fundamental improvements
cited in this report are well within the state of the art of cur-
rent technology and should be introduced into the ISS Pro-
gram as soon as possible. In the areas of communications
and robotics, in fact, they have already been developed.
With farsighted management and timely increases in fund-
ing, these upgrades and enhancements would ensure that the
ISS remains at the leading edge of long-term space research.
REFERENCES
Butina, T. 1998. Logistics and Maintenance Planning. Presentation by T.
Butina, manager, Logistics and Maintenance, to the Committee on the
Engineering Challenges to the Long-Term Operation of the International
Space Station. NASA Johnson Space Center, Houston, Texas, Decem-
ber 17, 1998.
CAV (Cost Assessment and Validation Task Force). 1998. Report of the
Cost Assessment and Validation Task Force on the International Space
Station. Washington, D.C.: National Aeronautics and Space Adminis-
tration.
NASA(National Aeronautics and Space Administration). 1998a. Phase 1
Lessons Learned. August 26, 1998. Houston, Texas: NASA Johnson
Space Center.
NASA. 1998b. Current Manifest of Assembly Critical Spares: Working
Paper. December 11, 1998. Houston, Texas: NASA Johnson Space
Center.
Representative terms from entire chapter:
international space
