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Appendix D
SHUTTLE UTILIZATION
Before the loss of Challenger, the shuttle fleet was fully
booked. There were even indications that shuttle was overbooked.
Presentations to the panel from several sources indicated that the
demonstrated flight rate of 10-12 flights per year was severely
stressing shuttle operations capabilities at all the affected NASA
centers. The future manifest through 1991 indicated a still higher
flight rate.
Post Challenger, the achievable fleet manifest will be
significantly less than the pre-Challenger manifest. The difference
between the 2 is usually called the "backlog." If accepted at face
value, this backlog would call for flight rates approaching 20 per
year well into the 1990s in order to reduce it to zero. Some
immediate relief was obtained by off-loading payloads to ELVs, a more
vigorous action by the DoD than NASA but done nonetheless. The August
15, 1986 Statement by the President indicates that commercial
satellites in the 1990s (once the post-Challenger transition is
completed) also will be off-loaded. The panel anticipates further
reduction of the backload by acknowledging that satellites not
launched during the transition phase represent "services not
delivered," i.e., the blocks of satellites that were to be launched
will simply be pushed out in time and future buys reduced
accordingly. Some satellites may simply not be launched at all--by
the time they could be launched they would be obsolete for the purpose
they were to serve.
The backlog is also likely to be reduced by what is called
"discounting" of the future manifest. Experience shows that launch
schedules a year or more in advance are likely to be too great by
about 30 percent. The reasons have to do with delays in payload
delivery, unscheduled downtime of the launch vehicles, cancellation or
stretchout of programs for funding reasons, etc. Whatever the cause,
the discounting phenomenon is well documented for both shuttle and ELV
fleets.
Another clear factor in the size of the backlog, at least in
past, is the price charged for a shuttle launch. (There are more
customers for a free launch than for a "recovered cost" launch.)
Reduced flight rates and reduced performance will increase per-flight
costs relative to ELYs for customers charged for shuttle service.
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the
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The question then remains of what flight rate reasonably matches
both the capability of a shuttle fleet and a realistic utilization
(demand). From a purely technical point of view (i.e., putting aside
funding considerations), there will clearly be a demand for
man-critical flights such as Spacelabs, life and earth science
experiments, recovery and repair missions. There will be a demand for
shuttle-unique missions (sorties, short-duration on-orbit R&D, and
certain classified low-orbit missions). Collectively, these might
amount to 3 or 4 flights per year.
The demand for physical sciences was initially very high,
particularly since physical sciences missions weren't assessed launch
costs as part of project costs. But a severe disenchantment has set
in with unexpected costs, procedures, man-rating specifications and
delays, particularly for physical science missions that could be done
at least as well, if not better, technically on free flyers launched
by ELYs. In the long run, the demand will be for a launch capability
that preserves the momentum and opportunity for engaging outstanding
scientific talent in meaningful research. Therefore, until the
shuttle is seen to fulfill its original purpose, the demand for
physical sciences flights is likely to drop. In the short run, the
physical sciences utilization may well be determined by the price, if
any, that such missions are assessed for launch costs. Priorities
being what they are, the utilization rate of shuttle for physical
sciences might be a 1-2 equivalent shuttle flights per year. (Note:
The number of payloads considerably exceeds the number of equivalent
shuttle flights.)
The greatest change in utilization, however, is likely for
geosynchronous and other high-altitude missions. For these missions,
the shuttle is "Just a truck." If fully costed, it is an expensive
truck. With the cancellation of Centaur as a shuttle-compatible upper
stage, the shuttle is, at least temporarily, no longer a
high-performance path to high orbit. The ELVs should be expected to
take over much of that capability. Where lesser performance is
acceptable, cost may be the determinate. As noted in Appendix E, the
total national launch cost is relatively independent of the
shuttle-ELV mix, implying that customers could choose what appeared
most cost effective to them. Many, but perhaps not all, would opt for
ELVs, depending on the price and availability of the various future
launch options.
The demand for the shuttle for Space Station launches was, until
recently, relatively high--8-10 flights per year. Testimony of John
Hodge to the House Subcommittee on Space Science and Applications
(July 21, 1986) indicated that "Depending upon the future composition
of this Nation's space launch fleet, it would be possible that the
current Space Station would need to use both the shuttle and
expendable launch vehicles in support of Space Station needs." It is
the panel's estimate that the demand in the 1990s to support the
current Space Station design will be roughly equivalent to 2 more
Orbiters with an appropriate provision for a replacement if and when
needed. It wouldn't be surprising if 1-2 flights per year were
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required for experimental purposes prior to the increased flight rate
during construction.
Estimating the demand for the Strategic Defense Initiative (SDI)
is best done in 2 parts. Barring drastic changes in the SDI program,
there will be a continuing need for research flights requiring manned
intervention, sortie, recovery and repair missions--essentially
"proof-of-concept" flights of technologically very advanced systems.
The shuttle could be a good match to these systems, especially if it
is important to bring them back for analysis and modification. The SDI
Office, however, estimates its utilization at only 1-9 flights per
year for less than 10 years and no shuttle use in the deployment
phase. However, even if the decision were made early in the l990s to
go into full-scale development, the impact on the shuttle fleet
wouldn't be felt for at least 5 years. A more likely occurrence would
be the development of a new launch vehicle (heavy lift, unmanned?)
specifically for SDI weight lifting.
One major consideration suggests a significantly reduced shuttle
utilization as compared with the NASA manifests. Projected costs in
the l990s of the NASA civil mission model (payloads and
transportation) used in the NASA/DoD Space Transportation Architecture
Study show a "bow wave" in costs far above likely funding, dropping
well below later, indicating a major shift of programs into the next
decade.
All things considered, a rate of 8-10 flights per year in the
early to mid-199Os, prior to the construction of the Space Station,
does not appear to be much off the track for a well-operated shuttle
fleet of 3 Orbiters. If the demand turns out to be greater, the
primary long lead item will be another Orbiter.
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Representative terms from entire chapter:
flight rate
