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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 l0-l2 flights per year was severely stressing shuttle operations capabilities at all the affected NASA centers. The future manifest through l99l 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 l990s 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 l5, l986 Statement by the President indicates that commercial satellites in the l990s (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 allâby 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 the 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 ELVs for customers charged for shuttle service. 39
40 The question then remains of what flight rate reasonably matches both the capability of a shuttle fleet and a realistic utilization (demandJ7From 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 ELVs. 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 l-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 highâ8-l0 flights per year. Testimony of John Hodge to the House Subcommittee on Space Science and Applications (July 2l, l986) 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 l990s 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 l-2 flights per year were
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 missionsâessentially "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 l-2 flights per year for less than l0 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-l0 flights per year in the early to mid-l990s, 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.
