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Preamble This report was requested following the Challenger .loss and several months before the President's August l5, l966, statement announcing intent to build a fourth space shuttle and to end NASA's launching of commercial satellites. The assessments requested in the letter of April 2l, l9fat>, from Congressman Boland to the Administrator of NASA (Appendix A.), in the opinion of the aa hoc panel, remain timely but with a few minor changes in assumptions. The l6-month standdown is replaced by a 24-month standdown. The assumption on shuttle launching of commercial satellite payloads is modified to reflect both the near-term shuttle program and manifest and the longer-term intent expressed in the President's statement. Early in its deliberations, the ad hoc panel found that it had to make an assumption regarding whether the national intent was to have a sustained manned spacetlight programâone in which manned flight was a regular and continuing occurrence year in and year outâor to treat the shuttle fleet as a declining resource (like the Apollo), which in due course would, through use or accident, diminish to zero. It also had to decide whether the requested assessments should apply to the transition period between now and l99l or to the period thereafter when both the shuttle and ELV fleets presumably would be available for launch. The panel, considering the nature of the requested assessments, decided to assume a sustained manned flight program and to consider flight rates in both the post-l99l time frame and the build up before l99l. Discussions of these assumptions can be found in the appendixes. It is the understanding of the panel that the purpose of the assessments is to estimate flight rates for a 3- or 4-Orbiter fleet. Both fleet sizes are therefore addressed without making any recommendation on which fleet size is preferable or needed. (It is clear, however, that the Space Station program has assumed the existence of a "robust shuttle fleet" of at least the 3- or 4-Orbiter size, from which its own flight rate demands would have to be satisfied.) Congressman Boland's letter also asks for an examination of the assumptions behind the shuttle manifest for the foreseeable future. This matter raises the issue of expendable launch vehicle (ELV) availabilityâfor ELVs are the alternative to shuttle launches. The
Air Force has recently procured a number of heavy-lift ELVs (Titan IVs) and is negotiating to begin production of a medium-lift ELV (MLV). The early production of these vehicles seems likely to be devoted to DoD payloads. Even were production lines for existing ELVs to be reactivated immediately, it would take several years for vehicles to become available. Thus, the availability of ELVs as a shuttle alternative for other than DoD payloads is likely to be severely limited until at least around l990. MSA and commercial interests have yet to decide to procure ELVs. Thus, particularly in the coming interim period, NASA and commercial interests that have contracted for launch service will be depending on the shuttle as the most immediate launch capability, with corresponding pressure on its manifest.* For activities requiring the specialized use of people, the shuttle cannot be replaced by ELVs. Before addressing the questions raised by the House Appropriations Committee, the panel will state certain fundamentals drawn from its members' association with research, development, operations, logistics, fleet maintenance, and space activities. These fundamentals must be recognized if shuttle flight rates and manifests are to be discussed without misunderstanding. One fundamental is that in addressing flight rate, there is an essential distinction between capability and demand. Capability refers to the number of flights that can be mounted given the equipment, people, spare parts, and facilities available. Capability is thus the available supply of launch services. Demand, on the other hand, refers to the number and configuration of payloads to be launched. While this distinction is clear enough, there is often confusion since both capability and demand are discussed in terms of flight rates. The panel will address the shuttle capability in terms of the sustainable flight rate. This is the rate of flights that can be sustained over a substantial period of time and after buildup from the cautious resumption of flight subsequent to the Challenger accident. This buildup will, of course, require some period of time, perhaps 2 years, before the sustainable rate can be reached. For short periods of time, a launch rate in excess of that sustainable can be achieved with adequate planning, lead time, and a minimum of changes. The panel will refer to this as the surge rate, recognizing that it places severe stresses on people and facilities. It cannot be sustained for longer than a brief period, approximately 4 months. The shuttle fleet concept is also fundamental. The fleet Orbiter inventory is the number of Orbiters on hand at any given time; today it is 3. The number of schedulable Orbiters is fewer than the inventory because of a number of fundamental factors, some common with *The statement by the President, dated August l5, l986, precludes continuing launch of commercial satellites by space shuttle. It appears at this time that certain contracted commitments will be honored.
fleets of other flight vehicles such as those operated by the Air Force and commercial airlines (e.g., age of hardware, availability of spares, damage, normal wear). The panel's experience suggests that the schedulable Orbiter fleet is smaller than the inventory by almost one Orbiter. Thus today, the schedulable fleet is only a bit in excess of 2. Therefore, the Orbiter fleet flight rate in the remainder of this report will be calculated on that basis. The reasons for this discounting of the Orbiter inventory arise from essential scheduled maintenance of the flight articles and the possibility of damage or needed modifications to an Orbiter that would keep it or the whole fleet out of service for a significant period. Reliable, sustainable flight rates hinge upon other factors as well. Underfunded logistics has been a recognized problem tor the shuttle program in the past. Today there is still not an adequate complement of spares on hand. This has necessitated cannibalization to keep the fleet flying and has lengthened the turnaround interval for individual Orbiters. In this report the panel attempted to estimate sustainable flight rates based on certain conditions, e.g., adequate spares, logistics, and all the facilities needed for turnaround and training. These conditions will not be necessarily satisfied under programs now in place at NASA. If they are not, a further decrease of sustainable flight rates would be in order. Another fundamental concern is the industrial base for the manufacture of Orbiters. Because there is a sufficient probability of an Orbiter-involved accident over the operational lifetime of the Orbiter fleet, the capability to produce and repair Orbiters should be maintained. Without it, there will be no viable shuttle fleet. With a small number of flight articles, such as the inventory of Orbiters, no management can sustain a reliable flight schedule since contingencies and new requirements will surely arise from unanticipated events. In other words, the partial equivalent of a contingency Orbiter (one available within a time period that would not seriously disrupt schedules, perhaps 2 years at maximum) should be in the construction process. This is consistent with the President's declaration for a fourth Orbiter and with the panel's judgment that over a period of years (l5-20) there must be replacements available because of possible Orbiter wearout (there are no reliable statistics at present on Orbiter life)* or irreparable damage in an accident. There have been suggestions that a new-technology reusable launch vehicle is in prospect for the l990-2000 time frame. Even then, any such vehicle is likely to be shuttlelike. Barring an unforeseen, new, space initiative, the panel believes that the shuttle fleet, with improvements, will be required until at least the year 2000 and probably well beyond if the United States is to have a sustained manned space program. *Regarding wearout, it is well to note that the Orbiter is stressed near its design limits each time it is launched and returns to Earth. An ordinary airliner is rarely, if ever, so stressed.
On the demand side of shuttle launches, the situation is quite fluid. An important point is that the payload backlog from today's extended launch standdown is not as large as it may appear to be. Many payloads now listed will not be launched at all since they will have missed a window of opportunity. Lack of reliable launch schedules and available insurance for payloads will depress not only future demand, but also 'the backlog. Just how large this effect will be is difficult to judge. The principal point is that supply and demand will always tend to come into balance. As launches using shuttles resume, there will be a buildup phase before reaching a sustainable flight rate. This report comments on both phases, but does not attempt to evaluate in detail the buildup operations. However, it is evident that a period of caution will be prudent regardless of the apparent demand for launches and the unavailability of ELVs. Present NASA planning appears to reflect this philosophy.
