[QUOTE=Stranger On A Train]
It’s not so much cost as budget planning that mandates a hard cutoff of funding for Shuttle missions. The cost of operating the Space Transportation System (STS) Shuttle isn’t just the expense of preparing individual launches themselves but also roughly fixed cost of maintaining the overhead for launch facilities and trained personnel. Indeed, if the STS program was able to sustain more launches per year, the costs of this overhead would be amortized over more launches and individual launch costs would be more competitive with expendable launch vehicles. It is necessary to cut this off in order to start funding production-level development of the successor Constellation system and facilities to be used therefore.
In addition, one of the selling points for the Ares launch system family used for Constellation is that it uses Shuttle-derived hardware which allows for adaptation of existing launch and integration facilities, ostensibly saving money versus building up new facilities from scratch. (The reality that it almost always costs more to make significant modifications to a system than to just build purpose-built equipment from scratch rarely penetrates the fictional, PowerPoint-dominated world of conceptual proposals.) Naturally, this means that you have to take the existing STS facilities out of operation and allow time for modification and pathfinding for your new system. While you are doing this you don’t have any way to support STS launches. Hence, a cutoff date and launch capability gap.
As for the “heat tile problem seems to be solved” I have to disagree. There is now a broad acknowledgment of this previously known problem by NASA management, but the solution–such as it can be said to exist at all–is a hacktastical risk mitigation plan of questionable value that increases cost and maintenance requirements, decreases manpower available for actual mission-related activities, and would likely not have fixed the problem which resulted in the catastrophic re-entry failure of Columbia, to wit a puncture in the reinforced carbon-carbon leading edge thermal protection which allowed overheating and structural collapse of the wing structure. Should another puncture of similar size occur, the only credible response would be to launch a rescue mission which (hopefully) would not experience the same failure. Like the post-Challenger In-Flight Crew Escape System (ICES) bail-out abort option, it exists primarily for management to say, “We’ve done everything practically possible to reduce crew hazards,” without actually fixing the problem (which would require major redesign and refit with likely reduced mission and lift capability).
Nor is the TPS puncture problem by any means the only standing safety issue with the Shuttle, as has been demonstrated in the post-Columbia safety-aware era; we’ve seen problems with leaking fuel tanks, cracked fuel lines, faulty switches, et cetera all of which have resulted in costly launch delays. Of course, these issues are part and parcel of expendable launch vehicles as well, and despite two failures the STS actually has quite a good history of completely successful missions and returns compared contemporary LVs like Titan III/IV, Delta II/III/IV, Atlas II/III; in fact, I believe the only American heavy launch systems with a better launch success rate are the Atlas V (with only about a dozen launches since introduction) and Saturn family. But because of the cost and hazard to personnel of the Shuttle, and the fact that it endures risk not only on the way up but also on the return flight, the level of scrutiny is higher than for expendable vehicles, and failures are extremely expensive both in increased hazard mitigation efforts and political/public support for the space program overall. When Boeing tilts a Delta over, Lloyd’s ups the premiums for the next few launches and mission assurance organizations get more funding to identify problems before they become failures. But when the Shuttle comes apart like a cheap gold watch, everything stops, Congressional hearings are held, and 60,000+ workers hold their breath to see if their careers are canceled along with the STS program.
Letting the Russians take care of getting American astronauts up to the ISS and back down may seem kind of risky, but in fact there is actually little we need the ISS for other than a place to go to. As scaled back as it has become, it essentially exists for the purposed of being a way-station to nowhere, and if we had to stop sending people up there for a few years over a disagreement about the quality of Russian versus American vodka, the net effect would be to limit the career ambitions of a few members of the astronaut corps and support personnel. Compared to the cost of running two concurrent manned launch vehicle programs, there’s no question, especially given the hard limitations of NASA’s budget.
The compromises built into the STS have more than cost impacts; indeed, to justify building the Shuttle at all, artificial restrictions were placed upon the use of expendable heavy launch vehicles in order to essentially give business to the STS program, i.e. requiring the Air Force and NRO to use the Shuttle as the primary platform for orbital delivery of reconnaissance satellites, which in turn drove the payload size and cross-range requirements on the Shuttle which in turn forced the use of lower safety margins and sub-optimal design. That shell game finally came apart along with Challenger, and the Air Force washed their hands of NASA launch deliveries and Blue Shuttle, but the compromises still remained, built into the design. Dennis R. Jenkins’ Space Shuttle: The History of the National Space Transportation System The First 100 Missions goes into extensive detail on early Shuttle development and the politics behind it for those who are really interested.
As for doing better today, the Constellation program is really a return to Apollo-era concepts (expendable two stage heavy launch vehicles with an additional Earth departure motor for transLunar injection, blunt-arsed conical capsule, separate lunar landing module, et cetera) updated to use modern avionics. This is essentially what we could have anticipated having in the 'Eighties and 'Nineties had we continued with the Apollo Plus and Apollo Applications programs. Far from doing better today, we’re just aspiring to do better than what could be done in the 'Seventies. It’s the smart, minimum risk and minimum development approach, but it can hardly be considered more advanced; and more disappointingly, this isn’t being viewed as an interim solution to a more mature and capable system, but the foundation for an entire class of human space launch vehicle operating for the next three or more decades.
Stranger
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Good stuff, thank you.
