NASA has delayed the next space shuttle launch from May until at least the first of July, in order to replace suspect engine cut-off (ECO) sensors in the external fuel tank. Discovery is slated to fly mission STS-121, the second of two engineering test flights in the return to flight sequence following the Columbia Disaster in 2003. Assuming the shuttle does fly in the July 1 to 19 window, almost a full year will have elapsed since the last flight.
NASA now finds itself at a critical juncture. For the agencyâ€™s plans to complete the ISS and develop the shuttleâ€™s successor to have any credibility, this next flight will need to go off almost flawlessly. NASA needs to demonstrate over the next few flights that the foam problem is both understood and fully resolved, and it also needs to demonstrate that it can ramp back up to the flight rate required to fly the remaining missions before the 2010 retirement date.
Therein lies a major problem: The shuttle is a highly complex, high performance, and frail experimental vehicle. On top of that, the fleet is aging. It seems hard to conceive that the remaining sixteen or seventeen shuttle flights will all fly on schedule, and without new problems appearing. Yet NASA does not appear to have a plan B. There seems to be an expectation that, because they have to make it work, they will.
This is not the first time. In the early days of station construction New Scientist ran an article, ISS Titanic, pointing out that a simple statistical analysis comparing shuttle reliability with the number of assembly flights manifested showed that the chances of losing a flight over the period of station assembly were unacceptably high. NASA didnâ€™t appear to have a plan for that, either. Ultimately, they gambled and lost.
Hopefully NASAâ€™s renewed safety focus can prevent the loss of another shuttle, but the very vigilance that guards against that eventuality also works against efforts to fly regularly. Shuttle managers have promised to â€œlisten to the hardwareâ€ â€“ but given the shuttleâ€™s age and complexity, itâ€™s almost certain that the more they listen, the more they will hear, and the less they will fly. Throw in the pressure to get the station assembly completed before the shuttle is retired in 2010, and the whole proposition looks even dicier.
So why fly shuttle at all? Why not retire it now and move on? In a perfect world, thatâ€™s exactly what should happen, but donâ€™t hold your breath. It sounds good on paper, but itâ€™s hard to imagine it happening in the real world where the shuttle program means jobs in congressional districts. Then thereâ€™s the International Space Station, with which NASA has painted itself into a very shuttle-shaped corner: The only vehicle that can loft ISS elements is the shuttle. Thereâ€™s no compelling technical reason that this should be so, the components were just designed that way to meet one of the stationâ€™s fundamental (political) requirements: providing a mission for shuttle. Scrapping shuttle and launching the ISS components some other way would see any money saved get spent modifying the station modules for a different launch vehicle, and would also introduce a delay of several years at a time when the ISS international partners are clamouring to have their modules launched earlier. It seems unlikely that NASA would be allowed to go this route, even if they wanted to.
So shuttle will fly, and likely run into further technical difficulties and delays, and cost overruns. Shuttle has become the project that wont die: NASA is stuck having to cannibalise other programs to feed it ever increasing sums of money, all so that it can be shut down to free up money for the Vision for Space Exploration.
The first step in NASAâ€™s plan to return to the moon, the orderly retirement of the Space Shuttle, may yet also prove to be the most challenging.