The future of the International Space Station, as well as that of the shuttle programme itself, hinges on the flight of the shuttle Discovery scheduled for Saturday.
NASA has already lost two shuttles and their crews – Challenger in 1986 and Columbia in 2003. NASA Administrator Michael Griffin has said that the loss of a third orbiter would end the shuttle programme. That nightmare scenario would ground manned US spaceflight until the completion of the shuttle's successor, the Crew Exploration Vehicle, now planned for 2014.
But less serious problems – such as the foam shedding on Discovery's previous flight in July 2005 – could delay further shuttle flights. Delays would leave the still-incomplete station in a holding pattern.
The flight "has to be considered a success to go ahead with the station," says John Logsdon of George Washington University, US, who served on the Columbia Accident Investigation Board.
That is because the shuttles bring crucial supplies to station crews. Shortages, particularly of water normally produced by the shuttle's fuel cells, forced the station crew to be reduced from three people to two when the shuttles were grounded for 2.5 years after the Columbia accident.
This skeleton crew spends most of its time doing maintenance and routine operations, with little time left for research. If Discovery launches successfully, European Space Agency astronaut Thomas Reiter will boost the ISS crew to three again.
But NASA hopes to have six people living on the station by 2009. To make that possible, the ISS must be expanded – and the shuttle is the only spaceship large enough to carry key research facilities and hardware to finish its construction.
NASA has tried to minimise the number of shuttle flights necessary for the task. By turning to Russian Soyuz capsules to rotate station crews, it has pared down its original plan to launch 22 more shuttles to the station after the upcoming Discovery launch. But after Discovery, it still plans 11 missions to carry large components to complete the station and an additional three to five to upgrade the station for a six-person crew.
"Four flights a year is not an ambitious flight rate," Logsdon told New Scientist. The shuttle flew 19 missions in the four years before the Columbia disaster. But changes intended to improve safety have reduced the time windows available for launch, and NASA will retire the shuttles at the end of 2010, so there is little room in the schedule for delays. "What is NASA to do except to make its best effort to fly these missions?" Logsdon says.
Indeed, NASA's efforts to ensure the shuttles are safe to fly could put even more constraints on the schedule if this launch uncovers new problems. NASA has taken 11 months to fix problems uncovered by Discovery's last flight in July 2005, and launching at that rate would leave time for only four more flights before grounding the shuttle. That would leave key research facilities on the ground, including the European Columbus Laboratory and the three-component Japanese laboratory.
Keep up-to-date on the mission by visiting our special report on the space shuttle. Read how this mission will boost the long-term crew of the International Space Station from two to three, what will happen in the event the shuttle is damaged on liftoff, and why astronauts will be dangling from a 30-metre "flagpole" during one of their spacewalks.
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18:00 07 October 2008
17:56 07 October 2008
