Space shuttle Discovery's upcoming mission may seem routine. The orbiter's crew will bring supplies and equipment to the International Space Station and drop off the European Space Agency's Thomas Reiter for a six-month stay aboard the outpost. But the astronauts also will test shuttle inspection and repair techniques vital to all future flights.
NPR science editor David Malakoff explains why the fate of the entire shuttle program now hangs on Discovery.
Q: Discovery's mission last August was a success, yet there's still significant anxiety at NASA around this mission. Why?
Most of the concern involves the foam insulation that covers the shuttle's external fuel tank. During the liftoff of the shuttle Columbia in January 2003, a big chunk of that foam broke off and hit the shuttle's wing, creating a hole that caused Columbia to break up during its return to Earth a few weeks later. NASA then redesigned the tank, but at least one dangerously large piece of foam also broke off during last year's launch. The space agency has now made more changes, but it is not clear if they will prevent flying foam from damaging the orbiter. Several of the agency's senior engineers believe more changes should be made before the shuttle is allowed to fly again, but senior managers believe the risks are acceptable.
What other safety changes has NASA made?
The agency has installed 13 cameras on board the shuttle and its rockets so that it can monitor the launch and watch for flying foam. An additional 107 ground-and air-based cameras will document every moment of Discovery's launch and climb to orbit. The astronauts also have kits that they can use to repair damage to the ceramic tiles that make up the shuttle's heat shield, but the kits are experimental. NASA also has the option of rigging Discovery to return to Earth on auto-pilot, without a crew. That way, the crew could take shelter aboard the International Space Station, and NASA could see if the repair kits actually work, without endangering the crew.
NASA says the risks at this point are to the shuttle itself, not the crew. Why?
Engineers believe the risk of a catastrophic launch failure is remote. A more likely -- but still unlikely -- scenario is that the shuttle's heat shield is damaged on liftoff, but the spacecraft reaches orbit. In that scenario, the astronauts take refuge on the International Space Station for up to 80 days, and a second shuttle would be sent to rescue them. Some could also return to Earth aboard Russian spacecraft. The damaged shuttle would either fly home on remote control (see above), or be intentionally dumped into the ocean.
Could this be the last shuttle flight?
Yes -- if the shuttle sustains serious damage, NASA chief Michael Griffin says he won't hesitate to end the program. It is likely the agency would then accelerate its plans to build a new, Apollo-style rocket that would send humans to the moon and, eventually, Mars. If this flight goes well, NASA hopes to complete more than a dozen shuttle flights to complete the space station. NASA plans to end the shuttle program in 2010.
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