NASA Shuffles Landing Plan for Some Station Astronauts

NASA has shuffled landing options for two astronauts headed to International Space Station later this year due to shuttle launch date uncertainties.

The U.S. space agency announced a plan Tuesday to swap the return trips of Canadian astronaut Robert Thirsk and American spaceflyer Nicole Stott this fall to ensure that future shuttle mission delays don?t extend Thirsk?s mission beyond the traditional six-month duration.

?It would just put him, timeline-wise, on an earlier return,? NASA spokesperson Nicole Cloutier-Lemasters told SPACE.com from the agency?s Johnson Space Center in Houston. ?This is just kind of a preemptive measure in case there is more slippage.?

NASA has up to six space shuttle missions on its 2009 schedule, with the first currently slated to launch aboard Discovery no earlier than March 12 on a construction flight to the International Space Station. Discovery?s STS-119 mission has been waylaid since Feb. 12 due to fuel valve concerns, but NASA officials have said that if they launch shuttle by around March 13 the delay should not affect launch targets for the rest of the year.

If Discovery is unable to launch in mid-March, NASA would have to stand down until around April 7 ? after a preplanned Russian Soyuz launch of a new crew to the space station. Delaying the spaceflight to April could cause a ripple delays for subsequent shuttle missions, some of which are expected to include station astronaut crew swaps.

Thirsk is currently slated to launch to the space station in late May aboard a Russian Soyuz rocket as part of the space station?s Expedition 20 ? the first six-person mission to the orbiting lab. He is Canada?s first long-duration astronaut and was slated to return home in November during NASA?s STS-129 shuttle mission.

Stott, meanwhile, is currently scheduled to launch toward the station in August aboard Discovery. She is also expected to join Expedition 20 and was due to return aboard the Russian Soyuz spacecraft that will launch Thirsk.

But NASA?s announcement today will swap the return seats for Thirsk and Stott, with the Canadian spaceflyer landing on the Soyuz and the American returning home on the November shuttle flight.

NASA officials said the swap ensures that Thirsk?s mission won?t exceed the typical six-month duration for station astronauts, even if the November shuttle flight is delayed. The longer astronauts fly in the weightless environment of space, the more exposure they have to space radiation, muscle and bone loss, the space agency has said.

?At this point we prefer to keep them [in space] around six months,? Cloutier-Lemasters said.

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