NASA Wrangles Plans for U.S. Astronaut's Earth Return
Expedition 14 flight engineer Sunita Williams dons an intrumented cap to perform a ALTEA experiment session to study astronaut exposure to cosmic radiation.
Credit: NASA.

The delay of NASA's next space shuttle flight has thrown a monkey wrench into plans to return a U.S. astronaut home from the International Space Station (ISS), mission managers said Tuesday.

NASA astronaut Sunita "Suni" Williams was slated to return to Earth in July with space shuttle Endeavour's STS-118 crew after a six-month flight that bridges the Expedition 14 and Expedition 15 station missions.

But the delay of the ISS construction flight immediately before Williams' return ticket - NASA's STS-117 mission to fly no earlier than mid-May - may push the astronaut's Earth homecoming later into this summer, Kirk Shireman, NASA's deputy ISS program manager, told reporters in a Tuesday briefing.

Hail damage to the space shuttle Atlantis' external tank prevented the orbiter's planned March 15 launch. NASA is expected to set a new liftoff target on April 10.

"We're looking at..exactly what that means and what the delay is, and we're certainly keeping Suni abreast of what the developments are on the ground," Shireman said. "Medically, we're talking to her and doing things as best we can to make her happy and perhaps launch some special items that'll make her more comfortable for that extended period of time.

"Aside from that, there's not a whole lot that we can do. She's up there, and [STS-118 is] the ride home and she knew that before she launched," Shireman added.

Williams launched to the ISS aboard the Discovery orbiter in December during NASA's STS-116 mission, where she replaced European Space Agency astronaut Thomas Reiter as a flight engineer on the Expedition 14 crew. Her crewmates, Expedition 14 commander Michael Lopez-Alegria and flight engineer Mikhail Tyurin, are scheduled to return to Earth on April 20 after their replacements arrive, but she will stay on for the first leg of Expedition 15.

The space station's Expedition 15 mission includes a convoluted series of ISS astronaut swaps that begin with the planned April 9 arrival of Williams' next crewmates - cosmonauts Fyodor Yurchikhin and Oleg Kotov - aboard their Russian-built Soyuz TMA-10 spacecraft.

Williams is due to be relieved by NASA astronaut Clayton Anderson, who will launch aboard Endeavour on the STS-118 mission and himself be replaced by U.S. spaceflyer Daniel Tani during the STS-120 shuttle mission currently targeted for a late August liftoff.

"It does add a lot of complexity," Williams said of the crew rotation plan during a preflight NASA interview.

NASA has historically limited its long duration astronauts to missions that span as close to six months as possible, though there is some leeway in determining their maximum flight time, mission managers said.

"There are no specific flight rules that dictate that. We have to look at the entire environment that they're in," Dave Alexander, NASA's lead Expedition 14 flight surgeon, said Tuesday, adding that factors such as physical fitness, space radiation exposure and mental health are examined. "Right now, the predictions are that Suni can stay for an extended period of time."

Shireman said that there is a remote possibility that Williams could return home with the STS-117 crew, but only if a significant problem arose with the preparations or timing of her STS-118 return trip. In that case, Anderson could be added as a seventh member of Atlantis' STS-117 crew.

"It's unlikely at this point, but not out of the realm of possibility," Shireman said.

Adding Clayton to the STS-117 mission prompts a series of challenges, the least of which being the fact that Discovery's cargo of new ISS solar arrays attached to a 17.5-ton pair of truss segments leaves little weight allowance for the Russian Sokol spacesuit, Soyuz seat liner and other vital supplies required for a new station crewmember, Shireman said.

The planned 11-day mission to perform three spacewalks to install those new solar arrays and also leaves little time for handover activities between Williams and Anderson, he added.

"So we'd prefer not to do that," Shireman said.

From a health standpoint, Williams - who joined NASA's astronaut corps hoping for a berth aboard the space station - is as sharp as ever for her long spaceflight, flight controllers said.

"She's fit and ready to continue on in most of her adventures," Alexander said.