ISS Expedition 10 Crew Prepares for Second Spacewalk
ISS Expedition 10 commander Leroy Chiao and flight engineer Salizhan Sharipov work outside the space station during their mission's first spacewalk. Chiao's red-striped legs and feet are visible at the upper left of this image, while Sharipov appears near the center behind the Matroiska radiation experiment, a Russian instrument designed to mimic the human body in space.
Credit: NASA TV.

Two astronauts living aboard the International Space Station (ISS) are gearing up for the final spacewalk of their six-month mission.

With just over one month left in their spaceflight, ISS Expedition 10 commander Leroy Chiao and flight engineer Salizhan Sharipov plan to step outside the station on March 28 to install a batch of antennas and hand-toss a small satellite into space.

"Their attitude continues to be super and they are certainly looking forward to this spacewalk," said Derek Hassman, NASA's Expedition 10 lead spacewalk director, of the ISS crew during a mission briefing Friday at Johnson Space Center.

Chiao and Sharipov are expected to install a series of space-to-space and global positioning system antennas to the Russian-built Zvezda service module during their spacewalk. The antennas will be used by a new European cargo ship - the Automated Transfer Vehicle Jules Verne - for navigation during docking maneuvers.

Sharipov will also toss the 11-pound (five-kilogram) Nanosat satellite into space with both hands the same way you would pass a basketball, said Scott Bleisath, NASA's lead spacewalk officer for Expedition 10.

The 12-inch (30-centimeter) long, transmitter-equipped Nanosat is an experiment designed to study small satellite control methods and operations.

Dealing with drift

Chiao and Sharipov will don Russian-built Orlan spacesuits and begin their spacewalk at 1:30 a.m. EST (1830 GMT) on March 28. The extravehicular activity (EVA) is scheduled to last about five hours and 40 minutes, ISS officials said.

During that time, the space station is expected to drift freely in space for about three hours - enough time for the ISS to circle the Earth twice - as its two functioning gyroscopes become overloaded due to an expected torque.

The torque has appeared in several of the last few spacewalks, though ISS flight controllers have not pinned down its source. They can, however, prepare for it hence the free-drift plan.

Russian thrusters will not be able to correct for the drift during that three-hour period because Chiao and Sharipov will be working near thruster nozzles at the time, NASA officials said.

A power failure to one of three stabilizing gyroscopes earlier this week has cut in half - from one hour to 30 minutes - the amount of time the U.S. attitude control system will function before the phantom torque overpowers it during the upcoming spacewalk, Hassman said.

"We feel comfortable that even with two [control moment gyroscopes] we can do the work, tolerate the drift, have the crew come back from their work and clean [the drift] up with Russian thrusters," Hassman added.

A new set of communications protocols should ensure that Expedition 10 spacewalkers are nowhere near the thrusters when they fire, ISS flight controllers said. During the last Expedition 10 spacewalk, a miscommunication between ground-based flight controllers and the ISS crew resulted in Chiao getting too close to the Russian thruster system while it was firing.

Chiao and Sharipov have spent 155 days living in space and are due to return to Earth on April 25, following six months of space station living. The upcoming spacewalk will mark the sixth EVA for Chiao and the second for Sharipov.

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