Twoastronauts living aboard the International Space Station (ISS) are gearing upfor the final spacewalk of their six-month mission.
With justover one month left in their spaceflight, ISS Expedition 10 commander Leroy Chiaoand flight engineer Salizhan Sharipov plan to step outside the station on March28 to install a batch of antennas and hand-toss a small satellite into space.
"Theirattitude continues to be super and they are certainly looking forward to thisspacewalk," said Derek Hassman, NASA's Expedition 10 lead spacewalk director,of the ISS crew during a mission briefing Friday at Johnson Space Center.
Chiao andSharipov are expected to install a series of space-to-space and globalpositioning system antennas to the Russian-built Zvezda service module during theirspacewalk. The antennas will be used by a new European cargo ship - theAutomated Transfer Vehicle Jules Verne - for navigation during dockingmaneuvers.
Sharipovwill also toss the 11-pound (five-kilogram) Nanosat satellite into space withboth hands the same way you would pass a basketball, said Scott Bleisath, NASA'slead spacewalk officer for Expedition 10.
The 12-inch(30-centimeter) long, transmitter-equipped Nanosat is an experiment designed tostudy small satellite control methods and operations.
Chiao andSharipov will don Russian-built Orlan spacesuits and begin their spacewalk at1:30 a.m. EST (1830 GMT) on March 28. The extravehicular activity (EVA) isscheduled to last about five hours and 40 minutes, ISS officials said.
During thattime, the space station is expected to drift freely in space for about threehours - enough time for the ISS to circle the Earth twice - as itstwo functioning gyroscopes become overloaded due to an expected torque.
The torquehas appeared in several of the last few spacewalks, though ISS flight controllershave not pinned down its source. They can, however, prepare for it hence thefree-drift plan.
Russianthrusters will not be able to correct for the drift during that three-hourperiod because Chiao and Sharipov will be working near thruster nozzles at thetime, NASA officials said.
A power failure toone of three stabilizing gyroscopes earlier this week has cut in half - from onehour to 30 minutes - the amount of time the U.S. attitude control system will functionbefore the phantom torque overpowers it during the upcoming spacewalk, Hassmansaid.
"We feelcomfortable 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 setof communications protocols should ensure that Expedition 10 spacewalkers arenowhere near the thrusters when they fire, ISS flight controllers said. Duringthe last Expedition 10 spacewalk,a miscommunicationbetween ground-based flight controllers and the ISS crew resulted in Chiaogetting too close to the Russian thruster system while it was firing.
Chiao andSharipov have spent 155 days living in space and are due to return to Earth onApril 25, following six months of space station living. The upcoming spacewalkwill mark the sixth EVA for Chiao and the second for Sharipov.
- Complete Coverage: ISS Expedition 10