Two Russian cosmonauts will inspect and remove an explosive bolt from the Russian Soyuz spacecraft during a Thursday spacewalk outside the International Space Station.
The spacewalk is slated to begin at 2:20 p.m. EDT (1820 GMT) as part of the ongoing Russian investigation into a malfunction that sent the two previous Soyuz spacecraft off-course during reentry. NASA officials have kept close watch on the proceedings.
?To date they haven?t come to a conclusive answer as to what was the cause,? said Mike Suffredini, program manager for the space station, at a Tuesday briefing. ?They continue to look at different scenarios.?
Ten explosive pyro bolts fire to help separate the Soyuz spacecraft from its propulsion module. The maneuver normally allows the Soyuz to turn its protective heat shield downward before reentry, but Russian engineers suspect that a failed explosive bolt caused the Soyuz modules to separate late during the most recent descent on April 19 this year.
The delayed separation subjected the latest Soyuz crew including cosmonaut commander Yuri Malenchenko, U.S. astronaut and Expedition 16 commander Peggy Whitson and South Korea?s first astronaut So-yeon Yi to a bumpy ballistic reentry with higher than normal gravitational loads. Yi described the frightening experience in detail and later underwent hospital treatment for neck and back pain.
6 hours in space
Space station commander Sergei Volkov and flight engineer Oleg Kononenko will undertake the nearly six-hour spacewalk, with Volkov wearing a red-striped Orlan spacesuit and Kononenko wearing a blue-striped spacesuit. Kononenko?s spacesuit helmet will also carry cameras normally worn on U.S. spacesuits.
That leaves U.S. astronaut Greg Chamitoff, the third member of the space station crew, to sit inside the Soyuz during the spacewalk. The Pirs airlock that the crew might normally use to evacuate will be used for the spacewalk, so ground controllers want Chamitoff in the Soyuz in case of the unlikely event that the airlock could not be re-pressurized.
The cosmonauts will ride the Strela hand-powered crane to the Soyuz and put protective covers on the nearby thrusters to prevent accidental contamination from debris.
Knonenko will use a knife for the first time during a spacewalk to cut away insulation, which then would allow him to inspect and photograph the area. He will also install a handrail and cover to protect fluid lines.
The knife was described as ?serrated with a dull tip? by Bob Dempsey, spacewalk flight director for the space station.
Volkov will then cut a wire tie between two explosive bolts next to the suspect bolt, and detach an electrical connector before unscrewing the bolt. He will remove the explosive bolt which has power roughly equivalent to a large M-80 firecracker and place it inside a stainless steel case that should hold against any unlikely firing of the bolt.
?We are very confident that this is a safe operation to do,? Dempsey said.
Suffredini noted that accidental firings of the pyro bolts are unheard of during the Soyuz spacecraft?s operational history. Russian engineers want to examine the bolt once it returns to Earth for any possible signs of space environment damage from electromagnetic or plasma forces surrounding the space station.
NASA officials also dismissed any coincidence between the malfunctions and the recently accelerated production of Soyuz spacecraft. The Russians have begun building more spacecraft to support the jump in the space station?s population next year, from three astronauts to a six-person crew.
?We have a good deal of confidence in their ability to produce those things,? Suffredini said.
If the cosmonauts have time at the end, they will also install a docking target on the Zvezda service module to prepare for a Russian mini-research module?s arrival on a future mission.
A second spacewalk is scheduled for July 15, when Volkov and Kononenko will need to outfit the Russian segment?s exterior, install a scientific experiment and retrieve another.
NASA will broadcast the Expedition 17 crew's spacewalk live on NASA TV beginning at 2:20 p.m. EST (1820 GMT) on July 10. Click here for SPACE.com's live coverage and mission updates.