Two Russian cosmonauts on the International Space Station on Thursday practiced a potentially explosive spacewalk that is hoped will reveal why two Soyuz spaceships experienced two off-course landings during the past year.
The cosmonauts hope to avoid similar problems when they use the currently docked Soyuz to return to Earth at the end of their mission in October. The risky procedure will involve taking an explosive bolt from the exterior of a docked Soyuz spacecraft and bringing it into the station itself.
One of the most delicate aspects of the July 10 spacewalk will be handling the bolt, which sources say packs twice the explosive force of an M-80 firecracker when ignited.
The explosive bolts are designed to break the connections between the spacecraft's crew capsule and its propulsion module during descent. Russian space engineers say the bolts at one particular location failed to work properly during each of the two previous Soyuz landings, in October 2007 and then again this April. As a result, in each case the landing capsule was twisted out of proper orientation and underwent excess heating on unshielded surfaces before tearing loose from the propulsion module and falling to Earth.
NASA will describe the plans for the six-hour spacewalk at a yet-to-be-scheduled news briefing, but some details already have emerged in the space agency's routine status reports. Space engineers in Houston revealed additional details during private discussions and in e-mails. They declined to be identified because they weren't officially authorized to discuss the plans.
The plans call for station commander Sergey Volkov and flight engineer Oleg Konenenko to venture outside the space station at about noon ET on July 10. Konenenko will perform the manual work while Volkov holds him in position at the end of a telescoping boom.
At the work site, Konenenko will place protective shrouds over the Soyuz's small steering thrusters, to prevent any accidental firing from damaging his spacesuit. Next, he will peel back insulation blankets over the particular section where the target bolt is located.
The separation structure between the two Soyuz modules consists of five pairs of explosive bolts, interspersed with five pusher springs. The firing of either bolt at any location provides clean separation there. Russian experts have told NASA that the bolts at position 5 apparently failed to fire during both previous Soyuz descents, preventing a clean separation.
When Konenenko removes one of the explosive bolts in position 5, he will open that latching mechanism, thus preventing a jam if the previous events are repeated. The Russians have told NASA that the remaining four latches will be adequate to hold the two modules together during any other maneuvers in space.
Konenenko will place the bolt in a shielded safety canister that happens to be aboard the station for a different purpose. With its rugged construction and screw-on lid, the box should provide both electrical shielding against static charges that might ignite the bolt, and physical containment if the bolt did somehow fire.
Source: Xinhua/Agencies
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