Next spacewalk will have an explosive twist

James Oberg NBC News space analyst

HOUSTON - Two Russian cosmonauts on the international space station practiced Thursday for a dramatic spacewalk planned in July, which will involve taking an explosive bolt from the exterior of a docked Soyuz spacecraft and bringing it into the station itself.

The risky operation is aimed at figuring out why similar bolts on earlier Soyuz spaceships misfired, leading to two rugged, off-course landings over 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.

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.

The July 10 spacewalk is aimed at avoiding a misfire during the next descent.

Advance word of plans
NASA will preview the plans for the six-hour spacewalk at a July 8 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 2:18 p.m. ET on July 10. Konenenko will perform most of the manual work while Volkov holds him in position at the end of a telescoping boom.

At the work site, Konenenko will place shrouds over the Soyuz's small steering thrusters, to protect against any propellant leaks. 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.

Volkov will remove one of the explosive bolts in position 5. That operation will open the latching mechanism at that position, 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.

The bolt will be placed in a shielded safety canister that was shipped up to the station in May for this operation. 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.

The plans call for the bolt to be brought back inside the station at the end of the spacewalk. Engineers in Houston said that, to their knowledge, no such pyrotechnic device has ever been brought into the space station in its 10-year history.

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