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Spacewalkers to cut open Soyuz and remove pyrobolt
Posted: July 9, 2008

Cosmonauts Sergei Volkov and Oleg Kononenko are preparing for a dramatic spacewalk Thursday to cut through insulation and remove an explosive bolt from their Soyuz re-entry craft. The goal is to help Russian engineers figure out what caused back-to-back module separation problems during the two most recent Soyuz re-entries - and to make sure the Soyuz now attached to the international space station will work properly when it carries Volkov, Kononenko and U.S. space tourist Richard Garriott back to Earth in October.

Training footage shows how the spacewalker will use a knife to cut through the Soyuz thermal covering. Credit: NASA TV
The cylindrical pyrobolt, which has an explosive yield roughly equivalent to an M-80 firework, will be locked in a blast-proof steel sleeve and brought back inside the international space station for eventual return to Earth. Mike Suffredini, space station program manager at the Johnson Space Center in Houston, said a detailed analysis showed no significant risk to the crew.

"We dream of a lot of wild things to do and after much analysis, sometimes we do them and sometimes we don't," Suffredini told reporters Tuesday. "In this case, both safety communities thoroughly looked at all the data surrounding this. So we have quite a bit of confidence we're perfectly safe for the crew to both remove the power connector from the charge, remove the pyrobolt from the mechanism and bring the pyrobolt, in the blast canister, inside. This has been done with all the rigor we would expect for a system that was critical like this."

The spacewalk is scheduled to begin around 2:21 p.m. Thursday and last about six hours. As a safety precaution, U.S. flight engineer Gregory Chamitoff will observe the spacewalk from inside the Soyuz spacecraft while his two crewmates work outside. The Soyuz is docked to the downward-facing Pirs module. If the cosmonauts have problems re-pressurizing the chamber after the spacewalk, they will join Chamitoff in the Soyuz and fly it to a different docking port Friday.

"We do not like to separate the crew from escape vehicle," said Bob Dempsey, a space station/spacewalk flight director. "Therefore Greg will be staying in there. He will have some laptops, books and computers to work on while he's there. And in the event of an unlikely contingency that the docking compartment could not be repressed, the Russian crew would enter the Soyuz, which would be used as a backup airlock."

The Soyuz TMA-12 spacecraft is made up of three connected modules, but only one of them - the central descent module - is designed to withstand the rigors of atmospheric entry and carry a crew back to Earth. The three modules separate, using explosive bolts, just before re-entry begins. The modules can safely separate if two of five connectors fail to work, although such failures result in steep, rougher-than-usual ballistic re-entries.

This artist's concept shows how the three modules of the Soyuz spacecraft are supposed to separate, with the crew aboard the middle section. Credit: NASA TV
"There are five locking bolts on the Soyuz that hold the instrument (and propulsion) module to the descent module," Dempsey said. "In a normal re-entry, these locks are released by pyrobolts, which explode and release the locks and then the instrument module is separated and the descent module re-enters the atmosphere. We'll be inspecting one of these locking assemblies, No. 5, and we'll be removing one of the two pyrobolts that are associated with that locking mechanism."

Engineers do not know of any problems that might affect the normal separation of the Soyuz TMA-12 crew module, but they don't yet know what caused separation problems last May 19 and Oct. 21.

In both cases, the upper orbital module separated from the crew module normally just before atmospheric entry, but the lower propulsion/instrumentation module hung up. Both spacecraft then flew steeper, so-called ballistic trajectories that subjected the crews to extreme buffeting until the lower modules broke free due to aerodynamic stress.

"Our desire is straight forward," Vladimir Solovyev, chief Russian flight director, told Volkov and Kononenko on Wednesday. "What we expect from you during this EVA is to take out one pyrobolt, thereby breaking this mechanical contact. Less of a priority is to return this pyrobolt. We would like to, of course, see what you notice before you start cutting the MLI (multi-layer insulation) and after you dig inside the niche through the cutout you make in the MLI.

"The important thing here to remember is that we would like to see as many pictures as possible," he said. "We have been holding meetings after meetings with different commissions to discuss the situation with the pyrobolts and what's happening with them. This is what we decided to do because we think we have exhausted all of the studies that exist on the ground. So we need to figure out what to do with this series of Soyuz vehicles.

"So, like I said, we need to break this mechanical contact, which brought us into the ballistic descent twice before. So again, make sure you take as many pictures as possible because as you know, we sometimes have video, sometimes we don't, sometimes we don't see very well what you're seeing. So we would like to look at that pyrobolt as well as possible, especially when you're inside the niche."

Training footage shows how the spacewalker will use a tool to reach the pyrobolt. Credit: NASA TV
Solovyev also reassured the cosmonauts, making their first spacewalk, that the pyrobolt poses no threat of an accidental detonation.

"Now for the pyrobolt, as you were told many times before, it cannot fire so you should not be concerned at all," he said. "It also withstands shock up to 100 Gs and does not fire, it's been tested. So if you really wanted to fire (it), you would have to really try to knock it with a hammer. But even then, it's not possible for it to fire."

The propulsion/instrumentation module is held to the descent module by five connectors, each one featuring two redundant explosive bolts. In the two most recent Soyuz re-entries, the hang up occurred at a specific connector, known as "plane 5," but engineers do not yet know whether one or both pyrobolts in the mechanism actually fired.

"To date, they haven't come to a conclusive answer as to root cause," Suffredini said. "They continue to look at different scenarios, even as far as looking at the (electrical) environment around the ISS to see if it's playing a role in any way, shape or form.

"The thing that they do know is in these last two flights, the same plane did not separate. And so they've spent quite a bit of time trying to figure out if there was any common cause to that plane that would lead them to why this was occurring. They've looked at the electrical system, the pyrobolts themselves, the mechanical system associated with the locking mechanism and nothing has turned up yet as to root cause."

Training footage shows the tight work area for the spacewalker removing the pyrobolt. Credit: NASA TV
Bringing a pyrobolt back to Earth after six months in space will give engineers additional insight into what might be going on. In the process, the plane 5 connector will be unlocked prior to entry and will not require the operation of a pyrobolt.

After exiting the Pirs airlock/docking module, Kononenko, anchored to the end of a telescoping boom, will use a knife to cut through insulation over the target connector. Using a NASA helmet cam - a first for a Russian spacewalk - he will carry out a detailed photo-visual inspection with Volkov before the station commander begins the job of removing the pyrobolt.

"We have looked very carefully at any risk that might be associated with removing a pyrobolt on orbit," Dempsey said. "The Russians have been looking at this for a long time and planning this EVA very carefully. Our specialists have looked at it very carefully and we are very confident this is a very safe operation to do."

Using a wrench, Volkov will unscrew a cap and pull out one of the two pyrobolts in the plane 5 connector. The explosive bolt then will be slid inside a steel sleeve that will serve as a blast-proof case. An insulation patch will be attached to the cut-out insulation to complete the inspection and removal procedure.

"For all devices like this, there is a potential for a static discharge but that's been accommodated," Suffredini said of the pyrobolt removal. "The kit has been set up so we don't have any accidental charging around or in the pyro mechanism itself.

"The other thing we've looked at is all of the systems that radiate while they're doing this work and whether there's any sensitivity to everything from ... the comm system to the plasma field around the vehicle when we're doing the EVAs. All these things have been looked at and determined that we don't have an environment that would cause these things to set themselves off.

Training footage shows a protective container for the spacewalkers to store the Soyuz pyrobolt. Credit: NASA TV
"So the first thing the crew does is disconnect it," Suffredini said. "At that point, it's still captured, it's in the mechanism, there's no risk to the crew during that process. After that, there is not a mechanism by which the bolt can be fired. And shortly after they pull it out they stick it in this blast proof canister and after that, via testing our Russian colleagues have done on the ground, the crew is protected. If the pyrobolt goes off, it will stay contained in that metal canister. Quite a bit of work has been done by both safety communities to confirm that the environment is such that we wouldn't accidentally set one of these things off from the time it comes out of the lock to the time we get it housed in the blast canister."

If enough time is available, the spacewalkers will install a docking target on the upper port of the Zvezda command module for the upcoming attachment of a new docking compartment next year.

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