Russian experts believe they have identified the "most probable cause" of the separation issue that has sent the past two Soyuz vehicles returning from the International Space Station (ISS) into potentially dangerous ballistic re-entries.

Experts in Moscow told William Gerstenmaier, NASA associate administrator for space operations, that the plasma environment around the space station seems to be degrading the igniter wire in one of the pyrotechnic bolts that separate the Soyuz crew compartment from its service module during re-entry, apparently preventing the bolt from detonating.

The phenomenon has been duplicated in a test chamber, Gerstenmaier said, making it "not conclusive but [the] leading scenario."

Fixes for the problem include a new type of pyro bolt, and a new Soyuz flight profile that may ease the phenomenon, he says. In case the bolt issue isn't the root cause of the failures, Russian engineers have addressed 25 other potential causes as well.

The Soyuz already at the station should be safe for re-entry, according to Gerstenmaier, since spacewalking cosmonauts removed the offending pyro bolt - one of 12 that separate the two Soyuz sections - last summer for inspection on the ground.

As Russia prepares to launch a Soyuz in October with the ballistic-entry fixes in place, NASA Administrator Michael Griffin says he's getting positive feedback as he makes the rounds on Capitol Hill pushing for authority to keep buying seats on the Soyuz capsules after Dec. 31, 2011.

NASA's exemption to the Iran, North Korea and Syria Nonproliferation Act expires on that date, blocking further U.S. payments to Russia for rides to the ISS. Because NASA's agreements with its other ISS partners include transportation, failure to extend the exemption would effectively ground Canadian, European and Japanese astronauts as well as those on the NASA payroll (Aerospace DAILY, Feb. 14, April 28).

"Every single person that I have talked to, on either the House or the Senate side, and on either side of the aisle, has said they understand, they are supportive," Griffin said.

Russia's invasion of Georgia has complicated his task, he said, because "it is very difficult for the Congress to understand why we should continue a practice of depending upon agreements with the Russians when they are busy invading another country."

But if the extension isn't granted, Griffin said, the U.S. would be "backing away from one of the areas, which is cooperation in space, where we work very well with the Russians."

Given the lead-time for Soyuz production, Griffin said he needs clearance this fall to finish negotiating a new contract in time to maintain a steady flow of vehicles into 2012. Because the law as written forbids the expenditure of U.S. funds after the end of 2011, Griffin said, NASA would not be able to buy seats on a Soyuz set for launch late in 2011 if it would return after the first of the year.

File photo of Soyuz: NASA