Spacewalk thruster incident alarms NASA

HOUSTON - The two men aboard the international space station could have been exposed to an unexpectedly hazardous situation during their otherwise highly successful spacewalk last week, MSNBC.com has learned.

Behind closed doors, the origin of what one source called a “major close-call incident” and NASA’s reaction to it are the subject of concern within the space agency and between the space station's U.S. and Russian partners.

U.S. astronaut Leroy Chiao and Russian cosmonaut Salizhan Sharipov spent five and a half hours working outside the space station last Thursday, performing a series of assembly and inspection tasks. It was the first spacewalk of the mission for the pair, who are halfway through their six-month stay on the station.

During the spacewalk, the station's stabilizing gyroscopes repeatedly became overloaded with a mysterious torque, and they had to be relieved periodically by firing rocket thrusters located on the Russian half of the station. On at least one occasion, and contrary to agreed upon mission rules, these thrusters appear to have been activated when the two crew members were working dangerously close to them.

This put them at risk of both thermal damage from the thrusters themselves and, more likely, to chemical contamination from the fuel used by the thrusters. Even in small amounts, any fuel splashed on the space suits could render the air toxic in the station when the men returned from their spacewalk.

That neither of those events actually happened isn't reassuring to those at NASA who want to know exactly how close the men were to the thruster plumes. Engineers at NASA who have spoken privately with MSNBC.com say they are studying the incident all the more intently because the next scheduled spacewalk, in March, could expose the crew to even more hazards of this kind.

Mark Geyer, the manager of space station operations for NASA, confirmed these reports late Monday, but insisted that the space team had treated the potential hazard with serious concern at the time.

A special investigative team is looking into the incident, Geyer said. "We want to know exactly where [Chiao and Sharipov] were," during the thruster firings, he said.

Russian mission control in charge
At a press conference prior to the spacewalk, NASA flight director Derek Hassman commented on the difficulties that reduction to a two-person crew since the Columbia disaster had created.

“One of the challenges of the two-person spacewalk is we don’t have the third crew member inside to respond to unforeseen situations or circumstances that, although unlikely, may arise,” he said. Events on the spacewalk would confirm his prescience.

Because this spacewalk used Russian suits, was from the Russian airlock, and involved work on the outside of the Russian module, the Moscow mission control center was in charge of all activities. The NASA center in Houston was staffed on an advisory level but had no operational authority.

Chiao used the “Orlan” suit with serial number 26, used four times by the previous American on ISS, Michael Fincke. Sharipov had suit number 27, which had never been used before. Although the Russians usually use suits with different colored stripes –- red or blue lines on the legs and arms -– for some reason no blue-lined suit was available, so aside from some small patches on their arms, the men looked identical.

Another unusual factor appeared just prior to the spacewalk. Because of the station’s orientation to the sun, the gearbox of the pointable dish antenna used for hi-speed communications had gotten too cold to safely operate. So although voice and telemetry signals could still be transmitted via smaller antennas, no television images were expected.

The spacewalk was authorized to proceed without television coverage.

“TV is highly desirable, but is not a hard requirement,” a NASA commentator explained. In Moscow, a Russian spokesman voiced the same sentiments to a Novosti reporter: “This trouble will not affect the fulfillment of the planned extravehicular activity,” he said.

Once the spacewalk began, however, television scenes were received intermittently, as the antenna temperature fluctuated near the critical limit and as the line-of-sight to relay satellites suffered frequent blockages from station structures. In Houston, controllers closely watched the images whenever they became available, but in Moscow, it seemed, they did not.

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