Spacewalk thruster incident alarms NASA

Astronaut and cosmonaut perform space walk at space station
U.S. astronaut Leroy Chiao and Russian cosmonaut Salizhan Sharipov work outside the space station last week.Reuters via NASA TV

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, 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 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.

Enter the thrusters
The spacewalk ended successfully after 5 hours and 28 minutes. The planned equipment had been deployed, and in an important discovery, the crewmen had noted some strange "goo" around the dump ports from Russian life support equipment that had been mysteriously malfunctioning in recent months.

But those who followed the spacewalk live on NASA TV, or later watched the tape, noticed some other strange events. Less than an hour into the spacewalk, the gyroscopes that keep the space station oriented had become overloaded and needed assistance.

“The Russian thrusters are now back in control of the space station,” the NASA commentator announced. “The crew is taking a pause to allow the thrusters to reestablish control” against what he called “a slight deviance” that was “nothing significant.”

“Now I can see the thruster firing,” one of the spacewalkers commented a few minutes later, as reported by an interpreter (both men were speaking Russian). Speaking to the other spacewalker, he continued: “It is very interesting to watch the thrusters firing right behind your back.”

Over the remaining hours of the spacewalk, while the men worked at various locations on the outside of the space station, the thrusters came on twice more. Television views would show the men in one area, and brief white thruster plumes appearing on another section of the module. But no audio discussion over the NASA TV channel gave any indication of any concern.

NASA’s internal status report, which is not distributed to the public, later contained a cryptic paragraph on thruster activity during the spacewalk: “Attitude control momentum again was observed to build up in the US [Control Moment Gyros] from reacting to external torques,” the report stated. This “required control authority transfer to [Russia’s Service Module] thrusters to permit gyro desaturation.” After a brief period, “control then returned to the CMGs”.

That is, the station was, as in normal, kept in position by spinning up or slowing down heavy gyroscopes on the U.S. section. But when something "torqued" (or forced to turn) the station to a degree beyond the ability of the gyroscopes to handle, or forced the gyros to spin at dangerously high rates, rocket thrusters on the Russian side had to be turned on to relieve the load on the gyroscopes.

NASA’s official public report made no mention of the orientation control issue or of the Russian thruster firings near the spacewalkers.

Where were the astronauts? However, within hours of the apparently uneventful completion of the spacewalk, the halls at NASA’s Johnson Space Center were abuzz with rumors about a serious contingency that had come up.

“You might want to ask about turning on a Russian thruster when the crew is in the keep-out zone,” one contact e-mailed me, “and the U.S. flight director is telling [the Russian] not to because they are [too close].”

Subsequent private inquiries obtained several different -– and sometimes conflicting –- accounts of the incident. Geyer, who spoke with only after the first version of this story was published, attributed the different versions to varying interpretations of what was shown in the TV images of the mission. While some at NASA thought it looked like the crew was in the "keep-out" zone, their exact location was unclear. Geyer denied reports that there had been a dispute between the U.S. and Russian officials as to whether to fire the thrusters and said that officials had followed correct safety protocols.

Sources explained that the Russian thrusters that control the station’s orientation are in two sets. For pitching and yawing (turning the station up-down and side-to-side), the thrusters of the docked Progress supply ship are wired into the station’s autopilot. But for rolling the station along its long axis, the Progress thrusters are too weak, so the main thrusters along the back rim of the Russian service module are used. Since rotation control involves the thruster pushing largely parallel to the station’s rim, the thruster plume sweeps out a large area near the station skin.

“Yes, a major close-call incident occurred,” one source claimed. While installing one experiment, he continued, the crew had to work close to a thruster. By prior agreement, when crewmen were in this zone, the Russian thrusters were supposed to remain disarmed. But if the thrusters were urgently needed, the crew was to be instructed to remain outside a "keep-out zone" until they could again be disarmed.

During a brief period when television views had become available, Houston controllers thought they saw the crew move to a worksite within such a zone. They then heard Moscow announce that the thrusters would be armed to respond to another gyro overload.

According to multiple sources, Hassman, the NASA flight director, told his Moscow counterpart that the crew was too close to the thruster. Moscow disagreed and told Hassman that the crew was safely at another worksite. But the NASA team could see on television that this wasn’t the case. It looked to some of those there that since the Russians  had assumed that no television would be available for the spacewalk, they were not even looking at the NASA video feed.

Witnesses delicately described “an exchange” between the two flight directors in Houston and Moscow, but the net result was that the Russian ground controllers did not tell the spacewalkers to leave the forbidden area, nor did they disarm the thrusters for more than ten minutes, until the overloaded gyros had been "desaturated". During this period, say sources, the crew reported thrusters firing near them.

"The video gives the appearance that the crew was in a worksite that had a keep-out zone, before the thrusters were inhibited," Geyer confirmed, noting it was up to the special investigation team to find out exactly where each spacewalker was.

But "there was never a disagreement [with Moscow] as to when to inhibit the thrusters," Geyer said, rejecting tales of a dispute.

He also rejected any suggestion that NASA officials had ignored the potential risks involved.

"Because of the possibility of contamination," Geyer said, "the team looked at all the flight rules and reference books for that contingency." They found that ground tests had shown that a splash of hazardous fuel residue on a spacesuit would quickly evaporate in the vacuum of space.

"An hour [of vacuum exposure] is sufficient to get way below any concern with toxicity," he said. Much more time than that was available before the two spacewalkers had to return to the station.

The mysterious 'phantom torque'
In Houston, NASA officials have set up a special team to investigate the incident. The group will determine what changes may be needed in U.S.-Russian control procedures before the next spacewalk in two months.

Meanwhile, NASA and Russia have conflicting theories about the cause of the "phantom torque" that is trying to push the station out of alignment during spacewalks.

"We don't have agreement," Geyer said. 

While the NASA TV commentator described the “phantom torque” as appearing “when the crew is imparting a force” to the outside of the station, a simple familiarity with Newton's Laws of Motions shows that this explanation is spurious.

There is no force without a counterbalancing force. Any push on the outside of the station that made the station turn away from its desired orientation, would require the pushing party -– the astronaut –- to go flying off into space. Just banging on the outside, as long as you are securely attached, creates no rotational forces.

What is actually happening is that something besides the spacewalkers’ motion is creating a genuine force against the side of the station. Somehow, a small amount of material is being sprayed away from the station, enough that over time the station builds up an unwanted rotation.

As reported on last year by, NASA believes this force comes from water vapor sprayed out the back of the Russian-made spacesuits to keep them cool. The Russians, however, do not want to blame their suits, and insist the force comes from slight air leakage from their airlock.

“Until it is resolved,” a source e-mailed, “we’ll continue to have this problem for every [Russian] EVA.”

Almost all of the work to be conducted during the crew’s second (and final) spacewalk will take place at the far end of the Russian segment, where the disturbing torques from their spacesuits will be greatest -– and where they will be closest to the Russian rocket thrusters that will have to be activated to counter these forces.

At the very least, NASA may reconsider its attitude toward performing such spacewalks without television coverage.

Geyer, for one, said he did not believe that the existing plans need to be changed: "We had clear agreement on flight rules and operations plans, on which worksite had thruster inhibits and which did not," he said. Those rules can work as long as ground controllers can be better aware of the location of the spacewalkers.

Many of the initial rumors expressed concern about an apparently complacent treatment of the potential exposure. Some space workers believed that officials had assumed, in the absence of proof, that there had been no contamination. This is the opposite of the proper attitude of assuming the worst until a better appraisal could be justified. Such thinking would remain too frighteningly similar to the one that failed to prevent and then failed to recognize the factors that killed seven astronauts only .

That isn't what happened, however, Geyer said. Nobody in Mission Control made any convenient assumptions about contamination not occurring, he said; the potential for a dangerous exposure was never discounted.

In fact, he said, officials went out of their way to remind the returning spacewalkers to check for possible damage.

"The normal plan is that when the crew is ready to come back in, they look over each other's suits for damage or discoloration,” Geyer said. "And we specifically reminded them not to forget to do so this time."

Nothing unusual was seen, and when the men got back inside and opened their visors to sniff the airlock atmosphere, they noticed no unusual odors either.