NBC News space analyst
Special to MSNBC
Updated: 4:01 p.m. ET Jan. 31, 2005
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 high-level dispute 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 turned slightly and needed to be readjusted 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 were 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 why safety measures weren't more closely followed. 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.
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, in would turn out, they did not.
Enter the thrusters
The spacewalk ended successfully after 5 hours and 38 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 again and again. 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, 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.
NASA warning reportedly ignored
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. Requests for additional information from NASA officials in Houston have not been answered.
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 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 orientation deviation.
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 became clear that since they had assumed that no television would be available for the spacewalk, the Russians 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 proper orientation had been restored. During this period, say sources, the crew reported thrusters firing near them.
Although some NASA engineers insisted that the crew would have to assume they had been contaminated, and should be instructed to inspect their suits and to make sure all sides of the suits were bathed in sunlight long enough to "bake out" any contamination, NASA eventually decided to assume that there had been no contamination. No special measures were requested. The Russians, meantime, continued to insist that nothing at all had happened.
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, neither side can agree on what is causing the so-called "phantom torque" that is pushing the station out of alignment during spacewalks to begin with.
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 MSNBC.com, 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 will likely redefine its authority for spacewalker safety with its Russian partners. It also may reconsider its nonchalant attitude toward performing such spacewalks without television coverage.
And as analysts more closely examine exactly where the crew was in relation to the Russian thrusters when they fired, NASA may also need to question the real-time thinking that led controllers to assume, 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 a culture remains too frighteningly similar to the one that failed to prevent and then failed to recognize the factors that killed seven astronauts only two years ago this week. "
© 2005 MSNBC Interactive
Posts
No comments:
Post a Comment