Attended by divers, astronaut Michael Foale and cosmonaut Alexander Kaleri practice for a spacewalk in an underwater training session that preceded their launch to the international space station.
By NBC News space analyst
Special to MSNBC
updated 2/23/2004 7:18:49 PM ET 2004-02-24T00:18:49

As the international space station's two crew members prepare to take the only scheduled spacewalk of their six-month mission, the prospect of leaving the outpost with no one inside has required some extraordinary preparations and raised some serious questions.

Russian cosmonaut Alexander Kaleri and U.S. astronaut Michael Foale will spend about six hours outside the station on Thursday, mounting and retrieving various scientific experiments, as well as preparing the station's back docking port to receive a new robot supply ship. If they have time, the two are also expected to inspect the outer skin of the station's Russian-made module. A loud noise from that direction startled the crew last November, and the crew will be looking for evidence it was caused by impact with "space junk."

The station has never been left unoccupied during a spacewalk before — and in documents written last year and cited Monday by The Washington Post , space station managers were quoted as saying such a situation posed "a risk not worth taking." But in private interviews with, spacewalk experts said Houston and Moscow had developed rigorous backup procedures for any conceivable contingency.

They said the initial risk assessment, prepared last summer, assumed that the U.S. space shuttle fleet would be close to resuming flights by now. Under those conditions, delaying the spacewalk for a few months would have been tolerable. But with the shuttle fleet's return to flight now more than a year away, and with elaborate emergency drills successfully performed by the crew, sources told they saw no safety issue that would rule out going ahead with the spacewalk.

They pointed out that the situation was by no means unprecedented: When Russia's Salyut and Mir space stations were flying in the 1980s and 1990s, its two-man crew went outside dozens of times, leaving the station to be monitored by Mission Control in Moscow. Back in the 1960s and 1970s, two American astronauts safely left the lunar module empty on the moon’s surface during every moonwalk.

Furthermore, over the more than three years since the international space station became permanently inhabited in November 2000, it was left unoccupied for several hours on four occasions when the crew flew their Soyuz transport spacecraft from one docking port to another. No problems arose.

Getting back in
After the first one-man spacewalks in the mid-1960s, both Russia and the U.S. adopted a "space buddy system" of having at least two crew members outside a spacecraft together. But since the grounding of the space shuttle fleet a year ago, the normal three-person station crew has been reduced to two in order to conserve supplies — and for a two-person spacewalk, simple arithmetic says there's nobody left to stay inside.

Aside from being available for any emergency such as loss of a guidance computer, or a fire, the presence of the third “inside” crew member has always been reassuring in case of any malfunction of the airlock hatches.

In at least one frightening case, 15 years ago, two Russian cosmonauts were stranded in vacuum when they could not properly seal their air lock’s outer door. They survived by entering an inner section of the Mir that they were able to depressurize by remote control.

Such a leak is much less likely to occur on the international space station because the hatch on the Russian-built Pirs module opens inward rather than outward, as it did on Mir. That means the internal air pressure squeezes the hatch more tightly closed, rather than putting more stress on the restraining latches.

Emergency escape route
Spacewalks from Pirs present their own peculiar problem, however. Because the unit is mainly a “docking adapter” (hence the use of the Russian word for “pier”) and only secondarily an airlock, it lies between the main station modules and whatever is docked to it.

This means that when the air lock is depressurized, the docked vehicle is isolated from the rest of the station. The Soyuz spacecraft is currently at this location, so if there had been a third crew member aboard during this spacewalk, for safety's sake they would have to remain inside the Soyuz while the two others were outside. This is because otherwise, failure to repressurize the airlock would have isolated the third person from the landing craft.

If the airlock hatch failed to seal properly at the end of the walk, the two spacesuited figures would have to enter the Soyuz, close its hatch and take off their suits. Then they would undock and fly over to another docking port to re-enter the station.

Failing that, they could safely return to Earth.

Cosmonaut Alexander Kaleri's feet and backpack can be seen on the near side of a hatch leading from the Pirs docking module to the Soyuz escape capsule, during a spacewalk training session in November.
Before agreeing to such a spacewalk, NASA insisted that this tricky procedure be tested in space.

“The first training session last November did not go well,” a NASA expert told on condition of anonymity. “Kaleri was the suited crew member and became lodged in the hatch. Foale had to assist him.” The station's Nov. 18 status report refers to Foale’s “active pushing” being needed to get the inflated suit through the narrow hatch.

Three months later, the maneuver was tried again. Instructions sent up to the crew described how it was to be done: “Translation through the narrow hatch opening will be done head first, with one arm extended forward and the other pressed alongside the body. Kaleri will be first, with Foale assisting and pushing if necessary.” Use of a pry bar was also specified.

On Feb. 19, the procedure worked, clearing the way for approval of the spacewalk itself.

Communication constraints
A second major feature of the crew’s preparation for the spacewalk involves shifting the wake-sleep cycle. They are normally on Greenwich Mean Time and sleep between about 2300 and 0700 GMT (6 p.m. to 2 a.m. ET). But in the days leading up to their spacewalk, the crew’s workday was shifted about five hours forward.

NASA representatives explained that this move was taken to “maximize Russian communications.” This is true as far as it goes — it is during this part of the day that the station’s orbit crosses directly across Russia — but the whole story is somewhat more complicated.

First, the time of day when the station crosses a particular region of Earth shifts on its own. On average, it’s about 24 minutes earlier every day. So if the spacewalk had been scheduled for a few weeks earlier or later, it could have occurred in any desired part of the crew’s normal workday.

Second, Russia’s communications constraints reflect their program’s continuing budget problems. In the 1980s, Russia had launched communications relay satellites very similar to NASA’s Tracking and Data Relay Satellite System, or TDRSS, and had equipped the Mir space station with a dish antenna to use this system, called Altair. When it was working, it allowed long periods of frequent communications between space and Earth, whether the station was over Russia or not.

But a similar antenna now installed on the station's Russian segment is unusable because the Russian Aviation and Space Agency can’t afford to launch replacement relay satellites. Although the factory in Krasnoyarsk built a new satellite in the mid-1990s, it wound up in a museum in St. Petersburg.

Chris van den Berg, a veteran amateur space tracker in the Netherlands, noted a few days ago: “It is clear that the lack of such a satellite is [of] great concern for Russian spaceflight authorities.” The Russians routinely rely on U.S. communications channels, but during critical mission events such as spacewalks they want to use their own systems — hence the need to perform the spacewalk while flying across ground sites on Russian territory.

The station's radio systems have been cross-linked to allow voice communications from the Russian segment to be routed through U.S. relay satellites, assuring nearly continuous voice coverage. However, telemetry from the crew's Russian-made spacesuits will be only available via direct line-of-sight communications to Russian ground sites.

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