Crew to Exit Space Station In Exercise

But "the Russians refuse to sign on the document unless EVA #9 is planned for as a requirement," the July summary said. "EVA #9 is essential" to the Russians' program because it brings in funding from the European and Japanese space agencies.

The July 31 summary indicates that, at a meeting on July 25, 2003, space station program manager Bill Gerstenmaier asked for an assessment of the spacewalk preparations and potential failures that would be of enough concern "to tell the Russians that the additional risk to plan for an EVA is unacceptable." In the document, the word "plan" is underlined.

Gerstenmaier and Hasbrook, in telephone interviews Friday, said they now feel entirely comfortable with the safety planning for the spacewalk.

The July memo "overstates where we are," Gerstenmaier said. "It sounds kind of bad. . . . It sounds like [the Russians] are holding us hostage," but actually represents a normal process of give and take.

He said he typically calls for arguments against doing something even when the team wants to do it, to get full information on the table before making a decision.

Although there were initial concerns about the spacewalk's risks, Gerstenmaier said that in the months since, the U.S. and Russian experts have worked through the rationale and mitigated the risks.

It became clear, Gerstenmaier and others said, that preparing for ATV's arrival next year would have eventually required two-man spacewalks with no one inside the station. And the presence of an experienced crew, the angle of the sun on the solar arrays that power the station, and other factors made this the best time for a test run.

Managers rejected the idea of waiting for the next Soyuz to arrive with a fresh crew of two, plus a short-term third passenger, and conducting the spacewalk before the old crew departed. That, they said, would keep too many people at the space station for too long, consuming too much food and water.

Readdy noted that he had called for an extra review of readiness for the exercise early this month, to air lingering concerns. And last week , the station crew members successfully completed a test to ensure that, if they had to abandon their orbital home, they would fit into the Soyuz "lifeboat" for a return to Earth.

Some of those involved in NASA's decision-making have expressed private concerns that the situation is leading the U.S. team to accept unnecessary risk mainly to keep the Russian partners happy.

"The legerdemain that is now being performed is to consider the station to be in contingency mode because we only have a two-man crew, therefore we can rewrite all the previous safety rules that would be violated to allow the EVA to proceed," said an engineer and health expert involved in the decision-making.

"I hear an echo," he said, referring to the gradual acceptance of increased risk -- "risk creep" -- within the space flight program that preceded the shuttle accidents of Challenger in 1986 and Columbia in 2003.

With no crew member inside the space station, the risk scenarios of most concern include loss of control over the station's orientation in space and loss of power or control over onboard heating and cooling systems, according to a series of recent NASA safety reviews. Other possible but less likely emergencies include an inability to repressurize the airlock, an onboard fire or a loss of air pressure inside the station because of a leak or puncture.

To assure the safest possible spacewalk, the orbital outpost must be reconfigured in a variety of ways that affect its normal operations and, as a NASA document notes, may "introduce vulnerabilities." Gerstenmaier compared it to readying your house before you go on vacation.

The preparations include adjusting valves to maximize fire detection and sealing most hatches.

Some onboard systems, such as the jet thrusters, will be disabled during the spacewalk to prevent contamination of the crew's spacesuits. This will leave the station's motions under the control of gyroscopes in a U.S. module. One of the four gyros has failed, and of the remaining three, one has shown abnormalities.

The station has been configured in this way many times before, the officials said, while the crew moved a Soyuz vehicle from one port to another. In the case of the spacewalk, the station will be in this "caretaker mode" for 36 hours instead of 16.

If the spacewalk had to be terminated in an emergency, the crew would have to close out its work, float to the airlock and repressurize it normally. That process, according to the safety reviews, would take two hours and 15 minutes.