The United States and Russia will proceed this week with a complicated and unprecedented spacewalk outside the international space station despite a last-minute dispute over the use of Russian equipment that threatened to delay things for a day, NASA engineers said yesterday.
The spacewalk by space station commander Gennady Padalka of Russia and science officer Mike Fincke of the United States, to replace a faulty circuit breaker, will be the first time that astronauts will use Russian spacesuits to work on the U.S. side of the station.
As a result, control of the six-hour walk will be overseen partly by controllers in Russia and partly by NASA in Houston, using two languages. The astronauts must make a long traverse from the Russian side of the station to the repair site on the U.S. side and may lose radio communications at some points. That could force them to use hand signals or to rendezvous at a predetermined "outpost" so they can resume speaking with ground controllers and each other.
The spacewalk is also only the second time that a U.S. astronaut will work outside without a third person to assist from within the spacecraft. A similar spacewalk in February ended prematurely when the cooling system malfunctioned in one of the Russian spacesuits.
The spacewalk has been planned for two months, since a circuit-breaker malfunction caused one of the station's four main gyroscopes to shut down. An earlier problem with another gyroscope left the station operating with only two, the minimum needed to keep the orbiting laboratory properly oriented.
Should another gyro fail, controllers could still position the station by using thrusters, but John Curry, lead flight director for the spacewalk, said in a news conference that "we don't want the thrusters to fire" during two other spacewalks planned for later in the year. Thruster fuel leaves a toxic residue, and the residue can become a hazard to the crew if it contaminates a spacesuit and is then carried into the space station.
The spacewalk is scheduled to begin Thursday at 5:50 p.m. Eastern time and to take six hours.
On Monday, it appeared that the walk would be delayed because of what Michael T. Suffredini, NASA international space station manager for integration and operations, called a "negotiation" with Russian officials over the in-kind compensation Russia will receive for the use of its equipment.
The 1998 memorandum of understanding signed between the United States and Russia established a barter arrangement for services provided for the space station by each nation. "We negotiate what we barter for the services," Suffredini said. "We try to balance out our contributions."
On Monday, Russian officials insisted that the in-kind compensation be agreed upon before the spacewalk goes forward, prompting NASA to announce that the spacewalk would be delayed for a day. However, Suffredini said at yesterday's news conference that the Russians had reconsidered and have agreed to proceed and "wrap up negotiations whenever we wrap up negotiations."
Complications in the planned spacewalk arose last month, when cooling systems in U.S. spacesuits also malfunctioned, rendering them unusable, and forcing Padalka and Fincke to revert to the Russian suits and the Russian airlock. That will require them to make a 45-minute transit across the Russian side of the station to reach the repair site.
The crippled circuit breaker is in a box about the size of a telephone book. It will be swapped out with another breaker box. If the gate protecting the breakers cannot be opened, the two astronauts will switch a cable to connect the affected gyroscope to a different circuit breaker.