Expedition 10 Commander Leroy Chiao spent the beginning of the week installing a new heat exchanger in Quest, the U.S. airlock. Working meticulously with stubborn bolts and attachments, Chiao swapped out the faulty heat exchanger with a new unit delivered earlier this month.
The job sets the stage to restore use of Quest as a base for spacewalks using U.S. spacesuits. The heat exchanger unit provides cooling for the U.S. spacesuits while they are connected to the airlock. Chiao finished the repair ahead of schedule and had spare time to work on several other tasks around the Station, such as replacing a hard drive in a laptop computer.
Flight Engineer Salizhan Sharipov began preparing the Russian Pirs Docking Compartment, which also serves as a Russian airlock, for the second and final spacewalk the pair will conduct. Chiao assisted by gathering U.S. tools, such as helmet lights and a tool caddy, which they will use in conjunction with the Russian equipment. They also gathered antennas and cabling they will install during the spacewalk. Sharipov and Chiao are scheduled to step outside March 28 for nearly six hours to continue the external outfitting of the Space Station and deploy a Russian satellite experiment.
Sharipov did further troubleshooting on the Elektron oxygen-generating system, which ran intermittently throughout the week. Its periodic shutdowns have caused no concern for the replenishment of oxygen in the Station cabin. Russian experts will continue to monitor its condition. The Elektron, which converts water into oxygen, is one of several methods that can be used to provide oxygen in the Station cabin.
Two control moment gyroscopes (CMGs) are maintaining the Station's orientation after a third gyroscope lost power on Wednesday. A circuit breaker, called a Remote Power Controller, failed and removed power from that gyroscope. Attempts to reset the breaker were unsuccessful. There is no impact to current Station activities. Two gyros are adequate to maintain the orientation of the complex.
Specialists are continuing to evaluate the condition of the circuit breaker. The circuit breaker could be replaced by conducting a spacewalk to perform that work, but the plans and timing of that activity remain to be determined. A fourth gyroscope that failed in June 2002 is set to be replaced on the Space Shuttle's Return to Flight mission, STS-114, this spring.
Also this week, the Station crew slid into their seats inside the attached Soyuz spacecraft to check their fit. The Soyuz seats are outfitted with customized cushions to protect the riders during landing. The fit of the cushions is checked periodically throughout the mission to ensure a comfortable and safe seat home for the crew. Chiao and Sharipov have about five weeks remaining until their return to Earth, with their undocking and landing in Kazakhstan scheduled for April 25.