Expedition 10 Commander Leroy Chiao spent the beginning of last 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 provides cooling for the suits, while they are connected to the airlock.

Chiao finished the repair ahead of schedule and had spare time to work on several other tasks, 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 crew's second and final spacewalk. 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 almost six hours to continue the external outfitting of the Station and deploy a German satellite experiment.

Sharipov did further troubleshooting on the Elektron oxygen-generating system, which ran intermittently throughout the week. The crew's oxygen supply has not been affected by this week's shutdowns.

Russian experts will continue to monitor its condition. The Elektron, which converts water into oxygen, is one of several methods used to provide oxygen.

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 Station activities. Two gyros are adequate to maintain the orientation of the complex.

Specialists are continuing to evaluate the condition of the circuit breaker. It could be replaced by conducting an unscheduled spacewalk, 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.

Early yesterday, the Service Module toilet shut down due to a faulty vacuum valve. It was quickly replaced by Sharipov, and the toilet was working again by yesterday afternoon.

Also this week the crew slid into their seats inside the Soyuz spacecraft docked to the Station to check their fit. The Soyuz seats are outfitted with customized cushions to protect the crew during landing.

The fit of the cushions is checked periodically throughout the mission to ensure a comfortable and safe seat home. Chiao and Sharipov have about five weeks remaining until their return to Earth, with their undocking and landing in Kazakhstan scheduled for April 26, Eastern time.

Chiao and Sharipov recently served as test subjects in a successful run of the Advanced Diagnostic Ultrasound in Microgravity (ADUM) experiment. The pair has performed ultrasound bone scans on each other by taking turns as operator and subject.

The bone scans were taken of the shoulder, elbow, knee and ankle, monitored remotely from the ground and videotaped and photographed for downlink.

ADUM investigates the diagnostic capability of ultrasound in medical contingencies relevant to the space environment and demonstrates the ability of minimally trained crew members to perform and interpret advanced ultrasound examinations.

It is the only medical imaging device available on the Station. Ultrasound may have direct application for the evaluation and diagnosis of 250 medical conditions of interest for treating exploration crews.

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