The week started out with Expedition 5 Commander Valery Korzun, NASA ISS Science Officer Peggy Whitson and Flight Engineer Sergei Treschev making sure station systems are ready to support installation of the next piece of the orbiting outpost's truss structure. They performed a final checkout of the Mobile Transporter, Canadarm2, the Quest airlock, and the spacewalk tools and equipment that already are on board. After those activities were complete, they began pre-packing items that will come home with them aboard Endeavour, which is set to launch with a replacement crew between 11 p.m. Sunday and 3 a.m. Monday CST.
Once the Port One (P1)1 truss is installed, the Expedition 5 crew will hand over control of the station to Expedition 6 Commander Ken Bowersox and Flight Engineers Nikolai Budarin and Don Pettit and return home with Endeavour's crew - Commander Jim Wetherbee, Pilot Paul Lockhart and Mission Specialists Mike Lopez-Alegria and John Herrington.
The visiting taxi crew - Commander Sergei Zalyotin, European Space Agency Flight Engineer Frank DeWinne from Belgium and Russian Flight Engineer Yuri Lonchakov - will undock from the station at 2:41 p.m. CST on Saturday. Zalyotin will fire the Soyuz deorbit engines at 5:10 p.m., bringing his crew in for a landing on the Kazakh steppes at 6:04 p.m.
The taxi crew, which rode into orbit aboard an upgraded Soyuz TMA capsule with more legroom and more modern cockpit controls, displays and computers, will ride home in the older Soyuz TM-34 return vehicle that has been at the station since April. A fresh Soyuz is delivered to the ISS every six months to provide an assured return capability for station residents in the unlikely event they would need to come home early.
During their eight-day stay on the station, the taxi crew conducted a host of medical, protein crystal growth and materials processing experiments. With DeWinne leading the investigations, the crew looked at human physiology in microgravity and how crystals grow and alloys form inside the Microgravity Science Glovebox in the Destiny Laboratory module.
Flight controllers in Houston are troubleshooting with the Carbon Dioxide Removal Assembly in the Destiny lab. CDRA is a system of absorption beds, tubing and valves that remove excess carbon dioxide from the atmosphere after it is expelled during breathing and vents it overboard. Two of six valves appear to be malfunctioning, causing the system to shut down several hours after it is started. The system supplements the station's Russian Vozdukh carbon dioxide removal system when more than three crewmembers are on board.
Troubleshooters have confirmed that a recent lab systems software update is not the cause of the problems, and they are refining their activation procedures to try to support the upcoming shuttle and Expedition 6 crews with CDRA using additional ground commanding. Lithium hydroxide canisters, which absorb carbon dioxide through a chemical process, may also be used to supplement the primary system; one canister was used during some of the CDRA troubleshooting activities.
The Elektron unit that generates oxygen by separating the oxygen and hydrogen atoms from water molecules also is not working properly. Korzun and Treschev conducted troubleshooting activities this week and are scheduled to replace the unit's liquid electrolysis module on Sunday. Additional oxygen is available in the Progress vehicle docked to the aft end of Zvezda. Oxygen and nitrogen also are available in tanks attached to the Quest airlock. Oxygen also is available from Russian oxygen generating "candles."
Saturday's departure of the taxi crew will set the stage for the launch of the shuttle Endeavour. The crew arrived at the Kennedy Space Center last night, and the launch countdown began today. Endeavour will take the 1 truss structure and additional resupply items, as well as two replacement valves for the station's CDRA system to the ISS. The three-pound aluminum replacement valves are about 5 by 9 by 6 inches, and look like valves in a home air conditioning system.