Foale and Kaleri spent two days replacing a liquids unit and a water flow system in the Russian Elektron oxygen-generation device in the Zvezda Service Module after weeks of troubleshooting efforts failed to coax it back into service. The Elektron produces oxygen for the Station atmosphere through electrolysis - the separation of hydrogen and oxygen from water that flows through a series of pumps and valves. The hydrogen is vented overboard.
Russian specialists spent several weeks trying to track down the most probable cause for repeated shutdowns of the system after just a few minutes of operation each time. They concluded that particles of potassium hydroxide electrolytes - a by-product of the electrolysis process - that created air bubbles in the liquids unit, resulting in the unit's repeated shutdowns, were the most probable cause of the problem.
Since last Saturday, the crew has derived oxygen from solid-fuel oxygen generation (SFOG) canisters activated in Zvezda. The crew has been using an average of two SFOGs each day since available air and oxygen were depleted from tanks in the Russian Progress supply vehicle following the first shutdown of the Elektron.
Russian engineers now plan to activate the refurbished Elektron Saturday for a few days of checkouts and diagnosis. If the Elektron repair proves successful, the SFOG canisters will no longer be needed. There is an ample supply of those canisters, as well as oxygen contained in the Quest airlock tanks, that could provide oxygen for the Station for several months.
To accommodate the Elektron repair, a few lower-priority tasks were moved to other days, including routine proficiency training for Foale on the Canadarm2 robotic arm.
On Friday, Foale did a leak check of the window in the Destiny laboratory. In January, a flex hose that helps to vent air from the inner panes of the window was found to be causing a minor pressure decay from the Station. The flex hose was replaced a few weeks ago, and the leak check revealed an airtight system.
Foale and Kaleri took advantage of the recently repaired high-tech treadmill to get in several rounds of intense exercise. A lengthy overhaul last week brought the system back into full operation.
Foale spent some time this week conducting experiments with a cellular biotechnology device to test methods for improved cell culture growth and with a device designed to measure the forces imparted on the joints of the lower extremities and the feet in the absence of gravity.
Foale and Kaleri also took time out from their schedule to answer questions from a syndicated talk show host from the Premiere Radio Networks and from students at the Howard Bishop Middle School in Gainesville, Fla.