Station commander Mike Fincke and space shuttle Endeavour astronaut Donald Pettit removed grommets from the urine processor's assembly, a procedure space agency engineers anticipate will keep the unit's centrifuge from coming in contact with a speed sensor and shutting down the processor when it heats up.

The unit had been shutting down after running for about two hours, the National Aeronautics and Space Administration said on its Web site.

The shuttle and space station crew members spent time Sunday transferring more cargo between the two spacecraft. They also prepared for the mission's fourth spacewalk scheduled for Monday.

Some crew members were to be interviewed by U.S. news networks ABC, CBS and NBC, as well as get some off-duty time, NASA said.

Two astronauts spent seven hours outside the spacecraft Saturday, lubricating a joint that moves the space station's solar array. They also replaced some trundle bearing assemblies.