CAPE CANAVERAL, Fla. -- Two days after International Space Station (ISS) engineers coaxed equipment that generates oxygen into working again, a problem was detected Sunday as the cooling system automatically prompted computers to turn off power throughout the outpost.
However, the trouble was quickly solved by flight controllers in Moscow and Houston and the station returned to normal operations within three hours, Bill Gerstenmaier, deputy ISS program manager for NASA, said Monday.
"We're back in a stable configuration, with everything back powered on," Gerstenmaier said. "This is kind of evidence of what happen everyday on a space station. You're always surprised sometimes by the hardware."
The cooling system problem was blamed on bad data being sent from a pump in the Russian Zvezda service module to a Russian computer that controls the flow of heat-dispelling water within the complex.
As a result, the Russian computer began turning off all electrical systems in the service module to reduce the amount of heat building up.
Then the computers in the U.S. Destiny science laboratory saw what the Russian computer was doing and why and began turning off equipment as well, Gerstenmaier said.
Flight controllers intervened almost immediately and were able to keep the station from losing its ability to maintain the direction it points, which is critical to keeping the electricity-generating solar arrays facing the sun at all times.
Meanwhile, the on-again, off-again trouble with the Russian Elektron oxygen generating system for the station seems to be working fine again thanks to a change in the way the system is managed.
The Elektron system makes oxygen by splitting water molecules into hydrogen and oxygen. The hydrogen is dumped overboard and the oxygen is pumped throughout the station.
As part of that system, a so-called buffer tank holds a small supply of water before the liquid is sent into the part of the machine that breaks it down into the two gases.
Gerstemaier said a sensor in that buffer tank failed, fooling the computer that controls the process into thinking the tank was empty. The Elektron equipment shut down, as it is supposed to do until the tank is refilled with water.
For now the computer has been instructed to ignore the failed sensor and Russian controllers are using a timer so they know when to refill the buffer tank with water. Eventually a new set of hardware will be sent to permanently take care of the problem.
Should the Elektron system completely fail, the three expedition crew members could survive until at least September with the other sources of oxygen they have on board, Gerstenmaier said.
None of the problems put the Expedition Four crew of Yuri Onufrienko, Dan Bursh and Carl Walz in any danger, officials said.
That crew is to return to Earth June 11 aboard shuttle Endeavour, which remains scheduled for launch from the Kennedy Space Center on May 30. The launch period extends from 4 to 8 p.m. EDT (2000 to 2400 GMT).
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