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Astronauts stuck with repairs of urine recycler at International Space Station news
24 November 2008

Astronauts on the International Space Station yesterday undertook one of the longest and hardest spacewalks of their mission when they made a second attempt in a seven hour repair work at the centrifuge in the distillation assembly of a hardware designed to convert urine into potable water.

The system, which converts urine and sweat into potable water, is of prime importance to the ISS as it plans to increase its six member crew.

The recycler was working for two hours at a time before shutting down and flight controllers on Earth had advised the station commander Michael Fincke and Endeavour astronaut Donald Pettit to undertake the space walk and remove mounts on which a centrifuge is attached to the recycling system. 

Last week, an attempt was made to repair the centrifuge, but, according to reports, the attempt failed, thereby filling the tanks aboard the ISS with urine at a fast pace.

The urine converter system, which has cost NASA $154 million, shut down again yesterday after the second attempt to repair it failed and now flight controllers on earth are contemplating to bring the processed urine samples back to earth when the shuttle Endeavour returns.

The premature shutdowns of the space station's new urine processor assembly appeared to have been fixed when the astronauts went outside the space station to fix them yesterday, but as time elapsed it was clear that the processor shut itself down and the same problem seems to continue.

Flight director Ginger Kerrick had told reporters on Saturday that the ground team have been meeting throughout the day and the ISS crew had isolated the source of the problem to the way the centrifuge is mounted in the distillation assembly.

"Their proposal is to remove those isolators and hard mount the distillation assembly. So folks are working on that procedure right now, it'll be scheduled on Mike Fincke tomorrow and we think it's going to be about two hours long. And after that, we will send some commands to it, they're working on that procedure as well, and we'll see if that solves the problem," he added.

Engineers on ground believe that thermal interference between a speed sensor and the centrifuge is the main problem as it causes the motor to slow down and draw more current than required.

The centrifuge which rotates when works is mounted on dampers to reduce vibrations and sound and engineers think that the dampers are "possibly allowing it to set itself up at a frequency that ultimately causes it to shift around, allowing one of the centrifuge speed sensors to come in contact with the spinning centrifuge," Kerrick said.

This causes the motor to work harder and draw more current than required thereby forcing it to shut down by itself.

At the press briefing, he said "There is a thermally induced physical interference that seems to be occurring at the same time in the processing and it's also aggravated by the fact that this system is on the isolators. They think that hard mounting this device will resolve the issue."

The astronauts were able to collect the processed sample of the water and will send it back with Endeavour, which will enable engineers at earth to evaluate the systems performance.

NASA managers could delay undocking the Endeavour by at least one day if engineers on Earth are able to say that the extra time would help in finding a solution to the problem.

Bringing back the sample of processed water is a worst case scenario for NASA as tests will take time and it may hamper the plans to boost the crew size when the astronauts return to the space station in May.

Ginger Kerrick said while engineers on Earth are finding a fix for the problem, NASA is also studying whether a six member crew can live at the space station with the urine processor working for two hours at a time.

But NASA wants to solve the problem before Endeavour returns to the space station in February as it will give them ample time to solve the problem before May.

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Astronauts stuck with repairs of urine recycler at International Space Station