Astronauts are gearing up for some of the most challenging and urgent repairs ever attempted at the International Space Station.
At sunrise Saturday, two NASA astronauts will go out on a spacewalk to replace a broken ammonia pump. The pump shut down last weekend and knocked out half of the space station's cooling system. The pump is supposed to drive ammonia through the lines and prevent equipment from overheating.
Engineers worked nonstop over the past week to come up with the emergency repair plan.
Douglas Wheelock and Tracy Caldwell Dyson will be dealing with fully pressurized ammonia lines. That will make their work even more difficult.
It will take two spacewalks to complete the job.
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