This morning, NASA began a 6.5 hour spacewalk in order to make critical repairs to the International Space Station. Astronauts Rick Mastracchio (a veteran of seven previous spacewalks) and Mike Hopkins (a spacewalk rookie) will be carrying out the procedures in order to replace a faulty piece of cooling equipment. It's the first of three scheduled spacewalks (the next on Monday, the third on Christmas Day) necessary to make the fix.

According to Time, the breakdown began 10 days ago as one of two identical cooling loops became too cold. NASA tried to fix the issue remotely but did not succeed. The problem eventually forced NASA to shut off all non-essential equipment inside the lab and stop nearly all research happening at the ISS.

The equipment in question is an ammonia pump containing a bad valve. NASA has replaced such a piece before (in 2010), and the three astronauts who performed that task are in Mission Control for today's activities. For a frame of reference on the item, Time wrote the 780-pound pump is roughly equal in size to a double-door refrigerator (though containing ammonia rather than groceries).

Given the recent Hollywood spotlight on spacewalks, NASA made a concerted effort to emphasize this was by no means a Gravity situation, telling NPR "no, no, no."