Update: The spacewalk ended early today, at 17:31 GMT, after NASA astronaut Tim Kopra reported some water in his helmet—likely from a cooling loop in his suit—and a failed CO2 sensor. But the spacewalkers had already completed their main objective: replacing a broken regulator for one of the station's eight power channels.
the Today, the two Tims aboard the International Space Station—Tim Peake, from the European Space Agency, and NASA's Tim Kopra—will strap on their space suits, open an airlock, and head out into the great abyss.
Space walks are always worry-making, but this particular excursion comes with some extra red flags. First off, Peake and Kopra will travel pretty far away from home: about 200 feet from the airlock, all the way down the ISS's starboard truss toward the outer solar panels. That's where the main work needs to happen.
For two months now, the International Space Station has been operating on backup power. Today, the astronauts will replace the cause, a broken regulator that controls the flow of power from some of the station's solar arrays.
That means the spacewalk has to happen in utter darkness. If sunlight hits the solar panels and generates energy during the swap, the astronauts risk a high-voltage spark. According to the European Space Agency, that gives the spacewalkers about 30 minutes to do their repair work while the ISS flies through the shadow of the Earth. They'll be out there for a total of six and half hours to complete other repairs—but hey, if they get done faster, something tells me they won't mind heading back in early.
