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Spur-of-the-moment spacewalk a first for NASA, space station

An impromptu spacewalk triggered by the sight of ammonia flakes drifting past a window of the International Space Station wraps up with a replaced pump and a plan for "additional detective work."

From top: [1] Small white ammonia flakes seen drifting beyond a window of the ISS on Thursday. [2] Marshburn and Cassidy bust out the toolkit. [3] A shot from one astronaut's helmet cam shows the other astronaut's gold helmet visor, along with an American flag shoulder patch (on the far right), a handheld camera and the other astronaut's gloved thumb (middle bottom), and the glowing Earth peeping through the rigging of the ISS (the white blotch middle left). In the direct center of the frame, you can see the other astronaut's right arm reaching back, as he hangs on to a railing attached to the space station. [4] Commander Chris Hadfield works a laptop inside the ISS, just prior to the spacewalk's end, as crewmember Pablo Andujar waits near the hatch.
NASA; screenshots by Edward Moyer/CNET

Saturday saw a first for NASA and the International Space Station, as two astronauts conducted an impromptu spacewalk to try to locate the source of a problem on the craft's exterior.

The space agency hadn't yet ordered such a spur-of-the-moment maneuver in regard to the ISS, according to the Associated Press, but when crewmembers on the craft spotted ammonia flakes floating through space beyond a window Thursday, the spacewalk was hastily planned.

After Mission Control and the ISS crewmembers prepped intensely -- for less than 48 hours -- astronauts Thomas Marshburn and Christopher Cassidy exited a hatch and made their way to the suspected source of the leaking ammonia. Though they replaced a pump for the liquid, which is used to cool the ISS' electronic equipment, it remained unclear whether the issue had been entirely resolved.

NASA called the leak significant but said it wasn't a safety threat. Mission Control explained that there had been "nothing to lose" by replacing the pump, the AP reported, and that "additional detective work" would take place.

NASA streamed live video of the five-and-a-half-hour spacewalk, which wrapped up near noon Pacific Time. Various cameras mounted on the craft provided fascinating views of the two space mechanics, tottering many miles above the Earth's luminous surface, and footage from the astronauts' helmet cams made recent Google Glass POV shots seem puny and unimpressive.

The helmet cams also allowed Mission Control to "go along for the ride" and conduct visual checks of the ISS' exterior.

Occasionally the NASA team back on Earth would ask that a picture be snapped of a particular area -- a spot of discoloration on a metal bar, for example. Such images from a handheld camera can be analyzed with care later.

The spacewalk provided an unexpected send off for Marshburn, who's scheduled to head back to Earth on Monday. Cassidy arrived on the ISS recently, for a month-and-a-half stay.

It was the fourth spacewalk for both astronauts, and their third together.