Washington: NASA ordered two astronauts for an impromptu spacewalk Saturday to find and, possibly, fix a serious leak at the International Space Station.
But Thomas Marshburn and Christopher Cassidy discovered "no smoking guns" as they worked to replace a suspect pump.
Marshburn has been on the space station since December and is set to return to Earth late Monday. Cassidy is a new arrival, on board for just 1 1/2 months.
On Thursday, the agency`s astronomers spotted flakes of frozen ammonia coolant drifting from the long frame that holds the solar panels on the left side.
Barely 48 hours later, the two astronomers hunted in vain for the leak as they inspected and removed an old pump. No new, major flaking occurred after that.
NASA had ordered up the fast, impromptu spacewalk hoping that ammonia flakes might lead the astronauts to the bedeviling hole or crack, which is too small to notice without a trail of icy evidence.
Despite the lack of visible damage, Mission Control ordered the spacewalkers to install a spare pump. The ammonia pump was the chief suspect going into Saturday`s spacewalk , and the fact that nothing amiss was found meant that the problem, in all likelihood, was going to continue to vex NASA in the weeks ahead.
Mission Control explained that there`s nothing to lose by putting in a fresh pump and pressing ahead with additional detective work, but noted that the mystery still remains.
NASA`s space station program manager Mike Suffredini said it`s a mystery as to why the leak erupted.
Possibilities include a micrometeorite strike or a leaky seal. Ammonia already had been seeping ever so slightly from the location, but it increased dramatically Thursday.