So far, so good. Two astronauts replaced an ammonia pump outside the International Space Station today, and early signs suggest that the move may have fixed a potentially dangerous leak, reports AP. Christopher Cassidy and Thomas Marshburn didn't spot any obvious signs of trouble, but no new leaks have been spotted since they replaced the pump. Small "snowflakes" of frozen ammonia were seen floating near the device earlier this week, and the astronauts' two-day turnaround for a spacewalk might be the fastest ever, reports NBC News. NASA will keep checking for leaks before declaring the problem fixed.