Spacewalkers Replace Pump, But Not Sure If Leak is Fixed

Two International Space Station (ISS) crew members successfully replaced a coolant pump in the ISS electrical system today, but there was no sign of the leak that led to this unprecedented ISS spacewalk.

Tom Marshburn and Chris Cassidy completed their tasks about an hour ahead of schedule today, finishing the spacewalk in 5.5 hours.  One objective of the spacewalk, successfully executed, was replacing an ammonia pump used to cool a solar array channel that provides electricity for the ISS.  There are eight channels, one for each solar array.   ISS crew members noticed “snowflakes” emanating from one of them on Thursday, signalling an ammonia leak.  That channel had shown signs of leaks in the past, origin unknown, but this time the amount was much greater.

NASA decided to conduct an emergency spacewalk not because the leak posed a threat to the space station or the astronauts, but because they hoped to spot the source of the leak while ammonia was still being released.  That part of the assignment was unrealized.   When Marshburn and Cassidy arrived at the site, there was no sign of an ammonia leak.  They replaced the pump because it was one obvious source of the problem, and when the new pump was activated, no leak was observed.  That might be a cause for celebration, but NASA officials stressed at a post-spacewalk news conference that it will be many weeks before they feel they are certain the new pump resolves the issue.

“We are happy.  We are very happy,” said ISS Deputy Program Manager Joel Montalbano about the overall success of the spacewalk. This is the first time in the “increment” ISS missions that a spacewalk has been planned and executed in such a short period of time.  The desire to view the leak as it was occurring, and the experience of Marshburn and Cassidy — who conducted two spacewalks together on a 2009 space shuttle mission, including working in this area of the ISS — drove the decision to move quickly.  Marshburn will be returning to Earth on Monday after almost 5 months on the space station, so today was a unique opportunity.