4 p.m. CDT Wednesday, April 14, 2010
Mission Control Center, Houston, Texas
STS-131 MCC Status Report #20
HOUSTON – As the crew on orbit took an afternoon break, teams on the ground continued troubleshooting problems with a jammed cooling system valve, assessing options and developing plans for a possible fourth spacewalk.

The closed valve is in a nitrogen tank assembly needed to pressurize a new ammonia tank installed on the International Space Station by Discovery’s astronauts. The ammonia tank was installed during three spacewalks by Mission Specialists Rick Mastracchio and Clayton Anderson.

With the help of a team of engineers, Mission Control has sent multiple commands to attempt to open the valve normally. The efforts included sending commands while the valve was at its coldest and hottest. So far, the attempts have not succeeded. Additional troubleshooting is planned while the crew sleeps this evening. The closed valve could degrade the performance of the station's cooling system under certain conditions.

A “tiger team” also is working to develop plans for a spacewalk that could be performed during Discovery's mission to replace the entire nitrogen tank assembly. A spare tank assembly is stored on the station’s truss structure. If the spacewalk is conducted during Discovery's flight, another day would need to be added to the mission. It also is possible the spacewalk, if it is needed at all, could be done after the shuttle has departed the station.

The combined shuttle and station crew has been told about the planning, but a decision on whether to perform a spacewalk is not expected until Thursday at the earliest. Thursday’s plan to close hatches between the Multi-Purpose Logistics Module Leonardo and the station’s Harmony module are unchanged.

Discovery's crew began their sleep period at 3:21 p.m. The next status report will be issued after crew wakeup, which is scheduled for 11:21 p.m., or earlier if warranted.

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