ISS Coolant Loop Problem May Delay Orbital's Cargo Resupply Launch

A problem with a flow control valve on one of the two International Space Station (ISS) coolant loops may delay the planned launch next week of Orbital Sciences Corporation’s Cygnus cargo resupply spacecraft.  The launch is currently scheduled for December 18.

Kenny Todd, ISS Mission Operations Integration Manager, said in an interview on NASA’s Space Station Live program this morning that the agency is still diagnosing the problem and determining what must be done to fix it.   Until more is known, he is delaying a “go/no-go” decision on Orbital’s launch because whenever another vehicle arrives at the ISS, certain levels of systems redundancy are required and NASA cannot meet those criteria under current circumstances.  NASA will revisit the situation on Monday and determine if a launch delay is necessary.

The launch window for this mission, designated Orbital-1 or simply Orb-1, is the company’s first flight of the Antares rocket and Cygnus spacecraft under NASA’s Commercial Resupply Services (CRS) contract.  Orbital has named this specific Cygnus spacecraft in honor of C. Gordon “Gordo” Fullerton, the former astronaut who passed away in August.  At one point in his career, Fullerton flew NASA NB-52B aircraft that were used to deploy Orbital’s air-launched Pegasus rocket.

Todd said the launch window for the Cygnus launch runs through December 21 or 22, and, if necessary, the launch could be delayed until the next launch window.   None of the 3,217 pounds of cargo on this mission is critical to ISS operations, Todd said.

The coolant loop malfunctioned yesterday.  ISS has two external thermal control loops that use ammonia as a coolant.  The ammonia must be kept at the proper temperature to ensure that when it flows through a heat exchanger, water that is also in the heat exchanger does not freeze.  If the ammonia becomes too cold, the system automatically shuts off.  That’s what happened yesterday. 

Ground-based engineers began to troubleshoot the issue and traced it back to a flow control valve in one of the loops, but they are still trying to determine exactly what went wrong and what is needed to fix it.   Meanwhile, the 6-person crew is safe and ISS is in a stable configuration, Todd said.  Still, NASA would like to get the loop working “sooner rather than later.”   All critical ISS systems can operate on just one loop, but both are needed for all systems to work and for redundancy.  NASA has moved all the critical systems over to the functioning loop, but some systems in Node 2 (Harmony), Japan’s Kibo module, and Europe’s Columbus module had to be turned off.

The ISS experienced a coolant loop problem in 2010 and Todd acknowledged that at first glance people might assume this is similar.  In 2010, however, a pump failed.  In this case, it is a flow control valve that “is in the same housing, but is a different piece of hardware” that regulates the temperature of the ammonia rather than moving the ammonia through the system like the pump.  NASA does not know whether a spacewalk is needed to repair the problem this time as it was in 2010, but, if so, Todd says the “choreography” will be similar and replacement pump modules are aboard.  He stressed that NASA needs to ensure that its spacesuits are in good order.   The last time the U.S. spacesuits were used, European Space Agency astronaut Luca Parmitano’s spacesuit filled with water because of a failure in its cooling system.

The video of this morning’s interview with Todd is posted on NASA’s YouTube channel.