NASA engineers continued efforts Sunday to regulate temperatures in one of two cooling loops on the International Space Station affected by the malfunction last week of a flow control valve in a cooling pump on the station's starboard truss. A Flow Control Valve in the starboard Pump Module that enables the flow of ammonia to cool station systems stopped positioning itself properly last Wednesday, resulting in a drop of temperature in Cooling Loop A. That necessitated the shutdown of some support systems on the station.
The temperature must be warm enough in the cooling lines to allow the system's heat exchangers to dissipate excess heat from the station through the external radiators on the complex. The primary heat rejection capability for station systems shifted last week to Cooling Loop B that uses a fully operational Pump Module on the port truss.
Efforts overnight to fine-tune the position of an isolation valve associated with the flow control system in the Pump Module into a "sweet spot" to assist the faulty Flow Control Valve in regulating the affected cooling loop's temperatures were still being evaluated as engineers continue to review the data, valve positioning techniques and additional methods of temperature management in the loop.
Meanwhile, parallel work is ongoing to either enable Orbital Sciences Corp. to launch its Antares rocket and the Cygnus cargo craft from the Wallops Flight Facility, Va. Thursday night at 9:19 p.m. EST on its first resupply mission to the space station, or for Expedition 38 astronauts Rick Mastracchio and Michael Hopkins to mount a suite of spacewalks beginning Thursday to replace the faulty pump.
The International Space Station Program continues to keep both options on the table pending further engineering analysis and troubleshooting efforts on the station's cooling system.
While the engineering work on the station's cooling loop continued, technicians at Wallops prepared to load time-critical science cargo in the Cygnus spacecraft Sunday afternoon to preserve several days of launch opportunities beginning Thursday night. The current schedule calls for the vehicle fairing to be installed on the Antares upper stage around Cygnus on Monday. The Antares rocket and attached Cygnus are scheduled to rollout to the launch pad at Wallops in the wee hours Tuesday.
Meanwhile, aboard the space station, Mastracchio and Hopkins continued to prepare their spacesuits and other equipment in the Quest airlock Sunday should they be called upon to conduct spacewalks to replace the Pump Module.