Update 1:30 p.m. EDT: NASA announced plans for a spacewalk to replace the failed MDM. According to NASA, "Such a spacewalk is one of the so-called “Big 12” spacewalks that station crews train to execute for the loss of a critical component on the complex." No date has been set for mission.
A backup computer aboard the International Space Station is unresponsive and NASA is mulling a possible spacewalk to replace it. The computer controls some robotics aboard the ISS and the six Expedition 39 crew members are not affected by the outage, although it may delay Monday’s SpaceX cargo resupply mission.
NASA announced the Multiplexer-Demultiplexer (MDM) computer, located on the exterior of the space station, was not responding to commands from mission control on Friday. A multiplexer can send multiple signals out, such as turning switches on and off, and instead of having several channels for each of the signals, all of the signals are sent as one signal to the demultiplexer, which then separates the signal into the multiple inputs.
The faulty MDM serves as a backup for the system used to attach a spacecraft to the ISS. SpaceX is planning to launch the Dragon spacecraft on Monday as part of the cargo resupply mission, and the spacecraft would arrive at the ISS on Wednesday. The main MDM is operating normally but if NASA wants to be cautious and have an operational backup computer for the resupply mission, the agency could delay the SpaceX mission until a later date.
A spacewalk would be needed if NASA wants to replace the unresponsive MDM. The space agency is currently evaluating its options and will announce a decision about the SpaceX launch and a spacewalk in the near future.
The MDM outage does not affect the six Expedition 39 crew members aboard the ISS or the scientific instruments or experiments aboard the space station. In 2013, NASA approved two spacewalks to repair a faulty ammonia pump module which is associated with two cooling loops that circulate ammonia around the ISS to cool internal and external instruments.
On Saturday, NASA announced its plans to go ahead with the cargo resupply mission launch. The SpaceX cargo resupply mission has already been delayed twice, and is currently scheduled for launch at 4:58 p.m. EDT on Monday. NASA said in its statement, "International Space Station Program officials and representatives of SpaceX decided Saturday to continue preparations for the launch of the Falcon 9 rocket and the Dragon cargo craft to the space station Monday from Launch Complex 40 at the Cape Canaveral Air Force Station, Fla., despite the failure Friday of a backup computer component that provides redundancy for commanding the Mobile Transporter rail car on the truss of the station." A meeting will be held on Sunday will decide if the SpaceX launch will happen on Monday.