Spaceflight Insider

ISS encounters power failure, can’t be fixed until 2016

International Space Station in orbit above Earth as seen by the crew of STS-130. NASA photo posted on SpaceFlight Insider

Photo Credit: NASA

The Expedition 45 crew on board the International Space Station encountered a bit of a problem on Friday, Nov. 13, 2015, when one of the eight power channels that keep the station running went down. While this poses no threat to the crew on board the orbiting laboratory, it might put a crimp in the ISS’ activities.

According to a report appearing on The Verge, the situation arose after a short circuit occurred in some of the station’s equipment. According to NASA’s Bob Jacobs, those systems were then switched over to a backup system.

In fact, the six crew members currently on the ISS have continued on with their normal assignments.

“On Friday afternoon (11:55 a.m. Houston Time), power channel 1B experienced an electrical event that telemetry points to a fault in the power channel’s Sequential Shunt Unit [SSU]. An SSU is responsible for regulating the power voltage levels generated by the solar arrays before it is passed to systems downstream,” NASA’s Dan Hout told SpaceFlight Insider. “A seamless power transfer was performed to recover loads from channel 1B to channel 1A. Currently operating on seven of eight power channels, no impact to station systems or operations. [The] crew was never in any danger.”

Throughout its 17-year history, the ISS has experienced a number of technical failures which has required necessary repairs, some of which have been worse than others:
  • In January 2004, a minor air leak was detected. Though it was not an immediate danger to the astronauts aboard, it took eight days before the leak was traced to its source. At that point, NASA had been planning to lock down the entire station and shut the hatches between major modules in an effort to isolate and find the leak.
  • On June 14, 2007, a computer failure deprived the ISS of the Russian attitude control thrusters and several environmental control systems. U.S.-built systems helped to compensate for some of the systems, but it took a couple of days before all of the Russian computers were back up.
  • In September of 2008, a damaged cooling panel was identified on the S1-3 radiator, but the problem didn’t seem serious until the STS-119 fly-around in March 2009 when the risk of an ammonia leak became evident. The potential leak issue was mitigated in May 2009.
  • In May 2013, an ammonia coolant leak was identified and astronauts undertook a spacewalk to replace the faulty pump controller box.

NASA noted that the ground team should be able to manage the power balance for the foreseeable future. Ground-based workarounds are still being looked into by flight controllers and engineers.

If it is determined that a repair and replacement is necessary, it would likely be similar to what was carried out during an extra-vehicular activity (EVA) that was conducted in October of 2014 (according to a CBS News report) to replace a malfunctioning SSU in a separate power channel (which had failed months earlier in May, 2014.)

The ISS is capable of executing all of the planned operations on seven power channels, including the upcoming berthing of the flight of the OA-4 Cygnus on Dec. 3. A spare exists on orbit, but the space agency as learned the value of redundancy. It will likely fly an additional spare as early as the SpX-8 mission, currently scheduled for early January.



Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

Reader Comments

Thomas Schluender

What are the manuevers and the crew’s actions required when a large manned space craft is approaching to dock with the space station? Is N.A.S.A. anticipating traffic management problems and rules?

Hello Thomas,
As the article states, this has happened before. There likely won’t be any issues as the power was switched over to backup systems.
Sincerely, Jason Rhian – Editor, SpaceFlight Insider

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