Having eventually fixed the toilet in the US segment, last weekend [31 July] the crew of the International Space Station were forced to reduce power, and suspend scientific experiments, when half their cooling system suddenly shut down.
Trouble arose on Saturday night when one of the two ammonia-fed cooling loops shut down, triggering alarms throughout the ISS.
The two ammonia lines ensure that all the station’s electronic equipment does not overheat.
Astronaut Tracy Caldwell Dyson set in motion equipment shutdown procedures and, with crewmate Douglas Wheelock, installed a jumper cable to keep all the rooms cool.
The Global Positioning System circuit, several power converters and a set of devices that route commands to various pieces of equipment were switched off.
Two of the four gyroscopes – part of the space station’s pointing and navigating system – were initially shut down but the crew installed a jumper cable to bring up a third gyroscope, leaving the station in a much more stable position, AP says.
Flight controllers tried to restart the disabled ammonia pump early on Sunday but the circuit breaker tripped again.
Here’s a Nasa statement on the loss of the cooling loop.
Space station astronauts didn’t make much progress during Saturday’s urgent spacewalk. The crew had to hammer loose a stuck connector. Then, an ammonia leak erupted. In the end, Douglas Wheelock and Tracy Caldwell Dyson were unable to remove the ammonia coolant pump that failed last weekend.
NASA originally estimated two spacewalks would be needed to replace the failed pump. After Saturday’s trouble, managers say three will now be necessary. The next spacewalk won’t be attempted until Wednesday at the earliest. Engineers need to figure out the next step.
And here’s a NASAtelevision clip of that first attempt to fix the problem during an 8 hour 3 minute space walk – the longest expedition crew spacewalk in history and the sixth longest in human spaceflight history. With a stunning backdrop, astronaut Doug Wheelock applies a tried and tested engineering technique to an uncooperative ammonia line. [Adds: To cheers from Mission Control]
As the latest BBC report notes
Next time the two astronauts will have to remove the failed unit and move a 355kg (780lbs) spare unit about 10m (30ft) in order to insert it into the gap.
The ammonia fluid lines will then have to be connected.
If the second of the two cooling units were to fail – said to be a highly unlikely scenario – then the astronauts would no longer be able to cool most of the components.
The crew would not be in immediate danger, however, as they could move to the Russian segment of the ISS, which has its own cooling system.
“Far above the world…”