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The failure of a second of four cooling pumps on the Alpha Magnetic Spectrometer on ISS threatens the science instrument’s ability to continue its observations.
The AMS continues to gather science data using the three remaining pumps. They are part of a liquid carbon dioxide cooling system that is meant to dissipate heat as the AMS, which is on the outside of the space station, cycles in and out of sunlight during each 90-minute orbit of Earth Only one pump is needed at any given time. One failed in February 2014 and at least one of the other three is showing possible signs of trouble.
Since the 8.5-tonne AMS began operating in 2011, it has tracked more than 69 billion cosmic rays flying through its detectors. Its goal is to search for antimatter and dark matter. In 2013, AMS scientists reported measuring numbers and energies of positrons that hinted at, but did not confirm, the existence of dark matter.
The news article suggests that the instrument is now working with only one reliable pump. It also is possible that repairs might be done by astronauts on ISS during a spacewalk.
Some background: AMS cost $2 billion and about 20 years to build. It only got launched because Congress ordered NASA to launch one more shuttle mission to ISS to get it there.