Astronauts Luca Parmitano and Andrew Morgan are conducting their third spacewalk on Monday in a series intended to fix the ageing Alpha Magnetic Spectrometer (AMS).
Parmitano, from the European Space Agency (ESA) and Morgan, from NASA, will bring the new AMS cooling pump system out of the airlock and install it.
Lead engineer Zhan Zhand will work in tandem with the astronauts to power the system off and then on again once it is installed by Parmitano.
The spacewalk started at 1:50 p.m. CET and will conclude at 8:30 p.m. CET.
AMS is a unique cosmic ray detector, the only magnet in space, taking data on the International Space Station since 2011.
CERN is live with commentary during the crucial stages of the spacewalk and scientists will be available to answer questions from the public.
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