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Spacewalk. European Space Agency (ESA) astronaut Michael Foale performing an extravehicular activity (EVA or spacewalk). He is working on the Hubble Space Telescope (HST) to replace one of the telescope's fine guidance sensors (FGS). The HST has three FGSs which together allow the telescope to find and view its target. The photograph was taken from the cargo bay of the space shuttle Discovery during mission STS-103 (19-27 December 1999). This mission was the third to service the HST since its launch in 1990. During this mission the HST's computer, gyroscopes and tape recorder were all replaced as well as one of the FGSs. (KEYSTONE/SCIENCE PHOTO LIBRARY/NASA)