spacetoday.net: Astronauts breeze through instrument replacement and repairs

Posted: Sun, May 17, 2009, 9:25 AM ET (1325 GMT)
STS-125: EVA #3 (NASA)

Spacewalking astronauts had few problems Saturday doing what had been considered one of the most difficult tasks of the STS-125 Hubble servicing mission. John Grunsfeld and Andrew Feustel easily completed repairs to the Advanced Camera for Surveys (ACS) instrument, opening up a panel, replacing a set of circuit boards, and installing a new power supply. The ACS failed in early 2007 when its backup power supply shortcircuited, and this repair had been considered one of the most difficult aspects of the mission as the instrument wasn't designed to be repaired in orbit. The ACS work came after the two astronauts removed and old corrective optics unit and replaced it with a new instrument, the Cosmic Origins Spectrograph. The fourth spacewalk of the mission will take place Sunday, when Mike Good and Mike Massimino will repair another instrument, the Space Telescope Imaging Spectrograph, and install a new stainless steel cover for one of the telescope's equipment bays.