Encyclopedia Astronautica
2002.03.06 - STS-109 Mission Status Report #12


The Hubble Space Telescope received a new "heart" today during a 6 hour, 48 minute spacewalk by astronauts John Grunsfeld and Rick Linnehan. The two installed a new Power Control Unit (PCU), replacing the original unit launched with the telescope in April 1990. The PCU serves as Hubble's central power switching station by distributing electricity to all systems, scientific instruments and the Nickel Hydrogen batteries.

In addition to eliminating an intermittent problem with the old PCU, the new unit also is capable of handling the extra 20 percent of power output being generated from Hubble's newly installed set of solar panels attached during back-to-back space walks Monday and Tuesday. Controllers at the Space Telescope Operations Control Center in Greenbelt, MD, powered Hubble down at 3:37 a.m. Wednesday for the first time since its launch in 1990.

Mission Specialist Nancy Currie operated the shuttle's robotic arm throughout the space walk, moving Grunsfeld and Linnehan to and from various worksites on the telescope and in Columbia's payload bay. Grunsfeld later told Mission Control that, "Nancy is my hero" for her work today.

Today's space walk started two hours late due to a water leak in Grunsfeld's spacesuit. After swapping the upper portion of his suit the space walk began at 2:28 a.m. Linnehan, working from the shuttle's robotic arm, began by removing 30 of the 36 connectors on the old PCU. He was then maneuvered by Currie to the shuttle's payload bay where he switched places with Grunsfeld in order to prepare the new PCU for installation. At 4:55 a.m. Grunsfeld, now working from the robotic arm, unhooked the remaining six PCU connectors, eased the old PCU out of the telescope and carried it to the shuttle's payload bay for return to Earth. Grunsfeld installed the new unit at 5:53 a.m. The connectors were mated to the new PCU by 7:19 a.m. Shortly thereafter, the new PCU passed its aliveness test at 8:02 a.m. and all functional tests were completed at 12:18 p.m.

Inside Columbia, the flight's other space walking team, Jim Newman and Mike Massimino looked toward the fourth space walk set to begin tomorrow at about 2:30 a.m. CST to replace the last of Hubble's original science instruments - the Faint Object Camera - with the Advanced Camera for Surveys.

The crew is scheduled to awaken at 9:52 p.m. CST Wednesday.

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