Live In Orbit: Spacewalkers Swap Hubble Batteries

Spacewalking astronauts outfitted NASA's Hubble Space Telescope will three new batteries today, completing the replacement of original equipment that has been powering the observatory for 19 years.

Anchored on the end of a 50-foot robot arm, Atlantis lead spacewalker John Grunsfeld unscrewed 14 bolts and disconnected six electrical connectors, then removed a set of three nickel-hydrogen batteries from a telescope bay just beneath one of its power-producing solar wings.

Robot arm operator Megan McArthur then drove Grunsfeld and the old battery pack back toward the forward section of the shuttle's payload bay, where spacewalking partner Drew Feustel was fetching a new set from a shuttle cargo bay carrier.

The two swapped battery packs and then McArthur moved Grunsfeld back up to the telescope.

Grunsfeld put the new battery pack in place and secured it with 14 bolts before hooking up six electrical connectors and swinging the bay door shut for a final time.

An "aliveness test" then was successfully completed by engineers at NASA's Space Telescope Operations Control Center at Goddard Space Flight Center in Greenbelt, Md.

"Really nice work on the batteries, guys," said Atlantis mission specialist Mike Good, who was directing the spacewalking work from inside the shuttle's crew cabin. "We're on our way here today."

Next on the agenda: The installation of a refurbished Fine Guidance Sensor. The FGS is one of three that enable the telescope to lock onto and track planets, stars, galaxies and other celestial targets.

The observatory is outfitted with fixed head star trackers that are used to point the telescope in the general direction of a target. The Fine Guidance Sensors lock on to specific targets.

The devices also enable scientists to perform astrometry: Measuring the position and movement of astronomical objects.

Grunsfeld and Feustel first will remove one of Hubble's three Fine Guidance Sensors -- FGS 2. They'll open an access door, attach a handling fixture, disconnect electrical cables and attachment clamps and then slide the 900-pound unit out of the observatory.

The old unit will be temporarily stowed in the shuttle's cargo bay, and then the refurbished FGS will be removed from a transport carrier.

Once the new unit is installed in the telescope, the old FGS will be placed in the transport carrier for a return to Earth.

The task is expected to take about two hours to complete.