Friday, May 15, 2009

Live in Orbit: Spacewalkers start gyro replacement

Atlantis spacewalkers Mike Massimino and Mike Good have opened doors to their first work area inside the Hubble Space Telescope on their mission's second spacewalk.

The pair needed to attach a tether to one door to keep it from swinging closed on the telescope's aft shroud, the largest section.

Then Massimino attached himself to a foot restraint in the shroud, a tight space in which he must be careful not to touch the inside of the telescope.

Earlier, Good grabbed the first of three sets of gyroscopes from the shuttle's cargo bay, which he will hand off to Massimino for installation inside of Hubble.

Massimino will remove an old set of gyros and hand it to Good to return to the payload bay. Three spring-loaded bolts and two electrical connectors must be removed.

The image at left shows the locations of the three sets of gyros. The crew will replace, in order, the right set (#2), left set (#3) and then middle set (#1).

Six new gyroscopes are packaged in pairs in what are called Rate Sensor Units, or RSUs. Each RSU weighs 24 pounds and measures 13 inches long by 10 inches wide by 9 inches high.

Hubble's three sets of gyros have been in operation since December 1999, and each has experienced problems.

Without at least two gyros working, Hubble wouldn't be able to point steadily at stars and planets to fix its cameras and record reliable data.

As a result, the new gyros are the mission's top priority, and should that ensure Hubble steers smoothly for at least another five years.

Here's a fact sheet explaining how the gyros work.

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