He is this latest mission's lead spacewalker, having logged hours of time in the vacuum of space on a mission in 2002 to repair the Hubble space telescope.

This mission will mark Dr. Linnehan's final shuttle flight and is his fourth trip into space.

His previous trips include:

> The Life Sciences and Microgravity Spacelab mission aboard the Space Shuttle Columbia in 1996.

> The Neurolab aboard Columbia as operator and test subject, observing the effects of low gravity on the brain and nervous system in 1998.

> and Servicing Mission 3B, where he helped upgrade the Hubble space telescope's systems and walked in space three times in 2002.