Astronauts John Grunsfeld and Rick Linnehan began their third spacewalk of the mission at 2:46 a.m. CST. Linnehan was given a ride on the shuttle's robotic arm to the aft shroud doors by Nancy Currie, working from the aft flight deck of Columbia. After the shroud doors were open, Linnehan was moved back to Columbia's payload bay to remove the NICMOS cryocooler from its carrier. Grunsfeld and Linnehan then installed the cryocooler inside the aft shroud and connected cables from its Electronics Support Module. That module was installed yesterday during a spacewalk by Jim Newman and Mike Massimino.
Next, with Grunsfeld on the end of the shuttle's robotic arm, the Cooling System Radiator was retrieved from its carrier in Columbia's payload bat and installed on the outside of Hubble. Linnehan fed wires from the radiator through the bottom of the telescope to Grunsfeld, who made the necessary connections to NICMOS. After ensuring that all the cables were properly connected and stowed, the pair closed both aft shroud doors and performed the final activities of the spacewalk to prepare the shuttle payload bay for landing.
Commander Scott Altman and Pilot Duane Carey provided photo and video documentation of the last spacewalk from inside the shuttle.
Initial tests of the new cooling system by the Space Telescope Operations Control Center in Greenbelt, Md. have all gone very well. NICMOS was originally installed on the second servicing mission to Hubble in 1997. The camera requires extremely low temperatures, but its solid-nitrogen cooling block was depleted earlier than expected. Engineers hope the new neon gas cooling system will restore the cold temperatures necessary for the camera to operate.
About an hour after the spacewalk, at 11:18 a.m., Columbia's smallest steering jets were fired for 36 minutes to boost the shuttle and Hubble's orbit by four statute miles. This reboost places Hubble in the proper orbit for its deployment from Columbia's payload bay early Saturday morning.
The crew began its sleep period at 1:52 p.m. and is scheduled to awaken at 9:52 p.m.