Hubble Spacewalkers Finish Top Mission Task
Frank Morring, Jr./Johnson Space Center, Houston.
More updates on STS-125 are being posted at the On Space blog
Astronauts Mike Good and Mike Massimino accomplished the top-priority task of the STS-125 mission to the Hubble Space Telescope May 15, but only after a virtuoso display of persistence and planning.
At the end of the second extravehicular activity (EVA) of the final servicing mission to the telescope, Hubble had six functioning gyros instead of three, a new wide-field camera and a replacement for data-handler that failed last fall. That met the top three goals for the crew of the space shuttle Atlantis, and left them in good shape to install the Cosmic Origins Spectrograph (COS) on May 16 -- the next priority -- and to try to repair the power system on the Advanced Camera for Surveys (ACS).
Getting to that point with hardware that has been in orbit for 19 years wasn't easy. Good and Massimino had the same problems with stuck bolts and misfit parts that plagued colleagues Drew Feustel and John Grunsfeld the day before (Aerospace DAILY, May 15). Their EVA ran one hour and 26 minutes overtime after problems installing one of the three new "rate sensor units" (RSUs) containing two gyros added 53 minutes to the gyro-replacement task.
The second RSU Massimino tried to bolt in place from an awkward position inside the telescope wouldn't seat properly, and eventually the EVA team in space and on the ground decided to install the third new RSU there instead. It worked, but the second unit wouldn't seat in the third and final position either.
That was where the planning came in. Tucked into one of the boxes that protected the new telescope hardware during launch was a spare RSU that had flown once before. It was refurbished after it was removed from the telescope in December 1999, and it fit back inside the orbiting observatory after a little jiggling by the spacewalkers.
Before closing the doors on the RSUs, Massimino managed to connect some cabling needed for the spacewalk on May 16, when Feustel and Grunsfeld were to install the COS and attempt the ACS repair. But he and Good were so far behind that Massimino had to replenish his oxygen to finish the final task of the EVA -- replacing one of two battery modules in the telescope.
Weighing 460 pounds each on the ground, the modules contain three nickel hydrogen batteries that have never been changed even though their nominal service life was only five years. The work went fairly smoothly, and the EVA ended after seven hours and 56 minutes.
Because the spacewalk was originally set to last six-and-a-half hours, mission managers decided to slip the mission timeline by one hour, sending the crew to bed an hour late at about 9:30 p.m. EDT and letting them sleep until 5:30 a.m. EDT on May 16.
Also on the schedule for the weekend was an attempt May 17 to repair the Space Telescope Imaging Spectrograph by replacing an electronics card in the instrument, a task that would require removing 111 screws and using an ingenious capture plate to keep them from becoming space debris. Also on tap for that EVA was the replacement of some degraded insulation on the outside of the telescope.
Photo credit: NASA TV
