STS-125 mission specialists John Grunsfeld and Drew Feustel are working outside of the shuttle again today for the mission’s third spacewalk. The spacewalk began at 9:35 a.m. EDT.
COSTAR was removed and stored for its return, and COS successfully installed on the telescope. Grunsfeld and Feustel now will begin work on the Advanced Camera for Surveys (ACS) repair. The spacewalkers will spend about two hours and 10 minutes working on the camera and will remove two of the four electronics cards that need to be replaced. Grunsfeld’s first task will be to install four guide studs that will be used later to install tools. Feustel will assist him with that job, and then the two will work together to remove a grid. To do so, Grunsfeld will fit a grid cutter over the grid. Tightening the 12 bolts on the grid cutter will cause a blade to cut off the 12 legs of the grid. The grid cutter also will trap the pieces of the grid, so that the spacewalkers don’t have to handle the sharp edges created by cutting the grid off.
For this spacewalk, the spacewalkers will focus on the installation of the telescope’s new Cosmic Origins Spectrograph, and the first part of the Advanced Camera for Surveys repair work. The work on the camera may be finished later in the mission if time permits or the Space Telescope Imaging Spectrograph repair on the fourth spacewalk is not successful. In that case, the rest of the Advanced Camera for Surveys work would be added to the fifth spacewalk, replacing the Fine Guidance Sensor work.
"This is really pretty historic," Grunsfeld said as he and Feustel hoisted out the phone booth-size box containing Hubble's old contacts. Hubble was launched in 1990 with a flawed mirror that left it nearsighted. But the newer science instruments have corrective lenses built in, making the 1993 contacts unnecessary. The latest addition, the cosmic spectrograph, is expected to provide greater insight into how planets, stars and galaxies formed.
Today's tasks and tomorrow, Sunday's, are considered to be the most difficult and delicate ever attempted while in orbit, as the thick and stiff gloves worn by the astronauts add another challenging twist to the matter. As an example there were more than 30 latches to get inside the camera and navigate a tricky corner to replace the burned-out power supply cards. In anticipation of this mission NASA designed new tools for the job.
The first two spacewalks of Atlantis' mission ended up running long because of unexpected difficulties. Hubble senior project scientist David Leckrone surmised late Friday that because the observatory went seven years without a tuneup, "it's gone wild again."
NASA hopes to keep Hubble working for another five to 10 years with all the improvements. No one will be back to Hubble, so everyone at NASA, the seven astronauts included, wants to squeeze in as much repair work as possible. Already, they have given Hubble an improved wide-field planetary camera, fresh batteries and gyroscopes, and a new science data unit to replace one that broke last fall. If all goes well, the fifth and final spacewalk is set for Monday and the telescope will be released from Atlantis on Tuesday.
This last mission to Hubble will total more than $1 billion.