Live In Orbit: Spacewalkers Tackle Toughest Task

Spacewalking astronauts are setting out to tackle a repair job unprecedented in degree of difficulty: Attempting to revive a failed planetary camera that was not designed to be fixed in orbit.

Atlantis lead spacewalker John Grunsfeld and mission specialist Drew Feustel just stowed a corrective optics package the size of a phone booth in a protective canister in the shuttle's cargo bay.

The Corrective Optics Space Telescope Axial Replacement, or COSTAR, served for 16 years as a set of contact lenses for the telescope's spectrographs. All Hubble instruments now have built-in corrective optics, so the COSTAR will fly back to Earth aboard Atlantis.

Now the astronauts are off to try to fix the Advanced Camera For Surveys, a planetary camera that was installed in 2002 but suffered several power failures in 2006 and 2007, knocking out two of its three channels.

Grunsfeld will attempt to outfit the camera with a new power supply and four new circuit boards. To do so, he'll have to cut shielding away from the camera and then remove a cover plate held in place with 32 tiny, non-captive screws that could float off into the telescope and cause serious damage.

In a bid to keep the screws from getting loose, Grunsfeld will put a specially designed "capture fixture" over the cover plate. Then he'll use a new mini-power tool to back the screws out into the capture fixture.

The cover plate and the capture fixture both will be pulled off the camera, enabling Grunsfeld to swap out the four failed circuit boards. The camera then will be equipped with a new set of circuit boards and a new low-voltage power supply to complete the repair.

The complicated job originally was supposed to be done over two spacewalks. The timeline, however, had to be squeezed so that the astronauts could add an extra job -- the installation of a new science instrument controller -- to their to-do list. The new Science Instrument Control & Data Handling unit was put in place on Thursday.

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