Live In Orbit: Astronauts Ahead Of Schedule

Two NASA astronauts are suited up in the airlock of shuttle Atlantis this morning, tracking almost an hour ahead of schedule for the fifth of five planned spacewalks to service the Hubble Space Telescope.

Atlantis mission specialists John Grunsfeld and Drew Feustel are nearing the end of a 40-minute period during which they breathe pure oxygen to rid gaseous nitrogen from their blood. The "pre-breathe" is done to ensure the astronauts don't suffer decompression sickness, or "the bends."

The spacewalkers are preparing for their final step before heading outside: depressurizing the airlock.

The astronauts are scheduled to start their spacewalk at 9:16 a.m. but they are running 45 minutes to an hour ahead of schedule.

On the to-do list today: Replace three nickel-hydrogen batteries, install a new Fine Guidance Sensor and equip Hubble with new thermal insulation blankets.