Live At KSC: Rescue Mission Countdown Under Way

The Atlantis astronauts are in the home stretch of their Hubble Space Telescope servicing flight and NASA is counting down to the launch of rescue mission the agency hopes it doesn't need to fly.

With Atlantis orbiting 184 miles above the planet, engineers on the ground are analyzing data gathered during an extensive survey of the shuttle's composite carbon wings and nose cap. The idea is to detect any micrometeorite or space debris damage that could endanger the astronauts during atmospheric reentry.

If engineers find critical damage that the crew cannot repair, then Endeavour would be launched early Saturday on a mission to bring home the stranded Hubble servicing crew. Four astronauts on Endeavour would rendezvous with link up with Atlantis and the stranded astronauts would use a shuttle robot arm to make spacewalking crawls from the crippled shuttle to Endeavour.

Here's the STS-400 Rescue Flight Plan.

A three-day launch countdown picked up here at Kennedy Space Center this morning so that NASA and a four-man Endeavour crew are in position to launch a rescue mission if engineers in fact detect critical damage. Countdown clocks here at NASA's shuttle homeport are ticking toward a 7:34 a.m. launch on Saturday.

Atlantis mission commander Scott "Scooter" Altman said he believes his crew was able to gather enough imagery and laser data for engineers on the ground to spot any damage that might have been done between an initial inspection on the second day of the Atlantis flight and the survey the crew performed Tuesday.

"We did a pretty complete survey yesterday. I was very happy with all the imagery and the activity that we had to make sure we got as good an inspection as possible," Altman said in a space-to-ground interview with reporters at different NASA field centers.

"So I feel very confident that we have all the data that we need," he said. "I'm letting the experts crunch that to make sure everything looks good, From our vantage point, we think it's probably looking very good for entry and we're looking forward to that."

NASA mission managers will review the data with engineers today, and they are expected to give Atlantis a preliminary go for a landing at 10:01 a.m. Friday.

Endeavour and the rescue crew -- Chris Ferguson, Eric Bow, Stephen Bowen and Shane Kimbrough -- will remain on call until the Atlantis crew fires shuttle maneuvering engines around 9 a.m. and begins an hour-long return to KSC.