Tuesday, April 06, 2010

Discovery prepares for station docking without radar

Discovery astronauts are closing in on the International Space Station, planning to dock early Wednesday without the usual radar capability due to an antenna failure.

NASA officials say at least two prior missions have encountered similar problems: STS-92 during a 2000 station docking, and STS-39 in a 1991 approach to a free flying satellite.

Back up procedures rely on systems that would be used anyway: star trackers, hand-held laser devices and Trajectory Control Sensors, or TCS, that help calculate the orbiter's distance from the station and approach speed.

"All of those systems are available, and we don't anticipate any issues whatsoever with performing the radar failed procedures (Wednesday) for the rendezvous," said LeRoy Cain, deputy shuttle program manager.

The dish-shaped Ku-band antenna that normally provides the radar and high-speed data transmission failed during its start-up after being deployed from the shuttle payload bay when Discovery reached orbit Monday.

The failure also forced the crew to tape today's heat shield inspection and prepare digital files for download from the space station following Discovery's planned arrival at 3:34 a.m. EDT.

Cain said he expects the video to be on the ground and available to image analysts by 11 a.m. He hopes to be able to inform the crew when they wake-up for Flight Day 4, around 8 p.m. Wednesday, of the results from preliminary damage assessments.

Parts of the starboard wing's underside could be blocked from closer inspection once the Leonardo cargo carrier is removed from Discovery and installed on the station's U.S. Harmony node, a task planned early Thursday.

During Tuesday afternoon's Mission Management Team meeting, managers watched a launch video that appeared to show a black tile ripping away from the edge of the rudder speed brake on Discovery's tail fin. Click here to watch the video.

Cain said the tiles are positioned there primarily to protect the fin from heat generated by the shuttle main engines during launch, and would likely be no concern for a planned April 18 re-entry through Earth's atmosphere.

"This is going to turn out to be a non-issue for us, I expect," he said.

Discovery's seven astronauts awoke at 8:21 p.m. today to "I Will Rise" by Chris Tomlin, a tune selected by the family of pilot and first-time shuttle flyer Jim Dutton, a 41-year-old Air Force colonel known by the call sign "Mash."

"It's just a great day to be in space, and we're looking forward to joining up with the International Space Station today," Dutton radioed to NASA's Mission Control Center in Houston.

"It looks like a good day for rendezvous," said Megan McArthur, an astronaut communicating with the crew from Houston.

"Agreed," replied Discovery commander Alan Poindexter, a 48-year-old Navy captain with the call sign "Dex."

Because of the antenna failure, McArthur again read the crew a list of instructions that would normally have been e-mailed in a Flight Day 3 Execute Package. Click here for a look back at the Flight Day 2 package.

She said she was looking forward to seeing the crew's faces once they reached the space station and could take advantage of its Ku-band capability to download live video.

"We're looking forward to seeing your smiling faces on downlink at last," she said.

During a nine-day stay at the station, Discovery will deliver more than 17,000 pounds of equipment and supplies and replace a coolant tank over three spacewalks.

IMAGE: At top, NASA astronauts Alan Poindexter (left) and James P. Dutton Jr., Discovery's commander and pilot, respectively, participate in a Sept. 11, 2009, training session in the shuttle mission simulator (SMS) in the Jake Garn Simulation and Training Facility at NASA's Johnson Space Center.

No comments: