Engineers are troubleshooting an apparent malfunction in the shuttle Discovery's Ku-band antenna system.

The computer controlled antenna is used as a radar dish during rendezvous operations and to transmit high-speed data, including television, to the ground via NASA communications satellites. The unit failed a self test after Discovery reached orbit Monday and subsequent troubleshooting and power cycling did not immediately resolve the problem.

If the antenna system cannot be recovered, the astronauts will use other instruments and data during approach to the International Space Station on Wednesday. The biggest near-term impact would be the loss of television transmission capability during a planned heat shield inspection Tuesday.

While the astronauts can record the video on board and downlink it later through the space station's Ku-band communications system, it would delay the analysis and likely impact the crew's timeline during docked operations. But engineers say it would not affect the overall goals of the mission.

"The ground team is continuing to work through all the different options to get that Ku-band antenna up and running," said mission control commentator Josh Byerly. "There's a few more checkouts that are to be performed. But what the teams here on the ground are continuing to do is work tomorrow's timeline with the assumption that that Ku-band antenna will not be able to be used during the inspection of Discovery's heat shield.

"There are backup procedures for that. Basically, what would happen is as this inspection is taking place ... the crew members will tape all of that on board. The crew will watch over very carefully on a monitor to see if there's any areas of concern on Discovery's heat shield. If they see anything of note, they will mark down the time and then once the shuttle gets docked with the International Space Station on Wednesday, all of that video will be replayed for the ground teams here in Houston ... to ensure Discovery's heat shield is in good shape."

What impact the loss of Ku capability might have on a post-undocking "late" heat shield inspection is not yet clear.

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