Electrical Glitch Delays Space Shuttle Discovery's Launch to Thursday

This story was updated at 7:45 p.m. EDT.

CAPE CANAVERAL, Fla. ? The space shuttle Discovery's final launch has been delayed at least 24 hours due to an electrical glitch with one of the orbiter's backup engine controllers.

Shuttle mission managers decided late today (Nov. 2) to delay Discovery's planned Wednesday launch to allow extra time for engineers to address the engine controller malfunction. The next attempt to launch the space shuttle will come no earlier than Thursday, Nov. 4, at 3:29 p.m. (1929 GMT), they said.

Engine controllers are computers that sit on the shuttle's three main engines and dictate their functions. Each main engine has two controllers ? a primary and a backup. [GRAPHIC: NASA's Space Shuttle ? From Top to Bottom]

During checkouts of the orbiter today, the backup controller for Discovery's Main Engine No. 3 did not turn on as expected, said Mike Moses, NASA's shuttle integration manager, in a news briefing. The controller eventually powered on, but voltage irregularities were subsequently observed, said he added.

"The signature coming out of that circuit showed another little glitch that was a little bit unexpected ? something we hadn't seen before," Moses explained. "They were two separate events at two separate times in the day, but we think the cause of that is a common cause."

Shuttle technicians will continue to analyze the available data overnight, and the decision to proceed with Thursday's launch will depend on whether mission managers feel they adequately understand the problem and its cause. They are expected to meet again tomorrow at 2 p.m. EDT (1800 GMT) to assess the situation.

"We fly with known risks, not unknown risks," Moses said. "Right now this risk is a little bit unknown."

Discovery is slated to liftoff from its seaside pad here at NASA's Kennedy Space Center to deliver a room of spare supplies and a new robot to the International Space Station. The shuttle's launch has already been delayed by two days as a result of other technical issues that have since been resolved.

Discovery was originally scheduled to launch Nov. 1, but the space agency delayed by one day after detecting helium and nitrogen leaks on the shuttle. That launch target slipped a day, too, because the repairs took longer than expected.

"Discovery isn't going out easy," said Mike Leinbach, NASA's shuttle launch director. "She's giving us a little bit of trouble, but that's fine. She'll fly perfectly when she does."

With the new Thursday launch date, however, Mother Nature could further complicate the situation. A weather front is pushing down into parts of central Florida that could ground the orbiter for longer, according to Kathy Winters, NASA's shuttle weather officer.

Current forecasts give Discovery dismal odds for good weather at launch time on Thursday.

There is a 70 percent chance that foul weather will cause yet another launch delay for the space shuttle, Winters said. The main concerns are low clouds and showers at the launch site, she added.

NASA has until Sunday, Nov. 7 to launch Discovery within the current window. After that, the space agency will have to wait until Dec. 1 to try again.

• GRAPHIC: NASA's Space Shuttle ? From Top to Bottom
• Gallery: Building Space Shuttle Discovery
• Video ? Space Shuttle Discovery: A Retrospective, Part 2, Part 3

Follow SPACE.com Staff Writer Denise Chow on Twitter @denisechow as she covers Discovery's final space voyage from Cape Canaveral, Fla. Click here for mission updates, new stories and a link to NASA's live webcast coverage.