This story was updated at 2:12 p.m. EDT.
CAPE CANAVERAL, Fla. ? NASA is counting down toward the final flight of space shuttle Discovery after engineers successfully repaired two minor gas leaks on the spacecraft in time for one last launch on Wednesday (Nov. 3).
Discovery's final launch has been delayed two days due to leaky helium and nitrogen seals found in the shuttle's right orbital maneuvering system pod last week.
Technicians raced to troubleshoot the problem and re-pressurize the orbiter's rocket engine in time for a targeted launch at 3:52 p.m. EDT (1952 GMT) on Wednesday. The official countdown toward liftoff began today (Oct. 31) at 2 p.m. EDT (1800 GMT).
"Work is on schedule," NASA test director Steve Payne told reporters in a status briefing this morning. "We completed flight pressurization ? all went well. That is behind us now."
Part of those repairs included replacing a valve on Discovery that had never been touched since the shuttle was built in the early 1980s, Payne said. [Gallery: Building Space Shuttle Discovery]
The weather forecast for Wednesday's launch calls for a 70 percent chance of acceptable conditions at the launch site, according to Kathy Winters, NASA's shuttle weather officer. The only major weather threats for launch are low clouds and a chance of isolated showers near the launch pad.
On its 11-day mission, Discovery will haul critical spare parts to the space station, including a storage room and a humanoid robot to assist the crew of the orbiting laboratory.
Discovery's final flight will be NASA's 133rd shuttle mission, before the space agency brings its 30-year space shuttle program to a close in 2011.
"She's been an incredible vehicle," Payne said. "She's always amazed us with everything she can do, and we expect this flight will be no different."
NASA will retire the three remaining shuttles in its fleet ? Discovery, Atlantis and Endeavour ? next year to make way for a new plan aimed at sending astronauts to visit an asteroid and Mars. Discovery is the oldest of NASA's space shuttles.
While the weather outlook for Wednesday looks promising, NASA is tracking some other storms that could stall Discovery's flight if it suffers another launch delay.
A weather front pushing down into parts of central Florida that could cause concerns if Discovery's launch is stalled another 24 hours or more, Winters said.
This incoming weather system could prohibit launch due to showers and even thunderstorms in the area, Winters said. Under these circumstances, forecasts currently estimate a 60 percent chance of favorable conditions if NASA officials were to delay the launch by 24 hours.
NASA has until Sunday, Nov. 7 to launch Discovery toward the International Space Station launch within the current window. After that, the space agency would have to wait until early December to try again.
- Gallery: The Construction of Space Shuttle Discovery
- Video ? Space Shuttle Discovery: A Retrospective, Part 2, Part 3
- Space Shuttle Discovery's Legacy: 26 Years of the Right Stuff
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.