After a two-day delay, NASA's countdown clocks began ticking Sunday toward the final launch of space shuttle Discovery.
A pair of gas leaks resulted in back-to-back launch postponements for Discovery. NASA test director Steve Payne said repairs took care of the problem and enabled the launch team to aim for a Wednesday liftoff.
Forecasters put the odds of good weather at 70 percent for the 3:52 p.m. liftoff.
Discovery is making its last trip to orbit. Its destination is the International Space Station. Aboard the shuttle is a pressurized compartment full of supplies — even a futuristic robot — that will remain permanently at the station.
The mission will last 11 days and feature two spacewalks.
This will be the 39th flight in 26 years for Discovery, NASA's oldest surviving shuttle and the fleet leader.
"She's been an incredible vehicle, and she caps a long and distinguished career with this particular flight," Payne told reporters. "She's always amazed us with everything that she can do. We expect this flight should be no different."
Discovery was supposed to blast off Monday but was sidelined by small leaks in the helium and nitrogen gas lines at the back of the spaceship. Technicians and engineers spent the past few days replacing suspect parts and testing the patched system.
"That is behind us now," Payne said.
Only one other shuttle launch remains on NASA's official schedule, in late February. That will end 30 years of shuttle flight unless money is forthcoming for an extra mission. The Obama administration wants NASA to focus on the next set of exploration vehicles.