The five Discovery astronauts and ground support teams Tuesday began staging their final long-duration rehearsal before the first launch of a NASA space shuttle in more than 21/2 years, officials said.

About 300 people at the Johnson Space Center took part in the 56-hour simulation of mission STS-26, a four-day shuttle flight, with as many as 200 others taking part in New Mexico and California, said spokesman Brian Welch.The scheduled 8 a.m. test got off to a late start because of a malfunction in the shuttle simulator, but the problem was corrected and countdown ended at 9:04 a.m., said spokesman Bill Green.

Commander Rick Hauck, pilot Richard Covey and mission specialists David Hilmers, Mike Lounge and George "Pinky" Nelson will face about 150 simulated problems during the lengthy test.

"The people who do the simulation, the `sim' supervisors, sort of wage a mental battle with the flight controllers," Welch said. "They will do everything they can to make it more difficult. They try to throw a problem at each major (flight) system."

Lounge and Nelson may have to wear spacesuits to wrestle a mock satellite in the space center water tank, the crew may be asked to make an unplanned landing, and early deployment of a $100 million NASA communications satellite may be thrown off schedule during the test.

"I will feel good if they work through the scenarios, if they understand what they did and why they did it," Welch said.

The rehearsal was scheduled to end by 5 p.m. Thursday, and a full day of debriefing will follow, Welch said.