A simulated shuttle mission designed to test the Discovery astronauts' trouble-shooting skills was halted just before a mock landing because of a real-life computer crash, NASA officials said.

The five astronauts were preparing to end their 56-hour mission Thursday afternoon by simulating a shuttle landing with a flat tire when the computer shutdown cut the rehearsal short."I'm sure they'll be looking at it to see why it went down, but nobody here considers it to be a big problem that the simulation ended early," said NASA Johnson Space Center spokesman James Hartsfield.

National Aeronautics and Space Administration officials stressed that there was no problem with any kind of computer used in actual flight control.

In Huntsville, Ala., meanwhile, engineers at Marshall Space Flight Center said Thursday's fifth and final test of seals and joints on the space shuttle booster rocket lifted their confidence in parts redesigned after the Challenger disaster.

"Based on all appearances the test was a complete success," said an assistant project mamager.