Technicians have tested the affected computers themselves and have virtually eliminated them as the cause of the problem, said James Hartsfield, a NASA spokesman with the Johnson Space Center in Houston.

That leaves wiring in the shuttle itself suspect, said Hartsfield. The half-second electrical short just after shuttle Columbia lifted off on July 23 shut down two engine controllers, which link with the spaceship's primary computers to control the flight into orbit. The shuttle has three main engines, each of which is equipped with two fully redundant controllers. When the electrical short zapped two of the controllers, backups immediately took over and Columbia was able to safely reach orbit.

Analysis of the shuttle's wiring is under way, said Hartsfield, but the process is slow-going, as access to the orbiter is difficult.

The electrical short was one of two glitches that tainted Columbia's otherwise textbook mission to deploy an X-ray telescope. An investigation into a hydrogen fuel leak, believed to be caused by a falling engine plug, is also under way.