A NASA spokesman said Tuesday "we're on track" for the start of the countdown Tuesday night for the much-delayed flight readiness firing of the space shuttle's engines.

The 22-second engine test, required before the shuttle Discovery can fly in space again, is scheduled for Wednesday morning. Malfunctions have forced the test to be postponed five times.Kennedy Space Center spokesman Dick Young said things were going so well that many workers involved in the test firing were sent home to rest for the countdown.

If this test succeeds, NASA officials will set a date for the first American manned space flight since the Challenger burst into flames on liftoff in January 1986. The Discovery launch date, already officially moved four times, is not likely to be before October because of all the test delays.

The flight readiness firing, as it's called, is an overall workout of the main engines, computer software, ground support equipment, communications lines and the launch teams.

The "call to stations" that begins the countdown was scheduled for 6:10 p.m. with the test set for 7:30 a.m. Wednesday. Without further problems, fueling of the shuttle's huge tank begins a half hour before midnight.