Discovery's astronauts conducted "Star Wars" experiments Monday as ground controllers struggled to fix two data recorders whose failure caused some other tests to be scrapped.

The crew observed atmospheric light, or aurora, with an instrument unaffected by the problem.Air Force Capt. Lindley Johnson, a program director, said 80 percent to 85 percent of the planned experiments for the set of five scientific instruments still could be achieved even if the recorders cannot be fixed.

"The tape recorders only record data from our secondary experiments," Johnson said. "It is a little disappointing to our secondary experimenters, but as far as overall success we're still quite happy with the data that it looks like we're getting."

Four attempts to get the tape recorders working failed Sunday night, NASA said. Engineers continued working on the problem Monday as the astronauts proceeded as planned with experiments involving the unaffected instruments.

The trouble began hours after Discovery thundered into orbit early Sunday on an eight-day mission devoted mostly to tests aimed at helping Pentagon scientists develop sensors for tracking and destroying missiles.

Johnson said both recorders turned on and worked as planned for four hours, then mysteriously failed. He said engineers have traced the problem to the recorders and not related equipment.