The Discovery astronauts snatched an orbiting "Star Wars" research satellite and packed it back in the shuttle's cargo bay after it studied exhaust plumes and rocket fuel sprayed into space.

The 4,200-pound satellite spent 38 hours in space collecting data on a series of tests designed to help scientists build a defense system that could track and destroy incoming enemy missiles.Discovery closed in on the $94 million satellite Thursday after the elaborate experiments were completed, and the crew snared it with the shuttle's robot arm.

Another propellant test was scheduled Friday with the satellite perched atop the 50-foot mechanical arm, which would be extended into space again. The craft also was to observe the Earth and the shuttle.

The experiment had been scheduled for early morning but was delayed while controllers tracked the paths of the two spent canisters already in orbit. NASA wanted to make sure the containers would not come too close to the shuttle.

"They were hoping for a great database, but they're getting more data than they ever expected," said Maj. Carolyn Channave, a spokeswoman for the Strategic Defense Initiative, better known as "Star Wars." "They're very impressed."