Discovery's astronauts poked a "Star Wars" probe back into space Friday for 24 hours of tests on the end of the ship's outstretched mechanical arm and got ready for a complex repair job.

Ground teams devised a last-ditch plan to fix two data recorders that have not worked since almost the beginning of the flight, hindering experiments by three scientific instruments.The repairs, which the seven astronauts planned to attempt Saturday, involved splicing cables and rerouting the flow of data. Details were radioed to the crew Friday so they could go over the procedures. The work was expected to take two to three hours.

"We're either going to get 100 percent of what the recorders would have been getting, or we'll get nothing," said NASA flight director Bob Castle.

The principal investigator of one of the instruments affected by the recorder trouble, Ed Fenimore, desperately hopes the plan will work. So far, he's gotten "zero data" from his X-ray detector, which he has been working on for 13 years.

"It's coming down to a real few final minutes. It's like a poker game where you put all the chips in," said Fenimore, an astrophysicist at Los Alamos National Laboratory in New Mexico.

As Discovery whirled around the world at 17,500 mph, the probe's infrared sensors and television cameras focused on the planet and atmospheric light, or aurora. A camera on the shuttle's 50-foot arm also occasionally displayed scenes from 160 miles below.