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NASA added a 10th day to Discovery's flight Tuesday so the crew can perform more experiments to learn about the damaging effects of space shuttle exhaust.

The six astronauts had been dimming the lights and even using flashlights whenever possible to conserve enough power for the extra day. Their efforts paid off."Good job," Mission Control told the crew in a written message.

The flight will now end next Monday.

Tuesday's other highlight for the crew was the planned late-afternoon release of a $14 million sun-gazing satellite named Spartan.

"It's a good day to deploy a Spartan and to continue our research on the Earth's environment," Mission Control said.

Spartan has two telescopes that will focus on the sun's corona, or outer atmosphere. The astronauts will retrieve the satellite Thursday for the trip home.

In the experiment on the effects of exhaust, the crew spent parts of the last three days firing steering jets toward monitors on the end of a boom extending from the cargo bay. With the extension of the mission, they will now have more time to do more tests Saturday.

NASA wants to determine whether jet plumes could damage a space station as a shuttle approaches for docking because shuttle Atlantis is to dock with Russia's Mir space station next May. The experiment also could help NASA design a planned international space station.

Discovery's jet-exhaust plumes were strong enough to shake the shuttle's 50-foot robot arm and a 32-foot extension carrying the monitors. And the jet firings themselves shook the whole shuttle.

Researchers on the ground said the plumes' effects didn't appear to be worse than expected, but they seemed dramatic enough to the crew.

"It's a pretty good force," astronaut Mark Lee said Monday. "It's kind of scary to see those jets fire and see them hit the arm and make it move. We're definitely worried about the forces that it could input to a structure up in space."

The experiment ran into the same snag Monday that it had the previous two days: trouble collecting data from the exhaust monitors. Crew members overcame the problem by flipping a circuit breaker.