Judge Clears Discovery for Takeoff Today : Space: Contentions by environmentalists that Ulysses probe created risk of nuclear disaster are rejected. Mission will examine sun’s poles.

A federal judge Friday cleared the way for the launching of the space shuttle Discovery early today after ruling that three environmental groups had failed to demonstrate that the launching could result in radioactive contamination over much of the East Coast.

The Discovery, scheduled for liftoff at 4:35 a.m. PDT, will carry the nuclear-powered Ulysses into orbit and then send the robotic spacecraft on a 2-billion-mile journey to the sun by way of Jupiter. During its five-year mission, the craft will generate electricity for its instruments by tapping into the energy released by the radioactive decay of 24 pounds of plutonium 238.

Protesters had argued that a cataclysmic accident could release the plutonium into the atmosphere, and they asked U.S. District Judge Oliver Gasch in Washington to delay the launching for at least a year.

In arguing for the National Aeronautics and Space Administration, Justice Department attorney Rebecca Donnellan said that such a postponement would cost $350 million. NASA has insisted that only nuclear power can supply the electricity the Ulysses probe will need when it travels through the dim light of the outer solar system, but critics insist that even NASA’s own documents show that a solar-powered craft, launched atop a Titan-Centaur unmanned rocket, could have done the job without the radioactive power supply.

With the court victory behind them, NASA officials looked forward to today’s launching and hoped for good weather. The weather was expected to be acceptable, but there was a 40% chance that showers would force another delay.

Six hours after liftoff, the five-man crew of the Discovery will deploy the Ulysses, built by the European Space Agency. The Ulysses will give scientists their first look ever at the poles of the sun and thus could help them understand such things as changes in solar temperatures that have a major impact on Earth.

But to go into a polar orbit around the sun, Ulysses must first fly to Jupiter, five times farther from the sun than is the Earth. It will pass over Jupiter close enough for the planet to fling the spacecraft down and into a huge orbit that will carry it over the poles of the sun.

No one has ever seen the poles of the sun because the Earth and the other planets orbit around the sun’s Equator. That incomplete picture has left scientists guessing about how the poles influence such things as sunspots and solar flares, which in turn are thought to have an impact on weather patterns on Earth.

The Discovery’s commander is Navy Capt. Richard N. Richards, 44, and the pilot is Marine Lt. Col. Robert D. Cabana, 41. Mission specialists are Air Force Maj. Thomas D. Akers, 39, and Navy Capt. William M. Shepherd, 41. The fifth member of the all-military crew is the first Coast Guardsman to fly in space, Cmdr. Bruce Melnick, 40, a mission specialist.

The flight is scheduled to end four days after launching with a landing at Edwards Air Force Base, Calif.