NASA managers and a federal judge cleared the shuttle Discovery for fueling Friday and blastoff Saturday to launch the nuclear-powered Ulysses solar probe, at long last ending a five-month launch drought.

Confident Discovery will prove leak-free, engineers began fueling the shuttle late Friday for a launch attempt at 7:35 a.m. Saturday, despite protests by anti-nuclear activists who said the mission should be grounded because of safety concerns."We're ready to go," said William Len-oir, chief of NASA's manned space program. "Discovery is ready. From where we sit right now, the one remaining question . . . is will the weather cooperate?"

Forecasters called for a 60 percent chance of acceptable weather at launch time and late Friday NASA officials said the countdown was proceeding smoothly and that all systems were "go" for blastoff.

The 36th shuttle flight marks NASA's first since April 24 because of a string of hydrogen fuel leaks that grounded the shuttles Columbia and Atlantis in May, July and September. But agency engineers said Friday that Discovery's plumbing was "tight" and that no leaks were expected.

Shuttle commander Richard "Dick" Richards, 44, co-pilot Robert Cabana, 41, flight engineer William Shepherd, 41, Bruce Melnick, 40, and Thomas Akers, 39, plan to launch Ulysses about six hours after liftoff and to glide to a landing Wednesday morning at Edwards Air Force Base, Calif.

Getting Discovery into orbit is critical to the National Aeronautics and Space Administration.