A storm of cosmic rays apparently caused by sunspots today knocked out for about 13 hours a vital satellite that relays data from the space shuttle Challenger to scientists on Earth.

The "cosmic hit" dealt another setback to Challenger's most important scientific experiment -- a powerful new imaging radar system that was to map large parts of the world.

The radar had already lost almost two days of observation time because of a faulty antenna on the shuttle.

The stricken craft is NASA's Tracking and Data Relay Satellite (TDRS), 22,400 miles above the equator over the south Atlantic. It is designed to dump its computer memory to Earth if it is hit by cosmic rays and must be reloaded with new instructions before its memory is restored.

After the TDRS went down about 9 a.m. EDT, engineers spent all day reprogramming its memory, and Mission Control said the satellite was working again at 10:05 p.m. EDT.

"I'm not sure what happened to the satellite, and I'm not sure anyone knows right now," Flight Director Cleon Lacefield said at the Johnson Space Center in Houston. "All I know is that its memory was wiped out . . . . "

The satellite is essential to the Earth-scanning radar. The radar picks up so much information that it must relay the data through its own high-speed antenna to the satellite, which in turn transmits it to Earth.

"We only are observing our high-priority sites right now," said Dr. Charles Elachi of California's Jet Propulsion Laboratory where the imaging radar was built. "Our estimate is we'll get no more than 50 or 60 percent of what we started out to get and we'll lose complete areas that we had planned to map with our radar."

Among the parts of the world the radar had planned to map but will probably lose are the entire Amazon River basin, the islands that make up Indonesia and the treacherous seas off the Cape of Good Hope, where waves of unusual size propagate to create a great hazard to shipping.

The high-priority sites that have been saved include Mount Shasta in the Cascade Mountain range in the western United States, huge wheat fields in Illinois, forests in West Germany and Florida, the Imperial Valley in California and ocean areas off the coast of Chile and in the North Sea where dangerous waves similar to those off the Cape of Good Hope often form without warning.

Meanwhile, tropical storm Josephine was gathering strength east of the Bahamas and posing a potential threat to Challenger's Saturday landing in Florida, from which it took off last Friday. Josephine had winds as high as 50 miles per hour today and appeared to be moving west-northwest at about five miles an hour.

"We have a high-pressure ridge above the Cape Canaveral that may push the storm through the Cape on Thursday," Lacefield said. "At the same time, we have a low-pressure system coming in from the west that could slow Josephine up and bring it near the Cape around landing day."

When he was asked if "there were any pools" being made in the Mission Control Center against a Cape landing, Lacefield replied: "Well, we are flying with Crippen."

His comment brought laughter because Challenger Commander Robert L. Crippen has been the commander of both previous shuttle flights targeted for landing at Florida's Kennedy Space Center that were "waved off" to California's Edwards Air Force Base because of bad weather at the Cape.

The shuttle crew of seven is now in the fourth day of an eight-day mission. Earlier today the cabin temperature suddenly rose to an uncomfortable 90 degrees Fahrenheit after the astronauts were told to dump the craft's waste water tanks with their heaters on so as to clear any ice that may have formed on outside vents.

On the previous shuttle mission, ice had blocked the vents and the astronauts had to knock it loose with the shuttle's mechanical arm.

But the only sign that it was warm came later during a live telecast of the crew's activities. All were in shirtsleeves, and astronaut Kathryn D. Sullivan, scheduled on Thursday to become the first American woman to walk in space, was wearing light-blue shorts.

Though they were in the fourth day in orbit, the crew members were so busy that they hardly had been heard from. Crippen and astronaut Sally K. Ride were doing almost all the talking. Navy oceanographer Paul Scully-Power had said only one thing since being spaceborne.

Canadian Navy Cmdr. Marc Garneau kept silent in spite of pleas from the Canadian press that he say something about being the first Canadian to go into space.

So laconic is Garneau that Canadian reporters refer to him as "the Right Stiff."