Heading into the home stretch of their seven-day mission, the members of the space shuttle Challenger's crew today had 12 of their 15 Spacelab experiments "up and running" so well that they got a green light to proceed with them until early Monday morning, the day they're due to land at Edwards Air Force Base in California.

Mission Manager Joseph Cremin reported that the scientific information sent back to Earth from Spacelab includes more than 200 billion pieces of data.

"We've had 2,484,000 frames of video alone. The data that has been collected equates to enough material to fill 44,000 books, each one of them 200 pages long," he said.

Mission Commander Robert F. Overmyer told Mission Control that he and his six crewmen were "in really good spirits" as they began the fifth day of their flight. "We're ready for a good day," he said.

The day included playtime with the two squirrel monkeys and two dozen white rats aboard the ship.

For the second consecutive day, the monkey that had been space-sick seemed fine, cavorting in his cage like a monkey at a zoo.

"We've got a couple of happy monkeys here today," astronaut/physician William E. Thornton said as he transmitted a telecast of the two in Spacelab. "They really enjoy human companionship; they like attention and they come right up to the window to look at us."

The televised rat was caught on camera eating a food bar, tumbling and turning in its cage. "The rats are all like this one. They've loved every minute of this flight," Thornton said.

The two experiments restored to service by in-flight repairs were working flawlessly.

An experiment that uses sound waves to move drops of liquids in a containerless environment was working so well that physicist Taylor W. Wang spent hours today showing it off to his colleagues on Earth. He rotated the large drop of water and glycerine clockwise and counterclockwise, slowly and quickly, and moved it in almost any direction he chose.

"It's amazing; it's totally different from what we thought," Wang said as he used a computer to move the drops around with three high-frequency sound waves. "One purpose of this experiment is to see if we can make pure and exotic metals and glasses in a containerless environment."

Another experiment involves photographing the auroras lighting the sky this time of year near the North and South Poles. By late today, 16 auroras, almost all of them strikingly brilliant and different, had been photographed.

Meanwhile, NASA announced that Sultan Salman Abdel Aziz Saud, 28, a nephew of King Fahd of Saudi Arabia, will be a member of the Discovery shuttle crew on a flight set for June 12.

The prince, an experienced pilot, will take photographs and help in a medical experiment.