Controllers at the Johns Hopkins University's Applied Physics Lab regained contact yesterday with the asteroid-bound NEAR spacecraft, more than a week after an unexplained computer glitch sent it into protective hibernation.

"We don't know what caused it. We may never know," said NEAR program manager Tom Coughlin. A backup computer has taken over flight operations.

NEAR (for Near Earth Asteroid Rendezvous) was assembled at APL in Laurel and launched in February 1996. It is beyond the orbit of Mars, circling the sun in pursuit of the asteroid Eros.

Plans to orbit Eros by January were canceled when a rocket failed to fire Dec. 23. NEAR snapped photos of Eros as it whizzed by and will make a second rendezvous attempt next year.

Coughlin said NEAR's primary flight computer unexpectedly "rebooted," or reset itself, Feb. 23. The reboot automatically sent NEAR into "Earth-safe," which shuts down most systems but keeps the craft's antenna aimed at Earth to await instructions.

Minutes later it retreated further, into "sun-safe," which turns its solar panels toward the sun but allows only periodic contact with the ground.

Controllers declared an emergency and asked engineers at the National Aeronautics and Space Administration's Deep Space Network to help them find NEAR and regain control.

Satellite computer resets can be caused by cosmic rays or high-energy particles from the sun. But Coughlin said NEAR is "hardened" by metal shielding and has never reset before.

"We don't think we're susceptible to that," he said, but "we will explore it."

Such glitches "scare you to death," Coughlin said. But NEAR's performance during the emergencies "is really a compliment to some of these people who designed the automatic systems on board," he said.

It takes 21 minutes for radio signals to travel between NEAR and Earth, so the spacecraft must protect itself without help from controllers.

"NEAR proved it can do that," Coughlin said.

Pub Date: 3/04/99