ROANOKE TIMES 

                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: SUNDAY, April 29, 1990                   TAG: 9004290081
SECTION: NATIONAL/INTERNATIONAL                    PAGE: A4   EDITION: METRO 
SOURCE: 
DATELINE:                                 LENGTH: Medium

TELESCOPE'S TROUBLES CONTINUING

Engineers tried unsuccessfully to resolve a problem with the Hubble Space Telescope's large communications antennae Saturday and said the $1.5 billion instrument may have to operate without full use of the antenna system.

The long-term impact on the science return from the Hubble mission, expected to last at least 15 years, was unclear, but engineers said they are optimistic.

"It's pure speculation at this point," said NASA's Jean Olivier, an engineer checking out the telescope's systems in orbit. "But I wouldn't expect the science would be seriously crippled."

NASA has set up a special team of experts nationwide to trouble-shoot the problem. Controllers are communicating meanwhile with the spacecraft by means of its smaller, slower low-gain antenna, but "about all we can do right now is maintain its health and safety," Olivier said.

The problem developed early Friday, when one of the two high-gain antennae was shut down by a computer when its swiveling motion developed too much force and alarmed the robot brain. The computer put the entire spacecraft into a semi-dormant state, known as a "safe mode." This maintained its fixed attitude in orbit and protected it until human controllers at Goddard Space Flight Center in Greenbelt told it what to do.

Engineers gradually brought the spacecraft back to a normal operating mode Saturday. Their next priority was to find a way to use the No. 1 high-gain antenna, which is functioning normally, without moving the No. 2 antenna, the one in difficulty.

However, both antennae are linked through the computer software so that it is impossible to send power to one without sending power to the other.

When engineers twice sent up a command for the healthy antenna to swivel while the No. 2 antenna remained motionless, the No. 2 antenna began to build up pressure and "dither" back and forth even though telemetry indicated it was not swiveling. This forced engineers to halt the operation, said Michael Harrington, who directs the check of the telescope's operation in orbit.

"My frustration level is a little higher today," he said, "but I think we'll solve it." - The Washington Post 


 by CNB