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

DATE: THURSDAY, May 10, 1990                   TAG: 9005100615
SECTION: NATIONAL/INTERNATIONAL                    PAGE: A/1   EDITION: EVENING 
SOURCE: Associated Press
DATELINE: WASHINGTON                                LENGTH: Medium

SPACE TELESCOPE THROWN OFF TARGET BY MATH MISTAKE

It was a math mistake everybody has made in a checkbook, but in this case it caused the Hubble Space Telescope to miss its target by trillions of miles.

Somebody added when he should have subtracted. Or vice versa.

Embarrassed NASA scientists gave that explanation Wednesday for the failure of the telescope to find two bright stars. The telescope missed its target by one-half degree - about the width of a full moon as seen from Earth.

"When we were trying to point the telescope to the center of a pretty rich star field with a high probability of acquisition we were really off to one side of that," said Jean Olivier, deputy manager of the Hubble project for the National Aeronautics and Space Administration.

Because of the math error and other problems, scientists won't be able to take the first star pictures with the telescope until next week, NASA said. When the Hubble was launched from the space shuttle Discovery on April 25, they expected the first picture within a week.

In the latest glitch, the telescope was looking for two stars of a certain brightness in the star cluster, but failed. Such guide stars are necessary to tell the telescope precisely where it is pointing; without them it is disoriented.

Astronomers relied on star charts made in the 1950s when they designed pointing instructions for the telescope, Olivier said. But the stars have moved since then from Earth's vantage point. The mistake was made when the scientists factored in the extent of that movement.

They corrected in the wrong direction.

"Instead of subtracting it they added it or vice versa," Olivier said.

"For several days we didn't understand what the problem was and we were thinking we maybe had some problem with the onboard system alignment or the onboard function of the fine guidance system," Olivier said. "Now we can take corrective action and point in the right direction."

More than $2.1 billion has been spent on the telescope and ground facilities. The Hubble has been ready for launch since 1985, maintained at a cost of $7 million a month.

by CNB