NASA marks Hubble's anniversary, says ills were magnified, plans repair

CAPE CANAVERAL, Fla. - NASA is marking the first anniversary of its Hubble Space Telescope launch this week, with plans for a late 1993 repair mission and assertions that the instrument's ills have been exaggerated.

The $2.5 billion telescope was lifted into space on the shuttle April 24, 1990, and a day later deployed by shuttle astronauts.

After contending with several early technical difficulties, the space agency disclosed on June 26 that the observatory was launched with a major optical flaw. It could not focus sharply on dim, distant objects.

"Looking back ... it was probably a mistake going to the media that quickly," said Ed Weiler, the telescope's chief scientist.

The space agency hopes to correct the focusing problem when spacewalking astronauts install a new Wide Field Planetary Camera on the 380-mile-high telescope in November 1993.

In the meantime, though, many people erroneously believe the Hubble is not functioning at all, Weiler said.

He believes the space telescope has begun to prove its scientific value with crisp images of Mars, a storm on distant Saturn and pictures of distant Jupiter as good as those taken years ago by the Voyager probes.

Hubble's greatest scientific contribution, though, has been in accurately establishing the distance to the Large Magellanic Cloud, he said.

Space telescope observations place it at a distance of 169,000 light years, a figure Weiler said is accurate within 5 percent.

Previous estimates have had an error of about 25 percent.

"This is really the first step in establishing a universal distance scale," Weiler said. "This is still the best optical telescope in the world even with spherical aberration."

The new wide-field camera NASA plans to install will cure the telescope's nearsightedness much like a pair of glasses corrects poor vision in a human.

The space agency also plans to replace the Hubble's big solar arrays, which supply it with electrical power.

Because of a design error, the arrays cause the telescope to vibrate for several minutes when it moves from darkness to light.

Changes in computer software have dampened the vibration some, but an annoying shimmy still cuts into the Hubble's efficiency.

Joseph Rothenberg, the telescope's associate director of flight projects, said two other repairs are planned.

They include replacement of an electronics box with a device containing two mirrors that will improve the operation of two spectrometers and the faint-object camera.

Lastly, the astronauts may replace one of six gyroscopes on the telescope.

Rothenberg said the extent of the repairs will depend on NASA's willingness to plan a mission with four six-hour spacewalks.

Only 15 hours will be required for the tasks, but planners would like a fourth session scheduled as a contingency, he said.