Experts try to coax Hubble to perform

Like interplanetary movie directors, scientists and image-processing experts are prompting the Hubble space telescope to produce some dazzling pictures for a critical but expectant public.

"Coming attractions may include pictures of a nearby galaxy with a possible black hole, Pluto and its moon Charon, Saturn, and the Crab nebula, a remnant of a supernova explosion," predicts Ray Villard, a spokesman for the Space Science Telescope Institute in Baltimore.

The Hubble's first significant computer-enhanced images, released in August, portrayed a cluster of 60 stars in a galaxy, a gaseous ring around a supernova - both 160,000 light years from Earth - and the dense core of a galaxy 40 million light years away. They proved the Hubble, despite its mirror troubles, still has unexpected viewing power.

Some experts say the images are 10 times better than pictures that could be obtained by current ground-based telescopes.

But the $2 billion Hubble, the most powerful telescope ever launched into space, still won't live up to expectations until it gets the equivalent of new spectacles to correct a severe case of myopia, which became apparent shortly after it opened its giant eye in the sky last April.

Using visible light focused by the telescope's two mirrors, a wide-field planetary camera on the spacecraft was expected to produce unprecedented views of galaxies, planets and stars that would rewrite astronomy textbooks. But a flaw in one of the mirrors has created fuzzy vision.

The Hubble's eyesight won't be corrected until a replacement camera, due for launch aboard a space shuttle between January and June 1993, is fitted to the telescope. Focus of the 595-pound camera, already being readied at NASA's Jet Propulsion Laboratory in Pasadena, Calif., will be modified to offset the mirror problem.

In effect, it will provide the new glasses that will sharpen the vision of the Hubble's near-sighted Cyclops eye.

"Studies of individual stars and strong, distant light sources such as quasars are still possible," says Stephen Maran, a scientist at NASA's Goddard Space Flight Center. "But the fuzzy image we're getting makes it difficult to zero in on very distant galaxies and tightly packed star clusters."

But even some of these more difficult distant pictures may become possible if some of the nation's leading image processors can work their magic and digitally enhance the Hubble's blurry vision.

A lot depends on finding the best possible focus and calibrating the filters for the wide-field planetary camera. It may take a few weeks or months to accomplish this, but images will improve significantly, says Richard L. White, associate astronomer at the Space Telescope Science Institute.

Achieving such a focus will be essential in manufacturing the backup camera in Pasadena. "What we're looking for now is the best prescription for those glasses," White told National Geographic.

Replacing the camera in orbit will be an exacting task. The shuttle must maneuver close to the telescope to grasp it with a robotic manipulator arm and then gently place it on a special cradle in the shuttle's large, open cargo bay. Payload specialists must leave the safe confines of the shuttle cabin to do the work.

"This involves a certain amount of risk," says Maran. "There's the danger to the astronauts, who are vulnerable to pieces of space junk or to tiny micrometeorites zipping around in space, and to the instrument, which they must carefully and precisely mount on the telescope."

It should be a straightforward repair mission. "But there's always a challenge in something like this," says Navy Capt. Bruce McCandless II, who worked as a payload specialist on the shuttle mission that deployed the Hubble.

NASA scientists point out the Hubble was designed to do much more than produce pretty pictures.

On-board instruments such as spectrographs, a high-speed photometer and fine-guidance sensors are expected to accomplish as much as 50 percent of the mission's planned scientific goals - even searching for some of astronomy's most elusive objects, planets orbiting other stars.

Likely Source of Hubble Error

The device for checking the shape of the Hubble space telescope's main mirror, called a null corrector, was set up with a spacing error of about 1.3 millimeters.

A metering rod was used to set up the device. The end was supposed to reflect a light beam centered by a pinhole. Investigators say the measurements were confused by light reflected from the end cap.