Astronomers hope for the best tonight

December 06, 1993|By Frank D. Roylance | Frank D. Roylance,Staff Writer

In an article in Monday's edition about repairs to the Hubbl Space Telescope, the name of Dr. Francesco Paresce, an astrophysicist at the Space Telescope Science Institute in Baltimore, was misspelled.

The Sun regrets the errors.

The replacement of the Hubble Space Telescope's Wide- Field/Planetary Camera -- scheduled to begin around midnight tonight -- may be the most important thing the Endeavour astronauts do this week for Earthbound astronomers.

Nicknamed "Whiff-pick" (for its abbreviation, WF/PC), the instrument is Hubble's workhorse, carrying out fully half the telescope's observations.

It is capable of "seeing" in both visible and ultraviolet wavelengths and transmitting what it sees back to Earth as photographic images or spectrographic data, which astronomers use to study the physics and chemistry of a star or galaxy.

FOR THE RECORD - CORRECTION

The camera was to have functioned as both the telescope's "wide-angle" and "telephoto" lens, focusing broadly on a galaxy, for example, then zooming in on the galactic core in a search for signs of a black hole.

But when engineers at the Goddard Space Flight Center in Greenbelt, Md., discovered in June 1990 that Hubble's primary mirror had been ground too flat, half of the camera's planned observations -- representing a quarter of all planned Hubble observations -- had to be shelved.

Keeping the camera busy

Astronomers reshuffled their priorities, however, and have kept the camera busy making discoveries among bright, high-contrast objects such as nearby galaxies and star clusters. It has also produced long-term observations of weather changes on Mars, Jupiter and Saturn.

But the primary mirror's defect curtailed the camera's ability to produce sharp images of very faint objects, especially objects in crowded fields of stars.

Among the hundreds of astronomers whose research was devastated by the defect was Dr. Francesco Paresci of the Space Telescope Science Institute in Baltimore. He had planned to use the camera to search for planets orbiting other stars.

Another institute astronomer, Dr. Michael Shara, had hoped to observe a recurrent nova -- a star that explodes every 20 or 30 years -- with the camera. His work, too, is riding on the success of tonight's repairs.

"We really need this and want this to succeed," he said.

Fortunately for these and other astronomers, a replacement camera was already under development at the Jet Propulsion Laboratory in California. Scientists had planned since 1985 to replace the camera during the first Hubble servicing mission with a new and improved model.

Once they fully understood the flaw in Hubble's main mirror, JPL engineers modified one of the new instrument's mirrors, grinding it to a "prescription" that precisely cancels the error in the telescope's primary mirror. If tonight's repairs go well, scientists hope, they will have restored or improved upon Hubble's original capability in wide field and planetary studies.

(Early Wednesday morning, the astronauts are to install COSTAR, which will provide corrective optics to three other Hubble instruments.)

Sharper pictures

WF/PC2 incorporates a new generation of electronic light detectors that are both smaller and more sensitive than the originals, especially to ultraviolet light. Astronomers are hopeful they will produce sharper, more detailed pictures.

The new camera also carries a series of tiny motors, or "actuators," which will allow engineers at Goddard to fine-tune the position of the instrument's mirrors by remote control, ensuring the precise alignment needed for the sharpest possible pictures.

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