Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: FRIDAY, July 20, 1990 TAG: 9007200662
SECTION: NATIONAL/INTERNATIONAL PAGE: A/1 EDITION: EVENING
SOURCE: The New York Times
DATELINE: LENGTH: Medium
A consortium of eight European governments, the European Southern Observatory, has already begun operating a prototype telescope using a corrective system that compensates for the atmosphere's distorting effects.
In a telephone interview from the consortium's headquarters in Garching, West Germany, Dr. Harry van der Laan, director of the consortium, said Thursday that the instrument, which is substantially larger than the Hubble telescope, has begun producing images that rival the quality of those that had been expected from the Hubble.
The new ground-based telescope is part of an observatory complex operated by the consortium at La Silla in Chile.
"Technically, we're still testing the system," van der Laan said. "But the sharpness of images we're getting is equal to the sharpness you would expect to obtain in space. Beginning in August, the telescope will be put to work on its first major research programs. It works."
The same system also will be used in a huge proposed telescope to be built in Chile that should be able to gather substantially more light than the Hubble telescope and provide an image that is just as sharp as the space telescope was supposed to achieve, van der Laan said.
The $1.5 billion Hubble telescope, launched on April 25, was intended to detect objects in space that are 25 times fainter than the dimmest objects observable from Earth. But a flaw, apparently in the Hubble's main light-gathering mirror, has prevented the 43-foot telescope from functioning properly.
One of the measures of a telescope's sharpness is its ability to distinguish between objects very close together. This ability, or resolving power, is expressed in terms of a unit called the arc second, an angle equivalent to one 3,600th of a degree.
The Hubble telescope was designed to have a resolving power of 0.10 arc seconds, but its poor optics smear out most of its imaging energy power to 0.8 or 0.9 arc seconds. The new European telescope has a resolving power of 1.7 arc seconds. The best resolution ever obtained for a ground-based telescope without adaptive optics was about 0.25 arc seconds.
The Hubble telescope was designed to incorporate 1960s-era technology and was built before the development of self-correcting optical systems driven by fast computers. Many astronomers contend that if a new space-based telescope were to be designed today it would be built very differently from the Hubble.
Van der Laan said that the success of the "adaptive optics" corrective system built into the European consortium's new telescope meant that similar adaptive optics would be used in the group's Very Large Telescope, an instrument that will dwarf all other existing or planned telescopes. Completion of this telescope at its observatory in Chile is scheduled for 1998.
All the new ground-based telescopes greatly exceed the light-gathering power of the Hubble telescope, which is a relatively small instrument. Light-gathering power is an important measure of a telescope's value.
The Very Large Telescope, combining light collected by four enormous mirrors, will have a light-gathering power more than 50 times greater than the Hubble telescope and 10 times greater than the 200-inch telescope at Mount Palomar, the largest existing American telescope.
"With its adaptive optics," van der Laan said, "the VLT will offer the image sharpness of a space-based telescope and a light-collecting power 50 times greater than that of the Hubble, at about one-tenth the Hubble's cost." The addition of adaptive optics to the $180 million Very Large Telescope is expected to increase the telescope's cost by about $7 million, he said.
Van der Laan said the consortium's optical scientists had long urged the National Aeronautics and Space Administration to install a self-corrective optical system on the Hubble Space Telescope.
"When you can't readily fix optical errors by hand," he said, "you must have some corrective system aboard the spacecraft itself."
The lack of such a system means that the Hubble's optical defects will have to be corrected by some future manned space mission capable of installing a new corrective lens.
by CNB