APn  07/20 0313  Better Telescope

Copyright, 1990. The Associated Press. All rights reserved.

By PAUL RECER    AP Science Writer

   WASHINGTON (AP) -- New technology may give ground telescopes a clearer view
of the stars than is possible from a repaired Hubble Space Telescope and at only
a fraction of the cost, according to a study published today.
   Horace W. Babcock, the former director of the Carnegie Institution
observatories, said in the journal Science that new telescope systems now being
developed hold the promise of seeing stellar objects as far away as those
thought to be visible only by a perfectly working Hubble.
   Babcock said the new system uses a mirror that can be warped, or deformed, in
a systematic way to compensate for the distortion of the atmosphere. The process
is called "adaptive optics."
   "Adaptive telescopes in the infrared will not match the resolution of the HST
(Hubble Space Telescope), but in the visible they may exceed it," Babcock's
paper said.
   Babcock said in an interview that even if the new telescope concepts fulfill
their promise, orbiting observatories still are needed because the Earth's
atmosphere scatters light in some parts of the spectrum, such as the
ultraviolet. Only telescopes in space, above the atmosphere, could collect such
light, he said.
   But for visible light, he said, adaptive optics could allow ground telescopes
to match or exceed the capabilities of Hubble.
   "These are more than just dreams," Babcock said.
   The European Southern Observatory in South America already is experimenting
with adaptive optics and "has proven the value of these systems" in the infrared
portion of the spectrum, he said.
   To adapt the technique for the visible spectrum will require more
experiments, he said, but researchers already have proven elements of the
system.
   Installing adaptive optics in a new telescope, Babcock said, would be "only a
fraction of the total cost" of the Hubble. He said an 8-meter telescope could be
built at some locations for about $40 million.
   NASA spent $1.5 billion to build the space telescope. Engineers learned last
month that it is crippled by a mirror that gives an out-of-focus view of the
universe. The flaw may be corrected in 1993 when a new camera is installed.
   John Manges, an optics engineer on the Hubble project at NASA's Goddard Space
Flight Center, said adaptive optics on ground telescopes could exceed the
clarity of Hubble "in years to come, eventually."
   Even now, he said, "adaptive optics are getting competitive with the Hubble
in the visible region."
   But Manges pointed out that even with new ground systems, an orbiting
telescope would have an advantage because it would not be affected by weather or
clouds. Ground observatories cannot work on cloudy nights and some are affected
by high winds. An orbiting telescope also is able to observe in the ultraviolet
portion of the spectrum, which is impossible from the ground, he said.
   Babcock said the adaptive optics system works by using a mirror that changes
shape rapidly with computer instructions.
   "When the right instructions are sent to a deformable mirror, it deviates
from flatness in such a way to correct for the distortions caused by the
atmosphere," he said. "This will compensate almost entirely for the distortion."
   A telescope with adaptive optics will first focus on a bright star and use
the twinkling light to establish a pattern. The shape of the deformable mirror
then is changed as needed to compensate for the twinkle caused by the
atmosphere.
   Babcock said the optics, in effect, create a circle of compensation through
which the telescope could look far into the universe.
   "Any faint object, if it falls within that circle, can be observed with very
high resolving power," he said. Asked if such a telescope could see objects 14
billion light years away, which is the range expected from a perfectly working
Hubble, Babcock said, "There is no reason why it shouldn't work at such a
distance."
   Science, which published the report, is the journal of the American
Association for the Advancement of Science.