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Subject: Revolutionary Vision Produces a Bigger and Better Telescope<By Kathy
Date: Mon, 26 Oct 92 04:30:31 EST
Message-ID: <39.1992Oct26.043031@AmeriCast.com>

Revolutionary Vision Produces a Bigger and Better Telescope<By
Kathy Sawyer=Washington Post Staff Writer=

Fifteen years ago, the experts laughed when a young California
scientist named Jerry Nelson outlined his revolutionary design
for a new kind of telescope.

Today, almost $100 million later, his far-out vision has been
converted into 270 tons of glass, steel and computerized gizmos
atop the forbidding summit of the dormant volcano Mauna Kea in
Hawaii.

By far the world's most powerful telescope for optical and in-
frared astronomy, the 10-meter (33-foot) Keck is for now the pa-
cesetter in a worldwide race to build astronomy's version of a
better mousetrap: a new generation of giant "eyes" that will har-
ness new technologies to peer at ever fainter and more distant
objects.

The Keck, whose segmented fly-eye mirror was completed earlier
this year, is designed to double the observing power of any ex-
isting telescope, and reveal details in infrared with two to
three times greater precision.Twin Facility Underway<

Though the Keck is still being "debugged," its performance in in-
itial tests has been so impressive that the people who paid for
it - the W. M. Keck Foundation, the California Institute of Tech-
nology and the University of California - recently broke ground
for construction of a twin facility nearby.

In telescopes, power generally depends on size: Bigger mirrors
capture more starlight. But until recently, the sheer unwieldi-
ness of large conventional mirrors appeared to set an engineering
limit on telescope size. The thickness required to give a re-
flecting monolith the necessary strength also made it massive.
The more the mass, the higher the chance that its own weight
would deform it, and the longer it would take to cool or heat it-
self nightly to match the surrounding temperature - a process
that alters its shape. These effects can destroy a mirror's abil-
ity to focus light.

The Hale Telescope on Mount Palomar in California, completed in
1947, features a 16 1/2-foot mirror that weighs 20 tons. After
casting, it took a year to cool and 11 years - including a break
for World War II - to grind to the desired shape. The Soviets
later built a 6-meter (20-foot) telescope whose mirror weighs 42
tons; by all accounts, this massiveness has impaired its perfor-
mance.

Using New Technologies<

Then in the 1970s, for the first time since Galileo, new computer
and other technologies enabled telescope engineers to consider
radical departures from standard design. Today, engineers are
developing large, rigid, single mirrors that are nevertheless
light because they are honeycombed with air, as well as large but
extremely thin "floppy" mirrors with elaborate supporting mechan-
isms to shape them.


Nelson's idea - originated in 1977 when he was 33 and working at
the University of California at Berkeley - was to build a mirror
out of 36 small, thin pieces - "like bathroom tiles," as he put
it. He proposed to grind and align them so precisely, using tiny
pressure sensors and push rods, that they would behave like one
big mirror. Though it would have about twice the diameter of the
20-ton Hale mirror, the total weight of all the glass, including
spare segments, was to be 14.4 tons.

At first, said a prominent astronomer who asked not to be named,
few in the field believed Nelson's idea could work. "The great
telescope experts, pushing that same idea, might not have gotten
as far. They didn't have the personality to spit in the face of
every expert in the world. . . . Nelson has chutzpah. He is un-
stoppable. He probably has a touch of the (Gen. H. Norman)
Schwarzkopf in him."

Overcoming the Skeptics<

Nelson, who describes himself as "thick-skinned and blockheaded,"
said that what it really took was "endless hours of computer
modeling . . . a lot of mathematics and very specialized
hardware. Our approach was to bury (the opposition) with facts."

In the early 1980s, he and his research team built a demonstra-
tion system and proved that the "pieces played well together," he
said. At this point, a lot of former skeptics took the leap of
faith - and the funding came through.

The team discovered that the optics industry, using conventional
methods, would require 30 years to build the segments. So they
invented their own technique.  They knew this would be the trick-
iest part, Nelson said, but it was even harder than expected.

Each of the 36 thin (three-inch thick) hexagonal mirror segments
had to be polished to a precise shape in order to perform proper-
ly as part of the whole. Each had to be formed asymmetrically, as
if it were a piece lifted from a single big curved mirror. This
required polishing tolerances 1,000 times more precise than a
single mirror.

The new procedure allowed optical workers to polish each segment
to a symmetrically curved shape in the normal way. But the mirror
blank was gripped in a metal "jig" that applied mathematically
determined forces to distort the glass surface slightly. When the
force was released, the polished segment relaxed into the re-
quired asymmetrical shape.

To work in the telescope, all the segments must hold their align-
ment relative to each other despite forces induced by the
telescope's motion across the sky, and despite changes in tem-
perature. This was the job of a complex network of 108 motorized
"actuators" and 168 electronic pressure sensors beneath the mir-
rors. The sensors detect the exact position of each segment and
send the data to a computer system. The computers then command
the array of actuators - motor-powered screws that push hydraulic
levers - to move the segments whatever microscopic distances are
required.  An Ideal Location<

This cycle is repeated twice each second, refining the mirrors'
alignment to a tolerance of less than a millionth of an inch.
This is the standard of accuracy required to focus starlight
properly.

The telescope's location at the 13,600-foot level of Mauna Kea,
with its cold, dry, low-oxygen atmosphere, is ideal for astrono-
my. Those same conditions, plus occasional wind gusts up to 150
mph, make it hostile to humans.

The team still wasn't sure the intricate system would work until
December 1990, when the telescope took its first look at the sky
with just nine of the mirror segments in place. Possibly the
worst fear, said  Terry Mast, who has worked with Nelson since
the beginning of the design effort, was that vibrations in the
control mechanisms would prevent the mirror from ever getting
still. "We only knew we were over the hump when we saw the first
pictures."

Some scientists still wonder if the Keck is not too complex. "The
early tests are very encouraging," said Frederic H. Chaffee Jr.,
director of the 15-foot Multiple Mirror Telescope at the Steward
Observatory in Arizona, the first "computer intensive" optical
telescope. "But there are a lot of bugs to work out. For example,
will it require constant vigilance when it's used night after
night?"<02:32 10-26C9999-----

Copyright 1992, The Washington Post.  This story is from the
Washington Post's Capitol Edition On-Line and is not to be ar-
chived or redistributed.

For more information, send-email to American Cybercasting Cor-
poration (usa@AmeriCast.COM)