NASA engineers in Alabama have been climbing a Texas mountain for
the past year to help astronomers reach deeper into space with the world’s
third-largest telescope.

The McDonald Observatory on Mount Fowlkes near Fort Davis, Texas, is
home to the Hobby-Eberly Telescope. When astronomers there needed expertise
in how to handle temperature extremes that affect the telescope’s viewing
capability, they hired the engineers of NASA’s Marshall Space Flight Center
in Huntsville, Ala.

With more than 30 years of experience developing sophisticated
optical systems for space exploration, the Marshall Center is NASA’s lead
center for optics manufacturing and technology development.

The University of Texas at Austin, which owns and operates the
McDonald Observatory, awarded the Marshall Center a $695,000 contract in
November 1999 to design a Segment Alignment Maintenance System for the
Hobby-Eberly Telescope.

John Rakoczy, lead engineer at Marshall working on the alignment
system, said the project is a chance for Marshall’s optics team to showcase
its talents by working on ground-based telescopes in addition to those
designed to operate in space. Other ground-based observatories could be
potential customers of Marshall’s optics facilities and team, Rakoczy said.

“By teaming our expertise with industries, not only do they benefit,
but the space program benefits as well,” Rakoczy said. “Working on the
Hobby-Eberly Telescope gives the McDonald Observatory the benefit of our
years of optics experience. At the same time, this project gives the
Marshall team the opportunity to further our knowledge about working with
segmented mirrors.”

With a 36-foot (11-meter) primary mirror made up of 91 hexagonal
segments, the telescope is the third largest in the world.

As telescopes have become bigger, both on the ground and in space,
the reflecting mirrors that make them work are increasingly being made in
segments – that is, with smaller mirrors fitted together to make one large
mirror. Since even small temperature fluctuations can cause these mirror
segments to move out of alignment, and thus limit a telescope’s focusing
capability, one remedy is to incorporate a system that will automatically
keep the segments aligned and in focus.

“Temperature changes are the great enemy of telescopes,” Rakoczy
said. “Even a fraction of a degree can affect alignment of large, segmented
mirrors. When you’ve got something as big as the Hobby-Eberly Telescope,
you’re trying to keep the mirror segments aligned within tens of

A nanometer is equal to one-billionth of a meter — a distance so
small that it can’t be seen with the human eye or even with a conventional
optical microscope. For comparison, the head of a pin is about a million
nanometers in diameter.

The alignment system uses electronic sensors to monitor the gaps
between mirror segments. When the sensors detect any change in mirror
alignment, the system compensates by sending computer-controlled directions
to a series of small motors under each mirror segment. These directions are
determined using highly sophisticated mathematical algorithms. Three motors,
or actuators, are under each mirror segment and move the segment back into
correct alignment.

The Marshall Center is developing the control system and software
and is responsible for overall system integration. The center is teamed with
Blue Line Engineering of Colorado Springs, Colo., which is providing the
sensors and electronics.

“Blue Line is responsible for defining the overall system
architecture and developing the sensor assemblies, local electronics, and
distributed system control processing – everything in the dome,” said Edward
“Sandy” Montgomery, manager of the program for the Marshall Center. “MSFC is
responsible for the part of the Segment Alignment Maintenance System
residing in the control room.”

A prototype system was successfully tested on a few of the mirrors
between October 2000 and April 2001 with a design review completed in May.
Final acceptance testing of the complete system will begin after fabrication
and installation this fall.

The following Web link contains more information on the Hobby-Eberly

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Jerry Berg
Media Relations Department
(256) 544-0034

The Web

News Release


Hobby-Eberly on the Web

Marshall Space Flight Center
Media Relations Department
(256) 544-0034
(256) 544-5852 (fax)