NASA IRTF: Providing Mission Support for NASA
by Louise Good
At a time when news about
astronomy is dominated by observations made from space or with giant ground-based
observatories, you may be surprised to learn that NASA still regards a
3-meter telescope as essential to its mission. The NASA Infrared Telescope
Facility (IRTF), a 3-meter (10-foot) telescope on Mauna Kea, is managed
by the University of Hawaii through the Institute for Astronomy. Since
it became operational in 1979, NASA has supported the IRTF because it provides
time-critical observations in support of solar system exploration missions.
Mauna Kea's dry, stable air is a huge advantage for the IRTF, which is
able to study objects that would be difficult or impossible to observe
from a lower altitude because water vapor in the atmosphere blocks radiation
at some infrared wavelengths.
IRTF Division Chief Alan
Tokunaga explains the importance of the IRTF this way: "The IRTF fulfills
a need for the planetary astronomy community by providing access to a dedicated
planetary telescope at one of the best sites on Earth. It is an integral
part of the planetary astronomy research program at NASA. The IRTF also
complements planetary observations obtained at larger telescopes, such
as the 8-meter Gemini North Telescope and the 10-meter Keck telescopes.
A large telescope has clear advantages in light-gathering power, and is
the instrument of choice for observations of faint sources. However, many
solar system objects and many other celestial objects are bright enough
and do not require the light-gathering power of an 8- or 10-meter telescope."
Because half the IRTF's
observing time goes to planetary projects, it has been able to provide
extensive long-term observations to image the atmospheres of Jupiter and
Saturn and to study the composition of small objects in the solar system
(satellites, comets, asteroids). What happened when the Galileo spacecraft
arrived at Jupiter illustrates the value of the IRTF. Because Galileo's
main antenna was disabled, it was unable to provide detailed images of
the entry point for the probe that was to enter Jupiter's atmosphere. Observations
by the IRTF provided clear evidence that the probe entered a hot spot in
the atmosphere of Jupiter, a piece of information critical to accurately
interpreting the data sent back by the probe.
IRTF is also now a major
source of new information on the composition of asteroids, especially the
ones that come very close to the Earth. These "near-Earth asteroids" are
particularly interesting because we need to know where they come fromÑsome
of these occasionally hit the Earth with major consequences.
The IRTF also gives students
and researchers hands-on experience in using instruments and obtaining
observations, and it allows a rapid response to changing research needs.
In addition, unique instruments that support planetary science are tested
and used there.
But while Mauna Kea is
the best site in the world for an astronomical observatory, its altitude
makes it somewhat difficult for human beings to function as they would
at sea level. Fortunately, remote observing over the Internet is now routine
at the IRTF, as well as at most of the other telescopes on Mauna Kea. While
telescope operators still work at the summit, some astronomers now observe
on the IRTF from the mid-level facility at Hale Pohaku, from the IfA's
Hilo and Manoa offices, and even from their home institutions on the mainland
and in other countries. This saves traveling time and money, and it also
enables scheduling that is more flexible, since a night of observing time
is then more easily divided among several projects.
Lars Bergknut (left),
foreman of the IRTF day crew, works with technician Sammie Pung to attach
MIRSI, a new infrared camera, to the back of the IRTF.
As part of the cooperative
agreement between NASA and UH, NASA provides the IRTF with an operating
budget of $3.3 million dollars per year. Additional funds come from the
National Science Foundation for the development of new instruments. UH
faculty and students receive 15 percent of the observing time. Other astronomers
may apply for the rest of the time, which is evenly divided between planetary
and nonplanetary projects.
A team of committed
IfA employees is continually upgrading and optimizing the telescope and
its instruments. This group includes over 20 engineers, technicians, computer
programmers, administrative staff, and of course, scientists. Most work
in Hilo and on the Mauna Kea summit; some are based in Manoa.
One of the newest IRTF
staff members is Deputy Division Chief Eric Tollestrup. Actually, he is
not really new to the IRTF, since as a UH graduate student (PhD, 1987),
he used it for his dissertation. When the IRTF first opened, the only infrared
cameras available had a single element (1 pixel) that was used to painstakingly
scan an area of the sky. As part of his graduate work at IfA, Tollestrup
built one of the first infrared arrays that enabled users of the telescope
to "see" a larger area of the sky at a time. This array had 32 x 32 pixels. The NSFCam now in use has 256 x 256 pixels, and IRTF Support Scientist John Rayner
is working on a new camera that uses an array that is 2048 pixels square. "Back
in the early 1980s, the old AT1 photometer was in a box the size of a toaster.
The box containing SpeX (one of the facility instruments now mounted on
the back of the telescope), is the size of a large desk, and it weighs
over 1,000 pounds," Tollestrup explained. In fact, so many things
have been added to the back of the telescope that it was recently checked
by structural engineers to make sure it would not collapse under the weight.
Indeed, a lot has changed
since Tollestrup first used the IRTF. One of the most obvious changes is
the outside of the dome. What used to be white is now a shiny silver to
better reflect the Sun's heat, one of the many measures taken to reduce
heat inside the dome, where the temperature is near freezing. All infrared
instruments must be kept very cold to avoid introducing thermal noise from
the surrounding environment and the telescope itself. Most are kept in
a dewar, a high-tech thermos to which a refrigerant (liquid nitrogen or
liquid helium) is added. However, the facility instruments on the IRTF
are enclosed in closed-cycle coolers (rather like big freezers) that allow
them to be left mounted on the telescope for long periods of time.
As part of the ongoing
effort to improve the IRTF, Systems Programmer Tony Denault (shown here
in the Hilo IRTF lab) is leading the team to develop a new telescope control
system. The current one, which was state of the art when it was created
in the 1970s, will be replaced soon.
The people who work at
the telescope on a daily basis include Superintendent George Koenig, Foreman
Lars Bergknut, and technicians Imai Namahoe, Sammie Pung, and Maury McQuat.
They maintain and repair the telescope, and its building, dome, and instruments.
At night, when most observations take place, Telescope Operators Bill Golisch,
Dave Griep, and Paul Sears take over.
For more information:
Why Use an Infrared Telescope?
Some Recent Solar System
Discoveries Made with the IRTF
IRTF Web site