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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