With a successful launch, Cornell team prepares to survey the Infrared sky

By David Brand and Blaine P. Friedlander Jr.

Artist's rendering of the telescope with its communication antenna turned toward Earth NASA/JPL-Caltech

Since 1984 Houck has been heading a NASA team at Cornell developing an instrument called the Infrared Spectrograph (IRS) which could provide new information about the early universe, studying nascent stars that previousluy have been hidden from view by clouds of insterstellar dust. The observatory consists of a telescope with a 33.5-inch-diameter (85-centimeter) mirror, the Cornell spectrograph and two other instruments designed to detect infrared radiation, much of which cannot be observed from the ground because it is blocked by the Earth's atmosphere.

The IRS, said Houck, who is the Kenneth A. Wallace Professor of Astronomy, "will be the best instrument on board the observatory for the job of providing detailed physical information about distant targets." The instrument provides a spectrum of a distant object. Whereas an image merely indicates where an object is and what it looks like, a spectrum puts the object "under the microscope" and dissects it.

The IRS breaks up incoming light into its component colors (its spectrum) and measures the strength of each. The distribution of light in the colors - and particularly the presence of gaps and surpluses, called absorption and emission lines - forms a unique Ūngerprint for an object. This fingerprint reveals clues to the composition of a remote object, its temperature and its motion.

The IRS will peer into deep regions of the universe not visible optically, and, it is hoped, will provide clues about when star and galaxy formation began. The IRS can penetrate obscuring galactic dust and observe ultra-frigid, newly forming stars in the coldest regions of the universe.

Cornell's $39 million IRS contract is with the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which is managing the SIRTF mission. Although the mission will be largely tracked at JPL, the flood of IRS data will be mined at the IRS Science Center (ISC) in the Space Sciences Building. The IRS team has 34 different observing projects, from quasars to the giant planets and their satellites. Two dozen researchers from Cornell and around the United States are involved, including Terry Herter, Cornell professor of astronomy, research associate Dan Weedman and staff scientist Don Barry, as well as former Cornell graduate students Tom Roellig, deputy investigator, now at NASA Ames Research Center, and Tom Soifer, coinvestigator, now at California Institute of Technolgy.

The orbiting telescope is the last mission of NASA's Great Observatories program, which includes the Hubble Space Telescope, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory. It also is the first mission of the space agency's Origins Program, aimed at studying the formation of galaxies, as well as stars and planets, to provide basic information about the origins of life in the universe.

During the five-year life of the $500 million SIRTF mission, according to Houck, astronomers probably will gain a new view of the heavens. "This telescope will be 100 to 1,000 times more sensitive than any previous infrared instrument," he notes.

The observatory will trail the Earth in its orbit around the sun, with the instruments functioning in an environment where temperatures are slightly above absolute zero.

Cornell's SIRTF/Infrared Spectrograph (IRS) team, with principal investigator, professor of astronomy James Houck, seated in foreground. Cornell University Photography Copyright © Cornell University

The two other instruments on SIRTF, a multiband imaging photometer and an infrared array camera, will be concerned mainly with discovering new targets. The three instruments are encased in the observatory's cryogenic telescope assembly - also containing the telescope itself and the liquid helium cooling tank, maintained at a degree or so above absolute zero because infrared detectors are extremely sensitive to heat.

Some of the most exciting discoveries are likely to come from the first, close-up infrared look at galaxies formed in the early universe - blue compact dwarf galaxies ranging in distance from 3 to 30 million light years and composed largely of helium and hydrogen. Indeed, these galaxies contain as little as 2 percent of the solar system's share of heavy elements.

"This will be an opportunity to measure the infrared properties of galaxies that might be similar to the galaxies formed soon after the big bang," said Houck. In the optical part of the spectrum these dwarf galaxies are characterized by blue colors, a high surface brightness and narrow emission lines -- all the hallmarks of recent star formation, but only a hint of what infrared observation might reveal.

In 1978 Houck conducted infrared experiments from airplanes. It was then that he and his colleagues persuaded NASA there was an opportunity for placing a great telescope into space to study the infrared band of the spectrum and perhaps uncover previously unseen parts of the universe. NASA agreed and sent out a request for proposals in 1983. In April 1984 Houck received the space agency award. That award, after several design and mission changes, has become the IRS.

In the first two years of SIRTF's expected life span, the Cornell team is guaranteed 875 hours of observing time, beginning three months after launch. "The sensitivity of SIRTF is such that five minutes of observing time will achieve the same sensitivity as a year of observing on any previous infrared spectrometer, ground-based or in space," said Houck.