News Release

* Until HUT's maiden flight, the part of the spectrum it observes was a largely unexplored region. Only two previous space instruments had studied objects in that range of the UV spectrum. The Copernicus satellite observed some of the brightest stars in our galaxy in the far ultraviolet region at very high spectral resolution during the 1970s, and the Voyager probes studied the outer planets and a few other objects in the far and extreme UV wavelengths at very low resolution in the 1980s. HUT is much more sensitive than either of these earlier instruments, enabling it to observe much fainter stars, galaxies and quasars.

* Johns Hopkins astrophysicists and engineers designed and built HUT in Baltimore and at the university's Applied Physics Laboratory in Laurel, Md.

* HUT was one of four telescopes included in the Astro-1 mission, which flew aboard the space shuttle Columbia for nine days in December 1990.

* HUT is one of three telescopes included on the Astro-2 mission, scheduled for launch on the space shuttle Endeavour in March 1995. Astro-2 is planned to last up to 16 days.

* HUT is 12 feet long, 4 feet in diameter and weighs about 1,700 pounds. It has a 36-inch-diameter (0.9-meter) primary mirror. HUT and the two other Astro-2 telescopes will be mounted on two pallets in the shuttle's payload bay. All three instruments are attached to an Instrument Pointing System that allows astronauts to aim the telescopes precisely at astronomical targets.

* HUT separates UV light into a spectrum that can be studied in detail, just as visible light can be separated into its component colors, or wavelengths. By breaking light into its constituent colors, scientists can learn about the chemical composition, temperature and other properties of objects.

* HUT uses a special television camera to identify desired targets and to verify that the telescope is pointing accurately during observations. This information is important for the other Astro telescopes as well.

* HUT's principal investigator is Arthur F. Davidsen, a Johns Hopkins professor of physics and astronomy who has led the HUT project since its inception in the late 1970s. Astrophysicist Samuel T. Durrance, a principal research scientist at Johns Hopkins, will fly on the shuttle as a payload specialist. Dr. Durrance was a payload specialist on Astro-1, when he became the university's first astronaut. Gerard A. Kriss, a member of the research faculty at Johns Hopkins, has overseen the overall preparations of the telescope for its flight on Astro-2.

* HUT has been improved significantly for Astro-2, and should be about three times more sensitive to radiation in the far ultraviolet spectrum.

Improvements include:
The primary mirror has been coated with silicon carbide, replacing the iridium coating on the original HUT mirror. Silicon carbide is much more reflective to far UV light.

The spectrograph grating, which diffracts UV light into a spectrum, also has been coated with silicon carbide, replacing the grating's original coating of osmium.

The photocathode, an essential component of the detector that senses ultraviolet light, has been given a new coat of cesium iodide, since the original coat lost sensitivity with age. The inside of the spectrograph is kept in a vacuum at all times to maintain the coating's sensitivity to UV light.

* All of these changes, along with improvements to the Instrument Pointing System, should allow HUT scientists to gather up to 10 times more data than they did on the first Astro mission.

* HUT will be used to study a wide variety of objects, ranging from our own galactic neighborhood and solar system to very distant objects near the edge of the observable universe. The highest priority for Astro-2 will be to search for the intergalactic medium left over from the primordial fireball that many scientists believe marked the birth of the universe about 10 billion to 20 billion years ago. HUT astronomers will attempt to analyze light shining through this gas by observing distant quasars.

* More than two dozen faculty, staff and students are currently involved in the HUT project.

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