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Astro finally eyes X-ray and UV universe.

Astro finally eyes X-ray and UV universe

After nearly two days of delays in orbit caused by technical problems that robbed the Astro Observatory of at least 10 percent of its viewing targets, the shuttle-borne astronomical probe began feasting its "eyes" on a host of galaxies, supernovas and ultrahot stars glowing with X-rays and ultraviolet light undetectable by ground-based telescopes.

"It's like walking into a smorgasbord," said mission scientist Ted Gull on Dec. 4. "Our plate is there and we'd like to fill it quite full."

The shuttle Columbia lifted off with Astro in its cargo bay early on the morning of Dec. 2, setting out for a 10-day journey through space. Originally scheduled to fly in February 1986 -- a month after the Challenger accident -- Astro has failed to achieve launch in four attempts since last May.

The observatory features two ultraviolet spectrographs, an ultraviolet camera and a broad-band X-ray telescope. Among its first accomplishments:

* The highest-resolution ultraviolet spectrum ever obtained of Earth's uppermost atmosphere, which extends beyond Columbia's orbit. Researchers must correct for this atmospheric "airglow" in order to interpret Astro's measurements of ultraviolet emissions from distant stars and galaxies.

* A short-exposure spectrum in the ultraviolet, which includes previously undetected wavelengths below 1,200 angstroms emitted by a Seyfert Type I galaxy called NGC4151, whose spiral arms spew intense radiation as the galactic center sucks in matter. Such spectra may help reveal whether a black hole lurks at the galaxy's core.

* A preliminary X-ray spectrum of the bright binary star Capella, showing emission lines from ionized iron and silicon. The emissions' relative intensities provide clues to how fast this Milky Way member burns its nuclear fuel.

These successes notwithstanding, the mission's early days were severely hampered by problems with one of the shuttle's two computer keyboards, the X-ray telescope's automated pointing system, and the automated pointing system for the three ultraviolet instruments. The pointer setbacks prevented observations of at least 25 of the 250 planned viewing targets, says Gull.

On Dec. 4, software specialists finished repairing the pointing system for the X-ray telescope. Several other software adjustments had improved the alignment of the three computer-guided pointers for the ultraviolet instruments and had reduced one pointer's excessive light sensitivity, helping the ultraviolet trio to lock onto astronomical objects in unison.

The shuttle astronauts must still resort occasionally to the time-consuming task of using a "joystick" and TV images -- much like a video game -- to help the ultraviolet instruments' automatic and manual pointers keep target objects in view.

With the malfunctioning keyboard down for the duration, the shuttle crew has had to operate both Astro and Columbia with a single keyboard, further reducing observing time, says mission manager Jack Jones.
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Title Annotation:Astro Observatory, ultraviolet
Author:Cowen, Ron
Publication:Science News
Date:Dec 8, 1990
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