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After Long Wait, Astro Set to Go

Astronomers expect craft will give them views of cosmos even better than Hubble telescope can. SPACE MISSION

MOVE over Hubble telescope. Here comes Astro. It is a battery of ultraviolet and X-ray telescopes that turns a space shuttle into an orbiting observatory. Now nestled snugly in Columbia's payload bay, it is ready for launch May 17 at the Kennedy Space Center.

Astronomers expect the nearly nine-day Astro-1 mission to give them views of the cosmos they cannot get from the ground. These include observations that even the Hubble instruments cannot make. Astro's equipment is sensitive to ultraviolet and X-ray wavelengths, some of which lie below Hubble's range.

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Furthermore, unlike the automated Hubble satellite, the Astro observatory will have a human team along with it to run the instruments. Four of the seven crew members make up an orbiting team of professional astronomers.

At one point during the mission, they will even act as schoolteachers to give an illustrated lecture from space on the electromagnetic spectrum. This will be linked with further experiments and discussion in a laboratory at the Marshall Space Flight Center in Huntsville, Ala. Selected students will also have a question-and-answer session with the orbiting astronauts. This project should produce a video and other materials for use in science classes.

For astronomers, this is the other major observing program, along with the Hubble telescope, which they have been anticipating for many years. The original concepts for the instruments date to 1978. The mission itself was to have flown in March 1986 in time to include Comet Halley among its targets. But the Challenger accident Jan. 28 that year put both the Hubble telescope launch and Astro-1 on hold for four years.

For Astro team members, the disappointment was especially bitter because they thought they had lost a once-in-a-lifetime opportunity to observe a comet close at hand with their equipment. Now they have a second chance. Comet Austin, which appeared unexpectedly this spring, should be in a prime position for study as it recedes from the sun during mid-May.

Theodore Gull - Astro mission scientist at Goddard Space Flight Center in Greenbelt, Md. - says that, all told, ``the standdown has been helpful.'' It has given team members extra time to improve their instruments and to learn to use them more skillfully. It also has given time to add a fourth instrument - an X-ray telescope to supplement the three ultraviolet telescopes originally planned. ``So in a sense, we've expanded. That's good,'' Dr. Gull says.

He adds that the team is especially pleased that Comet Austin has showed up. ``It makes up for [missing Halley]. It looks like it's going to be brighter. And from the information we have on it, this is not a periodic comet. It's one from the outer solar system. So there's going to be much more fundamental information here than with Comet Halley. We're excited about it,'' he says.

The 1987 supernova star explosion provides another new opportunity. It erupted in the large Magellanic Cloud - a small galaxy that is a companion of the Milky Way galaxy. The remains of that explosion now are expanding into interstellar space. This will be a target both for the Hubble telescope and for Astro instruments flown on this and future missions.

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``This will be an exciting period of time over the next 20 years because we've never had the opportunity with modern instrumentation to look at a supernova as it gradually interacts with the interstellar medium,'' Gull says.

Now that they will finally have their chance in orbit, Astro astronomers plan to make the most of their observing time. Their fast-paced schedule includes some 290 pointings of their instruments at more than 200 objects. These range from close-in objects such as the comet to very faint distant sources. In all cases, the observations will be made by the ``light' of ultraviolet and X-ray emissions that cannot penetrate the atmosphere. But at the mission's planned height of 218 miles, Astro instruments will have clear views. In fact, astronomers expect to make their first general census of the sky as seen in the ultraviolet.

Gull notes that the list of objects Astro now will be able to observe is 20 percent or more greater than it would have been in 1986. This is another bonus of the delay.

While Astro team members are grateful for the new opportunities, Gull emphasizes that the Challenger disaster came as a great shock to them - especially to the two team payload specialists schedule to fly with the equipment. Yet those specialists are ready to fly now. ``In a very positive sense, they know the risks involved. But they feel the return is well worth it,'' Gull says.

Unlike the automated Hubble satellite, Astro needs onboard human attention. The Hubble telescope moves slowly and has plenty of time to make observations. Astro telescopes must change targets fast. The shuttle will maneuver to help in the aiming. Then the onboard team will control instrument movements, change filters, and fix any glitches quickly.

``We need immediate response to the observation to make it as efficient as possible. That's why we demonstrated the need for astronauts,'' Gull says.

Four astronomers will tend the equipment. Ronald Parise of Computer Sciences Corporation and Samuel Durrance of Johns Hopkins University will fly as payload specialists, meaning they are not professional astronauts. Jeffrey Hoffman and Robert Parker, who are astronauts as well as astronomers, will be mission specialists. Other crew members include Vance Brand, mission commander; Guy Gardner, pilot; and John Lounge, an astrophysicist who will serve as a general mission specialist but who is not part of the formally designated science crew.

Astro is a reusable setup that could be refurbished, updated, and reflown many times. The instruments ride on movable pads that aim them at targets and provide general power and electronic services. These pads are part of the Spacelab that transforms a shuttle into an on-orbit laboratory and that was supplied by the European Space Agency. For Astro missions, the pressurized part of Spacelab where humans work is left behind since crew members control Astro from the shuttle aft deck.

Originally, four Astro missions were planned. But now the shuttle schedule may be too tight to accommodate all of them. NASA will decide on a second flight after this mission. Nevertheless, Gull looks forward to a long life for Astro. He notes that NASA has had ``some good success stories'' with equipment durability. He cites, for example, the International Ultraviolet Explorer satellite that is still working 12 years after launch in spite of a two- to three-year life expectancy.