Shuttle team wrings success out of failure

Challenger's crew is savoring the taste of success with its demanding orbital mission, despite continuing problems with an important instrument pointing system. This system -- known in space lingo as the IPS -- is designed to orient telescopes and other instruments with high accuracy. So far the $60 million unit, supplied by the European Space Agency, has not been able to track targets this way. The problem apparently stems from the software that controls the system.

Nevertheless, most other instruments and experiments are working so well that, at one point, mission specialist Karl G. Henize said the crew is feeling ``a lot of joy.''

Mission scientist Eugene W. Urban says the equipment is getting ``into real scientific observing'' of the sun, of distant cosmic objects, and of the Earth's outer atmosphere. From now on, he says, Mission 51-F ``is going to be very exciting for all of us.''

By making the most of the flexibility of the shuttle system and its crew, flight controllers and the 51-F scientific team are wringing a great deal of success out of a mission that could have been an embarrassing failure.

Because of premature shutdown of one of the craft's three main engines at liftoff, Challenger has been orbiting 45 to 50 miles lower than intended. This has affected some of the observations and experiments for the ship within Earth's thin outer atmosphere. Observations of the sun by ultraviolet (UV) light, for example, are more difficult because this atmosphere absorbs some of the UV. Loss of the high-precision tracking capability of the IPS was also a blow to astronomers whose sun-observing instrument s depend partly on the IPS system.

Despite these setbacks, the science team and engineers at the Marshall Space Flight Center in Huntsville, Ala., and at the Johnson Space Center in Houston have found ways to compensate.

To begin with, the IPS has been able to lock onto targets, even if it could not track them as desired. Also, the tracking ability of one of the sun-observing instruments -- an ultraviolet high-resolution telescope -- has enabled mission astronomers to get much of the solar data they want despite the IPS problem.

At this writing, IPS engineers were still trying to work out the bugs in the software. They reported some progress, but the problem had not yet been solved. Testing the IPS, and locating and correcting any faults, are main objectives of this mission. The system is to play a crucial role in the shuttle-based Astro mission that is to study Halley's comet next March.

If the IPS can be made to work while Challenger is on orbit, the mission might be extended an extra day to test the system, according to Dr. Urban. Challenger would then land Tuesday instead of Monday, as now planned.

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