Astro malfunctions leave scientists dismayed

December 04, 1990|By Frank D. Roylance | Frank D. Roylance,Evening Sun Staff

Astronomers at the Marshall Space Flight Center in Huntsville, Ala., were described as "worried" today as equipment failures continued to plague their $148 million Astro Observatory aboard the space shuttle Columbia.

The four Astro telescopes were idled for nine hours overnight after a computer on board the shuttle failed.

"Since then, the computer has come back up and we are able to point, but for most of the night things haven't been stable enough to do observations," said Knox Long, a spokesman for the Hopkins Ultraviolet Telescope team at Marshall.

With the mission now in its third day, Long said, "people are worried but they're still optimistic that things will eventually be made to work. And they're still hopeful of doing good science when that happens."

Meanwhile, NASA technicians today continued to trouble-shoot the troublesome telescope pointing system.

Lisa Hooker, a spokeswoman for the Hopkins team said, "We're obviously losing targets with each hour [the pointing problems remained unfixed]. It will reach a point where we can't recover them all."

HUT is one of four telescopes that make up the Astro Observatory launched aboard Columbia Sunday.

The four telescopes were to have begun astronomical observations shortly after midnight yesterday.

Because of problems with the Instrument Pointing System (IPS), scientists said they have lost about 10 percent of scheduled observations.

The Astro Observatory's 10 days in space were booked solid with 230 planned "pointings."

"We'll not get all the science we want to get, but we will still get very important science when we get the pointing system to work," said mission scientist Ted Gull of Goddard Space Flight Center in Greenbelt.

NASA officials expressed confidence they could get it working. Meanwhile, shuttle astronauts, including Hopkins' research scientist Samuel T. Durrance, were aiming Astro's three ultraviolet telescopes with hand-operated joysticks.

The first scientific observation did not take place until 11:30 a.m. yesterday, when the Hopkins HUT team performed a spectrographic observation of the outermost fringes of Earth's atmosphere -- above the shuttle's 220-mile-high orbit.

Later in the day, the HUT team made additional observations whenever they could, as Astro moved through its pre-determined schedule of "pointings."

"Any time they can get the IPS to hold still for a second, we are trying to get anything," Hooker said.

An observation at 12:30 p.m. of the brightest known galaxy in the sky, called NGC4151, proved that HUT "will indeed be able to get good spectra," Hooker said.

Later yesterday, HUT and the Wisconsin Ultraviolet Photo Polarimeter successfully observed as star known as HR1099.

Long described the objects as "not targets of major interest, or if they were, [their light was] not in the slit [HUT's aperture] long enough to get publishable data."

The Broad-Band X-ray Telescope made a successful observation the Crab Nebula, the brightest X-ray source in the sky. The data was relayed to Huntsville for analysis.

Hooker said Hopkins team leader Arthur F. Davidsen was "jumping up and down" with delight at the results of the first observation, of Earth's outermost atmosphere.

The spectrograph is needed to analyze the chemical composition of the wispy traces of air that extend into space beyond the shuttle's orbit.

The atmosphere's composition must be understood so that scientists can subtract its effects from their spectrographic analyses of light from distant stars and galaxies. That light is altered as it passes through the traces of atmosphere to reach the telescope.

The IPS pointing system controls the aim of all three of Astro's ultraviolet telescopes, including HUT, which swivel simultaneously on one platform like a single observatory.

Goddard's Broad Band X-ray Telescope is mounted separately in the cargo bay and controlled by a pointing system directed from Greenbelt.

The IPS is guided by three "star trackers" that search for and lock onto three predetermined "guide stars" for each telescope target. The star trackers appeared to be the source of problems the IPS was having in finding and locking on to its targets.

Mission manager Jack Jones said yesterday that the one device had proved to be more sensitive than expected, and could not identify its guide stars because of the profusion of stars that it saw. New computer instructions were sent to the tracker to reduce its sensitivity.

Technicians also had to reprogram the IPS to allow for changes in the relative aims of the three star trackers, which changed from predicted alignments due to the zero gravity environment of space.

The first corrections improved the IPS performance, but controllers said it should be working 10 times better than it is, and that additional instructions were needed to fine-tune the system's performance.

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