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Antenna jam delays Hubble's first light.

Antenna jam delays Hubble's first light

A few days after astronauts eased the Hubble Space Telescope into orbit from the shuttle Discovery, Earth-bound engineers still struggled cautiously to get the costly instrument working. Before seeing even a glimmer of light from space, the telescope automatically put itself on "safe hold" when a cable

apparently jammed the swivel mounting of one of its two principal antennas.

These antennas will relay observations of stars and other astronomical objects through a pair of tracking satellites to the ground (SN: 1/6/90, p.8). After analyzing the problem, however, Jean Olivier, the telescope's deputy project manager at NASA's Marshall Space Flight Center in Huntsville, Ala., said the effect on the telescope's overall science mission will probably prove "very small."

Hubble's principal, or "high-gain," antennas are designed to turn through an angle of plus or minus 93[degrees] in each of their two swivel directions. To prevent recurrence of the jamming difficulty, engineers tentatively decided early this week to limit the antennas to plus or minus 78[degrees]. In this way they hope to avoid having the telescope "safe itself" again, shutting down its various systems while engineers analyze a problem.

The telescope "has many more levels of safety systems than any vehicle we've ever flown," says David R. Skillman, the project's chief engineer at NASA's Goddard Space Flight Center in Greenbelt, Md. "The safe-mode systems have been tested and exercised very well. It's pretty idiot-resistant."

The limited antenna motion may mean that the telescope cannot always send its data directly to Earth through the satellites, says Michael M. Harrington of Marshall. He notes, however, that a possible alternative may be to store the information on one of three onboard tape recorders and transmit it to Earth at more convenient times.

After engineers finish checking out the antenna system, the next big event on the schedule is "first light" -- the space telescope's first observation of a light source in the heavens. Astronomers plan to target a portion of a star cluster known as NGC 3532 in a Milky Way constellation called Carina, about 1,500 light-years from Earth and readily visible to the naked eye in the southern sky.

The space telescope's first look at an astronomical object will come via the wide-field planetary camera, one of five scientific instruments onboard. The date of "first light" will depend on when the engineers manage to move the telescope past its initial difficulties, but it could come as early as May 5.
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Title Annotation:Hubble Space Telescope
Author:Eberhart, Jonathan
Publication:Science News
Date:May 5, 1990
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