Getting ready to help the Hubble

NASA plans repair strategy for Hubble

Seldom has public fascination with a science project soared and plummeted as dramatically as it did with NASA's 1990 launch of the $2.5 billion Hubble Space Telescope.

Within weeks of its April 25 deployment, the space agency announced the observatory had been launched into its 380-mile high orbit with an undiscovered flaw in its 94-inch wide primary mirror.

The edges of the reflector had been ground flatter to the naked eye than specified, a small but significant optical defect that escaped the notice of NASA as well as the mirror's manufacturer.

Scientifically, the mistake meant astronomers could not precisely focus the 42-foot long telescope on the distant celestial objects -- its intended function.

According to the specification, the mirror's shape should be so precise that 70 percent of the light from a distant star should be tightly concentrated. Instead, only 15 percent of the light falls within a specified region.

Using ground-based computers, astronomy teams have managed to enhance the Hubble's fuzzy images, supplying researchers with new-found evidence of mysterious black holes, and making other discoveries that help explain the evolution of the universe.

Even before the space telescope was launched, NASA had planned to dispatch spacewalking shuttle astronauts on periodic service calls to re-equip the telescope with new, more sensitive cameras and electronics over its planned 15-year life span.

The infamous optical problems, though, added a new urgency to the first service call, now planned for late 1993 or early 1994. The telescope has accumulated enough difficulties to require at least three six-hour spacewalks by two pairs of astronauts.

This is the repair strategy:

Replace the original wide field planetary camera, used in the observation of relatively large nearby objects like Mars, Jupiter and the other planets in the solar system. The 610-pound wedge-shaped apparatus can be removed from the back of the telescope like a large drawer. The replacement camera array incorporates small "relay" mirrors ground to a prescription that will remove the aberration in the light from the flawed primary mirror.

Replace the telephone booth-sized high-speed photometer with a new device called the Corrective Optics Space Telescope Axial Replacement, or Costar, an assembly of precisely shaped mirrors that will correct the light from the flawed primary mirror as it enters three other Hubble instruments. They are the faint object camera and two spectrographs, a trio of instruments to observe distant, barely visible stars and to discern their physical composition, temperatures and pressures.

Replace the twin solar arrays, the wing-like devices that produce electricity from sunlight.

Replace four of the gyroscopes and an electronic control assembly that help stabilize the observatory.

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Hubble Space Telescope repairs

What needs fixing.

Scientific Instrument section:

Contains planterary camera, photometer, gyroscopes and electronic controls.

1. Shuttle rendezvous with Hubble; brings telescope into cargo bay's maintenance platform.

2. Two astronauts, using miniature robots and power tools, will replace telephone booth-sized instruments. Repairs will require at least three six-hour space walks.

3. Astronaut on flight deck, ground control check circuitry, conduct tests.

4. Manipulator arm places telescope back in orbit.