REPAIRING HUBBLE

The shuttle Endeavour is to lift off Wednesday at 3:57 a.m. on a complex, 11-day flight to repair the Hubble Space Telescope. This is no ordinary fix-it mission. From jittery solar arrays to a built-in focusing flaw, the Hubble is in need of a good mechanic. Five six-hour space-walks using four of seven crew members are planned.

THE FIX-IT-LIST

Listed in order of importance, not in order in which the astronauts will accomplish them.

1. Replace 40-foot solar arrays to stop unwanted flapping motion caused by temperature changes. Ensures adequate electrical power.
2. Replace two gyroscopes. Ensures continued stability for pointing the telescope at target stars. Three of the telescope's six gyroscopes are not working. Three are required.
3. Replace Wide Field Planetary Camera with wedge-shaped, 600-pound Wide Field Planetary Camera II, The $100 million instrument contains tiny mirrors to correct distortion from flawed primary mirror.
4. Insert 640-pound Corrective Optics Space Telescope Axial Replacement, or COSTAR. The $50 million, phone booth-sized device contains 10 small mirrors to correct distortion from primary mirror as radiance enters telescope's faint object camera, high resolution spectrograph and faint object spectrograph. The observatory's high speed photometer is removed to make room.
5. Replace magnetometer on top of telescope. One of two on the observatory and part of a system that controls the telescope's attitude in response to Earth's magnetic field.
6. Replace two more gyroscopes and associated electronics control box. Increases Hubble's stability.
7. Replace electronic drive mechanism that keeps the deployed solar panels aimed at the sun.
8. Four items on a secondary list. Astronauts will do these as time permits:
A. Install new data and electronics cable for Goddard High Resolution Spectrograph;
B: Repair telescope's flight systems computer. Two of computer's six memory units have faltered;
C: Replace the second magnetometer;
D: Replace electronics control box for two gyroscopes and their fuse plugs.

THE BOTTOM LINE

COST OF REPAIRS: $293 million for equipment and training.
COST OF LAUNCH: $413.5 million.
TOTAL COST: $706.5 million.
VITAL STATISTICS
Launched: April 24, 1990.
Investment: $3 billion.
Size: 43 feet long, 14 feet in diameter, weighing 26,000 pounds.
Orbit: Circles the Earth every 95 minutes at an altitude of about 370 miles.
History: Named for astronomer Edwin Hubble, who is credited with discovering the rapid expansion of the universe. Congress authorized the telescope in 1977.

REMEDY FOR THE FLAW

The telescope's 94-inch primary mirror was launched with a flaw. The very edge of the mirror is too flat by 1/50th the width of a human hair. The mirror will be left in place but astronauts will install two large optical devices, the Wide Field Planetary Camera and the Corrective Optics Telescope Axial Replacement, equipped with small mirrors to correct the distorted light stream from the flawed mirror as it enters the Hubble's four observing instruments. They will provide the telescope with an optical correction much as a pair of eyeglasses on a near-sighted human.

GRABBING THE HUBBLE

Endeavour will launch into 355-mile high orbit, maneuver toward a rendezvous on third day, grab the telescope with the robot arm and stow it vertically in the cargo bay. Spacewalks begin on day four. Repaired telescope will be released on day 9.

CREW

NASA has chosen an all-veteran crew for only the second time in 59 shuttle missions. Crew is divided into two groups. a flight crew and a spacewalk team. Flight team: Mission commander Dick Covey, pilot Ken Bowersox, robot arm operator and flight engineer Claude Nicollier. Spacewalk team: Story Musgrave, Jeff Hoffman, Tom Akers, and Kathy Thornton.