
                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: WEDNESDAY, December 8, 1993                   TAG: 9312080137
SECTION: NATL/INTL                    PAGE: A2   EDITION: METRO 
SOURCE: The Washington Post
DATELINE: HOUSTON                                LENGTH: Medium

4TH SPACEWALK MIGHT BE MAGIC

The crew of the space shuttle Endeavour was hoping for a grand slam Tuesday night as it prepared for its fourth spacewalk of the 11-day repair mission, this time to install the second and final set of corrective optics required to improve the blurry vision of the Hubble Space Telescope.

The high-flying mechanics, operating in alternating pairs with remarkable efficiency, have worked on the telescope nightly since late Saturday, replacing solar-power panels, gyroscopes and other non-optical equipment. Tuesday morning - to the delight of anxious astronomers - they installed an improved replacement for the telescope's workhorse camera.

Known as the Wide Field/Planetary Camera, it represents about 50 percent of the telescope's scientific capacity. The $23.9 million WFPC 2 replacement unit contains an optical system designed to reverse the effects of an error in the shape of the telescope's main mirror. Astronauts slid the extremely delicate apparatus into place about an hour ahead of schedule.

The scheduled centerpiece of this morning's orbital drama was to be installation of the other half of the new optical equipment: a 700-pound box the size of a phone booth called the Corrective Optics Space Telescope Axial Replacement. It contains a system of small arms designed to unfold and extend correctively ground mirrors the size of dimes, nickels and quarters in front of the telescope's remaining instruments, correcting the effect of Hubble's focusing problem.

The two optical packages together, if they pass a routine six- or eight-week checkout, should restore at least 90 percent of the telescope's promised capability, scientists said. The Hubble, launched in April 1990, was designed to provide the greatest leap for astronomers since the invention of the telescope, bringing into sharp focus for the first time objects as distant as the outer edges of the universe.

The spacewalking team of Kathryn C. "K.T." Thornton and Tom Akers planned to step out of the airlock for the final optical fix before 11 p.m. Tuesday. By then, the telescope was to have been rotated 90 degrees on its turntable to expose the day's worksite on its silvery flank. Over the next few hours, they were scheduled to remove the telescope's least-used instrument, the High Speed Photometer, to make room for COSTAR.

In a procedure similar to the one used to install the new camera the previous morning, they were scheduled to slide the massive box onto guide rails and - like a huge vertical dresser drawer - into the cavity left by HSP. They were then to connect an electrical grounding strap, make electrical attachments and close and latch the protective doors in the telescope's outer hull.

by CNB