Shuttle Set for Crucial Flight to Save Satellite

After three weeks of delays caused by minor difficulties on the launch pad, the space shuttle Columbia is scheduled to take off at 5:06 a.m. PST Monday on a launch and rescue flight. It is the most ambitious shuttle mission to date and the first of 10 flights now scheduled for this year.

If the weather cooperates Monday, Columbia will launch an 8-ton Navy communications satellite the next morning. Then it will spend two days chasing down and capturing the Long Duration Exposure Facility (LDEF), a school bus-sized satellite whose decaying orbit threatens to bring it crashing into the atmosphere next month.

Launched in 1984, LDEF was designed to be recovered from orbit within a year, but scheduling delays and then the January, 1986, Challenger explosion have kept it in space for nearly six years and changed the recovery into a rescue.

LDEF’s orbit has been decaying rapidly, and this mission will be NASA’s last chance to retrieve the craft.

During their 10-day mission, the second-longest so far, the five astronauts also will perform medical and other experiments to help the space agency gear up for 16-day and 28-day flights scheduled in the future. At the end of the mission, Columbia’s landing will be trickier than usual because of its unusually heavy cargo.

Columbia was originally scheduled for launch Dec. 18, the last leg of NASA’s ambitious plan to fly six missions in 1989. But it ran into problems resulting from a two-year, $50-million refurbishment of pad 39A, last used for a launch of Columbia on Jan. 12, 1986, only 16 days before the Challenger explosion.

Since then, the launch complex has been extensively modified to improve weather protection for workers servicing the shuttle and to provide new escape routes for the shuttle crew should an accident occur. But reactivating the complex proved more complicated than expected and provoked several delays in December, leading ultimately to the mission’s postponement until after the holidays.

Last week, officials said the pad was prepared and the shuttle was ready for launch. However, the weather appeared chancy, which could push back the mission another day or two.

On Saturday, NASA weather forecasters were predicting only a 40% chance of suitable weather conditions for launch on Monday. Rain showers and heavy clouds from a slow-moving cold front would violate tough post-Challenger launch guidelines.

LDEF is the first satellite specifically designed to be launched from the shuttle, then returned to Earth. (Two malfunctioning communications satellites have been returned to Earth for repair and relaunch.) Its objective is to study how a variety of different materials used in the construction of satellites and spacecraft hold up in the relatively hostile conditions of space.

The core of the 30-by-14-foot, 10 1/2-ton satellite is a cylindrical frame of aluminum rings and rods welded and bolted together. It is designed to hold as many as 86 experimental trays, but has no guidance or propulsion systems.

As originally envisioned, LDEF would have been retrieved from space about a year after its original launch, fitted with new experimental trays and returned to orbit.

The $20-million vehicle currently carries 57 experiments designed by 200 researchers from the United States and eight foreign countries. Among the items being tested are metals, alloys, plastics, electronic devices, sensors of various sorts, glass optical fibers and even a packet of tomato seeds.

During LDEF’s time in space, those materials have been exposed to sharp swings in temperature as the satellite’s orbit carried it from the Earth’s shadow into direct sunlight; attack by atomic oxygen and bombardment by cosmic rays, cosmic dust, micrometeorites and debris from failed satellites.

Unlike the molecular oxygen that supports life on Earth, atomic oxygen is highly reactive, weakening organic materials and some metals by eating away at them. The presence of atomic oxygen outside the Earth’s atmosphere was discovered when astronauts discerned a faint orange glow surrounding the shuttle in orbit.

Spacecraft designers are particularly curious about how atomic oxygen affects the high-strength, lightweight plastic and carbon fiber composites in satellites. Long-term effects of space exposure are also crucial to the design of NASA’s upcoming space station, as well as to the proposed orbital components of the Strategic Defense Initiative, all of which must maintain their performance after long periods in space.

“The LDEF will tell us a great deal about how we ought to build a 30-year space station,” said mission specialist Bonnie Dunbar, who will use Columbia’s manipulator arm to grasp the satellite and put it in the payload bay. “We need this information. It’s critical.”

According to NASA’s William Kinard, the project’s chief scientist, the entire vehicle will be disassembled and studied, “even down to the welds, the electric motors, the bolts.”

Although LDEF itself probably has not weakened substantially, researchers fear that many of the experiments may have become so fragile they won’t withstand the stress of the shuttle’s re-entry and landing.

To preserve critical data in case some experiments disintegrate during re-entry, mission specialist Marsha S. Ivins will spend three to five hours in the payload bay photographing each of the 57 experiments while Dunbar rotates LDEF with the manipulator arm. Only then will the satellite be stowed inside the shuttle.

The great mass of LDEF also poses a potential problem in landing the shuttle. When it touches down at Edwards Air Force Base on Jan. 18, Columbia will be at least 5 tons heavier than any previous shuttle, necessitating changes in its flight path and great delicacy in maneuvering by the two pilots, Navy Capt. Daniel C. Brandenstein and Lt. Cmdr. James D. Wetherbee. The fifth crew member is mission specialist G. David Low.

Because of the weight, Columbia will touch down on the concrete runway at Edwards rather than on the longer dry lake bed runway normally used. NASA officials fear the increased weight would cause Columbia’s tires to sink too deeply into dirt.