Seeds of Success Stranded in Space
SPACE SHUTTLE: SATELLITE RESCUE MISSION
SHUTTLE astronauts are ready to go after a stranded satellite whose rescue would turn an embarrassing failure into a scientific success. In need of rescue is the 21,600-pound Long Duration Exposure Facility (LDEF). The 57 experiments on board it involve a variety of materials, including 12.5 million tomato seeds. Placed on orbit April 7, 1984, by an earlier shuttle crew, LDEF was to have been retrieved in about one year to see what happened to its cargo.
Launch schedule glitches and the 1986 Challenger accident repeatedly postponed that retrieval. Now the space shuttle Columbia is set to take off from the Kennedy Space Center Dec. 18 to end the LDEF team's long-duration frustration. Still, the half-decade wait could be an investment that produces unexpectedly valuable data for many of the 200 United States and foreign experimenters.
``None of the experiments are going to be a dead loss,'' says William Kinard, LDEF chief scientist of the National Aeronautics and Space Administration (NASA) Langley Research Center. He notes that the purpose is to study effects of such factors as cosmic rays, atomic oxygen from the outer atmosphere, micrometeorites and space junk, and the effects of weightlessness. The prolonged exposure should make most experiments ``5 to 6 times more valuable'' than planned, he says. He expects even the seeds to be viable. Control seeds set aside in 1984 still sprout at the George W. Park Seed Company, which coordinates that experiment.
Astronauts Daniel Brandenstein (commander) and James Wetherbee (pilot) will fly Columbia with Bonnie Dunbar, G. David Low, and Marsha Ivins traveling as mission specialists.
LDEF is a 12-sided polyhedron - 30 feet long by 14 feet across - with experiments mounted in trays along its sides and ends. It is an inert spacecraft with no on-board propulsion or attitude control thrusters and no radio contact with Earth. In 1984, astronauts used the shuttle's movable arm to place this school-bus size craft on orbit.
Dr. Kinard says that LDEF has remained a very stable craft with a stable drag due to the residual atmosphere through which it travels. Changes in its orbit reflect the density of that thin gas. Radar tracking of LDEF has yielded very accurate density data, including the outer atmosphere's response to solar activity, Kinard explains.
Now this air drag has lowered LDEF's orbit from 295 miles to 213 miles. It will reenter Earth's atmosphere at the end of February if left to itself. So Columbia's mission is an all or nothing effort.
Even if that mission succeeds, it will be a bittersweet triumph.
The highlight of the April 1984 mission was the Ace Satellite Repair Company, as the astronaut crew billed itself. It repaired the Solar Max satellite while in orbit, significantly extending its life. Astronauts could have done this again. But NASA has neither the money nor an available shuttle mission to service Solar Max now. It has abandoned it to a fiery re-entry, within a few weeks.
In 1984, NASA hailed both LDEF deployment and the Solar Max repair as examples of unique services the shuttle could offer. It hoped to run a business renting experimental space on retrievable satellites launched as often as every 18 months. That prospect evaporated with the LDEF delays.
If Columbia cannot rescue LDEF, several hundred sizable chunks - 10 to 100 pounds each - could fall along the reentry track, Kinard says. This lies between 28.5 degrees north and south latitudes. Much of that track is over open sea. But mission specialist Low says it is important to retrieve the satellite because ``it looks bad for the the United States to allow something like that to come in.'' The same could be said for the 6,000-pound Solar Max whose reentry will scatter debris along the same path.