LDEF Satellite Big Success Gleaning Space-Effects Data
Schoolchildren participate in Earth orbiter's experiments
REMEMBER the Long Duration Exposure Facility (LDEF) satellite that the space shuttle Columbia rescued a little over a year ago? It's turning out to be a treasure chest of scientific and engineering data. LDEF chief scientist William Kinard of the National Aeronautics and Space Administration's Langley Research Center in Hampton, Va., says the 200 experimenters in nine countries ``are still very early in the data analysis.'' And yet, there already are ``an awful lot of exciting results.''
In fact, Dr. Kinard explains, it now is obvious that LDEF is providing a set of basic data on what happens to materials on Earth orbit which will help improve the design of future spacecraft. So, he says he is ``very pleased'' with the LDEF mission which, at one point, looked as though it could end in failure.
LDEF is a bus-size 8,500-pound framework shaped as a 12-sided prism 30 feet long by 14 feet in diameter. When its 86 trays were loaded with 57 experiments, it made a 22,500-pound satellite that the shuttle Challenger left in a 295-mile-high orbit on April 6, 1984. A second mission was to retrieve the satellite 11 months later. But schedule delays and Challenger's loss stranded LDEF for five years and nine months.
When astronaut Bonnie Dunbar pulled the stranded satellite into Columbia's cargo bay on Jan. 12, 1990, its orbit had decayed to below 180 miles. LDEF was in danger of burning up in the atmosphere. The LDEF team also wondered how many of the experiments would still be viable. The experiments and associated equipment aimed to sample the orbital environment and test the effects of prolonged exposure on a variety of materials. But they weren't designed to be exposed to that hostile environment for nearly six years.
That was especially true of 12.5 million tomato seeds from the Park Seed Company. In a cooperative project with NASA and hundreds of schools, the company planned to distribute the seeds to schoolchildren. The young experimenters would grow the seeds and compare the plants with ``controls'' - that is, plants grown from identical seed kept on the ground.
As it turned out, the seeds survived. The experiments have been conducted. Park Seeds plant scientist James Alston says he expects a final report probably will be out in April, but it already is obvious that the project is a success.
The work has yielded some useful information. Minor mutations, such as changes in leaf form, have shown up - indicating some effect from the long orbital exposure. However, Dr. Alston explains: ``The main point is the kids have gone through the scientific process. The learning has taken place.'' He adds that the pupils have shared an experience about which they can say ``no one else in the whole history of the world has done this.''
The LDEF experiments also are delighting scientists with unexpected findings. For example, cosmic ray physicist John Gregory of the University of Alabama in Huntsville has detected unusually high amounts of the radioactive isotope beryllium 7. He says it came as ``a complete surprise'' to find amounts of this short-lived isotope on the front of LDEF that were 10 to 100 times higher than would have been expected. He explains that the beryllium must be coming up from lower down in the atmosphere - an upward flow of material that was not suspected.
Materials scientist Donald L. Kinser of Vanderbilt University in Nashville, Tenn., says he was surprised at what happened to some of his glass samples. He was looking for degradation by the space environment. Instead, he found pollution from LDEF itself. All but one of six samples showed no degradation. But one sample was coated with carbonaceous material from deteriorating paint.
``We hadn't expected this,'' Dr. Kinser says. He considers it an important finding because it alerts spacecraft designers to the fact that materials, such as paints, may not be as harmless as they thought.
``I expect that, as we work along, we're going to see a lot of surprises,'' Kinard says. He also notes that one of the early results bears on the global warming debate. There is concern that the calibration of satellite instruments that measure heat radiation from Earth may drift over time so that their data could be inconsistent. However, a comparable radiometer on LDEF remained stable throughout the mission. ``That's a very significant finding,'' Kinard says.