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RESULTS from the US satellite retrieved from orbit in January, known
as the long duration exposure facility, are providing a wealth of information
for designers of the international space station, Freedom.

NASA’s Langley research centre designed the LDEF for repeated missions,
each lasting about 10 months. The idea was to study the effects of exposure
to space on biological and electronic systems on the spacecraft. The Challenger
accident condemned the LDEF to a longer stay in space than intended.

In January, after six years, the shuttle retrieved the LDEF shortly
before its orbit decayed and it burned up entering the atmosphere. The team
which is analysing and collating data gathered by LDEF will announce its
results at a conference in the US in January. But a paper at last week’s
astronautical congress outlined one example of how the LDEF’s results will
modify work on future space projects.

One test structure, called the thermal control surface, was designed
to protect instruments from rapid swings in temperature. It consisted of
silver Teflon glued to aluminium and, before the launch of the LDEF, engineers
cleaned the surface according to ‘standard practices for space applications’.
When they had finished, the surface appeared shiny and silvery. However,
after the LDEF was retrieved, the surface ‘had a milky white background
with yellow streaks running in parallel’.

The principal investigator for the experiment, Don Wilkes, believes
that some adhesive was smeared on the surface of the Teflon as engineers
smoothed it onto the aluminium. Although the surface was cleaned, some adhesive
may have remained. In orbit, ultraviolet radiation darkened the adhesive
streaks and atomic oxygen eroded the Teflon, he said.

Bill Kinnard, one of the authors of the paper, said that the conclusions
provided ‘an important lesson, which is certainly not new but nevertheless
relevant’. Kinnard and his co-authors added that ‘many of the anomalies
to LDEF’s systems examined so far were produced by inadequate or inappropriate
ground procedure.’