TIME: Almanac 1993/TIME Almanac 1993.iso/time/121090/1210320.000

Text File | 1992-08-28 | 3.7 KB | 87 lines

                                                                              SPACE, Page 78

Roots of the Hubble's Troubles


NASA could have spotted the telescope's flaw before the launch

By David Bjerklie -- Reported by Jerry Hannifin/Washington


    Anyone can make a mistake. But when it sabotages a $1.5
billion project, the blunder is not easily forgiven. And when
evidence of the mistake is repeatedly ignored until it is too
late to fix the problem, then the episode becomes scandalous.

    That was the case with the ill-fated Hubble Space Telescope,
according to a remarkably frank investigative report issued
last week by the National Aeronautics and Space Administration.
The flaw that crippled the telescope's primary mirror was not
obvious until after the instrument was launched last spring.
Yet technicians at the company that made the mirror had
indications of trouble long before the telescope went into
space -- and apparently never told the design team about the
disturbing signs. Meanwhile, managers at NASA who had
responsibility for the Hubble project paid little attention to
the details of the telescope's construction. "There were at
least three cases where there was clear evidence that a problem
had developed, and it was missed all three times," said Lew
Allen, the director of NASA's Jet Propulsion Laboratory and the
head of the six-member investigating committee that wrote the
Hubble report.

    There was more than enough time to catch the telescope's
flaw. Rough grinding of the mirror began in 1978, final
polishing was not finished until 1981, and the completed
telescope sat on the ground for four years after the space
shuttle program was disrupted by the Challenger explosion. The
mirror's manufacturer, Connecticut-based Perkin-Elmer Corp.,*
told NASA that the standards of precision established for the
mirror were not only met but exceeded. The only problem was that
the mirror had been painstakingly polished into the wrong
shape.

    To achieve the exacting specifications for the mirror,
Perkin-Elmer used an optics template, a tubular array of
smaller mirrors and lenses linked by connecting rods, to guide
the grinding and polishing processes. When the Allen committee
tested this template assembly, it found that there was a
critical error of 1.3 mm (0.05 in.) in the placement of the
template's components. The Hubble mirror was carefully fashioned
to match exactly this error in the template.

    What was worse, the company's reliance on this system was
absolute. Though backup analyses pointed to a major flaw in the
mirror, stated the report, these "indicators of error were
discounted at the time as being themselves flawed." The
evidence of the problem was never analyzed in detail by the
engineers and scientists most qualified to do so. NASA accepted
Perkin-Elmer's decision to rely solely on the precision of the
template, when instead the space agency should have been alert
"to the fragility of the process and the possibility of gross
error."

    Fortunately, the damage is not beyond repair. NASA plans to
perform an in-orbit service call on the space telescope in
1993. In the meantime, pictures from the Hubble can be
sharpened by computer enhancement. The telescope has taken some
surprisingly good shots, including images of a gas jet
streaming from a newborn star and a huge storm on Saturn.

    But the Hubble cannot focus on distant stars nearly as
sharply as had been expected. Its performance was compromised
by mistakes that were easily avoidable. That is clear even
without the benefit of optically perfect hindsight.


* The company's optics division has since been sold to a General

Systems.