RSF@SU-AI.ARPA (04/02/84)
From: Ross Finlayson <RSF@SU-AI.ARPA>
n064 1530 01 Apr 84
BC-JUPITER
By JOHN NOBLE WILFORD
c.1984 N.Y. Times News Service
PASADENA, Calif. - The pieces are finally coming together in an
ambitious project to explore Jupiter and its four major moons.
After years of budgetary battles over the Galileo project, delays
and equipment changes, officials of the Jet Propulsion Laboratory
here say they believe they now have a launching date they can keep -
May 1986.
One piece, the spacecraft, is being assembled at the laboratory and
prepared for rigorous ground tests, scheduled to begin in two months.
The spacecraft is designed to orbit Jupiter 11 times over a 20-month
period, weaving in and out of the paths of the Jovian moons and
taking close-up photographs of at least one moon on each orbit.
Another piece, a separate module called the Probe, was delivered to
the laboratory in February and will be fitted into the main
spacecraft. The module, built by the Hughes Aircraft Co. under the
direction of the Ames Research Center in Mountain View, Calif., is
designed to be deployed by the spacecraft for a parachute-assisted
descent into Jupiter's dense atmosphere. The probe is expected to
return data for an hour until high temperatures and pressures destroy
it.
Work on a third element of the project, a modified Centaur rocket,
was also reported to be proceeding on schedule at the General
Dynamics Co. in San Diego. The high-energy rocket, ordinarily used
for launchings from the ground, is being adapted to boost the Galileo
vehicles after they are deployed into an earth orbit by the space
shuttle. Resorting to the Centaur, rather than the troubled Air Force
inertial upper stage rocket, is one of the changes that has delayed
the mission.
John R. Casani, the Galileo project manager, said in an interview
last week that ''everything looks good'' for getting the 5,600-pound
spacecraft and its Centaur rocket ready for liftoff in May 1986. His
optimism is in sharp contrast to the situation two years ago, when it
appeared for a time the Reagan administration, in a move to reduce
the civilian space budget, might cancel the Galileo project and wipe
out the entire planetary exploration program.
Twice before, launching plans were set back because the shuttle was
not available or because of problems in developing a booster rocket.
When the project was initiated in 1977, the goal was to launch the
craft in 1982.
A launching in 1986 would send the spacecraft into an orbit of
Jupiter in August 1988. Two Pioneers and two Voyagers have flown by
the Jovian system, but none have gone into orbit for a longer look.
The $860 million mission promises to give scientists their first
detailed, close-range view of the chemical composition and physical
properties of the solar system's largest planet and its four
prominent satellites, each of which appears to be a world unto
itself. Scientists believe Jupiter is made of the original material
from which stars form, largely unmodified by thermonuclear processes.
Only two important questions about the mission remain, Casani said.
Will engineering changes assure the spacecraft's sensitive
electronics a safe ride through the hazardous Jovian radiation belts?
Will the spacecraft be re-directed to inspect an asteroid on its
voyage out between Mars and Jupiter?
That the first question arose is a reflection of the Galileo
spacecraft's technological sophistication.
Further miniaturizing of the microscopic wiring on the silicon
computer chips, which greatly increases the craft's data-processing
capability, made the chips vulnerable to a phenomenon known as
''single-event upset.''
A single impact of cosmic rays or Jupiter radiation did not usually
affect the larger computer chips used on earlier craft. Their size
and greater electrical charge protected them. But a new analysis
indicated that Jupiter's radiation, though low in energy, was enough
to disrupt the smaller, lower-powered computer circuits. One zap
might switch a critical circuit from off to on or on to off, thereby
disrupting all data processing.
About 50 chips are being redesigned with new wiring to be
''cosmic-ray safe,'' Casani said. The radiation shielding is being
added by the Sandia Corp. of Albuquerque, N.M. If these corrections
fail to solve the problem, he said, the entire microprocessing unit
will have to be replaced.
In neither case, he said, was the problem likely to jeopardize
Galileo's launching schedule. The other question, whether Galileo
should also attempt to fly past an asteroid, must be resolved before
the end of this year, if there is to be time to develop computer
instructions for such an encounter.
Since the spacecraft must go through the asteroid belt between Mars
and Jupiter anyway, it was determined that, with certain mid-course
maneuvers, Galileo could fly close enough to obtain detailed pictures
of one of the larger asteroids, the 120-mile-wide Amphitrite.
The price to be paid would be a delay of three to four months in
Galileo's arrival at Jupiter. Such a delay increases the mission's
cost and the chances of something going wrong before reaching Jupiter.
Dr. Torrence V. Johnson, the project scientist, said many planetary
researchers were advocating that the space agency adopt a policy of
including an asteroid rendezvous in all its missions to the outer
planets. A decision is expected later this year.
nyt-04-01-84 1824est
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