From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Galileo's Atmospheric Probe Passes Health Checks
Followup-To: sci.space
News-Software: VAX/VMS VNEWS 1.3-4   
Keywords:  Galileo, Jupiter, Ames, JPL
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Wed, 16 Dec 1992 01:01:52 GMT

Paula Cleggett-Haleim
Headquarters, Washington, D.C.               December 15, 1992
(Phone: 202/358-0883)

Pete Waller
Ames Research Center, Mountain View, Calif.
(Phone:  415/604-3938)

RELEASE:  92-224

GALILEO'S ATMOSPHERIC PROBE PASSES HEALTH CHECKS

     The Galileo spacecraft and its atmospheric probe are now
halfway on their complex trip to Jupiter, and the first full tests
since launch 3 years ago show that the probe is in good shape, say
NASA officials.

     "We have, for the first time since launch 3 years ago, checked
out the entire probe spacecraft system and run it through a full
mission sequence," said Benny Chin, Probe Project Manager, NASA's
Ames Research Center, Mountain View, Calif.

     "All systems working together, including the seven scientific
instruments, are functioning well and will meet mission
objectives," he said.

     The probe is being carried over most of the half billion miles
to Jupiter by the Galileo orbiter.  At 51,358,400 miles from the
planet, the probe will separate from the orbiter and fly on by
itself.  This will occur on July 10, 1995, 5 months before arrival
at Jupiter.

     The probe will make history's first entry into the atmosphere
of an outer planet on Dec. 7, 1995.  It will slam into Jupiter's
atmosphere at 115,000 mph, fast enough to jet from Los Angeles to
New York in 90 seconds.  Deceleration to about Mach 1 -- the speed
of sound -- will take just a few minutes, causing a buildup of heat
so intense it will be like flying through a nuclear explosion.

     The Galileo probe then will plunge 400 miles through the
planet's brilliantly colored cloud layers into the hot, dense
atmosphere below -- making history's first direct measurements of
Jupiter.  As it descends, the probe will gather scientific data
about the giant planet's swirling clouds, violent winds and star-
like composition, providing clues to the origin of the solar
system.

     Health of the Galileo probe was checked in a mission sequence
test on Nov. 20, 1992, and a functions test on Dec. 2.  Data
analysis since then has confirmed that all of the craft's systems
are in good condition.  A suspected loss of battery power, for
example, did not occur.  Battery voltages are at the levels of
launch day, Oct. 18, 1989.

     Entry into Jupiter's atmosphere is the most hazardous in the
solar system because the planet's immense gravitational pull
creates tremendous speeds.  At maximum deceleration, as the craft
slows from 115,000 mph to 100 mph, the probe will hurtle against a
force 350 times Earth's gravity.

     Its incandescent shock wave will be as bright as the sun and
reach temperatures up to 28,000 degrees Fahrenheit.  After entry,
the fore and aft heat shields of the deceleration module will be
shed by deploying a small pilot parachute and then a large main
chute, exposing the descent module to Jupiter's hydrogen/helium
atmosphere.

     The probe's total weight is 747 pounds.  The deceleration
module weighs 484 pounds.  The inner descent module carries seven
scientific instruments, weighing 66 pounds.

     "The tests show that all the instrument parameters are within
normal limits," said Ames' Dr. Richard Young, Probe Project
Scientist.

     To make the first direct measurements of Jupiter, he said, the
probe carries  an atmosphere structure instrument, a mass
spectrometer for atmosphere composition, a cloud instrument, an
energetic particle instrument, a lightning detector, a helium
detector and a radiometer to chart energy flow in the atmosphere.

     Together, they will characterize Jupiter's ionosphere and its
atmosphere (composition, temperature, and density), measure wind
speeds, cloud characteristics, lightning, the important ratio of
helium to hydrogen and the atmosphere's energy balance.

     "Because of its size, make-up of original solar system
material, and being the biggest of the 'gas giant' outer planets,
Jupiter is a scientific treasure trove," said Young.  "On the
science side, everything is fine so far.  We can't wait to get
there," he said.

     As the probe passes through Jupiter's colored cloud layers,
its computer will receive information, process it and transmit the
coded signal to the Galileo orbiter, which will relay the data by
radio to Earth.  The probe descent mission will last about 75
minutes.  At this point, a combination of extreme heat, high
pressure and degraded battery power will silence the probe forever.

     The probe project is managed by the Ames Research Center.  The
overall Galileo mission is managed by NASA's Jet Propulsion
Laboratory, Pasadena, Calif.
- end -

NOTE TO EDITORS:  Dramatic mission animation, with new segments on
Jupiter's deep atmosphere will be telecast via NASA-Select on
Tuesday, Dec. 15, 1 p.m. EST and repeated at other times during the
day.  This will be carried on Satcom F-2R, Transponder 13, 72
degrees west longitude, 3960 MegaHertz; audio 6.8 MHz, vertical
polarization.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Choose a job you love, and
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | you'll never have to work
|_____|/  |_|/       |_____|/                     | a day in you life. 

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