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Date: Thu, 12 Oct 89 03:24:50 -0400 (EDT)
Subject: SPACE Digest V10 #138

SPACE Digest                                     Volume 10 : Issue 138

Today's Topics:
	   STS-34 Press Kit [2 of 3] [Revised] (Forwarded)
----------------------------------------------------------------------

Date: 9 Oct 89 19:20:10 GMT
From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov  (Peter E. Yee)
Subject: STS-34 Press Kit [2 of 3] [Revised] (Forwarded)

before reaching Jupiter, Galileo's probe must separate from the orbiter. 
The spacecraft turns to aim the probe precisely for its entry point in the
Jupiter atmosphere, spins up to 10 revolutions per minute and releases
the spin-stabilized probe.  Then the Galileo orbiter maneuvers again to
aim for its own Jupiter encounter and resumes its scientific
measurements of the interplanetary environment underway since the
launch more than 5 years before.

     While the probe is still approaching Jupiter, the orbiter will have its
first two satellite encounters.  After passing within 20,000 miles of
Europa, it will fly about 600 miles above Io's volcano-torn surface,
twenty times closer than the closest flyby altitude of Voyager in 1979.

AT JUPITER


The Probe at Jupiter

     The probe mission has four phases:  launch, cruise, coast and
entry-descent.  During launch and cruise, the probe will be carried by the
orbiter and serviced by a common umbilical.  The probe will be dormant
during cruise except for annual checkouts of spacecraft systems and
instruments.  During this period, the orbiter will provide the probe with
electric power, commands, data transmission and some thermal control.

     Six hours before entering the atmosphere, the probe will be shooting
through space at about 40,000 mph.  At this time, its command unit
signals "wake up" and instruments begin collecting data on lightning, radio
emissions and energetic particles.

     A few hours later, the probe 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 -- should
take just a few minutes.  At maximum deceleration as the craft slows
from 115,000 mph to 100 mph, it will be hurtling against a force 350
times Earth's gravity.  The incandescent shock wave ahead of the probe
will be as bright as the sun and reach searing temperatures of up to
28,000 degrees Fahrenheit.  After the aerodynamic braking has slowed the
probe, it will drop its heat shields and deploy its parachute.  This will
allow the probe to float down about 125 miles through the clouds, passing
from a pressure of 1/10th that on Earth's surface to about 25 Earth
atmospheres.

     About 4 minutes after probe entry into JupiterUs atmosphere, a pilot
chute deploys and explosive nuts shoot off the top section of the probe's
protective shell.  As the cover whips away, it pulls out and opens the main
parachute attached to the inner capsule.  What remains of the probe's
outer shell, with its massive heat shield, falls away as the parachute
slows the instrument module.

     From there on, suspended from the main parachute, the probe's capsule
with its activated instruments floats downward toward the bright clouds
below.

     The probe will pass through the white cirrus clouds of ammonia
crystals - the highest cloud deck.  Beneath this ammonia layer probably lie
reddish-brown clouds of ammonium hydrosulfides.  Once past this layer,
the probe is expected to reach thick water clouds.  This lowest cloud layer
may act as a buffer between the uniformly mixed regions below and the
turbulent swirl of gases above.

     Jupiter's atmosphere is primarily hydrogen and helium.  For most of its
descent through Jupiter's three main cloud layers, the probe will be
immersed in gases at or below room temperature.  However, it may
encounter hurricane winds up to 200 mph and lightning and heavy rain at
the base of the water clouds believed to exist on the planet.  Eventually,
the probe will sink below these clouds, where rising pressure and
temperature will destroy it.  The probe's active life in Jupiter's
atmosphere is expected to be about 75 minutes in length.  The probe
batteries are not expected to last beyond this point, and the relaying
orbiter will move out of reach.

     To understand this huge gas planet, scientists must find out about its
chemical components and the dynamics of its atmosphere.  So far,
scientific data are limited to a two-dimensional view (pictures of the
planet's cloud tops) of a three-dimensional process (Jupiter's weather). 
But to explore such phenomena as the planet's incredible coloring, the
Great Red Spot and the swirling shapes and high-speed motion of its
topmost clouds, scientists must penetrate Jupiter's visible surface and
investigate the atmosphere concealed in the deep-lying layers below.

     A set of six scientific instruments on the probe will measure, among
other things, the radiation field near Jupiter, the temperature, pressure,
density and composition of the planet's atmosphere from its first faint
outer traces to the hot, murky hydrogen atmosphere 100 miles below the
cloud tops.  All of the information will be gathered during the probe's
descent on an 8-foot parachute.  Probe data will be sent to the Galileo
Orbiter 133,000 miles overhead then relayed across the half billion miles
to Deep Space Network stations on Earth.

     To return its science, the probe relay radio aboard the orbiter must
automatically acquire the probe signal below within 50 seconds, with a
success probability of 99.5 percent.  It must reacquire the signal
immediately should it become lost.

     To survive the heat and pressure of entry, the probe spacecraft is
composed of two separate units:  an inner capsule containing the
scientific instruments, encased in a virtually impenetrable outer shell. 
The probe weighs 750 pounds.  The outer shell is almost all heat shield
material.


The Orbiter at Jupiter

     After releasing the probe, the orbiter will use its main engine to go
into orbit around Jupiter.  This orbit, the first of 10 planned, will have a
period of about 8 months.  A close flyby of Ganymede in July 1996 will
shorten the orbit, and each time the Galileo orbiter returns to the inner
zone of satellites, it will make a gravity-assist close pass over one or
another of the satellites, changing Galileo's orbit while making close
observations.  These satellite encounters will be at altitudes as close as
125 miles above their surfaces.  Throughout the 22-month orbital phase,
Galileo will continue observing the planet and the satellites and continue
gathering data on the magnetospheric environment. 


SCIENTIFIC ACTIVITIES

     Galileo's scientific experiments will be carried out by more than 100
scientists from six nations.  Except for the radio science investigation,
these are supported by dedicated instruments on the Galileo orbiter and
probe.  NASA has appointed 15 interdisciplinary scientists whose studies
include data from more than one Galileo instrument.

     The instruments aboard the probe will measure the temperatures and
pressure of Jupiter's atmosphere at varying altitudes and determine its
chemical composition including major and minor constituents (such as
hydrogen, helium, ammonia, methane, and water) and the ratio of hydrogen
to helium.  Jupiter is thought to have a bulk composition similar to that of
the primitive solar nebula from which it was formed.  Precise
determination of the ratio of hydrogen to helium would provide an
important factual check of the Big Bang theory of the genesis of the
universe.

     Other probe experiments will determine the location and structure of
Jupiter's clouds, the existence and nature of its lightning, and the amount
of heat radiating from the planet compared to the heat absorbed from
sunlight.

     In addition, measurements will be made of Jupiter's numerous radio
emissions and of the high-energy particles trapped in the planet's
innermost magnetic field.  These measurements for Galileo will be made
within a distance of 26,000 miles from Jupiter's cloud tops, far closer
than the previous closest approach to Jupiter by Pioneer 11.  The probe
also will determine vertical wind shears using Doppler radio
measurements made of probe motions from the radio receiver aboard the
orbiter.

     Jupiter appears to radiate about twice as much energy as it receives
from the sun and the resulting convection currents from Jupiter's internal
heat source towards its cooler polar regions could explain some of the
planet's unusual weather patterns.

     Jupiter is over 11 times the diameter of Earth and spins about two and
one-half times faster -- a jovian day is only 10 hours long.  A point on the
equator of Jupiter's visible surface races along at 28,000 mph.  This rapid
spin may account for many of the bizarre circulation patterns observed on
the planet.


Spacecraft Scientific Activities

     The Galileo mission and systems were designed to investigate three
broad aspects of the Jupiter system: the planet's atmosphere, the
satellites and the magnetosphere.  The spacecraft is in three segments to
focus on these areas: the atmospheric probe; a non-spinning section of the
orbiter carrying cameras and other remote sensors; and the spinning main
section of the orbiter spacecraft which includes the propulsion module,
the communications antennas, main computers and most support systems
as well as the fields and particles instruments, which sense and measure
the environment directly as the spacecraft flies through it.


Probe Scientific Activities

     The probe will enter the atmosphere about 6 degrees north of the
equator.  The probe weighs just under 750 pounds and includes a
deceleration module to slow and protect the descent module, which
carries out the scientific mission.

     The deceleration module consists of an aeroshell and an aft cover
designed to block the heat generated by slowing from the probe's arrival
speed of about 115,000 miles per hour to subsonic speed in less than 2
minutes.  After the covers are released, the descent module deploys its
8-foot  parachute and its instruments, the control and data system, and
the radio-relay transmitter go to work.

     Operating at 128 bits per second, the dual L-band transmitters send
nearly identical streams of scientific data to the orbiter.  The probe's
relay radio aboard the orbiter will have two redundant receivers that
process probe science data, plus radio science and engineering data for
transmission to the orbiter communications system.  Minimum received
signal strength is 31 dBm.  The receivers also measure signal strength and
Doppler shift as part of the experiments for measuring wind speeds and
atmospheric absorption of radio signals.

     Probe electronics are powered by long-life, high-discharge-rate
34-volt lithium batteries, which remain dormant for more than 5 years
during the journey to Jupiter.  The batteries have an estimated capacity of
about 18 amp-hours on arrival at Jupiter.


Orbiter Scientific Activities

     The orbiter, in addition to delivering the probe to Jupiter and relaying
probe data to Earth, will support all the scientific investigations of
Venus, the Earth and moon, asteroids and the interplanetary medium,
Jupiter's satellites and magnetosphere, and observation of the giant
planet itself.

     The orbiter weighs about 5,200 pounds including about 2,400 pounds of
rocket propellant to be expended in some 30 relatively small maneuvers
during the long gravity-assisted flight to Jupiter, the large thrust
maneuver which puts the craft into its Jupiter orbit, and the 30 or so trim
maneuvers planned for the satellite tour phase.

     The retropropulsion module consists of 12 10-newton thrusters, a
single 400-newton engine, and the fuel, oxidizer, and pressurizing-gas
tanks, tubing, valves and control equipment.  (A thrust of 10 newtons
would support a weight of about 2.2 pounds at Earth's surface).  The
propulsion system was developed and built by
Messerschmitt-Bolkow-Blohm and provided by the Federal Republic of
Germany.

     The orbiter's maximum communications rate is 134 kilobits per second
(the equivalent of about one black-and-white image per minute); there are
other data rates, down to 10 bits per second, for transmitting engineering
data under poor conditions.  The spacecraft transmitters operate at
S-band and X-band (2295 and 8415 megahertz) frequencies between Earth
and on L-band between the probe.

     The high-gain antenna is a 16-foot umbrella-like reflector unfurled
after the first Earth flyby.  Two low-gain antennas (one pointed forward
and one aft, both mounted on the spinning section) are provided to support
communications during the Earth-Venus-Earth leg of the flight and
whenever the main antenna is not deployed and pointed at Earth.  The
despun section of the orbiter carries a radio relay antenna for receiving
the probe's data transmissions.

     Electrical power is provided to Galileo's equipment by two radioisotope
thermoelectric generators.  Heat produced by natural radioactive decay of
plutonium 238 dioxide is converted to approximately 500 watts of
electricity (570 watts at launch, 480 at the end of the mission) to operate
the orbiter equipment for its 8-year active period.  This is the same type
of power source used by the Voyager and Pioneer Jupiter spacecraft in
their long outer-planet missions, by the Viking lander spacecraft on Mars
and the lunar scientific packages left on the Moon.

     Most spacecraft are stabilized in flight either by spinning around a
major axis or by maintaining a fixed orientation in space, referenced to
the sun and another star.  Galileo represents a hybrid of these techniques,
with a spinning section rotating ordinarily at 3 rpm and a "despun" section
which is counter-rotated to provide a fixed orientation for cameras and
other remote sensors.

     Instruments that measure fields and particles, together with the main
antenna, the power supply, the propulsion module, most of the computers
and control electronics, are mounted on the spinning section.  The
instruments include magnetometer sensors mounted on a 36-foot boom to
escape interference from the spacecraft; a plasma instrument detecting
low-energy charged particles and a plasma-wave detector to study waves
generated in planetary magnetospheres and by lightning discharges; a
high-energy particle detector; and a detector of cosmic and Jovian dust.

     The despun section carries instruments and other equipment whose
operation depends on a fixed orientation in space.  The instruments include
the camera system; the near-infrared mapping spectrometer to make
multispectral images for atmosphere and surface chemical analysis; the
ultraviolet spectrometer to study gases and ionized gases; and the
photopolarimeter radiometer to measure radiant and reflected energy.  The
camera system is expected to obtain images of Jupiter's satellites at
resolutions from 20 to 1,000 times better than Voyager's best.

     This section also carries a dish antenna to track the probe in Jupiter's
atmosphere and pick up its signals for relay to Earth.  The probe is carried
on the despun section, and before it is released, the whole spacecraft is
spun up briefly to 10 rpm in order to spin-stabilize the probe.

     The Galileo spacecraft will carry out its complex operations, including
maneuvers, scientific observations and communications, in response to
stored sequences which are interpreted and executed by various on-board
computers.  These sequences are sent up to the orbiter periodically
through the Deep Space Network in the form of command loads. 

GROUND SYSTEMS

     Galileo communicates with Earth via NASA's Deep Space Network
(DSN), which has a complex of large antennas with receivers and
transmitters located in the California desert, another in Australia and a
third in Spain, linked to a network control center at NASAUs Jet Propulsion
Laboratory in Pasadena, Calif.  The spacecraft receives commands, sends
science and engineering data, and is tracked by Doppler and ranging
measurements through this network.

     At JPL, about 275 scientists, engineers and technicians, will be
supporting the mission at launch, increasing to nearly 400 for Jupiter
operations including support from the German retropropulsion team at
their control center in the FGR.  Their responsibilities include spacecraft
command, interpreting engineering and scientific data from Galileo to
understand its performance, and analyzing navigation data from the DSN. 
The controllers use a set of complex computer programs to help them
control the spacecraft and interpret the data.

     Because the time delay in radio signals from Earth to Jupiter and back
is more than an hour, the Galileo spacecraft was designed to operate from
programs sent to it in advance and stored in spacecraft memory.  A single
master sequence program can cover 4 weeks of quiet operations between
planetary and satellite encounters.  During busy Jupiter operations, one
program covers only a few days.  Actual spacecraft tasks are carried out
by several subsystems and scientific instruments, many of which work
from their own computers controlled by the main sequence.

     Designing these sequences is a complex process balancing the desire to
make certain scientific observations with the need to safeguard the
spacecraft and mission.  The sequence design process itself is supported
by software programs, for example, which display to the scientist maps of
the instrument coverage on the surface of an approaching satellite for a
given spacecraft orientation and trajectory.  Notwithstanding these aids,
a typical 3-day satellite encounter may take efforts spread over many
months to design, check and recheck.  The controllers also use software
designed to check the command sequence further against flight rules and
constraints.

     The spacecraft regularly reports its status and health through an
extensive set of engineering measurements.  Interpreting these data into
trends and averting or working around equipment failures is a major task
for the mission operations team.  Conclusions from this activity become
an important input, along with scientific plans, to the sequence design
process.  This too is supported by computer programs written and used in
the mission support area.

     Navigation is the process of estimating, from radio range and Doppler
measurements, the position and velocity of the spacecraft to predict its
flight path and design course-correcting maneuvers.  These calculations
must be done with computer support.  The Galileo mission, with its
complex gravity-assist flight to Jupiter and 10 gravity-assist satellite
encounters in the Jovian system, is extremely dependent on consistently
accurate navigation.

     In addition to the programs that directly operate the spacecraft and
are periodically transmitted to it, the mission operations team uses
software amounting to 650,000 lines of programming code in the sequence
design process; 1,615,000 lines in the telemetry interpretation; and
550,000 lines of code in navigation.  These must all be written, checked,
tested, used in mission simulations and, in many cases, revised before the
mission can begin.

Science investigators are located at JPL or other university laboratories
and linked by computers.  From any of these locations, the scientists can
be involved in developing the sequences affecting their experiments and,
in some cases, in helping to change preplanned sequences to follow up on
unexpected discoveries with second looks and confirming observations.


JUPITER'S SYSTEM

     Jupiter is the largest and fastest-spinning planet in the solar system. 
Its radius is more than 11 times Earth's, and its mass is 318 times that of
our planet.  Named for the chief of the Roman gods, Jupiter contains more
mass than all the other planets combined.  It is made mostly of light
elements, principally hydrogen and helium.  Its atmosphere and clouds are
deep and dense, and a significant amount of energy is emitted from its
interior.

     The earliest Earth-based telescopic observations showed bands and
spots in Jupiter's atmosphere.  One storm system, the Red Spot, has been
seen to persist over three centuries.

     Atmospheric forms and dynamics were observed in increasing detail
with the Pioneer and Voyager flyby spacecraft, and Earth-based infrared
astronomers have recently studied the nature and vertical dynamics of
deeper clouds.

     Sixteen satellites are known.  The four largest, discovered by the
Italian scientist Galileo Galilei in 1610, are the size of small planets. 
The innermost of these, Io, has active sulfurous volcanoes, discovered by
Voyager 1 and further observed by Voyager 2 and Earth-based infrared
astronomy.  Io and Europa are about the size and density of Earth's moon (3
to 4 times the density of water) and probably rocky inside.  Ganymede and
Callisto, further out from Jupiter, are the size of Mercury but less than
twice as dense as water.  Their cratered surfaces look icy in Voyager
images, and they may be composed partly of ice or water.

     Of the other satellites, eight (probably captured asteroids) orbit
irregularly far from the planet, and four (three discovered by the Voyager
mission in 1979) are close to the planet.  Voyager also discovered a thin
ring system at Jupiter in 1979.

     Jupiter has the strongest planetary magnetic field known.  The
resulting magnetosphere is a huge teardrop-shaped, plasma-filled cavity
in the solar wind pointing away from the sun.  JupiterUs magnetosphere is
the largest single entity in our solar system, measuring more than 14
times the diameter of the sun.  The inner part of the magnetic field is
doughnut- shaped, but farther out it flattens into a disk.  The magnetic
poles are offset and tilted relative to Jupiter's axis of rotation, so the
field appears to wobble with Jupiter's rotation (just under 10 hours),
sweeping up and down across the inner satellites and making waves
throughout the magnetosphere. 


WHY JUPITER INVESTIGATIONS ARE IMPORTANT

     With a thin skin of turbulent winds and brilliant, swift-moving clouds,
the huge sphere of Jupiter is a vast sea of liquid hydrogen and helium. 
Jupiter's composition (about 88 percent hydrogen and 11 percent helium
with small amounts of methane, ammonia and water) is thought to
resemble the makeup of the solar nebula, the cloud of gas and dust from
which the sun and planets formed.  Scientists believe Jupiter holds
important clues to conditions in the early solar system and the process of
planet formation.

     Jupiter may also provide insights into the formation of the universe
itself.  Since it resembles the interstellar gas and dust  that are thought
to have been created in the "Big Bang," studies of Jupiter may help
scientists calibrate models of the beginning of the universe.

     Though starlike in composition, Jupiter is too small to generate
temperatures high enough to ignite nuclear fusion, the process that
powers the stars.  Some scientists believe that the sun and Jupiter began
as unequal partners in a binary star system.  (If a double star system had
developed, it is unlikely life could have arisen in the solar system.)  While
in a sense a "failed star," Jupiter is almost as large as a planet can be.  If
it contained more mass, it would not have grown larger, but would have
shrunk from compression by its own gravity.  If it were 100 times more
massive, thermonuclear reactions would ignite, and Jupiter would be a
star.

     For a brief period after its formation, Jupiter was much hotter, more
luminous, and about 10 times larger than it is now, scientists believe. 
Soon after accretion (the condensation of a gas and dust cloud into a
planet), its brightness dropped from about one percent of the Sun's to
about one billionth -- a decline of ten million times.

     In its present state Jupiter emits about twice as much heat as it
receives from the Sun.  The loss of this heat -- residual energy left over
from the compressive heat of accretion -- means that Jupiter is cooling
and losing energy at a tremendously rapid rate.  Temperatures in Jupiter's
core, which were about 90,000 degrees Fahrenheit in the planet's hot,
early phase, are now about 54,000 degrees Fahrenheit, 100 times hotter
than any terrestrial surface, but 500 times cooler than the temperature at
the center of the sun.  Temperatures on Jupiter now range from 54,000
degrees Fahrenheit at the core to minus 248 degrees Fahrenheit at the top
of the cloud banks.

     Mainly uniform in composition, Jupiter's structure is determined by
gradations in temperature and pressure.  Deep in Jupiter's interior there is
thought to be a small rocky core, comprising about four percent of the
planet's mass.  This "small" core (about the size of 10 Earths) is
surrounded by a 25,000-mile-thick layer of liquid metallic hydrogen. 
(Metallic hydrogen is liquid, but sufficiently compressed to behave as
metal.)  Motions of this liquid "metal" are the source of the planet's
enormous magnetic field.  This field is created by the same dynamo effect
found in the metallic cores of Earth and other planets.

     At the outer limit of the metallic hydrogen layer, pressures equal three
million times that of Earth's atmosphere and the temperature has cooled
to 19,000 degrees Fahrenheit.

     Surrounding the central metallic hydrogen region is an outer shell of
"liquid" molecular hydrogen.  Huge pressures compress Jupiter's gaseous
hydrogen until, at this level, it behaves like a liquid.  The liquid hydrogen
layer extends upward for about 15,000 miles.  Then it gradually becomes
gaseous.  This transition region between liquid and gas marks, in a sense,
where the solid and liquid planet ends and its atmosphere begins.

     From here, Jupiter's atmosphere extends up for 600 more miles, but
only in the top 50 miles are found the brilliant bands of clouds for which
Jupiter is known.  The tops of these bands are colored bright yellow, red
and orange from traces of phosphorous and sulfur.  Five or six of these
bands, counterflowing east and west, encircle the planet in each
hemisphere.  At one point near Jupiter's equator, east winds of 220 mph
blow right next to west winds of 110 mph.  At boundaries of these bands,
rapid changes in wind speed and direction create large areas of turbulence
and shear.  These are the same forces that create tornados here on Earth. 
On Jupiter, these "baroclinic instabilities" are major phenomena, creating
chaotic, swirling winds and spiral features such as White Ovals.

     The brightest cloud banks, known as zones, are believed to be higher,
cooler areas where gases are ascending.  The darker bands, called belts,
are thought to be warmer, cloudier regions of descent.

     The top cloud layer consists of white cirrus clouds of ammonia
crystals, at a pressure six-tenths that of Earth's atmosphere at sea level
(.6 bar).  Beneath this layer, at a pressure of about two Earth atmospheres
(2 bars) and a temperature of near minus 160 degrees Fahrenheit, a
reddish-brown cloud of ammonium hydrosulfide is predicted.

     At a pressure of about 6 bars, there are believed to be clouds of water
and ice.  However, recent Earth-based spectroscopic studies suggest that
there may be less water on Jupiter than expected.  While scientists
previously believed Jupiter and the sun would have similar proportions of
water, recent work indicates there may be 100 times less water on
Jupiter than if it had a solar mixture of elements.  If this is the case,
there may be only a thin layer of water-ice at the 6 bar level.

     However, Jupiter's cloud structure, except for the highest layer of
ammonia crystals, remains uncertain.  The height of the lower clouds is
still theoretical -- clouds are predicted to lie at the temperature levels
where their assumed constituents are expected to condense.  The Galileo
probe will make the first direct observations of Jupiter's lower
atmosphere and clouds, providing crucial information.

     The forces driving Jupiter's fast-moving winds are not well understood
yet.  The classical explanation holds that strong currents are created by
convection of heat from Jupiter's hot interior to the cooler polar regions,
much as winds and ocean currents are driven on Earth, from equator to
poles.  But temperature differences do not fully explain wind velocities
that can reach 265 mph.  An alternative theory is that pressure
differences, due to changes in the thermodynamic state of hydrogen at
high and low temperatures, set up the wind jets.

     Jupiter's rapid rotation rate is thought to have effects on wind
velocity and to produce some of Jupiter's bizarre circulation patterns,
including many spiral features.  These rotational effects are known as
manifestations of the Coriolis force.  Coriolis force is what determines
the spin direction of weather systems.  It basically means that on the
surface of a sphere (a planet), a parcel of gas farther from the poles has a
higher rotational velocity around the planet than a parcel closer to the
poles.  As gases then move north or south, interacting parcels with
different velocities produce vortices (whirlpools).  This may account for
some of Jupiter's circular surface features.

Jupiter spins faster than any planet in the solar system.  Though 11 times
Earth's diameter, Jupiter spins more than twice as fast (once in 10 hours),
giving gases on the surface extremely high rates of travel -- 22,000 mph
at the equator, compared with 1000 mph for air at Earth's equator. 
Jupiter's rapid spin also causes this gas and liquid planet to flatten
markedly at the poles and bulge at the equator.

     Visible at the top of Jupiter's atmosphere are eye-catching features
such as the famous Great Red Spot and the exotic White Ovals, Brown
Barges and White Plumes.  The Great Red Spot, which is 25,000 miles wide
and large enough to swallow three Earths, is an enormous oval eddy of
swirling gases.  It is driven by two counter-flowing jet streams, which
pass, one on each side of it, moving in opposite directions, each with
speeds of 100-200 mph.  The Great Red Spot was first discovered in 1664,
by the British scientist Roger Hook, using Galileo's telescope.  In the three
centuries since, the  huge vortex has remained constant in latitude in
Jupiter's southern equatorial belt.  Because of its stable position,
astronomers once thought it might be a volcano.

     Another past theory compared the Great Red Spot to a gigantic
hurricane.  However, the GRS rotates anti-cyclonically while hurricanes
are cyclonic features (counterclockwise in the northern hemisphere,
clockwise in the southern) -- and the dynamics of the Great Red Spot
appear unrelated to moisture.

  The Great Red Spot most closely resembles an enormous tornado, a huge
vortex that sucks in smaller vortices.  The Coriolis effect  created by
Jupiter's fast spin, appears to be the key to the dynamics that drive the
spot.

     The source of the Great Red Spot's color remains a mystery.  Many
scientists now believe it to be caused by phosphorus, but its spectral line
does not quite match that of phosphorus.  The GRS may be the largest in a
whole array of spiral phenomena with similar dynamics.  About a dozen
white ovals, circulation patterns resembling the GRS, exist in the
southern latitudes of Jupiter and appear to be driven by the same forces. 
Scientists do not know why these ovals are white.

     Scientists believe the brown barges, which appear like dark patches on
the planet, are holes in the upper clouds, through which the reddish-brown
lower cloud layer may be glimpsed.  The equatorial plumes, or white
plumes, may be a type of wispy cirrus anvil cloud.


SPACECRAFT CHARACTERISTICS

            
                          Orbiter                   Probe

Mass,lbs.                 5,242                     744
Propellant, lbs.          2,400                     none
Height (in-flight)        15 feet                   34 inches
Inflight span             30 feet
(w/oboom)
Instrument payload       10 instruments            6 instruments
Payload mass, lbs.       260                       66
Electric power, watts    570-480                   730
                         (RTGs)         (Lithium-sulfur battery)


GALILEO MANAGEMENT

     The Galileo Project is managed for NASA's Office of Space Science and
Applications by the NASA Jet Propulsion Laboratory, Pasadena, Calif.  This
responsibility includes designing, building, testing, operating and tracking
Galileo.  NASA's Ames Research Center, Moffett Field, Calif. is responsible
for the atmosphere probe, which was built by Hughes Aircraft Company, El
Segundo, Calif.

     The probe project and science teams will be stationed at Ames during
pre-mission, mission operations, and data reduction periods.  Team
members will be at Jet Propulsion Laboratory for probe entry.

     The Federal Republic of Germany has furnished the orbiter's
retropropulsion module and is participating in the scientific
investigations.  The radioisotope thermoelectric generators were designed
and built for the U.S.  Department of Energy by the General Electric
Company.


GALILEO ORBITER AND PROBE SCIENTIFIC INVESTIGATIONS

Listed by experiment/instrument and including the Principal Investigator
and scientific objectives of that investigation:

PROBE

Atmospheric Structure; A. Seiff, NASA's Ames Research Center;
temperature, pressure, density, molecular weight profiles;

Neutral Mass Spectrometer; H. Niemann, NASA's Goddard Space Flight
Center; chemical composition

Helium Abundance; U. von Zahn, Bonn University, FRG; helium/hydrogen
ratio

Nephelometer; B. Ragent, NASA's Ames Research Center; clouds,
solid/liquid particles

Net Flux Radiometer; L. Sromovsky, University of Wisconsin-Madison;
thermal/solar energy profiles

Lightning/Energetic Particles; L. Lanzerotti, Bell Laboratories; detect
lightning, measuring energetic particles


ORBITER (DESPUN PLATFORM)

Solid-State Imaging Camera; M. Belton, National Optical Astronomy
Observatories (Team Leader); Galilean satellites at 1-km resolution or
better

Near-Infrared Mapping Spectrometer; R. Carlson, NASA's Jet Propulsion
Laboratory; surface/atmospheric composition, thermal mapping

Ultraviolet Spectrometer; C. Hord, University of Colorado; atmospheric
gases, aerosols

Photopolarimeter Radiometer; J. Hansen, Goddard Institute for Space
Studies; atmospheric particles, thermal/reflected radiation


ORBITER (SPINNING SPACECRAFT SECTION)

Magnetometer; M. Kivelson, University of California at Los Angeles;
strength and fluctuations of magnetic fields

Energetic Particles; D. Williams, Johns Hopkins Applied Physics
Laboratory; electrons, protons, heavy ions in magnetosphere and
interplanetary space

Plasma; L. Frank, University of Iowa; composition, energy, distribution of
magnetospheric ions

Plasma Wave; D. Gurnett, University of Iowa; electromagnetic waves and
wave-particle interactions

Dust; E. Grun, Max Planck Institute; mass, velocity, charge of submicron
particles

Radio Science - Celestial Mechanics; J. Anderson, JPL (Team Leader);
masses and motions of bodies from spacecraft tracking;

Radio Science - Propagation; H. T. Howard, Stanford University; satellite
radii, atmospheric structure both from radio propagation


INTERDISCIPLINARY INVESTIGATORS

F. P. Fanale; University of Hawaii

P. Gierasch; Cornell University

D. M. Hunten; University of Arizona

A. P. Ingersoll; California Institute of Technology

H. Masursky; U.  S.  Geological Survey

D. Morrison; Ames Research Center

M. McElroy; Harvard University

G. S. Orton; NASA's Jet Propulsion Laboratory

T. Owen; State University of New York, Stonybrook

J. B. Pollack; NASA's Ames Research Center

C. T  Russell; University of California at Los Angeles

C. Sagan; Cornell University

G. Schubert; University of California at Los Angeles

J. Van Allen; University of Iowa


STS-34 INERTIAL UPPER STAGE (IUS-19)

     The Inertial Upper Stage (IUS) will again be used with the Space
Shuttle, this time to transport NASA's Galileo spacecraft out of Earth's
orbit to Jupiter, a 2.5-billion-mile journey.       

     The IUS has been used previously to place three Tracking and Data
Relay Satellites in geostationary orbit as well as to inject the Magellan
spacecraft into its interplanetary trajectory to Venus.  In addition, the
IUS has been selected by the agency for the Ulysses solar polar orbit
mission.

     After 2 1/2 years of competition, Boeing Aerospace Co., Seattle, was
selected in August 1976 to begin preliminary design of the IUS.  The IUS
was developed and built under contract to the Air Force Systems
Command's Space Systems Division.  The Space Systems Division is
executive agent for all Department of Defense activities pertaining to the
Space Shuttle system.  NASA, through the Marshall Space Flight Center,
Huntsville, Ala., purchases the IUS through the Air Force and manages the
integration activities of the upper stage to NASA spacecraft. 


Specifications

     IUS-19, to be used on mission STS-34, is a two-stage vehicle weighing
approximately 32,500 lbs.  Each stage has a solid rocket motor (SRM),
preferred over liquid-fueled engines because of SRM's relative simplicity,
high reliability, low cost and safety.

     The IUS is 17 ft. long and 9.25 ft. in diameter.  It consists of an aft
skirt, an aft stage SRM generating approximately 42,000 lbs. of thrust, an
interstage, a forward-stage SRM generating approximately 18,000 lbs. of
thrust, and an equipment support section.       


Airborne Support Equipment

     The IUS Airborne Support Equipment (ASE) is the mechanical, avionics
and structural equipment located in the orbiter.  The ASE supports the IUS
and the Galileo in the orbiter payload bay and elevates the combination for
final checkout and deployment from the orbiter.

     The IUS ASE consists of the structure, electromechanical mechanisms,
batteries, electronics and cabling to support the Galileo/IUS.  These ASE
subsystems enable the deployment of the combined vehicle; provide,
distribute and/or control electrical power to the IUS and spacecraft;
provide plumbing to cool the radioisotope thermoelectric generator (RTG)
aboard Galileo; and serve as communication paths between the IUS and/or
spacecraft and the orbiter.


IUS Structure

     The IUS structure is capable of supporting loads generated internally
and also by the cantilevered spacecraft during orbiter operations and the
IUS free flight.  It is made of aluminum skin-stringer construction, with
longerons and ring frames.      


Equipment Support Section 

     The top of the equipment support section contains the spacecraft
interface mounting ring and electrical interface connector segment for
mating and integrating the spacecraft with the IUS.  Thermal isolation is
provided by a multilayer insulation blanket across the interface between
the IUS and Galileo.

     The equipment support section also contains the avionics which
provide guidance, navigation, control, telemetry, command and data
management, reaction control and electrical power.  All mission-critical
components of the avionics system, along with thrust vector actuators,
reaction control thrusters, motor igniter and pyrotechnic stage separation
equipment are redundant to assure reliability of better than 98 percent.


IUS Avionics Subsystems

     The avionics subsystems consist of the telemetry, tracking and
command subsystems; guidance and navigation subsystem; data
management; thrust vector control; and electrical power subsystems. 
These subsystems include all the electronic and electrical hardware used
to perform all computations, signal conditioning, data processing and
formatting associated with navigation, guidance, control, data and
redundancy management.  The IUS avionics subsystems also provide the
equipment for communications between the orbiter and ground stations as
well as electrical power distribution.

     Attitude control in response to guidance commands is provided by
thrust vectoring during powered flight and by reaction control thrusters
while coasting.  Attitude is compared with guidance commands to
generate error signals.  During solid motor firing, these commands gimble
the IUS's movable nozzle to provide the desired pitch and yaw control.  The
IUS's roll axis thrusters maintain roll control.  While coasting, the error
signals are processed in the computer to generate thruster commands to
maintain the vehicle's altitude or to maneuver the vehicle.  

     The IUS electrical power subsystem consists of avionics batteries, IUS
power distribution units, a power transfer unit, utility batteries, a
pyrotechnic switching unit, an IUS wiring harness and umbilical and
staging connectors.  The IUS avionics system provides 5-volt electrical
power to the Galileo/IUS interface connector for use by the spacecraft
telemetry system.


IUS Solid Rocket Motors

     The IUS two-stage vehicle uses a large solid rocket motor and a small
solid rocket motor.  These motors employ movable nozzles for thrust
vector control.  The nozzles provide up to 4 degrees of steering on the
large motor and 7 degrees on the small motor.  The large motor is the
longest-thrusting duration SRM ever developed for space, with the
capability to thrust as long as 150 seconds.  Mission requirements and
constraints (such as weight) can be met by tailoring the amount of
propellant carried.  The IUS-19 first-stage motor will carry 21,488 lb. of
propellant; the second stage 6,067 lb.        


Reaction Control System 

The reaction control system controls the Galileo/IUS spacecraft attitude
during coasting, roll control during SRM thrustings, velocity impulses for
accurate orbit injection and the final collision-avoidance maneuver after
separation from the Galileo spacecraft.  

As a minimum, the IUS includes one reaction control fuel tank with a
capacity of 120 lb. of hydrazine.  Production options are available to add a
second or third tank.  However, IUS-19 will require only one tank.


IUS To Spacecraft Interfaces

Galileo is physically attached to the IUS at eight attachment points,
providing substantial load-carrying capability while minimizing the
transfer of heat across the connecting points.   Power, command and data
transmission between the two are provided by several IUS interface
connectors.   In addition, the IUS provides a multilayer insulation blanket
of aluminized Kapton with polyester net spacers across the Galileo/IUS
interface, along with an aluminized Beta cloth outer layer.  All IUS
thermal blankets are vented toward and into the IUS cavity, which in turn
is vented to the orbiter payload bay.  There is no gas flow between the
spacecraft and the IUS.  The thermal blankets are grounded to the IUS
structure to prevent electrostatic charge buildup.


Flight Sequence

After the orbiter payload bay doors are opened in orbit, the orbiter will
maintain a preselected attitude to keep the payload within thermal
requirements and constraints. 

On-orbit predeployment checkout begins, followed by an IUS command link
check and spacecraft communications command check.  Orbiter trim
maneuvers are normally performed at this time.  

     Forward payload restraints will be released and the aft frame of the
airborne-support equipment will tilt the Galileo/IUS to 29 degrees.  This
will extend the payload into space just outside the orbiter payload bay,
allowing direct communication with Earth during systems checkout.  The
orbiter then will be maneuvered to the deployment attitude.  If a problem
has developed within the spacecraft or IUS, the IUS and its payload can be
restowed.

     Prior to deployment, the spacecraft electrical power source will be
switched from orbiter power to IUS internal power by the orbiter flight
crew.  After verifying that the spacecraft is on IUS internal power and
that all Galileo/IUS predeployment operations have been successfully
completed, a GO/NO-GO decision for deployment will be sent to the crew
from ground support.

     When the orbiter flight crew is given a "Go" decision, they will
activate the ordnance that separates the spacecraft's umbilical cables. 
The crew then will command the electromechanical tilt actuator to raise
the tilt table to a 58-degree deployment position.  The orbiter's RCS
thrusters will be inhibited and an ordnance-separation device initiated to
physically separate the IUS/spacecraft combination from the tilt table.

     Six hours, 20 minutes into the mission, compressed springs provide the
force to jettison the IUS/Galileo from the orbiter payload bay at
approximately 6 inches per second.  The deployment is normally performed
in the shadow of the orbiter or in Earth eclipse.  

     The tilt table then will be lowered to minus 6 degrees after IUS and its
spacecraft are deployed.  A small orbiter maneuver is made to back away
from IUS/Galileo.  Approximately 15 minutes after deployment, the
orbiter's OMS engines will be ignited to move the orbiter away from its
released payload.

     After deployment, the IUS/Galileo is controlled by the IUS onboard
computers.  Approximately 10 minutes after IUS/Galileo deployment from
the orbiter, the IUS onboard computer will send out signals used by the
IUS and/or Galileo to begin mission sequence events.  This signal will also
enable the IUS reaction control system.  All subsequent operations will be
sequenced by the IUS computer, from transfer orbit injection through
spacecraft separation and IUS deactivation. 

     After the RCS has been activated, the IUS will maneuver to the
required thermal attitude and perform any required spacecraft thermal
control maneuvers.

     At approximately 45 minutes after deployment from the orbiter, the

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End of SPACE Digest V10 #138
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