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  <Version>2.2.6</Version>
  <Observatory>
    <ResourceID>spase://CDPP/Observatory/AMDA/Galileo</ResourceID>
    <ResourceHeader>
      <ResourceName>Galileo</ResourceName>
      <AlternateName>Galileo Orbiter</AlternateName>
      <AlternateName>Jupiter Orbiter-Probe</AlternateName>
      <ReleaseDate>2012-11-27T00:00:00Z</ReleaseDate>
      <Description>
Science Objectives
==================
The Galileo mission consists of two spacecraft: an orbiter and an atmospheric probe. The orbiter will be the sixth spacecraft to explore the Jovian magnetosphere, but the first to be placed into orbit around the giant planet. Scientific objectives addressed by the orbiter are to: (1) investigate the circulation and dynamics of the Jovian atmosphere; (2) investigate the upper Jovian atmosphere and ionosphere; (3) characterize the morphology, geology, and physical state of the Galilean satellites; (4) investigate the composition and distribution of surface minerals on the Galilean satellites; (5) determine the gravitational and magnetic fields and dynamic properties of the Galilean satellites; (6) study the atmospheres, ionospheres, and extended gas clouds of the Galilean satellites; (7) study the interaction of the Jovian magnetosphere with the Galilean satellites; and, (8) characterize the vector magnetic field and the energy spectra, composition, and angular distribution of energetic particles and plasma to a distance of 150 Rj.

Spacecraft Overview
===================

The structure of the orbiter is divided into two sections. The main body of the spacecraft, comprised of the electronics bays, propellant system, RTG and science booms, and high-gain antenna, rotates at rates of 3.25 or 10.5 rpm. The despun section, aft of the main body, uses an electric motor to drive it counter to the rotation of the main section. This dual spin attitude control system accommodates instruments which require stable, accurate pointing (the imaging instruments) and those which benefit from repetitive, broad-angular coverage (the various particles and fields instruments). The length of the spacecraft is 9 m and, with the high-gain antenna (HGA) deployed, is 4.6 m in diameter.

Power is provided to the spacecraft through the use of two radioisotope thermal generators (RTGs), each of which is located at the end of a short boom. The magnetometer sensors and plasma wave antenna are located on yet another boom, 10.9 m in length.

Although it was intended that communications with the Deep Space Network (DSN) would be primarily through the HGA (which would remain pointing toward the Earth at all times), thermal constraints forced the use of the two low-gain antennas prior to the first Earth flyby. HGA deployment was planned thereafter, but at least three of the HGA "ribs" were unable to be moved much beyond their launch configurations, thereby jeopardizing the total science return of the mission. Several attempts have been made to deploy the antenna through a variety of techniques.

QUICK FACTS
===========

Spacecraft
==========

Dimensions: 5.3 meters (17 feet) high; magnetometer boom extends 11 meters (36 feet) to one side

Weight: 2,223 kilograms (2.5 tons, or 4,902 pounds), including 118 kilograms (260 pounds) of science instruments and 925 kilograms (2040 pounds) of propellant

Power: 570 watts (at launch) from radioisotope thermoelectric generators

Science instruments: Solid-state imaging camera, near-infrared mapping spectrometer,
ultraviolet spectrometer, photopolarimeter radiometer, magnetometer, energetic particles detector, plasma investigation, plasma wave subsystem, dust detector, heavy ion counter

Atmospheric Probe
=================

Size: 127 centimeters (50 inches) diameter, 91 centimeters (36 inches) high

Weight: 339 kilograms (750 pounds)

Science instruments: Atmospheric structure, neutral mass spectrometer, helium abundance,
nephelometer, net flux radiometer, lightning/energetic particles, doppler wind experiment

Mission
=======

Launch: Oct. 18, 1989 from Kennedy Space Center, Fla., on space shuttle Atlantis on mission STS-34

End of Mission: Sep. 21, 2003

Primary mission: October 1989 to December 1997

Extended missions: Three, from 1997 to 2003

Venus flyby: Feb. 10, 1990, at altitude of 16,000 km (10,000 mi)

Earth flybys: Dec. 8, 1990, at altitude of 960 km (597 mi); Dec. 8, 1992 at altitude of
303 km (188 mi)

Asteroid Gaspra flyby: Oct. 29, 1991, at 1,601 km (1,000 mi)

Comet Shoemaker-Levy 9: Impacts of comet fragments into Jupiter observed while en route
in July 1994

Asteroid Ida flyby: Aug. 28, 1993, at 2,400 km (1,400 mi)

Atmospheric probe release: July 12, 1995

Probe speed into Jupiter's atmosphere: 47.6 km per second (106,000 mi per hour) Jupiter arrival and orbit insertion: Dec. 7, 1995

Probe atmospheric entry and relay: Dec. 7, 1995

Number of Jupiter orbits during entire mission: 34

Number of flybys of Jupiter moons: Io 7, Callisto 8, Ganymede 8, Europa 11, Amalthea 1

  Mission Overview
  ================

The Galileo mission utilizes a single launch of a combined
    Orbiter and Probe using the space shuttle Atlantis and an
    inertial upper stage (IUS) to inject the Galileo spacecraft
    on its interplanetary trajectory to Jupiter. The launch
    window occurs from October 12, 1989 to November 21, 1989.
    Since the IUS does not have the energy to inject Galileo on
    a direct trajectory to Jupiter, the spacecraft will instead
    be launched first towards Venus for the first leg of its
    Venus-Earth-Earth gravity assist (VEEGA) trajectory to
    Jupiter. Target-of-opportunity science observations will be
    made at Venus (closest approach February 10, 1990), the
    first Earth encounter (closest approach to Earth and Moon
    December 8, 1990), the asteroid Gaspra (closest approach
    October 29, 1991), the second Earth encounter (closest
    approach to Earth and Moon December 8, 1992), and the
    asteroid Ida (closest approach August 28, 1993).

    At about 150 days before Galileo arrives at Jupiter, the
    Probe is separated from the Orbiter. From this moment in
    time, the Probe is on a ballistic trajectory to the Probe
    entry point, about 6 degrees north latitude, into the
    atmosphere of Jupiter. Using its 400 Newton engine for the
    first time, the Orbiter executes an Orbiter deflection
    maneuver to keep from following the Probe into the
    atmosphere of Jupiter, and to retarget the Orbiter to the
    proper encounter conditions required for the Jupiter Orbit
    Insertion phase of the mission.

    A close flyby (about 1,000 kilometer altitude) of the Jovian
    satellite Io occurs in this phase for the purpose of science
    observations as well as to slow the Orbiter down relative to
    Jupiter by nearly 200 meters/second in order to reduce the
    propellant required during the Jupiter Orbit Insertion (JOI)
    400 Newton engine burn to capture Galileo into Jupiter's
    orbit. Perijove of about 4 Jupiter radii occurs about 4
    hours after Io encounter. A few minutes after perijove
    passage, the Probe entry and beginning of the relay of data
    from the Probe to the Orbiter occurs.

    The Probe mission and data relay lasts 75 minutes, after
    which JOI is performed, slowing the Orbiter down relative to
    Jupiter by about 630 meters/second. The initial orbit period
    is about 200 days. A large 400 Newton engine burn is
    performed at the first apojove in order to raise perijove
    from 4 Jupiter radii to about 9 Jupiter radii, thus allowing
    at least 11 orbits with 10 targeted satellite encounters to
    be completed by the Orbiter without exceeding the allowed
    total accumulated radiation exposure at the spacecraft. Only
    three orbits would be allowed before exceeding this limit if
    perijove were allowed to stay at 4 Jupiter radii, where the
    radiation environment is very severe. Also during this
    perijove raise maneuver, Galileo is targeted to the
    satellite Ganymede, the first of its Galilean satellite
    encounters following JOI.

    At this point, the targeting to satellite encounters begins,
    such that a satellite tour consisting of a minimum of 10
    targeted satellite encounters is achieved within the 23
    month period allotted for the satellite tour. During the
    course of the satellite tour, the orientation, shape and
    size of the spacecraft orbits around the Jovian system,
    referred to as petals because of how the spacecraft orbits
    appear on a plan view of the Jovian satellite tour
    trajectory, is controlled almost exclusively by gravity
    assists of the satellites themselves. The orbit periods are
    pumped down by successive encounters with the satellites
    from the initial 200 days to approximately 35-40 days
    between encounters. At the 8th orbit, when the orbit petal
    orientation is approximately in the anti-sun direction, the
    period is again pumped up to about 100 days, allowing one of
    the primary objectives, probing the Jovian magnetotail, to
    be accomplished. After this magnetotail orbit, the period is
    again pumped down, by gravity assist encounters with the
    Jovian satellites, to 35-40 days for the final 2-3 targeted
    encounters.
          </Description>
      <Acknowledgement/>
      <Contact>
        <PersonID>spase://SMWG/Person/Torrence.V.Johnson</PersonID>
        <Role>ProjectScientist</Role>
      </Contact>
      <InformationURL>
        <Name>NSSDC's Master Catalog</Name>
        <URL>http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1989-084B</URL>
        <Description>Information about the Galileo Orbiter mission</Description>
      </InformationURL>
    </ResourceHeader>
    <Location> 
      <ObservatoryRegion>Jupiter</ObservatoryRegion>   
      <ObservatoryRegion>Jupiter</ObservatoryRegion>
      <ObservatoryRegion>Asteroid</ObservatoryRegion>
      <ObservatoryRegion>Heliosphere</ObservatoryRegion>
      <ObservatoryRegion>Earth.Magnetosphere</ObservatoryRegion>
      <ObservatoryRegion>Earth.Magnetosphere.Magnetotail</ObservatoryRegion>
    </Location>
  </Observatory>
</Spase>