Planetary Data System Banner
Home Data Services Tools Documents Related Sites About PDS Sitemap

Mission Information

MISSION_NAME VOYAGER
MISSION_NAME_OR_ALIAS MJS77
MISSION_START_DATE 1972-07-01
MISSION_STOP_DATE NULL
MISSION_DESCRIPTION
 
    Mission Overview
    ================
      The twin Voyager spacecraft, over the course of a dozen years,
      drew back the curtain on nearly half of the solar system.  From
      launch in 1977 through the spectacular parting shots of Neptune
      at the outer reaches of the solar system in 1989, this pair of
      spacecraft explored four planets -- Jupiter, Saturn, Uranus and
      Neptune -- as well as dozens of moons, and the rings and
      magnetic environments of those planetary systems.
 
      The Voyagers were designed to take advantage of a rare geometric
      arrangement of the outer planets that occurs only once every 176
      years.  This configuration allows a single spacecraft to swing
      by all four gas giants without the need for large onboard
      propulsion systems; the flyby of each planet both accelerates
      the spacecraft and bends its flight path.  Without these gravity
      assists, the flight time to Neptune would have been 30 years.
 
      The second of the two Voyager spacecraft, Voyager 2, was
      launched first, on 20 August 1977.  It was followed on 5
      September 1977 by Voyager 1, which was put on a faster, shorter
      trajectory to Jupiter.  Both launches took place from the Cape
      Canaveral Air Force Station in Florida.
 
      Eighteen months after launch, Voyager 1 reached Jupiter, 650
      million kilometers away.  The spacecraft made its closest
      approach on 5 March 1979, while Voyager 2 followed on 9 July
      of the same year.  Images streamed back from the pair of
      spacecraft showing the complex, swirling turbulence of
      Jupiter's atmosphere in exquisite detail.  A giant storm, three
      times the size of Earth, raged in Jupiter's upper atmosphere,
      surrounded by rippling currents that rotated about it.
      Voyager 1 found nine active volcanoes erupting on Io, the
      innermost of Jupiter's four major moons.  Four months later,
      Voyager 2 found that eight of the nine volcanoes were still
      active.  A thin, dusty ring was also discovered around Jupiter,
      forcing revision of theories about origins and mechanics of
      planetary ring systems.
 
      At Saturn, both Voyagers took high-resolution images to help
      determine ring composition and dynamics.  The Voyager 1
      encounter took place in November 1980 and the Voyager 2
      encounter was in August 1981.  Voyager 1 was targeted to fly
      close to Saturn's largest moon Titan.  This resulted in a
      south polar passage of Saturn, which redirected the spacecraft
      northward of the ecliptic.
 
      Voyager 2 continued on to Uranus where ten new moons were
      discovered in the Uranus system.  The planet's magnetic
      field was found to be significantly offset from the planet's
      axis of rotation.
 
      In August 1989, Voyager 2 flew past Neptune.  Because Neptune
      receives so little sunlight, many scientists had expected to
      see a placid, featureless planet.  Instead, Voyager showed a
      dynamic atmosphere with winds blowing westward, opposite the
      direction of rotation, at speeds faster than the winds of any
      other planet.  Neptune revealed its Great Dark Spot, a storm
      system that resembled Jupiter's Great Red Spot, and a smaller,
      eastwardly moving cloud, called 'scooter', which went around
      the planet about every 16 hours.  The blue planet was circled
      by diffuse, dusty rings; six new moons were discovered.
 
      Voyager 2 passed over the north polar region on Neptune,
      using the planet's gravity to redirect the trajectory for a
      final encounter -- with Neptune's largest moon Triton.  It then
      departed the solar system southward of the ecliptic.
 
      At about the same time as Voyager 2 was encountering Neptune,
      Voyager 1, continuing its journey to the edge of the solar
      system on the north side of the ecliptic, turned its cameras
      back to look at the planets and take one last parting shot.
      Voyager 1's 'family portrait' illustrates the vastness of the
      solar system and the huge expanses of emptiness within which
      the outer planets lie.
 
      Both Voyagers are now headed for the outer boundary of the
      solar system, where the Sun becomes just one of many
      contributors to the interstellar environment.  That edge is
      thought to be somewhere between 8 billion and 23 billion
      kilometers from the Sun.  Engineers are optimistic that the
      Voyagers will still be transmitting data when that boundary is
      encountered sometime in the first quarter of the twenty-first
      century.
 
      The spacecraft were assembled at and the mission was managed by
      the Jet Propulsion Laboratory, Pasadena, CA.  Early parts of
      the mission have been described in more detail by
      [MORRISON1982].
 
 
    Mission Phases
    ==============
 
      VOYAGER 1 LAUNCH
      ----------------
        The launch vehicle for Voyager 1 was a Titan/Centaur.  The
        first stage Titan was powered by both solid and liquid fuel
        engines.  The Centaur stage, 20 meters long and 3 meters in
        diameter burned a fuel combination of liquid hydrogen and
        liquid oxygen.  The Titan boosted the Voyager Centaur
        combination into low Earth orbit, and the Centaur plus a
        small solid fuel rocket provided the energy for Voyager 1 to
        escape Earth orbit.
 
        Spacecraft Id                  : VG1
        Mission Phase Start Time       : 1977-09-05
        Mission Phase Stop Time        : 1977-09-05
        Spacecraft Operations Type     : LAUNCH
 
 
      VOYAGER 1 EARTH-JUPITER CRUISE
      ------------------------------
        During the period between Launch and Jupiter Encounter,
        Voyager 1 probed the interplanetary medium and conducted
        tests and calibrations of its systems.
 
        Spacecraft Id                  : VG1
        Mission Phase Start Time       : 1977-09-05
        Mission Phase Stop Time        : 1979-01-06
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 1 JUPITER ENCOUNTER
      ---------------------------
        The Voyager 1 flyby of Jupiter took place on 5 March 1979 at
        12:04:36 UTC with the spacecraft closest approach only 348890
        kilometers from the center of Jupiter.  Among the highlights
        of the encounter were the discovery of a faint ring and one
        new satellite.  Satellite encounter information is given
        below; 'UNK' denotes 'unknown' at time of this writing.  The
        Voyager 1 Jupiter encounter is described in more detail by
        [STONE&LANE1979A].
 
          Satellite    Satellite     Radial    Closest  Approach
             Name      Dimensions   Distance    Date    Distance
                          (km)        (km)     (1979)     (km)
          ---------   -----------  ----------  ------  ---------
          Metis            40         128,000    UNK       UNK
          Adrastea      24x20x14      129,000    UNK       UNK
          Amalthea    270x166x150     181,300   5 Mar    420,200
          Thebe         110x90        222,000    UNK       UNK
          Io              3630        422,000   5 Mar     20,570
          Europa          3138        661,000   5 Mar    733,760
          Ganymede        5262      1,070,000   5 Mar    114,710
          Callisto        4800      1,883,000   6 Mar    126,400
          Leda             16      11,094,000    UNK       UNK
          Himalia          186     11,480,000    UNK       UNK
          Lysithia         36      11,720,000    UNK       UNK
          Elara            76      11,737,000    UNK       UNK
          Ananke           30      21,200,000    UNK       UNK
          Carme            40      22,600,000    UNK       UNK
          Pasiphae         50      23,500,000    UNK       UNK
          Sinope           36      23,700,000    UNK       UNK
 
        Spacecraft Id                  : VG1
        Target Name                    : JUPITER
        Mission Phase Start Time       : 1979-01-06
        Mission Phase Stop Time        : 1979-04-13
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 1 JUPITER-SATURN CRUISE
      -------------------------------
        During the period between Jupiter Encounter and Saturn
        Encounter, Voyager 1 probed the interplanetary medium,
        observed selected celestial targets, and conducted tests and
        calibrations of its systems.  Mission planners used the 16
        months to develop and test activity sequences which would be
        used during the Saturn Encounter.
 
        Spacecraft Id                  : VG1
        Mission Phase Start Time       : 1979-04-13
        Mission Phase Stop Time        : 1980-08-22
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 1 SATURN ENCOUNTER
      --------------------------
        The Voyager 1 flyby of Saturn took place on 12 November 1980
        at 23:46 UTC with the spacecraft closest approach only 184300
        kilometers from the center of Saturn.  Among the highlights
        of the encounter were the separate encounter with Titan,
        discovery of intricate patterns within the ring system, and
        observation of variations among the many moons of Saturn.
        Closest approaches to some of the satellites were on the
        dates and at the distances shown below.  'UNK' denotes
        'unknown' at the time of this writing.  The encounter is
        described in more detail by [STONE&MINER1981].
 
          Satellite    Satellite     Radial     Closest Approach
             Name      Dimensions   Distance    Date     Distance
                          (km)        (km)     (1980)      (km)
          ---------   -----------  ----------  ------  ----------
          Pan              10         133,583   12 Nov      UNK
          Atlas          40x20        137,670    UNK      219,000
          Prometheus  140x100x80      139,353    UNK      300,000
          Pandora      110x90x80      141,700   12 Nov    270,000
          Epimetheus  140x120x100     151,472   13 Nov    121,000
          Janus       220x200x160     151,422   12 Nov    297,000
          Mimas           392         185,520   12 Nov     88,440
          Enceladus       520         238,020   12 Nov    202,040
          Tethys         1060         294,660   12 Nov    415,670
          Telesto      34x28x26       294,660   12 Nov    233,000
          Calypso      34x22x22       294,660   13 Nov    432,000
          Dione          1120         377,400   12 Nov    161,520
          Helene       36x32x30       377,400   13 Nov    237,000
          Rhea           1530         527,040   12 Nov     73,980
          Titan          5150       1,221,860   12 Nov      6,490
          Hyperion    410x260x220   1,481,000   13 Nov    880,440
          Iapetus        1460       3,560,830   14 Nov  2,470,000
          Phoebe          220      12,952,000    UNK   13,500,000
 
        Spacecraft Id                  : VG1
        Target Name                    : SATURN
        Mission Phase Start Time       : 1980-08-22
        Mission Phase Stop Time        : 1980-12-14
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 1 INTERSTELLAR MISSION
      ------------------------------
        After conclusion of the Saturn Encounter, Voyager 1 left the
        ecliptic at an angle of about 30 degrees.  Its scan platform
        instruments were turned off, but some of the remaining
        instruments (primarily fields and particles) continued to
        monitor the environment in the outer solar system as the
        spacecraft traveled outward toward the heliopause.
 
        Spacecraft Id                  : VG1
        Mission Phase Start Time       : 1980-12-14
        Mission Phase Stop Time        : UNK
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 2 LAUNCH
      ----------------
        The launch vehicle for Voyager 2 was a Titan/Centaur.  The
        first stage Titan was powered by both solid and liquid fuel
        engines.  The Centaur stage, 20 meters long and 3 meters in
        diameter burned a fuel combination of liquid hydrogen and
        liquid oxygen.  The Titan boosted the Voyager Centaur
        combination into low Earth orbit, and the Centaur plus a
        small solid fuel rocket provided the energy for Voyager 2 to
        escape Earth orbit.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1977-08-20
        Mission Phase Stop Time        : 1977-08-20
        Spacecraft Operations Type     : LAUNCH
 
 
      VOYAGER 2 EARTH-JUPITER CRUISE
      ------------------------------
        During the period between Launch and Jupiter Encounter,
        Voyager 2 probed the interplanetary medium and conducted
        tests and calibrations of its systems.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1977-08-20
        Mission Phase Stop Time        : 1979-04-25
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 2 JUPITER ENCOUNTER
      ---------------------------
        The Voyager 2 flyby of Jupiter took place on 9 July 1979 at
        22:29 UTC.  This was 18 weeks after the Voyager 1 Jupiter
        Encounter and was at a closest approach distance of 721670
        kilometers from the center of Jupiter.  The Voyager 2
        trajectory was chosen to complement that of Voyager 1,
        including a much closer approach to Europa, probing southern
        latitudes in Jupiter's atmosphere, and an extensive
        investigation of Jupiter's magnetotail.  Satellite encounter
        information is given below; 'UNK' denotes 'unknown' at time
        of this writing.  The Voyager 2 Jupiter encounter is
        described in more detail by [STONE&LANE1979B].
 
          Satellite    Satellite     Radial     Closest Approach
             Name      Dimensions   Distance    Date    Distance
                          (km)        (km)     (1979)     (km)
          ---------   -----------  ----------  ------  ---------
          Metis            40         128,000    UNK       UNK
          Adrastea      24x20x14      129,000    UNK       UNK
          Amalthea    270x166x150     181,300   9 Jul    558,370
          Thebe         110x90        222,000    UNK       UNK
          Io              3630        422,000   9 Jul  1,129,900
          Europa          3138        661,000   9 Jul    205,720
          Ganymede        5262      1,070,000   9 Jul     62,130
          Callisto        4800      1,883,000   8 Jul    214,930
          Leda             16      11,094,000    UNK       UNK
          Himalia          186     11,480,000    UNK       UNK
          Lysithia         36      11,720,000    UNK       UNK
          Elara            76      11,737,000    UNK       UNK
          Ananke           30      21,200,000    UNK       UNK
          Carme            40      22,600,000    UNK       UNK
          Pasiphae         50      23,500,000    UNK       UNK
          Sinope           36      23,700,000    UNK       UNK
 
        Spacecraft Id                  : VG2
        Target Name                    : JUPITER
        Mission Phase Start Time       : 1979-04-25
        Mission Phase Stop Time        : 1979-08-05
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 2 JUPITER-SATURN CRUISE
      -------------------------------
        During the period between Jupiter Encounter and Saturn
        Encounter, Voyager 2 probed the interplanetary medium,
        observed selected celestial targets, and conducted tests and
        calibrations of its systems.  Mission planners used the 22
        months to develop and test activity sequences which would be
        used during the Saturn Encounter.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1979-08-05
        Mission Phase Stop Time        : 1981-06-05
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 2 SATURN ENCOUNTER
      --------------------------
        The Voyager 2 closest approach to Saturn was on 26 August
        1981 at 03:24 UTC and at a distance of 161000 km from the
        center of Saturn.  The trajectory was chosen so that the
        spacecraft could obtain a gravitational assist from Saturn
        and continue on to Uranus; the timing was selected to provide
        better views of several satellites than had been obtained
        from Voyager 1.  Design of science sequences was influenced
        by Voyager 1 results.  Satellite encounters were on the dates
        and at the closest approach distances shown below; 'UNK'
        denotes 'unknown' at the time of this writing.  The
        scan platform seized temporarily 110 minutes after Saturn
        closest approach, causing the central computer to disable
        further commands and resulting in loss of some data.  When
        commanded again three days later (at low rate), it moved as
        instructed.  A gyroscope calibration error between closest
        approach and five hours later also caused loss of data.
        Scan platform activities ended on 5 September 1981.  This
        encounter is described in more detail by [STONE&MINER1982].
 
          Satellite    Satellite     Radial      Closest Approach
             Name      Dimensions   Distance     Date     Distance
                          (km)        (km)      (1981)      (km)
          ---------   -----------  ----------   ------  ----------
          Pan              10         133,583   26 Aug       UNK
          Atlas          40x20        137,670   26 Aug     287,000
          Prometheus  140x100x80      139,353   26 Aug     247,000
          Pandora      110x90x80      141,700   26 Aug     107,000
          Epimetheus  140x120x100     151,472   26 Aug     147,000
          Janus       220x200x160     151,422   26 Aug     223,000
          Mimas           392         185,520   26 Aug     309,930
          Enceladus       520         238,020   26 Aug      87,010
          Tethys         1060         294,660   25 Aug      93,010
          Telesto      34x28x26       294,660   26 Aug     270,000
          Calypso      34x22x22       294,660   26 Aug     151,590
          Dione          1120         377,400   26 Aug     502,310
          Helene       36x32x30       377,400   25 Aug     314,090
          Rhea           1530         527,040   26 Aug     645,260
          Titan          5150       1,221,860   24 Aug     666,190
          Hyperion    410x260x220   1,481,000   24 Aug     431,370
          Iapetus        1460       3,560,830   22 Aug     908,680
          Phoebe          220      12,952,000    4 Sep   2,075,640
 
        Spacecraft Id                  : VG2
        Target Name                    : SATURN
        Mission Phase Start Time       : 1981-06-05
        Mission Phase Stop Time        : 1981-09-25
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 2 SATURN-URANUS CRUISE
      ------------------------------
        During the period between Saturn Encounter and Uranus
        Encounter, Voyager 2 probed the interplanetary medium,
        observed selected celestial targets, and conducted tests and
        calibrations of its systems.  Mission planners used the 49
        months to develop and test activity sequences which would be
        used during the Uranus Encounter.  Considerable attention was
        paid to the scan platform capabilities, following its seizure
        during the Saturn Encounter.  Full scan platform operation
        was restored before the end of 1981.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1981-09-25
        Mission Phase Stop Time        : 1985-11-04
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 2 URANUS ENCOUNTER
      --------------------------
        The Voyager 2 closest approach to Uranus was on 24 January
        1986 at 17:59 UTC at a distance of 107000 km from the
        center of Uranus.  The trajectory was chosen so that the
        spacecraft could obtain a gravitational assist from Uranus
        and continue on to Neptune; NASA permission for the Neptune
        Encounter was granted during the approach to Uranus.  The
        timing of the Uranus closest approach was selected to
        provide a close approach to Miranda and to allow capture of
        radio occultation data at the DSN tracking station in
        Australia (southern declination of Uranus meant that
        Australia was preferred for DSN tracking).  Radio
        occultation data were also collected using the 64-m
        antenna at Parkes in Australia.  Satellite encounters were
        on the dates and at the closest approach distances shown
        below.  'UNK' denotes 'unknown' at the time of this writing.
        Satellite images were improved by implementation of image
        motion compensation on the spacecraft.  Reed-Solomon encoding
        was used for the first time; real-time imaging data rates
        were reduced by almost 70 percent.  Ground antennas were
        arrayed to increase receiving aperture.  This encounter is
        described in more detail by [STONE&MINER1986].
 
          Satellite    Satellite     Radial      Closest Approach
             Name      Dimensions   Distance     Date     Distance
                          (km)        (km)      (1986)      (km)
          ---------   -----------  ----------   ------  ----------
          Cordelia         26         49,800      UNK       UNK
          Ophelia          30         53,800      UNK       UNK
          Bianca           42         59,200      UNK       UNK
          Juliet           62         61,800      UNK       UNK
          Desdemona        54         62,700      UNK       UNK
          Rosalind         84         64,400      UNK       UNK
          Portia          108         66,100      UNK       UNK
          Cressida         54         69,900      UNK       UNK
          Belinda          66         75,300      UNK       UNK
          Puck            154         86,000      UNK       UNK
          Miranda         472        129,900    24 Jan     29,000
          Ariel         1,158        190,900    24 Jan    127,000
          Umbriel       1,172        265,969    24 Jan    325,000
          Titania       1,580        436,300    24 Jan    365,200
          Oberon        1,524        583,400    24 Jan    470,600
 
        Spacecraft Id                  : VG2
        Target Name                    : URANUS
        Mission Phase Start Time       : 1985-11-04
        Mission Phase Stop Time        : 1986-02-25
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 2 URANUS-NEPTUNE CRUISE
      -------------------------------
        During the period between Uranus Encounter and Neptune
        Encounter, Voyager 2 probed the interplanetary medium,
        observed selected celestial targets, and conducted tests and
        calibrations of its systems.  Mission planners used the 39
        months to develop and test activity sequences which would be
        used during the Neptune Encounter.
 
        The DSN used this time to add a 34-m tracking antenna at the
        Madrid complex, to increase the diameter of their 64-m
        antennas to 70 meters, and to make the 70-m systems more
        efficient.  A special microwave link was installed to permit
        the Parkes radio telescope to be arrayed with the Canberra
        DSN antenna in Australia.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1986-02-25
        Mission Phase Stop Time        : 1989-06-05
        Spacecraft Operations Type     : CRUISE
 
 
      VOYAGER 2 NEPTUNE ENCOUNTER
      ---------------------------
        The Voyager 2 closest approach to Neptune was on 25 August
        1989 at 03:56 UTC at a distance of 29240 km from the
        center of Neptune.  The trajectory and timing were chosen so
        that the spacecraft could obtain a gravitational assist from
        Neptune and continue on for an encounter with Neptune's large
        satellite Triton about five hours later (closest approach at
        09:10 UTC).  The timing was also selected so that radio
        occultation data would be collected at the DSN tracking
        station in Australia (southern declination of Neptune meant
        that Australia was preferred for DSN tracking).  Radio
        occultation data were again collected with the Parkes antenna
        and with a new 64-m antenna at Usuda in Japan.  Satellite
        encounters were on the dates and at the closest approach
        distances shown below.  'UNK' denotes 'unknown' at the
        time of this writing.  Data rates were increased over those
        at Uranus by including the Very Large Array (VLA) in New
        Mexico for receiving and by taking advantage of DSN upgrades
        made over the previous three years.  This encounter is
        described in more detail by [STONE&MINER1989].
 
          Satellite    Satellite     Radial      Closest Approach
             Name      Dimensions   Distance     Date     Distance
                          (km)        (km)      (1989)      (km)
          ---------   -----------  ----------   ------  ----------
          Naiad            54          48,000   25 Aug       UNK
          Thalassa         80          50,000   25 Aug       UNK
          Despina         180          52,500   25 Aug       UNK
          Galatea         150          62,000   25 Aug       UNK
          Larissa         190          73,600   25 Aug      60,180
          Proteus         400         117,600   25 Aug      97,860
          Triton        2,700         354,760   25 Aug      39,790
          Nereid          340       5,509 090   25 Aug   4,652,880
 
        Spacecraft Id                  : VG2
        Target Name                    : NEPTUNE
        Mission Phase Start Time       : 1989-06-05
        Mission Phase Stop Time        : 1989-10-02
        Spacecraft Operations Type     : FLYBY
 
 
      VOYAGER 2 INTERSTELLAR MISSION
      ------------------------------
        After conclusion of the Neptune Encounter, Voyager 2 left the
        ecliptic at an angle of about -30 degrees.  Its scan platform
        instruments were turned off, but some of the remaining
        instruments (primarily fields and particles) continued to
        monitor the environment in the outer solar system as the
        spacecraft traveled outward toward the heliopause.  During
        the Shoemaker-Levy 9 impact with Jupiter in July 1994, the
        ultraviolet spectrometer was trained on Jupiter and radio
        signals were recorded; but no emissions from the impact were
        detected.
 
        Spacecraft Id                  : VG2
        Mission Phase Start Time       : 1989-10-02
        Mission Phase Stop Time        : UNK
        Spacecraft Operations Type     : CRUISE
MISSION_OBJECTIVES_SUMMARY
 
    Mission Objectives Summary
    ==========================
      Voyager's primary objective was exploration of the two giant
      planets, Jupiter and Saturn, their magnetospheres, and their
      satellites.  Major emphasis was placed on studying the
      satellites, many of which are planet-sized worlds, in as much
      detail as possible.  The study of Titan, the only satellite in
      the solar system known to have an extensive atmosphere, was
      nearly as high a priority as studies of Saturn itself
      [MORRISON1982].  After the successful Voyager 1 encounter with
      Titan, it was decided to expand the Voyager objectives to
      include at least Uranus; Uranus and Neptune could both be
      reached by proper reprogramming of the Voyager 2 trajectory.
      Comparative studies then could include the four largest planets
      in the solar system.
 
      Eleven investigations were approved for the Voyager mission.
      Investigation names and Principal Investigators, or Team
      Leaders in the cases of ISS and RSS, are shown in the table
      below; the trailing 'S' stands for 'subsystem' in most
      acronyms.
 
        Investigation, P/I or T/L                            Acronym
        ------------------------------------------------     -------
        Imaging Science Investigation                          ISS
                       B.A. Smith
        Infrared Interferometer and Radiometer Investigation   IRIS
                       R.A. Hanel (Jupiter - Uranus)
                       B.J. Conrath (Neptune)
        Photopolarimeter Investigation                         PPS
                       C.F. Lillie (Voyager 1 Jupiter)
                       C.W. Hord (Voyager 2 Jupiter)
                       A.L. Lane (Saturn - Neptune)
        Radio Science Investigation                            RSS
                       V.R. Eshleman (Jupiter)
                       G.L. Tyler (Saturn - Neptune)
        Ultraviolet Spectrometer Investigation                 UVS
                       A.L. Broadfoot
        Magnetometer Investigation                             MAG
                       N.F. Ness
        Plasma Science Investigation                           PLS
                       H.S. Bridge (Jupiter - Uranus)
                       J.W. Belcher (Neptune)
        Plasma Wave Investigation                              PWS
                       F.L. Scarf (Jupiter - Uranus)
                       D.A. Gurnett (Neptune)
        Planetary Radio Astronomy Investigation                PRA
                       J.W. Warwick
        Low-Energy Charged Particle Investigation              LECP
                       S.M. Krimigis
        Cosmic Ray Investigation                               CRS
                       R.E. Vogt (Jupiter - Saturn)
                       E.C. Stone (Uranus - Neptune)
 
 
      Broadly stated, the science goals of the mission were: high
      resolution imaging of the gas planets and inference of
      atmospheric dynamics; high resolution imaging of satellites and
      inference of geologic processes; spectral measurements of
      atmospheres and satellite surfaces, inference of compositions,
      and inference of thermal properties and structure;
      identification and study of aerosols and surface physical
      structure using polarized light; occultation measurement of
      atmospheric thermal, ionospheric charged particle, and ring
      structure; and measurement of magnetic fields and particle
      environments and inference of Sun-planet-satellite
      interactions, magnetospheric structure, and mechanisms within
      each planetary system for generating the observed fields.
 
 
      Jupiter
      -------
        The largest planet in the solar system, Jupiter is composed
        mainly of hydrogen and helium, with small amounts of methane,
        ammonia, water vapor, traces of other compounds and a core of
        melted rock and ice.  One of the objectives of Voyager was to
        quantify the composition of the atmospheres of Jupiter and
        the other giant planets.
 
        Colorful latitudinal bands, atmospheric clouds, and storms
        characterize Jupiter's dynamic atmosphere.  By taking a
        series of images, Voyager could show the time variability of
        the atmosphere.  The Great Red Spot was revealed as a complex
        storm moving in a counterclockwise direction.  An array of
        other smaller storms and eddies were found throughout the
        banded clouds.
 
        Jupiter is now known to possess 16 moons.  An objective of
        the Voyager mission was to search for new moons and to obtain
        high resolution quantitative measurements on those that had
        been discovered earlier.  Active volcanism on the satellite
        Io was easily the most surprising discovery at Jupiter.  It
        was the first time active volcanoes had been seen on another
        body in the solar system.  Together, the Voyagers observed
        the eruption of nine volcanoes on Io, and there is evidence
        that other eruptions occurred between the Voyager encounters.
 
        Although interpretations vary, the cratered surfaces of the
        terrestrial planets (and the Moon) are believed to contain
        the record of small body populations in the inner solar
        system from as far back as 4 billion years ago.  One of the
        objectives of the Voyager mission was to obtain similar
        cratering data from satellites in the outer solar system.
        Impact craters on Io have been obliterated by that satellite's
        volcanism.  Rather than craters, Europa was distinguished by
        a large number of intersecting linear features with almost no
        topographic relief.  There is a possibility that Europa is
        internally active due to tidal heating at a level one-tenth
        or less than that of Io and that the crust is very thin (less
        than 30 kilometers).  Ganymede has two distinct types of
        terrain -- cratered and grooved -- suggesting that its entire
        icy crust has been under tension from global tectonic
        processes.  Callisto has a very old, heavily cratered crust
        showing remnant rings of enormous impact craters.  The
        largest craters have apparently been erased by the flow of
        the icy crust over geologic time.  Almost no topographic
        relief is apparent in the ghost remnants of the immense
        impact basins, identifiable only by their light color and the
        surrounding subdued rings of concentric ridges.
 
        Indirect evidence from Pioneer 10/11 suggested the presence
        of a thin ring around Jupiter.  One of the objectives of the
        Voyager mission was to search more systematically for such a
        ring, and to quantify both the number-density and the size
        distribution of particles within rings in the outer solar
        system.  A faint, dusty ring of material was found around
        Jupiter.  Its outer edge is 129,000 kilometers from the
        center of the planet, and it extends inward about 30,000
        kilometers.
 
        Two new, small satellites, Adrastea and Metis, were found
        orbiting just outside the ring.  A third new satellite,
        Thebe, was discovered between the orbits of Amalthea and Io.
 
        Jupiter's rings and moons exist within an intense radiation
        belt of electrons and ions trapped in the planet's magnetic
        field.  These particles and fields comprise the jovian
        magnetosphere, or magnetic environment, which extends three
        to seven million kilometers toward the Sun, and stretches in
        a windsock shape at least as far as Saturn's orbit -- a
        distance of 750 million kilometers (460 million miles).
 
        As the magnetosphere rotates with Jupiter, it sweeps past Io
        and strips away about 1,000 kilograms (one ton) of material
        per second.  The material forms a torus, a doughnut-shaped
        cloud of ions that glow in the ultraviolet.  The heavy ions
        in the torus migrate outward, and their pressure inflates the
        jovian magnetosphere to more than twice its expected size.
        Some of the more energetic sulfur and oxygen ions fall along
        the magnetic field into the planet's atmosphere, resulting in
        auroras.
 
 
      Saturn
      ------
        A major objective of the Voyager mission was to determine in
        which ways the gas giants are the same and in which ways they
        are different.  Saturn, like Jupiter, is mostly hydrogen and
        helium.  Its hazy yellow hue has broad atmospheric banding
        similar to (but much fainter than) that found on Jupiter.  It
        also has a complex ring system, the details of which were
        sketchy before Voyager, but which represented an important
        objective in themselves.
 
        It is thought that the rings formed from one or more moons
        that were shattered by impacts of comets and meteoroids.  The
        resulting material, ranging in size from dust to house-sized
        particles, has accumulated in a broad plane in which both the
        shape and density vary in ways which depend intricately on
        gravitational interactions with satellites.  This is most
        obviously demonstrated by the relationship between the F-ring
        and two small moons that 'shepherd' the ring material.  The
        variation in the separation of the moons from the ring may
        explain the ring's kinked appearance.  Shepherding moons were
        also found by Voyager 2 at Uranus.  Very diffuse rings and
        'spokes' (neither detected from Earth) were also found by
        Voyager.
 
        Winds blow at extremely high speeds on Saturn -- up to 1,800
        kilometers per hour.  Their primarily easterly direction
        indicates that the winds are not confined to the top cloud
        layer but must extend at least 2,000 kilometers downward into
        the atmosphere.
 
        Saturn has 18 known satellites ranging from Phoebe, a small
        moon that travels in a retrograde orbit and is probably a
        captured asteroid, to Titan, the planet-sized moon with
        an atmosphere that had been detected from Earth before
        Voyager.  A major objective of Voyager was to
        investigate these satellites and, in particular, to learn a
        great deal more about Titan.  Titan's surface temperature and
        pressure were found to be 94 K and 1.6 atmospheres.
        Photochemistry converts some atmospheric methane to other
        organic molecules, such as ethane, that may accumulate in
        lakes or oceans.  Other more complex hydrocarbons form the
        haze particles that eventually fall to the surface, coating
        it with a thick layer of organic matter.  The chemistry in
        Titan's atmosphere may resemble that which occurred on Earth
        before life evolved.
 
        The most active surface of any moon seen in the Saturn system
        was that of Enceladus.  The bright surface of this moon,
        marked by faults and valleys, showed evidence of tectonically
        induced change.  Voyager 1 found that the surface of Mimas is
        dominated by a crater so large that the impact nearly broke
        the satellite apart.
 
        Saturn's magnetic field is weaker than Jupiter's, extending
        only one or two million kilometers.  The axis of the field is
        almost perfectly aligned with Saturn's rotation axis.
 
 
      Uranus
      ------
        Uranus is distinguished by the fact that it is tipped on its
        side.  This unusual orientation is thought to be the result
        of a collision with a planet-sized body early in the solar
        system's history.  Clues to this event, as well as more basic
        data about this planet (which has polar regions exposed to
        sunlight or hidden in darkness for long periods) were
        important Voyager objectives.  At about the time of Voyager's
        launch, observations from Earth showed that Uranus was
        circled by rings -- not bright and wide, as was the case
        for Saturn, but extremely narrow and very dark.
 
        Voyager 2 found that one of the most striking influences of
        the orientation of the rotation axis is its effect on the
        tail of the magnetic field, which is itself tilted 60 degrees
        from the planet's axis of rotation.  The magnetotail was
        shown to be twisted by the planet's rotation into a long
        corkscrew shape behind Uranus.
 
        The existence of a magnetic field at Uranus was not known
        until Voyager's arrival.  The intensity of the field is
        roughly comparable to that of Earth's, though it varies much
        more from point to point because of its large offset from the
        center of the planet.  The peculiar orientation of the
        magnetic field suggests that the field is generated at an
        intermediate depth in the interior where the pressure is high
        enough for water to become electrically conducting.
 
        Radiation belts at Uranus were found to be similar in
        intensity to those at Saturn.  The intensity of radiation
        within the belts is such that irradiation would quickly
        darken (within 100,000 years) any methane trapped in the icy
        surfaces of the inner moons and ring particles.  This may
        have contributed to the darkened surfaces of the moons and
        ring particles, which have lower albedos than coal and are
        almost uniform in color.
 
        A high layer of haze was detected around the sunlit pole,
        which also was found to radiate large amounts of ultraviolet
        light, a phenomenon dubbed 'dayglow'.  Surprisingly, the
        illuminated and dark poles, and most of the planet, show
        nearly the same temperature at the cloud tops.
 
        Voyager found 10 new moons, bringing the total number at
        Uranus to 15.  Most of the new moons are small, with the
        largest measuring about 150 kilometers in diameter.
 
        The five large moons appear to be ice-rock conglomerates like
        the satellites of Saturn.  Titania is marked by huge fault
        systems and canyons indicating some degree of geologic
        (probably tectonic) activity in its history.  Ariel has the
        brightest and possibly youngest surface of all the Uranian
        moons and also appears to have undergone geologic activity
        that led to many fault valleys and what seem to be extensive
        flows of icy material.  Little geologic activity has occurred
        on Umbriel or Oberon, judging by their old and dark surfaces.
 
        The moon Miranda, innermost of the five large moons, was
        revealed to be one of the strangest bodies yet seen in the
        solar system.  Detailed images from Voyager's flyby of the
        moon showed huge fault canyons as deep as 20 kilometers,
        terraced layers, and a mixture of old and young surfaces.
        One theory holds that Miranda may be a reaggregation of
        material from an earlier time when the moon was fractured by
        a violent impact.
 
        All nine rings discovered from Earth in the 1970's were
        studied by the spacecraft and showed the Uranian rings to be
        distinctly different from those at Jupiter and Saturn.  The
        ring system may be relatively young and did not form at the
        same time as Uranus.  Particles that make up the rings may be
        remnants of a moon that was fractured by a high-velocity
        impact or torn up by gravitational effects.
 
 
      Neptune
      -------
        Less was known about Neptune than about Uranus at the
        beginning of the Voyager mission.  Approximately the same
        size as Uranus, Neptune was expected to be a twin except for
        having a rotation axis more likely to be normal to the
        ecliptic.  About five years before the Voyager 2 Neptune
        encounter, evidence began accumulating that Neptune had
        atmospheric structure and (possibly) rings.  The ring data
        were very ambiguous; only exotic ring models (transient
        rings, partial rings, polar rings, etc.) were consistent
        with the observations from Earth.
 
        Even though Neptune receives only three percent as much
        sunlight as Jupiter, it is a dynamic planet and showed
        several large, dark spots reminiscent of Jupiter's
        hurricane-like storms.  The largest spot, dubbed the Great
        Dark Spot, is about the size of Earth and is similar to the
        Great Red Spot on Jupiter.  A small, irregularly shaped,
        eastward-moving cloud was observed 'scooting' around Neptune
        approximately once every 16 hours.
 
        Long bright clouds, similar to cirrus clouds on Earth, were
        seen high in Neptune's atmosphere.  At low northern
        latitudes, Voyager captured images of cloud streaks casting
        their shadows on cloud decks below.
 
        The strongest winds on any planet were measured on Neptune.
        Most of the winds blow westward, or opposite to the rotation
        of the planet.  Near the Great Dark Spot, winds blow up to
        2,000 kilometers an hour.
 
        The magnetic field of Neptune, like that of Uranus, turned
        out to be highly tilted -- 47 degrees from the rotation axis
        and offset at least 0.55 radii (about 13,500 kilometers or
        8,500 miles) from the physical center.  The extreme
        orientation may be characteristic of flows in the interiors
        of both Uranus and Neptune -- and not related, in the Uranus
        case, to the planet's rotation axis tilt or to any possible
        field reversals at either planet.  Voyager studies of radio
        emissions caused by the magnetic field revealed the length
        of a Neptunian day (16.11 hours).  The spacecraft also
        detected auroras, though they are much weaker than those on
        Earth and other planets.
 
        Triton, the largest Neptunian moon, was shown to be not only
        the most intriguing satellite of the system, but also one
        of the most interesting in all the solar system.  Intricate
        surface patterns suggest a remarkable geologic history,
        while Voyager 2 images captured active geyser-like eruptions
        spewing invisible nitrogen gas and dark dust particles
        several kilometers into the tenuous atmosphere.  Triton's
        relatively high density and retrograde orbit offer strong
        evidence that it is not an original member of Neptune's
        family but, rather, is a captured object.  If so, tidal
        heating could have melted Triton in its originally eccentric
        orbit, and the moon may have been liquid for as long as one
        billion years after its capture by Neptune.
 
        An extremely thin atmosphere extends about 800 kilometers
        above Triton's surface.  Nitrogen ice particles may form thin
        clouds a few kilometers above the surface.  The atmospheric
        pressure at the surface is about 14 microbars, 1/70,000th the
        surface pressure on Earth.  The surface temperature is about
        38 K -- the coldest known temperature of any body in the
        solar system.
 
        The new moons found at Neptune by Voyager are all small and
        remain close to Neptune's equatorial plane.
 
        Searches for 'ring arcs,' or partial rings, showed that
        Neptune's rings actually are complete, but are so diffuse and
        the material in them so fine that they could not be fully
        resolved from Earth.  The arcs are confined by the actions of
        nearby satellites.  Particle sizes are smaller than at Uranus.
 
 
      Interstellar Mission
      --------------------
        The Voyager spacecraft are continuing to return data about
        interplanetary space and some of our stellar neighbors near
        the edges of the Solar System.  Their fields, particles, and
        waves instruments are studying the environment around them.
        In May 1993, the plasma wave experiment began picking up radio
        emissions that originate at the heliopause, the outer edge of
        our solar system, where the interstellar medium restricts the
        outward flow of the solar wind and confines it within a
        magnetic bubble called the heliosphere.  By studying the
        radio emissions, scientists now theorize the heliopause
        exists some 90 to 120 astronomical units from the Sun.
 
        The Voyagers have also become space-based ultraviolet
        observatories and their unique location in the universe gives
        astronomers the best vantage point they have ever had for
        looking at celestial objects that emit ultraviolet radiation.
 
        The cameras on the spacecraft have been turned off and the
        ultraviolet instrument is the only experiment on the scan
        platform that is still functioning.  Voyager scientists
        expect to continue to receive data from the ultraviolet
        spectrometers at least until the year 2000.  At that time,
        there will not be enough electrical power for the heaters to
        keep the ultraviolet instrument warm enough to operate.
 
        Yet there are several other fields and particle instruments
        that can continue to send back data as long as the spacecraft
        can stay alive.  They include the cosmic ray subsystem, the
        low-energy charge particle instrument, the magnetometer, the
        plasma subsystem, the plasma wave subsystem and the planetary
        radio astronomy instrument.
REFERENCE_DESCRIPTION Kohlhase, C.E. and P.A. Penzo, Voyager Mission Description, Space Sci.Rev., Vol. 21, pp. 77-101, 1977.

Morrison, D., Voyages to Saturn, NASA SP-451, 227 pp., National Aeronautics andSpace Administration, Washington, DC, 1982.

Stone, E.C., and A.L. Lane, Voyager 1 encounter with the Jovian system,Science, 204, 945-948, 1979.

Stone, E.C., and A.L. Lane, Voyager 2 encounter with the Jovian system,Science, 206, 925-927, 1979.

Stone, E.C., and E.D. Miner, Voyager 1 encounter with the Saturnian system,Science, 212, 159-163, 1981.

Stone, E.C., and E.D. Miner, Voyager 2 encounter with the Saturnian system,Science, 215, 499-504, 1982.

Stone, E.C., and E.D. Miner, Voyager 2 encounter with the Uranian system,Science, 233, 39-43, 1986.

Stone, E.C., and E.D. Miner, Voyager 2 encounter with the Neptunian system,Science, 246, 1417-1421, 1989.