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