Mission Information
MISSION_NAME VIKING
MISSION_ALIAS VIKING75
MISSION_START_DATE 1975-08-20T12:00:00.000Z
MISSION_STOP_DATE 1983-02-01T12:00:00.000Z
MISSION_DESCRIPTION
Mission Overview
    ================
      The Viking mission to Mars consisted of four spacecraft: the
      two orbiters VO1 and VO2, and the landers VL1 and VL2
      [SOFFEN1977].  During cruise to Mars the landers were attached
      to the orbiters; the combined spacecraft were then known as
      Viking 1 and 2.  The role of the orbiters was to transport the
      landers to Mars, to carry reconnaissance instruments for
      certifying the landing sites, to act as relay stations for
      lander data, and to perform their own scientific
      investigations.  The initial orbit periapses were placed over
      the candidate landing sites to allow for maximum viewing
      resolution and relay of the lander data.  After the primary
      lander missions were completed, the orbiters' orbits were
      allowed to drift so that the entire planetary surface could be
      systematically mapped by the three remote sensing experiments.
 
      The Viking 1 spacecraft was launched August 20, 1975, and
      arrived at Mars on June 19, 1976.  Lander 1 was deployed to the
      Mars surface on July 20, 1976.  The VO1 orbital inclination of
      38-39 degrees was chosen to optimize communication with  VL1.
      Viking 2 was launched September 9, 1975 and arrived at Mars
      August 7, 1976.  VL2 landed on September 3, 1976, at a more
      northerly site than VL1.  The VO2 orbit was correspondingly
      more inclined than VO1; initially 55 degrees, it was later
      adjusted to 80 degrees, providing particularly good coverage
      of polar regions.  The areocentric locations of VL1 and VL2
      have since been determined to be (22.270N, 48.264W) and
      (47.669N, 226.032W), respectively [YODER&STANDISH1997].
 
 
    Mission Phases
    ==============
      The timeline for the Viking Mission is divided into a number of
      mission phases in terms of the types of observations and level
      of activity.  The references [SNYDER1977], [SNYDER1979],
      [MOOREETAL1987], and [SNYDER&MOROZ1992] provide detailed
      descriptions of these mission phases.  A summary of the mission
      phases and the relevant dates are described below.  Before Mars
      encounter and orbit insertion the orbiter and lander spacecraft
      are considered as one spacecraft with the same mission phases.
      The primary missions for all four spacecraft (VL1, VO1, VL2,
      and VO2) are listed separately because each has a different
      starting date.  All mission phases after the primary mission
      are listed only once because all four spacecraft operated
      together.
 
 
      VIKING 1 MARS LAUNCH
      --------------------
        The Viking 1 spacecraft was launched on August 20, 1975 on a
        Titan Centaur 3 booster from Cape Canaveral, Florida.
 
         Spacecraft Id:                 : VO1, VL1
         Target Name                    : MARS
         Mission Phase Start Time       : 1975-08-20
         Mission Phase Stop Time        : 1975-08-20
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING 1 MARS CRUISE
      --------------------
        The Viking 1 spacecraft, consisting of the VO1 orbiter and
        VL1 lander, cruised to Mars for about 10 months, during which
        time the spacecraft was checked periodically.
 
         Spacecraft Id:                 : VO1, VL1
         Target Name                    : MARS
         Mission Phase Start Time       : 1975-08-20
         Mission Phase Stop Time        : 1976-06-19
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING 2 MARS LAUNCH
      --------------------
        The Viking 2 spacecraft was launched on September 9, 1975 on
        a Titan Centaur 3 booster from Cape Canaveral, Florida.
 
         Spacecraft Id:                 : VO2, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1975-09-09
         Mission Phase Stop Time        : 1975-09-09
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING 2 MARS CRUISE
      --------------------
        The Viking 2 spacecraft, consisting of the VO2 orbiter and
        VL2 lander, cruised to Mars for about 11 months, during which
        time the spacecraft was checked periodically.
 
         Spacecraft Id:                 : VO2, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1975-09-09
         Mission Phase Stop Time        : 1976-08-07
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING ORBITER 1 PRIMARY MISSION
      --------------------------------
        The Viking Orbiter 1 spacecraft entered Mars orbit on June
        19, 1976.  Operations commenced by supporting the selection
        of a landing site for VL1.  Throughout the Primary Mission,
        the VO1 spacecraft supported communications with the landers
        and made observations of the Martian surface and atmosphere.
        The Primary Mission ended at the start of the solar
        conjunction in November, 1976.
 
         Spacecraft Id:                 : VO1
         Target Name                    : MARS
         Mission Phase Start Time       : 1976-06-19
         Mission Phase Stop Time        : 1976-11-15
         Spacecraft Operations Type     : ORBITER
 
 
      VIKING LANDER 1 PRIMARY MISSION
      -------------------------------
        The Viking Lander 1 spacecraft separated from the VO1 orbiter
        and descended to the Martian surface on July 20, 1976.  The
        Primary Mission focused on the collection and analysis of
        soil samples and the characterization of the landing site and
        atmosphere.  The Primary Mission ended at the start of the
        solar conjunction in November, 1976.
 
         Spacecraft Id:                 : VL1
         Target Name                    : MARS
         Mission Phase Start Time       : 1976-07-20
         Mission Phase Stop Time        : 1976-11-15
         Spacecraft Operations Type     : LANDER
 
 
      VIKING ORBITER 2 PRIMARY MISSION
      --------------------------------
        The Viking Orbiter 2 spacecraft entered Mars orbit on August
        7, 1976.  Operations commenced by supporting the selection of
        a landing site for VL2.  Throughout the Primary Mission, the
        VO2 spacecraft supported communications with the landers and
        made observations of the Martian surface and atmosphere.  The
        Primary Mission ended at the start of the solar conjunction
        in November, 1976.
 
         Spacecraft Id:                 : VO2
         Target Name                    : MARS
         Mission Phase Start Time       : 1976-08-07
         Mission Phase Stop Time        : 1976-11-15
         Spacecraft Operations Type     : ORBITER
 
 
      VIKING LANDER 2 PRIMARY MISSION
      -------------------------------
        The Viking Lander 2 spacecraft separated from the VO2 orbiter
        and descended to the Martian surface on September 3, 1976.
        The Primary Mission focused on the collection and analysis of
        soil samples and the characterization of the landing site and
        atmosphere.  The Primary Mission ended at the start of the
        solar conjunction in November, 1976.
 
         Spacecraft Id:                 : VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1976-09-03
         Mission Phase Stop Time        : 1976-11-15
         Spacecraft Operations Type     : LANDER
 
 
      VIKING EXTENDED MISSION
      -----------------------
        The Viking Extended Mission began after solar conjunction.
        The two orbiters continued to observe the surface and
        atmosphere of Mars.  The two lander spacecraft analyzed
        additional soil samples and dug three deep holes in the
        surface.  All four spacecraft monitored the planet through
        the cycle of seasons.  During the winter season, the landers
        operated in an automatic manner designed to allow the
        spacecraft to survive the cold temperatures and still return
        some data.
 
         Spacecraft Id:                 : VO1, VL1, VO2, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1976-11-15
         Mission Phase Stop Time        : 1978-05-31
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING CONTINUATION MISSION
      ---------------------------
        Primary objectives of the Continuation Mission were to make
        orbital observations at times of the Mars year that were
        missed due to landing site selection and solar conjunction
        and to collect high resolution surface images when the
        atmosphere was clear.  A radio science solar conjunction
        relativity experiment was also done during the Continuation
        Mission.  Lander activities consisted of measurements by the
        imaging, meteorology, and XRFS instruments operating in a
        fully automated manner.  Viking Orbiter 2 developed a leak in
        its propulsion system and lost its attitude control gas.  VO2
        was turned off on July 25, 1978 after 706 orbits around Mars.
 
         Spacecraft Id:                 : VO1, VL1, VO2, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1978-05-25
         Mission Phase Stop Time        : 1979-02-26
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING INTERIM PERIOD
      ---------------------
        The Interim Period mission phase occurred during the time of
        the Voyager 2 encounter with Jupiter.  Thus, communications
        to and from the Viking spacecraft were limited.  The landers
        continued to operate in an automated manner making imaging
        and meteorology observations.  A final VL2 surface sampler
        sequence was conducted during this mission phase as an
        engineering test in the cold temperatures of mid winter.
        Orbital data stored on spacecraft tape recorders and not
        returned during the Continuation Mission were downlinked
        during the Interim Period.
 
         Spacecraft Id:                 : VO1, VL1, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1979-02-26
         Mission Phase Stop Time        : 1979-07-19
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING SURVEY MISSION
      ---------------------
        The prime scientific objective for VO1 during the Survey
        Mission was to obtain high resolution images of possible
        future landing sites.  The plan for the landers was to
        collect image and meteorology data for as long as possible.
        Because VL2 no longer had a direct downlink capability, it
        meant that VL2 could return data only as long as VO1 provided
        a relay link, once every seven weeks.  Communications with
        VL2 ended on April 11, 1980 after its batteries could no
        longer hold a charge.  VL2 operated on the surface of Mars
        for 1281 sols.  VO1 consumed the last of its attitude control
        gas on August 7, 1980 and was turned off after 1485 orbits
        around Mars.
 
         Spacecraft Id:                 : VO1, VL1, VL2
         Target Name                    : MARS
         Mission Phase Start Time       : 1979-07-19
         Mission Phase Stop Time        : 1980-08-07
         Spacecraft Operations Type     : ORBITER, LANDER
 
 
      VIKING COMPLETION MISSION
      -------------------------
        Viking Lander 1 continued to operated in its automatic mode
        during the Completion Mission.  The observation sequences
        were cyclic.  VL1 returned via direct downlink image and
        meteorology data about once a week with image sequences
        repeating every 37 sols.  The VL1 high-gain antenna was
        programmed to track the Earth until December, 1994.  However,
        communications were lost in November 1982 after a command
        sequence uplink.
 
         Spacecraft Id:                 : VL1
         Target Name                    : MARS
         Mission Phase Start Time       : 1980-08-07
         Mission Phase Stop Time        : 1982-11-19
         Spacecraft Operations Type     : LANDER
MISSION_OBJECTIVES_SUMMARY
Mission Objectives Overview
  ===========================
    Exploration of Mars, and the Viking Mission in particular, has
    been part of a larger quest -- the search for better
    understanding of the formation and history of the solar system.
    For Mars, the specific objectives have included:
 
        1) evolution and current structure of its interior;
        2) characteristics of the surface, including its chemistry
           and physical nature;
        3) evolution and current composition and structure of its
           atmosphere;
        4) nature of the climate, including controls on both daily
           and seasonal variations;
        5) whether life is, or ever has been, present.
 
    Although most Viking investigations could be defended on one or
    more of the first four objectives, virtually all secondarily
    addressed the fifth.  On the other hand, the investigations
    which focused primarily on objective #5 barely scratched the
    surface of that single question; the nature of life -- and
    especially its expression on another planet -- is not well
    understood.  According to [SOFFEN1977], 'It was finally decided
    to send a set of biological tests that range in their
    environmental setting from a totally aqueous milieu, rich in
    organics, to a Marslike environment with no water or any other
    additives.  Even so, only a very narrow set of all
    possibilities could be tested on the small samples
    acquired ...'.
 
    The Viking investigations and their primary objectives are
    summarized in the paragraphs below.  More information is
    available in [SOFFEN1977], [SNYDER1977], [SNYDER1979], and
    [SNYDER&MOROZ1992].
 
 
    Orbiter Imaging
    ---------------
      An early objective was assisting in landing site selection
      and certification.  Once the landers were safely in place,
      the Orbiter imaging system was used to provide a geologic
      context for the surface observations.  Globally, images were
      collected to provide high-resolution mosaics and maps at
      resolutions approaching 100 meters.  Stereo pairs of images
      could be used to derive local topography; photoclinometry
      could be used on single images to derive elevations and
      slopes at lower accuracy.  Images were also used to infer
      the origin and history of major terrain types, including
      disruptive events such as apparent catastrophic floods.
      Crater morphologies which suggest a permafrost layer pointed
      toward complex interactions of regolith and atmosphere.
      The Orbiter imaging system was also used to monitor
      atmospheric changes including clouds, hazes, and suspended
      particles.  Images of the satellites Phobos and Deimos
      showed their surfaces from distances as close as 100 km.
 
 
    Mars Atmospheric Water Detector (MAWD)
    --------------------------------------
      MAWD was designed to measure the water vapor content of the
      atmosphere from orbit.  Patterns were sought as a function
      of local time, season, latitude, and elevation.  Objectives
      of the investigation included better understanding of both
      diurnal and seasonal transport of water vapor as well as
      location of sources and sinks.
 
 
    Infrared Thermal Mapping (IRTM)
    -------------------------------
      IRTM measured reflections and emissions in several infrared
      bands from orbit.  These data could be used to infer the
      physical properties of surface materials including the
      relative proportions of rock, sand, and dust.  Apparent
      surface temperatures were used to infer the composition of
      polar ices, assisting in development of atmospheric
      circulation models.
 
 
    Radio Science
    -------------
      Radio tracking of the Landers allowed determination of their
      positions on the surface, the planetary rotation axis, the
      spin rate, and moment of inertia.  Tracking of the Orbiters
      allowed determination of a gravity field for Mars.  Radio
      occultations yielded planetary radii and atmospheric
      temperature-pressure profiles at dozens of locations.  Radio
      observations were also conducted to measure structure in the
      solar corona and to test a prediction of general relativity
      associated with passage of the radio path through the Sun's
      gravitational field.
 
 
    Entry Science
    -------------
      During descent each landing module measured both the physical
      structure and chemical composition of the atmosphere.  The
      composition of the ionosphere allowed inference of dominant
      reactions.  At lower altitudes isotopic ratios could be used
      to infer age of the atmosphere and an earlier composition.
      Measurements such as mean molecular weight, density profile,
      and composition near the surface could be used to interpret
      measurements from other instruments.  Measurements at
      different altitudes could be used to determine how well the
      atmosphere was mixed.
 
 
    Lander Imaging
    --------------
      Lander images were used to select samples for testing in the
      biology and physical properties investigations; they were also
      used to select sites for experiments using the sampler arm.
      Images recorded trenches that were dug, rocks that were
      overturned, footpads that penetrated the surface, and magnets
      that were covered by iron-bearing loose material.  Images were
      used to determine the distribution and appearance of rocks
      and other materials near the landing sites, leading to
      improved understanding of both the local area and its
      history.  Images of the atmosphere were used to estimate the
      opacity due to suspended particles; images of materials at
      the site were used to infer wind stress and rates of erosion.
      One unfulfilled objective of Lander imaging was detection of
      signs of life at each site.
 
 
    Physical and Magnetic Properties
    --------------------------------
      The sampler arm and sample collector on each Lander were
      used in conjunction with the Lander imaging system to
      determine density, cohesion, and other physical properties
      of the surface material.  Repeated failure to collect rocks
      in the 1 cm size range suggested they are scarce, which has
      implications for creation and destruction of material in
      that size range.  Visual evidence that magnets were
      saturated was important in estimating the concentration and
      state of iron in surface particles.
 
 
    Seismology
    ----------
      The objectives of the Lander seismology investigation were
      to detect seismic events or to set limits on the activity
      level of Mars compared with Earth.  One local event was
      detected at VL2, allowing estimation of crustal thickness
      and damping.  In practice the seismology investigation
      supported the meteorology investigation since most seismic
      signals turned out to be caused by wind.
 
 
    Meteorology
    -----------
      The Lander meteorology investigation sought to characterize
      local atmospheric conditions; those in turn would constrain
      global models.  Diurnal and seasonal trends were sought;
      effects of dust storms were also measured.
 
 
    Inorganic Chemistry
    -------------------
      Elemental compositions of soils at each Lander site were
      determined using X-Ray Flourescence Spectrometers.  Results
      were to be compared with compositions of terrestrial analogs
      but were found to be 'dissimilar to any single known mineral
      or rock type' [TOULMINETAL1977].  With addition of physical
      properties, the recent history of duricrust could be inferred.
      The fact that these materials were very similar at the two
      Landing sites can be used in modeling transport of dust and
      other small diameter particles.
 
 
    Molecular Analysis
    ------------------
      The Gas Chromatograph Mass Spectrometer gave composition of
      the atmosphere at each landing site; the result was
      consistent with the entry science composition.  Isotope ratios
      were used to infer the amount of outgassing and, from that,
      the volume of volatiles which may have been lost from Mars
      over geologic time.  Surface samples were analyzed in an
      attempt to detect organics and to measure the amount of water
      present.  Both are questions important in the search for life.
 
 
    Biology
    -------
      The original objectives of the Lander biology experiment were
      to detect presumed Martian life forms by their release of
      metabolic products upon addition of heat, water, a dilute
      aqueous solution of simple nutrients, and a concentrated
      mixture of many organic compounds.  After sudden and
      surprising positive results, which were not consistent with
      expectations or with other observations, the objectives were
      expanded to include abiotic interpretations.
REFERENCE_DESCRIPTION Moore, H.J., R.E. Hutton, G.D. Clow, and C.R. Spitzer, Physical properties of the surface materials at the Viking landings sites on Mars, USGS Professional Paper 1389, 1987.

Snyder, C.W., and I.V. Moroz, Spacecraft Exploration of Mars, in Mars, Kieffer et al., eds., Univ. of Arizona Press, Tucson, 1992.

Snyder, C.W., 'The Missions of the Viking Orbiters', Journal of Geophysical Research, vol. 82, p. 3971, 1977.

Snyder, C.W., 'The Extended Mission of Viking', Journal of Geophysical Research, vol. 84, p. 7917, 1979.

Soffen, G.A., 'The Viking Project', Journal of Geophysical Research, vol. 82, p. 3959, 1977.

Toulmin, P., A.K. Baird, B.C. Clark, K. Keil, H.J. Rose, R.P. Christian, P.H. Evans, and W.C. Kelliher, Geochemical and Mineralogical Interpretation of the Viking Inorganic Chemical Results, J. Geophys. Res., 82, 4625-4634, 1977.

Yoder, C.F., and E.M. Standish, Martian Precession and Rotation from Viking Lander Range Data, J. Geophys. Res., 102, 4065-4080, 1997