Mission Overview
    ================
      Mars Observer was launched September 25, 1992 from Cape
      Canaveral on a Titan III built by Martin Marietta Corporation,
      with an upper Transfer Orbit Stage from Orbital Sciences
      Corporation.
 
      On August 21, 1993, flight controllers lost contact with the
      Mars Observer spacecraft when an expected transmission that was
      part of the pre-Mars-Orbit-Insertion sequence failed to occur.
      Subsequent attempts to re-establish communication with the
      spacecraft proved unsuccessful.
 
      After the 11-month transit the spacecraft was to be injected
      into an elliptical orbit around Mars with periapsis near the
      north pole.  The orbit would then be adjusted through a series
      of maneuvers to a near-circular, sun-synchronous (2 am/pm), low
      altitude, near-polar orbit.  Due to the non-uniformity of the
      gravity field, the altitude was to vary from 376 km near the
      south pole to 430 km near the north pole.  During the Martian
      year in this mapping orbit the instruments were to acquire data
      in a systematic program of global mapping.  At the end of the
      mission the spacecraft could have been boosted to a permanent
      quarantine orbit.
 
      The Mars orbit insertion (MOI) period was to end one month
      before solar conjunction and the beginning of the dust storm
      period.  The playback data rate for a 10-hour link would vary
      by a factor of 4 with Earth-Mars distance during the mission.
      The continuous data rate to the tape recorders was about one
      fifth the playback rate for a 10-hour link to a 34 m NASA Deep
      Space Network tracking station.  The normal sequence of
      collecting scientific data would be to record continuously for
      24 hours and then to play the data back in one 10-hour link.
      The mapping orbit would be a 117-minute orbit with a 7-day
      repeat cycle.  As a result, the planet would be repeatedly
      mapped in 26-day cycles with a 58.6 km nominal path separation.
      Orbit trim adjustments would make it possible to obtain uniform
      coverage during the course of the mission with an ultimate
      spacing of ground tracks at the equator or 3.1 km.
 
      The Mars Observer spacecraft provided a three-axis stabilized,
      nadir-oriented platform for the continuous observations of Mars
      by the science instruments.  The spacecraft was built by the
      General Electric Astro-Space Division.  The Gamma Ray
      Spectrometer and Magnetometer sensor assemblies were mounted on
      individual booms on the spacecraft.  All other instruments were
      rigidly mounted to the spacecraft structure.  No movable scan
      platform was provided; the spacecraft was to be continuously
      nadir pointed, rotating at the orbital rate.  Those instruments
      that required scanning or multiple fields of view had internal
      scanning mechanisms.
 
    Mission Phases
    ==============
      The following sections outline the planned mission phases for
      Mars Observer.  For each phase, the spacecraft operations type
      was ORBITER, and the target was MARS.
 
 
 
 
      LAUNCH
      ------
        This stage includes the period of time starting from the Mars
        Observer launch and extending to the transmission of the
        first cruise sequence, two days after launch.
 
 
          Mission Phase Start Time      : 1992-09-25
          Mission Phase Stop Time       : 1992-09-27
 
 
 
      CRUISE
      ------
        There was an 11-month transit time between launch and orbit
        insertion of the Mars Observer spacecraft.
 
 
          Mission Phase Start Time      : 1992-09-27
          Mission Phase Stop Time       : 1993-08-24
 
 
 
      ENCOUNTER
      ---------
        The Encounter phase, also known as the Mars Orbit Insertion
        (MOI) period was to end just before solar conjunction and the
        beginning of the dust storm period.  Since it was
        scientifically important to make observations for an entire
        global mapping cycle (26 days) before the onset of a major
        dust storm, it was hoped that the fuel margin would permit a
        shorter MOI phase than expected.  Final deployment of all
        booms would be completed and a spacecraft and instrument
        checkout would be completed prior to the start of the mapping
        phase.
 
        The orbit insertion strategy was to use four large braking
        maneuvers to successively reduce the spacecraft energy: first
        into a 3-day elliptical orbit, next into a 1-day elliptical
        orbit, then into a 4.2-hour elliptical orbit, and finally
        into the near-circular mapping orbit.
 
 
          Mission Phase Start Time      : 1993-08-24
          Mission Phase Stop Time       : 1993-11-24
 
 
 
      MAPPING
      -------
        The mapping phase includes the systematic mapping
        observations that last 687 Earth days, as well as the
        subsequent support activities of the Mars 94 mission.
 
 
         Mission Phase Start Time       : 1993-11-24
         Mission Phase Stop Time        : 1996-02-01

Mission Objectives Overview
    ===========================
      The primary geoscience objectives for Mars Observer include the
      global definition of the topography and gravitational fields,
      global determination of the elemental and mineralogical
      character of surface materials, and determination of the nature
      of the magnetic field around Mars.  The primary climatology
      objectives are the determination of the time and space
      distribution, abundances, sources and sinks of volatile
      material and dust over a seasonal cycle, as well as the
      delineation of atmospheric structure and dynamics.  Mars
      Observer will provide a basic global understanding of Mars as
      it exists today and will provide a framework for understanding
      its past.