Instrument Overview
    ===================
      During aerobraking, the accelerometers measure the change in velocity of
      the spacecraft due to aerodynamic forces. The dominant force is along the
      spacecraft y-direction. The spacecraft y-axis is approximately into the
      wind. Data are provided at 1 second intervals and recorded in units of
      m/s^2.
 
 
    Scientific Objectives
    =====================
      Accelerometer data were used to characterize the nature of the atmosphere,
      to determine the effect of the atmosphere on each orbit, and to predict
      the effect of the atmosphere on future orbits.
 
 
    Calibration
    ===========
      The instrument was calibrated on each orbit to determine drift in
      instrument bias.  Bias is determined by monitoring the accelerometer
      instrument during periods of inactivity before and after entering the
      atmosphere. The bias acceleration is then estimated over the entire pass
      by trending the data from the pre- and post-atmospheric entry periods.
      The pre- and post-atmospheric periods were defined by instrument turn-on
      and turn-off times and a lower limit on the altitude of data used for
      calibration, typically 250 km.
 
 
    Operational Considerations
    ==========================
      The instrument readings are affected by changes in temperature.  The
      instrument is mounted in the inertial measurement unit (IMU) and the
      temperature of the IMU is by temperature sensors.
 
 
    Operational Modes
    =================
      The data from the accelerometer are passed to the telemetry deck during an
      aerobraking pass from the time the s/c reaches aerobraking orientation
      until the s/c returns to nominal orbit attitude.
 
 
    Measured Parameters
    ===================
      An accelerometer is an instrument that measures the acceleration of the
      case of the sensor due to external forces.  All accelerometers have a
      'proof mass' and it is the tendency of the proof mass to move relative to
      the case that is a measure of the acceleration of the case.  Early
      accelerometers produced output that was directly related to acceleration;
      but modern sensors integrate the internally measured signal to reduce
      noise and the output is proportional to the change in velocity over the
      integration time.  In high precision accelerometers, like those on ODY,
      the proof mass is an electronically floating mass.  The electromagnetic
      field is varied to keep the proof mass stationary relative to the case.
      The current required to accomplish this is proportional to the
      acceleration. The accelerometers on ODY are sensitive to acceleration of
      the center of mass (c.m.) of the s/c, pseudo-accelerations (i.e.
      centrifugal) due to rigid motion of the s/c about the c.m., and
      differences in gravitational force at the proof mass and the c.m. of the
      s/c (gravity gradient).