Data Set Overview
  =================

    The Lunar Prospector spacecraft trajectory data set consists of
    spacecraft position determinations in numerous coordinate systems
    at one minute intervals. The data set also contains the spacecraft
    velocity as a function of time.  This data set is derived by using
    the spacecraft position data set from the Lunar Prospector level
    zero data archive (LP-L-6-POSITION-V1.0). The SPICE SPK kernel
    LP_EPHEM.TSP that is included on the archive volume provides
    ephemeris data for the Sun, Earth, and Moon. These data are combined
    with the Lunar Prospector location relative to the Moon in order
    to generate trajectory data that will facilitate the analysis of
    both the magnetometer and the electron reflectometer data sets.

    Each file in the spacecraft trajectory data set covers one month of
    time.

  Science Objectives
  ==================

    The Lunar Prospector science objectives relevant to this data set are
    to map the Moon's surface composition and its magnetic field, and to
    determine the frequency and location of gas release events.  A
    special emphasis of the science objectives is to search for polar
    water ice deposits [BINDERETAL1998].  The spacecraft position data
    are used to locate where on the Moon science data were acquired.

  Coordinate Systems
  ==================

    Selenographic: These data are a repeat of the values generated by
    the Goddard Flight Dynamics Analysis Branch for the level zero data.
    The selenographic coordinate system provided is an east longitude
    system where the prime meridian is defined in [DAVIESETAL1994]. A
    negligible amount of flattening (1x10**-30) is used for the Moon.
    Thus, selenographic latitude is nearly equal to selenocentric
    latitude with almost no error.  The mean radius and GM of the Moon
    used to generate this data set are 1738 km and 4902.8014 km**3/s**2,
    respectively. Both spherical (SG) and Cartesian (SEL) representations
    of the selenographic coordinate system are provided. In the Cartesian
    representation, the Z-axis is aligned with the lunar spin axis,
    positive in the direction of angular momentum. The X-axis lies in
    the equatorial plane and points in the direction of the prime
    meridian. Y completes the right-handed set.

    Selenocentric Solar Ecliptic (SSE): The SSE coordinate system has
    its X-axis along the instantaneous Moon-Sun line, positive towards
    the Sun. The Z-axis is parallel to the upward normal to the Earth's
    ecliptic plane, and Y completes the right-handed set. Distances are
    measured from the lunar center of mass and are reported in units
    of kilometers.

    Geocentric Solar Ecliptic (GSE): The GSE coordinate system has
    its X-axis along the instantaneous Earth-Sun line, positive towards
    the Sun. The Z-axis is parallel to the upward normal to the Earth's
    ecliptic plane, and Y completes the right-handed set. Distances are
    measured from the Earth center of mass and are reported in units
    of Earth radii where 1 Re = 6372 km.

    Geocentric Solar Magnetospheric (GSM): The GSM coordinate system has
    its X-axis along the instantaneous Earth-Sun line, positive towards
    the Sun (same as GSE X-axis!). The X-Z plane is defined to contain
    the the Earth's dipole (passes through 78.565 deg North, 69.761 deg
    West). Y completes the right-handed set. Distances are measured from
    the Earth center of mass and are reported in units of Earth radii
    where 1 Re = 6372 km.

    Definitions of the GSE and GSM coordinate systems come from
    [RUSSELL1971]. The Earth's dipole location used in the GSM coordinate
    system definition is based on the 1970 IGRF model as stated in that
    reference.

Confidence Level Overview
  =========================

    Error bars are not provided with the original spacecraft position
    data set. All values in this data set are reported to the nearest
    kilometer. The actual error bars are probably larger than 1 km and
    different in the 'along track', cross-track', and 'altitude'
    directions.

  Data Coverage and Quality
  =========================

    Spacecraft position data exist for the entire Lunar Prospector
    Primary and Extended Missions.