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.