The OrbitTools Libraries are implementations of NORAD algorithms for determining satellite location and velocity in Earth orbit.　The algorithms come from the December, 1980 NORAD document "Space Track Report No. 3".　The orbital algorithms implemented in OrbitTools are: SGP4, for "near-Earth" objects, and SDP4 for "deep space" objects.　These algorithms are widely used in the satellite tracking community and produce very accurate results when provided with current NORAD two-line element data.