Norad Object

The Norad propagator, for use with NORAD two-line elements (TLEs), evolves the orbit equations of motion using a Brower theory implemented as a combination of SGP4 and SDP4 algorithms. For Spacecraft with periods less than 225 minutes, the method used is the SGP4 algorithm. Spacecraft with periods greater than 225 minutes are propagated with the SDP4 algorithm. As emphasized by Hoots, the most important point in propagating space objects given their NORAD two-line element (TLE) sets is to note that not any prediction model will suffice. This is because the NORAD element sets are "mean" values obtained by removing periodic variations in a particular way. Good predictions are only obtained if the element set is used with the NORAD algorithm that removed these variations. The Norad propagator is included in FreeFlyer to provide the ability to propagate the large number of Spacecraft that are tracked by NORAD by using the published sets of TLE’s. Note: ForceModel settings are ignored for the Norad Propagator. When using the Norad Propagator for near-earth propagation it is necessary to set the BSTAR term of the Norad TLE to the Cd property of the Spacecraft. This is done automatically if importing the spacecraft state from a TLE file.