SGP4 is a Simplified General Perturbations mathematical model, which is used to calculate the position of satellites relative to the Earth. The most frequently used model is SGP4, which is used with Two-Line Element (TLE) sets provided by NORAD and NASA.
SGP4 is used for near earth objects with short duration orbital periods (less than 255 minutes). This more than covers all current amateur satellites and the International Space Station. For example, the ISS is about 250 miles above the earth and has an orbital period of about 94 minutes, while FunCube-1 (AO-73) satellite is about 400 miles above the earth and has an orbital period of 97 minutes.
While the original SGP4 calculations were described in Fortran IV back in 1988, they have been ported to many languages, included Python. Due to the critical nature of these prediction models, there are fully automated suites of tests that can be used to validate their accuracy.
A fully tested python version of sgP4 can be found here: https://pypi.python.org/pypi/sgp4/
Inputs are TLE data and desired time. Output is positional vector and velocity.
