SGP4 is an algorithm designed to be used with TLE data, which has a specific set of mean elements computed by Kozai theory. Using it with a set of classical orbit elements can lead to discrepancies. Hence, we need to do two things:
[x] Add a J4 orbit propagator for mission analysis, which can receive as input the mean orbital elements.
[x] Allow SGP4 to be initialized in the API only using TLEs.
SGP4 is an algorithm designed to be used with TLE data, which has a specific set of mean elements computed by Kozai theory. Using it with a set of classical orbit elements can lead to discrepancies. Hence, we need to do two things: