Using the SGP4 Propagator
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The United States Space Force SGP4 algorithm version 8.1 is included in FreeFlyer's installation package through the AstroStds library. The included DLL files are stored in the FreeFlyer installation directory under "Support Files\Engine\Third Party\64_Bit\AstroStdsSgp4Prop". This directory also includes a license file to enable users to access the open source SGP4 implementation. See the Two-Line Element Set File page for more information.
See Setting up an Integrator for information on configuring a Spacecraft object to use any integration method (including SGP4) for propagation.
SGP4 Propagator Configuration
Users have the option to provide their own library and license files for use with the SGP4 propagator, which enables the ability to upgrade to new versions of the AstroStds library as desired. These options can be configured through the global Solar System object as shown below.
Note: FreeFlyer supports versions 8.x of the AstroStds library, and compatibility is not guaranteed for other versions.
The AstroStds library also supports the SGP4-XP (Extended Precision) algorithm, which is used with TLE data in ephemeris type 4 and includes Solar Radiation Pressure modeling, the Jacchia-70 atmosphere density model, and additional perturbation modeling for Earth-based and deep-space trajectories. The SGP4-XP propagator produces similar accuracy to many numerical integrators, while maintaining a significant advantage in terms of computational speed. To configure a Spacecraft to use the SGP4-XP propagator (and thus generate a type 4 ephemeris for any simulated TLE data), set the EphemerisType property as shown below:
•SGP4 Properties and Methods