Choosing an Integrator 
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Choosing an Integrator appropriate to the task can significantly improve FreeFlyer's performance. FreeFlyer can utilize several integrators with varying degrees of accuracy and speed, from a simple Two Body, to the robust RungeKutta 8(9). The following table summarizes details about the integrators that are provided for the Spacecraft. For detailed information on a specific integrator, follow the links shown below.
Integrator Summary TableBelow is a table of the integrators available in FreeFlyer and some relative accuracy and speed values of them compared to each other. In every integrator's case, it is especially helpful for Spacecraft in specific orbits and orbital regimes such that its advantages come into play. Because of that, some insight is provided below into what each integrator is recommended for and what it isn't recommended for. Speed and accuracy were determined by varying the integrator type and step size in sample LEO, GPS, and GEO orbit regimes, illustrating common propagation scenarios. Individual results will vary. All speed values are percentages relative to the run time of the RK89 integrator. All accuracy values are expressed as orders of magnitude relative to the accuracy of the Two Body integrator.
Note: The specific RungeKutta integration method used in FreeFlyer is the RungeKuttaVerner method.
SP and SGP4 PropagatorsIn addition to the above integrators, the Air Force Space Command SGP4 (General Perturbations) and SP (Special Perturbations) propagators (supplied in DLLs) can be used. Explore the section below for instructions on using these DLLs with FreeFlyer.
See Also•Integrator Properties and Methods •Solar System settings that affect Spacecraft Propagation
