Propagator Controls

Two sets of propagator controls are available: one set for use during estimation and simulation processes and another set which may be enabled for use in ephemeris prediction. When enabled, the predict controls are applied during ephemeris predictions generated at the end of processes (Filter, Smoother, Simulator, Least Squares) and during ephemeris predictions generated directly from satellite objects.

In the special case where a finite maneuver is modeled in the prediction interval and the Gauss-Jackson integrator specified for use in prediction, the Gauss-Jackson integrator is used up to the maneuver time, a maneuver integrator is used to cross the maneuver, then the Gauss-Jackson integrator is restarted. If the maneuver has custom integrator setting, those settings are used during the maneuver time span, otherwise the nominal integrator settings are used to cross the maneuver.

The following Propagator Controls can be set for each satellite:

Propagator Controls
Control	Description
IntegrationMethod - BulirschStoer	Integration method based on Richardson extrapolation with automatic step size control.
IntegrationMethod - RK4	Runge-Kutta integration method of 4th order with no error control for the integration step size.
IntegrationMethod - RKF 7(8)	Runge-Kutta-Fehlberg integration method of 7th order with 8th order error control for the integration step size.
IntegrationMethod - RKV 8(9)	Runge-Kutta-Verner integration method of 8th order with 9th order error control for the integration step size.
IntegrationMethod - Gauss-Jackson*	12th order Gauss-Jackson integration method with no error control implemented for the integration step size. This option is restricted for use during ephemeris prediction since it must be restarted after measurement updates. The Gauss-Jackson integration method requires smaller time steps than most of the single step methods with a step of 30 seconds being appropriate for LEO.
MinimumAltitude**	Limits propagation of ephemeris for a satellite when it is approaching the surface of its central body. The value is honored if drag is not being modeled. If drag is modeled and a variable step size is used, then the selected drag model will provide its minimum valid altitude. If drag is modeled and a fixed step size is used, then the minimum allowed altitude is 90 km.
Enabled*	Boolean flag indicating if custom integrator settings are desired for use in ephemeris prediction. See description of where these settings would be used above.
UseVOP	The UseVOP attribute is a boolean flag; if true, a variation of parameters in universal variables formulation of the equations of motion is used. If false, the Cowell formulation is used. Not available in combination with Gauss-Jackson integration method.
PredictorCorrectorScheme	Full Correction - Use a full evaluation of the acceleration model at the end of a Gauss-Jackson integration step. This method is more accurate than the Pseudo Correction method. Pseudo Correction - Use a pseudo-evaluation where only the two body acceleration is updated. This method is more efficient than the Full Correction method.
MaxCorrectorIterations	Maximum number of corrector iterations allowed in Gauss-Jackson predictor/corrector integration scheme. Valid for the Gauss-Jackson integration method only.
StepSize	Select a StepControlMethod (below) and enter the appropriate parameters.

Step Control Methods

The following step control methods and parameters are available for defining step size:

StepControlMethod Options
StepControlMethod	Parameter	Description
Fixed	Time	Enter the step size (in time) to be used during fixed time step integration. This step size will be used when the eccentricity is below the eccentricity threshold. Must be greater than 0.
	TrueAnomaly	Enter the step size (in true anomaly) to be used during fixed true anomaly step integration. This step size will be used when the eccentricity is above the eccentricity threshold. Must be greater than 0.
	EccentricityThreshold	Enter a value for the eccentricity of the orbit above which the propagator will take fixed steps (approximately) in true anomaly as opposed to fixed steps in time. Must be greater than 0.
RelativeError***	ErrorTolerance	Nominally 1e-13.
	MinStepSize	Nominally 1 sec.
	MaxStepSize	Nominally 86400 sec.

* Only available in predict integrator settings.

** Not available for a GPS satellite.

*** Not available with the RK4 or Gauss-Jackson integration methods.