RK89 Object

Description

The Runge Kutta 8(9) propagator uses 8th order Runge-Kutta propagation with 9th order error control to propagate the spacecraft orbit. See expanded description.

Runge Kutta 8(9) solves the Cartesian formulation of the orbit equations of motion using a Runge-Kutta 8(9) integrator. This method consumes more memory than the other Runge Kutta integrators but takes fewer propagation steps for a specified accuracy. The RK8(9) Propagator is a ninth order embedded Runge-Kutta integrator that maintains eighth order numerical accuracy. This integrator uses Fehlberg-style embedding, with coefficients derived by Verner. Integration with the RK8(9) integrator proceeds through sixteen intermediate stages, accumulating data from each stage and using these data to produce a final, accurate integration step. The RK8(9) Propagator uses the mean of J2000 Earth-centered Equatorial representation of the orbital elements, expressed in the Cartesian coordinate system (MJ2000 Earth Equatorial Cartesian coordinates) to represent the spacecraft’s state for integration. To this state it applies the forces specified in the ForceModel (also expressed in MJ2000 Earth Equatorial Cartesian coordinates) in order to determine how to move the spacecraft through time. The RK8(9) Propagator can be run in either fixed-step or variable-step mode. When the propagator is run in variable step mode, the integration step size is controlled by the user-specified error tolerance. Each integration step can have a different step size. This mode allows FreeFlyer to move the spacecraft in time (i.e., propagates the spacecraft) with the largest possible time step consistent with the specified error tolerance. The fixed-step mode ensures that every propagation step moves the spacecraft the same amount of time. FreeFlyer maintains the specified error tolerance for fixed step propagation by keeping the step size at the specified step size when the tolerance would allow a larger time step. If the tolerance forces the time step to be smaller than the specified value, FreeFlyer will take multiple steps internally, and report the results after the accumulated propagation reaches the desired time step.

Inheritance Hierarchy: Object->Propagator->Integrator->RK89

Available In Editions:

Engineer

Mission

Timing Precision Mode

This page describes functionality in nanosecond timing precision mode.

Click here to see the documentation for this object in millisecond timing precision mode.

Name	Description	Attributes
AllowErrorViolation	Determines whether the error tolerance may be violated once the minimum step size is reached. If this property is set to true, and the integrator step error does not meet the tolerance at 1 ms step size, the state is automatically advanced 1 ms ahead and a warning is generated.	Type: Variable Access: Read/Write
CalculateSTM	Flag indicating whether or not to calculate the state transition matrix at each integration step as part of the state integration. If the PropagateCovariance flag is set to TRUE on the SpacecraftODProperties object or if the Spacecraft is in an estimation process, the STM is always calculated. If the Spacecraft.Propagator is not an Integrator type then this property is ignored.	Type: Variable Access: Read/Write
DeclaredName	The name of the object as declared.	Type: String Access: Read-Only
DisplayName	The name displayed for this object in output windows such as views, plots, and reports.	Type: String Access: Read/Write
FixedStep	Flag denoting whether the propagator is being run in fixed-step mode (i.e. constant StepSize) or in variable-step mode (i.e. variable StepSize).	Type: Variable Access: Read/Write
ForceModel	A force model.	Type: ForceModel Access: Read-Only
LargeCurvature	Flag that signifies whether the integration has failed due to a large curvature in the force field. (1 = Integration Failed, 0 = Integration Nominal, -1 = No Integration has been performed).	Type: Variable Access: Read-Only
MaxTries	The maximum number of times to attempt to change the step size in the integration process in order to meet the specified error tolerance. If the specified error tolerance is not met after MaxTries attempts, an error is thrown.	Type: Variable Access: Read/Write
ObjectId	The unique identifier for the object.	Type: Variable Access: Read-Only
ObjectType	The type of the object.	Type: String Access: Read-Only
RelativeErrorThreshold	If the absolute error is less than this value, then the absolute error is compared against the tolerance. Otherwise the relative error is compared against the tolerance. Set a very large value (e.g. 1e100) to ensure the RK89.Tolerance is treated as an absolute error tolerance. Set a very small value (e.g. 1e-100) to ensure that the RK89.Tolerance is treated as a relative error tolerance.	Type: Variable Access: Read/Write
StepJustTaken	The size of the previous step taken by the integration process.	Type: TimeSpan Access: Read-Only Units: s
StepsAttempted	This represents the sum of the successful and failed steps. This property will closely reflect the performance of the integrator since it is a measure of the total number of steps executed by the integrator.	Type: Variable Access: Read-Only
StepsFailed	This property is incremented once each time the integrator steps the spacecraft forward and the integrator tolerance is not met. A high ratio of the number of failed to successful steps may suggest that the integrator tolerance is too high.	Type: Variable Access: Read-Only
StepSize	The number of seconds the propagated object is advanced when the Step command is executed.	Type: TimeSpan Access: Read/Write Units: s
StepsRequested	Represents the count of integration steps requested by the user. This property will be incremented once each time the FreeFlyer engine advances the spacecraft to a desired epoch. For the Step command, this property will be incremented once. For interval methods and Step-to commands, this property will be incremented each time bisection is performed unitl the condition is met. Abnormally high values on this property can indicate that the IntervalStopAccuracy may be too strict.	Type: Variable Access: Read-Only
StepsSuccessful	This property is incremented for every successful step of the integrator. Since it may take several steps to reach the desired epoch at the specified tolerance, the number of successful steps may be greater than the number of requested steps.	Type: Variable Access: Read-Only
StepToTake	The maximum possible size of the next step to take in the integration process based on the relative error tolerance. When the StepSize property is set, this property is initialized with the new StepSize value and is updated after the next step is taken.	Type: TimeSpan Access: Read-Only Units: s
STM	Returns the State Transition Matrix. The matrix is always a square where the length of each side is determined by the total number of properties being estimated or considered.	Type: Matrix Access: Read-Only
STMCalculationMethod	A flag indicating the method to be used to calculate the state transition matrix. Note that even if the CalculateSTM property is set to FALSE, this property still applies if the SpacecraftODProperties.PropagateCovariance flag is to TRUE or if the Spacecraft is included in an estimation process.	Type: Variable Access: Read/Write
Tolerance	When the Step command is executed, intermediate integration steps are taken to ensure that the local error never exceeds this value.	Type: Variable Access: Read/Write
ToleranceMode	Determines how the relative error tolerance is calculated.	Type: Variable Access: Read/Write