org.orekit.forces.empirical

Class ParametricAcceleration

java.lang.Object

org.orekit.forces.AbstractForceModel

org.orekit.forces.empirical.ParametricAcceleration

All Implemented Interfaces:

ForceModel

public class ParametricAcceleration
extends AbstractForceModel

This class implements a parametric acceleration.

Parametric accelerations are intended to model lesser-known forces, estimating a few defining parameters from a parametric function using orbit determination. Typical parametric functions are polynomial (often limited to a constant term) and harmonic (often with either orbital period or half orbital period).

An important operational example is the infamous GPS Y-bias, which is thought to be related to a radiator thermal radiation. Other examples could be to model leaks that produce roughly constant trust in some spacecraft-related direction.

The acceleration direction is considered constant in either:

• inertial frame
• spacecraft frame
• a dedicated attitude frame overriding spacecraft attitude (this could for example be used to model solar arrays orientation if the force is related to solar arrays)

If the direction of the acceleration is unknown, then three instances of this class should be used, one along the X axis, one along the Y axis and one along the Z axis and their parameters estimated as usual.

Since:

10.3

Author:

Luc Maisonobe, Bryan Cazabonne

Constructor Summary

Constructors

Constructor and Description
ParametricAcceleration(Vector3D direction, AttitudeProvider attitudeOverride, AccelerationModel accelerationModel) Simple constructor.
ParametricAcceleration(Vector3D direction, boolean isInertial, AccelerationModel accelerationModel) Simple constructor.

Method Summary

Modifier and Type	Method and Description
<T extends CalculusFieldElement<T>> FieldVector3D<T>	acceleration(FieldSpacecraftState<T> state, T[] parameters) Compute acceleration.
Vector3D	acceleration(SpacecraftState state, double[] parameters) Compute acceleration.
boolean	dependsOnPositionOnly() Check if force models depends on position only.
Stream<EventDetector>	getEventsDetectors() Get the discrete events related to the model.
<T extends CalculusFieldElement<T>> Stream<FieldEventDetector<T>>	getFieldEventsDetectors(Field<T> field) Get the discrete events related to the model.
List<ParameterDriver>	getParametersDrivers() Get the drivers for force model parameters.
void	init(SpacecraftState initialState, AbsoluteDate target) Initialize the force model at the start of propagation.

Methods inherited from class org.orekit.forces.AbstractForceModel

complainIfNotSupported, getParameterDriver, isSupported

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.orekit.forces.ForceModel

addContribution, addContribution, getParameters, getParameters, init

Constructor Detail

ParametricAcceleration

public ParametricAcceleration(Vector3D direction,
                              boolean isInertial,
                              AccelerationModel accelerationModel)

Simple constructor.

Parameters:

direction - acceleration direction in overridden spacecraft frame

isInertial - if true, direction is defined in the same inertial frame used for propagation (i.e. SpacecraftState.getFrame()), otherwise direction is defined in spacecraft frame (i.e. using the propagation attitude law)

accelerationModel - acceleration model used to compute the contribution of the empirical acceleration direction

ParametricAcceleration

public ParametricAcceleration(Vector3D direction,
                              AttitudeProvider attitudeOverride,
                              AccelerationModel accelerationModel)

Simple constructor.

Parameters:

direction - acceleration direction in overridden spacecraft frame frame used for propagation (i.e. SpacecraftState.getFrame()), otherwise direction is defined in spacecraft frame (i.e. using the propagation attitude law)

attitudeOverride - provider for attitude used to compute acceleration

accelerationModel - acceleration model used to compute the contribution of the empirical acceleration direction

Method Detail

dependsOnPositionOnly

public boolean dependsOnPositionOnly()

Check if force models depends on position only.

Returns:

true if force model depends on position only, false if it depends on velocity, either directly or due to a dependency on attitude

getParametersDrivers

public List<ParameterDriver> getParametersDrivers()

Get the drivers for force model parameters.

Returns:

drivers for force model parameters

init

public void init(SpacecraftState initialState,
                 AbsoluteDate target)

Initialize the force model at the start of propagation. This method will be called before any calls to ForceModel.addContribution(SpacecraftState, TimeDerivativesEquations), ForceModel.addContribution(FieldSpacecraftState, FieldTimeDerivativesEquations), ForceModel.acceleration(SpacecraftState, double[]) or ForceModel.acceleration(FieldSpacecraftState, CalculusFieldElement[])

The default implementation of this method does nothing.

Parameters:

initialState - spacecraft state at the start of propagation.

target - date of propagation. Not equal to initialState.getDate().

acceleration

public Vector3D acceleration(SpacecraftState state,
                             double[] parameters)

Compute acceleration.

Parameters:

state - current state information: date, kinematics, attitude

parameters - values of the force model parameters

Returns:

acceleration in same frame as state

acceleration

public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(FieldSpacecraftState<T> state,
                                                                         T[] parameters)

Compute acceleration.

Type Parameters:

T - type of the elements

Parameters:

state - current state information: date, kinematics, attitude

parameters - values of the force model parameters

Returns:

acceleration in same frame as state

getEventsDetectors

public Stream<EventDetector> getEventsDetectors()

Get the discrete events related to the model.

Returns:

stream of events detectors

getFieldEventsDetectors

public <T extends CalculusFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventsDetectors(Field<T> field)

Get the discrete events related to the model.

Type Parameters:

T - extends CalculusFieldElement<T>

Parameters:

field - field to which the state belongs

Returns:

stream of events detectors