org.orekit.forces.gravity
Class CunninghamAttractionModel

java.lang.Object
  org.orekit.parameter.Parameterizable
      org.orekit.parameter.JacobiansParameterizable
          org.orekit.forces.gravity.CunninghamAttractionModel

All Implemented Interfaces:

Serializable, ForceModel, GradientModel, AttractionModel, IJacobiansParameterizable, IParameterizable

public class CunninghamAttractionModel
extends JacobiansParameterizable
implements ForceModel, GradientModel, AttractionModel

This class represents the gravitational field of a celestial body.

The algorithm implemented in this class has been designed by Leland E. Cunningham (Lockheed Missiles and Space Company, Sunnyvale and Astronomy Department University of California, Berkeley) in his 1969 paper: On the computation of the spherical harmonic terms needed during the numerical integration of the orbital motion of an artificial satellite (Celestial Mechanics 2, 1970).

The implementation of this class enables the computation of partial derivatives by finite differences with respect to the central attraction coefficient.

Warning: using a 0x0 Earth potential model is equivalent to a simple Newtonian attraction. However computation times will be much slower since this case is not particularized and hence conversion from body frame (often ITRF) to integration frame is necessary.

Author:

Fabien Maussion, Luc Maisonobe, Véronique Pommier-Maurussane

See Also:

Serialized Form

Field Summary

static String

RADIUS Parameter name for equatorial radius.

Fields inherited from interface org.orekit.forces.gravity.AttractionModel

MU

Constructor Summary

CunninghamAttractionModel(Frame centralBodyFrame, double equatorialRadius, double mu, double[][] C, double[][] S)
Creates a new instance.

CunninghamAttractionModel(Frame centralBodyFrame, double equatorialRadius, double mu, double[][] C, double[][] S, int degreePD, int orderPD)
Creates a new instance.

CunninghamAttractionModel(Frame centralBodyFrame, Parameter equatorialRadius, Parameter mu, double[][] C, double[][] S)
Creates a new instance using Parameter.

CunninghamAttractionModel(Frame centralBodyFrame, Parameter equatorialRadius, Parameter mu, double[][] C, double[][] S, int degreePD, int orderPD)
Creates a new instance using Parameter.

Method Summary

void	addContribution(SpacecraftState s, TimeDerivativesEquations adder) Compute the contribution of the force model to the perturbing acceleration.
void	addDAccDParam(SpacecraftState s, Parameter param, double[] dAccdParam) Compute acceleration derivatives with respect to additional parameters.
void	addDAccDState(SpacecraftState s, double[][] dAccdPos, double[][] dAccdVel) Compute acceleration derivatives with respect to state parameters.
Vector3D	computeAcceleration(PVCoordinates pv, AbsoluteDate date) Method to compute the acceleration.
Vector3D	computeAcceleration(SpacecraftState s) Compute the acceleration due to the force.
boolean	computeGradientPosition() This method returns true if the acceleration partial derivatives with respect to position have to be computed.
boolean	computeGradientVelocity() This method returns true if the acceleration partial derivatives with respect to velocity have to be computed.
EventDetector[]	getEventsDetectors() Get the discrete events related to the model.
double	getMu() Get the central attraction coefficient &mu.

Methods inherited from class org.orekit.parameter.JacobiansParameterizable

addJacobiansParameter, addJacobiansParameter, addJacobiansParameter, supportsJacobianParameter

Methods inherited from class org.orekit.parameter.Parameterizable

addParameter, getParameters, supportsParameter

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.orekit.parameter.IParameterizable

getParameters, supportsParameter

Field Detail

RADIUS

public static final String RADIUS

Parameter name for equatorial radius.

See Also:

Constant Field Values

Constructor Detail

CunninghamAttractionModel

public CunninghamAttractionModel(Frame centralBodyFrame,
                                 double equatorialRadius,
                                 double mu,
                                 double[][] C,
                                 double[][] S)
                          throws IllegalArgumentException

Creates a new instance.

Parameters:

centralBodyFrame - rotating body frame

equatorialRadius - reference equatorial radius of the potential

mu - central body attraction coefficient (m³/s²)

C - un-normalized coefficients array (cosine part)

S - un-normalized coefficients array (sine part)

Throws:

IllegalArgumentException - if coefficients array do not match

CunninghamAttractionModel

public CunninghamAttractionModel(Frame centralBodyFrame,
                                 double equatorialRadius,
                                 double mu,
                                 double[][] C,
                                 double[][] S,
                                 int degreePD,
                                 int orderPD)
                          throws IllegalArgumentException

Creates a new instance.

Parameters:

centralBodyFrame - rotating body frame

equatorialRadius - reference equatorial radius of the potential

mu - central body attraction coefficient (m³/s²)

C - un-normalized coefficients array (cosine part)

S - un-normalized coefficients array (sine part)

degreePD - degree for partial derivatives

orderPD - order for partial derivatives

Throws:

IllegalArgumentException - if coefficients array do not match or degree and/or order for partial derivatives is higher than degree and/or order for acceleration

CunninghamAttractionModel

public CunninghamAttractionModel(Frame centralBodyFrame,
                                 Parameter equatorialRadius,
                                 Parameter mu,
                                 double[][] C,
                                 double[][] S)
                          throws IllegalArgumentException

Creates a new instance using Parameter.

Parameters:

centralBodyFrame - rotating body frame

equatorialRadius - reference equatorial radius of the potential

mu - parameter representing central body attraction coefficient (m³/s²)

C - parameter representing un-normalized coefficients array (cosine part)

S - un-normalized coefficients array (sine part)

Throws:

IllegalArgumentException - if coefficients array do not match

CunninghamAttractionModel

public CunninghamAttractionModel(Frame centralBodyFrame,
                                 Parameter equatorialRadius,
                                 Parameter mu,
                                 double[][] C,
                                 double[][] S,
                                 int degreePD,
                                 int orderPD)
                          throws IllegalArgumentException

Creates a new instance using Parameter.

Parameters:

centralBodyFrame - rotating body frame

equatorialRadius - reference equatorial radius of the potential

mu - parameter representing central body attraction coefficient (m³/s²)

C - parameter representing un-normalized coefficients array (cosine part)

S - un-normalized coefficients array (sine part)

degreePD - degree for partial derivatives

orderPD - order for partial derivatives

Throws:

IllegalArgumentException - if coefficients array do not match or degree and/or order for partial derivatives is higher than degree and/or order for acceleration

Method Detail

addContribution

public void addContribution(SpacecraftState s,
                            TimeDerivativesEquations adder)
                     throws OrekitException

Compute the contribution of the force model to the perturbing acceleration..

Specified by:

addContribution in interface ForceModel

Parameters:

s - current state information: date, kinematics, attitude

adder - object where the contribution should be added

Throws:

OrekitException - if some specific error occurs

getEventsDetectors

public final EventDetector[] getEventsDetectors()

Get the discrete events related to the model..

Specified by:

getEventsDetectors in interface ForceModel

Returns:

array of events detectors or null if the model is not related to any discrete events

computeGradientPosition

public boolean computeGradientPosition()

This method returns true if the acceleration partial derivatives with respect to position have to be computed..

Specified by:

computeGradientPosition in interface GradientModel

Returns:

true if the derivatives have to be computed, false otherwise

computeGradientVelocity

public boolean computeGradientVelocity()

This method returns true if the acceleration partial derivatives with respect to velocity have to be computed..

Specified by:

computeGradientVelocity in interface GradientModel

Returns:

true if the derivatives have to be computed, false otherwise

computeAcceleration

public Vector3D computeAcceleration(SpacecraftState s)
                             throws OrekitException

Compute the acceleration due to the force..

Specified by:

computeAcceleration in interface ForceModel

Parameters:

s - current state information: date, kinematics, attitude

Returns:

acceleration in the SpacecraftState frame

Throws:

OrekitException - if some specific error occurs

computeAcceleration

public Vector3D computeAcceleration(PVCoordinates pv,
                                    AbsoluteDate date)

Method to compute the acceleration. This method has been implemented in order to validate the force model only. The reason is that for the validation context, we do not want to set up an instance of the SpacecraftState object to avoid the inertial frame of the spacecraft orbit.

(see Story #V82 and Feature #34 on https://www.orekit.org/forge/issues/34)

Out of the validation context, one must use the method Vector3D computeAcceleration(final SpacecraftState s)

Fixes bug #97: Numerical stability errors for high order gravity field. (see https://www.orekit.org/forge/issues/97) The error and was due to the acceleration being computed as r^n * (cn * gradC + sn * gradS). As order n increased r^n increased up to exceed floating point limits whereas the gradient decreased. In fact r^n * grad was always a normal floating point number despite both terms were not. The fix involved changing the loops so the gradients did include the r^n part.

Parameters:

pv - PV coordinates of the spacecraft

date - date

Returns:

acceleration vector

addDAccDState

public final void addDAccDState(SpacecraftState s,
                                double[][] dAccdPos,
                                double[][] dAccdVel)
                         throws OrekitException

Compute acceleration derivatives with respect to state parameters..

Specified by:

addDAccDState in interface IJacobiansParameterizable

Parameters:

s - spacecraft state

dAccdPos - acceleration derivatives with respect to position

dAccdVel - acceleration derivatives with respect to velocity

Throws:

OrekitException - if derivatives cannot be computed

addDAccDParam

public void addDAccDParam(SpacecraftState s,
                          Parameter param,
                          double[] dAccdParam)
                   throws OrekitException

Compute acceleration derivatives with respect to additional parameters.
No parameter is supported by this force model.

Specified by:

addDAccDParam in interface IJacobiansParameterizable

Parameters:

s - spacecraft state

param - the parameter with respect to which derivatives are required

dAccdParam - acceleration derivatives with respect to specified parameters

Throws:

OrekitException - if derivatives cannot be computed

getMu

public double getMu()

Get the central attraction coefficient &mu..

Specified by:

getMu in interface AttractionModel

Returns:

mu central attraction coefficient (m³/s²)