org.orekit.forces.gravity

Class CunninghamAttractionModel

java.lang.Object

org.orekit.forces.AbstractForceModel

org.orekit.forces.gravity.CunninghamAttractionModel

All Implemented Interfaces:

ForceModel, TideSystemProvider

public class CunninghamAttractionModel
extends AbstractForceModel
implements TideSystemProvider

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).

Note that this class can often not be used for high degrees (say above 90) as most modern gravity fields are provided as normalized coefficients and the un-normalization process to convert these coefficients underflows at degree and order 89. This class also does not provide analytical partial derivatives (it uses finite differences to compute them) and is much slower than HolmesFeatherstoneAttractionModel (even when no derivatives are computed). For all these reasons, it is recommended to use the Holmes-Featherstone model rather than this class.

This class uses finite differences to compute derivatives and the steps for finite differences are initialized in the constructor.

Author:

Fabien Maussion, Luc Maisonobe, Véronique Pommier-Maurussane

See Also:

HolmesFeatherstoneAttractionModel

Constructor Summary

Constructors

Constructor and Description
CunninghamAttractionModel(Frame centralBodyFrame, UnnormalizedSphericalHarmonicsProvider provider, double hPosition) Creates a new instance.

Method Summary

Modifier and Type	Method and Description
FieldVector3D<DerivativeStructure>	accelerationDerivatives(AbsoluteDate date, Frame frame, FieldVector3D<DerivativeStructure> position, FieldVector3D<DerivativeStructure> velocity, FieldRotation<DerivativeStructure> rotation, DerivativeStructure mass) Compute acceleration derivatives with respect to state parameters.
FieldVector3D<DerivativeStructure>	accelerationDerivatives(SpacecraftState s, String paramName) Compute acceleration derivatives with respect to additional parameters.
void	addContribution(SpacecraftState s, TimeDerivativesEquations adder) Compute the contribution of the force model to the perturbing acceleration.
EventDetector[]	getEventsDetectors() Get the discrete events related to the model.
ParameterDriver[]	getParametersDrivers() Get the drivers for force model parameters.
TideSystem	getTideSystem() Get the TideSystem used in the gravity field.

Methods inherited from class org.orekit.forces.AbstractForceModel

complainIfNotSupported, getParameter, getParameterDriver, getParametersNames, isSupported, setParameter

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

init

Constructor Detail

CunninghamAttractionModel

public CunninghamAttractionModel(Frame centralBodyFrame,
                                 UnnormalizedSphericalHarmonicsProvider provider,
                                 double hPosition)

Creates a new instance.

Parameters:

centralBodyFrame - rotating body frame

provider - provider for spherical harmonics

hPosition - step used for finite difference computation

Since:

6.0

Method Detail

getTideSystem

public TideSystem getTideSystem()

Get the TideSystem used in the gravity field.

Specified by:

getTideSystem in interface TideSystemProvider

Returns:

tide system used in the gravity field

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

accelerationDerivatives

public FieldVector3D<DerivativeStructure> accelerationDerivatives(AbsoluteDate date,
                                                                  Frame frame,
                                                                  FieldVector3D<DerivativeStructure> position,
                                                                  FieldVector3D<DerivativeStructure> velocity,
                                                                  FieldRotation<DerivativeStructure> rotation,
                                                                  DerivativeStructure mass)
                                                           throws OrekitException

Compute acceleration derivatives with respect to state parameters.

The derivatives should be computed with respect to position, velocity and optionnaly mass. The input parameters already take into account the free parameters (6 or 7 depending on derivation with respect to mass being considered or not) and order (always 1). Free parameters at indices 0, 1 and 2 correspond to derivatives with respect to position. Free parameters at indices 3, 4 and 5 correspond to derivatives with respect to velocity. Free parameter at index 6 (if present) corresponds to to derivatives with respect to mass.

Specified by:

accelerationDerivatives in interface ForceModel

Parameters:

date - current date

frame - inertial reference frame for state (both orbit and attitude)

position - position of spacecraft in reference frame

velocity - velocity of spacecraft in reference frame

rotation - orientation (attitude) of the spacecraft with respect to reference frame

mass - spacecraft mass

Returns:

acceleration with all derivatives specified by the input parameters own derivatives

Throws:

OrekitException - if derivatives cannot be computed

accelerationDerivatives

public FieldVector3D<DerivativeStructure> accelerationDerivatives(SpacecraftState s,
                                                                  String paramName)
                                                           throws OrekitException

Compute acceleration derivatives with respect to additional parameters.

Specified by:

accelerationDerivatives in interface ForceModel

Parameters:

s - spacecraft state

paramName - name of the parameter with respect to which derivatives are required

Returns:

acceleration with all derivatives specified by the input parameters own derivatives

Throws:

OrekitException - if derivatives cannot be computed

getEventsDetectors

public 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

getParametersDrivers

public ParameterDriver[] getParametersDrivers()

Get the drivers for force model parameters.

Specified by:

getParametersDrivers in interface ForceModel

Returns:

drivers for force model parameters