org.orekit.forces.gravity

Class HolmesFeatherstoneAttractionModel

java.lang.Object

org.orekit.forces.AbstractForceModel

org.orekit.forces.gravity.HolmesFeatherstoneAttractionModel

All Implemented Interfaces:

ForceModel, TideSystemProvider

public class HolmesFeatherstoneAttractionModel
extends AbstractForceModel
implements TideSystemProvider

This class represents the gravitational field of a celestial body.

The algorithm implemented in this class has been designed by S. A. Holmes and W. E. Featherstone from Department of Spatial Sciences, Curtin University of Technology, Perth, Australia. It is described in their 2002 paper: A unified approach to he Clenshaw summation and the recursive computation of very high degree and order normalised associated Legendre functions (Journal of Geodesy (2002) 76: 279–299).

This model directly uses normalized coefficients and stable recursion algorithms so it is more suited to high degree gravity fields than the classical Cunningham Droziner models which use un-normalized coefficients.

Among the different algorithms presented in Holmes and Featherstone paper, this class implements the modified forward row method. All recursion coefficients are precomputed and stored for greater performance. This caching was suggested in the paper but not used due to the large memory requirements. Since 2002, even low end computers and mobile devices do have sufficient memory so this caching has become feasible nowadays.

Since:

6.0

Author:

Luc Maisonobe

Constructor Summary

Constructors

Constructor and Description
HolmesFeatherstoneAttractionModel(Frame centralBodyFrame, NormalizedSphericalHarmonicsProvider provider) Creates a new instance.

Method Summary

Modifier and Type	Method and Description
<T extends CalculusFieldElement<T>> FieldVector3D<T>	acceleration(FieldSpacecraftState<T> s, T[] parameters) Compute acceleration.
Vector3D	acceleration(SpacecraftState s, 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.
double	getMu() Get the central attraction coefficient μ.
List<ParameterDriver>	getParametersDrivers() Get the drivers for force model parameters.
TideSystem	getTideSystem() Get the TideSystem used in the gravity field.
double[]	gradient(AbsoluteDate date, Vector3D position, double mu) Compute the gradient of the non-central part of the gravity field.
<T extends CalculusFieldElement<T>> T[]	gradient(FieldAbsoluteDate<T> date, FieldVector3D<T> position, T mu) Compute the gradient of the non-central part of the gravity field.
double	nonCentralPart(AbsoluteDate date, Vector3D position, double mu) Compute the non-central part of the gravity field.
double	value(AbsoluteDate date, Vector3D position, double mu) Compute the value of the gravity field.

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, init

Constructor Detail

HolmesFeatherstoneAttractionModel

public HolmesFeatherstoneAttractionModel(Frame centralBodyFrame,
                                         NormalizedSphericalHarmonicsProvider provider)

Creates a new instance.

Parameters:

centralBodyFrame - rotating body frame

provider - provider for spherical harmonics

Since:

6.0

Method Detail

dependsOnPositionOnly

public boolean dependsOnPositionOnly()

Check if force models depends on position only.

Specified by:

dependsOnPositionOnly in interface ForceModel

Returns:

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

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

getMu

public double getMu()

Get the central attraction coefficient μ.

Returns:

mu central attraction coefficient (m³/s²)

value

public double value(AbsoluteDate date,
                    Vector3D position,
                    double mu)

Compute the value of the gravity field.

Parameters:

date - current date

position - position at which gravity field is desired in body frame

mu - central attraction coefficient to use

Returns:

value of the gravity field (central and non-central parts summed together)

nonCentralPart

public double nonCentralPart(AbsoluteDate date,
                             Vector3D position,
                             double mu)

Compute the non-central part of the gravity field.

Parameters:

date - current date

position - position at which gravity field is desired in body frame

mu - central attraction coefficient to use

Returns:

value of the non-central part of the gravity field

gradient

public double[] gradient(AbsoluteDate date,
                         Vector3D position,
                         double mu)

Compute the gradient of the non-central part of the gravity field.

Parameters:

date - current date

position - position at which gravity field is desired in body frame

mu - central attraction coefficient to use

Returns:

gradient of the non-central part of the gravity field

gradient

public <T extends CalculusFieldElement<T>> T[] gradient(FieldAbsoluteDate<T> date,
                                                        FieldVector3D<T> position,
                                                        T mu)

Compute the gradient of the non-central part of the gravity field.

Type Parameters:

T - type of field used

Parameters:

date - current date

position - position at which gravity field is desired in body frame

mu - central attraction coefficient to use

Returns:

gradient of the non-central part of the gravity field

acceleration

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

Compute acceleration.

Specified by:

acceleration in interface ForceModel

Parameters:

s - 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> s,
                                                                         T[] parameters)

Compute acceleration.

Specified by:

acceleration in interface ForceModel

Type Parameters:

T - type of the elements

Parameters:

s - 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.

Specified by:

getEventsDetectors in interface ForceModel

Returns:

stream of events detectors

getFieldEventsDetectors

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

Description copied from interface: ForceModel

Get the discrete events related to the model.

Specified by:

getFieldEventsDetectors in interface ForceModel

Type Parameters:

T - extends CalculusFieldElement<T>

Parameters:

field - field to which the state belongs

Returns:

stream of events detectors

getParametersDrivers

public List<ParameterDriver> getParametersDrivers()

Get the drivers for force model parameters.

Specified by:

getParametersDrivers in interface ForceModel

Returns:

drivers for force model parameters