Package org.orekit.forces.gravity

Class J2OnlyPerturbation

java.lang.Object

org.orekit.forces.gravity.J2OnlyPerturbation

All Implemented Interfaces:

ForceModel, EventDetectorsProvider, ParameterDriversProvider

public class J2OnlyPerturbation
extends Object
implements ForceModel

J2-only force model. This class models the oblateness part alone of the central body's potential (degree 2 and order 0), whilst avoiding the computational overhead of generic NxM spherical harmonics.

This J2 coefficient has same magnitude and opposite sign than the so-called unnormalized C20 coefficient.

This class should not be used in combination of HolmesFeatherstoneAttractionModel, otherwise the J2 term would be taken into account twice.

Author:

Romain Serra

Field Summary

Fields inherited from interface org.orekit.propagation.events.EventDetectorsProvider

DATATION_ACCURACY

Constructor Summary

Constructors

Constructor	Description
J2OnlyPerturbation(double mu, double rEq, double constantJ2, Frame frame)	Constructor with constant J2.
J2OnlyPerturbation(double mu, double rEq, TimeScalarFunction j2OverTime, Frame frame)	Constructor with TimeScalarFunction.
J2OnlyPerturbation(UnnormalizedSphericalHarmonicsProvider harmonicsProvider, Frame frame)	Constructor with spherical harmonics provider.

Method Summary

Modifier and Type	Method	Description
<T extends CalculusFieldElement<T>> FieldVector3D<T>	acceleration(FieldSpacecraftState<T> state, T[] parameters)	Compute acceleration.
Vector3D	acceleration(SpacecraftState state, double[] parameters)	Compute acceleration.
static <T extends CalculusFieldElement<T>> FieldVector3D<T>	computeAccelerationInJ2Frame(FieldVector3D<T> positionInJ2Frame, double mu, double rEq, T j2)	Compute acceleration in J2 frame.
static Vector3D	computeAccelerationInJ2Frame(Vector3D positionInJ2Frame, double mu, double rEq, double j2)	Compute acceleration in J2 frame.
boolean	dependsOnPositionOnly()	Check if force model depends on position only at a given, fixed date.
Frame	getFrame()	Getter for frame.
double	getJ2(AbsoluteDate date)	Return J2 at requested date.
<T extends CalculusFieldElement<T>> T	getJ2(FieldAbsoluteDate<T> date)	Return J2 at requested date (Field version).
double	getMu()	Getter for mu.
List<ParameterDriver>	getParametersDrivers()	Get the drivers for parameters.
double	getrEq()	Getter for equatorial radius.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.orekit.propagation.events.EventDetectorsProvider

getDateDetector, getEventDetectors, getFieldDateDetector, getFieldEventDetectors

Methods inherited from interface org.orekit.forces.ForceModel

addContribution, addContribution, dependsOnAttitudeRate, getEventDetectors, getFieldEventDetectors, init, init

Methods inherited from interface org.orekit.utils.ParameterDriversProvider

getNbParametersDriversValue, getParameterDriver, getParameters, getParameters, getParameters, getParameters, getParametersAllValues, getParametersAllValues, isSupported

Constructor Detail

J2OnlyPerturbation

public J2OnlyPerturbation(double mu,
                          double rEq,
                          TimeScalarFunction j2OverTime,
                          Frame frame)

Constructor with TimeScalarFunction. It is the user's responsibility to make sure the Field and double versions are consistent with each other.

Parameters:

mu - central body's gravitational constant

rEq - central body's equatorial radius

j2OverTime - J2 coefficient as a function of time.

frame - frame where J2 applies

J2OnlyPerturbation

public J2OnlyPerturbation(double mu,
                          double rEq,
                          double constantJ2,
                          Frame frame)

Constructor with constant J2.

Parameters:

mu - central body gravitational constant

rEq - central body's equatorial radius

constantJ2 - constant J2 coefficient

frame - frame where J2 applies

J2OnlyPerturbation

public J2OnlyPerturbation(UnnormalizedSphericalHarmonicsProvider harmonicsProvider,
                          Frame frame)

Constructor with spherical harmonics provider.

Parameters:

harmonicsProvider - spherical harmonics provider of unnormalized coefficients

frame - frame where J2 applies

Method Detail

getMu

public double getMu()

Getter for mu.

Returns:

mu

getrEq

public double getrEq()

Getter for equatorial radius.

Returns:

equatorial radius

getFrame

public Frame getFrame()

Getter for frame.

Returns:

frame

getJ2

public double getJ2(AbsoluteDate date)

Return J2 at requested date.

Parameters:

date - epoch at which J2 coefficient should be retrieved

Returns:

J2 coefficient

getJ2

public <T extends CalculusFieldElement<T>> T getJ2(FieldAbsoluteDate<T> date)

Return J2 at requested date (Field version).

Type Parameters:

T - field

Parameters:

date - epoch at which J2 coefficient should be retrieved

Returns:

J2 coefficient

dependsOnPositionOnly

public boolean dependsOnPositionOnly()

Check if force model depends on position only at a given, fixed date.

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

acceleration

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

Compute acceleration.

Specified by:

acceleration in interface ForceModel

Parameters:

state - current state information: date, kinematics, attitude

parameters - values of the force model parameters at state date, only 1 value for each parameterDriver

Returns:

acceleration in same frame as state

computeAccelerationInJ2Frame

public static Vector3D computeAccelerationInJ2Frame(Vector3D positionInJ2Frame,
                                                    double mu,
                                                    double rEq,
                                                    double j2)

Compute acceleration in J2 frame.

Parameters:

positionInJ2Frame - position in J2 frame@

mu - gravitational parameter

rEq - equatorial radius

j2 - J2 coefficient

Returns:

acceleration in J2 frame

acceleration

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

Compute acceleration.

Specified by:

acceleration in interface ForceModel

Type Parameters:

T - type of the elements

Parameters:

state - current state information: date, kinematics, attitude

parameters - values of the force model parameters at state date, only 1 value for each parameterDriver

Returns:

acceleration in same frame as state

computeAccelerationInJ2Frame

public static <T extends CalculusFieldElement<T>> FieldVector3D<T> computeAccelerationInJ2Frame(FieldVector3D<T> positionInJ2Frame,
                                                                                                double mu,
                                                                                                double rEq,
                                                                                                T j2)

Compute acceleration in J2 frame. Field version.

Type Parameters:

T - field type

Parameters:

positionInJ2Frame - position in J2 frame@

mu - gravitational parameter

rEq - equatorial radius

j2 - J2 coefficient

Returns:

acceleration in J2 frame

getParametersDrivers

public List<ParameterDriver> getParametersDrivers()

Get the drivers for parameters.

Specified by:

getParametersDrivers in interface ParameterDriversProvider

Returns:

drivers for parameters