org.orekit.propagation.analytical

Class EcksteinHechlerPropagator

java.lang.Object

org.orekit.propagation.AbstractPropagator

org.orekit.propagation.analytical.AbstractAnalyticalPropagator

org.orekit.propagation.analytical.EcksteinHechlerPropagator

All Implemented Interfaces:

Propagator, PVCoordinatesProvider

public class EcksteinHechlerPropagator
extends AbstractAnalyticalPropagator

This class propagates a SpacecraftState using the analytical Eckstein-Hechler model.

The Eckstein-Hechler model is suited for near circular orbits (e < 0.1, with poor accuracy between 0.005 and 0.1) and inclination neither equatorial (direct or retrograde) nor critical (direct or retrograde).

Note that before version 7.0, there was a large inconsistency in the generated orbits, and it was fixed as of version 7.0 of Orekit, with a visible side effect. The problems is that if the circular parameters produced by the Eckstein-Hechler model are used to build an orbit considered to be osculating, the velocity deduced from this orbit was inconsistent with the position evolution! The reason is that the model includes non-Keplerian effects but it does not include a corresponding circular/Cartesian conversion. As a consequence, all subsequent computation involving velocity were wrong. This includes attitude modes like yaw compensation and Doppler effect. As this effect was considered serious enough and as accurate velocities were considered important, the propagator now generates Cartesian orbits which are built in a special way to ensure consistency throughout propagation. A side effect is that if circular parameters are rebuilt by user from these propagated Cartesian orbit, the circular parameters will generally not match the initial orbit (differences in semi-major axis can exceed 120 m). The position however will match to sub-micrometer level, and this position will be identical to the positions that were generated by previous versions (in other words, the internals of the models have not been changed, only the output parameters have been changed). The correctness of the initialization has been assessed and is good, as it allows the subsequent orbit to remain close to a numerical reference orbit.

If users need a more definitive initialization of an Eckstein-Hechler propagator, they should consider using a propagator converter to initialize their Eckstein-Hechler propagator using a complete sample instead of just a single initial orbit.

Author:

Guylaine Prat

See Also:

Orbit

Field Summary

Fields inherited from interface org.orekit.propagation.Propagator

DEFAULT_LAW, DEFAULT_MASS, EPHEMERIS_GENERATION_MODE, MASTER_MODE, SLAVE_MODE

Constructor Summary

Constructors

Constructor and Description
EcksteinHechlerPropagator(Orbit initialOrbit, AttitudeProvider attitudeProv, double referenceRadius, double mu, double c20, double c30, double c40, double c50, double c60) Build a propagator from orbit, attitude provider and potential.
EcksteinHechlerPropagator(Orbit initialOrbit, AttitudeProvider attitudeProv, double mass, double referenceRadius, double mu, double c20, double c30, double c40, double c50, double c60) Build a propagator from orbit, attitude provider, mass and potential.
EcksteinHechlerPropagator(Orbit initialOrbit, AttitudeProvider attitudeProv, double mass, UnnormalizedSphericalHarmonicsProvider provider) Build a propagator from orbit, attitude provider, mass and potential provider.
EcksteinHechlerPropagator(Orbit initialOrbit, AttitudeProvider attitude, double mass, UnnormalizedSphericalHarmonicsProvider provider, UnnormalizedSphericalHarmonicsProvider.UnnormalizedSphericalHarmonics harmonics) Private helper constructor.
EcksteinHechlerPropagator(Orbit initialOrbit, AttitudeProvider attitudeProv, UnnormalizedSphericalHarmonicsProvider provider) Build a propagator from orbit, attitude provider and potential provider.
EcksteinHechlerPropagator(Orbit initialOrbit, double referenceRadius, double mu, double c20, double c30, double c40, double c50, double c60) Build a propagator from orbit and potential.
EcksteinHechlerPropagator(Orbit initialOrbit, double mass, double referenceRadius, double mu, double c20, double c30, double c40, double c50, double c60) Build a propagator from orbit, mass and potential.
EcksteinHechlerPropagator(Orbit initialOrbit, double mass, UnnormalizedSphericalHarmonicsProvider provider) Build a propagator from orbit, mass and potential provider.
EcksteinHechlerPropagator(Orbit initialOrbit, UnnormalizedSphericalHarmonicsProvider provider) Build a propagator from orbit and potential provider.

Method Summary

Modifier and Type	Method and Description
protected double	getMass(AbsoluteDate date) Get the mass.
CartesianOrbit	propagateOrbit(AbsoluteDate date) Extrapolate an orbit up to a specific target date.
void	resetInitialState(SpacecraftState state) Reset the propagator initial state.
protected void	resetIntermediateState(SpacecraftState state, boolean forward) Reset an intermediate state.

Methods inherited from class org.orekit.propagation.analytical.AbstractAnalyticalPropagator

acceptStep, addEventDetector, basicPropagate, clearEventsDetectors, getEventsDetectors, getGeneratedEphemeris, getPvProvider, propagate

Methods inherited from class org.orekit.propagation.AbstractPropagator

addAdditionalStateProvider, getAdditionalStateProviders, getAttitudeProvider, getFixedStepSize, getFrame, getInitialState, getManagedAdditionalStates, getMode, getPVCoordinates, getStartDate, getStepHandler, isAdditionalStateManaged, propagate, setAttitudeProvider, setEphemerisMode, setEphemerisMode, setMasterMode, setMasterMode, setSlaveMode, setStartDate, updateAdditionalStates

Methods inherited from class java.lang.Object

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

Constructor Detail

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 UnnormalizedSphericalHarmonicsProvider provider)

Build a propagator from orbit and potential provider.

Mass and attitude provider are set to unspecified non-null arbitrary values.

Parameters:

initialOrbit - initial orbit

provider - for un-normalized zonal coefficients

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 AttitudeProvider attitude,
                                 double mass,
                                 UnnormalizedSphericalHarmonicsProvider provider,
                                 UnnormalizedSphericalHarmonicsProvider.UnnormalizedSphericalHarmonics harmonics)

Private helper constructor.

Parameters:

initialOrbit - initial orbit

attitude - attitude provider

mass - spacecraft mass

provider - for un-normalized zonal coefficients

harmonics - provider.onDate(initialOrbit.getDate())

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 double referenceRadius,
                                 double mu,
                                 double c20,
                                 double c30,
                                 double c40,
                                 double c50,
                                 double c60)

Build a propagator from orbit and potential.

Mass and attitude provider are set to unspecified non-null arbitrary values.

The C_n,0 coefficients are the denormalized zonal coefficients, they are related to both the normalized coefficients C_n,0 and the J_n one as follows:

C_n,0 = [(2-δ_0,m)(2n+1)(n-m)!/(n+m)!]^½ C_n,0

C_n,0 = -J_n

Parameters:

initialOrbit - initial orbit

referenceRadius - reference radius of the Earth for the potential model (m)

mu - central attraction coefficient (m³/s²)

c20 - un-normalized zonal coefficient (about -1.08e-3 for Earth)

c30 - un-normalized zonal coefficient (about +2.53e-6 for Earth)

c40 - un-normalized zonal coefficient (about +1.62e-6 for Earth)

c50 - un-normalized zonal coefficient (about +2.28e-7 for Earth)

c60 - un-normalized zonal coefficient (about -5.41e-7 for Earth)

See Also:

Constants

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 double mass,
                                 UnnormalizedSphericalHarmonicsProvider provider)

Build a propagator from orbit, mass and potential provider.

Attitude law is set to an unspecified non-null arbitrary value.

Parameters:

initialOrbit - initial orbit

mass - spacecraft mass

provider - for un-normalized zonal coefficients

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 double mass,
                                 double referenceRadius,
                                 double mu,
                                 double c20,
                                 double c30,
                                 double c40,
                                 double c50,
                                 double c60)

Build a propagator from orbit, mass and potential.

Attitude law is set to an unspecified non-null arbitrary value.

The C_n,0 coefficients are the denormalized zonal coefficients, they are related to both the normalized coefficients C_n,0 and the J_n one as follows:

C_n,0 = [(2-δ_0,m)(2n+1)(n-m)!/(n+m)!]^½ C_n,0

C_n,0 = -J_n

Parameters:

initialOrbit - initial orbit

mass - spacecraft mass

referenceRadius - reference radius of the Earth for the potential model (m)

mu - central attraction coefficient (m³/s²)

c20 - un-normalized zonal coefficient (about -1.08e-3 for Earth)

c30 - un-normalized zonal coefficient (about +2.53e-6 for Earth)

c40 - un-normalized zonal coefficient (about +1.62e-6 for Earth)

c50 - un-normalized zonal coefficient (about +2.28e-7 for Earth)

c60 - un-normalized zonal coefficient (about -5.41e-7 for Earth)

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 AttitudeProvider attitudeProv,
                                 UnnormalizedSphericalHarmonicsProvider provider)

Build a propagator from orbit, attitude provider and potential provider.

Mass is set to an unspecified non-null arbitrary value.

Parameters:

initialOrbit - initial orbit

attitudeProv - attitude provider

provider - for un-normalized zonal coefficients

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 AttitudeProvider attitudeProv,
                                 double referenceRadius,
                                 double mu,
                                 double c20,
                                 double c30,
                                 double c40,
                                 double c50,
                                 double c60)

Build a propagator from orbit, attitude provider and potential.

Mass is set to an unspecified non-null arbitrary value.

The C_n,0 coefficients are the denormalized zonal coefficients, they are related to both the normalized coefficients C_n,0 and the J_n one as follows:

C_n,0 = [(2-δ_0,m)(2n+1)(n-m)!/(n+m)!]^½ C_n,0

C_n,0 = -J_n

Parameters:

initialOrbit - initial orbit

attitudeProv - attitude provider

referenceRadius - reference radius of the Earth for the potential model (m)

mu - central attraction coefficient (m³/s²)

c20 - un-normalized zonal coefficient (about -1.08e-3 for Earth)

c30 - un-normalized zonal coefficient (about +2.53e-6 for Earth)

c40 - un-normalized zonal coefficient (about +1.62e-6 for Earth)

c50 - un-normalized zonal coefficient (about +2.28e-7 for Earth)

c60 - un-normalized zonal coefficient (about -5.41e-7 for Earth)

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 AttitudeProvider attitudeProv,
                                 double mass,
                                 UnnormalizedSphericalHarmonicsProvider provider)

Build a propagator from orbit, attitude provider, mass and potential provider.

Parameters:

initialOrbit - initial orbit

attitudeProv - attitude provider

mass - spacecraft mass

provider - for un-normalized zonal coefficients

EcksteinHechlerPropagator

public EcksteinHechlerPropagator(Orbit initialOrbit,
                                 AttitudeProvider attitudeProv,
                                 double mass,
                                 double referenceRadius,
                                 double mu,
                                 double c20,
                                 double c30,
                                 double c40,
                                 double c50,
                                 double c60)

Build a propagator from orbit, attitude provider, mass and potential.

The C_n,0 coefficients are the denormalized zonal coefficients, they are related to both the normalized coefficients C_n,0 and the J_n one as follows:

C_n,0 = [(2-δ_0,m)(2n+1)(n-m)!/(n+m)!]^½ C_n,0

C_n,0 = -J_n

Parameters:

initialOrbit - initial orbit

attitudeProv - attitude provider

mass - spacecraft mass

referenceRadius - reference radius of the Earth for the potential model (m)

mu - central attraction coefficient (m³/s²)

c20 - un-normalized zonal coefficient (about -1.08e-3 for Earth)

c30 - un-normalized zonal coefficient (about +2.53e-6 for Earth)

c40 - un-normalized zonal coefficient (about +1.62e-6 for Earth)

c50 - un-normalized zonal coefficient (about +2.28e-7 for Earth)

c60 - un-normalized zonal coefficient (about -5.41e-7 for Earth)

Method Detail

resetInitialState

public void resetInitialState(SpacecraftState state)

Reset the propagator initial state.

Specified by:

resetInitialState in interface Propagator

Overrides:

resetInitialState in class AbstractPropagator

Parameters:

state - new initial state to consider

resetIntermediateState

protected void resetIntermediateState(SpacecraftState state,
                                      boolean forward)

Reset an intermediate state.

Specified by:

resetIntermediateState in class AbstractAnalyticalPropagator

Parameters:

state - new intermediate state to consider

forward - if true, the intermediate state is valid for propagations after itself

propagateOrbit

public CartesianOrbit propagateOrbit(AbsoluteDate date)

Extrapolate an orbit up to a specific target date.

Specified by:

propagateOrbit in class AbstractAnalyticalPropagator

Parameters:

date - target date for the orbit

Returns:

extrapolated parameters

getMass

protected double getMass(AbsoluteDate date)

Get the mass.

Specified by:

getMass in class AbstractAnalyticalPropagator

Parameters:

date - target date for the orbit

Returns:

mass mass