Package org.orekit.propagation.analytical.tle

Class TLEPropagator

java.lang.Object

org.orekit.propagation.AbstractPropagator

org.orekit.propagation.analytical.AbstractAnalyticalPropagator

org.orekit.propagation.analytical.tle.TLEPropagator

All Implemented Interfaces:

Propagator, PVCoordinatesProvider

Direct Known Subclasses:

DeepSDP4, SGP4

public abstract class TLEPropagator
extends AbstractAnalyticalPropagator

This class provides elements to propagate TLE's.

The models used are SGP4 and SDP4, initially proposed by NORAD as the unique convenient propagator for TLE's. Inputs and outputs of this propagator are only suited for NORAD two lines elements sets, since it uses estimations and mean values appropriate for TLE's only.

Deep- or near- space propagator is selected internally according to NORAD recommendations so that the user has not to worry about the used computation methods. One instance is created for each TLE (this instance can only be get using selectExtrapolator(TLE) method, and can compute position and velocity coordinates at any time. Maximum accuracy is guaranteed in a 24h range period before and after the provided TLE epoch (of course this accuracy is not really measurable nor predictable: according to CelesTrak, the precision is close to one kilometer and error won't probably rise above 2 km).

This implementation is largely inspired from the paper and source code Revisiting Spacetrack Report #3 and is fully compliant with its results and tests cases.

Author:

Felix R. Hoots, Ronald L. Roehrich, December 1980 (original fortran), David A. Vallado, Paul Crawford, Richard Hujsak, T.S. Kelso (C++ translation and improvements), Fabien Maussion (java translation)

See Also:

TLE

Field Summary

Fields

Modifier and Type	Field	Description
protected double	a	final semi major axis.
protected double	a0dp	original recovered semi major axis.
protected double	beta0	sqrt (1 - e2).
protected double	beta02	1 - e2.
protected double	c1	C1 from SPTRCK #3.
protected double	c2	C2 from SPTRCK #3.
protected double	c4	C4 from SPTRCK #3.
protected double	coef	coef for SGP C3 computation.
protected double	coef1	coef for SGP C5 computation.
protected double	cosi0	cosinus original inclination.
protected double	e	final eccentricity.
protected double	e0sq	original eccentricity squared.
protected double	eeta	original eccentricity * eta.
protected double	eta	eta from SPTRCK #3.
protected double	etasq	eta squared.
protected double	i	final inclination.
protected double	omega	final perigee argument.
protected double	omgdot	common parameter for perigee argument (omega) computation.
protected double	perige	perigee, expressed in KM and ALTITUDE.
protected double	s4	s* new value for the contant s.
protected double	sini0	sinus original inclination.
protected double	t2cof	3/2 * C1.
protected double	theta2	cos io squared.
protected TLE	tle	Initial state.
protected double	tsi	tsi from SPTRCK #3.
protected TimeScale	utc	UTC time scale.
protected double	xl	L from SPTRCK #3.
protected double	xmdot	common parameter for mean anomaly (M) computation.
protected double	xn0dp	original recovered mean motion.
protected double	xnodcf	common parameter for raan (OMEGA) computation.
protected double	xnode	final RAAN.
protected double	xnodot	common parameter for raan (OMEGA) computation.

Fields inherited from interface org.orekit.propagation.Propagator

DEFAULT_MASS

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	TLEPropagator(TLE initialTLE, AttitudeProvider attitudeProvider, double mass)	Protected constructor for derived classes.
protected	TLEPropagator(TLE initialTLE, AttitudeProvider attitudeProvider, double mass, Frame teme)	Protected constructor for derived classes.

Method Summary

Modifier and Type	Method	Description
protected AbstractMatricesHarvester	createHarvester(String stmName, RealMatrix initialStm, DoubleArrayDictionary initialJacobianColumns)	Create the harvester suitable for propagator.
static TleGenerationAlgorithm	getDefaultTleGenerationAlgorithm(TimeScale utc, Frame teme)	Get the default TLE generation algorithm.
Frame	getFrame()	Get the frame in which the orbit is propagated.
protected List<String>	getJacobiansColumnsNames()	Get the names of the parameters in the matrix returned by MatricesHarvester.getParametersJacobian(org.orekit.propagation.SpacecraftState).
protected double	getMass(AbsoluteDate date)	Get the mass.
static double	getMU()	Get the Earth gravity coefficient used for TLE propagation.
PVCoordinates	getPVCoordinates(AbsoluteDate date)	Get the extrapolated position and velocity from an initial TLE.
TLE	getTLE()	Get the underlying TLE.
protected Orbit	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.
static TLEPropagator	selectExtrapolator(TLE tle)	Selects the extrapolator to use with the selected TLE.
static TLEPropagator	selectExtrapolator(TLE tle, AttitudeProvider attitudeProvider, double mass)	Selects the extrapolator to use with the selected TLE.
static TLEPropagator	selectExtrapolator(TLE tle, AttitudeProvider attitudeProvider, double mass, Frame teme)	Selects the extrapolator to use with the selected TLE.
static TLEPropagator	selectExtrapolator(TLE tle, Frame teme)	Selects the extrapolator to use with the selected TLE.
static TLEPropagator	selectExtrapolator(TLE tle, Frame teme, AttitudeProvider attitudeProvider)	Selects the extrapolator to use with the selected TLE.
protected abstract void	sxpInitialize()	Initialization proper to each propagator (SGP or SDP).
protected abstract void	sxpPropagate(double t)	Propagation proper to each propagator (SGP or SDP).

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

acceptStep, addEventDetector, basicPropagate, clearEventsDetectors, getEphemerisGenerator, getEventDetectors, getPvProvider, propagate

Methods inherited from class org.orekit.propagation.AbstractPropagator

addAdditionalStateProvider, getAdditionalStateProviders, getAttitudeProvider, getHarvester, getInitialState, getManagedAdditionalStates, getMultiplexer, getStartDate, initializeAdditionalStates, initializePropagation, isAdditionalStateManaged, propagate, setAttitudeProvider, setStartDate, setupMatricesComputation, stateChanged, updateAdditionalStates, updateUnmanagedStates

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.Propagator

clearStepHandlers, getPosition, getPVCoordinates, setStepHandler, setStepHandler

Field Detail

tle

protected TLE tle

Initial state.

utc

protected final TimeScale utc

UTC time scale.

xnode

protected double xnode

final RAAN.

a

protected double a

final semi major axis.

e

protected double e

final eccentricity.

i

protected double i

final inclination.

omega

protected double omega

final perigee argument.

xl

protected double xl

L from SPTRCK #3.

a0dp

protected double a0dp

original recovered semi major axis.

xn0dp

protected double xn0dp

original recovered mean motion.

cosi0

protected double cosi0

cosinus original inclination.

theta2

protected double theta2

cos io squared.

sini0

protected double sini0

sinus original inclination.

xmdot

protected double xmdot

common parameter for mean anomaly (M) computation.

omgdot

protected double omgdot

common parameter for perigee argument (omega) computation.

xnodot

protected double xnodot

common parameter for raan (OMEGA) computation.

e0sq

protected double e0sq

original eccentricity squared.

beta02

protected double beta02

1 - e2.

beta0

protected double beta0

sqrt (1 - e2).

perige

protected double perige

perigee, expressed in KM and ALTITUDE.

etasq

protected double etasq

eta squared.

eeta

protected double eeta

original eccentricity * eta.

s4

protected double s4

s* new value for the contant s.

tsi

protected double tsi

tsi from SPTRCK #3.

eta

protected double eta

eta from SPTRCK #3.

coef

protected double coef

coef for SGP C3 computation.

coef1

protected double coef1

coef for SGP C5 computation.

c1

protected double c1

C1 from SPTRCK #3.

c2

protected double c2

C2 from SPTRCK #3.

c4

protected double c4

C4 from SPTRCK #3.

xnodcf

protected double xnodcf

common parameter for raan (OMEGA) computation.

t2cof

protected double t2cof

3/2 * C1.

Constructor Detail

TLEPropagator

@DefaultDataContext
protected TLEPropagator(TLE initialTLE,
                        AttitudeProvider attitudeProvider,
                        double mass)

Protected constructor for derived classes.

This constructor uses the default data context.

Parameters:

initialTLE - the unique TLE to propagate

attitudeProvider - provider for attitude computation

mass - spacecraft mass (kg)

See Also:

TLEPropagator(TLE, AttitudeProvider, double, Frame)

TLEPropagator

protected TLEPropagator(TLE initialTLE,
                        AttitudeProvider attitudeProvider,
                        double mass,
                        Frame teme)

Protected constructor for derived classes.

Parameters:

initialTLE - the unique TLE to propagate

attitudeProvider - provider for attitude computation

mass - spacecraft mass (kg)

teme - the TEME frame to use for propagation.

Since:

10.1

Method Detail

selectExtrapolator

@DefaultDataContext
public static TLEPropagator selectExtrapolator(TLE tle)

Selects the extrapolator to use with the selected TLE.

This method uses the default data context.

Parameters:

tle - the TLE to propagate.

Returns:

the correct propagator.

See Also:

selectExtrapolator(TLE, Frame)

selectExtrapolator

public static TLEPropagator selectExtrapolator(TLE tle,
                                               Frame teme)

Selects the extrapolator to use with the selected TLE.

Parameters:

tle - the TLE to propagate.

teme - TEME frame.

Returns:

the correct propagator.

Since:

10.1

See Also:

selectExtrapolator(TLE, Frame, AttitudeProvider)

selectExtrapolator

public static TLEPropagator selectExtrapolator(TLE tle,
                                               Frame teme,
                                               AttitudeProvider attitudeProvider)

Selects the extrapolator to use with the selected TLE.

Parameters:

tle - the TLE to propagate.

teme - TEME frame.

attitudeProvider - provider for attitude computation

Returns:

the correct propagator.

Since:

12.2

selectExtrapolator

@DefaultDataContext
public static TLEPropagator selectExtrapolator(TLE tle,
                                               AttitudeProvider attitudeProvider,
                                               double mass)

Selects the extrapolator to use with the selected TLE.

This method uses the default data context.

Parameters:

tle - the TLE to propagate.

attitudeProvider - provider for attitude computation

mass - spacecraft mass (kg)

Returns:

the correct propagator.

See Also:

selectExtrapolator(TLE, AttitudeProvider, double, Frame)

selectExtrapolator

public static TLEPropagator selectExtrapolator(TLE tle,
                                               AttitudeProvider attitudeProvider,
                                               double mass,
                                               Frame teme)

Selects the extrapolator to use with the selected TLE.

Parameters:

tle - the TLE to propagate.

attitudeProvider - provider for attitude computation

mass - spacecraft mass (kg)

teme - the TEME frame to use for propagation.

Returns:

the correct propagator.

Since:

10.1

getMU

public static double getMU()

Get the Earth gravity coefficient used for TLE propagation.

Returns:

the Earth gravity coefficient.

getPVCoordinates

public PVCoordinates getPVCoordinates(AbsoluteDate date)

Get the extrapolated position and velocity from an initial TLE.

Parameters:

date - the final date

Returns:

the final PVCoordinates

sxpInitialize

protected abstract void sxpInitialize()

Initialization proper to each propagator (SGP or SDP).

sxpPropagate

protected abstract void sxpPropagate(double t)

Propagation proper to each propagator (SGP or SDP).

Parameters:

t - the offset from initial epoch (min)

resetInitialState

public void resetInitialState(SpacecraftState state)

Reset the propagator initial state.

For TLE propagator, calling this method is only recommended for covariance propagation when the new state differs from the previous one by only adding the additional state containing the derivatives.

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

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

propagateOrbit

protected Orbit 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

getTLE

public TLE getTLE()

Get the underlying TLE. If there has been calls to #resetInitialState or #resetIntermediateState, it will not be the same as given to the constructor.

Returns:

underlying TLE

getFrame

public Frame getFrame()

Get the frame in which the orbit is propagated.

The propagation frame is the definition frame of the initial state, so this method should be called after this state has been set, otherwise it may return null.

Specified by:

getFrame in interface Propagator

Overrides:

getFrame in class AbstractPropagator

Returns:

frame in which the orbit is propagated

See Also:

Propagator.resetInitialState(SpacecraftState)

createHarvester

protected AbstractMatricesHarvester createHarvester(String stmName,
                                                    RealMatrix initialStm,
                                                    DoubleArrayDictionary initialJacobianColumns)

Create the harvester suitable for propagator.

Overrides:

createHarvester in class AbstractPropagator

Parameters:

stmName - State Transition Matrix state name

initialStm - initial State Transition Matrix ∂Y/∂Y₀, if null (which is the most frequent case), assumed to be 6x6 identity

initialJacobianColumns - initial columns of the Jacobians matrix with respect to parameters, if null or if some selected parameters are missing from the dictionary, the corresponding initial column is assumed to be 0

Returns:

harvester to retrieve computed matrices during and after propagation

getJacobiansColumnsNames

protected List<String> getJacobiansColumnsNames()

Get the names of the parameters in the matrix returned by MatricesHarvester.getParametersJacobian(org.orekit.propagation.SpacecraftState).

Overrides:

getJacobiansColumnsNames in class AbstractAnalyticalPropagator

Returns:

names of the parameters (i.e. columns) of the Jacobian matrix

getDefaultTleGenerationAlgorithm

public static TleGenerationAlgorithm getDefaultTleGenerationAlgorithm(TimeScale utc,
                                                                      Frame teme)

Get the default TLE generation algorithm.

Parameters:

utc - UTC time scale

teme - TEME frame

Returns:

a TLE generation algorithm

Since:

12.0