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 and 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_LAW, DEFAULT_MASS, EPHEMERIS_GENERATION_MODE, MASTER_MODE, SLAVE_MODE

Constructor Summary

Constructors

Modifier	Constructor and 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 and Description
Frame	getFrame() Get the frame in which the orbit is propagated.
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, Frames frames) 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, getEventsDetectors, getGeneratedEphemeris, getPvProvider, propagate

Methods inherited from class org.orekit.propagation.AbstractPropagator

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

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

getDefaultLaw

Field Detail

tle

protected final 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, Frames)

selectExtrapolator

public static TLEPropagator selectExtrapolator(TLE tle,
                                               Frames frames)

Selects the extrapolator to use with the selected TLE.

Parameters:

tle - the TLE to propagate.

frames - set of Frames to use in the propagator.

Returns:

the correct propagator.

Since:

10.1

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.

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.

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)