TLEPropagator (ORbit Extrapolation KIT 9.2 API)

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 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	Description
`protected`	`TLEPropagator(TLE initialTLE, AttitudeProvider attitudeProvider, double mass)`	Protected constructor for derived classes.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	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.
`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, 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

- Field Detail
  - tle
```
protected final TLE tle
```
    Initial state.
  - 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
```
protected TLEPropagator(TLE initialTLE,
                        AttitudeProvider attitudeProvider,
                        double mass)
                 throws OrekitException
```
    Protected constructor for derived classes.
    
    Parameters:
    
    initialTLE - the unique TLE to propagate
    
    attitudeProvider - provider for attitude computation
    
    mass - spacecraft mass (kg)
    
    Throws:
    
    OrekitException - if some specific error occurs
- Method Detail
  - selectExtrapolator
```
public static TLEPropagator selectExtrapolator(TLE tle)
                                        throws OrekitException
```
    Selects the extrapolator to use with the selected TLE.
    
    Parameters:
    
    tle - the TLE to propagate.
    
    Returns:
    
    the correct propagator.
    
    Throws:
    
    OrekitException - if the underlying model cannot be initialized
  - selectExtrapolator
```
public static TLEPropagator selectExtrapolator(TLE tle,
                                               AttitudeProvider attitudeProvider,
                                               double mass)
                                        throws OrekitException
```
    Selects the extrapolator to use with the selected TLE.
    
    Parameters:
    
    tle - the TLE to propagate.
    
    attitudeProvider - provider for attitude computation
    
    mass - spacecraft mass (kg)
    
    Returns:
    
    the correct propagator.
    
    Throws:
    
    OrekitException - if the underlying model cannot be initialized
  - 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)
                               throws OrekitException
```
    Get the extrapolated position and velocity from an initial TLE.
    
    Parameters:
    
    date - the final date
    
    Returns:
    
    the final PVCoordinates
    
    Throws:
    
    OrekitException - if propagation cannot be performed at given date
  - sxpInitialize
```
protected abstract void sxpInitialize()
                               throws OrekitException
```
    Initialization proper to each propagator (SGP or SDP).
    
    Throws:
    
    OrekitException - if some specific error occurs
  - sxpPropagate
```
protected abstract void sxpPropagate(double t)
                              throws OrekitException
```
    Propagation proper to each propagator (SGP or SDP).
    
    Parameters:
    
    t - the offset from initial epoch (min)
    
    Throws:
    
    OrekitException - if current state cannot be propagated
  - resetInitialState
```
public void resetInitialState(SpacecraftState state)
                       throws OrekitException
```
    Reset the propagator initial state.
    
    Specified by:
    
    resetInitialState in interface Propagator
    
    Overrides:
    
    resetInitialState in class AbstractPropagator
    
    Parameters:
    
    state - new initial state to consider
    
    Throws:
    
    OrekitException - if initial state cannot be reset
  - resetIntermediateState
```
protected void resetIntermediateState(SpacecraftState state,
                                      boolean forward)
                               throws OrekitException
```
    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
    
    Throws:
    
    OrekitException - if initial state cannot be reset
  - 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)
                        throws OrekitException
```
    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
    
    Throws:
    
    OrekitException - if some parameters are out of bounds
  - 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)

Class TLEPropagator

Field Summary

Fields inherited from interface org.orekit.propagation.Propagator

Constructor Summary

Method Summary

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

Methods inherited from class org.orekit.propagation.AbstractPropagator

Methods inherited from class java.lang.Object

Field Detail

tle

xnode

a

e

i

omega

xl

a0dp

xn0dp

cosi0

theta2

sini0

xmdot

omgdot

xnodot

e0sq

beta02

beta0

perige

etasq

eeta

s4

tsi

eta

coef

coef1

c1

c2

c4

xnodcf

t2cof

Constructor Detail

TLEPropagator

Method Detail

selectExtrapolator

selectExtrapolator

getMU

getPVCoordinates

sxpInitialize

sxpPropagate

resetInitialState

resetIntermediateState

getMass

propagateOrbit

getTLE

getFrame