org.orekit.propagation

Class SpacecraftState

java.lang.Object

org.orekit.propagation.SpacecraftState

All Implemented Interfaces:

Serializable, TimeInterpolable<SpacecraftState>, TimeShiftable<SpacecraftState>, TimeStamped

public class SpacecraftState
extends Object
implements TimeStamped, TimeShiftable<SpacecraftState>, TimeInterpolable<SpacecraftState>, Serializable

This class is the representation of a complete state holding orbit, attitude and mass information at a given date.

It contains an orbital state at a current AbsoluteDate both handled by an Orbit, plus the current mass and attitude. Orbit and state are guaranteed to be consistent in terms of date and reference frame. The spacecraft state may also contain additional states, which are simply named double arrays which can hold any user-defined data.

The state can be slightly shifted to close dates. This shift is based on a simple keplerian model for orbit, a linear extrapolation for attitude taking the spin rate into account and no mass change. It is not intended as a replacement for proper orbit and attitude propagation but should be sufficient for either small time shifts or coarse accuracy.

The instance SpacecraftState is guaranteed to be immutable.

Author:

Fabien Maussion, Véronique Pommier-Maurussane, Luc Maisonobe

See Also:

NumericalPropagator, Serialized Form

Constructor Summary

Constructors

Constructor and Description
SpacecraftState(Orbit orbit) Build a spacecraft state from orbit only.
SpacecraftState(Orbit orbit, Attitude attitude) Build a spacecraft state from orbit and attitude provider.
SpacecraftState(Orbit orbit, Attitude attitude, double mass) Build a spacecraft state from orbit, attitude provider and mass.
SpacecraftState(Orbit orbit, Attitude attitude, double mass, Map<String,double[]> additional) Build a spacecraft state from orbit, attitude provider and mass.
SpacecraftState(Orbit orbit, Attitude attitude, Map<String,double[]> additional) Build a spacecraft state from orbit and attitude provider.
SpacecraftState(Orbit orbit, double mass) Create a new instance from orbit and mass.
SpacecraftState(Orbit orbit, double mass, Map<String,double[]> additional) Create a new instance from orbit and mass.
SpacecraftState(Orbit orbit, Map<String,double[]> additional) Build a spacecraft state from orbit only.

Method Summary

Methods

Modifier and Type	Method and Description
SpacecraftState	addAdditionalState(String name, double... value) Add an additional state.
void	ensureCompatibleAdditionalStates(SpacecraftState state) Check if two instances have the same set of additional states available.
double	getA() Get the semi-major axis.
double[]	getAdditionalState(String name) Get an additional state.
Map<String,double[]>	getAdditionalStates() Get an unmodifiable map of additional states.
Attitude	getAttitude() Get the attitude.
AbsoluteDate	getDate() Get the date.
double	getE() Get the eccentricity.
double	getEquinoctialEx() Get the first component of the eccentricity vector (as per equinoctial parameters).
double	getEquinoctialEy() Get the second component of the eccentricity vector (as per equinoctial parameters).
Frame	getFrame() Get the inertial frame.
double	getHx() Get the first component of the inclination vector (as per equinoctial parameters).
double	getHy() Get the second component of the inclination vector (as per equinoctial parameters).
double	getI() Get the inclination.
double	getKeplerianMeanMotion() Get the keplerian mean motion.
double	getKeplerianPeriod() Get the keplerian period.
double	getLE() Get the eccentric latitude argument (as per equinoctial parameters).
double	getLM() Get the mean latitude argument (as per equinoctial parameters).
double	getLv() Get the true latitude argument (as per equinoctial parameters).
double	getMass() Gets the current mass.
double	getMu() Get the central attraction coefficient.
Orbit	getOrbit() Gets the current orbit.
TimeStampedPVCoordinates	getPVCoordinates() Get the TimeStampedPVCoordinates in orbit definition frame.
TimeStampedPVCoordinates	getPVCoordinates(Frame outputFrame) Get the TimeStampedPVCoordinates in given output frame.
boolean	hasAdditionalState(String name) Check if an additional state is available.
SpacecraftState	interpolate(AbsoluteDate date, Collection<SpacecraftState> sample) Get an interpolated instance.
SpacecraftState	shiftedBy(double dt) Get a time-shifted state.
Transform	toTransform() Compute the transform from orbite/attitude reference frame to spacecraft frame.

Methods inherited from class java.lang.Object

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

Constructor Detail

SpacecraftState

public SpacecraftState(Orbit orbit)
                throws OrekitException

Build a spacecraft state from orbit only.

Attitude and mass are set to unspecified non-null arbitrary values.

Parameters:

orbit - the orbit

Throws:

OrekitException - if default attitude cannot be computed

SpacecraftState

public SpacecraftState(Orbit orbit,
               Attitude attitude)
                throws IllegalArgumentException

Build a spacecraft state from orbit and attitude provider.

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

Parameters:

orbit - the orbit

attitude - attitude

Throws:

IllegalArgumentException - if orbit and attitude dates or frames are not equal

SpacecraftState

public SpacecraftState(Orbit orbit,
               double mass)
                throws OrekitException

Create a new instance from orbit and mass.

Attitude law is set to an unspecified default attitude.

Parameters:

orbit - the orbit

mass - the mass (kg)

Throws:

OrekitException - if default attitude cannot be computed

SpacecraftState

public SpacecraftState(Orbit orbit,
               Attitude attitude,
               double mass)
                throws IllegalArgumentException

Build a spacecraft state from orbit, attitude provider and mass.

Parameters:

orbit - the orbit

attitude - attitude

mass - the mass (kg)

Throws:

IllegalArgumentException - if orbit and attitude dates or frames are not equal

SpacecraftState

public SpacecraftState(Orbit orbit,
               Map<String,double[]> additional)
                throws OrekitException

Build a spacecraft state from orbit only.

Attitude and mass are set to unspecified non-null arbitrary values.

Parameters:

orbit - the orbit

additional - additional states

Throws:

OrekitException - if default attitude cannot be computed

SpacecraftState

public SpacecraftState(Orbit orbit,
               Attitude attitude,
               Map<String,double[]> additional)
                throws IllegalArgumentException

Build a spacecraft state from orbit and attitude provider.

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

Parameters:

orbit - the orbit

attitude - attitude

additional - additional states

Throws:

IllegalArgumentException - if orbit and attitude dates or frames are not equal

SpacecraftState

public SpacecraftState(Orbit orbit,
               double mass,
               Map<String,double[]> additional)
                throws OrekitException

Create a new instance from orbit and mass.

Attitude law is set to an unspecified default attitude.

Parameters:

orbit - the orbit

mass - the mass (kg)

additional - additional states

Throws:

OrekitException - if default attitude cannot be computed

SpacecraftState

public SpacecraftState(Orbit orbit,
               Attitude attitude,
               double mass,
               Map<String,double[]> additional)
                throws IllegalArgumentException

Build a spacecraft state from orbit, attitude provider and mass.

Parameters:

orbit - the orbit

attitude - attitude

mass - the mass (kg)

additional - additional states (may be null if no additional states are available)

Throws:

IllegalArgumentException - if orbit and attitude dates or frames are not equal

Method Detail

addAdditionalState

public SpacecraftState addAdditionalState(String name,
                                 double... value)

Add an additional state.

SpacecraftState instances are immutable, so this method does not change the instance, but rather creates a new instance, which has the same orbit, attitude, mass and additional states as the original instance, except it also has the specified state. If the original instance already had an additional state with the same name, it will be overridden. If it did not have any additional state with that name, the new instance will have one more additional state than the original instance.

Parameters:

name - name of the additional state

value - value of the additional state

Returns:

a new instance, with the additional state added

See Also:

hasAdditionalState(String), getAdditionalState(String), getAdditionalStates()

shiftedBy

public SpacecraftState shiftedBy(double dt)

Get a time-shifted state.

The state can be slightly shifted to close dates. This shift is based on a simple keplerian model for orbit, a linear extrapolation for attitude taking the spin rate into account and neither mass nor additional states changes. It is not intended as a replacement for proper orbit and attitude propagation but should be sufficient for small time shifts or coarse accuracy.

As a rough order of magnitude, the following table shows the interpolation errors obtained between this simple shift method and an Eckstein-Heschler propagator for an 800km altitude nearly circular polar Earth orbit with body center pointing. Beware that these results may be different for other orbits.

interpolation time (s)	position error (m)	velocity error (m/s)	attitude error (°)
60	20	1	0.001
120	100	2	0.002
300	600	4	0.005
600	2000	6	0.008
900	4000	6	0.010

Specified by:

shiftedBy in interface TimeShiftable<SpacecraftState>

Parameters:

dt - time shift in seconds

Returns:

a new state, shifted with respect to the instance (which is immutable) except for the mass which stay unchanged

interpolate

public SpacecraftState interpolate(AbsoluteDate date,
                          Collection<SpacecraftState> sample)
                            throws OrekitException

Get an interpolated instance.

Note that the state of the current instance may not be used in the interpolation process, only its type and non interpolable fields are used (for example central attraction coefficient or frame when interpolating orbits). The interpolable fields taken into account are taken only from the states of the sample points. So if the state of the instance must be used, the instance should be included in the sample points.

Note that this method is designed for small samples only (say up to about 10-20 points) so it can be implemented using polynomial interpolation (typically Hermite interpolation). Using too much points may induce Runge's phenomenon and numerical problems (including NaN appearing).

The additional states that are interpolated are the ones already present in the instance. The sample instances must therefore have at least the same additional states has the instance. They may have more additional states, but the extra ones will be ignored.

As this implementation of interpolation is polynomial, it should be used only with small samples (about 10-20 points) in order to avoid Runge's phenomenon and numerical problems (including NaN appearing).

Specified by:

interpolate in interface TimeInterpolable<SpacecraftState>

Parameters:

date - interpolation date

sample - sample points on which interpolation should be done

Returns:

a new instance, interpolated at specified date

Throws:

OrekitException - if interpolation cannot be performed

getOrbit

public Orbit getOrbit()

Gets the current orbit.

Returns:

the orbit

getDate

public AbsoluteDate getDate()

Get the date.

Specified by:

getDate in interface TimeStamped

Returns:

date

getFrame

public Frame getFrame()

Get the inertial frame.

Returns:

the frame

hasAdditionalState

public boolean hasAdditionalState(String name)

Check if an additional state is available.

Parameters:

name - name of the additional state

Returns:

true if the additional state is available

See Also:

addAdditionalState(String, double[]), getAdditionalState(String), getAdditionalStates()

ensureCompatibleAdditionalStates

public void ensureCompatibleAdditionalStates(SpacecraftState state)
                                      throws OrekitException,
                                             DimensionMismatchException

Check if two instances have the same set of additional states available.

Only the names and dimensions of the additional states are compared, not their values.

Parameters:

state - state to compare to instance

Throws:

OrekitException - if either instance or state supports an additional state not supported by the other one

DimensionMismatchException - if an additional state does not have the same dimension in both states

getAdditionalState

public double[] getAdditionalState(String name)
                            throws OrekitException

Get an additional state.

Parameters:

name - name of the additional state

Returns:

value of the additional state

Throws:

OrekitException - if no additional state with that name exists

See Also:

addAdditionalState(String, double[]), hasAdditionalState(String), getAdditionalStates()

getAdditionalStates

public Map<String,double[]> getAdditionalStates()

Get an unmodifiable map of additional states.

Returns:

unmodifiable map of additional states

See Also:

addAdditionalState(String, double[]), hasAdditionalState(String), getAdditionalState(String)

toTransform

public Transform toTransform()

Compute the transform from orbite/attitude reference frame to spacecraft frame.

The spacecraft frame origin is at the point defined by the orbit, and its orientation is defined by the attitude.

Returns:

transform from specified frame to current spacecraft frame

getMu

public double getMu()

Get the central attraction coefficient.

Returns:

mu central attraction coefficient (m^3/s^2)

getKeplerianPeriod

public double getKeplerianPeriod()

Get the keplerian period.

The keplerian period is computed directly from semi major axis and central acceleration constant.

Returns:

keplerian period in seconds

getKeplerianMeanMotion

public double getKeplerianMeanMotion()

Get the keplerian mean motion.

The keplerian mean motion is computed directly from semi major axis and central acceleration constant.

Returns:

keplerian mean motion in radians per second

getA

public double getA()

Get the semi-major axis.

Returns:

semi-major axis (m)

getEquinoctialEx

public double getEquinoctialEx()

Get the first component of the eccentricity vector (as per equinoctial parameters).

Returns:

e cos(ω + Ω), first component of eccentricity vector

See Also:

getE()

getEquinoctialEy

public double getEquinoctialEy()

Get the second component of the eccentricity vector (as per equinoctial parameters).

Returns:

e sin(ω + Ω), second component of the eccentricity vector

See Also:

getE()

getHx

public double getHx()

Get the first component of the inclination vector (as per equinoctial parameters).

Returns:

tan(i/2) cos(Ω), first component of the inclination vector

See Also:

getI()

getHy

public double getHy()

Get the second component of the inclination vector (as per equinoctial parameters).

Returns:

tan(i/2) sin(Ω), second component of the inclination vector

See Also:

getI()

getLv

public double getLv()

Get the true latitude argument (as per equinoctial parameters).

Returns:

v + ω + Ω true latitude argument (rad)

See Also:

getLE(), getLM()

getLE

public double getLE()

Get the eccentric latitude argument (as per equinoctial parameters).

Returns:

E + ω + Ω eccentric latitude argument (rad)

See Also:

getLv(), getLM()

getLM

public double getLM()

Get the mean latitude argument (as per equinoctial parameters).

Returns:

M + ω + Ω mean latitude argument (rad)

See Also:

getLv(), getLE()

getE

public double getE()

Get the eccentricity.

Returns:

eccentricity

See Also:

getEquinoctialEx(), getEquinoctialEy()

getI

public double getI()

Get the inclination.

Returns:

inclination (rad)

See Also:

getHx(), getHy()

getPVCoordinates

public TimeStampedPVCoordinates getPVCoordinates()

Get the TimeStampedPVCoordinates in orbit definition frame. Compute the position and velocity of the satellite. This method caches its results, and recompute them only when the method is called with a new value for mu. The result is provided as a reference to the internally cached TimeStampedPVCoordinates, so the caller is responsible to copy it in a separate TimeStampedPVCoordinates if it needs to keep the value for a while.

Returns:

pvCoordinates in orbit definition frame

getPVCoordinates

public TimeStampedPVCoordinates getPVCoordinates(Frame outputFrame)
                                          throws OrekitException

Get the TimeStampedPVCoordinates in given output frame. Compute the position and velocity of the satellite. This method caches its results, and recompute them only when the method is called with a new value for mu. The result is provided as a reference to the internally cached TimeStampedPVCoordinates, so the caller is responsible to copy it in a separate TimeStampedPVCoordinates if it needs to keep the value for a while.

Parameters:

outputFrame - frame in which coordinates should be defined

Returns:

pvCoordinates in orbit definition frame

Throws:

OrekitException - if the transformation between frames cannot be computed

getAttitude

public Attitude getAttitude()

Get the attitude.

Returns:

the attitude.

getMass

public double getMass()

Gets the current mass.

Returns:

the mass (kg)