org.orekit.attitudes

Class YawSteering

java.lang.Object

org.orekit.attitudes.GroundPointing

org.orekit.attitudes.YawSteering

All Implemented Interfaces:

AttitudeProvider, AttitudeProviderModifier

public class YawSteering
extends GroundPointing
implements AttitudeProviderModifier

This class handles yaw steering law.

Yaw steering is mainly used for low Earth orbiting satellites with no missions-related constraints on yaw angle. It sets the yaw angle in such a way the solar arrays have maximal lighting without changing the roll and pitch.

The motion in yaw is smooth when the Sun is far from the orbital plane, but gets more and more square like as the Sun gets closer to the orbital plane. The degenerate extreme case with the Sun in the orbital plane leads to a yaw angle switching between two steady states, with instantaneaous π radians rotations at each switch, two times per orbit. This degenerate case is clearly not operationally sound so another pointing mode is chosen when Sun comes closer than some predefined threshold to the orbital plane.

This class can handle (for now) only a theoretically perfect yaw steering (i.e. the yaw angle is exactly the optimal angle). Smoothed yaw steering with a few sine waves approaching the optimal angle will be added in the future if needed.

This attitude is implemented as a wrapper on top of an underlying ground pointing law that defines the roll and pitch angles.

Instances of this class are guaranteed to be immutable.

Author:

Luc Maisonobe

See Also:

GroundPointing

Constructor Summary

Constructors

Constructor and Description
YawSteering(Frame inertialFrame, GroundPointing groundPointingLaw, PVCoordinatesProvider sun, Vector3D phasingAxis) Creates a new instance.

Method Summary

Modifier and Type	Method and Description
<T extends RealFieldElement<T>> FieldAttitude<T>	getAttitude(FieldPVCoordinatesProvider<T> pvProv, FieldAbsoluteDate<T> date, Frame frame) Compute the attitude corresponding to an orbital state.
Attitude	getAttitude(PVCoordinatesProvider pvProv, AbsoluteDate date, Frame frame) Compute the attitude corresponding to an orbital state.
<T extends RealFieldElement<T>> FieldAttitude<T>	getBaseState(FieldPVCoordinatesProvider<T> pvProv, FieldAbsoluteDate<T> date, Frame frame) Compute the base system state at given date, without compensation.
Attitude	getBaseState(PVCoordinatesProvider pvProv, AbsoluteDate date, Frame frame) Compute the base system state at given date, without compensation.
<T extends RealFieldElement<T>> TimeStampedFieldPVCoordinates<T>	getTargetPV(FieldPVCoordinatesProvider<T> pvProv, FieldAbsoluteDate<T> date, Frame frame) Compute the target point position/velocity in specified frame.
TimeStampedPVCoordinates	getTargetPV(PVCoordinatesProvider pvProv, AbsoluteDate date, Frame frame) Compute the target point position/velocity in specified frame.
AttitudeProvider	getUnderlyingAttitudeProvider() Get the underlying (ground pointing) attitude provider.

Methods inherited from class org.orekit.attitudes.GroundPointing

getBodyFrame

Methods inherited from class java.lang.Object

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

Constructor Detail

YawSteering

public YawSteering(Frame inertialFrame,
                   GroundPointing groundPointingLaw,
                   PVCoordinatesProvider sun,
                   Vector3D phasingAxis)

Creates a new instance.

Parameters:

inertialFrame - frame in which orbital velocities are computed

groundPointingLaw - ground pointing attitude provider without yaw compensation

sun - sun motion model

phasingAxis - satellite axis that must be roughly in Sun direction (if solar arrays rotation axis is Y, then this axis should be either +X or -X)

Since:

7.1

Method Detail

getUnderlyingAttitudeProvider

public AttitudeProvider getUnderlyingAttitudeProvider()

Get the underlying (ground pointing) attitude provider.

Specified by:

getUnderlyingAttitudeProvider in interface AttitudeProviderModifier

Returns:

underlying attitude provider, which in this case is a GroundPointing instance

getTargetPV

public TimeStampedPVCoordinates getTargetPV(PVCoordinatesProvider pvProv,
                                            AbsoluteDate date,
                                            Frame frame)

Compute the target point position/velocity in specified frame.

This method is public only to allow users to subclass this abstract class from other packages. It is not intended to be used directly.

Specified by:

getTargetPV in class GroundPointing

Parameters:

pvProv - provider for PV coordinates

date - date at which target point is requested

frame - frame in which observed ground point should be provided

Returns:

observed ground point position (element 0) and velocity (at index 1) in specified frame

getTargetPV

public <T extends RealFieldElement<T>> TimeStampedFieldPVCoordinates<T> getTargetPV(FieldPVCoordinatesProvider<T> pvProv,
                                                                                    FieldAbsoluteDate<T> date,
                                                                                    Frame frame)

Compute the target point position/velocity in specified frame.

Specified by:

getTargetPV in class GroundPointing

Type Parameters:

T - type of the fiels elements

Parameters:

pvProv - provider for PV coordinates

date - date at which target point is requested

frame - frame in which observed ground point should be provided

Returns:

observed ground point position (element 0) and velocity (at index 1) in specified frame

getBaseState

public Attitude getBaseState(PVCoordinatesProvider pvProv,
                             AbsoluteDate date,
                             Frame frame)

Compute the base system state at given date, without compensation.

Parameters:

pvProv - provider for PV coordinates

date - date at which state is requested

frame - reference frame from which attitude is computed

Returns:

satellite base attitude state, i.e without compensation.

getBaseState

public <T extends RealFieldElement<T>> FieldAttitude<T> getBaseState(FieldPVCoordinatesProvider<T> pvProv,
                                                                     FieldAbsoluteDate<T> date,
                                                                     Frame frame)

Compute the base system state at given date, without compensation.

Type Parameters:

T - type of the field elements

Parameters:

pvProv - provider for PV coordinates

date - date at which state is requested

frame - reference frame from which attitude is computed

Returns:

satellite base attitude state, i.e without compensation.

Since:

9.0

getAttitude

public Attitude getAttitude(PVCoordinatesProvider pvProv,
                            AbsoluteDate date,
                            Frame frame)

Compute the attitude corresponding to an orbital state.

Specified by:

getAttitude in interface AttitudeProvider

Overrides:

getAttitude in class GroundPointing

Parameters:

pvProv - local position-velocity provider around current date

date - current date

frame - reference frame from which attitude is computed

Returns:

attitude attitude on the specified date and position-velocity state

getAttitude

public <T extends RealFieldElement<T>> FieldAttitude<T> getAttitude(FieldPVCoordinatesProvider<T> pvProv,
                                                                    FieldAbsoluteDate<T> date,
                                                                    Frame frame)

Compute the attitude corresponding to an orbital state.

Specified by:

getAttitude in interface AttitudeProvider

Overrides:

getAttitude in class GroundPointing

Type Parameters:

T - type of the field elements

Parameters:

pvProv - local position-velocity provider around current date

date - current date

frame - reference frame from which attitude is computed

Returns:

attitude attitude on the specified date and position-velocity state