YawSteering.java
/* Copyright 2002-2020 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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package org.orekit.attitudes;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldPVCoordinates;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedAngularCoordinates;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/**
* This class handles yaw steering law.
* <p>
* 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.
* </p>
* <p>
* The motion in yaw is smooth when the Sun is far from the orbital plane,
* but gets more and more <i>square like</i> 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.
* </p>
* <p>
* 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.
* </p>
* <p>
* This attitude is implemented as a wrapper on top of an underlying ground
* pointing law that defines the roll and pitch angles.
* </p>
* <p>
* Instances of this class are guaranteed to be immutable.
* </p>
* @see GroundPointing
* @author Luc Maisonobe
*/
public class YawSteering extends GroundPointing implements AttitudeProviderModifier {
/** Pointing axis. */
private static final PVCoordinates PLUS_Z =
new PVCoordinates(Vector3D.PLUS_K, Vector3D.ZERO, Vector3D.ZERO);
/** Underlying ground pointing attitude provider. */
private final GroundPointing groundPointingLaw;
/** Sun motion model. */
private final PVCoordinatesProvider sun;
/** Normal to the plane where the Sun must remain. */
private final PVCoordinates phasingNormal;
/** Creates a new instance.
* @param inertialFrame frame in which orbital velocities are computed
* @param groundPointingLaw ground pointing attitude provider without yaw compensation
* @param sun sun motion model
* @param 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
*/
public YawSteering(final Frame inertialFrame,
final GroundPointing groundPointingLaw,
final PVCoordinatesProvider sun,
final Vector3D phasingAxis) {
super(inertialFrame, groundPointingLaw.getBodyFrame());
this.groundPointingLaw = groundPointingLaw;
this.sun = sun;
this.phasingNormal = new PVCoordinates(Vector3D.crossProduct(Vector3D.PLUS_K, phasingAxis).normalize(),
Vector3D.ZERO,
Vector3D.ZERO);
}
/** Get the underlying (ground pointing) attitude provider.
* @return underlying attitude provider, which in this case is a {@link GroundPointing} instance
*/
public AttitudeProvider getUnderlyingAttitudeProvider() {
return groundPointingLaw;
}
/** {@inheritDoc} */
public TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame) {
return groundPointingLaw.getTargetPV(pvProv, date, frame);
}
/** {@inheritDoc} */
public <T extends RealFieldElement<T>> TimeStampedFieldPVCoordinates<T> getTargetPV(final FieldPVCoordinatesProvider<T> pvProv,
final FieldAbsoluteDate<T> date,
final Frame frame) {
return groundPointingLaw.getTargetPV(pvProv, date, frame);
}
/** Compute the base system state at given date, without compensation.
* @param pvProv provider for PV coordinates
* @param date date at which state is requested
* @param frame reference frame from which attitude is computed
* @return satellite base attitude state, i.e without compensation.
*/
public Attitude getBaseState(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame) {
return groundPointingLaw.getAttitude(pvProv, date, frame);
}
/** Compute the base system state at given date, without compensation.
* @param pvProv provider for PV coordinates
* @param date date at which state is requested
* @param frame reference frame from which attitude is computed
* @param <T> type of the field elements
* @return satellite base attitude state, i.e without compensation.
* @since 9.0
*/
public <T extends RealFieldElement<T>> FieldAttitude<T> getBaseState(final FieldPVCoordinatesProvider<T> pvProv,
final FieldAbsoluteDate<T> date, final Frame frame) {
return groundPointingLaw.getAttitude(pvProv, date, frame);
}
/** {@inheritDoc} */
@Override
public Attitude getAttitude(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame) {
// attitude from base attitude provider
final Attitude base = getBaseState(pvProv, date, frame);
// Compensation rotation definition :
// . Z satellite axis is unchanged
// . phasing axis shall be aligned to sun direction
final PVCoordinates sunDirection = new PVCoordinates(pvProv.getPVCoordinates(date, frame),
sun.getPVCoordinates(date, frame));
final PVCoordinates sunNormal =
PVCoordinates.crossProduct(PLUS_Z, base.getOrientation().applyTo(sunDirection));
final TimeStampedAngularCoordinates compensation =
new TimeStampedAngularCoordinates(date,
PLUS_Z, sunNormal.normalize(),
PLUS_Z, phasingNormal,
1.0e-9);
// add compensation
return new Attitude(frame, compensation.addOffset(base.getOrientation()));
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> FieldAttitude<T> getAttitude(final FieldPVCoordinatesProvider<T> pvProv,
final FieldAbsoluteDate<T> date, final Frame frame) {
final Field<T> field = date.getField();
final FieldVector3D<T> zero = FieldVector3D.getZero(field);
final FieldPVCoordinates<T> plusZ = new FieldPVCoordinates<>(FieldVector3D.getPlusK(field), zero, zero);
// attitude from base attitude provider
final FieldAttitude<T> base = getBaseState(pvProv, date, frame);
// Compensation rotation definition :
// . Z satellite axis is unchanged
// . phasing axis shall be aligned to sun direction
final FieldPVCoordinates<T> sunDirection =
new FieldPVCoordinates<>(pvProv.getPVCoordinates(date, frame),
new FieldPVCoordinates<>(field,
sun.getPVCoordinates(date.toAbsoluteDate(), frame)));
final FieldPVCoordinates<T> sunNormal =
plusZ.crossProduct(base.getOrientation().applyTo(sunDirection));
final TimeStampedFieldAngularCoordinates<T> compensation =
new TimeStampedFieldAngularCoordinates<>(date,
plusZ, sunNormal.normalize(),
plusZ, new FieldPVCoordinates<>(field, phasingNormal),
1.0e-9);
// add compensation
return new FieldAttitude<>(frame, compensation.addOffset(base.getOrientation()));
}
}