YawSteering.java
/* Copyright 2002-2016 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.attitudes;
import org.apache.commons.math3.geometry.euclidean.threed.Vector3D;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedAngularCoordinates;
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 {
/** Serializable UID. */
private static final long serialVersionUID = 20150529L;
/** 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 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)
* @deprecated as of 7.1, replaced with {@link #YawSteering(Frame, GroundPointing, PVCoordinatesProvider, Vector3D)}
*/
@Deprecated
public YawSteering(final GroundPointing groundPointingLaw,
final PVCoordinatesProvider sun,
final Vector3D phasingAxis) {
super(groundPointingLaw.getBodyFrame());
this.groundPointingLaw = groundPointingLaw;
this.sun = sun;
this.phasingNormal = new PVCoordinates(Vector3D.crossProduct(Vector3D.PLUS_K, phasingAxis).normalize(),
Vector3D.ZERO,
Vector3D.ZERO);
}
/** 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)
* @exception OrekitException if the frame specified is not a pseudo-inertial frame
* @since 7.1
*/
public YawSteering(final Frame inertialFrame,
final GroundPointing groundPointingLaw,
final PVCoordinatesProvider sun,
final Vector3D phasingAxis)
throws OrekitException {
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} */
protected TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame)
throws OrekitException {
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.
* @throws OrekitException if some specific error occurs
*/
public Attitude getBaseState(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame)
throws OrekitException {
return groundPointingLaw.getAttitude(pvProv, date, frame);
}
/** {@inheritDoc} */
@Override
public Attitude getAttitude(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame)
throws OrekitException {
// 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()));
}
}