CelestialBodyPointed.java
- /* Copyright 2002-2024 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,
- * 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.hipparchus.Field;
- import org.hipparchus.CalculusFieldElement;
- import org.hipparchus.geometry.euclidean.threed.FieldRotation;
- import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
- import org.hipparchus.geometry.euclidean.threed.Rotation;
- import org.hipparchus.geometry.euclidean.threed.Vector3D;
- import org.orekit.frames.FieldStaticTransform;
- import org.orekit.frames.FieldTransform;
- import org.orekit.frames.Frame;
- import org.orekit.frames.StaticTransform;
- import org.orekit.frames.Transform;
- 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;
- /**
- * This class handles a celestial body pointed attitude provider.
- * <p>The celestial body pointed law is defined by two main elements:
- * <ul>
- * <li>a celestial body towards which some satellite axis is exactly aimed</li>
- * <li>a phasing reference defining the rotation around the pointing axis</li>
- * </ul>
- *
- * <p>
- * The celestial body implicitly defines two of the three degrees of freedom
- * and the phasing reference defines the remaining degree of freedom. This definition
- * can be represented as first aligning exactly the satellite pointing axis to
- * the current direction of the celestial body, and then to find the rotation
- * around this axis such that the satellite phasing axis is in the half-plane
- * defined by a cut line on the pointing axis and containing the celestial
- * phasing reference.
- * </p>
- * <p>
- * In order for this definition to work, the user must ensure that the phasing
- * reference is <strong>never</strong> aligned with the pointing reference.
- * Since the pointed body moves as the date changes, this should be ensured
- * regardless of the date. A simple way to do this for Sun, Moon or any planet
- * pointing is to choose a phasing reference far from the ecliptic plane. Using
- * <code>Vector3D.PLUS_K</code>, the equatorial pole, is perfect in these cases.
- * </p>
- * <p>Instances of this class are guaranteed to be immutable.</p>
- * @author Luc Maisonobe
- */
- public class CelestialBodyPointed implements AttitudeProvider {
- /** Frame in which {@link #phasingCel} is defined. */
- private final Frame celestialFrame;
- /** Celestial body to point at. */
- private final PVCoordinatesProvider pointedBody;
- /** Phasing reference, in celestial frame. */
- private final Vector3D phasingCel;
- /** Satellite axis aiming at the pointed body, in satellite frame. */
- private final Vector3D pointingSat;
- /** Phasing reference, in satellite frame. */
- private final Vector3D phasingSat;
- /** Creates new instance.
- * @param celestialFrame frame in which <code>phasingCel</code> is defined
- * @param pointedBody celestial body to point at
- * @param phasingCel phasing reference, in celestial frame
- * @param pointingSat satellite vector defining the pointing direction
- * @param phasingSat phasing reference, in satellite frame
- */
- public CelestialBodyPointed(final Frame celestialFrame,
- final PVCoordinatesProvider pointedBody,
- final Vector3D phasingCel,
- final Vector3D pointingSat,
- final Vector3D phasingSat) {
- this.celestialFrame = celestialFrame;
- this.pointedBody = pointedBody;
- this.phasingCel = phasingCel;
- this.pointingSat = pointingSat;
- this.phasingSat = phasingSat;
- }
- /** {@inheritDoc} */
- @Override
- public Attitude getAttitude(final PVCoordinatesProvider pvProv,
- final AbsoluteDate date, final Frame frame) {
- final PVCoordinates satPV = pvProv.getPVCoordinates(date, celestialFrame);
- // compute celestial references at the specified date
- final PVCoordinates bodyPV = pointedBody.getPVCoordinates(date, celestialFrame);
- final PVCoordinates pointing = new PVCoordinates(satPV, bodyPV);
- final Vector3D pointingP = pointing.getPosition();
- final double r2 = Vector3D.dotProduct(pointingP, pointingP);
- // evaluate instant rotation axis due to sat and body motion only (no phasing yet)
- final Vector3D rotAxisCel = new Vector3D(1 / r2, Vector3D.crossProduct(pointingP, pointing.getVelocity()));
- // fix instant rotation to take phasing constraint into account
- // (adding a rotation around pointing axis ensuring the motion of the phasing axis
- // is constrained in the pointing-phasing plane)
- final Vector3D v1 = Vector3D.crossProduct(rotAxisCel, phasingCel);
- final Vector3D v2 = Vector3D.crossProduct(pointingP, phasingCel);
- final double compensation = -Vector3D.dotProduct(v1, v2) / v2.getNormSq();
- final Vector3D phasedRotAxisCel = new Vector3D(1.0, rotAxisCel, compensation, pointingP);
- // compute transform from celestial frame to satellite frame
- final Rotation celToSatRotation =
- new Rotation(pointingP, phasingCel, pointingSat, phasingSat);
- // build transform combining rotation and instant rotation axis
- Transform transform = new Transform(date, celToSatRotation, celToSatRotation.applyTo(phasedRotAxisCel));
- if (frame != celestialFrame) {
- // prepend transform from specified frame to celestial frame
- transform = new Transform(date, frame.getTransformTo(celestialFrame, date), transform);
- }
- // build the attitude
- return new Attitude(date, frame, transform.getRotation(), transform.getRotationRate(), transform.getRotationAcceleration());
- }
- /** {@inheritDoc} */
- @Override
- public Rotation getAttitudeRotation(final PVCoordinatesProvider pvProv,
- final AbsoluteDate date,
- final Frame frame) {
- final Vector3D satPosition = pvProv.getPosition(date, celestialFrame);
- // compute celestial references at the specified date
- final Vector3D bodyPosition = pointedBody.getPosition(date, celestialFrame);
- final Vector3D pointingP = bodyPosition.subtract(satPosition);
- // compute static transform from celestial frame to satellite frame
- final Rotation celToSatRotation = new Rotation(pointingP, phasingCel, pointingSat, phasingSat);
- StaticTransform staticTransform = StaticTransform.of(date, celToSatRotation);
- if (frame != celestialFrame) {
- // prepend static transform from specified frame to celestial frame
- staticTransform = StaticTransform.compose(date, frame.getStaticTransformTo(celestialFrame, date), staticTransform);
- }
- return staticTransform.getRotation();
- }
- /** {@inheritDoc} */
- @Override
- public <T extends CalculusFieldElement<T>> FieldAttitude<T> getAttitude(final FieldPVCoordinatesProvider<T> pvProv,
- final FieldAbsoluteDate<T> date,
- final Frame frame) {
- final Field<T> field = date.getField();
- final FieldPVCoordinates<T> satPV = pvProv.getPVCoordinates(date, celestialFrame);
- // compute celestial references at the specified date
- final FieldPVCoordinates<T> bodyPV = new FieldPVCoordinates<>(field,
- pointedBody.getPVCoordinates(date.toAbsoluteDate(),
- celestialFrame));
- final FieldPVCoordinates<T> pointing = new FieldPVCoordinates<>(satPV, bodyPV);
- final FieldVector3D<T> pointingP = pointing.getPosition();
- final T r2 = FieldVector3D.dotProduct(pointingP, pointingP);
- // evaluate instant rotation axis due to sat and body motion only (no phasing yet)
- final FieldVector3D<T> rotAxisCel =
- new FieldVector3D<>(r2.reciprocal(), FieldVector3D.crossProduct(pointingP, pointing.getVelocity()));
- // fix instant rotation to take phasing constraint into account
- // (adding a rotation around pointing axis ensuring the motion of the phasing axis
- // is constrained in the pointing-phasing plane)
- final FieldVector3D<T> v1 = FieldVector3D.crossProduct(rotAxisCel, phasingCel);
- final FieldVector3D<T> v2 = FieldVector3D.crossProduct(pointingP, phasingCel);
- final T compensation = FieldVector3D.dotProduct(v1, v2).negate().divide(v2.getNormSq());
- final FieldVector3D<T> phasedRotAxisCel = new FieldVector3D<>(field.getOne(), rotAxisCel, compensation, pointingP);
- // compute transform from celestial frame to satellite frame
- final FieldRotation<T> celToSatRotation =
- new FieldRotation<>(pointingP, new FieldVector3D<>(field, phasingCel),
- new FieldVector3D<>(field, pointingSat), new FieldVector3D<>(field, phasingSat));
- // build transform combining rotation and instant rotation axis
- FieldTransform<T> transform = new FieldTransform<>(date, celToSatRotation, celToSatRotation.applyTo(phasedRotAxisCel));
- if (frame != celestialFrame) {
- // prepend transform from specified frame to celestial frame
- transform = new FieldTransform<>(date, frame.getTransformTo(celestialFrame, date), transform);
- }
- // build the attitude
- return new FieldAttitude<>(date, frame,
- transform.getRotation(), transform.getRotationRate(), transform.getRotationAcceleration());
- }
- /** {@inheritDoc} */
- @Override
- public <T extends CalculusFieldElement<T>> FieldRotation<T> getAttitudeRotation(final FieldPVCoordinatesProvider<T> pvProv,
- final FieldAbsoluteDate<T> date,
- final Frame frame) {
- final Field<T> field = date.getField();
- final FieldVector3D<T> satPosition = pvProv.getPosition(date, celestialFrame);
- // compute celestial references at the specified date
- final FieldVector3D<T> bodyPosition = new FieldVector3D<>(field,
- pointedBody.getPosition(date.toAbsoluteDate(), celestialFrame));
- final FieldVector3D<T> pointingP = bodyPosition.subtract(satPosition);
- // compute rotation from celestial frame to satellite frame
- final FieldRotation<T> celToSatRotation =
- new FieldRotation<>(pointingP, new FieldVector3D<>(field, phasingCel),
- new FieldVector3D<>(field, pointingSat), new FieldVector3D<>(field, phasingSat));
- // build static transform combining rotation and instant rotation axis
- FieldStaticTransform<T> staticTransform = FieldStaticTransform.of(date, celToSatRotation);
- if (frame != celestialFrame) {
- // prepend static transform from specified frame to celestial frame
- staticTransform = FieldStaticTransform.compose(date, frame.getStaticTransformTo(celestialFrame, date), staticTransform);
- }
- return staticTransform.getRotation();
- }
- }