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OREKIT (ORbits Extrapolation KIT) is a low level space dynamics library.
It provides basic elements (orbits, dates, attitude, frames ...) and
various algorithms to handle them (conversions, analytical and numerical
propagation, pointing ...).
/* 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.CalculusFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathArrays;
import org.orekit.bodies.Ellipsoid;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/**
* This class handles body center pointing attitude provider.
*
* This class represents the attitude provider where the satellite z axis is
* pointing to the body frame center.
*
* The object BodyCenterPointing is guaranteed to be immutable.
*
* @see GroundPointing
* @author Véronique Pommier-Maurussane
*/
public class BodyCenterPointing extends GroundPointing {
/** Body ellipsoid. */
private final Ellipsoid ellipsoid;
/** Creates new instance.
* @param inertialFrame frame in which orbital velocities are computed
* @param shape Body shape
* @since 7.1
*/
public BodyCenterPointing(final Frame inertialFrame, final Ellipsoid shape) {
super(inertialFrame, shape.getFrame());
this.ellipsoid = shape;
}
/** {@inheritDoc} */
@Override
public TimeStampedPVCoordinates getTargetPV(final PVCoordinatesProvider pvProv,
final AbsoluteDate date, final Frame frame) {
// spacecraft coordinates in body frame
final TimeStampedPVCoordinates scInBodyFrame = pvProv.getPVCoordinates(date, getBodyFrame());
// central projection to ground (NOT the classical nadir point)
final double u = scInBodyFrame.getPosition().getX() / ellipsoid.getA();
final double v = scInBodyFrame.getPosition().getY() / ellipsoid.getB();
final double w = scInBodyFrame.getPosition().getZ() / ellipsoid.getC();
final double d2 = u * u + v * v + w * w;
final double d = FastMath.sqrt(d2);
final double ratio = 1.0 / d;
final Vector3D projectedP = new Vector3D(ratio, scInBodyFrame.getPosition());
// velocity
final double uDot = scInBodyFrame.getVelocity().getX() / ellipsoid.getA();
final double vDot = scInBodyFrame.getVelocity().getY() / ellipsoid.getB();
final double wDot = scInBodyFrame.getVelocity().getZ() / ellipsoid.getC();
final double dDot = MathArrays.linearCombination(u, uDot, v, vDot, w, wDot) / d;
final double ratioDot = -dDot / d2;
final Vector3D projectedV = new Vector3D(ratio, scInBodyFrame.getVelocity(),
ratioDot, scInBodyFrame.getPosition());
// acceleration
final double uDotDot = scInBodyFrame.getAcceleration().getX() / ellipsoid.getA();
final double vDotDot = scInBodyFrame.getAcceleration().getY() / ellipsoid.getB();
final double wDotDot = scInBodyFrame.getAcceleration().getZ() / ellipsoid.getC();
final double dDotDot = (MathArrays.linearCombination(u, uDotDot, v, vDotDot, w, wDotDot) +
uDot * uDot + vDot * vDot + wDot * wDot - dDot * dDot) / d;
final double ratioDotDot = (2 * dDot * dDot - d * dDotDot) / (d * d2);
final Vector3D projectedA = new Vector3D(ratio, scInBodyFrame.getAcceleration(),
2 * ratioDot, scInBodyFrame.getVelocity(),
ratioDotDot, scInBodyFrame.getPosition());
final TimeStampedPVCoordinates projected =
new TimeStampedPVCoordinates(date, projectedP, projectedV, projectedA);
return getBodyFrame().getTransformTo(frame, date).transformPVCoordinates(projected);
}
/** {@inheritDoc} */
public > TimeStampedFieldPVCoordinates getTargetPV(final FieldPVCoordinatesProvider pvProv,
final FieldAbsoluteDate date, final Frame frame) {
// spacecraft coordinates in body frame
final TimeStampedFieldPVCoordinates scInBodyFrame = pvProv.getPVCoordinates(date, getBodyFrame());
// central projection to ground (NOT the classical nadir point)
final T u = scInBodyFrame.getPosition().getX().divide(ellipsoid.getA());
final T v = scInBodyFrame.getPosition().getY().divide(ellipsoid.getB());
final T w = scInBodyFrame.getPosition().getZ().divide(ellipsoid.getC());
final T d2 = u.pow(2).add(v.pow(2)).add(w.pow(2));
final T d = d2.sqrt();
final T ratio = d.reciprocal();
final FieldVector3D projectedP = new FieldVector3D<>(ratio, scInBodyFrame.getPosition());
// velocity
final T uDot = scInBodyFrame.getVelocity().getX().divide(ellipsoid.getA());
final T vDot = scInBodyFrame.getVelocity().getY().divide(ellipsoid.getB());
final T wDot = scInBodyFrame.getVelocity().getZ().divide(ellipsoid.getC());
//we aren't using the linearCombination in the library
final T dDot = (u.multiply(uDot).add(v.multiply(vDot)).add(w.multiply(wDot))).divide(d);
final T ratioDot = dDot.multiply(-1).divide(d2);
final FieldVector3D projectedV = new FieldVector3D<>(ratio, scInBodyFrame.getVelocity(),
ratioDot, scInBodyFrame.getPosition());
// acceleration
final T uDotDot = scInBodyFrame.getAcceleration().getX().divide(ellipsoid.getA());
final T vDotDot = scInBodyFrame.getAcceleration().getY().divide(ellipsoid.getB());
final T wDotDot = scInBodyFrame.getAcceleration().getZ().divide(ellipsoid.getC());
final T dDotDot = u.multiply(uDotDot).add(v.multiply(vDotDot)).add(w.multiply( wDotDot)
.add(uDot.pow(2).add(vDot.pow(2)).add(wDot.pow(2)).subtract(dDot.pow(2))))
.divide(d);
final T ratioDotDot = (dDot.pow(2).multiply(2).subtract(d.multiply(dDotDot))).divide(d.multiply(d2));
final FieldVector3D projectedA = new FieldVector3D<>(ratio, scInBodyFrame.getAcceleration(),
ratioDot.multiply(2), scInBodyFrame.getVelocity(),
ratioDotDot, scInBodyFrame.getPosition());
final TimeStampedFieldPVCoordinates projected =
new TimeStampedFieldPVCoordinates<>(date, projectedP, projectedV, projectedA);
return getBodyFrame().getTransformTo(frame, date.toAbsoluteDate()).transformPVCoordinates(projected);
}
}