ConstantThrustManeuver.java
/* Copyright 2002-2017 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.forces.maneuvers;
import java.util.stream.Stream;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitInternalError;
import org.orekit.forces.AbstractForceModel;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.DateDetector;
import org.orekit.propagation.events.EventDetector;
import org.orekit.propagation.events.FieldDateDetector;
import org.orekit.propagation.events.FieldEventDetector;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.FieldEventHandler;
import org.orekit.propagation.numerical.FieldTimeDerivativesEquations;
import org.orekit.propagation.numerical.TimeDerivativesEquations;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.Constants;
import org.orekit.utils.ParameterDriver;
/** This class implements a simple maneuver with constant thrust.
* <p>The maneuver is defined by a direction in satellite frame.
* The current attitude of the spacecraft, defined by the current
* spacecraft state, will be used to compute the thrust direction in
* inertial frame. A typical case for tangential maneuvers is to use a
* {@link org.orekit.attitudes.LofOffset LOF aligned} attitude provider
* for state propagation and a velocity increment along the +X satellite axis.</p>
* @author Fabien Maussion
* @author Véronique Pommier-Maurussane
* @author Luc Maisonobe
*/
public class ConstantThrustManeuver extends AbstractForceModel {
/** Parameter name for thrust. */
public static final String THRUST = "thrust";
/** Parameter name for flow rate. */
public static final String FLOW_RATE = "flow rate";
/** Thrust scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double THRUST_SCALE = FastMath.scalb(1.0, -5);
/** Flow rate scaling factor.
* <p>
* We use a power of 2 to avoid numeric noise introduction
* in the multiplications/divisions sequences.
* </p>
*/
private static final double FLOW_RATE_SCALE = FastMath.scalb(1.0, -12);
/** Driver for thrust parameter. */
private final ParameterDriver thrustDriver;
/** Driver for flow rate parameter. */
private final ParameterDriver flowRateDriver;
/** State of the engine. */
private boolean firing;
/** Start of the maneuver. */
private final AbsoluteDate startDate;
/** End of the maneuver. */
private final AbsoluteDate endDate;
/** Direction of the acceleration in satellite frame. */
private final Vector3D direction;
/** Simple constructor for a constant direction and constant thrust.
* <p>
* Calling this constructor is equivalent to call {@link
* #ConstantThrustManeuver(AbsoluteDate, double, double, double, Vector3D, String)
* ConstantThrustManeuver(date, duration, thrust, isp, direction, "")},
* hence not using any prefix for the parameters drivers names.
* </p>
* @param date maneuver date
* @param duration the duration of the thrust (s) (if negative,
* the date is considered to be the stop date)
* @param thrust the thrust force (N)
* @param isp engine specific impulse (s)
* @param direction the acceleration direction in satellite frame.
*/
public ConstantThrustManeuver(final AbsoluteDate date, final double duration,
final double thrust, final double isp,
final Vector3D direction) {
this(date, duration, thrust, isp, direction, "");
}
/** Simple constructor for a constant direction and constant thrust.
* <p>
* If the {@code driversNamePrefix} is empty, the names will
* be {@link #THRUST "thrust"} and {@link #FLOW_RATE "flow rate"}, otherwise
* the prefix is prepended to these fixed strings. A typical use case is to
* use something like "1A-" or "2B-" as a prefix corresponding to the
* name of the thruster to use, so separate parameters can be adjusted
* for the different thrusters involved during an orbit determination
* where maneuvers parameters are estimated.
* </p>
* @param date maneuver date
* @param duration the duration of the thrust (s) (if negative,
* the date is considered to be the stop date)
* @param thrust the thrust force (N)
* @param isp engine specific impulse (s)
* @param direction the acceleration direction in satellite frame
* @param driversNamePrefix prefix for the {@link #getParametersDrivers() parameters drivers}
* @since 9.0
*/
public ConstantThrustManeuver(final AbsoluteDate date, final double duration,
final double thrust, final double isp,
final Vector3D direction,
final String driversNamePrefix) {
if (duration >= 0) {
this.startDate = date;
this.endDate = date.shiftedBy(duration);
} else {
this.endDate = date;
this.startDate = endDate.shiftedBy(duration);
}
final double flowRate = -thrust / (Constants.G0_STANDARD_GRAVITY * isp);
this.direction = direction.normalize();
firing = false;
ParameterDriver tpd = null;
ParameterDriver fpd = null;
try {
tpd = new ParameterDriver(driversNamePrefix + THRUST, thrust, THRUST_SCALE,
0.0, Double.POSITIVE_INFINITY);
fpd = new ParameterDriver(driversNamePrefix + FLOW_RATE, flowRate, FLOW_RATE_SCALE,
Double.NEGATIVE_INFINITY, 0.0 );
} catch (OrekitException oe) {
// this should never occur as valueChanged above never throws an exception
throw new OrekitInternalError(oe);
}
this.thrustDriver = tpd;
this.flowRateDriver = fpd;
}
/** {@inheritDoc} */
@Override
public boolean dependsOnPositionOnly() {
return false;
}
/** {@inheritDoc} */
@Override
public void init(final SpacecraftState s0, final AbsoluteDate t) {
// set the initial value of firing
final AbsoluteDate sDate = s0.getDate();
final boolean isForward = sDate.compareTo(t) < 0;
final boolean isBetween =
startDate.compareTo(sDate) < 0 && endDate.compareTo(sDate) > 0;
final boolean isOnStart = startDate.compareTo(sDate) == 0;
final boolean isOnEnd = endDate.compareTo(sDate) == 0;
firing = isBetween || (isForward && isOnStart) || (!isForward && isOnEnd);
}
/** Get the thrust.
* @return thrust force (N).
*/
public double getThrust() {
return thrustDriver.getValue();
}
/** Get the specific impulse.
* @return specific impulse (s).
*/
public double getISP() {
final double thrust = getThrust();
final double flowRate = getFlowRate();
return -thrust / (Constants.G0_STANDARD_GRAVITY * flowRate);
}
/** Get the flow rate.
* @return flow rate (negative, kg/s).
*/
public double getFlowRate() {
return flowRateDriver.getValue();
}
/** {@inheritDoc} */
@Override
public void addContribution(final SpacecraftState s, final TimeDerivativesEquations adder)
throws OrekitException {
if (firing) {
// compute thrust acceleration in inertial frame
final double[] parameters = getParameters();
adder.addNonKeplerianAcceleration(acceleration(s, parameters));
// compute flow rate
adder.addMassDerivative(parameters[1]);
}
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> void
addContribution(final FieldSpacecraftState<T> s,
final FieldTimeDerivativesEquations<T> adder)
throws OrekitException {
if (firing) {
final T[] parameters = getParameters(s.getDate().getField());
// compute thrust acceleration in inertial frame
adder.addNonKeplerianAcceleration(acceleration(s, parameters));
// compute flow rate
adder.addMassDerivative(parameters[1]);
}
}
/** {@inheritDoc} */
@Override
public Vector3D acceleration(final SpacecraftState state, final double[] parameters) {
if (firing) {
final double thrust = parameters[0];
return new Vector3D(thrust / state.getMass(),
state.getAttitude().getRotation().applyInverseTo(direction));
} else {
return Vector3D.ZERO;
}
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
final T[] parameters) {
if (firing) {
// compute thrust acceleration in inertial frame
final T thrust = parameters[0];
return new FieldVector3D<>(s.getMass().reciprocal().multiply(thrust),
s.getAttitude().getRotation().applyInverseTo(direction));
} else {
// constant (and null) acceleration when not firing
return FieldVector3D.getZero(s.getMass().getField());
}
}
/** {@inheritDoc} */
@Override
public Stream<EventDetector> getEventsDetectors() {
// in forward propagation direction, firing must be enabled
// at start time and disabled at end time; in backward
// propagation direction, firing must be enabled
// at end time and disabled at start time
final DateDetector startDetector = new DateDetector(startDate).
withHandler((SpacecraftState state, DateDetector d, boolean increasing) -> {
firing = d.isForward();
return EventHandler.Action.RESET_DERIVATIVES;
});
final DateDetector endDetector = new DateDetector(endDate).
withHandler((SpacecraftState state, DateDetector d, boolean increasing) -> {
firing = !d.isForward();
return EventHandler.Action.RESET_DERIVATIVES;
});
return Stream.of(startDetector, endDetector);
}
/** {@inheritDoc} */
@Override
public ParameterDriver[] getParametersDrivers() {
return new ParameterDriver[] {
thrustDriver, flowRateDriver
};
}
/** {@inheritDoc} */
@Override
public <T extends RealFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventsDetectors(final Field<T> field) {
// in forward propagation direction, firing must be enabled
// at start time and disabled at end time; in backward
// propagation direction, firing must be enabled
// at end time and disabled at start time
final FieldDateDetector<T> startDetector = new FieldDateDetector<>(new FieldAbsoluteDate<>(field, startDate)).
withHandler((FieldSpacecraftState<T> state, FieldDateDetector<T> d, boolean increasing) -> {
firing = d.isForward();
return FieldEventHandler.Action.RESET_DERIVATIVES;
});
final FieldDateDetector<T> endDetector = new FieldDateDetector<>(new FieldAbsoluteDate<>(field, endDate)).
withHandler((FieldSpacecraftState<T> state, FieldDateDetector<T> d, boolean increasing) -> {
firing = !d.isForward();
return FieldEventHandler.Action.RESET_DERIVATIVES;
});
return Stream.of(startDetector, endDetector);
}
}