Java tutorial
/* Copyright 2002-2015 CS Systmes d'Information * Licensed to CS Systmes 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 fr.cs.examples.attitude; import java.text.DecimalFormat; import java.text.DecimalFormatSymbols; import java.util.Locale; import java.util.SortedSet; import java.util.TreeSet; import org.apache.commons.math3.geometry.euclidean.threed.RotationOrder; import org.apache.commons.math3.geometry.euclidean.threed.Vector3D; import org.apache.commons.math3.util.FastMath; import org.orekit.attitudes.AttitudeProvider; import org.orekit.attitudes.AttitudesSequence; import org.orekit.attitudes.LofOffset; import org.orekit.bodies.CelestialBodyFactory; import org.orekit.errors.OrekitException; import org.orekit.errors.PropagationException; import org.orekit.frames.FramesFactory; import org.orekit.frames.LOFType; import org.orekit.orbits.KeplerianOrbit; import org.orekit.orbits.Orbit; import org.orekit.propagation.Propagator; import org.orekit.propagation.SpacecraftState; import org.orekit.propagation.analytical.EcksteinHechlerPropagator; import org.orekit.propagation.events.EclipseDetector; import org.orekit.propagation.events.EventDetector; import org.orekit.propagation.events.handlers.ContinueOnEvent; import org.orekit.propagation.sampling.OrekitFixedStepHandler; import org.orekit.time.AbsoluteDate; import org.orekit.time.TimeScalesFactory; import org.orekit.utils.AngularDerivativesFilter; import org.orekit.utils.Constants; import org.orekit.utils.PVCoordinates; import org.orekit.utils.PVCoordinatesProvider; import fr.cs.examples.Autoconfiguration; /** Orekit tutorial for Earth observation attitude sequence. * <p>This tutorial shows how to easily switch between day and night attitude modes.<p> * @author Luc Maisonobe */ public class EarthObservation { /** Program entry point. * @param args program arguments (unused here) */ public static void main(String[] args) { try { // configure Orekit Autoconfiguration.configureOrekit(); final SortedSet<String> output = new TreeSet<String>(); // Initial state definition : date, orbit final AbsoluteDate initialDate = new AbsoluteDate(2004, 01, 01, 23, 30, 00.000, TimeScalesFactory.getUTC()); final Vector3D position = new Vector3D(-6142438.668, 3492467.560, -25767.25680); final Vector3D velocity = new Vector3D(505.8479685, 942.7809215, 7435.922231); final Orbit initialOrbit = new KeplerianOrbit(new PVCoordinates(position, velocity), FramesFactory.getEME2000(), initialDate, Constants.EIGEN5C_EARTH_MU); // Attitudes sequence definition final AttitudeProvider dayObservationLaw = new LofOffset(initialOrbit.getFrame(), LOFType.VVLH, RotationOrder.XYZ, FastMath.toRadians(20), FastMath.toRadians(40), 0); final AttitudeProvider nightRestingLaw = new LofOffset(initialOrbit.getFrame(), LOFType.VVLH); final PVCoordinatesProvider sun = CelestialBodyFactory.getSun(); final PVCoordinatesProvider earth = CelestialBodyFactory.getEarth(); final EventDetector dayNightEvent = new EclipseDetector(sun, 696000000., earth, Constants.WGS84_EARTH_EQUATORIAL_RADIUS).withHandler(new ContinueOnEvent<EclipseDetector>()); final EventDetector nightDayEvent = new EclipseDetector(sun, 696000000., earth, Constants.WGS84_EARTH_EQUATORIAL_RADIUS).withHandler(new ContinueOnEvent<EclipseDetector>()); final AttitudesSequence attitudesSequence = new AttitudesSequence(); final AttitudesSequence.SwitchHandler switchHandler = new AttitudesSequence.SwitchHandler() { public void switchOccurred(AttitudeProvider preceding, AttitudeProvider following, SpacecraftState s) { if (preceding == dayObservationLaw) { output.add(s.getDate() + ": switching to night law"); } else { output.add(s.getDate() + ": switching to day law"); } } }; attitudesSequence.addSwitchingCondition(dayObservationLaw, nightRestingLaw, dayNightEvent, false, true, 10.0, AngularDerivativesFilter.USE_R, switchHandler); attitudesSequence.addSwitchingCondition(nightRestingLaw, dayObservationLaw, nightDayEvent, true, false, 10.0, AngularDerivativesFilter.USE_R, switchHandler); if (dayNightEvent.g(new SpacecraftState(initialOrbit)) >= 0) { // initial position is in daytime attitudesSequence.resetActiveProvider(dayObservationLaw); } else { // initial position is in nighttime attitudesSequence.resetActiveProvider(nightRestingLaw); } // Propagator : consider the analytical Eckstein-Hechler model final Propagator propagator = new EcksteinHechlerPropagator(initialOrbit, attitudesSequence, Constants.EIGEN5C_EARTH_EQUATORIAL_RADIUS, Constants.EIGEN5C_EARTH_MU, Constants.EIGEN5C_EARTH_C20, Constants.EIGEN5C_EARTH_C30, Constants.EIGEN5C_EARTH_C40, Constants.EIGEN5C_EARTH_C50, Constants.EIGEN5C_EARTH_C60); // Register the switching events to the propagator attitudesSequence.registerSwitchEvents(propagator); propagator.setMasterMode(180.0, new OrekitFixedStepHandler() { public void init(final SpacecraftState s0, final AbsoluteDate t) { } public void handleStep(SpacecraftState currentState, boolean isLast) throws PropagationException { try { DecimalFormatSymbols angleDegree = new DecimalFormatSymbols(Locale.US); angleDegree.setDecimalSeparator('\u00b0'); DecimalFormat ad = new DecimalFormat(" 00.000;-00.000", angleDegree); // the Earth position in spacecraft frame should be along spacecraft Z axis // during nigthtime and away from it during daytime due to roll and pitch offsets final Vector3D earth = currentState.toTransform().transformPosition(Vector3D.ZERO); final double pointingOffset = Vector3D.angle(earth, Vector3D.PLUS_K); // the g function is the eclipse indicator, its an angle between Sun and Earth limb, // positive when Sun is outside of Earth limb, negative when Sun is hidden by Earth limb final double eclipseAngle = dayNightEvent.g(currentState); output.add(currentState.getDate() + " " + ad.format(FastMath.toDegrees(eclipseAngle)) + " " + ad.format(FastMath.toDegrees(pointingOffset))); } catch (OrekitException oe) { throw new PropagationException(oe); } } }); // Propagate from the initial date for the fixed duration SpacecraftState finalState = propagator.propagate(initialDate.shiftedBy(12600.)); // we print the lines according to lexicographic order, which is chronological order here // to make sure out of orders calls between step handler and event handlers don't mess things up for (final String line : output) { System.out.println(line); } System.out.println("Propagation ended at " + finalState.getDate()); } catch (OrekitException oe) { System.err.println(oe.getMessage()); } } }