SolarRadiationPressure.java

  1. /* Copyright 2002-2023 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.forces.radiation;

  19. import java.lang.reflect.Array;
  20. import java.util.List;

  22. import org.hipparchus.CalculusFieldElement;
  23. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  24. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  25. import org.hipparchus.util.FastMath;
  26. import org.hipparchus.util.Precision;
  27. import org.orekit.bodies.OneAxisEllipsoid;
  28. import org.orekit.frames.Frame;
  29. import org.orekit.propagation.FieldSpacecraftState;
  30. import org.orekit.propagation.SpacecraftState;
  31. import org.orekit.time.AbsoluteDate;
  32. import org.orekit.time.FieldAbsoluteDate;
  33. import org.orekit.utils.Constants;
  34. import org.orekit.utils.ExtendedPVCoordinatesProvider;
  35. import org.orekit.utils.FrameAdapter;
  36. import org.orekit.utils.OccultationEngine;
  37. import org.orekit.utils.ParameterDriver;

  39. /** Solar radiation pressure force model.
  40.  * <p>
  41.  * Since Orekit 11.0, it is possible to take into account
  42.  * the eclipses generated by Moon in the solar radiation
  43.  * pressure force model using the
  44.  * {@link #addOccultingBody(ExtendedPVCoordinatesProvider, double)}
  45.  * method.
  46.  * <p>
  47.  * Example:<br>
  48.  * <code> SolarRadiationPressure srp = </code>
  49.  * <code>                      new SolarRadiationPressure(CelestialBodyFactory.getSun(), Constants.EIGEN5C_EARTH_EQUATORIAL_RADIUS,</code>
  50.  * <code>                                     new IsotropicRadiationClassicalConvention(50.0, 0.5, 0.5));</code><br>
  51.  * <code> srp.addOccultingBody(CelestialBodyFactory.getMoon(), Constants.MOON_EQUATORIAL_RADIUS);</code><br>
  52.  *
  53.  * @author Fabien Maussion
  54.  * @author &Eacute;douard Delente
  55.  * @author V&eacute;ronique Pommier-Maurussane
  56.  * @author Pascal Parraud
  57.  */
  58. public class SolarRadiationPressure extends AbstractRadiationForceModel {

  60.     /** Reference distance for the solar radiation pressure (m). */
  61.     private static final double D_REF = 149597870000.0;

  63.     /** Reference solar radiation pressure at D_REF (N/m²). */
  64.     private static final double P_REF = 4.56e-6;

  66.     /** Margin to force recompute lighting ratio derivatives when we are really inside penumbra. */
  67.     private static final double ANGULAR_MARGIN = 1.0e-10;

  69.     /** Threshold to decide whether the S/C frame is Sun-centered. */
  70.     private static final double SUN_CENTERED_FRAME_THRESHOLD = 2. * Constants.SUN_RADIUS;

  72.     /** Reference flux normalized for a 1m distance (N). */
  73.     private final double kRef;

  75.     /** Sun model. */
  76.     private final ExtendedPVCoordinatesProvider sun;

  78.     /** Spacecraft. */
  79.     private final RadiationSensitive spacecraft;

  81.     /** Simple constructor with default reference values.
  82.      * <p>When this constructor is used, the reference values are:</p>
  83.      * <ul>
  84.      *   <li>d<sub>ref</sub> = 149597870000.0 m</li>
  85.      *   <li>p<sub>ref</sub> = 4.56 10<sup>-6</sup> N/m²</li>
  86.      * </ul>
  87.      * @param sun Sun model
  88.      * @param centralBody central body shape model (for umbra/penumbra computation)
  89.      * @param spacecraft the object physical and geometrical information
  90.      * @since 12.0
  91.      */
  92.     public SolarRadiationPressure(final ExtendedPVCoordinatesProvider sun,
  93.                                   final OneAxisEllipsoid centralBody,
  94.                                   final RadiationSensitive spacecraft) {
  95.         this(D_REF, P_REF, sun, centralBody, spacecraft);
  96.     }

  98.     /** Complete constructor.
  99.      * <p>Note that reference solar radiation pressure <code>pRef</code> in
  100.      * N/m² is linked to solar flux SF in W/m² using
  101.      * formula pRef = SF/c where c is the speed of light (299792458 m/s). So
  102.      * at 1UA a 1367 W/m² solar flux is a 4.56 10<sup>-6</sup>
  103.      * N/m² solar radiation pressure.</p>
  104.      * @param dRef reference distance for the solar radiation pressure (m)
  105.      * @param pRef reference solar radiation pressure at dRef (N/m²)
  106.      * @param sun Sun model
  107.      * @param centralBody central body shape model (for umbra/penumbra computation)
  108.      * @param spacecraft the object physical and geometrical information
  109.      * @since 12.0
  110.      */
  111.     public SolarRadiationPressure(final double dRef, final double pRef,
  112.                                   final ExtendedPVCoordinatesProvider sun,
  113.                                   final OneAxisEllipsoid centralBody,
  114.                                   final RadiationSensitive spacecraft) {
  115.         super(sun, centralBody);
  116.         this.kRef = pRef * dRef * dRef;
  117.         this.sun  = sun;
  118.         this.spacecraft = spacecraft;
  119.     }

  121.     /** {@inheritDoc} */
  122.     @Override
  123.     public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {

  125.         final AbsoluteDate date         = s.getDate();
  126.         final Frame        frame        = s.getFrame();
  127.         final Vector3D     position     = s.getPosition();
  128.         final Vector3D     sunPosition  = sun.getPosition(date, frame);
  129.         final Vector3D     sunSatVector = position.subtract(sunPosition);
  130.         final double       r2           = sunSatVector.getNormSq();

  132.         // compute flux
  133.         final double   ratio = getLightingRatio(s, sunPosition);
  134.         final double   rawP  = ratio  * kRef / r2;
  135.         final Vector3D flux  = new Vector3D(rawP / FastMath.sqrt(r2), sunSatVector);

  137.         return spacecraft.radiationPressureAcceleration(s, flux, parameters);

  139.     }

  141.     /** {@inheritDoc} */
  142.     @Override
  143.     public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
  144.                                                                              final T[] parameters) {

  146.         final FieldAbsoluteDate<T> date         = s.getDate();
  147.         final Frame                frame        = s.getFrame();
  148.         final FieldVector3D<T>     position     = s.getPosition();
  149.         final FieldVector3D<T>     sunPosition  = sun.getPosition(date, frame);
  150.         final FieldVector3D<T>     sunSatVector = position.subtract(sunPosition);
  151.         final T                    r2           = sunSatVector.getNormSq();

  153.         // compute flux
  154.         final T                ratio = getLightingRatio(s, sunPosition);
  155.         final T                rawP  = ratio.multiply(kRef).divide(r2);
  156.         final FieldVector3D<T> flux  = new FieldVector3D<>(rawP.divide(r2.sqrt()), sunSatVector);

  158.         return spacecraft.radiationPressureAcceleration(s, flux, parameters);

  160.     }

  162.     /** Check whether the frame is considerer Sun-centered.
  163.      *
  164.      * @param sunPositionInFrame Sun position in frame to test
  165.      * @return true if frame is considered Sun-centered
  166.      * @since 12.0
  167.      */
  168.     private boolean isSunCenteredFrame(final Vector3D sunPositionInFrame) {
  169.         // Frame is considered Sun-centered if Sun (or Solar System barycenter) position
  170.         // in that frame is smaller than SUN_CENTERED_FRAME_THRESHOLD
  171.         return sunPositionInFrame.getNorm() < SUN_CENTERED_FRAME_THRESHOLD;
  172.     }


  175.     /** Get the lighting ratio ([0-1]).
  176.      * @param state spacecraft state
  177.      * @param sunPosition Sun position in S/C frame at S/C date
  178.      * @return lighting ratio
  179.      * @since 12.0 added to avoid numerous call to sun.getPosition(...)
  180.      */
  181.     private double getLightingRatio(final SpacecraftState state, final Vector3D sunPosition) {

  183.         // Check if S/C frame is Sun-centered
  184.         if (isSunCenteredFrame(sunPosition)) {
  185.             // We are in fact computing a trajectory around Sun (or solar system barycenter),
  186.             // not around a planet, we consider lighting ratio will always be 1
  187.             return 1.0;
  188.         }

  190.         final List<OccultationEngine> occultingBodies = getOccultingBodies();
  191.         final int n = occultingBodies.size();

  193.         final OccultationEngine.OccultationAngles[] angles = new OccultationEngine.OccultationAngles[n];
  194.         for (int i = 0; i < n; ++i) {
  195.             angles[i] = occultingBodies.get(i).angles(state);
  196.         }
  197.         final double alphaSunSq = angles[0].getOccultedApparentRadius() * angles[0].getOccultedApparentRadius();

  199.         double result = 0.0;
  200.         for (int i = 0; i < n; ++i) {

  202.             // compute lighting ratio considering one occulting body only
  203.             final OccultationEngine oi  = occultingBodies.get(i);
  204.             final double lightingRatioI = maskingRatio(angles[i]);
  205.             if (lightingRatioI == 0.0) {
  206.                 // body totally occults Sun, total eclipse is occurring.
  207.                 return 0.0;
  208.             }
  209.             result += lightingRatioI;

  211.             // Mutual occulting body eclipse ratio computations between first and secondary bodies
  212.             for (int j = i + 1; j < n; ++j) {

  214.                 final OccultationEngine oj = occultingBodies.get(j);
  215.                 final double lightingRatioJ = maskingRatio(angles[j]);
  216.                 if (lightingRatioJ == 0.0) {
  217.                     // Secondary body totally occults Sun, no more computations are required, total eclipse is occurring.
  218.                     return 0.0;
  219.                 } else if (lightingRatioJ != 1) {
  220.                     // Secondary body partially occults Sun

  222.                     final OccultationEngine oij = new OccultationEngine(new FrameAdapter(oi.getOcculting().getBodyFrame()),
  223.                                                                         oi.getOcculting().getEquatorialRadius(),
  224.                                                                         oj.getOcculting());
  225.                     final OccultationEngine.OccultationAngles aij = oij.angles(state);
  226.                     final double maskingRatioIJ = maskingRatio(aij);
  227.                     final double alphaJSq       = aij.getOccultedApparentRadius() * aij.getOccultedApparentRadius();

  229.                     final double mutualEclipseCorrection = (1 - maskingRatioIJ) * alphaJSq / alphaSunSq;
  230.                     result -= mutualEclipseCorrection;

  232.                 }

  234.             }
  235.         }

  237.         // Final term
  238.         result -= n - 1;

  240.         return result;
  241.     }

  243.     /** Get the lighting ratio ([0-1]).
  244.      * @param state spacecraft state
  245.      * @return lighting ratio
  246.      * @since 7.1
  247.      */
  248.     public double getLightingRatio(final SpacecraftState state) {
  249.         return getLightingRatio(state, sun.getPosition(state.getDate(), state.getFrame()));
  250.     }

  252.     /** Get the masking ratio ([0-1]) considering one pair of bodies.
  253.      * @param angles occultation angles
  254.      * @return masking ratio: 0.0 body fully masked, 1.0 body fully visible
  255.      * @since 12.0
  256.      */
  257.     private double maskingRatio(final OccultationEngine.OccultationAngles angles) {

  259.         // Sat-Occulted/ Sat-Occulting angle
  260.         final double sunSatCentralBodyAngle = angles.getSeparation();

  262.         // Occulting apparent radius
  263.         final double alphaCentral = angles.getLimbRadius();

  265.         // Occulted apparent radius
  266.         final double alphaSun = angles.getOccultedApparentRadius();

  268.         // Is the satellite in complete umbra ?
  269.         if (sunSatCentralBodyAngle - alphaCentral + alphaSun <= ANGULAR_MARGIN) {
  270.             return 0.0;
  271.         } else if (sunSatCentralBodyAngle - alphaCentral - alphaSun < -ANGULAR_MARGIN) {
  272.             // Compute a masking ratio in penumbra
  273.             final double sEA2    = sunSatCentralBodyAngle * sunSatCentralBodyAngle;
  274.             final double oo2sEA  = 1.0 / (2. * sunSatCentralBodyAngle);
  275.             final double aS2     = alphaSun * alphaSun;
  276.             final double aE2     = alphaCentral * alphaCentral;
  277.             final double aE2maS2 = aE2 - aS2;

  279.             final double alpha1  = (sEA2 - aE2maS2) * oo2sEA;
  280.             final double alpha2  = (sEA2 + aE2maS2) * oo2sEA;

  282.             // Protection against numerical inaccuracy at boundaries
  283.             final double almost0 = Precision.SAFE_MIN;
  284.             final double almost1 = FastMath.nextDown(1.0);
  285.             final double a1oaS   = FastMath.min(almost1, FastMath.max(-almost1, alpha1 / alphaSun));
  286.             final double aS2ma12 = FastMath.max(almost0, aS2 - alpha1 * alpha1);
  287.             final double a2oaE   = FastMath.min(almost1, FastMath.max(-almost1, alpha2 / alphaCentral));
  288.             final double aE2ma22 = FastMath.max(almost0, aE2 - alpha2 * alpha2);

  290.             final double P1 = aS2 * FastMath.acos(a1oaS) - alpha1 * FastMath.sqrt(aS2ma12);
  291.             final double P2 = aE2 * FastMath.acos(a2oaE) - alpha2 * FastMath.sqrt(aE2ma22);

  293.             return 1. - (P1 + P2) / (FastMath.PI * aS2);
  294.         } else {
  295.             return 1.0;
  296.         }

  298.     }

  300.     /** Get the lighting ratio ([0-1]).
  301.      * @param state spacecraft state
  302.      * @param sunPosition Sun position in S/C frame at S/C date
  303.      * @param <T> extends CalculusFieldElement
  304.      * @return lighting ratio
  305.      * @since 12.0 added to avoid numerous call to sun.getPosition(...)
  306.      */
  307.     private <T extends CalculusFieldElement<T>> T getLightingRatio(final FieldSpacecraftState<T> state, final FieldVector3D<T> sunPosition) {

  309.         final T one  = state.getDate().getField().getOne();
  310.         if (isSunCenteredFrame(sunPosition.toVector3D())) {
  311.             // We are in fact computing a trajectory around Sun (or solar system barycenter),
  312.             // not around a planet, we consider lighting ratio will always be 1
  313.             return one;
  314.         }
  315.         final T zero = state.getDate().getField().getZero();
  316.         final List<OccultationEngine> occultingBodies = getOccultingBodies();
  317.         final int n = occultingBodies.size();

  319.         @SuppressWarnings("unchecked")
  320.         final OccultationEngine.FieldOccultationAngles<T>[] angles =
  321.         (OccultationEngine.FieldOccultationAngles<T>[]) Array.newInstance(OccultationEngine.FieldOccultationAngles.class, n);
  322.         for (int i = 0; i < n; ++i) {
  323.             angles[i] = occultingBodies.get(i).angles(state);
  324.         }
  325.         final T alphaSunSq = angles[0].getOccultedApparentRadius().multiply(angles[0].getOccultedApparentRadius());

  327.         T result = state.getDate().getField().getZero();
  328.         for (int i = 0; i < n; ++i) {

  330.             // compute lighting ratio considering one occulting body only
  331.             final OccultationEngine oi  = occultingBodies.get(i);
  332.             final T lightingRatioI = maskingRatio(angles[i]);
  333.             if (lightingRatioI.isZero()) {
  334.                 // body totally occults Sun, total eclipse is occurring.
  335.                 return zero;
  336.             }
  337.             result = result.add(lightingRatioI);

  339.             // Mutual occulting body eclipse ratio computations between first and secondary bodies
  340.             for (int j = i + 1; j < n; ++j) {

  342.                 final OccultationEngine oj = occultingBodies.get(j);
  343.                 final T lightingRatioJ = maskingRatio(angles[j]);
  344.                 if (lightingRatioJ.isZero()) {
  345.                     // Secondary body totally occults Sun, no more computations are required, total eclipse is occurring.
  346.                     return zero;
  347.                 } else if (lightingRatioJ.getReal() != 1) {
  348.                     // Secondary body partially occults Sun

  350.                     final OccultationEngine oij = new OccultationEngine(new FrameAdapter(oi.getOcculting().getBodyFrame()),
  351.                                                                         oi.getOcculting().getEquatorialRadius(),
  352.                                                                         oj.getOcculting());
  353.                     final OccultationEngine.FieldOccultationAngles<T> aij = oij.angles(state);
  354.                     final T maskingRatioIJ = maskingRatio(aij);
  355.                     final T alphaJSq       = aij.getOccultedApparentRadius().multiply(aij.getOccultedApparentRadius());

  357.                     final T mutualEclipseCorrection = one.subtract(maskingRatioIJ).multiply(alphaJSq).divide(alphaSunSq);
  358.                     result = result.subtract(mutualEclipseCorrection);

  360.                 }

  362.             }
  363.         }

  365.         // Final term
  366.         result = result.subtract(n - 1);

  368.         return result;
  369.     }

  371.     /** Get the lighting ratio ([0-1]).
  372.      * @param state spacecraft state
  373.      * @param <T> extends CalculusFieldElement
  374.      * @return lighting ratio
  375.      * @since 7.1
  376.      */
  377.     public <T extends CalculusFieldElement<T>> T getLightingRatio(final FieldSpacecraftState<T> state) {
  378.         return getLightingRatio(state, sun.getPosition(state.getDate(), state.getFrame()));
  379.     }

  381.     /** Get the masking ratio ([0-1]) considering one pair of bodies.
  382.      * @param angles occultation angles
  383.      * @param <T> type of the field elements
  384.      * @return masking ratio: 0.0 body fully masked, 1.0 body fully visible
  385.      * @since 12.0
  386.      */
  387.     private <T extends CalculusFieldElement<T>> T maskingRatio(final OccultationEngine.FieldOccultationAngles<T> angles) {


  390.         // Sat-Occulted/ Sat-Occulting angle
  391.         final T occultedSatOcculting = angles.getSeparation();

  393.         // Occulting apparent radius
  394.         final T alphaOcculting = angles.getLimbRadius();

  396.         // Occulted apparent radius
  397.         final T alphaOcculted = angles.getOccultedApparentRadius();

  399.         // Is the satellite in complete umbra ?
  400.         if (occultedSatOcculting.getReal() - alphaOcculting.getReal() + alphaOcculted.getReal() <= ANGULAR_MARGIN) {
  401.             return occultedSatOcculting.getField().getZero();
  402.         } else if (occultedSatOcculting.getReal() - alphaOcculting.getReal() - alphaOcculted.getReal() < -ANGULAR_MARGIN) {
  403.             // Compute a masking ratio in penumbra
  404.             final T sEA2    = occultedSatOcculting.multiply(occultedSatOcculting);
  405.             final T oo2sEA  = occultedSatOcculting.multiply(2).reciprocal();
  406.             final T aS2     = alphaOcculted.multiply(alphaOcculted);
  407.             final T aE2     = alphaOcculting.multiply(alphaOcculting);
  408.             final T aE2maS2 = aE2.subtract(aS2);

  410.             final T alpha1  = sEA2.subtract(aE2maS2).multiply(oo2sEA);
  411.             final T alpha2  = sEA2.add(aE2maS2).multiply(oo2sEA);

  413.             // Protection against numerical inaccuracy at boundaries
  414.             final double almost0 = Precision.SAFE_MIN;
  415.             final double almost1 = FastMath.nextDown(1.0);
  416.             final T a1oaS   = min(almost1, max(-almost1, alpha1.divide(alphaOcculted)));
  417.             final T aS2ma12 = max(almost0, aS2.subtract(alpha1.multiply(alpha1)));
  418.             final T a2oaE   = min(almost1, max(-almost1, alpha2.divide(alphaOcculting)));
  419.             final T aE2ma22 = max(almost0, aE2.subtract(alpha2.multiply(alpha2)));

  421.             final T P1 = aS2.multiply(a1oaS.acos()).subtract(alpha1.multiply(aS2ma12.sqrt()));
  422.             final T P2 = aE2.multiply(a2oaE.acos()).subtract(alpha2.multiply(aE2ma22.sqrt()));

  424.             return occultedSatOcculting.getField().getOne().subtract(P1.add(P2).divide(aS2.multiply(occultedSatOcculting.getPi())));
  425.         } else {
  426.             return occultedSatOcculting.getField().getOne();
  427.         }

  429.     }

  431.     /** {@inheritDoc} */
  432.     @Override
  433.     public List<ParameterDriver> getParametersDrivers() {
  434.         return spacecraft.getRadiationParametersDrivers();
  435.     }

  437.     /** Compute min of two values, one double and one field element.
  438.      * @param d double value
  439.      * @param f field element
  440.      * @param <T> type of the field elements
  441.      * @return min value
  442.      */
  443.     private <T extends CalculusFieldElement<T>> T min(final double d, final T f) {
  444.         return (f.getReal() > d) ? f.getField().getZero().newInstance(d) : f;
  445.     }

  447.     /** Compute max of two values, one double and one field element.
  448.      * @param d double value
  449.      * @param f field element
  450.      * @param <T> type of the field elements
  451.      * @return max value
  452.      */
  453.     private <T extends CalculusFieldElement<T>> T max(final double d, final T f) {
  454.         return (f.getReal() <= d) ? f.getField().getZero().newInstance(d) : f;
  455.     }

  457. }
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