Merge branch 'develop' into issue-818

Fixes #818

src/changes/changes.xml

@@ -24,6 +24,9 @@
       <action dev="bryan" type="fix" issue="818">
         Use observed solar flux instead of adjusted in DTM2000 model.
       </action>
+      <action dev="evan" type="fix" issue="798">
+        Allow DSST event detection when propagating backwards.
+      </action>
       <action dev="evan" type="remove" issue="586">
         Remove InertialProvider.EME2000_ALIGNED, Propagator.DEFAULT_LAW. Use
         InertialProvider.of(Frame).

src/main/java/org/orekit/propagation/semianalytical/dsst/forces/AbstractGaussianContribution.java

@@ -1820,10 +1820,14 @@ public abstract class AbstractGaussianContribution implements DSSTForceModel {
             final Slot slot = new Slot(jMax, interpolationPoints);
             final AbsoluteDate first = meanStates[0].getDate();
             final AbsoluteDate last = meanStates[meanStates.length - 1].getDate();
-            if (first.compareTo(last) <= 0) {
+            final int compare = first.compareTo(last);
+            if (compare < 0) {
                 slots.addValidAfter(slot, first);
-            } else {
+            } else if (compare > 0) {
                 slots.addValidBefore(slot, first);
+            } else {
+                // single date, valid for all time
+                slots.addValidAfter(slot, AbsoluteDate.PAST_INFINITY);
             }
             return slot;
         }

src/main/java/org/orekit/propagation/semianalytical/dsst/forces/DSSTTesseral.java

@@ -1733,10 +1733,14 @@ public class DSSTTesseral implements DSSTForceModel {
             final Slot         slot  = new Slot(mMax, jMax, interpolationPoints);
             final AbsoluteDate first = meanStates[0].getDate();
             final AbsoluteDate last  = meanStates[meanStates.length - 1].getDate();
-            if (first.compareTo(last) <= 0) {
+            final int compare = first.compareTo(last);
+            if (compare < 0) {
                 slots.addValidAfter(slot, first);
-            } else {
+            } else if (compare > 0) {
                 slots.addValidBefore(slot, first);
+            } else {
+                // single date, valid for all time
+                slots.addValidAfter(slot, AbsoluteDate.PAST_INFINITY);
             }
             return slot;
         }

src/main/java/org/orekit/propagation/semianalytical/dsst/forces/DSSTThirdBody.java

@@ -3087,10 +3087,14 @@ public class DSSTThirdBody implements DSSTForceModel {
             final Slot         slot  = new Slot(jMax, interpolationPoints);
             final AbsoluteDate first = meanStates[0].getDate();
             final AbsoluteDate last  = meanStates[meanStates.length - 1].getDate();
-            if (first.compareTo(last) <= 0) {
+            final int compare = first.compareTo(last);
+            if (compare < 0) {
                 slots.addValidAfter(slot, first);
-            } else {
+            } else if (compare > 0) {
                 slots.addValidBefore(slot, first);
+            } else {
+                // single date, valid for all time
+                slots.addValidAfter(slot, AbsoluteDate.PAST_INFINITY);
             }
             return slot;
         }

src/main/java/org/orekit/propagation/semianalytical/dsst/forces/DSSTZonal.java

@@ -1481,10 +1481,14 @@ public class DSSTZonal implements DSSTForceModel {
             final Slot         slot  = new Slot(maxFrequencyShortPeriodics, interpolationPoints);
             final AbsoluteDate first = meanStates[0].getDate();
             final AbsoluteDate last  = meanStates[meanStates.length - 1].getDate();
-            if (first.compareTo(last) <= 0) {
+            final int compare = first.compareTo(last);
+            if (compare < 0) {
                 slots.addValidAfter(slot, first);
-            } else {
+            } else if (compare > 0) {
                 slots.addValidBefore(slot, first);
+            } else {
+                // single date, valid for all time
+                slots.addValidAfter(slot, AbsoluteDate.PAST_INFINITY);
             }
             return slot;
         }

src/test/java/org/orekit/propagation/events/CloseEventsDsstOsculatingTest.java

+/*
+ * Licensed to the Hipparchus project under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.propagation.events;
+
+import org.hipparchus.ode.ODEIntegrator;
+import org.hipparchus.ode.nonstiff.DormandPrince853Integrator;
+import org.orekit.bodies.CelestialBodyFactory;
+import org.orekit.propagation.PropagationType;
+import org.orekit.propagation.Propagator;
+import org.orekit.propagation.SpacecraftState;
+import org.orekit.propagation.semianalytical.dsst.DSSTPropagator;
+import org.orekit.propagation.semianalytical.dsst.forces.DSSTThirdBody;
+import org.orekit.utils.Constants;
+
+/** Test events with the DSST Propagator.
+*
+* @author Evan Ward
+*/
+public class CloseEventsDsstOsculatingTest extends CloseEventsAbstractTest {
+
+    @Override
+    public Propagator getPropagator(double stepSize) {
+        double[][] tol = DSSTPropagator.tolerances(1, initialOrbit);
+        ODEIntegrator integrator = new DormandPrince853Integrator(stepSize, stepSize, tol[0], tol[1]);
+        DSSTPropagator propagator = new DSSTPropagator(integrator, PropagationType.OSCULATING);
+        propagator.setInitialState(new SpacecraftState(initialOrbit));
+        double gm = Constants.EIGEN5C_EARTH_MU;
+        propagator.addForceModel(new DSSTThirdBody(CelestialBodyFactory.getMoon(), gm));
+        return propagator;
+    }
+
+}