Fix/integrator (#311)

* Add geosynchronous orbit computation and validation for longitude and latitude

* Bump version to 9.0.0-preview-4 for IO.Astrodynamics and 0.9.0.0-preview-4 for CLI

Author: sylvain-guillet

IO.Astrodynamics.Net/IO.Astrodynamics.CLI/IO.Astrodynamics.CLI.csproj

@@ -9,7 +9,7 @@
         <FileVersion>0.0.1</FileVersion>
         <PackAsTool>true</PackAsTool>
         <ToolCommandName>astro</ToolCommandName>
-        <Version>0.9.0.0-preview-3</Version>
+        <Version>0.9.0.0-preview-4</Version>
         <Title>Astrodynamics command line interface</Title>
         <Authors>Sylvain Guillet</Authors>
         <Description>This CLI allows end user to exploit IO.Astrodynamics framework </Description>

IO.Astrodynamics.Net/IO.Astrodynamics.Tests/Body/CelestialBodyTests.cs

@@ -270,6 +270,21 @@ public void GeosynchronousOrbit2()
         Assert.Equal(new Vector3(-1171.3783810266016, -2842.7805399479103, 2.354430257176734), orbit.ToStateVector().Velocity, TestHelpers.VectorComparer);
     }
 
+    [Fact]
+    public void GeosynchronousOrbitThrowsOnInvalidLongitude()
+    {
+        var epoch = new TimeSystem.Time(new DateTime(2021, 1, 1, 0, 0, 0, DateTimeKind.Unspecified), TimeFrame.TDBFrame);
+        Assert.Throws<ArgumentOutOfRangeException>(() => TestHelpers.EarthAtJ2000.GeosynchronousOrbit(4.0, 0.0, epoch));
+        Assert.Throws<ArgumentOutOfRangeException>(() => TestHelpers.EarthAtJ2000.GeosynchronousOrbit(-4.0, 0.0, epoch));
+    }
+
+    [Fact]
+    public void GeosynchronousOrbitThrowsOnInvalidLatitude()
+    {
+        var epoch = new TimeSystem.Time(new DateTime(2021, 1, 1, 0, 0, 0, DateTimeKind.Unspecified), TimeFrame.TDBFrame);
+        Assert.Throws<ArgumentOutOfRangeException>(() => TestHelpers.EarthAtJ2000.GeosynchronousOrbit(0.0, 2.0, epoch));
+        Assert.Throws<ArgumentOutOfRangeException>(() => TestHelpers.EarthAtJ2000.GeosynchronousOrbit(0.0, -2.0, epoch));
+    }
 
     [Fact]
     public void TrueSolarDayJan()

IO.Astrodynamics.Net/IO.Astrodynamics/Body/CelestialBody.cs

@@ -244,16 +244,32 @@ public double AngularVelocity(Time epoch)
         return (2.0 * Constants.PI) / siderealRotationPeriod.TotalSeconds;
     }
 
+    /// <summary>
+    /// Computes the Keplerian elements for a geosynchronous orbit at the specified longitude and latitude.
+    /// The latitude parameter defines the orbital inclination — for non-zero latitude, the satellite follows
+    /// an inclined geosynchronous orbit tracing a figure-eight ground track. The specified (longitude, latitude)
+    /// is the sub-satellite point only at the given epoch.
+    /// </summary>
+    /// <param name="longitude">Planetocentric longitude in radians, in range [-π, π].</param>
+    /// <param name="latitude">Planetocentric latitude in radians, in range [-π/2, π/2]. Defines the orbital inclination.</param>
+    /// <param name="epoch">The epoch at which to compute the orbit.</param>
+    /// <returns>Keplerian elements for the geosynchronous orbit.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when longitude or latitude is out of range.</exception>
     public KeplerianElements GeosynchronousOrbit(double longitude, double latitude, Time epoch)
     {
+        if (longitude < -Constants.PI || longitude > Constants.PI)
+            throw new ArgumentOutOfRangeException(nameof(longitude), longitude, "Longitude must be in range [-π, π] radians.");
+        if (latitude < -Constants.PI2 || latitude > Constants.PI2)
+            throw new ArgumentOutOfRangeException(nameof(latitude), latitude, "Latitude must be in range [-π/2, π/2] radians.");
+
         var sideralRotation2 = System.Math.Pow(SideralRotationPeriod(epoch).TotalSeconds, 2);
         var radius = System.Math.Cbrt((GM * sideralRotation2) / (4 * Constants.PI * Constants.PI));
         var bodyfFixedCoordinates = new Planetocentric(longitude, latitude, radius).ToCartesianCoordinates();
         var icrfPos = bodyfFixedCoordinates.Rotate(Frame.ToFrame(Frame.ICRF, epoch).Rotation);
         var icrfRot = Vector3.VectorZ.Rotate(Frame.ToFrame(Frame.ICRF, epoch).Rotation);
         var inertialVelocity = icrfRot.Cross(icrfPos).Normalize() * System.Math.Sqrt(GM / radius);
         var sv = new StateVector(icrfPos, inertialVelocity, this, epoch, Frame.ICRF);
-        return new KeplerianElements(radius, 0.0, sv.Inclination(), sv.AscendingNode(), (sv.ArgumentOfPeriapsis() + sv.MeanAnomaly()) % Constants._2PI, 0.0, this, epoch, sv.Frame);
+        return new KeplerianElements(radius, 0.0, sv.Inclination(), sv.AscendingNode(), sv.ArgumentOfPeriapsis() + sv.MeanAnomaly(), 0.0, this, epoch, sv.Frame);
     }
 
     /// <summary>

IO.Astrodynamics.Net/IO.Astrodynamics/IO.Astrodynamics.csproj

@@ -12,7 +12,7 @@
 
         <!-- NuGet package metadata (replaces IO.Astrodynamics.nuspec) -->
         <PackageId>IO.Astrodynamics</PackageId>
-        <Version>9.0.0-preview-3</Version>
+        <Version>9.0.0-preview-4</Version>
         <Authors>Sylvain Guillet</Authors>
         <Copyright>Sylvain Guillet</Copyright>
         <Title>IO Astrodynamics framework</Title>