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Add orbit extensions to public API (fixes #32)
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@HebaruSan
HebaruSan committed Nov 9, 2022
1 parent 3b1a6cc commit 7736a98
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Showing 2 changed files with 65 additions and 42 deletions.
5 changes: 5 additions & 0 deletions GameData/Astrogator/Astrogator-Changelog.cfg
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,11 @@ KERBALCHANGELOG
version = 1.0.0
versionName = Quite a show
versionKSP = 1.12
CHANGE
{
change = Add orbit extensions to public API
type = Add
}
}
VERSION
{
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102 changes: 60 additions & 42 deletions Source/PhysicsTools.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -441,10 +441,8 @@ public static double BurnToEscape(CelestialBody parent, Orbit fromOrbit, double
/// Speed change in m/s needed
/// </returns>
public static double BurnToEscape(CelestialBody parent, double periapsis, double speedAtInfinity)
{
double preBurnSpeed = SpeedAtPeriapsis(parent, periapsis, periapsis);
return SpeedToExitSOI(parent, periapsis, speedAtInfinity) - preBurnSpeed;
}
=> SpeedToExitSOI(parent, periapsis, speedAtInfinity)
- SpeedAtPeriapsis(parent, periapsis, periapsis);

/// <summary>
/// Calculate the absolute time when a satellite will be a given angle away from
Expand Down Expand Up @@ -647,7 +645,7 @@ public static Vector3d DeltaVToMatchPlanes(Orbit currentOrbit, Orbit target, dou
internal static class MuUtils
{
// acosh(x) = log(x + sqrt(x^2 - 1))
internal static double Acosh(double x)
public static double Acosh(double x)
=> Math.Log(x + Math.Sqrt(x * x - 1));
}

Expand All @@ -665,7 +663,11 @@ public static Vector3d SwapYZ(this Vector3d v)
=> new Vector3d(v.x, v.z, v.y);
}

internal static class MuMech_OrbitExtensions
/// <summary>
/// Extensions to calculate the AN and DN.
/// Borrowed from KAC's borrowing from r4m0n's MJ plugin.
/// </summary>
public static class MuMech_OrbitExtensions
{

/// <summary>
Expand Down Expand Up @@ -708,19 +710,53 @@ public static Vector3d SwappedRelativePositionAtUT(this Orbit o, double UT)
// These "Swapped" functions translate preexisting Orbit class functions into world space.
// The Orbit class uses a coordinate system in which the Y and Z coordinates are swapped.

// Normalized vector perpendicular to the orbital plane
// convention: as you look down along the orbit normal, the satellite revolves counterclockwise
internal static Vector3d SwappedOrbitNormal(this Orbit o)
/// <summary>
/// Normalized vector perpendicular to the orbital plane
/// convention: as you look down along the orbit normal, the satellite revolves counterclockwise
/// </summary>
/// <param name="o">An orbit</param>
/// <returns>Normal vector of the orbit in world space</returns>
public static Vector3d SwappedOrbitNormal(this Orbit o)
=> -o.GetOrbitNormal().SwapYZ().normalized;

/// <summary>
/// Returns the next time at which a will cross its ascending node with b.
/// For elliptical orbits this is a time between UT and UT + a.period.
/// For hyperbolic orbits this can be any time, including a time in the past if
/// the ascending node is in the past.
/// NOTE: this function will throw an ArgumentException if a is a hyperbolic orbit and the "ascending node"
/// occurs at a true anomaly that a does not actually ever attain
/// </summary>
/// <param name="a">Our orbit</param>
/// <param name="b">The other orbit</param>
/// <param name="UT">Minimum time of AN</param>
/// <returns>Time of AN</returns>
public static double TimeOfAscendingNode(this Orbit a, Orbit b, double UT)
=> a.TimeOfTrueAnomaly(a.AscendingNodeTrueAnomaly(b), UT);

/// <summary>
/// Returns the next time at which a will cross its descending node with b.
/// For elliptical orbits this is a time between UT and UT + a.period.
/// For hyperbolic orbits this can be any time, including a time in the past if
/// the descending node is in the past.
/// NOTE: this function will throw an ArgumentException if a is a hyperbolic orbit and the "descending node"
/// occurs at a true anomaly that a does not actually ever attain
/// </summary>
/// <param name="a">Our orbit</param>
/// <param name="b">The other orbit</param>
/// <param name="UT">Minimum time of DN</param>
/// <returns>Time of DN</returns>
public static double TimeOfDescendingNode(this Orbit a, Orbit b, double UT)
=> a.TimeOfTrueAnomaly(a.DescendingNodeTrueAnomaly(b), UT);

// Mean motion is rate of increase of the mean anomaly
internal static double MeanMotion(this Orbit o)
private static double MeanMotion(this Orbit o)
=> Math.Sqrt(o.referenceBody.gravParameter / Math.Abs(Math.Pow(o.semiMajorAxis, 3)));

// The mean anomaly of the orbit.
// For elliptical orbits, the value return is always between 0 and Tau
// For hyperbolic orbits, the value can be any number.
internal static double MeanAnomalyAtUT(this Orbit o, double UT)
private static double MeanAnomalyAtUT(this Orbit o, double UT)
=> o.eccentricity < 1
? clamp(o.meanAnomalyAtEpoch + o.MeanMotion() * (UT - o.epoch))
: o.meanAnomalyAtEpoch + o.MeanMotion() * (UT - o.epoch);
Expand All @@ -729,7 +765,7 @@ internal static double MeanAnomalyAtUT(this Orbit o, double UT)
// For elliptical orbits, this will be a time between UT and UT + o.period
// For hyperbolic orbits, this can be any time, including a time in the past, if
// the given mean anomaly occurred in the past
internal static double UTAtMeanAnomaly(this Orbit o, double meanAnomaly, double UT)
private static double UTAtMeanAnomaly(this Orbit o, double meanAnomaly, double UT)
{
double currentMeanAnomaly = o.MeanAnomalyAtUT(UT);
double meanDifference = meanAnomaly - currentMeanAnomaly;
Expand All @@ -740,18 +776,18 @@ internal static double UTAtMeanAnomaly(this Orbit o, double meanAnomaly, double

// True anomaly (in a's orbit) at which a crosses its ascending node
// with b's orbit.
internal static double AscendingNodeTrueAnomaly(this Orbit a, Orbit b)
private static double AscendingNodeTrueAnomaly(this Orbit a, Orbit b)
=> a.TrueAnomalyFromVector(Vector3d.Cross(b.SwappedOrbitNormal(), a.SwappedOrbitNormal()));

// True anomaly (in a's orbit) at which a crosses its descending node
// with b's orbit.
internal static double DescendingNodeTrueAnomaly(this Orbit a, Orbit b)
private static double DescendingNodeTrueAnomaly(this Orbit a, Orbit b)
=> a.TrueAnomalyFromVector(Vector3d.Cross(a.SwappedOrbitNormal(), b.SwappedOrbitNormal()));

// Converts a direction, specified by a Vector3d, into a true anomaly.
// The vector is projected into the orbital plane and then the true anomaly is
// computed as the angle this vector makes with the vector pointing to the periapsis.
internal static double TrueAnomalyFromVector(this Orbit o, Vector3d vec)
private static double TrueAnomalyFromVector(this Orbit o, Vector3d vec)
=> clamp(o.GetTrueAnomalyOfZupVector(vec));

// Originally by Zool, revised by The_Duck
Expand All @@ -760,7 +796,7 @@ internal static double TrueAnomalyFromVector(this Orbit o, Vector3d vec)
// For hyperbolic orbits the returned value can be any number.
// NOTE: For a hyperbolic orbit, if a true anomaly is requested that does not exist (a true anomaly
// past the true anomaly of the asymptote) then an ArgumentException is thrown
internal static double GetEccentricAnomalyAtTrueAnomaly(this Orbit o, double trueAnomaly)
private static double GetEccentricAnomalyAtTrueAnomaly(this Orbit o, double trueAnomaly)
{
double e = o.eccentricity;
double cosTA = Math.Cos(trueAnomaly);
Expand Down Expand Up @@ -789,43 +825,25 @@ internal static double GetEccentricAnomalyAtTrueAnomaly(this Orbit o, double tru
}
}

///Originally by Zool, revised by The_Duck
///Converts an eccentric anomaly into a mean anomaly.
///For an elliptical orbit, the returned value is between 0 and Tau
///For a hyperbolic orbit, the returned value is any number
internal static double GetMeanAnomalyAtEccentricAnomaly(this Orbit o, double E)
// Originally by Zool, revised by The_Duck
// Converts an eccentric anomaly into a mean anomaly.
// For an elliptical orbit, the returned value is between 0 and Tau
// For a hyperbolic orbit, the returned value is any number
private static double GetMeanAnomalyAtEccentricAnomaly(this Orbit o, double E)
=> o.eccentricity < 1
// Elliptical orbits
? clamp(E - (o.eccentricity * Math.Sin(E)))
// Hyperbolic orbits
: (o.eccentricity * Math.Sinh(E)) - E;

///NOTE: this function can throw an ArgumentException, if o is a hyperbolic orbit with an eccentricity
///large enough that it never attains the given true anomaly
internal static double TimeOfTrueAnomaly(this Orbit o, double trueAnomaly, double UT)
// NOTE: this function can throw an ArgumentException, if o is a hyperbolic orbit with an eccentricity
// large enough that it never attains the given true anomaly
private static double TimeOfTrueAnomaly(this Orbit o, double trueAnomaly, double UT)
=> o.UTAtMeanAnomaly(
o.GetMeanAnomalyAtEccentricAnomaly(
o.GetEccentricAnomalyAtTrueAnomaly(trueAnomaly)),
UT);

///Returns the next time at which a will cross its ascending node with b.
///For elliptical orbits this is a time between UT and UT + a.period.
///For hyperbolic orbits this can be any time, including a time in the past if
///the ascending node is in the past.
///NOTE: this function will throw an ArgumentException if a is a hyperbolic orbit and the "ascending node"
///occurs at a true anomaly that a does not actually ever attain
public static double TimeOfAscendingNode(this Orbit a, Orbit b, double UT)
=> a.TimeOfTrueAnomaly(a.AscendingNodeTrueAnomaly(b), UT);

///Returns the next time at which a will cross its descending node with b.
///For elliptical orbits this is a time between UT and UT + a.period.
///For hyperbolic orbits this can be any time, including a time in the past if
///the descending node is in the past.
///NOTE: this function will throw an ArgumentException if a is a hyperbolic orbit and the "descending node"
///occurs at a true anomaly that a does not actually ever attain
public static double TimeOfDescendingNode(this Orbit a, Orbit b, double UT)
=> a.TimeOfTrueAnomaly(a.DescendingNodeTrueAnomaly(b), UT);

// End code copied from Kerbal Alarm Clock
}

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