Task: Orbital elements





Java: public class OrbitalElements {
    private static class Vector {
        private double x, y, z;
 
        public Vector(double x, double y, double z) {
            this.x = x;
            this.y = y;
            this.z = z;
        }
 
        public Vector plus(Vector rhs) {
            return new Vector(x + rhs.x, y + rhs.y, z + rhs.z);
        }
 
        public Vector times(double s) {
            return new Vector(s * x, s * y, s * z);
        }
 
        public Vector div(double d) {
            return new Vector(x / d, y / d, z / d);
        }
 
        public double abs() {
            return Math.sqrt(x * x + y * y + z * z);
        }
 
        @Override
        public String toString() {
            return String.format("(%.16f, %.16f, %.16f)", x, y, z);
        }
    }
 
    private static Vector mulAdd(Vector v1, Double x1, Vector v2, Double x2) {
        return v1.times(x1).plus(v2.times(x2));
    }
 
    private static Vector[] rotate(Vector i, Vector j, double alpha) {
        return new Vector[]{
            mulAdd(i, Math.cos(alpha), j, Math.sin(alpha)),
            mulAdd(i, -Math.sin(alpha), j, Math.cos(alpha))
        };
    }
 
    private static Vector[] orbitalStateVectors(
        double semimajorAxis, double eccentricity, 
        double inclination, double longitudeOfAscendingNode, 
        double argumentOfPeriapsis, double trueAnomaly
    ) {
        Vector i = new Vector(1, 0, 0);
        Vector j = new Vector(0, 1, 0);
        Vector k = new Vector(0, 0, 1);
 
        Vector[] p = rotate(i, j, longitudeOfAscendingNode);
        i = p[0];
        j = p[1];
        p = rotate(j, k, inclination);
        j = p[0];
        p = rotate(i, j, argumentOfPeriapsis);
        i = p[0];
        j = p[1];
 
        double l = (eccentricity == 1.0) ? 2.0 : 1.0 - eccentricity * eccentricity;
        l *= semimajorAxis;
        double c = Math.cos(trueAnomaly);
        double s = Math.sin(trueAnomaly);
        double r = l / (1.0 + eccentricity * c);
        double rprime = s * r * r / l;
        Vector position = mulAdd(i, c, j, s).times(r);
        Vector speed = mulAdd(i, rprime * c - r * s, j, rprime * s + r * c);
        speed = speed.div(speed.abs());
        speed = speed.times(Math.sqrt(2.0 / r - 1.0 / semimajorAxis));
 
        return new Vector[]{position, speed};
    }
 
    public static void main(String[] args) {
        Vector[] ps = orbitalStateVectors(1.0, 0.1, 0.0, 355.0 / (113.0 * 6.0), 0.0, 0.0);
        System.out.printf("Position : %s\n", ps[0]);
        System.out.printf("Speed : %s\n", ps[1]);
    }
}



Python: import math

class Vector:
    def __init__(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z

    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y, self.z + other.z)

    def __mul__(self, other):
        return Vector(self.x * other, self.y * other, self.z * other)

    def __div__(self, other):
        return Vector(self.x / other, self.y / other, self.z / other)

    def __str__(self):
        return '({x}, {y}, {z})'.format(x=self.x, y=self.y, z=self.z)

    def abs(self):
        return math.sqrt(self.x*self.x + self.y*self.y + self.z*self.z)

def mulAdd(v1, x1, v2, x2):
    return v1 * x1 + v2 * x2

def rotate(i, j, alpha):
    return [mulAdd(i,math.cos(alpha),j,math.sin(alpha)), mulAdd(i,-math.sin(alpha),j,math.cos(alpha))]

def orbitalStateVectors(semimajorAxis, eccentricity, inclination, longitudeOfAscendingNode, argumentOfPeriapsis, trueAnomaly):
    i = Vector(1, 0, 0)
    j = Vector(0, 1, 0)
    k = Vector(0, 0, 1)

    p = rotate(i, j, longitudeOfAscendingNode)
    i = p[0]
    j = p[1]
    p = rotate(j, k, inclination)
    j = p[0]
    p  =rotate(i, j, argumentOfPeriapsis)
    i = p[0]
    j = p[1]

    l = 2.0 if (eccentricity == 1.0) else 1.0 - eccentricity * eccentricity
    l *= semimajorAxis
    c = math.cos(trueAnomaly)
    s = math.sin(trueAnomaly)
    r = 1 / (1.0 + eccentricity * c)
    rprime = s * r * r / l
    position = mulAdd(i, c, j, s) * r
    speed = mulAdd(i, rprime * c - r * s, j, rprime * s + r * c)
    speed = speed / speed.abs()
    speed = speed * math.sqrt(2.0 / r - 1.0 / semimajorAxis)

    return [position, speed]

ps = orbitalStateVectors(1.0, 0.1, 0.0, 355.0 / (113.0 * 6.0), 0.0, 0.0)
print "Position :", ps[0]
print "Speed    :", ps[1]