/// <summary>
///计算航天器是否在太阳光照中。1 为是， 0 为否。 可用于计算太阳光压。
/// Computes the fractional illumination of a spacecraft in the
/// vicinity of the Earth assuming a cylindrical shadow model
/// </summary>
/// <param name="satXyz_m">Spacecraft position vector [m]</param>
/// <param name="sunXyz_m"> Sun position vector [m]</param>
/// <returns> Illumination factor:
/// nu=0 Spacecraft in Earth shadow
/// nu=1 Spacecraft fully illuminated by the Sun</returns>
public static double Illumination(Geo.Algorithm.Vector satXyz_m, Geo.Algorithm.Vector sunXyz_m)
{
Geo.Algorithm.Vector e_Sun = sunXyz_m.DirectionUnit(); // Sun direction unit vector
double s = satXyz_m.Dot(e_Sun); // Projection of s/c position
return((s > 0 || (satXyz_m - s * e_Sun).Norm() > OrbitConsts.RadiusOfEarth) ? 1.0 : 0.0);
}