solar.c

00001 /*
00002  * Unit Solar
00003  *           Author:  Dr TS Kelso
00004  * Original Version:  1990 Jul 29
00005  * Current Revision:  1999 Nov 27
00006  *          Version:  1.30
00007  *        Copyright:  1990-1999, All Rights Reserved
00008  *
00009  *   Ported to C by: Neoklis Kyriazis  April 1 2001
00010  */
00011 
00012 #include "sgp4sdp4.h"
00013 
00014 /* Calculates solar position vector */
00015 void
00016 Calculate_Solar_Position(double _time, vector_t *solar_vector)
00017 {
00018   double mjd,year,T,M,L,e,C,O,Lsa,nu,R,eps;
00019 
00020   mjd = _time - 2415020.0;
00021   year = 1900 + mjd/365.25;
00022   T = (mjd + Delta_ET(year)/secday)/36525.0;
00023   M = Radians(Modulus(358.47583 + Modulus(35999.04975*T,360.0)
00024               - (0.000150 + 0.0000033*T)*Sqr(T),360.0));
00025   L = Radians(Modulus(279.69668 + Modulus(36000.76892*T,360.0)
00026               + 0.0003025*Sqr(T),360.0));
00027   e = 0.01675104 - (0.0000418 + 0.000000126*T)*T;
00028   C = Radians((1.919460 - (0.004789 + 0.000014*T)*T)*sin(M)
00029           + (0.020094 - 0.000100*T)*sin(2*M) + 0.000293*sin(3*M));
00030   O = Radians(Modulus(259.18 - 1934.142*T,360.0));
00031   Lsa = Modulus(L + C - Radians(0.00569 - 0.00479*sin(O)),twopi);
00032   nu = Modulus(M + C,twopi);
00033   R = 1.0000002*(1 - Sqr(e))/(1 + e*cos(nu));
00034   eps = Radians(23.452294 - (0.0130125 + (0.00000164 -
00035         0.000000503*T)*T)*T + 0.00256*cos(O));
00036   R = SGPAU*R;
00037   solar_vector->x = R*cos(Lsa);
00038   solar_vector->y = R*sin(Lsa)*cos(eps);
00039   solar_vector->z = R*sin(Lsa)*sin(eps);
00040   solar_vector->w = R;
00041 } /*Procedure Calculate_Solar_Position*/
00042 
00043 /*------------------------------------------------------------------*/
00044 
00045 /* Calculates stellite's eclipse status and depth */
00046 int
00047 Sat_Eclipsed(vector_t *pos, vector_t *sol, double *depth)
00048 {
00049   double sd_sun, sd_earth, delta;
00050   vector_t Rho, earth;
00051 
00052   /* Determine partial eclipse */
00053   sd_earth = ArcSin(xkmper/pos->w);
00054   Vec_Sub(sol,pos,&Rho);
00055   sd_sun = ArcSin(__sr__/Rho.w);
00056   Scalar_Multiply(-1,pos,&earth);
00057   delta = Angle(sol,&earth);
00058   *depth = sd_earth - sd_sun - delta;
00059   if( sd_earth < sd_sun )
00060     return( 0 );
00061   else
00062     if( *depth >= 0 )
00063       return( 1 );
00064     else
00065       return( 0 );
00066 
00067 } /*Function Sat_Eclipsed*/
00068 
00069 /*------------------------------------------------------------------*/