1 /*
2 * Unit Solar
3 * Author: Dr TS Kelso
4 * Original Version: 1990 Jul 29
5 * Current Revision: 1999 Nov 27
6 * Version: 1.30
7 * Copyright: 1990-1999, All Rights Reserved
8 *
9 * Ported to C by: Neoklis Kyriazis April 1 2001
10 */
11
12 #include "sgp4sdp4.h"
13
14 /* Calculates solar position vector */
15 void
Calculate_Solar_Position(double _time,vector_t * solar_vector)16 Calculate_Solar_Position(double _time, vector_t *solar_vector)
17 {
18 double mjd,year,T,M,L,e,C,O,Lsa,nu,R,eps;
19
20 mjd = _time - 2415020.0;
21 year = 1900 + mjd/365.25;
22 T = (mjd + Delta_ET(year)/secday)/36525.0;
23 M = Radians(Modulus(358.47583 + Modulus(35999.04975*T,360.0)
24 - (0.000150 + 0.0000033*T)*Sqr(T),360.0));
25 L = Radians(Modulus(279.69668 + Modulus(36000.76892*T,360.0)
26 + 0.0003025*Sqr(T),360.0));
27 e = 0.01675104 - (0.0000418 + 0.000000126*T)*T;
28 C = Radians((1.919460 - (0.004789 + 0.000014*T)*T)*sin(M)
29 + (0.020094 - 0.000100*T)*sin(2*M) + 0.000293*sin(3*M));
30 O = Radians(Modulus(259.18 - 1934.142*T,360.0));
31 Lsa = Modulus(L + C - Radians(0.00569 - 0.00479*sin(O)),twopi);
32 nu = Modulus(M + C,twopi);
33 R = 1.0000002*(1 - Sqr(e))/(1 + e*cos(nu));
34 eps = Radians(23.452294 - (0.0130125 + (0.00000164 -
35 0.000000503*T)*T)*T + 0.00256*cos(O));
36 R = AU*R;
37 solar_vector->x = R*cos(Lsa);
38 solar_vector->y = R*sin(Lsa)*cos(eps);
39 solar_vector->z = R*sin(Lsa)*sin(eps);
40 solar_vector->w = R;
41 } /*Procedure Calculate_Solar_Position*/
42
43 /*------------------------------------------------------------------*/
44
45 /* Calculates stellite's eclipse status and depth */
46 int
Sat_Eclipsed(vector_t * pos,vector_t * sol,double * depth)47 Sat_Eclipsed(vector_t *pos, vector_t *sol, double *depth)
48 {
49 double sd_sun, sd_earth, delta;
50 vector_t Rho, earth;
51
52 /* Determine partial eclipse */
53 sd_earth = ArcSin(xkmper/pos->w);
54 Vec_Sub(sol,pos,&Rho);
55 sd_sun = ArcSin(__sr__/Rho.w);
56 Scalar_Multiply(-1,pos,&earth);
57 delta = Angle(sol,&earth);
58 *depth = sd_earth - sd_sun - delta;
59 if( sd_earth < sd_sun )
60 return( 0 );
61 else
62 if( *depth >= 0 )
63 return( 1 );
64 else
65 return( 0 );
66
67 } /*Function Sat_Eclipsed*/
68
69 /*------------------------------------------------------------------*/
70