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/*
* Unit Solar
* Author: Dr TS Kelso
* Original Version: 1990 Jul 29
* Current Revision: 1999 Nov 27
* Version: 1.30
* Copyright: 1990-1999, All Rights Reserved
*
* Ported to C by: Neoklis Kyriazis April 1 2001
*/
#include "sgp4sdp4.h"
/* Calculates solar position vector */
void
Calculate_Solar_Position(double _time, vector_t *solar_vector)
{
double mjd,year,T,M,L,e,C,O,Lsa,nu,R,eps;
mjd = _time - 2415020.0;
year = 1900 + mjd/365.25;
T = (mjd + Delta_ET(year)/secday)/36525.0;
M = Radians(Modulus(358.47583 + Modulus(35999.04975*T,360.0)
- (0.000150 + 0.0000033*T)*Sqr(T),360.0));
L = Radians(Modulus(279.69668 + Modulus(36000.76892*T,360.0)
+ 0.0003025*Sqr(T),360.0));
e = 0.01675104 - (0.0000418 + 0.000000126*T)*T;
C = Radians((1.919460 - (0.004789 + 0.000014*T)*T)*sin(M)
+ (0.020094 - 0.000100*T)*sin(2*M) + 0.000293*sin(3*M));
O = Radians(Modulus(259.18 - 1934.142*T,360.0));
Lsa = Modulus(L + C - Radians(0.00569 - 0.00479*sin(O)),twopi);
nu = Modulus(M + C,twopi);
R = 1.0000002*(1 - Sqr(e))/(1 + e*cos(nu));
eps = Radians(23.452294 - (0.0130125 + (0.00000164 -
0.000000503*T)*T)*T + 0.00256*cos(O));
R = AU*R;
solar_vector->x = R*cos(Lsa);
solar_vector->y = R*sin(Lsa)*cos(eps);
solar_vector->z = R*sin(Lsa)*sin(eps);
solar_vector->w = R;
} /*Procedure Calculate_Solar_Position*/
/*------------------------------------------------------------------*/
/* Calculates stellite's eclipse status and depth */
int
Sat_Eclipsed(vector_t *pos, vector_t *sol, double *depth)
{
double sd_sun, sd_earth, delta;
vector_t Rho, earth;
/* Determine partial eclipse */
sd_earth = ArcSin(xkmper/pos->w);
Vec_Sub(sol,pos,&Rho);
sd_sun = ArcSin(__sr__/Rho.w);
Scalar_Multiply(-1,pos,&earth);
delta = Angle(sol,&earth);
*depth = sd_earth - sd_sun - delta;
if( sd_earth < sd_sun )
return( 0 );
else
if( *depth >= 0 )
return( 1 );
else
return( 0 );
} /*Function Sat_Eclipsed*/
/*------------------------------------------------------------------*/
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