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#include <math.h>
#include "norad.h"
#include "norad_in.h"
#define ao params[0]
#define qo params[1]
#define xlo params[2]
#define d1o params[3]
#define d2o params[4]
#define d3o params[5]
#define d4o params[6]
#define omgdt params[7]
#define xnodot params[8]
#define c5 params[9]
#define c6 params[10]
void DLL_FUNC SGP_init( double *params, const tle_t *tle)
{
double c1, c2, c3, c4, r1, cosio, sinio, a1, d1, po, po2no;
c1 = ck2*1.5;
c2 = ck2/4.;
c3 = ck2/2.;
r1 = ae;
c4 = xj3*(r1*(r1*r1))/(ck2*4.);
cosio = cos(tle->xincl);
sinio = sin(tle->xincl);
a1 = pow( xke / tle->xno, two_thirds);
d1 = c1/a1/a1*(cosio*3.*cosio-1.)/pow( 1.-tle->eo*tle->eo, 1.5);
ao = a1*(1.-d1*.33333333333333331-d1*d1-d1*
1.654320987654321*d1*d1);
po = ao*(1.-tle->eo*tle->eo);
qo = ao*(1.-tle->eo);
xlo = tle->xmo+tle->omegao+tle->xnodeo;
d1o = c3*sinio*sinio;
d2o = c2*(cosio*7.*cosio-1.);
d3o = c1*cosio;
d4o = d3o*sinio;
po2no = tle->xno/(po*po);
omgdt = c1*po2no*(cosio*5.*cosio-1.);
xnodot = d3o*-2.*po2no;
c5 = c4*.5*sinio*(cosio*5.+3.)/(cosio+1.);
c6 = c4*sinio;
}
int DLL_FUNC SGP( const double tsince, const tle_t *tle, const double *params,
double *pos, double *vel)
{
double
temp, rdot, cosu, sinu, cos2u, sin2u, a, e,
p, rr, u, ecose, esine, omgas, cosik, xinck,
sinik, axnsl, aynsl,
sinuk, rvdot, cosuk, coseo1, sineo1, pl,
rk, uk, xl, su, ux, uy, uz, vx, vy, vz, pl2,
xnodek, cosnok, xnodes, el2, eo1, r1, sinnok,
xls, xmx, xmy, tem2, tem5;
const double chicken_factor_on_eccentricity = 1.e-6;
int i, rval = 0;
/* Update for secular gravity and atmospheric drag */
a = tle->xno+(tle->xndt2o*2.+tle->xndd6o*3.*tsince)*tsince;
if( a < 0.)
rval = SXPX_ERR_NEGATIVE_MAJOR_AXIS;
e = e6a;
if( e > 1. - chicken_factor_on_eccentricity)
rval = SXPX_ERR_NEARLY_PARABOLIC;
if( rval)
{
for( i = 0; i < 3; i++)
{
pos[i] = 0.;
if( vel)
vel[i] = 0.;
}
return( rval);
}
a = ao * pow( tle->xno / a, two_thirds);
if( a * (1. - e) < 1. && a * (1. + e) < 1.) /* entirely within earth */
rval = SXPX_WARN_ORBIT_WITHIN_EARTH; /* remember, e can be negative */
if( a * (1. - e) < 1. || a * (1. + e) < 1.) /* perigee within earth */
rval = SXPX_WARN_PERIGEE_WITHIN_EARTH;
if (a > qo) e = 1.-qo/a;
p = a*(1.-e*e);
xnodes = tle->xnodeo+xnodot*tsince;
omgas = tle->omegao+omgdt*tsince;
r1 = xlo+(tle->xno+omgdt+xnodot+
(tle->xndt2o+tle->xndd6o*tsince)*tsince)*tsince;
xls = FMod2p(r1);
/* Long period periodics */
axnsl = e*cos(omgas);
aynsl = e*sin(omgas)-c6/p;
r1 = xls-c5/p*axnsl;
xl = FMod2p(r1);
/* Solve Kepler's equation */
r1 = xl-xnodes;
u = FMod2p(r1);
eo1 = u;
tem5 = 1.;
i = 0;
do
{
sineo1 = sin(eo1);
coseo1 = cos(eo1);
if (fabs(tem5) < e6a) break;
tem5 = 1.-coseo1*axnsl-sineo1*aynsl;
tem5 = (u-aynsl*coseo1+axnsl*sineo1-eo1)/tem5;
tem2 = fabs(tem5);
if (tem2 > 1.) tem5 = tem2/tem5;
eo1 += tem5;
}
while(i++ < 10);
/* Short period preliminary quantities */
ecose = axnsl*coseo1+aynsl*sineo1;
esine = axnsl*sineo1-aynsl*coseo1;
el2 = axnsl*axnsl+aynsl*aynsl;
pl = a*(1.-el2);
pl2 = pl*pl;
rr = a*(1.-ecose);
rdot = xke*sqrt(a)/rr*esine;
rvdot = xke*sqrt(pl)/rr;
temp = esine/(sqrt(1.-el2)+1.);
sinu = a/rr*(sineo1-aynsl-axnsl*temp);
cosu = a/rr*(coseo1-axnsl+aynsl*temp);
su = atan2(sinu, cosu);
/* Update for short periodics */
sin2u = (cosu+cosu)*sinu;
cos2u = 1.-2.*sinu*sinu;
rk = rr+d1o/pl*cos2u;
uk = su-d2o/pl2*sin2u;
xnodek = xnodes+d3o*sin2u/pl2;
xinck = tle->xincl+d4o/pl2*cos2u;
/* Orientation vectors */
sinuk = sin(uk);
cosuk = cos(uk);
sinnok = sin(xnodek);
cosnok = cos(xnodek);
sinik = sin(xinck);
cosik = cos(xinck);
xmx = -sinnok*cosik;
xmy = cosnok*cosik;
ux = xmx*sinuk+cosnok*cosuk;
uy = xmy*sinuk+sinnok*cosuk;
uz = sinik*sinuk;
vx = xmx*cosuk-cosnok*sinuk;
vy = xmy*cosuk-sinnok*sinuk;
vz = sinik*cosuk;
/* Position and velocity */
pos[0] = rk*ux*earth_radius_in_km;
pos[1] = rk*uy*earth_radius_in_km;
pos[2] = rk*uz*earth_radius_in_km;
if( vel)
{
vel[0] = (rdot*ux + rvdot * vx)*earth_radius_in_km;
vel[1] = (rdot*uy + rvdot * vy)*earth_radius_in_km;
vel[2] = (rdot*uz + rvdot * vz)*earth_radius_in_km;
}
return( rval);
} /* SGP */
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