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sgp4init.m
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sgp4init.m
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% -----------------------------------------------------------------------------
%
% procedure sgp4init
%
% this procedure initializes variables for sgp4.
%
% Author:
% Jeff Beck
% beckja@alumni.lehigh.edu
% 1.0 (aug 7, 2006) - update for paper dav
% original comments from Vallado C++ version:
% author : david vallado 719-573-2600 28 jun 2005
%
% inputs :
% satn - satellite number
% bstar - sgp4 type drag coefficient kg/m2er
% ecco - eccentricity
% epoch - epoch time in days from jan 0, 1950. 0 hr
% argpo - argument of perigee (output if ds)
% inclo - inclination
% mo - mean anomaly (output if ds)
% no - mean motion
% nodeo - right ascension of ascending node
%
% outputs :
% satrec - common values for subsequent calls
% return code - non-zero on error.
% 1 - mean elements, ecc >= 1.0 or ecc < -0.001 or a < 0.95 er
% 2 - mean motion less than 0.0
% 3 - pert elements, ecc < 0.0 or ecc > 1.0
% 4 - semi-latus rectum < 0.0
% 5 - epoch elements are sub-orbital
% 6 - satellite has decayed
%
% locals :
% CNODM , SNODM , COSIM , SINIM , COSOMM , SINOMM
% Cc1sq , Cc2 , Cc3
% Coef , Coef1
% cosio4 -
% day -
% dndt -
% em - eccentricity
% emsq - eccentricity squared
% eeta -
% etasq -
% gam -
% argpm - argument of perigee
% ndem -
% inclm - inclination
% mm - mean anomaly
% nm - mean motion
% perige - perigee
% pinvsq -
% psisq -
% qzms24 -
% rtemsq -
% s1, s2, s3, s4, s5, s6, s7 -
% sfour -
% ss1, ss2, ss3, ss4, ss5, ss6, ss7 -
% sz1, sz2, sz3
% sz11, sz12, sz13, sz21, sz22, sz23, sz31, sz32, sz33 -
% tc -
% temp -
% temp1, temp2, temp3 -
% tsi -
% xpidot -
% xhdot1 -
% z1, z2, z3 -
% z11, z12, z13, z21, z22, z23, z31, z32, z33 -
%
% coupling :
% getgravconst
% initl -
% dscom -
% dpper -
% dsinit -
% sgp4 -
%
% references :
% hoots, roehrich, norad spacetrack report #3 1980
% hoots, norad spacetrack report #6 1986
% hoots, schumacher and glover 2004
% vallado, crawford, hujsak, kelso 2006
% ----------------------------------------------------------------------------*/
function [satrec] = sgp4init(whichconst, satrec, xbstar, xecco, epoch, ...
xargpo, xinclo, xmo, xno, xnodeo);
% /* ------------------------ initialization --------------------- */
% /* ----------- set all near earth variables to zero ------------ */
satrec.isimp = 0; satrec.method = 'n'; satrec.aycof = 0.0;
satrec.con41 = 0.0; satrec.cc1 = 0.0; satrec.cc4 = 0.0;
satrec.cc5 = 0.0; satrec.d2 = 0.0; satrec.d3 = 0.0;
satrec.d4 = 0.0; satrec.delmo = 0.0; satrec.eta = 0.0;
satrec.argpdot = 0.0; satrec.omgcof = 0.0; satrec.sinmao = 0.0;
satrec.t = 0.0; satrec.t2cof = 0.0; satrec.t3cof = 0.0;
satrec.t4cof = 0.0; satrec.t5cof = 0.0; satrec.x1mth2 = 0.0;
satrec.x7thm1 = 0.0; satrec.mdot = 0.0; satrec.nodedot = 0.0;
satrec.xlcof = 0.0; satrec.xmcof = 0.0; satrec.nodecf = 0.0;
% /* ----------- set all deep space variables to zero ------------ */
satrec.irez = 0; satrec.d2201 = 0.0; satrec.d2211 = 0.0;
satrec.d3210 = 0.0; satrec.d3222 = 0.0; satrec.d4410 = 0.0;
satrec.d4422 = 0.0; satrec.d5220 = 0.0; satrec.d5232 = 0.0;
satrec.d5421 = 0.0; satrec.d5433 = 0.0; satrec.dedt = 0.0;
satrec.del1 = 0.0; satrec.del2 = 0.0; satrec.del3 = 0.0;
satrec.didt = 0.0; satrec.dmdt = 0.0; satrec.dnodt = 0.0;
satrec.domdt = 0.0; satrec.e3 = 0.0; satrec.ee2 = 0.0;
satrec.peo = 0.0; satrec.pgho = 0.0; satrec.pho = 0.0;
satrec.pinco = 0.0; satrec.plo = 0.0; satrec.se2 = 0.0;
satrec.se3 = 0.0; satrec.sgh2 = 0.0; satrec.sgh3 = 0.0;
satrec.sgh4 = 0.0; satrec.sh2 = 0.0; satrec.sh3 = 0.0;
satrec.si2 = 0.0; satrec.si3 = 0.0; satrec.sl2 = 0.0;
satrec.sl3 = 0.0; satrec.sl4 = 0.0; satrec.gsto = 0.0;
satrec.xfact = 0.0; satrec.xgh2 = 0.0; satrec.xgh3 = 0.0;
satrec.xgh4 = 0.0; satrec.xh2 = 0.0; satrec.xh3 = 0.0;
satrec.xi2 = 0.0; satrec.xi3 = 0.0; satrec.xl2 = 0.0;
satrec.xl3 = 0.0; satrec.xl4 = 0.0; satrec.xlamo = 0.0;
satrec.zmol = 0.0; satrec.zmos = 0.0; satrec.atime = 0.0;
satrec.xli = 0.0; satrec.xni = 0.0;
% sgp4fix - note the following variables are also passed directly via satrec.
% it is possible to streamline the sgp4init call by deleting the "x"
% variables, but the user would need to set the satrec.* values first. we
% include the additional assignment in case twoline2rv is not used.
satrec.bstar = xbstar;
satrec.ecco = xecco;
satrec.argpo = xargpo;
satrec.inclo = xinclo;
satrec.mo = xmo;
satrec.no = xno;
satrec.nodeo = xnodeo;
% /* -------------------- wgs-72 earth constants ----------------- */
% // sgp4fix identify constants and allow alternate values
global tumin mu radiusearthkm xke j2 j3 j4 j3oj2
[tumin, mu, radiusearthkm, xke, j2, j3, j4, j3oj2] = getgravc( whichconst );
ss = 78.0 / radiusearthkm + 1.0;
qzms2t = ((120.0 - 78.0) / radiusearthkm)^4;
x2o3 = 2.0 / 3.0;
% sgp4fix divisor for divide by zero check on inclination
% the old check used 1.0 + cos(pi-1.0e-9), but then compared it to
% 1.5 e-12, so the threshold was changed to 1.5e-12 for consistancy
temp4 = 1.5e-12;
satrec.init = 'y';
satrec.t = 0.0;
[ainv, ao, satrec.con41, con42, cosio, cosio2, einv, eccsq,...
satrec.method, omeosq, posq, rp, rteosq, sinio,...
satrec.gsto, satrec.no]...
= initl(...
satrec.ecco, epoch, satrec.inclo, satrec.no,...
satrec.satnum);
satrec.error = 0;
if (rp < 1.0)
% printf("# *** satn%d epoch elts sub-orbital ***\n", satn);
satrec.error = 5;
end
if ((omeosq >= 0.0 ) | ( satrec.no >= 0.0))
satrec.isimp = 0;
if (rp < (220.0 / radiusearthkm + 1.0))
satrec.isimp = 1;
end
sfour = ss;
qzms24 = qzms2t;
perige = (rp - 1.0) * radiusearthkm;
% /* - for perigees below 156 km, s and qoms2t are altered - */
if (perige < 156.0)
sfour = perige - 78.0;
if (perige < 98.0)
sfour = 20.0;
end
qzms24 = ((120.0 - sfour) / radiusearthkm)^4.0;
sfour = sfour / radiusearthkm + 1.0;
end
pinvsq = 1.0 / posq;
tsi = 1.0 / (ao - sfour);
satrec.eta = ao * satrec.ecco * tsi;
etasq = satrec.eta * satrec.eta;
eeta = satrec.ecco * satrec.eta;
psisq = abs(1.0 - etasq);
coef = qzms24 * tsi^4.0;
coef1 = coef / psisq^3.5;
cc2 = coef1 * satrec.no * (ao * (1.0 + 1.5 * etasq + eeta *...
(4.0 + etasq)) + 0.375 * j2 * tsi / psisq * satrec.con41 *...
(8.0 + 3.0 * etasq * (8.0 + etasq)));
satrec.cc1 = satrec.bstar * cc2;
cc3 = 0.0;
if (satrec.ecco > 1.0e-4)
cc3 = -2.0 * coef * tsi * j3oj2 * satrec.no * sinio / satrec.ecco;
end
satrec.x1mth2 = 1.0 - cosio2;
satrec.cc4 = 2.0* satrec.no * coef1 * ao * omeosq *...
(satrec.eta * (2.0 + 0.5 * etasq) + satrec.ecco *...
(0.5 + 2.0 * etasq) - j2 * tsi / (ao * psisq) *...
(-3.0 * satrec.con41 * (1.0 - 2.0 * eeta + etasq *...
(1.5 - 0.5 * eeta)) + 0.75 * satrec.x1mth2 *...
(2.0 * etasq - eeta * (1.0 + etasq)) * cos(2.0 * satrec.argpo)));
satrec.cc5 = 2.0 * coef1 * ao * omeosq * (1.0 + 2.75 *...
(etasq + eeta) + eeta * etasq);
cosio4 = cosio2 * cosio2;
temp1 = 1.5 * j2 * pinvsq * satrec.no;
temp2 = 0.5 * temp1 * j2 * pinvsq;
temp3 = -0.46875 * j4 * pinvsq * pinvsq * satrec.no;
satrec.mdot = satrec.no + 0.5 * temp1 * rteosq * satrec.con41 +...
0.0625 * temp2 * rteosq * (13.0 - 78.0 * cosio2 + 137.0 * cosio4);
satrec.argpdot = -0.5 * temp1 * con42 + 0.0625 * temp2 *...
(7.0 - 114.0 * cosio2 + 395.0 * cosio4) +...
temp3 * (3.0 - 36.0 * cosio2 + 49.0 * cosio4);
xhdot1 = -temp1 * cosio;
satrec.nodedot = xhdot1 + (0.5 * temp2 * (4.0 - 19.0 * cosio2) +...
2.0 * temp3 * (3.0 - 7.0 * cosio2)) * cosio;
xpidot = satrec.argpdot+ satrec.nodedot;
satrec.omgcof = satrec.bstar * cc3 * cos(satrec.argpo);
satrec.xmcof = 0.0;
if (satrec.ecco > 1.0e-4)
satrec.xmcof = -x2o3 * coef * satrec.bstar / eeta;
end
satrec.nodecf = 3.5 * omeosq * xhdot1 * satrec.cc1;
satrec.t2cof = 1.5 * satrec.cc1;
% // sgp4fix for divide by zero with xinco = 180 deg
if (abs(cosio+1.0) > 1.5e-12)
satrec.xlcof = -0.25 * j3oj2 * sinio *...
(3.0 + 5.0 * cosio) / (1.0 + cosio);
else
satrec.xlcof = -0.25 * j3oj2 * sinio *...
(3.0 + 5.0 * cosio) / temp4;
end
satrec.aycof = -0.5 * j3oj2 * sinio;
satrec.delmo = (1.0 + satrec.eta * cos(satrec.mo))^3;
satrec.sinmao = sin(satrec.mo);
satrec.x7thm1 = 7.0 * cosio2 - 1.0;
% /* --------------- deep space initialization ------------- */
if ((2*pi / satrec.no) >= 225.0)
satrec.method = 'd';
satrec.isimp = 1;
tc = 0.0;
inclm = satrec.inclo;
[sinim,cosim,sinomm,cosomm,snodm,cnodm,day,satrec.e3,satrec.ee2,...
em,emsq,gam,satrec.peo,satrec.pgho,satrec.pho,satrec.pinco,...
satrec.plo,rtemsq,satrec.se2,satrec.se3,satrec.sgh2,...
satrec.sgh3,satrec.sgh4,satrec.sh2,satrec.sh3,satrec.si2,...
satrec.si3,satrec.sl2,satrec.sl3,satrec.sl4,s1,s2,s3,s4,s5,...
s6,s7,ss1,ss2,ss3,ss4,ss5,ss6,ss7,sz1,sz2,sz3,sz11,sz12,...
sz13,sz21,sz22,sz23,sz31,sz32,sz33,satrec.xgh2,satrec.xgh3,...
satrec.xgh4,satrec.xh2,satrec.xh3,satrec.xi2,satrec.xi3,...
satrec.xl2,satrec.xl3,satrec.xl4,nm,z1,z2,z3,z11,z12,z13,...
z21,z22,z23,z31,z32,z33,satrec.zmol,satrec.zmos] = ...
dscom(epoch,satrec.ecco,satrec.argpo,tc,satrec.inclo,...
satrec.nodeo,satrec.no);
[satrec.ecco,satrec.inclo,satrec.nodeo,satrec.argpo,satrec.mo]...
= dpper(satrec.e3,satrec.ee2,satrec.peo,satrec.pgho,...
satrec.pho,satrec.pinco,satrec.plo,satrec.se2,satrec.se3,...
satrec.sgh2,satrec.sgh3,satrec.sgh4,satrec.sh2,satrec.sh3,...
satrec.si2,satrec.si3,satrec.sl2,satrec.sl3,satrec.sl4,...
satrec.t,satrec.xgh2,satrec.xgh3,satrec.xgh4,satrec.xh2,...
satrec.xh3,satrec.xi2,satrec.xi3,satrec.xl2,satrec.xl3,...
satrec.xl4,satrec.zmol,satrec.zmos,inclm,satrec.init,...
satrec.ecco,satrec.inclo,satrec.nodeo,satrec.argpo,satrec.mo);
argpm = 0.0;
nodem = 0.0;
mm = 0.0;
[em,argpm,inclm,mm,nm,nodem,satrec.irez,satrec.atime,...
satrec.d2201,satrec.d2211,satrec.d3210,satrec.d3222,...
satrec.d4410,satrec.d4422,satrec.d5220,satrec.d5232,...
satrec.d5421,satrec.d5433,satrec.dedt,satrec.didt,...
satrec.dmdt,dndt,satrec.dnodt,satrec.domdt,satrec.del1,...
satrec.del2,satrec.del3,...
... %ses,sghl,sghs,sgs,shl,shs,sis,sls,theta,...
satrec.xfact,satrec.xlamo,satrec.xli,satrec.xni] ...
= dsinit(...
cosim,emsq,satrec.argpo,s1,s2,s3,s4,s5,sinim,ss1,ss2,ss3,...
ss4,ss5,sz1,sz3,sz11,sz13,sz21,sz23,sz31,sz33,satrec.t,tc,...
satrec.gsto,satrec.mo,satrec.mdot,satrec.no,satrec.nodeo,...
satrec.nodedot,xpidot,z1,z3,z11,z13,z21,z23,z31,z33,em,...
argpm,inclm,mm,nm,nodem,satrec.ecco,eccsq);
end
% /* ----------- set variables if not deep space ----------- */
if (satrec.isimp ~= 1)
cc1sq = satrec.cc1 * satrec.cc1;
satrec.d2 = 4.0 * ao * tsi * cc1sq;
temp = satrec.d2 * tsi * satrec.cc1 / 3.0;
satrec.d3 = (17.0 * ao + sfour) * temp;
satrec.d4 = 0.5 * temp * ao * tsi *...
(221.0 * ao + 31.0 * sfour) * satrec.cc1;
satrec.t3cof = satrec.d2 + 2.0 * cc1sq;
satrec.t4cof = 0.25 * (3.0 * satrec.d3 + satrec.cc1 *...
(12.0 * satrec.d2 + 10.0 * cc1sq));
satrec.t5cof = 0.2 * (3.0 * satrec.d4 +...
12.0 * satrec.cc1 * satrec.d3 +...
6.0 * satrec.d2 * satrec.d2 +...
15.0 * cc1sq * (2.0 * satrec.d2 + cc1sq));
end
end % // if omeosq = 0 ...
% /* finally propogate to zero epoch to initialise all others. */
if(satrec.error == 0)
[satrec, r, v] = sgp4(satrec, 0.0);
end
satrec.init = 'n';
global idebug dbgfile
if idebug
debug6;
end
return;