example_sgp4/propagate.m at master · AlgorithmHub/example_sgp4 · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
function [r,v] = propagate(longstr1, longstr2, t)

    addpath('./sgp4');

    global tumin radiusearthkm xke j2 j3 j4 j3oj2
    global opsmode

    opsmode = 'a';
    wgs = 72;

    deg2rad  =   pi / 180.0;         %  0.01745329251994330;  % [deg/rad]
    xpdotp   =  1440.0 / (2.0*pi);   % 229.1831180523293;  % [rev/day]/[rad/min]

    revnum = 0;
    elnum  = 0;
    year   = 0;
    satrec.error = 0;

%   set the implied decimal points since doing a formated read
%   fixes for bad input data values (missing, ...)
    for (j = 11:16)
        if (longstr1(j) == ' ')
            longstr1(j) = '_';
        end
    end

    if (longstr1(45) ~= ' ')
        longstr1(44) = longstr1(45);
    end
    longstr1(45) = '.';

    if (longstr1(8) == ' ')
        longstr1(8) = 'U';
    end

    if (longstr1(10) == ' ')
        longstr1(10) = '.';
    end

    for (j = 46:50)
        if (longstr1(j) == ' ')
            longstr1(j) = '0';
        end
    end
    if (longstr1(52) == ' ')
        longstr1(52) = '0';
    end
    if (longstr1(54) ~= ' ')
        longstr1(53) = longstr1(54);
    end
    longstr1(54) = '.';

    longstr2(26) = '.';

    for (j = 27:33)
        if (longstr2(j) == ' ')
            longstr2(j) = '0';
        end
    end

    if (longstr1(63) == ' ')
        longstr1(63) = '0';
    end

    if ((length(longstr1) < 68) || (longstr1(68) == ' '))
        longstr1(68) = '0';
    end

%   parse first line
    carnumb = str2num(longstr1(1));
    satrec.satnum = str2num(longstr1(3:7));
    classification = longstr1(8);
    intldesg = longstr1(10:17);
    satrec.epochyr = str2num(longstr1(19:20));
    satrec.epochdays = str2num(longstr1(21:32));
    satrec.ndot = str2num(longstr1(34:43));
    satrec.nddot = str2num(longstr1(44:50));
    nexp = str2num(longstr1(51:52));
    satrec.bstar = str2num(longstr1(53:59));
    ibexp = str2num(longstr1(60:61));
    numb = str2num(longstr1(63));
    elnum = str2num(longstr1(65:68));

%   parse second line
    cardnumb = str2num(longstr2(1));
    satrec.satnum = str2num(longstr2(3:7));
    satrec.inclo = str2num(longstr2(8:16));
    satrec.nodeo = str2num(longstr2(17:25));
    satrec.ecco = str2num(longstr2(26:33));
    satrec.argpo = str2num(longstr2(34:42));
    satrec.mo = str2num(longstr2(43:51));
    satrec.no = str2num(longstr2(52:63));
    revnum = str2num(longstr2(64:68));

%   find no, ndot, nddot
    satrec.no   = satrec.no / xpdotp; % rad/min
    satrec.nddot= satrec.nddot * 10.0^nexp;
    satrec.bstar= satrec.bstar * 10.0^ibexp;

%   convert to sgp4 units
    satrec.a    = (satrec.no*tumin).^(-2/3);               % [er]
    satrec.ndot = satrec.ndot  / (xpdotp*1440.0);         % [rad/min^2]
    satrec.nddot= satrec.nddot / (xpdotp*1440.0*1440);    % [rad/min^3]

%   find standard orbital elements
    satrec.inclo = satrec.inclo * deg2rad;
    satrec.nodeo = satrec.nodeo * deg2rad;
    satrec.argpo = satrec.argpo * deg2rad;
    satrec.mo    = satrec.mo    * deg2rad;

    satrec.alta = satrec.a*(1.0 + satrec.ecco) - 1.0;
    satrec.altp = satrec.a*(1.0 - satrec.ecco) - 1.0;

%     // ----------------------------------------------------------------
%     // find sgp4epoch time of element set
%     // remember that sgp4 uses units of days from 0 jan 1950 (sgp4epoch)
%     // and minutes from the epoch (time)
%     // --------------------------------------------------------------
%     // ------------- temp fix for years from 1957-2056 ----------------
%     // ------ correct fix will occur when year is 4-digit in 2le ------
    if (satrec.epochyr < 57)
        year = satrec.epochyr + 2000;
    else
        year = satrec.epochyr + 1900;
    end

    [mon,day,hr,minute,sec] = days2mdh(year,satrec.epochdays);
    satrec.jdsatepoch = jday(year,mon,day,hr,minute,sec);

    sgp4epoch = satrec.jdsatepoch - 2433281.5; % days since 0 Jan 1950

    [satrec] = sgp4init(wgs, satrec, satrec.bstar, satrec.ecco, sgp4epoch, satrec.argpo, satrec.inclo, satrec.mo, satrec.no, satrec.nodeo);

    dut1 = 0.0;
    dat  = 32;
    xp   =  0.0;
    yp   =  0.0;
    lod  =  0.0;
    ddpsi = 0.0;
    ddeps = 0.0;
    timezone = 0;

    len = length(t);
    r = zeros(3,len);
    v = zeros(3,len);
    for ii = 1:len
        [satrec,r(:,ii),v(:,ii)] = sgp4(satrec,t(ii));
        [ut1, tut1, jdut1, utc, tai, tt, ttt, jdtt, tdb, ttdb, jdtdb ] = convtime ( year, mon, day, hr, minute, sec, timezone, dut1, dat );
        [r(:,ii),v(:,ii)] = teme2ecef(r(:,ii),v(:,ii),[0;0;0],ttt,jdut1,lod,xp,yp);
    end