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Documentation for C++ NORAD SGP4/SDP4 Implementation
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Developed by Michael F. Henry
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December, 2003
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Copyright © 2003-2005. All rights reserved.
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The files in this package implement the SGP4 and SDP4 algorithms described in the
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December, 1980 NORAD document "Space Track Report No. 3". The report provides
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FORTRAN IV implementations of each. These two orbital models, one for "near-earth"
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objects and one for "deep space" objects, are widely used in satellite tracking software
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and can produce very accurate results when used with current NORAD two-line element
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datum.
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The original NORAD FORTRAN IV SGP4/SDP4 implementations were converted to
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Pascal by Dr. TS Kelso in 1995. In 1996 these routines were ported in a straight-forward
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manner to C++ by Varol Okan. The SGP4/SDP4 classes here were written by Michael F.
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Henry in 2002-03 and are a modern C++ re-write of the work done by Okan. In addition
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to introducing an object-oriented architecture, the last residues of the original FORTRAN
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code (such as labels and gotos) were eradicated.
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The project files were compiled using Microsoft Visual Studio 7.0. Any compiler that
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supports the C++ Standard Template Library should work, including Visual Studio 6.0.
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The project generates a single executable, SxP4Test.exe, which calculates ECI position
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and velocity information for the test element sets originally published in the NORAD
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report. Also provided as an additional example is how to use the classes to calculate the
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look angle from a location on the earth to a satellite in orbit.
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Here is the correct program output:
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SGP4 Test
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1 88888U 80275.98708465 .00073094 13844-3 66816-4 0 8
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2 88888 72.8435 115.9689 0086731 52.6988 110.5714 16.05824518 105
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TSINCE X Y Z
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0.00 2328.97070437 -5995.22083333 1719.97065611
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360.00 2456.10787343 -6071.93868176 1222.89554078
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720.00 2567.56296224 -6112.50380175 713.96182588
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1080.00 2663.09017513 -6115.48274470 196.39907463
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1440.00 2742.55440194 -6079.66984186 -326.39149750
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XDOT YDOT ZDOT
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2.91207225 -0.98341531 -7.09081697
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2.67938906 -0.44828838 -7.22879265
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2.44024485 0.09811117 -7.31995951
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2.19612076 0.65241695 -7.36282421
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1.94849696 1.21107421 -7.35619305
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SDP4 Test
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1 11801U 80230.29629788 .01431103 00000-0 14311-1 8
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2 11801 46.7916 230.4354 7318036 47.4722 10.4117 2.28537848 6
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TSINCE X Y Z
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0.00 7473.37213351 428.95462549 5828.74786677
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360.00 -3305.22417985 32410.86360001 -24697.17732308
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720.00 14271.28695394 24110.46300337 -4725.76750899
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1080.00 -9990.05752318 22717.36123643 -23616.89356981
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1440.00 9787.87233694 33753.34427732 -15030.80628319
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XDOT YDOT ZDOT
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5.10715289 6.44468289 -0.18613182
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-1.30113547 -1.15131513 -0.28333528
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-0.32050442 2.67984097 -2.08405301
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-1.01667268 -2.29026701 0.72892308
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-1.09425038 0.92358954 -1.52230979
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Example output:
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AZ: 100.2 EL: 12.9
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A brief description of important classes:
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cTle – This class encapsulates a single set of NORAD two line elements.
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cEci – This class encapsulates Earth-Centered Inertial coordinates and velocity for a
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given moment in time.
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cOrbit – Given a cTle object, this class provides information about the orbit of the
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described satellite, including inclination, perigee, eccentricity, etc. Most importantly, it
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provides ECI coordinates/velocity for the satellite.
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CSite – Describes a location on the earth. Given the ECI coordinates of a satellite, this
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class can generate Azimuth/Elevation look angles to the satellite.
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cNoradBase, cNoradSGP4, cNoradSDP4 – These classes implement the NORAD
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SGP4/SDP4 algorithms. They are used by cOrbit to calculate the ECI
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coordinates/velocity of its associated satellite.
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For excellent information on the underlying physics of orbits, visible satellite
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observations, current NORAD TLE data, and other related material, see
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http://www.celestrak.com which is maintained by Dr. TS Kelso.
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Michael F. Henry
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December, 2003
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