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//
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// cOrbit.cpp
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//
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// Copyright (c) 2002-2003 Michael F. Henry
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//
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// mfh 11/15/2003
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//
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#include "stdafx.h"
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#include "cOrbit.h"
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#include "math.h"
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#include "time.h"
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#include "cVector.h"
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#include "cEci.h"
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#include "coord.h"
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#include "cJulian.h"
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#include "cNoradSGP4.h"
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#include "cNoradSDP4.h"
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//////////////////////////////////////////////////////////////////////
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cOrbit::cOrbit(const cTle &tle) :
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m_tle(tle),
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m_pNoradModel(NULL)
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{
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m_tle.Initialize();
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int epochYear = (int)m_tle.getField(cTle::FLD_EPOCHYEAR);
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double epochDay = m_tle.getField(cTle::FLD_EPOCHDAY );
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if (epochYear < 57)
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epochYear += 2000;
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else
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epochYear += 1900;
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m_jdEpoch = cJulian(epochYear, epochDay);
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m_secPeriod = -1.0;
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// Recover the original mean motion and semimajor axis from the
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// input elements.
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double mm = mnMotion();
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double rpmin = mm * 2 * PI / MIN_PER_DAY; // rads per minute
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double a1 = pow(XKE / rpmin, TWOTHRD);
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double e = Eccentricity();
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double i = Inclination();
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double temp = (1.5 * CK2 * (3.0 * sqr(cos(i)) - 1.0) /
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pow(1.0 - e * e, 1.5));
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double delta1 = temp / (a1 * a1);
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double a0 = a1 *
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(1.0 - delta1 *
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((1.0 / 3.0) + delta1 *
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(1.0 + 134.0 / 81.0 * delta1)));
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double delta0 = temp / (a0 * a0);
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m_mnMotionRec = rpmin / (1.0 + delta0);
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m_aeAxisSemiMinorRec = a0 / (1.0 - delta0);
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m_aeAxisSemiMajorRec = m_aeAxisSemiMinorRec / sqrt(1.0 - (e * e));
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m_kmPerigeeRec = XKMPER_WGS72 * (m_aeAxisSemiMajorRec * (1.0 - e) - AE);
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m_kmApogeeRec = XKMPER_WGS72 * (m_aeAxisSemiMajorRec * (1.0 + e) - AE);
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if (2.0 * PI / m_mnMotionRec >= 225.0)
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{
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// SDP4 - period >= 225 minutes.
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m_pNoradModel = new cNoradSDP4(*this);
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}
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else
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{
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// SGP4 - period < 225 minutes
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m_pNoradModel = new cNoradSGP4(*this);
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}
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}
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/////////////////////////////////////////////////////////////////////////////
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cOrbit::~cOrbit()
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{
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delete m_pNoradModel;
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}
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//////////////////////////////////////////////////////////////////////////////
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// Return the period in seconds
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double cOrbit::Period() const
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{
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if (m_secPeriod < 0.0)
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{
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// Calculate the period using the recovered mean motion.
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if (m_mnMotionRec == 0)
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m_secPeriod = 0.0;
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else
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m_secPeriod = (2 * PI) / m_mnMotionRec * 60.0;
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}
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return m_secPeriod;
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}
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//////////////////////////////////////////////////////////////////////////////
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// Returns elapsed number of seconds from epoch to given time.
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// Note: "Predicted" TLEs can have epochs in the future.
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double cOrbit::TPlusEpoch(const cJulian &gmt) const
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{
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return gmt.spanSec(Epoch());
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}
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//////////////////////////////////////////////////////////////////////////////
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// Returns the mean anomaly in radians at given GMT.
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// At epoch, the mean anomaly is given by the elements data.
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double cOrbit::mnAnomaly(cJulian gmt) const
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{
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double span = TPlusEpoch(gmt);
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double P = Period();
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assert(P != 0.0);
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return fmod(mnAnomaly() + (TWOPI * (span / P)), TWOPI);
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}
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//////////////////////////////////////////////////////////////////////////////
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// getPosition()
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// This procedure returns the ECI position and velocity for the satellite
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// at "tsince" minutes from the (GMT) TLE epoch. The vectors returned in
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// the ECI object are kilometer-based.
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// tsince - Time in minutes since the TLE epoch (GMT).
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bool cOrbit::getPosition(double tsince, cEci *pEci) const
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{
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bool rc;
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rc = m_pNoradModel->getPosition(tsince, *pEci);
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pEci->ae2km();
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return rc;
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}
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//////////////////////////////////////////////////////////////////////////////
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// SatName()
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// Return the name of the satellite. If requested, the NORAD number is
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// appended to the end of the name, i.e., "ISS (ZARYA) #25544".
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// The name of the satellite with the NORAD number appended is important
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// because many satellites, especially debris, have the same name and
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// would otherwise appear to be the same satellite in ouput data.
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string cOrbit::SatName(bool fAppendId /* = false */) const
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{
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string str = m_tle.getName();
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if (fAppendId)
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{
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string strId;
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m_tle.getField(cTle::FLD_NORADNUM, cTle::U_NATIVE, &strId);
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str = str + " #" + strId;
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}
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return str;
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}
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