cOrbit::cOrbit(const cTle &tle) :
m_tle(tle),
m_pNoradModel(NULL)
{
InitializeCachingVars();
int epochYear = (int)m_tle.GetField(cTle::FLD_EPOCHYEAR);
double epochDay = m_tle.GetField(cTle::FLD_EPOCHDAY );
if (epochYear < 57)
{
epochYear += 2000;
}
else
{
epochYear += 1900;
}
m_jdEpoch = cJulian(epochYear, epochDay);
m_secPeriod = -1.0;
// Recover the original mean motion and semimajor axis from the
// input elements.
double mm = MeanMotionTle();
double rpmin = mm * TWOPI / MIN_PER_DAY; // rads per minute
double a1 = pow(XKE / rpmin, 2.0 / 3.0);
double e = Eccentricity();
double i = Inclination();
double temp = (1.5 * CK2 * (3.0 * sqr(cos(i)) - 1.0) /
pow(1.0 - e * e, 1.5));
double delta1 = temp / (a1 * a1);
double a0 = a1 *
(1.0 - delta1 *
((1.0 / 3.0) + delta1 *
(1.0 + 134.0 / 81.0 * delta1)));
double delta0 = temp / (a0 * a0);
m_rmMeanMotionRec = rpmin / (1.0 + delta0);
m_aeAxisSemiMajorRec = a0 / (1.0 - delta0);
m_aeAxisSemiMinorRec = m_aeAxisSemiMajorRec * sqrt(1.0 - (e * e));
m_kmPerigeeRec = XKMPER_WGS72 * (m_aeAxisSemiMajorRec * (1.0 - e) - AE);
m_kmApogeeRec = XKMPER_WGS72 * (m_aeAxisSemiMajorRec * (1.0 + e) - AE);
if (TWOPI / m_rmMeanMotionRec >= 225.0)
{
// SDP4 - period >= 225 minutes.
m_pNoradModel = new cNoradSDP4(*this);
}
else
{
// SGP4 - period < 225 minutes
m_pNoradModel = new cNoradSGP4(*this);
}
}
Quaterniond cOrbit::RotationToReferenceFrame() const
{
Vector3d axisOfInclination(std::cos(-ArgumentOfPeriapsis()), std::sin(-ArgumentOfPeriapsis()), 0);
// not tested at nonzero inclinations
return
AngleAxisd(- LongitudeOfAscendingNode() - ArgumentOfPeriapsis(), Vector3d::UnitZ()) *
AngleAxisd(- Inclination(), axisOfInclination);
}
OrbitalElements::OrbitalElements(const Tle& tle)
{
/*
* extract and format tle data
*/
mean_anomoly_ = tle.MeanAnomaly(false);
ascending_node_ = tle.RightAscendingNode(false);
argument_perigee_ = tle.ArgumentPerigee(false);
eccentricity_ = tle.Eccentricity();
inclination_ = tle.Inclination(false);
mean_motion_ = tle.MeanMotion() * kTWOPI / kMINUTES_PER_DAY;
bstar_ = tle.BStar();
epoch_ = tle.Epoch();
/*
* recover original mean motion (xnodp) and semimajor axis (aodp)
* from input elements
*/
const double a1 = pow(kXKE / MeanMotion(), kTWOTHIRD);
const double cosio = cos(Inclination());
const double theta2 = cosio * cosio;
const double x3thm1 = 3.0 * theta2 - 1.0;
const double eosq = Eccentricity() * Eccentricity();
const double betao2 = 1.0 - eosq;
const double betao = sqrt(betao2);
const double temp = (1.5 * kCK2) * x3thm1 / (betao * betao2);
const double del1 = temp / (a1 * a1);
const double a0 = a1 * (1.0 - del1 * (1.0 / 3.0 + del1 * (1.0 + del1 * 134.0 / 81.0)));
const double del0 = temp / (a0 * a0);
recovered_mean_motion_ = MeanMotion() / (1.0 + del0);
/*
* alternative way to calculate
* doesnt affect final results
* recovered_semi_major_axis_ = pow(XKE / RecoveredMeanMotion(), TWOTHIRD);
*/
recovered_semi_major_axis_ = a0 / (1.0 - del0);
/*
* find perigee and period
*/
perigee_ = (RecoveredSemiMajorAxis() * (1.0 - Eccentricity()) - kAE) * kXKMPER;
period_ = kTWOPI / RecoveredMeanMotion();
}
