Class: Orbit::NoradSGP4

Inherits:
NoradBase show all
Defined in:
lib/orbit/norad_sgp4.rb

Instance Attribute Summary collapse

Attributes inherited from NoradBase

#m_aodp, #m_aycof, #m_betao, #m_betao2, #m_c1, #m_c3, #m_c4, #m_coef, #m_coef1, #m_cosio, #m_eeta, #m_eosq, #m_eta, #m_etasq, #m_omgdot, #m_perigee, #m_qoms24, #m_s4, #m_satEcc, #m_satInc, #m_sinio, #m_t2cof, #m_theta2, #m_tsi, #m_x1mth2, #m_x3thm1, #m_x7thm1, #m_xlcof, #m_xmdot, #m_xnodcf, #m_xnodot, #m_xnodp

Instance Method Summary collapse

Methods inherited from NoradBase

#final_position

Constructor Details

#initialize(orbit) ⇒ NoradSGP4

Returns a new instance of NoradSGP4.



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# File 'lib/orbit/norad_sgp4.rb', line 13

def initialize( orbit )
  @orbit = orbit

  super

  @m_c5     = 2.0 * @m_coef1 * @m_aodp * @m_betao2 *
             (1.0 + 2.75 * (@m_etasq + @m_eeta) + @m_eeta * @m_etasq)
  @m_omgcof = orbit.bstar * @m_c3 * Math.cos(orbit.arg_perigee)
  @m_xmcof  = -(2.0 / 3.0) * @m_coef * orbit.bstar * OrbitGlobals::AE / @m_eeta
  @m_delmo  = ((1.0 + @m_eta * Math.cos(orbit.mean_anomaly) ) ** 3.0)
  @m_sinmo  = Math.sin(orbit.mean_anomaly)

end

Instance Attribute Details

#m_c5 ⇒ Object

Returns the value of attribute m_c5.



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# File 'lib/orbit/norad_sgp4.rb', line 6

def m_c5
  @m_c5
end

#m_delmo ⇒ Object

Returns the value of attribute m_delmo.



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# File 'lib/orbit/norad_sgp4.rb', line 9

def m_delmo
  @m_delmo
end

#m_omgcof ⇒ Object

Returns the value of attribute m_omgcof.



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# File 'lib/orbit/norad_sgp4.rb', line 7

def m_omgcof
  @m_omgcof
end

#m_sinmo ⇒ Object

Returns the value of attribute m_sinmo.



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# File 'lib/orbit/norad_sgp4.rb', line 10

def m_sinmo
  @m_sinmo
end

#m_xmcof ⇒ Object

Returns the value of attribute m_xmcof.



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# File 'lib/orbit/norad_sgp4.rb', line 8

def m_xmcof
  @m_xmcof
end

#orbit ⇒ Object

Returns the value of attribute orbit.



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# File 'lib/orbit/norad_sgp4.rb', line 4

def orbit
  @orbit
end

Instance Method Details

#get_position(tsince) ⇒ Object 



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# File 'lib/orbit/norad_sgp4.rb', line 27

def get_position(tsince)
# puts "get_position( #{tsince} )"

# For @m_perigee less than 220 kilometers, the isimp flag is set and
# the equations are truncated to linear variation in Math.Sqrt a and
# quadratic variation in mean anomaly.  Also, the @m_c3 term, the
# delta omega term, and the delta m term are dropped.
isimp = false
if ((@m_aodp * (1.0 - @m_satEcc) / OrbitGlobals::AE) < (220.0 / OrbitGlobals::XKMPER + OrbitGlobals::AE))
 isimp = true
end

  d2 = 0.0
  d3 = 0.0
  d4 = 0.0

  t3cof = 0.0
  t4cof = 0.0
  t5cof = 0.0

  if (!isimp)
    c1sq = @m_c1 * @m_c1

    d2 = 4.0 * @m_aodp * @m_tsi * c1sq

    temp = d2 * @m_tsi * @m_c1 / 3.0

    d3 = (17.0 * @m_aodp + @m_s4) * temp
    d4 = 0.5 * temp * @m_aodp * @m_tsi *
      (221.0 * @m_aodp + 31.0 * @m_s4) * @m_c1
    t3cof = d2 + 2.0 * c1sq
    t4cof = 0.25 * (3.0 * d3 + @m_c1 * (12.0 * d2 + 10.0 * c1sq))
    t5cof = 0.2 * (3.0 * d4 + 12.0 * @m_c1 * d3 + 6.0 *
      d2 * d2 + 15.0 * c1sq * (2.0 * d2 + c1sq))
  end

  # Update for secular gravity and atmospheric drag.
  xmdf   = orbit.mean_anomaly + @m_xmdot * tsince
  omgadf = orbit.arg_perigee + @m_omgdot * tsince
  xnoddf = orbit.raan + @m_xnodot * tsince
  omega  = omgadf
  xmp    = xmdf
  tsq    = tsince * tsince
  xnode  = xnoddf + @m_xnodcf * tsq
  tempa  = 1.0 - @m_c1 * tsince
  tempe  = orbit.bstar * @m_c4 * tsince
  templ  = @m_t2cof * tsq

  if (!isimp)
     delomg = @m_omgcof * tsince
     delm = @m_xmcof * (((1.0 + @m_eta * Math.cos(xmdf) ) ** 3.0) - @m_delmo)
     temp = delomg + delm

     xmp = xmdf + temp
     omega = omgadf - temp

     tcube = tsq * tsince
     tfour = tsince * tcube

     tempa = tempa - d2 * tsq - d3 * tcube - d4 * tfour
     tempe = tempe + orbit.bstar * @m_c5 * (Math.sin(xmp) - @m_sinmo)
     templ = templ + t3cof * tcube + tfour * (t4cof + tsince * t5cof)
   end

  a  = @m_aodp * (tempa ** 2)
  e  = @m_satEcc - tempe


  xl = xmp + omega + xnode + @m_xnodp * templ
  xn = OrbitGlobals::XKE / (a ** 1.5)

  return final_position(@m_satInc, omgadf, e, a, xl, xnode, xn, tsince)
end