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Required Reading


   CSPICE_CONICS determines the state (position, velocity) of an orbiting 
   body from a set of elliptic, hyperbolic, or parabolic orbital elements. 

   For important details concerning this module's function, please refer to
   the CSPICE routine conics_c.


      elts    a double precision 8-vector containing the conic osculating 
              elements describing the orbit of a body around a primary. 
              The elements are, in order:
                 RP      Perifocal distance.
                 ECC     Eccentricity.
                 INC     Inclination.
                 LNODE   Longitude of the ascending node.
                 ARGP    Argument of periapse.
                 M0      Mean anomaly at epoch.
                 T0      Epoch.
                 MU      Gravitational parameter.
                 Units are km, rad, rad/sec, km**3/sec**2.  
                 The epoch T0 is given in ephemeris seconds past J2000. 
                 T0 is the instant at which the state of the body is 
                 specified by the elements. 
      et      the scalar double precision time in ephemeris seconds past
              J2000 at which the state of the orbiting body is to be 
   the call:
      cspice_conics, elts, et, state
      state   a double precision Cartesian 6-vector representing the state 
              (position and velocity) of the body at time 'et' 
              in kilometers and kilometers-per-second  (the first
              three components of 'state' represent the x-, y- and 
              z-components of the body's position; the last three 
              components form the corresponding velocity vector) 


   Any numerical results shown for this example may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

      ;; Calculate the difference between the
      ;; state elements of the Moon at some time as determined
      ;; from SPK data and the corresponding state elements 
      ;; determined from propagation of osculating elements.
      ;; Load the meta kernel listing the needed SPK, PCK, LSK
      ;; kernels.
      cspice_furnsh, ''
      ;; Convert the time of interest, provides as a string, to ephemeris time
      cspice_str2et, 'Dec 25, 2007', et
      ;; Make the cspice_spkezr call to retrieve the state of the
      ;; Moon w.r.t. the Earth in J2000. Use 'NONE' as aberration
      ;; correction since we are comparing geometric states.
      cspice_spkezr, 'Moon', et, 'J2000', 'NONE', 'EARTH', state, ltime    
      ;; cspice_oscelt requires body mass information, so load a
      ;; mass PCK kernel that contains gravitation constants.
      cspice_furnsh, '/kernels/gen/pck/masses3.tpc'
      ;; Read the gravitational parameter for Earth.
      cspice_bodvrd, 'EARTH', 'GM', 1, mu
      ;; Execute the cspice_oscelt call to convert the state 6-vector
      ;; to the osculating elements 8-vector, 'elts', at 'et'. The osculating 
      ;; elements are relative to the same frame as 'state'.
      ;; The elements describe the nominal orbit the Moon would follow 
      ;; in the absence of all other bodies in the solar system and
      ;; and all non-gravitational forces.
      ;; Note: the cspice_bodvrd call returns data as arrays, so 
      ;; to access the gravitational parameter (the only value in 
      ;; the array), we use 'mu[0]'.
      cspice_oscelt, state, et, mu[0], elts
      ;; Now, select a time one week from the initial epoch.
      later = et + 7.d * cspice_spd()
      ;; Use the osculating elements to calculate the state vector 
      ;; of the Moon at the 'later' epoch.
      cspice_conics, elts, later, later_state
      ;; Now retrieve the Moon's state at time 'later' from SPK
      ;; data.
      cspice_spkezr, 'Moon', later, 'J2000', 'NONE', 'EARTH', state, ltime    
      ;; Display the absolute diff between the vector output by 
      ;; cspice_conics and the state vector returned by cspice_spkezr.
      pert = later_state - state
      print, "Perturbation in     x: ", pert[0]
      print, "Perturbation in     y: ", pert[1]
      print, "Perturbation in     z: ", pert[2]
      print, "Perturbation in dx/dt: ", pert[3]
      print, "Perturbation in dy/dt: ", pert[4]
      print, "Perturbation in dz/dt: ", pert[5]
   IDL outputs:
      Perturbation in     x:       -7488.8162
      Perturbation in     y:        397.60470
      Perturbation in     z:        195.74585
      Perturbation in dx/dt:     -0.036152592
      Perturbation in dy/dt:    -0.0012792366
      Perturbation in dz/dt:    -0.0020145613



Required Reading



   -Icy Version 1.1.0, 16-MAY-2005, EDW (JPL)

       Added capability to process 8xN array 'elts' and
       N-vector 'et' input returning a 6xN 'state' array.

   -Icy Version 1.0.0, 16-JUN-2003, EDW (JPL)


   state from conic elements

Wed Apr  5 17:57:59 2017