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mice_spkpos

Table of contents
Abstract
I/O
Parameters
Examples
Particulars
Exceptions
Files
Restrictions
Required_Reading
Literature_References
Author_and_Institution
Version
Index_Entries

Abstract


   MICE_SPKPOS returns the position of a target body relative
   to an observing body, optionally corrected for light time
   (planetary aberration) and stellar aberration.

I/O


   Given:

      targ     the name of a target body.

               [1,c1] = size(target); char = class(target)

                  or

               [1,1] = size(target); cell = class(target)

               Optionally, you may supply the integer ID code for the object
               as an integer string, i.e. both 'MOON' and '301' are
               legitimate strings that indicate the Moon is the target body.

               The target and observer define a position vector
               whose position component points from the observer
               to the target.

      et       the ephemeris time(s), expressed as seconds past J2000
               TDB, at which the position of the target body relative to
               the observer is to be computed.

               [1,n] = size(et); double = class(et)

               `et' refers to time at the observer's location.

      ref      the name of the reference frame relative to which the output
               position vector should be expressed.

               [1,c2] = size(ref); char = class(ref)

                  or

               [1,1] = size(ref); cell = class(ref)

               This may be any frame supported by the SPICE
               system, including built-in frames (documented in the
               Frames Required Reading) and frames defined by a loaded
               frame kernel (FK).

               When `ref' designates a non-inertial frame, the
               orientation of the frame is evaluated at an epoch
               dependent on the selected aberration correction.

      abcorr   the aberration corrections to apply to the position of the
               target body to account for one-way light time and stellar
               aberration.

               [1,c3] = size(abcorr); char = class(abcorr)

                  or

               [1,1] = size(abcorr); cell = class(abcorr)

               `abcorr' may be any of the following:

                  'NONE'     Apply no correction. Return the
                             geometric position of the target
                             body relative to the observer.

               The following values of `abcorr' apply to the
               "reception" case in which photons depart from the
               target's location at the light-time corrected epoch
               et-lt and *arrive* at the observer's location at
               `et':

                  'LT'       Correct for one-way light time (also
                             called "planetary aberration") using a
                             Newtonian formulation. This correction
                             yields the position of the target at the
                             moment it emitted photons arriving at
                             the observer at `et'.

                             The light time correction uses an
                             iterative solution of the light time
                             equation (see -Particulars for details).
                             The solution invoked by the 'LT' option
                             uses one iteration.

                  'LT+S'     Correct for one-way light time and
                             stellar aberration using a Newtonian
                             formulation. This option modifies the
                             position obtained with the 'LT' option to
                             account for the observer's velocity
                             relative to the solar system
                             barycenter. The result is the apparent
                             position of the target---the position
                             of the target as seen by the
                             observer.

                  'CN'       Converged Newtonian light time
                             correction. In solving the light time
                             equation, the 'CN' correction iterates
                             until the solution converges (three
                             iterations on all supported platforms).

                             The 'CN' correction typically does not
                             substantially improve accuracy because
                             the errors made by ignoring
                             relativistic effects may be larger than
                             the improvement afforded by obtaining
                             convergence of the light time solution.
                             The 'CN' correction computation also
                             requires a significantly greater number
                             of CPU cycles than does the
                             one-iteration light time correction.

                  'CN+S'     Converged Newtonian light time
                             and stellar aberration corrections.


               The following values of `abcorr' apply to the
               "transmission" case in which photons *depart* from
               the observer's location at `et' and arrive at the
               target's location at the light-time corrected epoch
               et+lt:

                  'XLT'      "Transmission" case: correct for
                             one-way light time using a Newtonian
                             formulation. This correction yields the
                             position of the target at the moment it
                             receives photons emitted from the
                             observer's location at `et'.

                  'XLT+S'    "Transmission" case: correct for
                             one-way light time and stellar
                             aberration using a Newtonian
                             formulation  This option modifies the
                             position obtained with the 'XLT' option to
                             account for the observer's velocity
                             relative to the solar system
                             barycenter. The position indicates the
                             direction that photons emitted from the
                             observer's location must be "aimed" to
                             hit the target.

                  'XCN'      "Transmission" case: converged
                             Newtonian light time correction.

                  'XCN+S'    "Transmission" case: converged
                             Newtonian light time and stellar
                             aberration corrections.


               Neither special nor general relativistic effects are
               accounted for in the aberration corrections applied
               by this routine.

               Neither letter case or embedded blanks are significant
               in the `abcorr' string.

      obs      the name of a observing body.

               [1,c4] = size(obs); char = class(obs)

                  or

               [1,1] = size(obs); cell = class(obs)

               Optionally, you may supply the integer ID code
               for the object as an integer string, i.e. both
               'MOON' and '301' are legitimate strings that
               indicate the Moon is the observing body.

   the call:

      [ptarg] = mice_spkpos( targ, et, ref, abcorr, obs )

   returns:

      ptarg    the structure(s) containing the results of the calculation.

               [1,n] = size(ptarg); struct = class(ptarg)

               Each structure consists of the fields:

                  pos      the Cartesian state vector representing the
                           position of the target body relative
                           to the specified observer.

                           [3,1]  = size(ptarg(i).pos);
                           double = class(ptarg(i).pos)

                           `pos' is corrected for the specified aberrations,
                           and is expressed with respect to the reference
                           frame specified by `ref'.

                           The position points from the observer's location
                           at `et' to the aberration-corrected location of
                           the target. Note that the sense of the position
                           vector is independent of the direction of
                           radiation travel implied by the aberration
                           correction.

                           Units are always km.

                           Non-inertial frames are treated as follows:
                           letting `ltcent' be the one-way light time between
                           the observer and the central body associated
                           with the frame, the orientation of the frame is
                           evaluated at et-ltcent, et+ltcent, or `et'
                           depending on whether the requested aberration
                           correction is, respectively, for received
                           radiation, transmitted radiation, or is omitted.
                           `ltcent' is computed using the method indicated
                           by `abcorr'.

                  lt       the value(s) of the one-way light time between the
                           observer and target in seconds.

                           [1,1]  = size(ptarg(i).lt);
                           double = class(ptarg(i).lt)

                           If the target position is corrected for
                           aberrations, then `lt' is the one-way light time
                           between the observer and the light time corrected
                           target location.

               `ptarg' returns with the same vectorization measure (N) as
               `et'.

Parameters


   None.

Examples


   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.

   1) Load a planetary SPK, and look up the position of Mars
      as seen from the Earth in the J2000 frame with aberration
      corrections 'LT+S' (ligth time plus stellar aberration) at
      different epochs.

      Use the meta-kernel shown below to load the required SPICE
      kernels.


         KPL/MK

         File: spkpos_ex1.tm

         This meta-kernel is intended to support operation of SPICE
         example programs. The kernels shown here should not be
         assumed to contain adequate or correct versions of data
         required by SPICE-based user applications.

         In order for an application to use this meta-kernel, the
         kernels referenced here must be present in the user's
         current working directory.

         The names and contents of the kernels referenced
         by this meta-kernel are as follows:

            File name                        Contents
            ---------                        --------
            de430.bsp                        Planetary ephemeris
            mar097.bsp                       Mars satellite ephemeris
            naif0011.tls                     Leapseconds


         \begindata

            KERNELS_TO_LOAD = ( 'de430.bsp',
                                'mar097.bsp',
                                'naif0011.tls' )

         \begintext

         End of meta-kernel


      Example code begins here.


      function spkpos_ex1()

         %
         %  Load a set of kernels: an SPK file, a PCK
         %  file and a leapseconds file. Use a meta
         %  kernel for convenience.
         %
         cspice_furnsh( 'spkpos_ex1.tm' )

         %
         %  Define parameters for a position lookup:
         %
         %  Return the position vector of Mars (499) as seen from
         %  Earth (399) in the J2000 frame
         %  using aberration correction LT+S (light time plus
         %  stellar aberration) at the epoch
         %  July 4, 2003 11:00 AM PST.
         %
         target   = 'Mars';
         epoch    = 'July 4, 2003 11:00 AM PST';
         frame    = 'J2000';
         abcorr   = 'LT+S';
         observer = 'Earth';

         %
         %  Convert the epoch to ephemeris time.
         %
         et = cspice_str2et( epoch );

         %
         %  Look-up the position for the defined parameters.
         %
         starg = mice_spkpos( target, et, frame, abcorr, observer);

         %
         %  Output...
         %
         txt = sprintf( 'The position of    : %s', target);
         disp( txt )

         txt = sprintf( 'As observed from   : %s', observer );
         disp( txt )

         txt = sprintf( 'In reference frame : %s', frame );
         disp( txt )
         disp( ' ' )

         txt = sprintf( 'Scalar' );
         disp( txt )

         utc_epoch = cspice_et2utc( et, 'C', 3 );

         txt = sprintf( 'At epoch           : %s', epoch );
         disp( txt )

         txt = sprintf( '                   : i.e. %s', utc_epoch );
         disp( txt )

         txt = sprintf( ['R (kilometers)     : '                          ...
                          '%12.4f %12.4f %12.4f'], starg.pos );
         disp( txt )

         txt = sprintf( 'Light time (secs)  : %12.7f', starg.lt );
         disp( txt )

         disp(' between observer' )
         disp(' and target' )
         disp( ' ' )

         %
         % Create a vector of et's, starting at `epoch'
         % in steps of 100000 ephemeris seconds.
         %
         vec_et = [0:4]*100000. + et;

         disp( 'Vector' )
         vec_epoch = cspice_et2utc( vec_et, 'C', 3 );

         %
         % Look up the position vectors and light time values
         % corresponding to the vector of input
         % ephemeris time `vec_et'.
         %
         ptarg = mice_spkpos( target, vec_et, frame, abcorr, observer );

         for i=1:5

            txt = sprintf( 'At epoch (UTC)     : %s', vec_epoch(i,:) );
            disp( txt )

            txt = sprintf( ['R (kilometers)     : '                       ...
                            '%12.4f %12.4f %12.4f'], ptarg(i).pos );
            disp( txt )

            txt = sprintf( 'Light time (secs)  : %12.7f', ptarg(i).lt );
            disp( txt )

            disp(' between observer' )
            disp(' and target' )
            disp( ' ' )

         end

         %
         %  It's always good form to unload kernels after use,
         %  particularly in MATLAB due to data persistence.
         %
         cspice_kclear


      When this program was executed on a Mac/Intel/Octave6.x/64-bit
      platform, the output was:


      The position of    : Mars
      As observed from   : Earth
      In reference frame : J2000

      Scalar
      At epoch           : July 4, 2003 11:00 AM PST
                         : i.e. 2003 JUL 04 19:00:00.000
      R (kilometers)     : 73822235.3312 -27127919.1784 -18741306.2848
      Light time (secs)  :  269.6898816
       between observer
       and target

      Vector
      At epoch (UTC)     : 2003 JUL 04 19:00:00.000
      R (kilometers)     : 73822235.3312 -27127919.1784 -18741306.2848
      Light time (secs)  :  269.6898816
       between observer
       and target

      At epoch (UTC)     : 2003 JUL 05 22:46:40.000
      R (kilometers)     : 73140185.4372 -26390524.9551 -18446763.0157
      Light time (secs)  :  266.5640396
       between observer
       and target

      At epoch (UTC)     : 2003 JUL 07 02:33:20.000
      R (kilometers)     : 72456239.6858 -25681031.1854 -18163339.1239
      Light time (secs)  :  263.4803536
       between observer
       and target

      At epoch (UTC)     : 2003 JUL 08 06:20:00.000
      R (kilometers)     : 71771127.0353 -24999259.6270 -17890946.6135
      Light time (secs)  :  260.4395237
       between observer
       and target

      At epoch (UTC)     : 2003 JUL 09 10:06:40.000
      R (kilometers)     : 71085543.8563 -24345021.3427 -17629490.6857
      Light time (secs)  :  257.4422004
       between observer
       and target


Particulars


   A sister version of this routine exists named cspice_spkpos that returns
   the structure field data as separate arguments.

   Alternatively, if needed, the user can extract the field data from
   vectorized `ptarg' structures into separate arrays.

      Extract the N `pos' field data to a 6XN array `position':

         position = reshape( [ptarg(:).pos], 3, [] )

      Extract the N `lt' field data to a 1XN array `lighttime':

         lighttime = reshape( [ptarg(:).lt], 1, [] )


   Aberration corrections
   ======================

   In space science or engineering applications one frequently
   wishes to know where to point a remote sensing instrument, such
   as an optical camera or radio antenna, in order to observe or
   otherwise receive radiation from a target. This pointing problem
   is complicated by the finite speed of light: one needs to point
   to where the target appears to be as opposed to where it actually
   is at the epoch of observation. We use the adjectives
   "geometric," "uncorrected," or "true" to refer to an actual
   position or state of a target at a specified epoch. When a
   geometric position or state vector is modified to reflect how it
   appears to an observer, we describe that vector by any of the
   terms "apparent," "corrected," "aberration corrected," or "light
   time and stellar aberration corrected." The SPICE Toolkit can
   correct for two phenomena affecting the apparent location of an
   object: one-way light time (also called "planetary aberration") and
   stellar aberration.

   One-way light time
   ------------------

   Correcting for one-way light time is done by computing, given an
   observer and observation epoch, where a target was when the observed
   photons departed the target's location. The vector from the
   observer to this computed target location is called a "light time
   corrected" vector. The light time correction depends on the motion
   of the target relative to the solar system barycenter, but it is
   independent of the velocity of the observer relative to the solar
   system barycenter. Relativistic effects such as light bending and
   gravitational delay are not accounted for in the light time
   correction performed by this routine.

   Stellar aberration
   ------------------

   The velocity of the observer also affects the apparent location
   of a target: photons arriving at the observer are subject to a
   "raindrop effect" whereby their velocity relative to the observer
   is, using a Newtonian approximation, the photons' velocity
   relative to the solar system barycenter minus the velocity of the
   observer relative to the solar system barycenter. This effect is
   called "stellar aberration." Stellar aberration is independent
   of the velocity of the target. The stellar aberration formula
   used by this routine does not include (the much smaller)
   relativistic effects.

   Stellar aberration corrections are applied after light time
   corrections: the light time corrected target position vector is
   used as an input to the stellar aberration correction.

   When light time and stellar aberration corrections are both
   applied to a geometric position vector, the resulting position
   vector indicates where the target "appears to be" from the
   observer's location.

   As opposed to computing the apparent position of a target, one
   may wish to compute the pointing direction required for
   transmission of photons to the target. This also requires correction
   of the geometric target position for the effects of light time
   and stellar aberration, but in this case the corrections are
   computed for radiation traveling *from* the observer to the target.
   We will refer to this situation as the "transmission" case.

   The "transmission" light time correction yields the target's
   location as it will be when photons emitted from the observer's
   location at `et' arrive at the target. The transmission stellar
   aberration correction is the inverse of the traditional stellar
   aberration correction: it indicates the direction in which
   radiation should be emitted so that, using a Newtonian
   approximation, the sum of the velocity of the radiation relative
   to the observer and of the observer's velocity, relative to the
   solar system barycenter, yields a velocity vector that points in
   the direction of the light time corrected position of the target.

   One may object to using the term "observer" in the transmission
   case, in which radiation is emitted from the observer's location.
   The terminology was retained for consistency with earlier
   documentation.

   Below, we indicate the aberration corrections to use for some
   common applications:

      1) Find the apparent direction of a target for a remote-sensing
         observation.

            Use 'LT+S' or 'CN+S: apply both light time and stellar
            aberration corrections.

         Note that using light time corrections alone ('LT' or 'CN')
         is generally not a good way to obtain an approximation to
         an apparent target vector: since light time and stellar
         aberration corrections often partially cancel each other,
         it may be more accurate to use no correction at all than to
         use light time alone.


      2) Find the corrected pointing direction to radiate a signal
         to a target. This computation is often applicable for
         implementing communications sessions.

            Use 'XLT+S' or 'XCN+S: apply both light time and stellar
            aberration corrections for transmission.


      3) Compute the apparent position of a target body relative
         to a star or other distant object.

            Use 'LT', 'CN', 'LT+S', or 'CN+S' as needed to match the
            correction applied to the position of the distant
            object. For example, if a star position is obtained from
            a catalog, the position vector may not be corrected for
            stellar aberration. In this case, to find the angular
            separation of the star and the limb of a planet, the
            vector from the observer to the planet should be
            corrected for light time but not stellar aberration.


      4) Obtain an uncorrected position vector derived directly from
         data in an SPK file.

            Use 'NONE'.


      5) Use a geometric position vector as a low-accuracy estimate
         of the apparent position for an application where execution
         speed is critical.

            Use 'NONE'.


      6) While this routine cannot perform the relativistic
         aberration corrections required to compute positions
         with the highest possible accuracy, it can supply the
         geometric positions required as inputs to these computations.

            Use 'NONE', then apply relativistic aberration
            corrections (not available in the SPICE Toolkit).


   Below, we discuss in more detail how the aberration corrections
   applied by this routine are computed.

      Geometric case
      ==============

      mice_spkpos begins by computing the geometric position T(et) of the
      target body relative to the solar system barycenter (SSB).
      Subtracting the geometric position of the observer O(et) gives
      the geometric position of the target body relative to the
      observer. The one-way light time, lt, is given by

                | T(et) - O(et) |
         lt = -------------------
                        c

      The geometric relationship between the observer, target, and
      solar system barycenter is as shown:


         SSB ---> O(et)
          |      /
          |     /
          |    /
          |   /  T(et) - O(et)
          V  V
         T(et)


      The returned state consists of the position vector

         T(et) - O(et)

      and a velocity obtained by taking the difference of the
      corresponding velocities. In the geometric case, the
      returned velocity is actually the time derivative of the
      position.


      Reception case
      ==============

      When any of the options "LT", "CN", "LT+S", "CN+S" is selected
      for `abcorr', mice_spkpos computes the position of the target body at
      epoch et-lt, where `lt' is the one-way light time. Let T(t) and
      O(t) represent the positions of the target and observer
      relative to the solar system barycenter at time t; then `lt' is
      the solution of the light-time equation

                | T(et-lt) - O(et) |
         lt = ------------------------                            (1)
                         c

      The ratio

          | T(et) - O(et) |
        ---------------------                                     (2)
                  c

      is used as a first approximation to `lt'; inserting (2) into the
      right hand side of the light-time equation (1) yields the
      "one-iteration" estimate of the one-way light time ("LT").
      Repeating the process until the estimates of `lt' converge yields
      the "converged Newtonian" light time estimate ("CN").

      Subtracting the geometric position of the observer O(et) gives
      the position of the target body relative to the observer:
      T(et-lt) - O(et).

         SSB ---> O(et)
          | \     |
          |  \    |
          |   \   | T(et-lt) - O(et)
          |    \  |
          V     V V
         T(et)  T(et-lt)

      The position component of the light time corrected state
      is the vector

         T(et-lt) - O(et)

      The velocity component of the light time corrected state
      is the difference

         T_vel(et-lt)*(1-d(lt)/d(et)) - O_vel(et)

      where T_vel and O_vel are, respectively, the velocities of the
      target and observer relative to the solar system barycenter at
      the epochs et-lt and `et'.

      If correction for stellar aberration is requested, the target
      position is rotated toward the solar system
      barycenter-relative velocity vector of the observer. The
      rotation is computed as follows:

         Let r be the light time corrected vector from the observer
         to the object, and v be the velocity of the observer with
         respect to the solar system barycenter. Let w be the angle
         between them. The aberration angle phi is given by

            sin(phi) = v sin(w) / c

         Let h be the vector given by the cross product

            h = r X v

         Rotate r by phi radians about h to obtain the apparent
         position of the object.

      When stellar aberration corrections are used, the rate of change
      of the stellar aberration correction is accounted for in the
      computation of the output velocity.


      Transmission case
      ==================

      When any of the options "XLT", "XCN", "XLT+S", "XCN+S" is
      selected, mice_spkpos computes the position of the target body T at
      epoch et+lt, where `lt' is the one-way light time. `lt' is the
      solution of the light-time equation

                | T(et+lt) - O(et) |
         lt = ------------------------                            (3)
                          c

      Subtracting the geometric position of the observer, O(et),
      gives the position of the target body relative to the
      observer: T(et-lt) - O(et).

                 SSB --> O(et)
                / |    *
               /  |  *  T(et+lt) - O(et)
              /   |*
             /   *|
            V  V  V
        T(et+lt)  T(et)

      The position component of the light-time corrected state
      is the vector

         T(et+lt) - O(et)

      The velocity component of the light-time corrected state
      consists of the difference

         T_vel(et+lt)*(1+d(lt)/d(et)) - O_vel(et)

      where T_vel and O_vel are, respectively, the velocities of the
      target and observer relative to the solar system barycenter at
      the epochs et+lt and `et'.

      If correction for stellar aberration is requested, the target
      position is rotated away from the solar system barycenter-
      relative velocity vector of the observer. The rotation is
      computed as in the reception case, but the sign of the
      rotation angle is negated.


   Precision of light time corrections
   ===================================

      Corrections using one iteration of the light time solution
      ----------------------------------------------------------

      When the requested aberration correction is "LT", "LT+S",
      "XLT", or "XLT+S", only one iteration is performed in the
      algorithm used to compute lt.

      The relative error in this computation

         | LT_ACTUAL - LT_COMPUTED |  /  LT_ACTUAL

      is at most

          (V/C)**2
         ----------
          1 - (V/C)

      which is well approximated by (V/C)**2, where V is the
      velocity of the target relative to an inertial frame and C is
      the speed of light.

      For nearly all objects in the solar system V is less than 60
      km/sec. The value of C is ~300000 km/sec. Thus the
      one-iteration solution for LT has a potential relative error
      of not more than 4e-8. This is a potential light time error of
      approximately 2e-5 seconds per astronomical unit of distance
      separating the observer and target. Given the bound on V cited
      above:

         As long as the observer and target are separated by less
         than 50 astronomical units, the error in the light time
         returned using the one-iteration light time corrections is
         less than 1 millisecond.

         The magnitude of the corresponding position error, given
         the above assumptions, may be as large as (V/C)**2 * the
         distance between the observer and the uncorrected target
         position: 300 km or equivalently 6 km/AU.

      In practice, the difference between positions obtained using
      one-iteration and converged light time is usually much smaller
      than the value computed above and can be insignificant. For
      example, for the spacecraft Mars Reconnaissance Orbiter and
      Mars Express, the position error for the one-iteration light
      time correction, applied to the spacecraft-to-Mars center
      vector, is at the 1 cm level.

      Comparison of results obtained using the one-iteration and
      converged light time solutions is recommended when adequacy of
      the one-iteration solution is in doubt.


      Converged corrections
      ---------------------

      When the requested aberration correction is 'CN', 'CN+S',
      'XCN', or 'XCN+S', as many iterations as are required for
      convergence are performed in the computation of LT. Usually
      the solution is found after three iterations. The relative
      error present in this case is at most

          (V/C)**4
         ----------
          1 - (V/C)

      which is well approximated by (V/C)**4.

         The precision of this computation (ignoring round-off
         error) is better than 4e-11 seconds for any pair of objects
         less than 50 AU apart, and having speed relative to the
         solar system barycenter less than 60 km/s.

         The magnitude of the corresponding position error, given
         the above assumptions, may be as large as (V/C)**4 * the
         distance between the observer and the uncorrected target
         position: 1.2 cm at 50 AU or equivalently 0.24 mm/AU.

      However, to very accurately model the light time between
      target and observer one must take into account effects due to
      general relativity. These may be as high as a few hundredths
      of a millisecond for some objects.


   Relativistic Corrections
   =========================

   This routine does not attempt to perform either general or
   special relativistic corrections in computing the various
   aberration corrections. For many applications relativistic
   corrections are not worth the expense of added computation
   cycles. If however, your application requires these additional
   corrections we suggest you consult the astronomical almanac (page
   B36) for a discussion of how to carry out these corrections.

Exceptions


   1)  If name of target or observer cannot be translated to its NAIF
       ID code, the error SPICE(IDCODENOTFOUND) is signaled by a
       routine in the call tree of this routine.

   2)  If the reference frame `ref' is not a recognized reference
       frame, the error SPICE(UNKNOWNFRAME) is signaled by a routine
       in the call tree of this routine.

   3)  If the loaded kernels provide insufficient data to compute the
       requested position vector, an error is signaled by a routine
       in the call tree of this routine.

   4)  If an error occurs while reading an SPK or other kernel file,
       the error  is signaled by a routine in the call tree
       of this routine.

   5)  If any of the input arguments, `targ', `et', `ref', `abcorr'
       or `obs', is undefined, an error is signaled by the Matlab
       error handling system.

   6)  If any of the input arguments, `targ', `et', `ref', `abcorr'
       or `obs', is not of the expected type, or it does not have the
       expected dimensions and size, an error is signaled by the Mice
       interface.

Files


   This routine computes positions using SPK files that have been loaded
   into the SPICE system, normally via the kernel loading interface routine
   cspice_furnsh. See the routine cspice_furnsh and the SPK and KERNEL
   Required Reading for further information on loading (and unloading)
   kernels.

   If the output position `pos' is to be expressed relative to a
   non-inertial frame, or if any of the ephemeris data used to
   compute `pos' are expressed relative to a non-inertial frame in
   the SPK files providing those data, additional kernels may be
   needed to enable the reference frame transformations required to
   compute the position. Normally these additional kernels are PCK
   files or frame kernels. Any such kernels must already be loaded
   at the time this routine is called.

Restrictions


   None.

Required_Reading


   MICE.REQ
   SPK.REQ
   NAIF_IDS.REQ
   FRAMES.REQ
   TIME.REQ

Literature_References


   None.

Author_and_Institution


   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   B.V. Semenov        (JPL)
   E.D. Wright         (JPL)

Version


   -Mice Version 1.1.0, 02-NOV-2021 (EDW) (JDR)

       Edited the header comply with NAIF standard. Added
       example's problem statement and meta-kernel.

       Added -Parameters, -Exceptions, -Files, -Restrictions,
       -Literature_References and -Author_and_Institution sections.

       Updated -Particulars to reflect latest status of sister
       API cspice_spkpos.

       Eliminated use of "lasterror" in rethrow.

       Removed reference to the function's corresponding CSPICE header from
       -Required_Reading section.

   -Mice Version 1.0.3, 03-DEC-2014 (NJB) (BVS) (EDW)

       Corrections made to author identifier for 1.0.2, 07-NOV-2013
       to indicate institution.

       Discussion of light time corrections was updated. Assertions
       that converged light time corrections are unlikely to be
       useful were removed.

   -Mice Version 1.0.2, 07-NOV-2013 (EDW)

       -I/O descriptions edits to conform to Mice documentation format.

       Added aberration algorithm explanation to -Particulars section.

   -Mice Version 1.0.1, 22-DEC-2008 (EDW)

       Header edits performed to improve argument descriptions.
       These descriptions should now closely match the descriptions
       in the corresponding CSPICE routine.

   -Mice Version 1.0.0, 22-NOV-2005 (EDW)

Index_Entries


   using names get target position relative to an observer
   position relative to observer corrected for aberrations
   read ephemeris data
   read trajectory data


Fri Dec 31 18:44:28 2021