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Index Page spkssb_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       spkssb_c ( S/P Kernel, solar system barycenter )

       void spkssb_c ( SpiceInt           targ,
                       SpiceDouble        et,
                       ConstSpiceChar   * ref,
                       SpiceDouble        starg[6] )

#### Abstract

       Return the state (position and velocity) of a target body
       relative to the solar system barycenter.

#### Required_Reading

       SPK

#### Keywords

       EPHEMERIS

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       targ       I   Target body.
       et         I   Target epoch.
       ref        I   Target reference frame.
       starg      O   State of target.

#### Detailed_Input

       targ        is the standard NAIF ID code for a target body.

       et          is the epoch (ephemeris time) at which the state of the
                   target body is to be computed.

       ref         is the name of the reference frame relative to which the
                   output state vector should be expressed. This may be any
                   frame supported by the CSPICE frame system, including
                   dynamic and other non-inertial frames.

#### Detailed_Output

       starg       is a Cartesian state vector representing the position and
                   velocity of the target body, relative to the solar system
                   barycenter, at epoch `et'. This vector is rotated into the
                   specified reference frame. Units are always km and
                   km/sec.

#### Parameters

       None.

#### Exceptions

       1)  If sufficient information has not been "loaded" via the
           routine furnsh_c, spklef_c or the PCK kernel loaders, an error is
           signaled by a routine in the call tree of this routine.

       2)  If the `ref' input string pointer is null, the error
           SPICE(NULLPOINTER) is signaled.

       3)  If the `ref' input string has zero length, the error
           SPICE(EMPTYSTRING) is signaled.

#### Files

       See -Restrictions.

#### Particulars

       In order to compute the state of one body relative to another,
       the states of the two bodies must be known relative to a third
       body. One simple solution is to use the solar system barycenter
       as the third body.

       Ephemeris data from more than one segment may be required
       to determine the state of a body relative to the barycenter.
       spkssb_c reads as many segments as necessary, from as many
       files as necessary, using files that have been loaded by
       previous calls to furnsh_c or spklef_c (load ephemeris file).

#### Examples

       The numerical results shown for this example may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) In the following example, spkssb_c is used to display
          the distance from Earth (Body 399) to Mars (body 499) at
          a given epoch.

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

             KPL/MK

             File name: spkssb_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
                ---------                     --------
                de418.bsp                     Planetary ephemeris
                naif0009.tls                  Leapseconds

             \begindata

                KERNELS_TO_LOAD = ( 'de418.bsp',
                                    'naif0009.tls'  )

             \begintext

             End of meta-kernel

          Example code begins here.

          /.
             Program spkssb_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main ()
          {

             /.
             Define parameters for a state lookup:

             Return the state vector of Mars (499)
             and Earth (399) with respect to the Solar System
             Barycenter in the J2000 frame at epoch
             July 4, 2003 11:00 AM PST.
             ./
             #define EARTH   399
             #define EPOCH   "July 4, 2003 11:00 AM PST"
             #define FRAME   "J2000"
             #define MARS    499

             /.
             Local variables.
             ./
             SpiceDouble             dist;
             SpiceDouble             et;
             SpiceDouble             searth[6];
             SpiceDouble             smars [6];

             /.
             Load the required kernels.
             ./
             furnsh_c ( "spkssb_ex1.tm" );

             /.
             Convert the epoch to ephemeris time.
             ./
             str2et_c ( EPOCH, &et );

             /.
             Look-up the states for the defined parameters.
             ./
             spkssb_c ( EARTH, et, FRAME, searth );
             spkssb_c ( MARS,  et, FRAME, smars  );

             /.
             What measure of distance separates the two bodies
             at epoch.
             ./
             dist = vdist_c( searth, smars );

             printf ( "The absolute distance (km)     : %23.10f\n", dist  );
             printf ( "between Mars and Earth at epoch: %s\n",      EPOCH );

             return ( 0 );
          }

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

          The absolute distance (km)     :     80854819.7017317861
          between Mars and Earth at epoch: July 4, 2003 11:00 AM PST

          Note that the two spkssb_c calls could be replaced by

             spkgeo_c ( EARTH, et, frame, MARS, state, lt );

          or

             spkezr_c ( "EARTH", et, frame, "NONE", "MARS", state, lt );

          using the norm of the position components of the `state'
          vector to compute the distance between the bodies.

#### Restrictions

       1)  The ephemeris files to be used by spkssb_c must be loaded
           by furnsh_c or spklef_c before spkssb_c is called.

#### Literature_References

       None.

#### Author_and_Institution

       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       W.L. Taber          (JPL)
       I.M. Underwood      (JPL)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 1.0.3, 05-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard.

           Added example's meta-kernel and problem statement. Created complete code
           example from existing code fragments.

           Moved SPK required reading from -Literature_References to
           -Required_Reading section. Added references to furnsh_c as valid
           mechanism to load the SPK files used by this routine.

       -CSPICE Version 1.0.2, 20-NOV-2004 (NJB)

           Updated description of input argument `ref' to indicate all
           frames supported by CSPICE are allowed.

       -CSPICE Version 1.0.1, 14-OCT-2003 (EDW)

           Various minor corrections to the header.

       -CSPICE Version 1.0.0, 23-JUN-1999 (NJB) (WLT) (IMU)

#### Index_Entries

       state relative to solar system barycenter

#### Link to routine spkssb_c source file spkssb_c.c

    Fri Dec 31 18:41:13 2021