Procedure

     SPKSSB ( S/P Kernel, solar system barycenter )

     SUBROUTINE SPKSSB ( TARG, ET, REF, STARG )

Abstract

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

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INTEGER               TARG
     DOUBLE PRECISION      ET
     CHARACTER*(*)         REF
     DOUBLE PRECISION      STARG    ( 6 )

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 SPICELIB 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, SPKLEF or the PCK kernel loaders, an error is
         signaled by a routine in the call tree of this routine.

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 reads as many segments as necessary, from as many
     files as necessary, using files that have been loaded by
     previous calls to FURNSH or SPKLEF (load ephemeris file).

Examples

     In the following code fragment, SPKSSB is used to display
     the distance from Earth (Body 399) to Mars (body 499) at
     a series of epochs.

        CALL SPKLEF ( 'DE125.SPK', HANDLE )
         .
         .

        EARTH = 399
        MARS  = 499

        DO WHILE ( EPOCH .LE. END )
           CALL SPKSSB ( EARTH, EPOCH, 'J2000', SEARTH )
           CALL SPKSSB ( MARS,  EPOCH, 'J2000', SMARS  )

           CALL VSUB ( SMARS, SEARTH, SMARS )
           WRITE (*,*) EPOCH, VNORM ( SMARS )

           EPOCH = EPOCH + DELTA
        END DO

Restrictions

     1)  The ephemeris files to be used by SPKSSB must be loaded
         by FURNSH or SPKLEF before SPKSSB is called.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     H.A. Neilan        (JPL)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 2.0.4, 13-APR-2021 (JDR)

        Edited the header to comply with NAIF standard. Updated
        detailed description of arguments REF and STARG.

    SPICELIB Version 2.0.3, 18-MAY-2010 (BVS)

        Removed "C$" marker from text in the header.

    SPICELIB Version 2.0.2, 20-NOV-2004 (NJB)

        Updated description of input argument REF to indicate all
        frames supported by SPICELIB are allowed.

    SPICELIB Version 2.0.1, 24-JUN-1999 (WLT)

        Corrected code in $Examples section of the headers

    SPICELIB Version 2.0.0, 19-SEP-1995 (WLT)

        The routine was simplified by replacing all of the
        main body of code with a call to SPKGEO. By making
        this change the routine now supports non-inertial frames.

    SPICELIB Version 1.0.2, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.1, 22-MAR-1990 (HAN)

        Literature references added to the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (IMU)