Procedure

     SPKE05 ( Evaluate SPK record, type 5 )

     SUBROUTINE SPKE05 ( ET, RECORD, STATE )

Abstract

     Evaluate a single SPK data record from a segment of type 5
     (two body propagation between discrete state vectors).

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD   ( * )
     DOUBLE PRECISION      STATE    ( 6 )

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     ET         I   Target epoch.
     RECORD     I   Data record.
     STATE      O   State (position and velocity).

Detailed_Input

     ET       is a target epoch, specified as ephemeris seconds past
              J2000, at which a state vector is to be computed.

     RECORD   is a data record which, when evaluated at epoch ET,
              will give the state (position and velocity) of some
              body, relative to some center, in some inertial
              reference frame.

              The structure of RECORD is:

                  RECORD(1)
                     .            state of the body at epoch 1.
                     .
                     .
                  RECORD(6)

                  RECORD(7)
                     .
                     .            state of the body at epoch 2.
                     .
                  RECORD(12)
                  RECORD(13)      epoch 1 in seconds past 2000.
                  RECORD(14)      epoch 2 in seconds past 2000.
                  RECORD(15)      GM for the center of motion.

              Epoch 1 and epoch 2 are the times in the segment that
              bracket ET. If ET is less than the first time in the
              segment then both epochs 1 and 2 are equal to the
              first time. And if ET is greater than the last time
              then, epochs 1 and 2 are set equal to this last time.

Detailed_Output

     STATE    is the state produced by evaluating RECORD at ET.
              Units are km and km/sec.

Parameters

     None.

Exceptions

     1)  If there is a problem propagating, subject to the laws of two
         body motion, either of the states from RECORD to the requested
         time ET, an error is signaled by a routine in the call tree of
         this routine.

Files

     None.

Particulars

     This routine interpolates a state from the two reference states
     contained in RECORD.

     It is assumed that this routine is used in conjunction with
     the routine SPKR05 as shown here:

        CALL SPKR05 ( HANDLE, DESCR, ET, RECORD         )
        CALL SPKE05 (                ET, RECORD, STATE  )

     Where it is known in advance that the HANDLE, DESCR pair points
     to a type 05 data segment.

Examples

     The SPKEnn routines are almost always used in conjunction with
     the corresponding SPKRnn routines, which read the records from
     SPK files.

     The data returned by the SPKRnn routine is in its rawest form,
     taken directly from the segment. As such, it will be meaningless
     to a user unless he/she understands the structure of the data type
     completely. Given that understanding, however, the SPKRnn
     routines might be used to examine raw segment data before
     evaluating it with the SPKEnn routines.


     C
     C     Get a segment applicable to a specified body and epoch.
     C
           CALL SPKSFS ( BODY, ET, HANDLE, DESCR, IDENT, FOUND )

     C
     C     Look at parts of the descriptor.
     C
           CALL DAFUS ( DESCR, 2, 6, DCD, ICD )
           CENTER = ICD( 2 )
           REF    = ICD( 3 )
           TYPE   = ICD( 4 )

           IF ( TYPE .EQ. 5 ) THEN

              CALL SPKR05 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
              CALL SPKE05 ( ET, RECORD, STATE )
                  .
                  .  Check out the evaluated state.
                  .
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     K.R. Gehringer     (JPL)
     J.M. Lynch         (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.3.0, 12-AUG-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.2.0, 31-AUG-2005 (NJB)

        Updated to remove non-standard use of duplicate arguments
        in VADD call.

    SPICELIB Version 1.1.0, 29-FEB-1996 (KRG)

        The declaration for the SPICELIB function PI is now
        preceded by an EXTERNAL statement declaring PI to be an
        external function. This removes a conflict with any
        compilers that have a PI intrinsic function.

    SPICELIB Version 1.0.0, 01-APR-1992 (JML) (WLT) (IMU)