Procedure

     SPKR15 ( Read SPK record from segment, type 15 )

     SUBROUTINE SPKR15 ( HANDLE, DESCR, ET, RECORD )

Abstract

     Read a single SPK data record from a segment of type 15
     (Precessing Conic Propagation).

Required_Reading

     SPK

Keywords

     EPHEMERIS

Declarations

     IMPLICIT NONE

     INTEGER               HANDLE
     DOUBLE PRECISION      DESCR (5)
     DOUBLE PRECISION      ET
     DOUBLE PRECISION      RECORD(*)

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     HANDLE     I   File handle.
     DESCR      I   Segment descriptor.
     ET         I   Target epoch.
     RECORD     O   Data record.

Detailed_Input

     HANDLE,
     DESCR    are the file handle and segment descriptor for
              a SPK segment of type 15.

     ET       is a target epoch, for which a data record from
              a specific segment is required.

Detailed_Output

     RECORD   is the record from the specified segment 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.

Parameters

     None.

Exceptions

     1)  If the segment specified by DESCR is not a type 15 segment,
         the error SPICE(WRONGSPKTYPE) is signaled.

     2)  A type 15 segment should have exactly 16 values. If this
         is not the case, the error SPICE(MALFORMEDSEGMENT) is
         signaled.

Files

     See argument HANDLE.

Particulars

     This routine reads all of the data from a type 15 SPK segment.

     The structure of the data retrieved in RECORD is:

         RECORD(1)             epoch of the orbit elements at periapse
                               in ephemeris seconds past J2000.
         RECORD(2)-RECORD(4)   unit trajectory pole vector
         RECORD(5)-RECORD(7)   unit periapsis vector
         RECORD(8)             semi-latus rectum---p in the
                               equation:

                               r = p/(1 + ECC*COS(Nu))

         RECORD(9)             eccentricity
         RECORD(10)            J2 processing flag describing
                               what J2 corrections are to be
                               applied when the orbit is
                               propagated.

                                Value       Meaning
                                -----  -----------------------------
                                1      Regress line of nodes only.
                                2      Precess line of apsides only.
                                3      Don't use J2 corrections.
                                Other  Regress line of nodes
                                       and precess line of apsides.

         RECORD(11)-RECORD(13) unit central body pole vector
         RECORD(14)            central body GM
         RECORD(15)            central body J2
         RECORD(16)            central body radius

     Except for J2, units are radians, km, seconds.

Examples

     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 "dump" and check segment data for a
     particular epoch.


     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. 15 ) THEN
              CALL SPKR15 ( HANDLE, DESCR, ET, RECORD )
                  .
                  .  Look at the RECORD data.
                  .
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     S. Schlaifer       (JPL)
     W.L. Taber         (JPL)
     E.D. Wright        (JPL)

Version

    SPICELIB Version 1.1.1, 27-AUG-2021 (JDR)

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.1.0, 07-SEP-2001 (EDW)

        Replaced DAFRDA call with DAFGDA.
        Added IMPLICIT NONE.

    SPICELIB Version 1.0.0, 15-NOV-1994 (WLT) (SS)