Procedure

     SPKR17 ( Read SPK record from segment, type 17 )

     SUBROUTINE SPKR17 ( HANDLE, DESCR, ET, RECORD )

Abstract

     Read a single SPK data record from a segment of type 17
     (Equinoctial Elements).

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 17.

     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 17 segment,
         the error SPICE(WRONGSPKTYPE) is signaled.

     2)  A type 17 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 17 SPK segment.

     The structure of the data retrieved in RECORD is:

         RECORD(1) is the epoch of the orbit elements at
                   in ephemeris seconds past J2000.

         RECORD(2) is the semi-major axis (A) of the orbit.

         RECORD(3) is the value of H at the specified epoch.
                   ( E*SIN(ARGP+NODE) ).

         RECORD(4) is the value of K at the specified epoch
                   ( E*COS(ARGP+NODE) ).

         RECORD(5) is the mean longitude (MEAN0+ARGP+NODE)at
                   the epoch of the elements.

         RECORD(6) is the value of P (TAN(INC/2)*SIN(NODE))at
                   the specified epoch.

         RECORD(7) is the value of Q (TAN(INC/2)*COS(NODE))at
                        the specified epoch.

         RECORD(8) is the rate of the longitude of periapse
                   (dARGP/dt + dNODE/dt ) at the epoch of
                   the elements. This rate is assumed to hold
                   for all time.

         RECORD(9) is the derivative of the mean longitude
                   ( dM/dt + dARGP/dt + dNODE/dt ).  This
                   rate is assumed to be constant.

         RECORD(10) is the rate of the longitude of the ascending
                    node ( dNODE/dt).

         RECORD(11) Right Ascension of the pole of the
                    orbital reference system relative to the
                    reference frame of the associated SPK segment.

         RECORD(12) Declination of the pole of the
                    orbital reference system relative to the
                    reference frame of the associated SPK segment.

     Units are km, radians and radians/second.

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. 17 ) THEN
              CALL SPKR17 ( 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. Fixed textual
        description of SPK type in $Abstract.

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

        Replaced DAFRDA call with DAFGDA.
        Added IMPLICIT NONE.

    SPICELIB Version 1.0.0, 03-JAN-1997 (WLT) (SS)