Index Page
conics
A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X 

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

Procedure

      CONICS ( Determine state from conic elements )
 
      SUBROUTINE CONICS ( ELTS, ET, STATE )
 

Abstract

     Determine the state (position, velocity) of an orbiting body
     from a set of elliptic, hyperbolic, or parabolic orbital
     elements.

Required_Reading

     None.

Keywords

     CONIC
     EPHEMERIS

Declarations

 
      DOUBLE PRECISION      ELTS    ( 8 )
      DOUBLE PRECISION      ET
      DOUBLE PRECISION      STATE   ( 6 )
 

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     ELTS       I   Conic elements.
     ET         I   Input time.
     STATE      O   State of orbiting body at ET.

Detailed_Input

     ELTS       are conic elements describing the orbit of a body
                around a primary. The elements are, in order:

                      RP      Perifocal distance.
                      ECC     Eccentricity.
                      INC     Inclination.
                      LNODE   Longitude of the ascending node.
                      ARGP    Argument of periapse.
                      M0      Mean anomaly at epoch.
                      T0      Epoch.
                      MU      Gravitational parameter.

                Units are km, rad, rad/sec, km**3/sec**2.  The epoch
                is given in ephemeris seconds past J2000. The same
                elements are used to describe all three types
                (elliptic, hyperbolic, and parabolic) of conic orbit.

     ET         is the time at which the state of the orbiting body
                is to be determined, in ephemeris seconds J2000.

Detailed_Output

     STATE      is the state (position and velocity) of the body at
                time ET. Components are x, y, z, dx/dt, dy/dt, dz/dt.

Parameters

      None.

Exceptions

     1) If the eccentricity supplied is less than 0, the error
        'SPICE(BADECCENTRICITY)' is signalled.

     2) If a non-positive periapse distance is supplied, the error
       'SPICE(BADPERIAPSEVALUE)' is signalled.

     3) If a non-positive value for the attracting mass is supplied,
        the error 'SPICE(BADGM)',  is signalled.

     4) Errors such as an out of bounds value for ET are diagnosed
        by routines called by this routine.

Files

     None.

Particulars

     None.

Examples

     Let VINIT contain the initial state of a spacecraft relative to
     the center of a planet at epoch ET, and let GM be the gravitation
     parameter of the planet. The call

        CALL OSCELT ( VINIT, ET, GM, ELTS )

     produces a set of osculating elements describing the nominal
     orbit that the spacecraft would follow in the absence of all
     other bodies in the solar system and non-gravitational forces
     on the spacecraft.

     Now let STATE contain the state of the same spacecraft at some
     other epoch, LATER. The difference between this state and the
     state predicted by the nominal orbit at the same epoch can be
     computed as follows.

        CALL CONICS ( ELTS, LATER, NOMINAL )
        CALL VSUBG  ( NOMINAL, STATE, 6, DIFF )

        WRITE (*,*) 'Perturbation in x, dx/dt = ', DIFF(1), DIFF(4)
        WRITE (*,*) '                y, dy/dt = ', DIFF(2), DIFF(5)
        WRITE (*,*) '                z, dz/dt = ', DIFF(3), DIFF(6)

Restrictions

     None.

Literature_References

     [1] Roger Bate, Fundamentals of Astrodynamics, Dover, 1971.

Author_and_Institution

     I.M. Underwood  (JPL)
     W.L. Taber      (JPL)

Version

    SPICELIB Version 4.0.0, 26-MAR-1998 (WLT)

        There was a coding error in the computation of the mean
        anomaly in the parabolic case.  This problem has been
        corrected.

    SPICELIB Version 3.0.1, 15-OCT-1996 (WLT)

        Corrected a typo in the description of the units associated
        with the input elements.

    SPICELIB Version 3.0.0, 12-NOV-1992 (WLT)

        The routine was re-written to make use of NAIF's universal
        variables formulation for state propagation (PROP2B).  As
        a result, several problems were simultaneously corrected.

        A major bug was fixed that caused improper state evaluations
        for ET's that precede the epoch of the elements in the
        elliptic case.

        A danger of non-convergence in the solution of Kepler's
        equation has been eliminated.

        In addition to this reformulation of CONICS checks were
        installed that ensure the elements supplied are physically
        meaningful.  Eccentricity must be non-negative. The
        distance at periapse and central mass must be positive.  If
        not errors are signalled.

    SPICELIB Version 2.0.1, 10-MAR-1992 (WLT)

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

    SPICELIB Version 2.0.0, 19-APR-1991 (WLT)

        An error in the hyperbolic state generation was corrected.

    SPICELIB Version 1.0.0, 31-JAN-1990 (IMU)
Wed Apr  5 17:46:10 2017