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KPL/FK

SPICE Lunar Reference Frame Specification Kernel
   =====================================================================

Original file name:                   moon_080317.tf
   Creation date:                        2008 March 17 20:10
   Created by:                           Nat Bachman  (NAIF/JPL)
   Date of last revision:                2008 March 21 16:07
   Purpose of revision:

Changed names of PA system and frame from "principal axis" to 
      "principal axes."

Version description:

This frame kernel contains lunar frame specifications compatible
      with the current lunar binary PCK file

moon_pa_de421_1900-2050.bpc

The above PCK contains lunar orientation data from the DE-421 JPL
      Planetary Ephemeris.

The previous NAIF lunar frame specification kernel was

moon_071218.tf

That kernel is compatible with the DE-418-based lunar binary PCK
      file

moon_pa_de418_1950-2050.bpc
 
      The comment section below titled "Lunar body-fixed frame
      associations" discusses lunar frame association kernels. These
      kernels direct portions of the SPICE system that rely on default
      body-fixed reference frames to associate with the Moon either the
      MOON_ME or MOON_PA reference frames.

This file was modified on 26-FEB-2009 by Nat Bachman. The initial
   blank line was removed and this change description was added. 
   Nothing else has been changed.

Frames Specified by this Kernel
   =====================================================================

Frame Name       Relative to        Type   Frame ID
   --------------   -----------------  -----  --------
   MOON_PA          MOON_PA_DE421      FIXED  31000
   MOON_ME          MOON_ME_DE421      FIXED  31001
   MOON_PA_DE421    ICRF/J2000         PCK    31006
   MOON_ME_DE421    MOON_PA_DE421      FIXED  31007

Introduction
   =====================================================================

This kernel specifies lunar body-fixed reference frames for use by
   SPICE-based application software. These reference frames are
   associated with high-accuracy lunar orientation data provided by the
   JPL Solar System Dynamics Group's planetary ephemerides (both
   trajectory and lunar orientation data are stored in these ephemeris
   files). These ephemerides have names of the form DE-nnn (DE stands
   for "developmental ephemeris").

The frames specified by this kernel are realizations of two different
   lunar reference systems:

Principal Axes (PA) system 
      --------------------------
      The axes of this system are defined by the principal axes of the
      Moon. Due to the nature of the Moon's orbit and
      rotation, the Z axis of this system does not coincide with the
      Moon's mean spin axis, nor does the X axis coincide with the mean
      direction to the center of the Earth (in contrast with the ME
      system defined below).
 
      Lunar principal axes frames realizing the lunar PA system and
      specified by this kernel are associated with JPL planetary
      ephemerides. Each new JPL planetary ephemeris can (but does not
      necessarily) define a new realization of the lunar principal axes
      system. Coordinates of lunar surface features expressed in lunar
      PA frames can change slightly from one lunar ephemeris version to
      the next.

Mean Earth/Polar Axis (ME) system
      ---------------------------------
      The Lunar mean Earth/polar axis system is a lunar body-fixed
      reference system used in the IAU/IAG Working Group Report [2] to
      describe the orientation of the Moon relative to the ICRF frame.
      The +Z axis of this system is aligned with the north mean lunar
      rotation axis, while the prime meridian contains the the mean
      Earth direction.

This system is also sometimes called the "mean Earth/mean
      rotation axis" system or "mean Earth" system.
 
      The mean directions used to define the axes of a mean Earth/polar
      axis reference frame realizing the lunar ME system and specified
      by this kernel are associated with a given JPL planetary
      ephemeris version. The rotation between the mean Earth frame for
      a given ephemeris version and the associated principal axes frame
      is given by a constant matrix (see [1]).

For the current JPL planetary ephemeris (DE), this kernel includes
   specifications of the corresponding principal axes and mean Earth/
   polar axis frames. The names of these frames have the form

MOON_PA_DEnnn
     
   and

MOON_ME_DEnnn

respectively, where nnn is the version number of the DE. The set of
   DE-dependent frame specifications will grow over time; frame
   specifications pertaining to older DEs can be obtained from earlier
   versions of this frame kernel.

For each of the two reference systems, there is a corresponding
   "generic" frame specification:  these generic frames are simply
   aliases for the PA and ME frames associated with the latest DE. The
   generic frame names are

MOON_PA
      MOON_ME

These generic frame names are provided to enable SPICE-based
   applications to refer to the latest DE-based (or other) lunar
   rotation data without requiring code modifications as new kernels
   become available. SPICE users may, if they wish, modify this kernel
   to assign these frame aliases to other frames than those selected
   here, for example, older DE-based frames. NAIF recommends that, if
   this frame kernel is modified, the name of this file also be changed
   to avoid confusion.

Comparison of PA and ME frames
   ------------------------------

The rotation between the mean Earth frame for a given DE and the
   associated principal axes frame for the same DE is given by a
   constant matrix (see [1]). For DE-421, the rotation angle of this
   matrix is approximately 0.0288473 degrees; this is equivalent to
   approximately 875 m when expressed as a displacement along a great
   circle on the Moon's surface.

Comparison of DE-based and IAU/IAG report-based ME frames
   ---------------------------------------------------------

Within the SPICE system, a lunar ME frame specified by the
   rotational elements from the IAU/IAG Working Group report [2] is
   given the name IAU_MOON; the data defining this frame are provided
   in a generic text PCK.
 
   The orientation of the lunar ME frame obtained by applying the
   DE-based PA-to-ME rotation described above to the DE-based lunar
   libration data does not agree closely with the lunar ME frame
   orientation given by the rotational elements from the IAU/IAG
   Working Group report (that is, the IAU_MOON frame). The difference
   is due to truncation of the libration series used in the report's
   formula for lunar orientation (see [1]).
 
   In the case of DE-421, for the time period ~2000-2020, the
   time-dependent difference of these ME frame implementations has an
   amplitude of approximately 0.0051 degrees, which is equivalent to
   approximately 155 m, measured along a great circle on the Moon's
   surface, while the average value is approximately 0.00249 degrees,
   or 76 m.

Comparison of DE-421 and DE-418 Lunar Reference Frames
   ======================================================

The magnitudes of the rotational offsets between the
   DE-418 and DE-421 realizations of the MOON_PA and MOON_ME
   frames are discussed below.

Note that the angle ranges shown below are ordered as signed values,
   *not* by absolute value.

MOON_PA frame orientation differences
   -------------------------------------

Tests performed by NAIF indicate an approximately 0.45 microradian
   maximum rotation between the MOON_PA_DE418 and MOON_PA_DE421 frames,
   based on a sampling of orientation data over the time period
   2000-2020. This offset corresponds to a displacement of about 0.79 m
   along a great circle on the Moon's surface.

When the transformation from the MOON_PA_DE418 frame to the
   MOON_PA_DE421 frame is decomposed as a 1-2-3 Euler angle sequence,
   the offset angle ranges for each axis are:

X axis:     -3.8063e-07  to  -2.9746e-07 radians
      Y axis:     -2.5322e-07  to  -1.8399e-07 radians
      Z axis:     -9.9373e-08  to   6.0046e-08 radians

MOON_ME frame orientation differences
   -------------------------------------

Tests performed by NAIF indicate an approximately 0.27 microradian
   maximum rotation between the MOON_ME_DE418 and MOON_ME_DE421 frames,
   based on a sampling of orientation data over the time period
   2000-2020. This offset corresponds to a displacement of about 0.46 m
   along a great circle on the Moon's surface.

When the transformation from the MOON_ME_DE418 frame to the
   MOON_ME_DE421 frame is decomposed as a 1-2-3 Euler angle sequence,
   the offset angle ranges for each axis are:

X axis:     7.2260e-09   to   9.0391e-08 radians
      Y axis:     3.7643e-08   to   1.0691e-07 radians
      Z axis:    -2.4471e-07   to  -8.5296e-08 radians

Regarding Use of the ICRF in SPICE
   ==================================

The IERS Celestial Reference Frame (ICRF) is offset from the J2000
   reference frame (equivalent to EME 2000) by a small rotation:  the
   J2000 pole offset magnitude is about 18 milliarcseconds (mas) and
   the equinox offset magnitude is approximately 78 milliarcseconds
   (see [3]).
 
   Certain SPICE data products use the frame label "J2000" for data
   that actually are referenced to the ICRF. This is the case for SPK
   files containing JPL version DE-4nn planetary ephemerides, for
   orientation data from generic text PCKs, and for binary PCKs,
   including binary lunar PCKs used in conjunction with this lunar
   frame kernel.

Consequently, when SPICE computes the rotation between the "J2000"
   frame and either of the lunar PA or ME frames, what's computed is
   actually the rotation between the ICRF and the respective lunar
   frame.

Similarly, when SPICE is used to compute the state given by a JPL DE
   planetary ephemeris SPK file of one ephemeris object relative to
   another (for example, the state of the Moon with respect to the
   Earth), expressed relative to the frame "J2000," the state is
   actually expressed relative to the ICRF.

Because SPICE is already using the ICRF, users normally need not
   use the J2000-to-ICRF transformation to adjust results computed
   with SPICE.

Lunar body-fixed frame associations
   =====================================================================

By default, the SPICE system considers the body-fixed reference
   frame associated with the Moon to be the one named IAU_MOON. This
   body-frame association affects the outputs of the SPICE frame system
   routines

CIDFRM
      CNMFRM
  
   and of the SPICE time conversion and geometry routines

ET2LST
      ILLUM
      SRFXPT
      SUBPT
      SUBSOL

Also, any code that calls these routines to obtain results involving
   lunar body-fixed frames are affected. Within SPICE, the only
   higher-level system that is affected is the dynamic frame system.

NAIF provides "frame association" kernels that simplify changing the
   body-fixed frame associated with the Moon. Using FURNSH to load
   either of the kernels named below changes the Moon's body-fixed
   frame from its current value, which initially is IAU_MOON, to that
   shown in the right-hand column:

Kernel name          Lunar body-fixed frame        
      -----------          ----------------------
      moon_assoc_me.tf     MOON_ME
      moon_assoc_pa.tf     MOON_PA

For further information see the in-line comments in the association
   kernels themselves. Also see the Frames Required Reading section
   titled "Connecting an Object to its Body-fixed Frame."

In the N0062 SPICE Toolkit, the routines

ILLUM
      SRFXPT
      SUBPT
      SUBSOL

are superseded, respectively, by the routines

ILUMIN
      SINCPT
      SUBPNT
      SUBSLR

The newer routines don't require frame association kernels: the name
   of the target body's body-fixed reference frame is an input argument
   to these routines.

Using this Kernel
   =====================================================================

In order for a SPICE-based application to use reference frames
   specified by this kernel, the application must load both this kernel
   and a binary lunar PCK containing lunar orientation data for the
   time of interest. Normally the kernels need be loaded only once
   during program initialization.
 
   SPICE users may find it convenient to use a meta-kernel (also called
   a "FURNSH kernel") to name the kernels to be loaded. Below, we show
   an example of such a meta-kernel, as well as the source code of a
   small Fortran program that uses lunar body fixed frames. The
   program's output is included as well.
 
   The kernel names shown here are simply used as examples; users must
   select the kernels appropriate for their applications.
 
   Numeric results shown below may differ very slightly from those
   obtained on users' computer systems.

Meta-kernel
   -----------

KPL/MK

Example meta-kernel showing use of

- binary lunar PCK
        - generic lunar frame kernel (FK)
        - leapseconds kernel (LSK)
        - planetary SPK

17-MAR-2008 (NJB)

Note: to actually use this kernel, replace the @ characters
       below with backslashes (\). The backslash character cannot be
       used here, within the comments of this frame kernel, because the
       begindata and begintext strings would be interpreted as
       directives bracketing actual load commands.

This meta-kernel assumes that the referenced kernels exist
       in the user's current working directory.

@begindata

KERNELS_TO_LOAD = ( 'moon_pa_de421_1900-2050.bpc'
                                'moon_080317.tf'
                                'leapseconds.ker'
                                'de421.bsp'                  )

@begintext

Example program
   ---------------

PROGRAM EX1
            IMPLICIT NONE

INTEGER               FILSIZ
            PARAMETER           ( FILSIZ = 255 )

CHARACTER*(FILSIZ)    META

DOUBLE PRECISION      ET
            DOUBLE PRECISION      LT
            DOUBLE PRECISION      STME  ( 6 )
            DOUBLE PRECISION      STPA  ( 6 )

C
      C     Prompt user for meta-kernel name.
      C
            CALL PROMPT ( 'Enter name of meta-kernel > ', META )

C
      C     Load lunar PCK, generic lunar frame kernel,
      C     leapseconds kernel, and planetary ephemeris
      C     via metakernel.
      C
            CALL FURNSH ( META )

C
      C     Convert a time of interest from UTC to ET.
      C
            CALL STR2ET ( '2008 MAR 17 20:10:00', ET )

WRITE (*,*) 'ET (sec past J2000 TDB): ', ET
            WRITE (*,*) '   State of Earth relative to Moon'

C
      C     Find the geometric state of the Earth relative to the
      C     Moon at ET, expressed relative to the ME frame.
      C    
            CALL SPKEZR ( 'Earth',  ET,      'MOON_ME', 
           .              'NONE',   'Moon',  STME,      LT )

WRITE (*,*) '      In MOON_ME frame:'
            WRITE (*,*) STME

C
      C     Find the geometric state of the Earth relative to the
      C     Moon at ET, expressed relative to the PA frame.
      C    
            CALL SPKEZR ( 'Earth',  ET,      'MOON_PA', 
           .              'NONE',   'Moon',  STPA,      LT )

WRITE (*,*) '      In MOON_PA frame:'
            WRITE (*,*) STPA

END

Program output
   --------------

Enter name of meta-kernel > meta
       ET (sec past J2000 TDB):   259056665.
          State of Earth relative to Moon
             In MOON_ME frame:
        379892.825  33510.118 -12661.5278  0.0400357582  0.0117963334  0.115130508
             In MOON_PA frame:
        379908.634  33385.003 -12516.8859  0.0399957879  0.0117833314  0.115145731

References
   =====================================================================

[1]  J.G. Williams, D.H. Boggs and W.M. Folkner. "DE421 Lunar  
        Orbit, Physical Librations, and Surface Coordinates,"
        preprint of JPL IOM 335-JW,DB,WF-20080314-001, dated 
        March 14, 2008.

[2]  Seidelmann, P.K., Abalakin, V.K., Bursa, M., Davies, M.E.,
        Bergh, C. de, Lieske, J.H., Oberst, J., Simon, J.L., Standish,
        E.M., Stooke, P., and Thomas, P.C. (2002). "Report of the
        IAU/IAG Working Group on Cartographic Coordinates and Rotational
        Elements of the Planets and Satellites: 2000," Celestial
        Mechanics and Dynamical Astronomy, v.82, Issue 1, pp. 83-111.

[3]  Roncoli, R. (2005). "Lunar Constants and Models Document," 
        JPL D-32296.

Frame Specifications
   =====================================================================

MOON_PA is the name of the generic lunar principal axes (PA) reference
   frame. This frame is an alias for the principal axes frame defined
   by the latest version of the JPL Solar System Dynamics Group's
   planetary ephemeris.
 
   In this instance of the lunar reference frames kernel, MOON_PA is an
   alias for the lunar principal axes frame associated with the
   planetary ephemeris DE-421.

\begindata
 
      FRAME_MOON_PA                 = 31000
      FRAME_31000_NAME              = 'MOON_PA'
      FRAME_31000_CLASS             = 4
      FRAME_31000_CLASS_ID          = 31000
      FRAME_31000_CENTER            = 301

TKFRAME_31000_SPEC            = 'MATRIX'
      TKFRAME_31000_RELATIVE        = 'MOON_PA_DE421'
      TKFRAME_31000_MATRIX          = ( 1 0 0
                                        0 1 0
                                        0 0 1 )

\begintext

MOON_ME is the name of the generic lunar mean Earth/polar axis (ME)
   reference frame. This frame is an alias for the mean Earth/polar
   axis frame defined by the latest version of the JPL Solar System
   Dynamics Group's planetary ephemeris.
 
   In this instance of the lunar reference frames kernel, MOON_ME is an
   alias for the lunar mean Earth/polar axis frame associated with the
   planetary ephemeris DE-421.

\begindata

FRAME_MOON_ME                 = 31001
      FRAME_31001_NAME              = 'MOON_ME'
      FRAME_31001_CLASS             = 4
      FRAME_31001_CLASS_ID          = 31001
      FRAME_31001_CENTER            = 301
 
      TKFRAME_31001_SPEC            = 'MATRIX'
      TKFRAME_31001_RELATIVE        = 'MOON_ME_DE421'
      TKFRAME_31001_MATRIX          = ( 1 0 0
                                        0 1 0
                                        0 0 1 )

\begintext

MOON_PA_DE421 is the name of the lunar principal axes
   reference frame defined by JPL's DE-421 planetary ephemeris.

\begindata

FRAME_MOON_PA_DE421           = 31006
      FRAME_31006_NAME              = 'MOON_PA_DE421'
      FRAME_31006_CLASS             = 2
      FRAME_31006_CLASS_ID          = 31006
      FRAME_31006_CENTER            = 301

FRAME_MOON_PA_DE403          = 31002
      FRAME_31002_NAME              = 'MOON_PA_DE403'
      FRAME_31002_CLASS             = 2
      FRAME_31002_CLASS_ID          = 31002
      FRAME_31002_CENTER            = 301

\begintext

MOON_ME_DE421 is the name of the lunar mean Earth/polar
   axis reference frame defined by JPL's DE-421 planetary ephemeris.

Rotation angles are from reference [1].

\begindata
 
      FRAME_MOON_ME_DE421           = 31007
      FRAME_31007_NAME              = 'MOON_ME_DE421'
      FRAME_31007_CLASS             = 4
      FRAME_31007_CLASS_ID          = 31007
      FRAME_31007_CENTER            = 301

TKFRAME_31007_SPEC            = 'ANGLES'
      TKFRAME_31007_RELATIVE        = 'MOON_PA_DE421'
      TKFRAME_31007_ANGLES          = (   67.92     78.56     0.30    )
      TKFRAME_31007_AXES            = (   3,        2,        1       )
      TKFRAME_31007_UNITS           = 'ARCSECONDS'

\begintext

Updating this Kernel
   --------------------

When a new JPL DE providing lunar rotation data becomes available,
   the new lunar PA frame associated with that data set will be named

MOON_PA_DEnnn

where nnn is the version number of the DE.

The PCK body ID code associated with that data set will be

31008

The frame ID and class ID for this frame will also be 31008.

The generic PA frame specification will be updated to point to the
   new DE-specific PA frame. The rest of this frame specification
   is unchanged.

The ME frame name associated with the new data set will be named
 
      MOON_ME_DEnnn

The frame ID and class ID for this frame will be

31009

The rotational offset between this frame and the new DE-specific PA
   frame will need to be updated; this offset is DE-dependent.
    
   The generic ME frame specification will be updated to point to the
   new DE-specific ME frame. The rest of this frame specification
   is unchanged.

=====================================================================
   End of kernel

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File moon_080317.tf of Package python-skyfield (Revision ca10e2f3f0380a5ee8dddb9cc1af159b)

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