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--></style><title>New SPICE Kernels based on the DE421
Ephemeris</title></head><body>
<div>SPICE kernels based on JPL's new DE421 planet and lunar ephemeris
are now available on the NAIF server. See the announcement on the NAIF
home page: http://naif.jpl.nasa.gov.</div>
<div><br></div>
<div>Lunar Ephemeris and Orientation</div>
<div>-------------------------------</div>
<div><br></div>
<div>A PDF-format memo describing the production of the DE421 lunar
ephemeris and orientation source data used in making these kernels is
available from the NAIF server here:</div>
<div><br></div>
<div> <font face="Lucida Grande" color="#000000">
ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/<font
size="-4">de421_lunar_ephemeris_and_orientation.pdf</font></font></div
>
<div><br></div>
<div>The new DE421-based lunar frames kernel that is part of this set
of new kernels is a plain text file, easily read using any text
display device. Included in this FK is a good deal of descriptive
information, including comparisons of the lunar Principal Axes (PA)
and Mean Earth/Polar Axis (ME) frames, and comparisons of the PA and
ME frames as realized using DE421 versus their predecessors based on
DE418.</div>
<div><br></div>
<div>The existence of more than one (in particular, three!) lunar
orientation frames within the SPICE domain has created some
complication for SPICE users. The NAIF web page announcement mentioned
above, and the special SPICE tutorial on lunar and earth PCK and FK
("25_lunar-earth_pck-fk"), address these points.</div>
<div><br></div>
<div><br></div>
<div>Planet Ephemeris</div>
<div>----------------</div>
<div><br></div>
<div>The NAIF web page announcement mentioned above focuses on the
moon, but DE421 is appropriate for all planetary ephemeris uses.</div>
<div><br></div>
<div>A memo describing the overall production of the DE421 planet
ephemeris will eventually be available at this same location
("soon," but no specific date known).</div>
<div><br></div>
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