|Planetary Ephemeris Attributes|
|Filename||The name of the planetary ephemeris file in JPL DE format designated as plneph.nnn where nnn = the DE version. The planetary ephemeris file is the source of position information for the Sun, planets and the Moon and is also the source of lunar attitude. These files are typically found in the ODTK folder <install home>\STKData\Astro\PlanetEphem\lendian.|
|UseTDB||The JPL DE files use TDB (Barycentric Dynamical Time) as their independent variable. ODTK typically ignores this for earth orbiting satellites and uses Terrestrial Time (TT) to access the information since the max difference between TDB and TT is on the order of 1 msec. However the differences may be important when orbiting another planet or Moon, so the option to use TDB is provided to the user. Use TDB as the independent variable time scale for accessing the JPL DE file. Setting of true is recommended. When set to "false", TT will be used.|
DE200 : (includes nutations but not librations)
JED 2305424.5 (1599 DEC 09) to JED 2513360.5 (2169 MAR 31)
This ephemeris has been the basis of the Astronomical Almanac since 1984. It is based upon the dynamical equator and equinox of J2000 (see Standish, 1982 and Standish, 1990).
DE405 : (includes both nutations and librations)
JED 2305424.50 (1599 DEC 09) to JED 2525008.50 (2201 FEB 20)
Our latest ephemeris, created in May-June, 1997. DE405 is based upon the International Celestial Reference Frame (ICRF), the newly-adopted reference frame of the International Astronomical Union (IAU).
The frames of DE200 and DE405 differ by no more than about 0.01 arcseconds.
Note: The files supplied with ODTK do not cover the complete time spans of the available ephemeris as listed above.Information regarding JPL digital planetary ephemerides is maintained at http://ssd.jpl.nasa.gov/.