The name Jet Propulsion Laboratory Development Ephemeris (followed by a number), or its abbreviation JPL DE (+ number), designates one of a series of numbered versions of the astronomical ephemerides produced at the Jet Propulsion Laboratory in Pasadena, California, primarily for purposes of space navigation and astronomy. Some versions of these ephemerides are or have been in official use: for example, the Astronomical Almanac issues for 1984 onwards through 2002 were based on JPL ephemeris DE200, and for 2003 onwards the Astronomical Almanac has been based on JPL ephemeris DE405.[1]
Each such ephemeris was initially produced by numerical integration of equations of motion, including the effects not only of gravitational accelerations and relativistic corrections, but also tidal and figure effects and a model of the lunar librations.[2] The time argument of the integrated ephemerides is a relativistic coordinate time scale designated Teph.[3]
The resulting ephemeris data are stored or distributed in the form of a system of numerical coefficients (for Chebyshev polynomials) which can be used to recover (calculate) the positions of the major planets of the solar system (with the Moon and Pluto, and in some cases also with data for the lunar librations and/or earth-axis nutations) for a range of dates, usually both in the past and the future, according to the interval of the original numerical integration.
The positions given by the calculations represent the development, by integration of the chosen equations of motion, of a "best fit" set of initial conditions adjusted to a (large) selected set of observations. The observational data included in the fits by which each ephemeris is produced has been an evolving set, usually including: ranges (distances) to planets measured by radio signals from spacecraft, astronomical observations of planets and small bodies in the solar system, and data derived from lunar laser-ranging, among others.
There are many different versions of the JPL DE, each one with a 2- or 3-digit serial number following.[4] They differ according to the year the data was revised and released, and according to the accuracy and time-range that each JPL DE covers.