; de414.bsp LOG FILE ; ; Created 2006-04-25/17:03:32.00. ; ; BEGIN NIOSPK COMMANDS SPK_FILE = de414.bsp SOURCE_NIO_FILE = de414.nio BEGIN_TIME = CAL-ET 1599 DEC 09 00:00:00.000 END_TIME = CAL-ET 2201 FEB 20 00:00:00.000 ; END NIOSPK COMMANDS JPL Planetary Ephemeris DE414 E. M. Standish 21 April 2006 (Note: the following is the ASCII text portion of the original memo, which has been published in PDF format with assorted tables and figures. This ASCII version was produced for inclusion in the "comment area" of the SPICE SPK version of the ephemeris. Substitutions have been made for assorted italic, superscript and subscript characters. The tables and figures, of course, can not be included in this plain text.) The JPL Planetary Ephemeris DE414 was created in May 2005 and has been used by a number of people at JPL since then. DE414 is now JPL's latest and most accurate planetary ephemeris. This memo serves to document DE414 and to recommend its use for present-day spacecraft navigation. It is expected that a newer ephemeris will become available sometime later in the year when the observational data sets have been updated. Most of the basic features of the JPL planetary ephemerides have been documented previously (see Standish et al., 1995; Standish, 1998; Standish, 2003a; Standish, 2003b). Also available is a complete description of DE405, which has, since 2003, been the basis of the Astronomical Almanac. The description of DE405 will be published (hopefully soon) in the next version of the Explanatory Supplement to the Astronomical Almanac. This memo briefly discusses the reference system of DE414 and the numerical integration of the equations of motion, presents a table listing the full set of observational data to which DE414 was fit, mentions a couple of recent updates which are unique to DE414, presents a table of the more pertinent astronomical constants which were used in the creation of DE414, compares the ephemeris of each planet in DE414 to those in DE405, and briefly mentions the accuracies of DE414. ICRF : the Reference System of DE414 As discussed in previous memos, the JPL planetary ephemerides are now based upon the International Celestial Reference Frame (ICRF). This is accomplished by inclusion of the VLBI measurements into the observational data set. In particular, the Magellan observations of Venus and, especially, the MGS and Odyssey observations of Mars tie the inner planetary system onto the ICRF through the fitting process. The VLBI observations of Galileo do the same thing for Jupiter. The outer planets are referenced to the ICRF by transforming their FK5-based observations using a table provided by Morrison et al (1996) for the La Palma transit observations and angles provided by Kovalevsky (1996) for the other transit observations. In the future, these will be replaced by the formulae of Feissel and Mignard (1998). The reduction of ranging data requires the orientation of the earth in order to locate the antennas; for this, the earth orientation parameters from the International Earth Rotation Service (IERS) are used. These are also based upon the ICRF, and thus the orientation of the earth is consistent with the ephemerides. The Integration of DE414 DE414 is a fully-integrated ephemeris. The equations of motion are documented in Chapter 8 of the Explanatory Supplement (2007), available via ftp as mentioned above in the Introduction. The basic integrator is ``QIVA", a quadruple-precision version of ``DIVA", (Krogh, 1997). For the equations of motion, the newtonian part is computed in quadruple precision; all of the rest (relativity, asteroid perturbations, figure effects, tides, etc.) are computed in double precision. Such a mixed-precision integration requires about 16 minutes per century. There is the option of running totally in double precision for approximate accuracy; this requires only 35 seconds per century - 30 times faster than the mixed-precision mode. The Observational Data Fit by DE414 Table I presents a listing of the sets of observations fit by DE414. These data have been discussed previously in the memos mentioned above. Most of the data are available at: http://iau-comm4.jpl.nasa.gov/plan-eph-data/index.html. The following comments are pertinent: - The set of MGS and Odyssey ranging observations was extended to the end of April, 2005, and the set was condensed into normal points: all of the ranges from a single pass (single orbit around Mars) were combined into one representative point for fitting. As such, 128,392 raw points from MGS and 150,968 points from Odyssey were condensed into 8120 and 4082 points, respectively. - Up-to-date CCD observations of the five outermost planets and their satellites, taken at many observatories, especially the USNO at Flagstaff and JPL's Table Mountain, were added to the observation set. \item Two data sets were inadvertantly omitted from the fit for DE414: the Magellan doppler points of Venus, 1992-94, and the Galileo VLBI points of Jupiter, 1996-97. - In addition to the observations listed in Table I, there were -- 3488 range measurements to the NEAR spacecraft orbiting Eros. These were pre-fitted residuals with only the signature of the Earth-Moon mass ratio remaining; they were used in DE414 for the determination of only that single parameter. -- 6 points from the frame tie of Folkner et al (1993). --1 pseudo observation to enter the list of initial conditions into the solution program The Various Constants of DE414 Table II shows the masses of the planets in DE414, and, for comparison, the 1994 IAU ``Best Estimates" (Standish, 1995). In the future, for consistency with the gravity field models, the values for the earth and moon will be replaced using GM(moon) = 4902.8000 km3/sec2 and GM(earth)/GM(moon) = 81.300570 from Konopliv et al (2002), and the value for GM(mars system) will be replaced by 42828.375214, the system mass from Konopliv et al (2005). Table III lists the values of other dynamical parameters from the solution leading to DE414. Comparisons of DE414 to DE405 Figures 1 and 2 show comparisons between DE414 and DE405 for all of the planets, the sun, and the moon. The plots show heliocentric (geocentric for the moon) differences, DE405 - DE414, in right ascension, declination, and distance. Such comparisons are often more informative and provide a better estimate of realistic ephemeris uncertainties than those of formal covariances which are well-known to be optimistic, often by factors of 2**2, or 3**2, or even more. Thus, one may assume for DE405 vs. DE414, that most of the difference is due to errors in DE405, the older ephemeris; DE414 should be more accurate since the observational data set fit by DE414 is greater and more extensive in time. A more in-depth study for Mars is being prepared by W M Folkner, which will address the martian covariance for both present-day ephemerides, e.g. DE414, and for future ephemerides with assumptions about the acquisition of future Mars observations (VLBI and ranging measurements from MGS and Odyssey). Conclusions DE414 is the latest planetary ephemeris at JPL; it is recommended for present-day spacecraft navigation. It is expected that an improvement to DE414 will be produced within the next year, taking advantage of additional observational data and recently improved values for a number of the planetary masses. References Anderson, J.D., Colombo, G., Esposito, P.B., Lau, E.L. and Trager, G.B.: 1987, ``The Mass, Gravity Field, and Ephemeris of Mercury'', Icarus, 71, 337-349. Border, J.S.: 2003, email deliveries of VLBI points, Feissel, M. and Mignard, F.: 1998, ``The adoption of ICRS on 1 January 1998: meaning and consequences", Astron. Astrophys., 331, L33-L36. Explanatory Supplement to the Astronomical Almanac: to be published, 2007(?), P. K. Seidelmann, ed. Folkner, W.M., Charlot, P., Finger, M.H., Williams, J.G., Sovers, O.J., Newhall, X X, and Standish, E.M.: 1993, ``Determination of the extragalactic frame tie from joint analysis of radio interferometric and lunar laser ranging measurements", Astron. Astrophys., 287, 279-289. Jacobson, R.A., Campbell, J.K., Taylor, A.H. and Synnott,S.P.: 1992, ``The Masses of Uranus and its Major Satellites from Voyager Tracking Data and Earth-based Uranian Satellite Data'', Astron J., 103 (6), 2068-2078. Jacobson, R.A., Riedel, J.E. and Taylor, A.H.: 1991, ``The Orbits of Triton and Nereid from Spacecraft and Earth-based Observations'', Astron. Astrophys., 247, 565-575. Jacobson, R.A.: 2006, private communications. Konopliv, A.S., Miller, J.K., Owen, W.M., Yeomans, D.K. and Giorgini, J.D.: 2002, ``A Global Solution for the Gravity Field, Rotation, Landmarks, and Ephemeris of Eros", $Icarus$, 160, 289-299. Konopliv, A.S., Yoder, C.F., Standish, E.M., Yuan, D-N. and Sjogren, W.L.: 2005, ``A global solution for the Mars static and seasonal gravity, Mars orientation, Phobos and Deimos masses, and Mars Ephemeris", Icarus, in press. Kovalevsky, J.: 1996, private communication. Krogh, F.T.: 1997, Calif. Inst. of Technology, 2003 Math a la Carte, Inc. Morrison, L.V.: 1996: private communication. Null, G.W.: 1969, ``A Solution for the Mass and Dynamical Oblateness of Mars Using Mariner-IV Doppler Data'', Bull. Am. Astr. Soc., 1 (4), 356. Sjogren, W.L., Trager, G.B. and Roldan, G.R.: 1990, ``Venus: A Total Mass Estimate'', Geophys. Res. Let., 17(10), 1485-1488. Standish, E.M.,: 1995, "Report of the IAU WGAS Sub-Group on Numerical Standards", in "Highlights of Astronomy" (Appenzeller, ed.), pp. 180-184, Kluwer Academic Publishers, Dordrecht. Standish, E.M., Newhall, X X, Williams, J.G. and Folkner, W.F.: 1995, ``JPL Planetary and Lunar Ephemerides, DE403/LE403", JPL IOM 314.10-127. Standish, E.M.: 1998, ``JPL Planetary and Lunar Ephemerides, DE405/LE405",JPL IOM 312.F-98-048. Standish, E.M.: 2003a, ``JPL Planetary and Lunar Ephemerides, DE409/LE409",JPL IOM 312.N-03-007. Standish, E.M.: 2003b, ``JPL Planetary and Lunar Ephemerides, DE410/LE410",JPL IOM 312.N-03-009. Tholen, D.J. and Buie, M.W.: 1988, ``Circumstances for Pluto-Charon Mutual Events in 1989'', Astron.J., 96 (6), 1977-1982.