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               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.
 
 
 
 
 
