series of programs from the Jet Propulsion Laboratory. DE and
PEP
are
the only currently existing high-precision solar system ephemeris pro-
grams.
2.1. Motivation: Why a New Program?
The developmental origins of both
PEP
and the DE programs dates from
the early to mid 1960s. Both computer program design and language ca-
pabilities, as well as the precision of both observational data and the prac-
tical needs for that data, have advanced far beyond the anticipations of
three and a half decades ago when
PEP
and the
JPL
DE programs were
originally developed. Program technology that is several generations out
of date, combined with the practical inability to add further significant ca-
pabilities or modifications to
PEP
, has been deemed sufficient cause for
development of a new ephemeris program. Additional motivations are
that it is to the
USNO
's great advantage to have a comprehensive ephem-
eris capability in-house (especially since the
NAO
publishes the Astro-
nomical Almanac), and that Newcomb will provide a check against
PEP
and the JPL
DE
programs.
Finally, the creation of a modern ephemeris program provides an oppor-
tunity to simultaneously develop a flexible research tool for investigation
of solar system dynamics. The integration module of Newcomb is in large
part already completed and exists as a standalone program called
Newton.
14
This program is currently being used in the Astronomical Ap-
plications Department
15
for investigations of the dynamics of inner solar
system asteroids, the asteroidal "noise" in the motions of Earth and Mars,
and the dynamics of trans-Neptunian objects.
To highlight the difference between "old" and "new" programming, con-
sider the task of setting program input parameters. Appendix A contains a
typical input file used by
PEP
. Figure 7 shows how it is done using a GUI.
The intuitiveness of the
GUI
approach leads to substantial time savings in
coming up to speed in program usage, as well as actual use of the program
day to day. Even more valuable is that it allows a much more sophisti-
cated interface and a much more sophisticated set of program capabilities.
MURISON: MODELING PLANETARY MOTIONS
9 of 20
15
http://aa.usno.navy.mil/AA/
14
http://aa.usno.navy.mil/Newton/
