1.1. Introduction.
This chapter describes the top-level structure of
the planned Naval Observatory Solar System Ephem-
eris program, called Newcomb. Newcomb is in-
tended to be the successor of, and derives its
inheritance more or less from, PEP, the Planetary
Ephemeris Program at the Smithsonian Astrophysical
Observatory.
1
Computer program design and lan-
guage capabilities have advanced far beyond the an-
ticipations of more than three decades ago when PEP
was written. That, combined with the practical in-
ability to add further significant capabilities or modi-
fications to PEP, has been deemed sufficient cause
for development of a new ephemeris program. Addi-
tional motivations are that it is to the USNO's great
advantage to have a complete capability in-house,
and that Newcomb will provide a check against the
JPL DE program (as well as against PEP).
Chief among the advantages of writing a new
program is the opportunity to make use of object-
oriented design (OOD) and object-oriented program-
ming (OOP). Newcomb will be written in C++ and,
for the graphical user interface, in java. We will take
full advantage of standard OOP/OOD concepts and
techniques, including data encapsulation, template
classes, polymorphism, and multiple inheritance.
The benefits of a completely object-oriented ap-
proach are many, including faster prototyping and
development, fewer and more easily locatable coding
errors, vastly simpler and more intuitive design, more
sophisticated functionality, easily extensible archi-
tecture, and (most importantly) drastically reduced
maintenance costs. Another major benefit is that the
program can be up and running with minimal func-
tionality, allowing further capability to be easily and
painlessly incorporated as need arises.
Ease of extensibility is largely a result of object-
oriented design, but it is also directly related to how
good that design is. Hence, considerable effort is go-
ing into the design of Newcomb. Experience in the
software industry abundantly shows that the payoff
later on in terms of maintenance and extensibility is
far out of proportion to the effort expended early on
-- in the design stages -- of the program life cycle.
This chapter discusses some major design issues
and, more importantly, presents an initial framework
for further development.
1.2. Project Outline.
In this beginning part of the Newcomb project,
tasks naturally fall into three main categories: pro-
gram design, documentation, and science applica-
tions. A rough outline of the most obvious subjects
that must be addressed early on is:
I.
Design Issues
A.
numerical integration scheme
1.
object-oriented design
2.
Integrable objects have knowledge of
dynamical environment as well as the
ability to dynamically evolve in that
environment.
B.
exception handling
1.
all exceptions fully recoverable
2.
procedure stack traceback
C.
robust parameter estimation
1.
Singular Value Decomposition
(SVD)
2.
swipe a package from elsewhere
D.
graphical user interface
Chapter 1: Newcomb Project Outline and Top Level Program
Structure
Chapter 1: Top-Level Structure
D:\Newcomb\Documentation\NewcombManual.lwp
3 of 19
10:42pm April 23, 1997
1
Information on PEP may be found at
http://cfa-www.harvard.edu/~reasen/ssd.html
