Does there exist any software or algorithms for determining the
eccentricity, obliquity, and longitude of perihelion for Mars as a
function of year?

A similar item was developed by NASA's Goddard Institute of Space
Studies for Earth, <http://aom.giss.nasa.gov/srorbpar.html>.

I would be using these parameters as part of an solar insolation
model.

For my undergraduate senior project, I am building upon the work done
is this paper, <http://www.pnas.org/cgi/content/full/98/5/2132>. They
combined Viking pressure and temperature data with Mars Orbital Laser
Altimeter topography data, and computed the fraction of the martian
year during which pressure and temperature allow for liquid water to
be stable on the martian surface.

As for my research, I want to test for stability of water-salt
solutions, < http://www.spacedaily.com/news/mars-water-science-00a.html>
at different stages of Mars's orbital variation
<http://www.aas.org/publications/baas/v33n3/dps2001/310.htm>.

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Clarification of Question by rpavlick3-ga on 10 Nov 2003 21:16 PST

Actually, just any software won't do, it must be open source.

The code that you want is available from various free download sites
as VB source code.  The code contains high precision orbital
information for all the planets.  The code called NeoEmpherix  is
available at the author's site http://www.neoprogrammics.com The
author of this code can be contacted at Jay@NeoProgrammics.com

Its excellent code and I have used it extensively.

Hope this gets you out of trouble.

Neil