Regarding the naming convention, I am trying to stick to PEP8 as strictly as possible (sometimes, even in C) and to use overly explicit variable names. I had not noticed that you did that too for the structure member, with `longitude_of_ascending_node` and such. My objective is to have the code be as readable as possible to a newcomer (hence Python, too).
You should consider using my libtwobody project as a "backend" for your Python library. That is actually one of the design goals for the library, to provide low level primitive operations for higher level tasks and be usable from "scripting" languages.
Advantages over a simple implementation such as yours: proper handling of parabolic and near parabolic orbits, state of the art solvers for time of flight (Kepler's equation) and universal variable formulation. Additionally I've done some work with higher level algorithms for interplanetary trajectory planning.
The library may seem a bit cryptic if you're not too familiar with the literature on this subject, but it should not be too difficult to get up to speed with it. It might take a little bit of trivial software engineering to make it work to get it working as a dll but shouldn't be too much work. I'm happy to help, drop me an email (address in commit log) or contact me on irc (freenode, same nick as here on hn).
Regarding the naming convention, I am trying to stick to PEP8 as strictly as possible (sometimes, even in C) and to use overly explicit variable names. I had not noticed that you did that too for the structure member, with `longitude_of_ascending_node` and such. My objective is to have the code be as readable as possible to a newcomer (hence Python, too).