I had an interview with Boeing, and found out that they did work with Sybase to develop some DB extensions for just that purpose. I think they license them out, but that's not going to work well with your FOSS desires. Postgres seems to have extensions to allow temporal work - check here. http://pgfoundry.org/projects/temporal/
Both MySQL and Postgres support some GIS features, I would definitely recommend taking a look. I bookmarked this book about postGIS but I haven't read it: http://www.postgis.us/ .
If the databases can handle your queries efficiently then it could save you a lot of work and you won't have to do anything nasty.
From a quick back-of-the-envelope calculation, you should have under 20GB of data, so if you need to perform an inefficient computation with low latency storing it all in RAM isn't out of the question.