Well, finished for now...
Over the last month, I have accomplished the following:
1) Loading of game data from external XML files, enabling modding of the game's parameters. XML files contain information on the relative proportion of star types, the sizes of galaxies, the colors of stars, and so on. I have plans to use XML data to define game events, ship designs, and more.
2) Loading/saving of game objects from/to XML files. I likely have a bit more work to do in this area, but the base capability is there and works for now. I'll revisit this during later development as the need arises.
3) Refactoring of my object structure, moving away from inheritance and toward composition with interfaces. It feels more intuitive to me to assemble an object from smaller pieces than it does to inherit. With composition, you can mix and match as needed, provided you code to the interfaces that go with each piece.
My next step is to fully create a single StarSystem object--the data model, graphics for its view, and the controller that handles its events. I want to be able to experiment with level-of-detail changes, clicking and highlighting, audio effects, loading/saving it, switching between views of the model, and adding modifiers to its model data. The toughest part will likely be handling the graphics and views, as I've neglected that aspect of the game so far and am not sure how robust my current structure will be.
I'm guessing this work will take most of February to finish.