so i was talking with uhfgood and he suggested that Space Fortress was a bit like Star Castle. (i still have to look into Star Castle some more, yet.) i was reminded of a commodore64 game that i really liked when i was young and took a look around for some pictures to show him. i somehow tripped over a YouTube of gameplay!
for your viewing pleasure, i present someone else's playing of Survivor, one of the major inspirations for Space Fortress:
[edit 2: hey! i found a crappy youtube for star castle too! i guess you could liken space fortress to it, but that's pushing it imo.. lookie!