ScrumbleShip is the most accurate space combat simulation devised to date. Gather resources, construct a capital ship out of individual blocks, then pilot it with AI or human help against other players.
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GeneralVonDoom has gone ahead and constructed us a capital ship's reactor. I imagine something of this size would power very large ships, such as Insolent's S.S. Queen Mary Ann.
I love the detail work on heat transfer, to pull waste heat away from the sensitive reactor bits.
Cheers,
-Dirk