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Hey guys, been a while since I've been here, but man, I love these forums. Hey all, been a long time since I've been here, but man, I really love these forums. Anyway, I've been building rockets for a while now, both in stock and with Realism Overhaul. I've also become fascinated with real world rockets through all this and I've noticed there's one topic I rarely see posted about here that I'm very curious about. What's the real deal with rocket shape? Feel free to talk about KSP or real world, even though I know they're quite different. I'm primarily concerned with multistage stacks and the dimeter of the various stages. (But I'm also very interested in anything to do with this topic.) My big question is, what are the considerations when designing rocket's stages as far as diameter? I've seen rockets like the Falcon 9 or Arianne 5 have upper stages with the same diameter as the lower, while others, like the Saturn V or Atlas V don't. I would think that, aerodynamically, a rocket that is a consistent diameter with a good nose cone would have less drag than one that tapers, but I'm not positive about this. Also, in stock KSP, it's much more mass efficient to use smaller diameter upper stages, except that you then need an adapter, fairing, or other inter-stage element. In real life though, the upper stage shape doesn't have as much effect on mass, so it makes much more sense to go with a cylindrical rocket.