The beauty of Orion is that it's low tech, but should cost an obscene amount of reputation to unlock in career mode. If Orion had been pursued earnestly from the beginning, we'd have never built chemical rockets like we did. No need for fancy ICBMs when you have a fleet of near-torchship dreadnoughts that can schwack half a continent with a fraction of their payload. When you can put 100,000 tons into orbit like it's nothing, that's like the advent of cavalry, steam power, or the wheel.