The Autumn's launch from Reach is almost certainly flawed. I don't like it from a space ship point of view, or a storyline point of view. But the way Cody is going about this, basing calculations and methodologies on our current technologies and then making his usual all or nothing statements is even more flawed. Taking the effort to do some math doesn't excuse ignoring potential advances in propulsion technology between now and the 2500's, to say nothing of the radical new technologies like antigravity systems, which UNSC ships have and use (seemingly) both internally and externally.

We don't know how much more efficient the Autumn's engines / fuel supply is vs. modern day rockets. Off the top of my head I'm not sure we even know what the Autumn's main engines even are. With all the talk of redlining reactors in various Halo novels it's hard to imagine we're dealing with rockets and rocket fuel here. And what about that antigravity? If the technology is efficient enough it could drastically reduce the amount of energy needed to launch a ship into orbit. Perhaps even to the point that a few "rocket tugs" and the Autumn's main engines could do the job without causing a physics fail? Who know?! But maybe!

The line of thinking behind this whole thread seems to be Cody taking an equation he found on XKCD and running with it as fast as he could straight to clearly biased, clearly unconsidered, clearly intentionally provocative, and clearly unsupportable conclusions. And that's saying something considering we're dealing with video games set in the future.