Not really. Sandtrap, I absolutely fail to see how your theory makes sense in the context of the canon. It literally appears as if it's overly complex for the sake of being complex. The most logical solution is to say the pylons on the portal generator can open up further to generate a larger portal. Why? High Charity is stated twice to have been on its way to Earth. To keep things simple we just have it so the portal generator detects a large mass moving towards it and adjusts the portal size via the pylons to create a larger portal.

And, did you read my response on how that doesn't work either? Where's the portal getting all this power from after the keyship leaves? Maybe, to sustain the portal, that was fine and dandy, but taking energy to move the supports that keep it open and stable, as well as keeping the portal open in the first place while enlarging it to fit something that enormous seems not only risky, but like a hell of a big power draw. And we've still got the whole issue of High Charity in orbit. They'd have to come down in atmosphere to get to the portal. That high up in the sky, High Charity could have sent out flood pods across the planet and taken it without effort while it went through. And, as Grey stated, what about the remaining orbital platforms? Earth still had a few left and kicking up there. I'd still imagine that High Charity didn't have enough power to manage everything on the station, so it had moot for defenses, then those platforms probably would have ripped it a new one if it ended up in their sights. Edit- And, let's do so more math here. We take what you up there, and apply it to what we know, and what we see. Look at the arms of the portal when opened up. Let's take some simple, structure and visual based measurments here. See the arms? They are opened up by a little more than half way. Let's say, 55%, even 60%. Now, doing some calculations which I probably couldn't do even on my best days, let's assume these arms open up to 100%. Would the portal be large enough to fit High charity? At 55% to 60%, the portal is 1/3 the diameter of High Charity. You think it could make it the rest of the way? Help me out here on the maths since I couldn't finish things off. So, even if the portal is wide enough, that still leaves the issue of High Charity sitting all fine and dandy inside Earth's atmosphere with an entire station's worth of infected dropping off or being launched into the atmosphere, as well as making it past the remaining orbital defensive platforms.

High Charity is large enough to take any orbital rounds and maintain it's structural integrity. As for the power source, that's easy. The UNSC determined the portal generator was drawing immense amounts of energy from an unknown source. The map Meltdown holds the answer. The Forerunner reactor on Meltdown sends its energy wirelessly to a shield world in a nearby star system. If the UNSC can't determine where the portal generator's power supply is coming from, it's probably grabbing power from a remote reactor, built for the sole purpose of creating energy.

Okay, I can sit with that. Now then, what about the edited bit that i added in?