More Words, Deeper Hole

The ship supposedly has politics. If it has politics, rather than vicious arguments about risk management and consumables accounting and people taking showers that use more than 4 litres of water, it presumably has margin. Which means it's freaking vast.

So it's quite possible that it's got a crew of ten thousand or so, or more; they're building manufacturing capability for new technology as they get instructions transmitted to them. Probably also cursing their local indium shortage.

If was going to try to make that work as narrative I'd be talking about how someone came up with direct conversion, matter to energy, but the minimum scale is enormous and the exhaust is the sort of thing you'd normally associate with the spin poles of a black hole. No one can figure out how to use it on Earth, Cold Warriors determined to preserve the species managed to launch this one ship which was just everything and everyone packed really tightly, they grabbed a big hunk of nickel-iron for radiation shielding and something with volatiles to stack behind that and are pushing the whole big mass while they make stuff they're going to need at the destination. (That's still some millions of tonnes in launch mass, it's completely crazy as a thing to do, but it's something like an explanation.)

Of course then I have to explain why the exhaust isn't making the amateur astronomy press twice a week, but that's a fairly small conspiracy as these things go. (Or it's so far into the gamma you can't see it without an orbiting telescope?)