idk if most know how straightforward this is these days even without AI. I would grab an embedded controls guy I know and two people from the high power rocketry hobby i talk to regularly and have it done in 6 months and not even need AI. Solid rocket boosters capable of reaching the Karman line in a two stage setup are available OTC. Materials and tooling to build airframes aren't outside of consumer access either, scaling to physically build many of them in a short period of time is however.
You know, DARPA doesn't even need to be involved. Some rich person could just setup a contest with awards and see who shows up, it could be held out on one of those dry lakebeds in Nevada. I think the results would be very interesting.