"Truck"Not even worth a theoretical revision. The "truck" is just giving it a driver's seat, small engine, and wheels. It's not an engineering challenge to implement at all, and it's not a technological challenge because we'd just be literally taking the stuff from our civilian tech.
Assembly & TransportWhile it'd be
better for it to be transported in one piece, neither the difficulty nor quality should be notably impacted by the assembly & transport aspect. The cabin & trailer are trivial to separate with no R&D required
at all nor any legitimate engineering effort. Then it's just a matter of literally hooking them together once they're both at the same spot.
Athena & GuidanceWhat are the two things Athena is
extremely good at?
Targeting things and flying things.
What are the two things a missile's guidance system needs to do?
Targeting things and flying things.
It's not exactly the same, of course - there are differences between ground&space targets and air&orbital flight. But those two things should be easily covered by this design and Athena's learning capabilities. The core concepts - which would make up the extreme majority of the difficulty to design a theoretical new guidance system - are still completely intact. And we have a guidance system that can already learn.
Nuclear WarheadYou know about as much as a civilian could know today. So, the basic principle you are aware of, for sure, and some details, but not enough to just build one trivially.
But it also would not be hard by any means.
-NUKE, when asked about how much we already know about nuclear warheads.Plus the fact that we're building a simple & small-scale warhead. We're not trying to recreate the Tsar Bomba here. So this should be easy.
The Launcher ItselfThe Launcher's basically just 8 launch rails, an Athena node, and the truck. Not really hard.
SummarySo, to sum it up, we need to do some mild revisions facilitating Athena's learning process to handle the differences between ground&space targeting/flying, though they won't be particularly major differences. We need to take a civilian engine & wheels, stick an Athena core + launch rails on it. And we need to develop a small basic nuclear warhead, which has been stated to be relatively easy.
Of course, the difficulty is more than the sum of its parts. A missile is more complicated than "guidance + warhead", but this covers all the technological challenges and a decent portion of the engineering challenges. It ideally should be Normal, though it
could be Hard.