Hyperspace, physics defying naval battles in space, nanites, mech suits, implants, etc........
I'm sure there's more, but here's a different list.
Weaponize Kessler: Intentionally deliver more 'space debris' with the intent to silence the sky. Who would do this? A people, or government willing to give up the seductive promises of globalism for more local freedom. Now, this could be anyone from North Korea to a group of libertarians somewhere intent on stopping the imperial surveillance state.
Now, the imperial state would be deprived of easy global targeting, but it would still be able to physically move assets to your neck of the woods and start attacking, so.
Laser anti-aircraft cannon. There's already some prototypes out there. There was some sort of anti-drone system in use last time at Davos. In case of emergency, hit everything in the sky. Maybe plan ahead a little and keep an aviary. But, if you can keep everybody out of your sky, you are more free than the imaginary sense of freedom we get from imagining we can just go fly the globe and end up on an island somewhere.
WALLS: You've quieted the skies, and kept your airspace free. Probably by this time, the Empire has fallen. But maybe some ambition guys grab some weaponry, and head your way. You want great big beautiful walls. You want to take the lastest and greatest in earthquake and force dissipation technologies. You probably want to reach back, to Vauban- perhaps modified a bit, considering the laser cannon.
Inside the walls, tree crops amidst the dwellings. Some grazing (more during peacetime when you can graze outside the walls). Permaculture ideas- a food forest, but with robots as harvesters. Probably need a small nuclear reactor to power things. I consider that A: something that can be designed to not be a problem, and B: part of a plan to, if necessary fall back technologically in the most graceful way possible.
The fall back plan is this: start with as much power now, but bank on going to wood and people power as time goes on, because, as time goes on, if you are doing any good, you are going to have more wood and more people. But harvest is always a choke point, and this is why farms look like farms and not like forests- to make it easier to harvest.
As you might be able to tell, I don't see how we get to be a space-faring species yet. The people who have control are not looking up, they are looking down.