I am actually a proponent of RFG, I think its a powerful idea. But I know a few practical things that will for the foreseeable future prevent us from deploying such a system.
First, space systems are really expensive, and in most cases, once you launch its impossible to update anything but software. So what goes on orbit has to last for many years in the future using yesterdays technology.
Second, orbit dynamics means it takes lots of satellite to cover the globe with a capability to respond anytime and anywhere. Combine that with the expense of the system, and you can probably get a lot more by investing in Earth launched hypersonic systems. If I can get anywhere on the globe with hypersonics in 20 minutes, that’s as good as having to wait possibly hours for a satellite to get where the orbit mechanics are favorable to launch RFG. And its easier to maintain the hypersonic vehicle in the hanger.
Third, none of this is going to happen without someone knowing we have the capability or that we used it. If we had RFG’d the NK site, both Russia and China would know, and that would lead to all kinds of other problems.
Good observation on the hypersonic vs RFG “solutions”.
I’d say that RFG are more for “quiet hits”, like the NK nuke mountain - sure others might figure out what happened, but closer to “plausible deniability” than a hyper-cruise missile.
FYI: launching 3 RFGs via SpaceX Falcon Heavy cost $30M each, or 1 via Falcon 9 for $62M.
The tungsten itself per RFG is around $800,000.