Like some defense projects, I predict we'll outsource it to a private party, pay them public tax subsidies, and fail to hold them accountable when they go against our public defense interests.
I think the best we can hope for (apart from not having an asteroid heading our way at all) is that we'll have sufficient notice that something can be done. If we had a couple of years notice, there's a reasonable chance the deadline would be motivation enough to get something built.