Well, N towers are supposed to be enough. That’s the reason you should have N+1 in the first place.

Also this assumes that you can repair/replace a tower faster than it takes on average a tower to fail.

Well, if your infrastructure is mission critical, then you need one more as spare.

In this case a new one a qarter mile to the side with a redundant power supply. Mission control could be smack in the center between the launchpads.

Of course someone®©™ has to make sure, that the whole facility is only utilized in such a way that n-1 launchpads is considered 100% usage.

Rant/advice over from someone working in a data center, where spare machines are always in use, because someone©®™ said moar power is more important then reliability.