I must be missing something about this.

I mean, we have a bunch of designs that were tested and then mass produced. Many thousands of them, altogether.

They do need regular maintenance, of course. Such as replacing stuff that decayed, and stuff that got damaged by the radiation, or just air oxidation and whatever.

So what's the "designing" for? I find it hard to imagine that they'd be making substantive changes without any actual testing. Because they'd have no way to really know.

And conversely, I find it hard to imagine why we need to improve them. They're already too powerful to actually use on the Earth.

So doesn't the increased uncertainty outweigh some marginal increase in efficiency or power or whatever?