There's a structure on the moon. No one is sure how it got there, who put it there, or why. All they know is anyone who goes in dies. It can be in any number of ways, and for practically any reason. Even with the ability to create a duplicate of a person, and transmit that to the moon, the cost in lives is becoming prohibitive, because most people can't handle experiencing their own death. But if the secrets of the structure are going to be uncovered, Edward Hawks needs someone he can send in there to die. Again, and again, and again.
So that's the impetus for Rogue Moon, but Budrys isn't particularly interested in the object. No explanation for it is ever provided, save that different people will perceive its interior differently. Budrys' real concern is with people. What drives individuals, and how easily those drives can lead us down paths that trap us. How, once on those paths, it can be difficult to change course. How you have to live with the decisions you've made, right up until you die. You can't go back and change them, you can only deal with the results as best you can. I would say there's something in there about what we're prepared to do in the name of scientific discovery, but I think it's really just a reflection of Hawks' personality, his need to figure things out. I do think there's an interesting point about how technology often runs ahead of the ethical questions that accompany it. The cynical part of me would say that's because humans are too greedy to waste time worrying about such things in the race for progress, but I'm not sure it isn't that we simply can't perceive all the issues a particular advance might raise.
I read the book in the early summer of '04, when I went on a general reading binge for about six weeks. It was a little surprising, revisiting it, how much I'd forgotten. A lot of the details of the character interactions had slipped away entirely (I didn't remember either Claire or the personnel man, Connington). I'd also forgotten how fond Budrys is off letting the characters have long speeches about themselves. Here's one from Hawks:
'That's true of everyone. No one sees the world that others see. What do you want me to do: be made of brass? Hollow, and more enduring than flesh? Is that what you want a man to be?' Hawks leaned forward, tight creases slashing down across his hollow cheeks. 'Something that will still be the same when all the stars have burned out and the universe has gone cold? That will still be there when everything that ever lived is dead? Is that your idea of a respectable man?'
That, admittedly, is one of the shorter ones. Barker and some ensign spend over two pages quoting a back-and-forth between Merlin and Lancelot at one point, which seemed to be excessively beating the point to death.