How we cite our quotes: (Chapter.Paragraph) Note that chapters aren't numbered, so need to be numbered manually, 1 to 14.
Quote #1
"Do you know Sartorius?'
"In the same way as I know you—only from the photographs." (1.90-91)
Here it sounds like Kelvin is capable of distinguishing the image from the person. Later, though, he's going to get confused. And maybe we are, too; after all, what do we see of Sartorius except this story about him? Maybe Kelvin is already mistaken in thinking that there's a real Sartorius behind the image.
Quote #2
I had never lived on the Station, but during my training on Earth I had spent six weeks in an exact replica of it; when I reached a short aluminum stairway, I knew where it led. (4.1)
This is only the first exact replica we see in the novel. Kelvin thinks the replica helps him know where he is; Earth is a guide to space, what you've left behind you tells you where you are. It doesn't exactly work out that way for him, though. Watch that last replicated step there, Kelvin—it's a doozy.
Quote #3
I felt I was justified in thinking that I had defeated the "simulacra," and that behind the illusion, contrary to all expectation, I had found the real Rheya again—the Rheya of my memories, whom the hypothesis of madness would have destroyed. (5.158)
Kelvin has ejected Rheya into space, and he's congratulating himself on having rescued the real Rheya, who is in his head. But is there a real Rheya in his head? His memory of Rheya isn't any more real than the simulacra Rheya—in fact, they're the same real, since the simulacra is based on his memory. Kelvin is patting himself on the back without being sure which is his real back.