I’m trying to remember a TV series that I think was shown in the late-'70s. Could’ve been early-'80s, but I think it was '70s. Some astronauts are on a space ship, which was nothing more than the Space Shuttle with different graphics on it. As I recall, it was not actually supposed to be a shuttle, but some other vessel with greater capabilities. I think the crew were in suspended animation. When they returned to Earth (crash landed?) it’s sometime in the Future. Some catastrophe happened, and civilisation was set back quite a bit. So the astronauts were the technologically advanced ones.
Genesis II is too early. Earth II is too late, and was not set on Earth. Strange New World sounds familiar. It had a Shuttle-like craft, but it’s not exactly how I remember it. (Of course, I could be remembering it wrong.) John Saxon’s appearance is familiar too, as is the word ‘PAX’. But that looks like a movie, and not a series.
You were partly right with Genesis II. What you’re remembering is Planet Earth, which was the second pilot for G2. John Saxon replaced Alex Cord from the first pilot, but basically the idea is the same.