It was a series of novels where the astronauts visited a different planet each book. There were 4 astronauts - 2 Brits, an American, and a Russian. I’m guessing a British author, since one of the Brits was the Captain. By the last book, when they went to Pluto, the Captain had been promoted out of the astronaut program, but wound up piloting the rescue craft they conveniently built at the same time as the main craft.
I read them in the late 70’s, but they could be older. Thanks.