I have some of my dad's old Lego sets from the 1960s when he was a kid. There are circular discs that fit on top of each other to connect and form a rocket. Is this a Saturn V rocket model (the ones that took the Apollo astronauts to the moon) or perhaps some other rocket? What Lego sets like this were available in that period?
It's hard to answer this definitively without a picture identifying the exact parts you have, but this sounds a lot like the set Rocket Base (358-1) from 1973:
That was one of the first space themed sets. The round parts are similar to what you've described. It looks like an obvious tribute to the Apollo program, though it isn't licensed or branded that way.