Thanks for playing the game :). I forgot to make spacecraft on Suborbital Flight automatically return to Earth (I usually launch directly into Earth Orbit when testing. Launching into Suborbital Flight can save some thrust in certain situations, but it's a bit tedious).
The four rocket types, including the Saturn Rocket, are one-shot rockets, so it's expected that they're consumed after use. Only the Ion Thruster can be used multiple times. Roughly 1 Saturn Rocket can carry 5 mass components onto earth orbit, then other carried light rocket (like Juno in tutorial) and Ion thruster continue carry probe & astronaut to other planet. Players usually need several turns to build a large spacecraft and launch it into orbit, or they can launch Saturn Rockets over multiple turns to accumulate components in Earth Orbit before proceeding with the next step of their mission.
I also feel that the game lacks too much guidance :( The rulebook for Leaving Earth might be helpful, though some rules are different: https://soundingrocket.com/le/Leaving%20Earth%20-%20rules%20v4n.pdf Maybe I would improve guidance and polish it more after rating.