A random idea about Apollo.
Let's suppose that, around 1973, a Saturn IB send a CSM into a parking orbit.
Then, a Titan IIIE put its Centaur upper stage onto the same orbit. Rendez-vous, docking in LM fashion.
Do you think the Centaur had enough energy and propellants to send the CSM into a lunar orbit ? (ala Apollo 8, without Saturn V!)
Let's suppose that, around 1973, a Saturn IB send a CSM into a parking orbit.
Then, a Titan IIIE put its Centaur upper stage onto the same orbit. Rendez-vous, docking in LM fashion.
Do you think the Centaur had enough energy and propellants to send the CSM into a lunar orbit ? (ala Apollo 8, without Saturn V!)