I wonder how massive a vehicle meant for 6 astronauts must be if its purpose is to lift off from the Moon , cruise back to Earth and re-enter Earth's atmosphere to land below a parachute.

The laws of celestial mechanics being well known and computer capabilities being ever expanding, it should even be possible to lift off from the Moon and gain enough speed (perhaps 6,000 km/h) and acquire a specific trajectory , before shutting off the engine and free fall back to Earth in 63 hours (even without midcourse corrections) , to land at a pre-designated area, say 63.5 miles south south west of Salt Lake City. The astronauts would only need a life support system for 65 hours.
It shouldn't be that much and certainly not as much as anything needed to return back from Mars with!

Raoul