It's easy if you use additional payload available with bigger rockets.
Just like invention of the rocket engine enabled all kinds of rockets, the ability of having a lot of payload available for the mission enables all kinds of solutions for existing problems. Robotbeat is correct.
You need to determine what those solutions are before you figure out whether additional payload space is even necessary. I mean, if you just want more payload than is possible with the current largest launch vehicle, you send more rockets (and get redundancy for the return journey as a bonus!). Of course, there are mission design complications with sending multiple rockets, but there are also mission design complications involved in astronauts spending three years away from earth or even LEO that don't get handwaved away with extra mass too...