No, the big rocket is the easy bit which has been done many times before.
Designing a mission involving 1000 days in space with no prospect of resupply is the hard bit. And it's the likes of ESA and NASA that have visibly been spending money on research and testing for that bit, not the very successful private launch vehicle supplier and LEO constellation operator.
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.
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