SpaceX Starship
Musk has guessed that a city with a million people on Mars is enough to keep itself running. It should be able to create everything that the people need. The city does not need shipments from Earth by then. He guessed that the city needs at least ten thousand Starships full of humans. Each Starship can carry 100 passengers on board. To give the colony enough equipment and food, a hundred thousand Starships carrying cargo might launch to Mars. This guess does not have population growth.