Elon Musk says idea of self-sustaining city on Mars is currently too expensive

SpaceX CEO Elon Musk has said that the goal to have a self-sustaining city on Mars is currently far too expensive. He tweeted, "We need to accelerate progress towards fully reusable rockets." Musk further said the cost per ton for SpaceX's reusable rocket Falcon needs to come down by 1,000% from what it currently is to make the idea possible.