Musk figures the colony program — which he wants to be a collaboration between government and private enterprise — would end up costing about $36 billion. He arrived at that number by estimating that a colony that costs 0.25 percent or 0.5 percent of a nation’s gross domestic product (GDP) would be considered acceptable.
The United States' GDP in 2010 was $14.5 trillion; 0.25 percent of $14.5 trillion is $36 billion. If all 80,000 colonists paid $500,000 per seat for their Mars trip, $40 billion would be raised.
"Some money has to be spent on establishing a base on Mars. It’s about getting the basic fundamentals in place," Musk said. "That was true of the English colonies [in the Americas]; it took a significant expense to get things started. But once there are regular Mars flights, you can get the cost down to half a million dollars for someone to move to Mars. Then I think there are enough people who would buy that to have it be a reasonable business case."
The big reusable rocket
The fully reusable rocket that Musk wants to take colonists to Mars is an evolution of SpaceX's Falcon 9 booster, which launches Dragon.
"It’s going to be much bigger [than Falcon 9], but I don’t think we’re quite ready to state the payload. We’ll speak about that next year," Musk said, emphasizing that only fully reusable rockets and spacecraft would keep the ticket price for Mars migration as low as $500,000.
SpaceX is already testing what Musk calls a next-generation, reusable Falcon 9 rocket that can take off vertically and land vertically. The prototype, called Grasshopper, is a Falcon 9 first stage with landing legs.
Grasshoper has made two short flights. The first was on Sept. 21 and reached a height of 6 feet (2 meters); the second test, on Nov. 1, was to a height of 17.7 feet (5.4 m). A planned milestone for the Grasshopper project is to reach an altitude of 100 feet (30 m). [Grasshopper Rocket's 2-Story Test Flight (Video)]
"Over the next few months, we’ll gradually increase the altitude and speed," Musk said. "I do think there probably will be some craters along the way; we’ll be very lucky if there are no craters. Vertical landing is an extremely important breakthrough — extreme, rapid reusability. It’s as close to aircraft-like dispatch capability as one can achieve."
Musk wants to have a reusable Falcon 9 first stage, which uses Grasshopper technology, come back from orbit in "the next year or two." He then wants to use this vertical-landing technology for Falcon 9’s upper stage.
Musk hopes to have a fully reusable version of Falcon 9 in five or six years, but he acknowledged that those could be "famous last words."
A rocket stepping stone
Another stepping stone toward the planned reusable Mars rocket is SpaceX’s Falcon Heavy launcher. With a first flight planned for next year from Vandenberg Air Force Base in California, the Heavy is a Falcon 9 that has two Falcon 9 first stages bolted on either side.
Musk expects the Falcon Heavy to launch from Florida's Cape Canaveral eventually. This triple-first-stage rocket will be able to put 116,600 pounds (53,000 kilograms) into a 124-mile (200 kilometers) low-Earth orbit. But the Falcon Heavy is still much smaller than Musk’s fully reusable Mars rocket, which will also employ a new engine.
While Musk declines to state what the Mars rocket’s payload capability will be, he does say it will use a new staged combustion cycle engine called Raptor. The cycle involves two steps. Propellant — the fuel and oxidizer — is ignited in pre-burners to produce hot high-pressure gases that help pump propellant into the engine’s combustion chamber. The hot gases are then directed into the same chamber to aid in the combustion of the propellants.