Elon Musk has made no secret of his passion to make humanity a multiplanetary species by creating a self-sustaining society on Mars as a backup plan in case Earth is destroyed in a cataclysmic event. Today he provided some of the technical details of the Earth-Mars transportation system he wants to build, which will open opportunities for entrepreneurs and others to decide what happens on Mars. He will build the space equivalent of the Union Pacific railroad, but leave it to others to fill in the details of how a society will begin and grow there.

Musk, CEO and founder of SpaceX, spoke at a special session of the 2016 International Astronautical Congress (IAC2016) being held in Guadalajara, Mexico. These annual IAC meetings bring together space engineers, scientists, lawyers, and policy makers and his much-anticipated talk was aimed at that audience. An archived webcast of the presentation and slides are posted on the SpaceX website along with an animated video demonstrating how the system would work.

He identified four key technical requirements to make the effort affordable: full

reusability of the rockets, tankers, and spacecraft; refueling in orbit; propellant production on Mars; and using the right propellant (methane, since the constituents are readily available on Mars). His rockets could be used 1,000 times, the tankers 100 times, and the spacecraft 12 times. Each spacecraft could accommodate 100 passengers at first, growing to 200.

He explained in detail some of the engineering decisions made so far for the rocket, the Mars Transporter or Interplanetary Transport System. They include the use of carbon-fiber for the primary structure; the specific impulse of the Raptor rocket engines (382 seconds), one of which was just tested yesterday; and the number of engines (42 on the first stage plus 9 on the second stage). The rocket will have 3.6 times the lift-off thrust of the Saturn V rocket used for the Apollo lunar missions (which was 7.5 million pounds).

He asserted that using traditional methods like those used in the Apollo program it would cost $10 billion per person to go to Mars and he will reduce that to a price of $200,000 per person initially, dropping to half that over time. His spacecraft would transport 100-200 people at a time, with the Mars population growing to 1 million residents over 40-100 years.

He did not explain the provenance of his $10 billion per person cost other than saying it assumed an Apollo-like program. While a number of concepts for sending people to Mars have been put forward recently, including NASA’s, pricetags have not been revealed and none envision sending as many as 100 people at a time. Since he expressed a cost per person, the number of people traveling can make a significant difference.

Although he showed a timeline for accomplishing the first phase of the goal, he called it “intentionally fuzzy.” If everything went very well, the first humans could head to Mars in 10 years, he asserted, though at a later press conference he called that an “optimistic schedule” and an “aspiration.” He estimated that it would take an investment of $10 billion to develop the rocket before it would generate cash flow, a challenging amount of money to raise in such a short time. During his speech he said that it would take a “huge pubic private partnership” (PPP) to achieve this goal. In PPPs, the government and the private sector share the costs, implying that he expected the government — probably NASA — to participate. In the subsequent press conference, however, he insisted that he was not counting on any NASA money.

At one point he made light of the challenge of finding the money. The

first item on his funding slide is “steal underpants” (a reference to South

Park). The others include the two lines of business SpaceX currently is

engaged in — launching satellites and sending cargo and astronauts to

the International Space Station — plus Kickstarter and “profit.”

He spent considerable time on the technical aspects of the plan, but the fundamental point is that he believes humanity should have at least one other home to guard against potential extinction if Earth is beset by a cataclysmic event such as an asteroid strike. He has concluded that Mars is the place to establish that backup civilization. Not everyone will want to go to Mars, he acknowledges, but that is fine since the goal is not to move everyone to Mars, only to create a second home.

Once the rockets, spacecraft, tankers and propellant plants on Mars are in place, and fuel depots are positioned on one of the Martian moons or in the asteroid belt, the entire solar system would be opened for exploration, he enthused, showing slides of his rockets on Jupiter’s moon Europa, Saturn’s moon Enceladus, and flying over Saturn’s rings.

When asked if he planned to make the trip, Musk demurred. Noting how risky it will be in the beginning, he said that he would not want to go until he had a firm succession plan in place for SpaceX because he did not want it bought by investors whose only goal was profit, not colonization of Mars. He later added that he also wants to live to see his children grow up. He even joked that “if you are prepared to die you’re a candidate for going.”

Apart from the grandiose plans he espoused for sending people to Mars, he also wants to send robotic spacecraft at every planetary alignment opportunity. Mars and Earth are correctly aligned every 26 months. He is already working on the first of these missions, Red Dragon, for launch in 2018. It will send one of SpaceX’s Dragon spacecraft to Mars and test entry-descent-and-landing (EDL) for a propulsive landing on the surface, SpaceX has a Space Act Agreement with NASA where the agency will provide tracking and communication support in return for obtaining EDL data. Musk said that SpaceX will provide reliable services to send cargo to Mars every 26 months enabling customers to send 2-3 tons of cargo there.

It was a visionary speech that appealed to many in the crowd, but despite Musk’s evident passion, many question the realism of his plans. Even Musk said that his immediate goal is to create the dream of Mars in people’s mind, to “make it seem possible in our lifetimes.”

At the moment, however, SpaceX is attempting to get its only existing rocket, Falcon 9, back in service. It is still trying to determine why a Falcon 9 burst into flames on the launch pad during a routine pre-launch test on September 1 destroying the rocket and the Amos-6 communications satellite that was aboard. SpaceX said last Friday that they know what happened — a large breach in a helium tank in the second stage liquid oxygen tank– but not why. Musk was asked today whether he should be at IAC2016 talking about Mars instead of focusing on getting Falcon 9 back to flight. He replied that fixing Falcon 9 is his absolute top priority and his team is working on it, but a small amount of effort is being spent on these longer term plans. Musk had announced months ago that he would lay out his Mars transportation plans at IAC2016.