‘Fuck Earth!’ Elon Musk said to me, laughing. ‘Who cares about Earth?’ We were sitting in his cubicle, in the front corner of a large open-plan office at SpaceX headquarters in Los Angeles. It was a sunny afternoon, a Thursday, one of three designated weekdays Musk spends at SpaceX. Musk was laughing because he was joking: he cares a great deal about Earth. When he is not here at SpaceX, he is running an electric car company. But this is his manner. On television Musk can seem solemn, but in person he tells jokes. He giggles. He says things that surprise you.

When I arrived, Musk was at his computer, powering through a stream of single-line email replies. I took a seat and glanced around at his workspace. There was a black leather couch and a large desk, empty but for a few wine bottles and awards. The windows looked out to a sunbaked parking lot. The vibe was ordinary, utilitarian, even boring. After a few minutes passed, I began to worry that Musk had forgotten about me, but then suddenly, and somewhat theatrically, he wheeled around, scooted his chair over, and extended his hand. ‘I’m Elon,’ he said.

It was a nice gesture, but in the year 2014 Elon Musk doesn’t need much of an introduction. Not since Steve Jobs has an American technologist captured the cultural imagination like Musk. There are tumblrs and subreddits devoted to him. He is the inspiration for Robert Downey Jr’s Iron Man. His life story has already become a legend. There is the alienated childhood in South Africa, the video game he invented at 12, his migration to the US in the mid-1990s. Then the quick rise, beginning when Musk sold his software company Zip2 for $300 million at the age of 28, and continuing three years later, when he dealt PayPal to eBay for $1.5 billion. And finally, the double down, when Musk decided idle hedonism wasn’t for him, and instead sank his fortune into a pair of unusually ambitious startups. With Tesla he would replace the world’s cars with electric vehicles, and with SpaceX he would colonise Mars. Automobile manufacturing and aerospace are mature industries, dominated by corporate behemoths with plush lobbying budgets and factories in all the right congressional districts. No matter. Musk would transform both, simultaneously, and he would do it within the space of a single generation.

Musk announced these plans shortly after the bursting of the first internet bubble, when many tech millionaires were regarded as mere lottery winners. People snickered. They called him a dilettante. But in 2010, he took Tesla public and became a billionaire many times over. SpaceX is still privately held, but it too is now worth billions, and Musk owns two-thirds of it outright. SpaceX makes its rockets from scratch at its Los Angeles factory, and it sells rides on them cheap, which is why its launch manifest is booked out for years. The company specialises in small satellite launches, and cargo runs to the space station, but it is now moving into the more mythic business of human spaceflight. In September, NASA selected SpaceX, along with Boeing, to become the first private company to launch astronauts to the International Space Station (ISS). Musk is on an epic run. But he keeps pushing his luck. In every interview, there is an outlandish new claim, a seeming impossibility, to which he attaches a tangible date. He is always giving you new reasons to doubt him.

I had come to SpaceX to talk to Musk about his vision for the future of space exploration, and I opened our conversation by asking him an old question: why do we spend so much money in space, when Earth is rife with misery, human and otherwise? It might seem like an unfair question. Musk is a private businessman, not a publicly funded space agency. But he is also a special case. His biggest customer is NASA and, more importantly, Musk is someone who says he wants to influence the future of humanity. He will tell you so at the slightest prompting, without so much as flinching at the grandiosity of it, or the track record of people who have used this language in the past. Musk enjoys making money, of course, and he seems to relish the billionaire lifestyle, but he is more than just a capitalist. Whatever else might be said about him, Musk has staked his fortune on businesses that address fundamental human concerns. And so I wondered, why space?

Musk did not give me the usual reasons. He did not claim that we need space to inspire people. He did not sell space as an R & D lab, a font for spin-off technologies like astronaut food and wilderness blankets. He did not say that space is the ultimate testing ground for the human intellect. Instead, he said that going to Mars is as urgent and crucial as lifting billions out of poverty, or eradicating deadly disease.

‘I think there is a strong humanitarian argument for making life multi-planetary,’ he told me, ‘in order to safeguard the existence of humanity in the event that something catastrophic were to happen, in which case being poor or having a disease would be irrelevant, because humanity would be extinct. It would be like, “Good news, the problems of poverty and disease have been solved, but the bad news is there aren’t any humans left.”’

Musk has been pushing this line – Mars colonisation as extinction insurance – for more than a decade now, but not without pushback. ‘It’s funny,’ he told me. ‘Not everyone loves humanity. Either explicitly or implicitly, some people seem to think that humans are a blight on the Earth’s surface. They say things like, “Nature is so wonderful; things are always better in the countryside where there are no people around.” They imply that humanity and civilisation are less good than their absence. But I’m not in that school,’ he said. ‘I think we have a duty to maintain the light of consciousness, to make sure it continues into the future.’

People have been likening light to consciousness since the days of Plato and his cave because, like light, consciousness illuminates. It makes the world manifest. It is, in the formulation of the great Carl Sagan, the Universe knowing itself. But the metaphor is not perfect. Unlike light, whose photons permeate the entire cosmos, human-grade consciousness appears to be rare in our Universe. It appears to be something akin to a single candle flame, flickering weakly in a vast and drafty void.

Musk told me he often thinks about the mysterious absence of intelligent life in the observable Universe. Humans have yet to undertake an exhaustive, or even vigorous, search for extraterrestrial intelligence, of course. But we have gone a great deal further than a casual glance skyward. For more than 50 years, we have trained radio telescopes on nearby stars, hoping to detect an electromagnetic signal, a beacon beamed across the abyss. We have searched for sentry probes in our solar system, and we have examined local stars for evidence of alien engineering. Soon, we will begin looking for synthetic pollutants in the atmospheres of distant planets, and asteroid belts with missing metals, which might suggest mining activity.

The failure of these searches is mysterious, because human intelligence should not be special. Ever since the age of Copernicus, we have been told that we occupy a uniform Universe, a weblike structure stretching for tens of billions of light years, its every strand studded with starry discs, rich with planets and moons made from the same material as us. If nature obeys identical laws everywhere, then surely these vast reaches contain many cauldrons where energy is stirred into water and rock, until the three mix magically into life. And surely some of these places nurture those first fragile cells, until they evolve into intelligent creatures that band together to form civilisations, with the foresight and staying power to build starships.

‘At our current rate of technological growth, humanity is on a path to be godlike in its capabilities,’ Musk told me. ‘You could bicycle to Alpha Centauri in a few hundred thousand years, and that’s nothing on an evolutionary scale. If an advanced civilisation existed at any place in this galaxy, at any point in the past 13.8 billion years, why isn’t it everywhere? Even if it moved slowly, it would only need something like .01 per cent of the Universe’s lifespan to be everywhere. So why isn’t it?’

‘If you look at our current technology level, something strange has to happen to civilisations, and I mean strange in a bad way’

Life’s early emergence on Earth, only half a billion years after the planet coalesced and cooled, suggests that microbes will arise wherever Earthlike conditions obtain. But even if every rocky planet were slick with unicellular slime, it wouldn’t follow that intelligent life is ubiquitous. Evolution is endlessly inventive, but it seems to feel its way toward certain features, like wings and eyes, which evolved independently on several branches of life’s tree. So far, technological intelligence has sprouted only from one twig. It’s possible that we are merely the first in a great wave of species that will take up tool-making and language. But it’s also possible that intelligence just isn’t one of natural selection’s preferred modules. We might think of ourselves as nature’s pinnacle, the inevitable endpoint of evolution, but beings like us could be too rare to ever encounter one another. Or we could be the ultimate cosmic outliers, lone minds in a Universe that stretches to infinity.

Musk has a more sinister theory. ‘The absence of any noticeable life may be an argument in favour of us being in a simulation,’ he told me. ‘Like when you’re playing an adventure game, and you can see the stars in the background, but you can’t ever get there. If it’s not a simulation, then maybe we’re in a lab and there’s some advanced alien civilisation that’s just watching how we develop, out of curiosity, like mould in a petri dish.’ Musk flipped through a few more possibilities, each packing a deeper existential chill than the last, until finally he came around to the import of it all. ‘If you look at our current technology level, something strange has to happen to civilisations, and I mean strange in a bad way,’ he said. ‘And it could be that there are a whole lot of dead, one-planet civilisations.’

It is true that no civilisation can last long in this Universe if it stays confined to a single planet. The science of stellar evolution is complex, but we know that our mighty star, the ball of fusing hydrogen that anchors Earth and powers all of its life, will one day grow so large that its outer atmosphere will singe and sterilise our planet, and maybe even engulf it. This event is usually pegged for 5-10 billion years from now, and it tends to mark Armageddon in secular eschatologies. But our biosphere has little chance of surviving until then.

Five hundred million years from now, the Sun won’t be much larger than it is today but it will be swollen enough to start scorching the food chain. By then, Earth’s continents will have fused into a single landmass, a new Pangaea. As the Sun dilates, it will pour more and more radiation into the atmosphere, widening the daily swing between hot and cold. The supercontinent’s outer shell will suffer expansions and contractions of increasing violence. Its rocks will become brittle, and its silicates will begin to erode at unprecedented rates, taking carbon dioxide with them, down to the seafloor and into the deep crust. Eventually, the atmosphere will become so carbon-poor that trees will be unable to perform photosynthesis. The planet will be shorn of its forests, but a few plants will make a valiant last stand, until the brightening Sun kills them off, too, along with every animal that depends on them, which is to say every animal on Earth.

In a billion years, the oceans will have boiled away altogether, leaving empty trenches that are deeper than Everest is tall. Earth will become a new Venus, a hothouse planet where even the hardiest microbes cannot survive. And this is the optimistic scenario, for it assumes our biosphere will die of old age, and not something more sudden and stroke-like. After all, a billion years is a long time, long enough to make probabilistic space for all kinds of catastrophes, including those that have no precedent in human memory.

Of all the natural disasters that appear in our histories, the most severe are the floods, tales of global deluge inspired by the glacial melt at the end of the last Ice Age. There are a few stray glimmers of cosmic disasters, as in Plato’s Timaeus, when he tells the story of Phaeton, the son of the Sun god, who could not drive his father’s fiery chariot across the sky, and so crashed it into the Earth, burning the planet’s surface to a crisp. Plato writes:

That story, as it is told, has the fashion of a legend, but the truth of it lies in the occurrence of a shift of the bodies in the heavens which move round the Earth, and a destruction of the things on the Earth by fierce fire, which recurs at long intervals.

A remarkable piece of ancient wisdom, but on the whole, human culture is too fresh an invention to have preserved the scarier stuff we find in the geological record. We have no tales of mile-wide asteroid strikes, or super volcanoes, or the deep freezes that occasionally turn our blue planet white. The biosphere has bounced back from each of these shocks, but not before sacrificing terrifying percentages of its species. And even its most remarkable feats of resilience are cold comfort, for the future might subject Earth to entirely novel experiences.

Some in the space exploration community, including no less a figure than Freeman Dyson, say that human spaceflight is folly in the short term

A billion years will give us four more orbits of the Milky Way galaxy, any one of which could bring us into collision with another star, or a supernova shockwave, or the incinerating beam of a gamma ray burst. We could swing into the path of a rogue planet, one of the billions that roam our galaxy darkly, like cosmic wrecking balls. Planet Earth could be edging up to the end of an unusually fortunate run.

If human beings are to survive these catastrophes, both the black swans and the certainties, we will need to do what life has always done: move in the service of survival. We will need to develop new capabilities, as our aquatic forebears once evolved air-gulping lungs, and bony fins for crude locomotion, struggling their way onto land. We will need to harness the spirit that moved our own species to trek into new continents, so that our recent ancestors could trickle out to islands and archipelagos, before crossing whole oceans, on their way to the very ends of this Earth. We will need to set out for new planets and eventually, new stars. But need we make haste?

Some in the space exploration community, including no less a figure than the physicist Freeman Dyson, say that human spaceflight is folly in the short term. We humans are still in our technological infancy, after all, only a million years removed from the first control of fire. We have progressed quickly, from those first campfire sparks to the explosions we bottle in tall cylinders, to power our way out of Earth’s gravity well. But not everyone who sits atop our rockets returns safely. To seed a colony on another planet, we need astronaut safety to scale up. Perhaps we should park human missions for now, and explore space through the instruments of our cosmic drones, like the Voyager probe that recently slipped from the Solar System, to send us its impressions of interstellar space. We can resume human spaceflight later this century, or next, after we have reaped the full fruits of our current technological age. For all we know, revolutions in energy, artificial intelligence and materials science could be imminent. Any one of them would make human spaceflight a much easier affair.

‘There is an argument you often hear in space circles,’ I said to Musk, ‘where people say the focus on human space travel in the near-term is entirely misplaced – ’

‘What focus? There isn’t one, you know,’ he said, cutting me off.

‘But to the extent you’re advocating for one,’ I said, ‘there is an argument that says until we ramp up technologically, we’re better off sending probes because, as you know, the presence of a single human being on a spacecraft makes the engineering exponentially more difficult.’

‘Well, we are sending probes,’ Musk told me. ‘And they are very expensive probes, by the way. They aren’t exactly bargain-basement. The last RC car we sent to Mars cost more than $3 billion. That’s a hell of a droid. For that kind of money, we should be able to send a lot of people to Mars.’

There is a story Musk likes to tell, part of the founding myth of SpaceX, about how he stayed up late one night searching NASA’s website for information about a crewed mission to Mars. This was back in 2001, when the space shuttles were still flying, their launches providing a steady drumbeat of spectacle, just enough to convince the casual observer that human spaceflight wasn’t in serious decline. Today, it is impossible to sustain that delusion.

The idea that humans would one day venture into the sky is as old as mythology, but it wasn’t until the scientific revolution, when the telescope made the sky legible, that it began to seem like a realistic objective. In 1610, the astronomer Johannes Kepler wrote, in a letter to Galileo:

Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies.

After the hot air balloon and airplane were invented, a few visionaries moved on to planning for space colonisation itself. But it wasn’t until the Space Race, the extraordinary period of progress that began with Sputnik in 1957 and ended with the first Moon landing in 1969, that the idea of cosmic manifest destiny moved from the fringe to the mainstream. In the ensuing decades, it would inspire whole literatures and subcultures, becoming, in the process, one of the dominant secular narratives of the human future. But reality has not kept up.

It has been three years since NASA, the world’s best-funded space agency, fired a human being into orbit. Americans who wish to fly to the ISS must now ride on Russian rockets, launched from Kazakhstan, at the pleasure of Vladimir Putin. Even the successful trips are, in their own way, evidence of decline, because the space station sits a thousand times closer to Earth than the Moon. Watching NASA astronauts visit it is about as thrilling as watching Columbus sail to Ibiza. But that’s as good as it’s going to get for a while. The agency’s next generation rocket isn’t due until 2018, and its first iteration will barely best the Saturn V, the pyrotechnic beast that powered the Apollo missions. American presidents occasionally make bold, Kennedy-like pronouncements about sending humans to Mars. But as Musk discovered more than a decade ago, there are no real missions planned, and even optimists say it will be 2030 at the earliest.

It wasn’t supposed to be like this. Only a few decades ago, it seemed as though we were entering a new epoch of exploration, one that would shame the seafarers of the High Renaissance. We would begin by mastering lower Earth orbit, so that visits to space were safe and routine. Then we’d go to the Moon and build a permanent base there, a way station that would let us leap to the planets, each in quick succession, as though they were lily pads on a pond, and not massive moving worlds spaced by hundreds of millions of miles. We’d start with Mars and then shoot through the asteroid belt to Jupiter and its ocean-harbouring moons. We’d drink in Saturn’s sublimity, its slanted rings and golden hue, and then head for the outer giants, and the icy rubble at the Solar System’s edge. The Sun would look small out there, and the stars beckoning. We would spread through the Milky Way’s safe zone, the doughnut of gas and fire, billions of stars strong, that surrounds our galaxy’s violent core, and then we’d press out into intergalactic space. We’d use wormholes or warp drives, or some other vaguely sketched physics, to pretend away the millions of light years that separate us from Andromeda and the glittering web beyond it, whose glimpsable regions alone contain hundreds of billions of galaxies.

When Musk realized there were no missions to Mars on the books, he figured Americans had lost interest in space exploration. Two years later, the public response to the Columbia shuttle disaster convinced him otherwise. ‘It was in every newspaper, every magazine, every news station, even those that had nothing to do with space,’ he told me. ‘And yeah, seven people died and that was awful, but seven people die all the time, and nobody pays any attention to it. It’s obvious that space is deeply ingrained in the American psyche.’ Musk now sees the Space Race as a transient Cold War phenomenon, a technological pissing match fuelled by unsustainable public spending. ‘The Soviets were crowing after Sputnik, about how they had better technology than we did, and so therefore communism is better,’ he told me. ‘And so we set a really tough target and said we would beat them there, and money was no object. But once the ideological battle was won, the impetus went away, and money very quickly became an object.’

NASA’s share of the US federal budget peaked at 4.4 per cent in 1966, but a decade later it was less than 1 per cent, where it has remained ever since. The funding cut forced NASA to shutter the Saturn V production lines, along with the final three Moon landings, and a mission to Mars slated for the late 1980s. That’s why the agency’s website looked so barren when Musk visited it in 2001.

Aghast at this backsliding, and still thinking it a failure of will, Musk began planning a Mars mission of his own. He wanted to send a greenhouse to Mars, filled with plants that would become, in the course of their long journeying, the most distant travellers of all multicellular life. Images of lush, leafy organisms living on the red planet would move people, he figured, just as images of the Earth rising, sunlike, on the lunar plain had moved previous generations. With a little luck, the sentiment would translate into political will for a larger NASA budget.

When Musk went to price the mission with US launch companies, he was told transport would cost $60-80 million. Reeling, he tried to buy a refurbished Russian intercontinental ballistic missile to do the job, but his dealer kept raising the price on him. Finally, he’d had enough. Instead of hunting around for a cheaper supplier, Musk founded his own rocket company. His friends thought he was crazy, and tried to intervene, but he would not be talked down. Musk identifies strongly as an engineer. That’s why he usually takes a title like chief technical officer at the companies he runs, in addition to chief executive officer. He had been reading stacks of books about rockets. He wanted to try building his own.

Great migrations are often a matter of timing, of waiting for a strait to freeze, a sea to part, or a planet to draw near

Six years later, it all looked like folly. It was 2008, a year Musk describes as the worst of his life. Tesla was on the verge of bankruptcy. Lehman had just imploded, making capital hard to come by. Musk was freshly divorced and borrowing cash from friends to pay living expenses. And SpaceX was a flameout, in the most literal sense. Musk had spent $100 million on the company and its new rocket, the Falcon 1. But its first three launches had all detonated before reaching orbit. The fourth was due to lift off in early Fall of that year, and if it too blew apart in the atmosphere, SpaceX would likely have numbered among the casualties. Aerospace journalists were drafting its obituary already. Musk needed a break, badly. And he got it, in the form of a fully intact Falcon 1, riding a clean column of flame out of the atmosphere and into the history books, as the first privately funded, liquid-fuelled rocket to reach orbit.

SpaceX nabbed a $1.6 billion contract with NASA in the aftermath of that launch, and Musk used the money to expand rapidly. In the years since, he has reeled off 15 straight launches without a major failure, including the first private cargo flights to the ISS. Last year, he signed a 20-year lease on launch pad 39A, the hallowed stretch of Cape Canaveral concrete that absorbed the fire of Apollo’s rockets. Earlier this year, he bought a tract of land near Brownsville, Texas, where he plans to build a dedicated spaceport for SpaceX. ‘It took us ages to get all the approvals,’ he told me. ‘There were a million federal agencies that needed to sign off, and the final call went to the National Historic Landmark Association, because the last battle of the Civil War was fought a few miles away from our site, and visitors might be able to see the tip of our rocket from there. We were like, “Really? Have you seen what it’s like around there? Nobody visits that place.”’

Musk isn’t shy about touting the speed of his progress. Indeed, he has an Ali-like appetite for needling the competition. A Bloomberg TV interviewer once asked him about one of Tesla’s competitors and he laughed in response. ‘Why do you laugh?’ she said. ‘Have you seen their car?’ he replied, incredulously. This same streak of showmanship surfaced when Musk and I discussed the aerospace industry. ‘There have been a number of space startups,’ he told me. ‘But they have all failed, or their success was irrelevant.’

But SpaceX does have competitors, both industry giants and scrappy startups alike. The company has just spent three years in a dogfight to become the first commercial space outfit to launch US astronauts to the space station. The awarding of this contract became more urgent in March, after the US sanctioned Russia for rolling tanks into Crimea. A week later, Russia’s Deputy Prime Minister Dmitry Rogozin quipped: ‘After analysing the sanctions against our space industry, I suggest the US deliver its astronauts to the ISS with a trampoline.’

SpaceX was an early favourite to win the contract, but it was never a lock. Critics have hammered the company for delaying launches, and in August it suffered a poorly timed mishap, when one of its test rockets blew up shortly after lift-off. In the end, NASA split the contract between Boeing and SpaceX, giving each six launches. Musk said that he would move into human missions, win or lose, but his progress would have been slowed considerably. The contract is only for short hops to lower Earth orbit, but it will give Musk the chance to demonstrate that he can do human spaceflight better than anyone else. And it will give him the money and reputation he needs to work up to a more extraordinary feat of engineering, one that has not been attempted in more than four decades: the safe transport of human beings to a new world.

Great migrations are often a matter of timing, of waiting for a strait to freeze, a sea to part, or a planet to draw near. The distance between Earth and Mars fluctuates widely as the two worlds whirl around in their orbits. At its furthest, Mars is a thousand times further than the Moon. But every 26 months they align, when the faster moving Earth swings into position between Mars and the Sun. When this alignment occurs where their orbits are tightest, Mars can come within 36 million miles, only 150 times further than the Moon. The next such window is only four years away, too soon to send a crewed ship. But in the mid-2030s, Mars will once again burn bright and orange in our sky, and by then Musk might be ready to send his first flurry of missions, to seed a citylike colony that he expects to be up and running by 2040.

‘SpaceX is only 12 years old now,’ he told me. ‘Between now and 2040, the company’s lifespan will have tripled. If we have linear improvement in technology, as opposed to logarithmic, then we should have a significant base on Mars, perhaps with thousands or tens of thousands of people.’

Musk told me this first group of settlers will need to pay their own way. ‘There needs to be an intersection of the set of people who wish to go, and the set of people who can afford to go,’ he said. ‘And that intersection of sets has to be enough to establish a self-sustaining civilisation. My rough guess is that for a half-million dollars, there are enough people that could afford to go and would want to go. But it’s not going to be a vacation jaunt. It’s going to be saving up all your money and selling all your stuff, like when people moved to the early American colonies.’

Even at that price, a one-way trip to Mars could be a tough sell. It would be fascinating to experience a deep space mission, to see the Earth receding behind you, to feel that you were afloat between worlds, to walk a strange desert under an alien sky. But one of the stars in that sky would be Earth, and one night, you might look up at it, through a telescope. At first, it might look like a blurry sapphire sphere, but as your eyes adjusted, you might be able to make out its oceans and continents. You might begin to long for its mountains and rivers, its flowers and trees, the astonishing array of life forms that roam its rainforests and seas. You might see a network of light sparkling on its dark side, and realise that its nodes were cities, where millions of lives are coming into collision. You might think of your family and friends, and the billions of other people you left behind, any one of which you could one day come to love.

The austerity of life on Mars might nurture these longings into regret, or even psychosis. From afar, the Martian desert evokes sweltering landscapes like the Sahara or the American West, but its climate is colder than the interior of Antarctica. Mars used to be wrapped in a thick blanket of atmosphere, but something in the depths of time blew it away, and the patchy remains are too thin to hold in heat or pressure. If you were to stroll onto its surface without a spacesuit, your eyes and skin would peel away like sheets of burning paper, and your blood would turn to steam, killing you within 30 seconds. Even in a suit you’d be vulnerable to cosmic radiation, and dust storms that occasionally coat the entire Martian globe, in clouds of skin-burning particulates, small enough to penetrate the tightest of seams. Never again would you feel the sun and wind on your skin, unmediated. Indeed, you would probably be living underground at first, in a windowless cave, only this time there would be no wild horses to sketch on the ceiling.

‘Even at a million people you’re assuming an incredible amount of productivity per person, because you would need to recreate the entire industrial base on Mars’

It is possible that Mars could one day be terraformed into an Earthly paradise, but not anytime soon. Even on our planet, whose natural systems we have studied for centuries, the weather is too complex to predict, and geoengineering is a frontier technology. We know we could tweak the Earth’s thermostat, by sending a silvery mist of aerosols into the stratosphere, to reflect away sunlight. But no one knows how to manufacture an entire atmosphere. On Mars, the best we can expect is a crude habitat, erected by robots. And even if they could build us a Four Seasons, near a glacier or easily mined ore, videoconferencing with Earth won’t be among the amenities. Messaging between the two planets will always be too delayed for any real-time give and take.

Cabin fever might set in quickly on Mars, and it might be contagious. Quarters would be tight. Governments would be fragile. Reinforcements would be seven months away. Colonies might descend into civil war, anarchy or even cannibalism, given the potential for scarcity. US colonies from Roanoke to Jamestown suffered similar social breakdowns, in environments that were Edenic by comparison. Some individuals might be able to endure these conditions for decades, or longer, but Musk told me he would need a million people to form a sustainable, genetically diverse civilisation.

‘Even at a million, you’re really assuming an incredible amount of productivity per person, because you would need to recreate the entire industrial base on Mars,’ he said. ‘You would need to mine and refine all of these different materials, in a much more difficult environment than Earth. There would be no trees growing. There would be no oxygen or nitrogen that are just there. No oil.’

I asked Musk how quickly a Mars colony could grow to a million people. ‘Excluding organic growth, if you could take 100 people at a time, you would need 10,000 trips to get to a million people,’ he said. ‘But you would also need a lot of cargo to support those people. In fact, your cargo to person ratio is going to be quite high. It would probably be 10 cargo trips for every human trip, so more like 100,000 trips. And we’re talking 100,000 trips of a giant spaceship.’

Musk told me all this could happen within a century. He is rumoured to have a design in mind for this giant spaceship, a concept vehicle he calls the Mars Colonial Transporter. But designing the ship is the easy part. The real challenge will be driving costs down far enough to launch whole fleets of them. Musk has an answer for that, too. He says he is working on a reusable rocket, one that can descend smoothly back to Earth after launch, and be ready to lift off again in an hour.

‘Rockets are the only form of transportation on Earth where the vehicle is built anew for each journey,’ he says. ‘What if you had to build a new plane for every flight?’ Musk’s progress on reusable rockets has been slow, but one of his prototypes has already flown a thousand metres into the air, before touching down softly again. He told me full reusability would reduce mission costs by two orders of magnitude, to tens of dollars per pound of weight. That’s the price that would convert Earth’s launch pads into machine guns, capable of firing streams of spacecraft at deep space destinations such as Mars. That’s the price that would launch his 100,000 ships.

All it takes is a glance over your shoulder, to the alien world of 1914, to remind yourself how much can happen in a century. But a million people on Mars sounds like a techno-futurist fantasy, one that would make Ray Kurzweil blush. And yet, the very existence of SpaceX is fantasy. After talking with Musk, I took a stroll through his cathedral-like rocket factory. I wandered the rows of chromed-out rocket engines, all agleam under blue neon. I saw white tubes as huge as stretched-out grain silos, with technicians crawling all over them, their ant-farm to-and-fro orchestrated from above, by managers in glass cube offices. Mix in the cleanroom jumpsuits and the EDM soundtrack, and the place felt something like Santa’s workshop as re-imagined by James Cameron. And to think: 12 years ago, this whole thrumming hive, this assembly line for spaceships, did not even exist, except as a hazy notion, a few electrified synapses in Musk’s overactive imagination.

Who am I to say what SpaceX will accomplish in a century’s time? For all I know Musk will be hailed as a visionary by then, a man of action without parallel in the annals of spaceflight. But there are darker scenarios, too. Musk could push the envelope, and see his first mission to Mars end in tragedy. Travel to Mars could prove elusive, like cold fusion. It might be one of those feats of technology that is always 25 years away. Musk could come to be seen as a cultural artifact, a personification of our post-Apollo hangover. An Icarus.

I asked Musk if he’d made peace with the possibility that his project could still be in its infancy, when death or infirmity forces him to pass the baton. ‘That’s what I expect will be the case,’ he said. ‘Make peace with it, of course. I’ve thought about that quite a lot. I’m trying to construct a world that maximises the probability that SpaceX continues its mission without me,’ he said. I nodded toward a cluster of frames on his wall, portraits of his five sons. ‘Will you give it to them?’ He told me he had planned to give it to an institution, or several, but now he thinks that a family influence might be stabilising. ‘I just don’t want it to be controlled by some private equity firm that would milk it for near-term revenue,’ he said. ‘That would be terrible.’

‘We need to be laser-focused on becoming a multi-planet civilisation. That’s the next step’

This fear, that the sacred mission of SpaceX could be compromised, resurfaced when I asked Musk if he would one day go to Mars himself. ‘I’d like to go, but if there is a high risk of death, I wouldn’t want to put the company in jeopardy,’ he told me. ‘I only want to go when I could be confident that my death wouldn’t result in the primary mission of the company falling away.’ It’s possible to read Musk as a Noah figure, a man obsessed with building a great vessel, one that will safeguard humankind against global catastrophe. But he seems to see himself as a Moses, someone who makes it possible to pass through the wilderness – the ‘empty wastes,’ as Kepler put it to Galileo – but never sets foot in the Promised Land.

Before I left SpaceX, I wanted to know how far Musk thought human exploration would go. When a man tells you that a million people will live on Mars within a century, you want to know his limits, if only for credibility’s sake. ‘Do you think we will go to the stars?’ I asked him.

‘Wow,’ he said. ‘It’s pretty hard to get to another star system. Alpha Centauri is four light years away, so if you go at 10 per cent of the speed of light, it’s going to take you 40 years, and that’s assuming you can instantly reach that speed, which isn’t going to be the case. You have to accelerate. You have to build up to 20 or 30 per cent and then slow down, assuming you want to stay at Alpha Centauri and not go zipping past.’ To accentuate this last point, Musk made a high-pitched zooming noise, like kids make when playing with toy spaceships.

I pressed him about star travel a bit more, but he stayed tight. ‘It’s just hard,’ he said. ‘With current life spans, you need generational ships. You need antimatter drives, because that’s the most mass-efficient. It’s doable, but it’s super slow.’

‘So you’re skeptical,’ I said. He cracked then, but only a little.

‘I’m not saying I’m skeptical of the stars,’ he said. ‘I just wonder what humanity will even look like when we try to do that. If we can establish a Mars colony, we can almost certainly colonise the whole Solar System, because we’ll have created a strong economic forcing function for the improvement of space travel. We’ll go to the moons of Jupiter, at least some of the outer ones for sure, and probably Titan on Saturn, and the asteroids. Once we have that forcing function, and an Earth-to-Mars economy, we’ll cover the whole Solar System. But the key is that we have to make the Mars thing work. If we’re going to have any chance of sending stuff to other star systems, we need to be laser-focused on becoming a multi-planet civilisation. That’s the next step.’

You can see why NASA has given Musk a shot at human spaceflight. He makes a great rocket but, more than that, he has the old vision in him. He is a revivalist, for those of us who still buy into cosmic manifest destiny. And he can preach. He says we are doomed if we stay here. He says we will suffer fire and brimstone, and even extinction. He says we should go with him, to that darkest and most treacherous of shores. He promises a miracle.