Above: Blue Origin's founder Jeff Bezos.

There are perhaps psychological factors, too, driving these wealthy men to spend billions on hurling rockets into space. Arrogance, vanity and self-aggrandisement must all play a role.

In Musk’s case, a miserable childhood could partly explain his extra-terrestrial ambitions. In the biography Elon Musk: How The Billionaire CEO Of SpaceX And Tesla Is Shaping Our Future, author Ashlee Vance describes how the “reserved, geeky, know-it-all outsider” had an atrocious relationship with his now estranged father, and was bullied viciously at school in South Africa. “The boy crept up behind Musk, kicked him in the head, and then shoved him down the stairs,” he writes of one school incident. “Musk tumbled down the entire flight, and a handful of boys pounced on him, some of them kicking Musk in the side and the ringleader bashing his head against the ground.” The beating required hospital treatment. Musk later had plastic surgery on his broken nose. 

Davenport suggests this childhood bullying may have instilled a combative attitude in the adult Musk which helped him challenge “the military-industrial complex that has dominated the space industry in the US for a long time. Musk had to scrap and fight his way into the market. It’s hard enough to build a rocket that can get to orbit, but in addition to that he had to break into a market that had been dominated by some very big companies, and win the trust of the US government, [proving that] this eccentric billionaire from South Africa with no experience in space could be successful in the industry. That was not an easy task.”

As a youngster, Bezos was geeky too, obsessed with computer games and Star Trek. He later named his dog Kamala, and his holding company Zefram, LLC, after characters from the sci-fi series. He even managed to secure a cameo role as an alien in the 2016 movie Star Trek: Beyond. As his biographer J.R. MacGregor explains in Jeff Bezos: The Force Behind The Brand: “He is the kind of guy who could tell you why the Starship Enterprise can go into warp and why it maxes out at Warp 9.”

Ultimately, though, the strongest motivation for these space barons is one another. There’s no doubt there’s serious antagonism between the equally iron-willed bosses of SpaceX, Blue Origin and Virgin Galactic. But, just like the space race between USA and the Soviet Union in the 1960s, rivalry fuels rockets. As Davenport explains, “They know the only way they’re going to succeed is if they have someone else driving them. Bezos and Musk know the value of competition.”

So who’s going to cross the finish line first? More to the point, what is the finish line? First human being on Mars, perhaps?

Davenport says it’s clear that, technologically, SpaceX is well ahead of the pack, with a flight manifest that includes multiple rocket-launches into orbit and cargo resupply missions to the International Space Station. By contrast, Blue Origin’s rockets have not yet reached orbit.

“But neither company has successfully flown a human being into space,” Davenport warns. “If you’re talking about Mars, I think it will be a collaborative effort. Mars is so difficult that it will take many members of industry alongside NASA and other countries as well.” He talks of the tension between SpaceX, “a hard-charging California company which still retains its start-up ethos”, and NASA, “a much more cautious, risk-averse government agency”. He adds: “Ultimately, [for Mars] maybe the sweet spot is somewhere between the two.”

SpaceX claims it will send crewed missions to Mars by 2024, eventually building a permanent base there. With slightly less chutzpah, Blue Origin has its sights set on establishing a Moon base as a stepping stone to the Red Planet. Even if you take this all with a pinch of salt, you’ve got to admire the Silicon Valley bravado.

Musk is 47 years old, Bezos 54, and Branson 68. Obviously none will live to see human beings spreading out across the Solar System. So perhaps their ultimate goal is to be lionised in history as great space pioneers.

In a thousand years’ time, will space-faring humans remember these billionaires in the same league as Christopher Columbus, Ferdinand Magellan and Neil Armstrong? “If they’re successful, they will be seen as the entrepreneurs and visionaries who enabled the infrastructure that opened up space to the masses,” says Davenport.

Interestingly, while everyone remembers the likes of Columbus, Magellan and Armstrong, no one remembers the engineers who built the craft that transported them. Perhaps it won’t be our space billionaires who are lionised, rather the astronauts who ride their rockets, and eventually set foot on other planets.

“That would make sense,” Davenport concludes. “After all, they will be the ones risking their lives.”