How much would it cost to build a city on Mars? According to Elon Musk, it could be the most expensive construction project in human history — and cost up to an eighth of the value of the entire global economy.

The SpaceX CEO’s vision includes not only sending the first humans to Mars, but to use that mission as a starting point to build a permanent settlement. Assuming all goes to plan, Musk believes that a self-sustaining city could take shape as early as 2050.

What happens after that point is anyone’s guess. Inverse has spoken to experts from a number of fields, who have flagged a series of issues those first inhabitants will need to address. They could mutate and develop new physical attributes, they could find the city’s confines stifling and develop a national identity, and they could develop a new, ground-up economy.

Musk has previously suggested SpaceX could offer a return ticket to Mars at around the same price point as the median house in the United States. That would run to around $200,000, with the logic that someone could sell their house and move to Mars. Inter-Earth trips, expected to send people between major cities in less than an hour, could cost in the four-figure range.

These figures are nothing compared to the expected cost for the Starship mission.

Guenter Lang, an economics professor at Kühne Logistics University in Germany, told Inverse in May that the trip would still likely seem a wild adventure to many rather than a serious investment, meaning it could skew toward the richer.

So if SpaceX is looking to start a new city in just three decades, how much would it cost?

“Between $100B and $10T,” Musk declared via Twitter on August 10.

“What about what you said about 1,000,000 tons of cargo to Mars for a self-sustaining city… real estimate, back-of-envelope calc or figure of speech?” asked Twitter user Alexandre J. Tourville.

“Approx min payload to Mars to nearest order of magnitude, so at $100k/ton, cost would be $100B,” Musk responded.

How much would it cost to have a city on Mars? Here's Elon's math he shared with a follower on Twitter this past weekend. Twitter

SpaceX Mars City: The Price to Build a New Mars City

Musk has pegged the ultimate price of establishing this city at somewhere between $100 billion and $10 trillion.

The calculations are based on the assumption that a city would require one million tons of cargo from Earth to function at a minimum. Musk said as much during a July 2019 interview with CBS News, comparing the scale of the challenge with that of the lunar lander that didn’t have to carry so much. On Saturday, he clarified that this was to the nearest order of magnitude.

During an August conversation with Chinese billionaire Jack Ma, Musk claimed the venture would cost somewhere between half a percent to one percent of the world’s gross domestic product. The figure rests somewhere between the amount humanity spends on cosmetics and the amount it spends on healthcare.

It’s unclear how SpaceX will pay for this, as its rocket launches in 2018 brought in $2 billion revenue. Starlink, the company’s upcoming internet connectivity satellite constellation, could plug the gap: an internal company estimate suggested it could bring in $20 billion revenue by 2025.

At the low estimate, SpaceX may only need in the region of $3 billion per year to fund its Mars city over a 30-year period.

SpaceX's Starship, as envisioned for a Mars settlement. Elon Musk/Twitter

The cost of setting up this city would depend on how much it costs to send each ton to Mars. If it’s $100,000 to send each ton, Musk explained Saturday, that would set the price at around $100 billion. Musk estimated in 2017 that the current price is around $140,000 per ton, but cited the $100,000 figure as feasible.

Musk’s figures leave a broad section open. Here’s what $100 billion could also cover:

$100 billion is also enough to meet Doctor Evil’s ransom demands in Austin Powers:

What about $10 trillion, the upper bound of Musk’s figure?

It sounds like an unbelievable amount of money, but it’s still a fraction of global wealth. Real estate is estimated to be worth around $217 trillion total, around the same amount as global debt for individuals and nations combined. Wealth invested in derivatives is somewhere between $544 trillion and a staggering $1.2 quadrillion.

Nonetheless, in terms of the cost of building a new city, it’s an absolutely astronomical figure.

Elon Musk, speaking at a September 2018 event where he detailed plans to fly a Japanese billionaire around the moon. SpaceX

SpaceX Mars City: How to Build a City

SpaceX is expected to use the Starship to kickstart its city. This is a stainless steel rocket, fully reusable, with enough pressurized cabin space to comfortably hold around 100 people on a trip to Mars lasting three to six months. The Starship itself measures 160 feet, but when paired with the Super Heavy booster the entire construction measures 383 feet. It’s designed to take over 100 tons of payload as far as Mars, assuming SpaceX can solve the issue of adding more fuel in orbit.

The company unveiled its plan to send humans to Mars in September 2017, explaining how two unmanned Starships would first land, then around two years later when the Earth and Mars are close again, the firm would send two manned and two unmanned ships. These people would be tasked with setting up a propellant depot, refueling the ship with liquid oxygen and methane to return home.

Over the course of 10 orbital synchronizations, flying when the Earth and Mars are closest, Musk claims it is possible to establish a city. To reach the 2050 deadline, Musk stated, the team would probably have to start by around 2024. Principal Mars development engineer for SpaceX Paul Wooster explained in September 2018 that the future inhabitants would have to expand beyond the propellant depot to create recycling schemes, landing pads, habitats, greenhouses and further life support schemes.

In September 2019, Musk unveiled the first prototype of the company’s Starship rocket. The Mk.1 model, constructed at the firm’s Boca Chica facility, was demonstrated as part of a wide-ranging presentation that explained how the company plans to build multiple vessels in rapid succession. The following month, aerial footage of the company’s Florida facility showed work underway on two more Starships. The company aims to host a 20-kilometer test jump, followed by an orbital jump.

From there, the goal is to host several ambitious missions. This includes launching a telecommunications satellite by 2021, dropping supplies on the moon in 2022, and sending Japanese billionaire Yusaku Maezawa around the moon by 2023. From there, the versatile nature of the Starship should enable the firm to both build a base on the moon and Mars city at the same time.

SpaceX's BFR, an earlier version of the Starship, landing on Mars. SpaceX

SpaceX Mars City: Why Musk Wants to Do It

It’s going to be ridiculously expensive, it’s not going to be fun for the early inhabitants, and there’s a chance the whole thing fails and collapses into an overpriced disaster. So, why is Musk doing it?

In short, because he sees it as a reason to look forward to the future. At a September 2018 event, he explained:

“There’s so many things that make people sad or depressed about the future, but I think becoming a space-faring civilization is one of those things that makes you excited about the future…that is the intent of BFR [now known as Starship], is to make people excited about the future.”

The most expensive project of all time? It could break humanity free from the confines of Earth and spark a new era in its history.