Scientists have discovered that potatoes can be grown and beer can be brewed on Mars. But before you book your next vacation with SpaceX and rock up to Matt Damon’s space diner on an empty stomach, it’s worth considering how you’ll pay for those delicious Martian Fries.

The concept of money in space isn’t sexy. You never see Luke Skywalker wiring terrorist funds to remote rebel factions or Captain Picard doing payroll late on Friday nights in the movies. But as Martian colonies come closer reality, the details of exactly how commerce could work are pretty hazy.

“Academic space law circles are already discussing this issue, and the European Space Agency (ESA) is thinking about it too,” says Chris Newman, a bonafide space law professor from Sunderland University in the UK. “Legislators and policymakers are realizing that space is a proper area of economic activity. There’s a cultural shift going on: space is moving from being exclusively for the scientific elite to something commercial and available to the masses.”

Since the collapse of the Soviet Union and its space program, the chances of the red planet becoming a communist utopia have effectively fallen to nil. SpaceX, NASA, and the United Arab Emirates all have plans to establish colonies on Mars within the next 100 years, and none of them will be doing it for free. As competing communities struggle to survive and thrive on the red planet, inevitably they’ll have to figure out how to economically co-exist.

“The granular detail of currency transactions and trading agreements between the colonies is going to be tough,” says Newman. “We only have to look at Brexit to see the difficulties that international trading arrangements can bring. Are we going to export that hostility to our space colonies? Ideally, we’ll aim to do more than just replicate Planet Earth’s economic issues.”

The U.S. dollar is the global reserve currency of the world, meaning that just about wherever you go on Earth you’ll find somebody who wants to sell you shit for dead presidents. But taking enough cold hard cash to Mars becomes a problem quickly thanks to the sheer physical weight of currencies. Dollar bills might not seem too heavy, but stack a million of them together and the pile will weigh more than a metric ton. With cargo space limited and every extra pound adding to the fuel consumption of Mars missions, we’ll never be able to launch enough green bills to sustain a Martian colony.

Good luck using credit cards 30 million miles from a good wifi signal. Getty Images / NASA

Situations like this are why credit cards were invented though, right? The problem is that processing a card transaction these days requires an internet connection, and right now, wifi is pretty patchy over there. The Mars Rover transmits pictures of the bleak Martian landscape over a satellite connection that’s half the speed your mom’s dial-up connection was in the ‘90s. Data is transmitted to one of two Mars orbital satellites, which have a maximum bandwidth of around 2 mbps — nowhere enough to handle a significant number of financial transactions, let alone an entire planet’s appetite for cat GIFs alongside.

To address this, the ESA has invented the first ever gigabit laser-based transmitter, called the European Data Relay System. Laser beams carry more information than an electromagnetic signal, but that won’t get the data back to Earth any quicker. Because of the enormous distance between the two planets and the limitations of the speed of light, it takes an average of 28 minutes for a ping sent from Mars to make it to Earth and come back again.

“Data is relayed back to Earth as efficiently as we can manage, but as the planet gets busier with new missions this will become a problem if a dedicated communication system isn’t provided,” says Craig Brown, telecoms delegate for the ESA and space innovation lead at Innovate UK, a British governmental agency that supports new technologies. “Sending video, images and text will work if you’re patient. But ‘real-time’ communications such as those needed for credit card transactions are unfeasible.”

With card transactions typically timing out after just 40 seconds, it’s unlikely you’ll be able to use your Mastercard on Mars. And when Earth and Mars are on opposite sides of the sun from each other, solar radiation interferes with electromagnetic transmissions, making it impossible to communicate at all with or without laser beams. This is called solar conjunction and only happens every couple of years.

“A conjunction will put Mars out of communication with Earth for two weeks once every two years,” explains Brown. “We need to decide if a dedicated system to deal with this downtime of communications is enough to justify a whole new — and expensive — solution.”

It’ll probably take more than a couple weeks for Mars to go full Mad Max, but without the ability to pay for Netflix subscriptions, who knows what boredom will lead to.

With cash and credit cards ruled out, it seems like the only remaining option is to build a payments processing network on Mars itself. This was the ambition behind MarsCoin, a cryptocurrency designed for the red planet. Like Bitcoin, MarsCoin uses a blockchain to maintain a public ledger of every transaction and this data is stored across various nodes rather than a single central processor. While it may be theoretically possible to deploy this system on Mars, laggy internet will prevent it from ever being directly connected to Earth’s economy.

Whatever it is that early space colonists use to do business on Mars, chances are they’ll need a lot of it to sustain their miserable lives on such an inhospitable planet. Whether they’re spending U.S. dollars, MarsCoin or something completely different, they’ll mostly be using it to pay extortionate prices for water and oxygen. And it’s unlikely that any amount of Mars money is going to buy them a ticket back to Earth.