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NASA wants you to know it is on a Journey to Mars. For the last few years, the space agency has done everything it can to work those three words into press releases, public statements and YouTube videos. Nearly all of NASA鈥檚 current activities, it says, will culminate in landing humans on the Red Planet in the 2030s.

But recently, NASA has admitted this journey is going nowhere fast. Last month, its chief of human space flight, William Gerstenmaier, acknowledged that the space agency doesn鈥檛 have the cash to put people on Mars, even with small increases in its budget to keep up with inflation.

鈥淚 can鈥檛 put a date on humans on Mars,鈥� Gerstenmaier told a meeting of the American Institute for Aeronautics and Astronautics. 鈥淎t the budget levels we described 鈥� this roughly 2 per cent increase 鈥� we don鈥檛 have the surface systems available for Mars.鈥�

This admission ruffled few feathers in the world of space policy, where the fact that NASA鈥檚 Mars plans are vague and unlikely to come off is an open secret. After all, the current Journey to Mars campaign is just the latest in a string of unrealised exploration plans (see timeline).

So is it time for NASA to give up on Mars? Perhaps someone else could do it first?

Alongside NASA, countries such as Russia and China have made noises in the direction of Mars. And then there are the private enterprises, like SpaceX. But the chances of them reaching Mars first are small. The reality is, if the world鈥檚 best-funded space agency can鈥檛 afford a crewed mission, no one can. Elon Musk has already cancelled plans for an uncrewed SpaceX Mars mission in 2018, so his grander crewed missions are unlikely to blast off soon.

鈥淭o make it in the 2030s you would have to add billions per year 鈥� the current NASA budget isn鈥檛 even close鈥�

Without a drastic shift in NASA鈥檚 space policy, there will be no humans on Mars within the next two decades. So what might that shift look like? Could a massive increase in funding, on the scale of President John F. Kennedy鈥檚 Apollo programme, revive NASA鈥檚 ailing plans?

鈥淚t would take large bags of cash,鈥� says at the Harvard-Smithsonian Center for Astrophysics in Massachusetts. 鈥淭o make it in the 2030s, you would have to add billions per year 鈥� the current budget isn鈥檛 even close.鈥�

That budget was signed by President Trump in March, but in April he was keen to hurry things along. During a call to NASA astronauts on the International Space Station (ISS), he asked about Mars and seemed surprised to hear the 2030s timeline.

鈥淲ell, we want to try and do it during my first term or, at worst, during my second term, so we鈥檒l have to speed that up a little bit, OK?鈥� he said.

It remains to be seen if Trump stumps up the cash to make that happen. But even if NASA received billions of dollars more per year, it still wouldn鈥檛 guarantee success.

鈥淚t鈥檚 not just money, there are a lot of technological uncertainties that need to be addressed,鈥� says , a space policy expert at George Washington University in Washington DC. 鈥淧ouring money in might make them go away, but you could find out that they鈥檙e showstoppers.鈥�

Prickly problems

The first step in any Mars journey is designing a spacecraft to carry astronauts and a rocket to blast them on their way. NASA already has the Orion capsule and Space Launch System rocket in production for this.

But these aren鈥檛 enough by themselves for a successful trip. Radiation shielding, life support, a landing system and the supplies astronauts will need to survive on the Martian surface all remain prickly problems that NASA has barely started to tackle. The answers will involve shipping a whole load of stuff to Mars.

If you thought luggage was a problem on an aeroplane, it is a killer when it comes to space flight. Between food, water and life support, humans need a lot more supplies than robots, and every gram of added mass makes a spacecraft harder to launch and land. Even the lighter missions to land robots on Mars don鈥檛 have a great track record 鈥� the majority have ended in failure.

At the bare minimum, a landing crew and all their baggage would weigh 10 times more than the 1-tonne Curiosity rover, the heaviest thing we have landed on Mars, says McDowell. Right now, we just don鈥檛 know how to do that.

鈥淭hings don鈥檛 scale linearly 鈥� you can鈥檛 just take what we鈥檙e doing with the robots and scale it up,鈥� he says. If NASA were to use a parachute to slow a crewed spacecraft鈥檚 descent through the tenuous Martian atmosphere, he says, it would have to be the size of New York City. That鈥檚 why NASA used an ambitious 鈥�sky crane鈥� platform to lower Curiosity to the surface, but even scaling this up would be difficult.

Maybe we don鈥檛 need to solve all these problems at once. While some space advocates say a Mars mission must be fully planned and budgeted from day one, of the Coalition for Deep Space Exploration takes a different approach.

鈥淚f that were true, we would have never gotten to the moon,鈥� she says. 鈥淲hen they started with the moon work, they had no idea how they were going to do it, and they certainly didn鈥檛 have the budget to do it.鈥�

If your goal is to get to Mars one day, without setting a specific deadline, NASA has its money in the right places for research and development, she says. 鈥淚t鈥檚 like we鈥檙e building a skyscraper. We can start building before we鈥檝e completely designed the top two floors, which are the most expensive real estate.鈥�

And NASA doesn鈥檛 have to go it alone. The agency already has contracts with SpaceX and other commercial partners to develop technology for an eventual crewed mission, but a larger-scale collaboration like the ISS might be the best way forward.

鈥淭he only way for NASA to put humans on Mars by 2050 is to pair up with other countries or groups in industry,鈥� says Logsdon. 鈥淎 NASA-led international effort could potentially send humans to Mars in the first half of the 2040s.鈥�

Ironically, ending one international effort may be necessary for NASA to afford a new one. The agency spends about $1.5 billion a year on the ISS, about 8 per cent of its budget. Right now, all the international partners are committed to the station until 2024. At that point, they could choose to hand it over to industry or decommission it.

鈥淎 NASA-led international effort could potentially send humans to Mars in the first half of the 2040s鈥�

Yet as the home of microgravity experiments, the space station could be crucial to a mission to Mars, especially when it comes to testing technology and figuring out how the human body adapts to being in space.

鈥淵ou could end up cutting off your nose to spite your face,鈥� says Dittmar. 鈥淚f you decommission the station in 2024 and then realise you need it 鈥� oops! What do you do then?鈥�

An alternative approach could be to shift NASA鈥檚 focus to putting humans in orbit around the Red Planet, rather than onto it. Then the agency could work on how to sustain astronauts so far from home without having to develop a second spacecraft for landing on Mars 鈥� a huge cost saving.

鈥淭hey could decouple the let鈥檚-go-to-Mars distance problem from the landing problem,鈥� says McDowell. He says that the best plan may be to send astronauts to land on Mars鈥檚 moon Phobos first, since it isn鈥檛 big enough to have the gravity or atmosphere that make Mars so difficult.

So while there won鈥檛 be humans on Mars any time soon, they might get pretty close, says McDowell. 鈥淗aving astronauts trundling around Phobos with the enormous disc of Mars above them鈥� I think that would be pretty cool.鈥�

This article appeared in print under the headline 鈥淔ailure to launch鈥�