“If God wanted man to become a spacefaring species, He would have given man a moon.” The famed rocket scientist Krafft Ehricke uttered those words in 1984. He wanted to highlight how we could use the moon as a springboard to expand human civilization into the rest of the solar system. This was more than a decade on from the last Apollo mission to the moon, and Ehricke was watching NASA and the rest of the US space program retreat from hopes of exploring more distant worlds like Mars and focus instead on Earth’s orbit. 

America is finally seeking a return to the moon with Artemis, an ambitious (and unrealistic) goal of sending astronauts by 2024. But for the White House and NASA, the mission is about more than just getting humans back on the lunar surface. The moon is also a perfect base from which to establish a follow-up program to travel to Mars. For both destinations, the goal isn’t simply to plant a flag and return to Earth—it’s to maintain a permanent presence for people to live and work. 

“We’re going back to the moon for scientific discovery, economic benefits, and inspiration for a new generation of explorers,” NASA administrator Jim Bridenstine said September 21 as the agency published its latest plans for the Artemis program. “As we build up a sustainable presence, we’re also building momentum toward those first human steps on the Red Planet.”

But the agency never clearly explained how this is supposed to happen. The most important projects that are supposed to enable Artemis—the next-gen Space Launch System rocket and the Orion crew capsule—are not yet finished. Most experts agree the program is underfunded. The chief of human exploration at NASA has been replaced three times in just the last year. The agency does not even have a lunar lander picked out. So even if we get to the moon in 2024 (by no means a given), how do we ensure a Mars settlement comes next?

“The biggest problem we have right now is we don’t know how to live and work productively off planet Earth,” says Clive Neal, a geologist at the University of Notre Dame and an expert in lunar exploration. “We have no clue.” We’ve never properly tested out the technologies we’d need to live and work in space for months or years on end, in harsh environments with much colder temperatures, much higher amounts of radiation, lower levels of gravity, and a lack of oxygen and water.

“But we’ve got our own lab in our backyard with which to try these things,” says Neal. He and many colleagues recently authored a new report released by Explore Mars, an advocacy group promoting sustainable space exploration. The report identifies dozens of activities and technologies critical to Mars exploration that can be developed and tested through Artemis and ongoing lunar exploration efforts. 

Some things essential to Mars will be proven on the moon almost immediately after the launch of Artemis III (the planned 2024 crewed mission to the lunar surface). Life support is at the top of the list. Humans have never built long-term habitats on another world before. While we’ll be applying much of what we’ve learned from long-duration missions on the International Space Station, we’ll still need to ensure that a moon base and a Mars base can provide essential needs like food, water, and shelter. 

Building and testing those systems requires experience. “I think the key thing will be getting more people immersed in the lunar environment,” says Joe Cassady, the executive director for space operations at Aerojet Rocketdyne and one of the lead editors of the Explore Mars report. From the outset, we’ll need a collection of experiences and data from a huge range of different astronauts, across missions lasting weeks or months. Those experiences will inform how engineers build habitats, space suits, and surface transportation systems suited for humans.

In order to ensure that these habitats can last over time, you need to build something sustainable. Launch windows for Mars missions (when the planet is closest to Earth) come only every 26 months, so any round-trip Mars mission would have to involve some time waiting for this window to open up again. If the journey takes, say, nine months, you’d have to spend a minimum of three to four months on Mars before it would be feasible to start heading home. You can either bring enough provisions to last all those months, or you can look to off-world resources. And the first option is pretty much a non-starter. “You have to use local resources,” says Neal. “Trying to take everything with you to keep Martian astronauts safe and well simply won’t work.”

Water ice will be a vital resource. It could supply water and oxygen to sustain life-support systems, and it could also be split into hydrogen and oxygen to be used as rocket fuel. It could be used as shielding against space radiation and micrometeorite bombardment for any shelters that are built on the moon.

We know there’s plenty of water ice on Mars. And we’re pretty sure there’s a lot of water ice on the moon as well, making it a perfect environment to test out the technologies we need to prospect those reserves, mine them, purify them, and turn them into something that can help keep a settlement going. 

Those technologies would be very similar for both worlds. The moon is a more extreme environment, which means “if it works on the moon, it’ll work on Mars,” says Neal. He hopes engineers will design “world-agnostic” equipment.

The presence of water ice also somewhat bolsters the argument for running a spacecraft propulsion system based on hydrogen rather than methane (something SpaceX is pursuing with its Raptor engines). The report stipulates that while hydrogen can be produced locally on both worlds, methane can be produced from local resources only on Mars, where an atmosphere heavy in carbon dioxide provides a ready source of carbon. “Any methane production on the moon would require the importation of a carbon source,” the report states.

The report also recommends using power systems that aren't completely dependent on the sun. On Mars, with its greater distance and dusty atmosphere, solar power arrays would have more trouble turning sunlight into energy. 

Nuclear power seems to be the most obvious approach. It wouldn’t take too much power to keep a shelter on the moon going, but it would take enormous amounts of energy to run the sort of mining operations required to harvest and process water ice. Mining industry experts have told Neal they will likely be looking at systems that can provide power in megawatt ranges. “That was a wake-up call,” he says. “People in the planetary world hadn’t made these connections with the mining industry.” Solar, in this case, would be more of a backup source of power on both worlds, rather than a primary one. And there are few safer environments to test out new nuclear systems than the moon—an unpopulated, desolate environment.

The moon is also just a better place to simulate a Mars mission, particularly when it comes to Gateway, the planned space station designed for lunar orbit. It will essentially serve as a staging ground for any NASA missions to the lunar surface (crewed and robotic alike), as well as for deep-space missions to Mars later. The first two elements of Gateway (the power and propulsion module, and the habitation module) are slated to launch in 2023. 

In their report, Cassady his colleagues suggested that one approach might be to have a crew stay on the lunar Gateway space station for 60 to 90 days, conduct a simulated Mars mission on the lunar surface for 30-some days, and then complete another stay at Gateway for 90 days before coming home. That would be a compressed version of a Mars mission. It would simulate the changing microgravity conditions faced on such a journey, and give astronauts a taste of what a Mars mission might actually feel like. NASA’s new Artemis outline goes as far as to say that “the Gateway-to-surface operational system is also analogous to how a human Mars mission may work—with the ability for crew to remain in orbit and deploy to the surface.”

Lastly, a Mars settlement won’t work well unless we develop autonomous systems that don’t need close oversight. Ground crews on Earth can still control things on the moon in almost real time, but the lag in communications from Earth to Mars can be up to 22.4 minutes. “If a disaster [on Mars] strikes like what happened with Apollo 13, you don’t have a team of engineers on the ground to diagnose and solve the problem in real time,” says Casey Dreier, a space policy expert with the Planetary Society. The moon is the only good environment we have to really test and improve automated systems that can reliably operate without that type of human control. 

There is a concern the US space program could face a sharp pivot in priorities after the November election, as has happened in years past. But so far the Democratic Party seems on board. The wording in its 2020 platform reads:“We support NASA's work to return Americans to the moon and go beyond to Mars, taking the next step in exploring our solar system.” Dreier points out that the development of the Space Launch System and Orion are almost complete. And there’s also a lot of international buy-in for Gateway, with Europe, Japan, Canada, and possibly Russia all set to play a role in its development. Reversing course now would be extremely difficult, even if it were desirable. 

None of these plans are set in stone, however. NASA’s new Artemis outline spells out better than ever how the agency intends to return humans to the moon by 2024 but is remarkably light on detailing how it plans to meet the technology benchmarks for a sustainable moon base that would help us get to Mars. 

Even at a time when Ehricke’s words are closer than ever to being realized, it’s going to take a lot of determination to leap from the moon to the Red Planet.

Correction 9/25/20: The original story inaccurately described Clive Neal as an engineer. Neal is a geologist.