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Why mining the water on the Moon could open up space exploration

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‘Water is the oil of space’

Image: NASA

Moon-mining enthusiasts were particularly gleeful this week when researchers claimed that they had found definitive evidence that water ice exists on the surface of the Moon. There’s even more water ice than we thought up there, too, and we know exactly where a lot of it is. That may make it even easier to mine this water in the future.

Long before this discovery, researchers have been eager to scoop up any water that may be lurking on the lunar surface. It’s a resource that could be incredibly valuable for future long-term missions on the Moon since water is essential for life to function here on Earth. It could be recycled inside a lunar habitat or used for drinking water or bathing. It could also be used to help plants grow on the Moon, which are needed to nourish future lunar inhabitants.

But perhaps the biggest and most immediate application for lunar water is making rocket propellant. The main components of water — hydrogen and oxygen — are two of the biggest materials that are used to power rockets right now. And making rocket propellant out of the water on the Moon could drastically cut down on the cost of doing ambitious missions in space. Right now, rockets leaving Earth must carry all the propellant they need with them. But by leveraging lunar ice, rockets could potentially refuel once they get to space, allowing them to reach distant locations for less money.

“The idea would be to get a sort of supply chain started outside of Earth for certain products — in particular, for water as a propellant — so that it could be much easier to navigate to space from one body to another,” Julie Brisset, a research associate at the Florida Space Institute, tells The Verge.

Getting anything into space is expensive. If you want your satellite to break free of Earth’s gravity, you need a lot of propellant to fuel the ride to orbit. In fact, most of the weight of a rocket at launch is just the propellant needed to get the thing into space. And the deeper into space you want to go, the more propellant you need. Greater energy is needed to get farther and farther away from the planet’s pull. So missions into deeper space become even more costly to pay for all the extra propellant needed to get there and the bigger rocket to house that propellant.

But what if instead of taking all the propellant you need with you from Earth, you refill your gas tank with propellant that’s already in space? Then, deep-space missions become more like cross-country road trips. “Just imagine if you had to drive out to Denver and there were no gas stations along the way and you had to bring all your gas with you from New York,” George Sowers, a professor at the Colorado School of Mines and former vice president at the United Launch Alliance, tells The Verge. “You probably couldn’t do it in your car. You would have to tow all the fuel you need.” That’s why the idea of lunar mining is so enticing. Water from the Moon could be mined, broken apart into rocket fuel, and transported to a propellant depot either near the Moon or in low Earth orbit. Then, rockets wouldn’t have to be so big to house all their propellant. They could simply dock with a depot and refuel for longer trips to space.

Transporting propellant from the Moon to other locations in space is nowhere near as pricey as transporting it from Earth. The Moon has one-sixth the gravity of Earth, meaning it takes less energy to break away from the surface. Sowers recently did an analysis on how much it would cost to transport lunar propellant to different locations from space. And getting lunar water to low Earth orbit, for instance, is still cheaper than sending it from Earth, even though our planet is closer. “If you’re going to use that propellant in low Earth orbit, it’s still maybe a 20 or 30 percent savings, using lunar propellant versus Earth propellant,” says Sowers.

Scientists have been fantasizing about turning lunar water into rocket fuel for decades now, as evidence has mounted that the lunar poles may be prime for mining. In 1994, a joint probe from NASA and the US military called Clementine found evidence that water exists in craters at the Moon’s poles. These places never see the Sun’s light and never reach temperatures above -250 degrees Fahrenheit. Multiple missions to the Moon since have indicated that water may be present in these locations as well. In 2009, NASA slammed a spacecraft called LCROSS into a crater at the Moon’s south pole, to see what kind of materials the impact kicked up. NASA found that there was about 5 percent water in what was ejected.

A map of exposed lunar water ice made with data from the Chandrayaan-1 spacecraft.
Image: NASA

However, research published this week in the Proceedings of the National Academy of Sciences indicates that some areas of the Moon may be overflowing in water. Researchers at the University of Hawaii and Brown University analyzed data gathered from India’s Chandrayaan-1 spacecraft, which launched to the Moon in 2008. Using one of the vehicle’s instruments, they were able to pinpoint areas of ice on the Moon by measuring the reflectiveness of the water. They also observed these locations in infrared light, which allowed them to determine if the water was in ice form and not vapor or a liquid. Not only did they confirm that water ice is exposed on the lunar surface, but some areas of the ground are made up of 20 to 30 percent ice. Depending on how deep into the surface the ice goes, that could be ample fodder for rocket propellant.

“We really don’t need to be that concentrated everywhere,” says Phil Metzger, planetary physicist at the University of Central Florida and co-founder of NASA’s Swamp Works at Kennedy Space Center. “We only need some locations to be higher concentration in order to have enough water to provide all of the space transportation needs for the next 30 years.”

A propellant depot in low Earth orbit opens up a lot of opportunities for new kinds of missions in space. One idea is something called a space tug — a rocket that stays in space, refueling over and over, in order to ferry satellites to their final destinations. Right now, satellites going into high orbits above Earth are deployed into an initial transfer orbit and then spend six months to a year slowly raising themselves higher with onboard thrusters. During that time, the satellite can’t do its job, so it doesn’t make any money. But with a space tug, satellites could be deployed into much lower orbits with smaller rockets, and then a reusable rocket already in space could “tug” the probe to its final orbit in just a few days. That saves satellite operators money: they don’t need as big of a rocket to get their payload into space, and they have more time to make money from their probes.

So yes, Moon-water-as-fuel is appealing, but it won’t be easy to start mining water in space. First, there needs to be an extensive prospecting campaign. Thanks to the PNAS study, researchers have basically created a map showing where to find the juiciest chunks of water ice at the lunar poles. The next step is to send landers and rovers to those areas to figure out the best location to target and what the consistency of the ice is. Scientists still don’t know if the ice is in the form of slush mixed in with the dirt or if it’s like solid bricks fused together with other surface material. “We know how to design the equipment to extract it. We just don’t know which set of equipment to use,” says Metzger.

NASA has been working on robot designs that could be used to scoop up Moon and Mars dirt.
Image: NASA

One idea is scooping up the lunar soil with an excavation robot that hauls the materials to a processor. That processor then separates the ice from the soil through heating and breaks the water into its basic parts with electricity. Some of the resulting fuel is then used to launch the rest of the water off of the Moon on a transport vehicle, sending it to whatever propellant depot needs it in space.

Of course, all of this will be expensive. “It comes down to a cost analysis,” says Metzger. “Is it cheaper to launch rocket fuel from the Earth, or is it cheaper to launch the equipment into space one time and then maintain that equipment and use it to continually create rocket fuel in space?” Based on analysis done by Metzger, Brisset, and Sowers, they estimate that it’ll take a decade for investing in Moon mining to be profitable. But because lunar mining is so risky, it’s possible not a lot of venture capitalists will want to jump in right away.

That’s why the team suggests that NASA should get involved by partially funding early mining development efforts. That way, commercial investors will be more likely to pitch in if a credible government agency is involved and bearing some of the costs.

NASA wouldn’t just be doing investors a favor, either: the space agency has suggested that it might need up to 100 metric tons of propellant each year to power vehicles leaving the lunar surface from a base, according to Sowers’ analysis. If they had to ship all of that from Earth, it would cost around $3.5 billion per year. The savings from making Moon fuel could make missions to the Moon and Mars cheaper. “It would make Mars missions lower cost, and it makes pretty much everything we do beyond Earth affordable,” says Sowers. For example, using lunar propellant to refuel rockets would lower the cost of going to the Moon from Earth by a factor of three, according to Sowers. That’s an important detail, given NASA is looking to do human missions to the Moon once again.

“I’ve been saying for years now that water is the oil of space,” says Sowers, adding: “If NASA’s plans are to create a permanent human presence on the Moon, the first thing NASA needs to do is build a production facility for propellant.”