Lunar miners were particularly jubilant this week when scientists said they had found compelling evidence for water ice on the lunar surface. There is much more ice there than we thought, and now we know exactly where it lies. This can greatly simplify future water extraction.
Long before this discovery, scientists were trying to find any water that might be hiding on the lunar surface. It is a resource that will be incredibly valuable for future long-term missions to the Moon, as water is essential for life here on Earth. It can be recycled in the lunar habitat or used for drinking or bathing. Also, with its help, it would be possible to grow the plants necessary to feed future lunar inhabitants.
Perhaps the largest and most immediate use for lunar water is in rocket fuel. The main components of water - hydrogen and oxygen - are two of the most important materials used in rocket fuel. And if you make rocket fuel from water on the Moon, it would be great to save money on ambitious missions in space. For now, rockets leaving Earth must carry all the fuel they need with them. But using lunar ice, rockets could be refueled while in space, and reach farther places for less money.
Is water better than oil?
“The idea is to create a kind of off-Earth supply chain for certain products - in particular for water as a fuel - to make it much easier to move from one body to another in space,” says Julie Brisset. Research Fellow, Florida Space Institute.
Delivering something into space is always expensive. If you want your satellite to escape Earth's gravity, you will need a lot of fuel to get it into orbit. In fact, most of the weight that a rocket carries when launching comes from fuel. And the deeper into space you go, the more fuel you need. More energy is needed to break away from the planet's gravity. Therefore, missions to deep space are becoming more and more expensive, because a large rocket is needed and a lot of fuel is needed.
But what if, instead of taking fuel on Earth, you could fill the tank with fuel that is already in space? Then missions to deep space would become as mundane as travel from one city to another. “Just imagine you had to get out of Denver and there were no gas stations on the way and you had to carry gas all the way to New York,” says George Sowers, professor at the Colorado School of Mines and former vice president of United Launch. Alliance. “You definitely won't get all this in the car. We'll have to take a trailer. This is why the idea of lunar development is so exciting to the mind. Water on the moon could be mined, broken up into rocket fuel, and transported to either circumlunar or low earth orbit. Rockets don't need to be large to carry all the fuel with them. They could just dock with a gas station and refuel for long journeys.
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Transporting fuel from the Moon to other places in space will be much cheaper than transporting it from Earth. On the moon, one-sixth of the Earth's gravity, which means less energy is needed to break away from the surface. Sowers recently analyzed the cost of transporting lunar fuel to different locations in space. Delivering lunar water to low Earth orbit, for example, is cheaper than sending it from Earth, although our planet is closer. “If you are going to use this fuel in low Earth orbit, the savings will be 20-30 percent if you use lunar fuel instead of terrestrial one,” says Sowers.
Scientists have been fantasizing about converting lunar water into rocket fuel for decades, since evidence has surfaced of the lunar poles being suitable for developing ice. In 1994, a joint study by NASA and the US military called Clementine showed that water exists in craters at the lunar poles. These places never see the light of the Sun and never reach temperatures above -250 degrees Fahrenheit. Several missions to the moon have since confirmed that there may be water in the area. In 2009, NASA dropped the LCROSS spacecraft into a crater at the moon's south pole to see what materials the impact would eject. It was found that the discharge was 5% water.
However, a study published this week in PNAS shows that some areas of the moon could be submerged in water. Scientists from the University of Hawaii and Brown University analyzed data collected by the Indian apparatus "Chandranayan-1" that went to the moon in 2008. Using one of the craft's instruments, they were able to map areas of ice on the moon by measuring the reflectivity of the water. They also scanned these places in infrared light and determined that the water took the form of ice, and not liquid or vapor. They not only confirmed that water ice is present on the moon's surface, but that some areas on earth are 20-30 percent ice. Depending on how deep the ice goes beneath the surface, it would be possible to map out where the propellant components will be extracted.
A fuel depot in low Earth orbit opens up new possibilities for missions in space. For example, one could build a space tug - a rocket that sits in space, refueling over and over again, and takes the satellites to the desired destination. Now satellites, which are launched into high orbit, spend from six months to a year to slowly rise higher using onboard engines. During this time, they cannot do their job and do not bring money. But with a space tug, satellites could be deployed in lower orbits with small rockets, and then used by the space tug to get the satellites into the desired orbit in just a few days. This would save the satellite operators money: they would not have to launch a large rocket to get their cargo into space.and they would have had more time to work with their companion.
So yeah, moon water is cool as fuel, but it won't be easy to start mining it. First, you need to do extensive reconnaissance. Thanks to the PNAS study, scientists have essentially created a map showing where to look for the juiciest areas of water ice at the lunar poles. The next step will be to send the landing modules and rovers to find the best sites. Scientists do not yet know whether the ice is in the form of slush mixed with ice, or in the form of solid blocks mixed with other surface material. “We know how to design extraction equipment. We just don't know what equipment to use,”says Metzger.
One idea is to dig up the lunar soil with an excavator that sends material to a processor. The processor separates the ice from the soil during the heating process and breaks the water into basic constituents using electricity. Some of the resulting fuel is then used to launch the rest of the water from the Moon in a vehicle to the fuel depot.
Of course, all this will be expensive. “It all comes down to a cost analysis,” says Metzger. "Is it cheaper to launch rocket fuel from Earth, or is it cheaper to launch equipment into space once and then maintain that equipment and use it to continuously create rocket fuel in space?" Based on analysis by Metzger, Brissé, and Sowers, they concluded that it would take ten years to invest in mining on the moon to profit. But since lunar mining is a risky business, venture capitalists may not want to be actively involved in this business.
This is why the team suggests that NASA should co-finance early mining developments. Thus, commercial investors are more likely to partner with a reputable agency that can bear some of the costs.
NASA will not provide a service to investors: the space agency has suggested that up to 100 metric tons of fuel may be required each year to fuel spacecraft leaving the lunar surface from base. If all this is launched from Earth, it will require about 3.5 billion dollars a year. Savings from the creation of lunar fuel will make missions to the Moon and Mars cheaper. “Missions to Mars would be cheaper, and everything we do outside of Earth, too,” says Sowers. For example, using lunar fuel to refuel rockets would cut the cost of flying to the moon from Earth by a factor of three, Sowers said. This is important considering that NASA is about to conduct a human mission to the moon again.
Ilya Khel