This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Alex Ellery, Canada Research Chair for Space Robotics and Space Technology at Carleton University
People make crucial decisions every day, often without thinking. However, there are some things that can be predicted, such as the fact that if you continue to consume finite resources without recycling them, they will eventually run out.
However, when we set our sights to return to the moon, all of our bad habits will follow us, including an urge for unrestrained consumerism.
The prospect of returning to the moon has been a source of excitement since 1994, when the Clementine spacecraft discovered water ice on the moon. After two decades of doldrums following Apollo's end, excitement has returned to the moon. This was due to a lack of motivation.
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Everything changed when that water came along. Water ice deposits can be found at the poles, hidden in depths of craters which are permanently without sunlight.
We have improved our ability to recycle water and oxygen, thanks to the International Space Station. Although this makes it less valuable to supply water locally for human consumption, the demand will increase as the human population grows on the moon. What to do with the water from the moon?
Two common answers are energy storage using fuel cells, and fuel and an oxidizer to propulsion. The first can be easily avoided: Fuel cells, which recycle hydrogen and oxygen by electrolysis after they have been recharged, are very leak-free.
Fuel and energy
Although it is not as compelling, the second reason d'tre to mine water on the Moon is much more complicated. SpaceX uses a methane/oxygen mixture in its rockets so that they don't require hydrogen propellant.
The idea is to extract a finite and precious resource and then burn it. This is similar to what we do with oil and natural gas. In-situ resource utilization is the technical name for the technology that allows space mining and uses of resources.
While oxygen isn't scarce on the moon (roughly 40% of its minerals contain oxygen), hydrogen is most definitely.
Water extraction from the moon
As a fuel and a reducer, hydrogen is extremely useful. Although the moon contains a lot of oxygen in its minerals, it needs hydrogen or another reductant to be released.
Ilmenite, an oxide of titanium and iron, is one example. It is also a common mineral found on the moon. It can be heated to approximately 1,000°C (1,800° Fahrenheit) using hydrogen to make water, iron metal (from where an iron-based technology could be used) or titanium oxide. Hydrogen can be electrolyzed to make hydrogen, which is then recycled and oxygen. The latter can be effectively liberated from the Ilmenite. We are jeopardizing the future prospects of future generations by burning hydrogen extracted water: this is the crux to sustainability.
There are also other more practical issues. How can we get to these water ice resources that are buried close to the lunar surface? They are found in hostile terrain, hidden from sunlight, in deep craters that do not receive solar power at temperatures around 40 Kelvin or -233 Degrees C (-390 Degree F). We have never had to conduct extensive mining operations at such low temperatures.
Continue reading: The US wants to change the rules of mining the moon
Peaks of everlasting light are mountain peaks that are located near the south pole and are exposed to nearly constant sunlight. NASA's Jet Propulsion Lab proposes that sunlight beams from huge reflectors at these peaks to craters.
Near-constant sunlight exposes the moon's surface to its eternal light peak. Image credit: NASA/Johns Hopkins University Applied Physics
These huge mirrors need to be shipped from Earth and placed on these peaks. Then they can be remotely controlled and controlled to illuminate the deep-craters. Robotic mining vehicles will then be able to explore the deep craters now illuminated and recover water ice by using the reflected sun's energy.
Water ice can be transformed into vapor by using direct thermal or microwave heating. However, because of its high heat potential, this will require a lot more energy which must be supplied to the mirrors. It can also be physically extracted and then melted at slightly lower temperatures.
Use the water
After recovering the water, it must be electrolyzed to make hydrogen and oxygen. They should be liquefied to store them in a small storage container.
While oxygen can be easily liquefied, hydrogen liquefies at 30 Kelvin, which is -243 degrees Celsius, or -405 degree F, at a minimum pressure of 15 bars. To liquefy hydrogen, and keep it liquid without boiling off, this requires additional energy. This cryogenically chilled hydrogen and oxygen (LH2/LOX), must be transported to the intended destination while keeping its low temperature.
Now we have our propellant stock for launching stuff to the moon.
A launchpad will be required to launch into orbit. It may be at the moon's equator. Polar launches to the Lunar Gateway will not be possible without a polar launch pad. A lunar launchpad will require extensive infrastructure development.
It is clear that water ice extraction from the lunar poles can be done quickly, but it requires complex infrastructure. In-situ resource utilization will not save money because of the costs associated with infrastructure installation.
Alternatives to extraction
There are many options. The most important benefits of mining water are the hydrogen reduction of ilmenite, which yields iron metal, rutile, and oxygen. The LH2/LOX mixture is dominated by oxygen. It requires no infrastructure. Small-sized solar concentrators may be integrated into processing units to generate thermal power. There is no need to travel long distances between supply and demand sites in order to deploy each unit.
We can thus achieve nearly the same function by using a more sustainable, feasible route to in-situ resource usage that also includes mining abundant ilmenite or other lunar minerals.
We can't keep making the same mistakes on Earth that are unsustainable. As we move into the solar system, we have the chance to make it right.
This article was republished by The Conversation under Creative Commons. You can read the original article.
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