Is asteroid mining possible and, if so, how would it work?
The age of science we live in is full of opportunities reaching far beyond our skies, though we still have a long way ahead of us in order to physically reach for alien worlds. For now, we can only hypothesis our future endeavors in the outer space and, in order to facilitate our mobility through space, we first need to find a shortcut that can eliminate one of our greatest problem in space exploration: our Earth's gravity.
Our planet is a massive cosmic body, with a massive gravitational field. When a spacecraft lifts off, it has to reach a speed of 28,968 km/h (18,000 mi/h) in order to reach its orbit around Earth, burning through a tremendous amount of fuel. As a result, astronomers have thought about different ways to continue space exploration from colonies located on alien worlds far smaller and far less denser than our planet, worlds where gravity is no longer an issue. The Moon's gravity is only 16% that of Earth's and Mars has only 36% of the gravity pull of Earth (also remember that Earth is the densest object in the entire Solar System, denser even than the Sun).
Yet there is something else inside our Solar System, something that has small gravitational fields and is also full of resources, precious to both humans and space exploration: the asteroids.
Now in order to talk about mining these objects, we first need to understand what an asteroid really is.
Earth, our home planet, is nothing more than a huge asteroid. In fact, during the formation of the inner planets, 4.5 billion years ago, dust particles collided with dust particles, pebbles with pebbles, asteroids with asteroids, planetesimals with other planetesimals, asteroids or comets, forming the four planets between the Sun and Jupiter: Mercury, Venus, Earth and Mars.
Beyond the reaches of the Red Planet we find the Asteroid Belt, a scattered ring of space debris that was supposed to become a planet, but failed because of Jupiter's immense gravitational field.
When planets form, it’s because of gravity, since in space any object (no matter how small) has a gravitational field. The larger the object, the larger its gravity becomes. And when an asteroid/planetesimal reaches at least 400km in diameter, its gravitational field starts shaping the object into a sphere. A perfect example would be Ceres, the largest object inside the Asteroid Belt, catalogued as a dwarf planet, but in fact an asteroid that failed to become a planet because of Jupiter's gravitational influence on the Asteroid Belt. If we eventually start mining asteroids in our Solar System, Ceres is the perfect place to start for building a colony.
As a G-Type asteroid (carbonaceous asteroid), Ceres contains a lot of carbon but it also contains huge amounts of water. Its surface area is slightly smaller than the country of Kazakhstan, 2.700.000 km^2, ensuring enough space for astronauts to build a colony, and providing a gravitational field safe enough for spacecrafts to land and lift off. The huge amount of water also means a huge amount of fuel by splitting the water molecules through electrolysis into hydrogen and oxygen, both extremely flammable. In fact, Ceres supposedly has enough water to be able to fuel 10 takeoffs a day for at least 200 years.
We now have the fuel and we have almost 2 million asteroids in a large orbit around the Sun. But remember: the cosmos is extremely dangerous, and besides gravity, water and carbon, Ceres would also provide us with radiation damage, extreme temperature variations, meteorite impacts and so on. For Ceres, considering it's a G-type carbonaceous asteroid, a solution would be to establish the colony under its surface, most of all to protect astronauts and astro-miners from cosmic radiation. Ceres has little to no atmosphere and no magnetic field to protect it from solar winds and radiation, therefore, the easiest solution is for everybody to stay underground.
Now we have ourselves a colony, what will we find?
Most asteroids in the Asteroid Belt are carbonaceous, just like Ceres; around 75% of them. So besides being carbon rich and some containing water, there isn't much else there. There are, however, the S-type asteroids, rich in silicates and some metals. And then, we have the M-type asteroids, very rich in metals and of great interest for future space mining. This category of asteroids is rare, as it makes up for only 10% of the total amount of objects found in the Asteroid Belt. However, M-type asteroids are the most precious, as they – hypothetically – contain large amounts of rare metals, such as gold, uranium, platinum, palladium, iridium and so on. We have to understand though that the term “large” is used in comparison to the surface resources on Earth. Remember, rare metals found on Earth are rare everywhere in the Universe, as most of them are born in supernova explosions. Some of the most common elements found on M-type asteroids could be processed directly by the spacecraft, or brought back to a colony or even Earth. Larger spacecrafts could be built directly on location inside the colonies, where gravity poses no issue for liftoff for heavy ships, such as those that could provide internal gravity through centrifugal force.
How could space mining work? It's all hypothetical, but there could be at least two ways with different variations. In case of a large asteroid, a spacecraft could land on it and drill for materials. However, if the asteroid is two small, space-miners could use a larger spacecraft with a gravitational pull that exceeds the gravitational pull of the asteroid. Remember, every object in space has gravity; therefore, a spacecraft could have a gravitational pull towards a small asteroid in orbit around the Sun.
But we need to ask ourselves: is space mining worth it? Yes, it is! But remember: we need to broaden our horizons and also consider using asteroids as outposts for exploring the moons of the two gas giants Jupiter and Saturn (and even those of the ice giants Uranus and Neptune), as they are far (far!) more interesting. Yes, there are some asteroids containing high amounts of gold, platinum and other rare metals, but mankind's future should lie in our ability to overcome our own limits, not wander the cosmos for the shiny remnants of past supernovas.