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My story is set in a somewhat recent period of time (within let's say 50 years) The material (raw metal and such) are extracted by splitting the asteroid and then sensors identify which pieces of rock are mineral/metal rich. After these pieces are collected they would be brought back to a large mother ship where the pieces of rock would be melted down and the material extracted.
Would this process be worth the expense and are there better ways this could be set up?
Depending on what you're using the minerals for, this might not only be worth it, but it might be the only possible way to access minerals in any quantity.
Let's start by taking a look at Apollo 11. The Command / Service modules of the Apollo 11 mission came in at nearly 29 metric tonnes and carried a fuel load (combined kerosine and liquid O2) of around 2.4 million litres to get it on its way to the Moon. I'll point out here that a ratio of mass to fuel load isn't necessarily helpful here as Saturn V was designed from the ground up to get that mass and size into orbit, but this ratio does show that even if you were shipping equivalent amounts of mass (one load at a time) into orbit to make something big, it's going to take massive amounts of fuel.
So; let's build something big.
The Constitution class Starship (TOS Enterprise) has several mass estimates that put it in the 180k metric tonne range. This is approximately 6,207 times the mass of the Apollo 11 Command & Service Module launch weight. The cost of launching 17 Apollo missions was considered too much for many Americans and the program was shut down (in part) because of the ongoing costs to the USA. Just getting the raw mass for a starship (not to mention the building crews, habitats, construction frames and gantries, etc.) would be 365 times the cost in fuel of the entire Apollo program. All this assumes that there's this much fuel to spare from our dwindling resources. Not practical, and potentially not possible.
BUT; we have an entire asteroid belt out there. The advantage (as sdfgeoff points out in his comment) of asteroids is that they have very little gravity to contend with. So, if the minerals are out there in the asteroids, then mining and refining them out there is a better option than trying to get all those minerals off the Earth.
The problem is going to be size and mineral content. The Asteroid belt between Mars and Jupiter comes in at a mass of around 4% that of the moon, and we don't know what percentage of that is usable in terms of minerals. Also, much of it is spread out once you get past Ceres and a couple of other really large asteroids making Ceres the obvious starting place. If we're talking around 50% mineral content (and that's likely very generous) you'd have more than enough materials for a fleet of starships, but you have to refine the materials first. That means smelters, factories, and energy. That's the biggest issue as we'd need energy out there and as there is no mass extinction of plants on Ceres recorded, there's no oil or other chemical energy store.
If we find reserves of Helium 3 though, in quantities similar to those found on the moon, you've got a massive amount (for a time at least) of minerals and energy available with very little energy cost in terms of gravity wells. You build your infrastructure first (refineries, factories, construction frames et al) and then whatever materials you have left go into ships or other space borne needs.
Eventually, we'd mine out the asteroids and then we'd have to look for other mineral sources in low gravity wells. One that we might consider would be the Moon, as even though there's an energy cost to getting minerals off it it's nowhere near as expensive as getting them off the Earth. Better yet, we'd look at the smaller moons around Mars or even the outer gas and ice giants, but then we'd need to find Helium 3 or some other mineral based energy reserve as well and those sites are remote at best. If our energy needs are being supplemented initially by solar, then their distance from the sun is also problematic.
Ultimately this problem comes down availability; not just in terms of the mineral resources themselves, but also the energy required to extract and transport them.
Mining Minerals on Earth is possible because we have massive energy reserves. Getting them out of the gravity well however will cost a lot of that energy.
Mining Minerals on asteroids would negate the energy cost of getting those minerals into space, but then there's very little energy (outside of a potential fuel for fusion reactors) to use out there in the first place.
So, if there's no energy source on those asteroids, then the answer is probably no. It's not worth it because the cost of the minerals comes at a cost of shipping energy up to those asteroids constantly. If the materials are being used on Earth, then again the answer may well be no, because the cost of getting the mining infrastructure up there in the first place would fund what you want to build.
But, if you're looking to build things in space and have an energy source available locally to the minerals, then it would certainly be worth considering if you're building anything at scale.
The value of asteroid mining is the materials already in space. Getting materials off Earth currently costs around $25K a kilo.
If the material is already in space, you can build spaceships, space stations, satellites probes, etc without the cost of the fuel to get it into orbit.
Once you have the technology to get there and back, it gets interesting.
There's two main advantages to asteroid mining compared to planet-based mining. As others have noted, if you need the materials for further construction in space, you save a lot in launch costs. But even if you want to ship the materials back to Earth, there's the second bit: most of the material the Earth is made of is pretty much inaccessible to us.
We only have access to a thin crust at the very top of a very massive planet. Even worse, many minerals have preferentially segregated deep below the crust, even all the way down to the planet's core. Many of those materials are very valuable - platinum, iridium, gold, silver, many rare earth metals; even iron and nickel. At the same time, there's plenty of ice in the asteroids, which could be used for in-situ fuel processing, dropping the shipping costs significantly.
Another great bonus is that asteroids often contain mostly pure metals, rather than ores. This might allow us to avoid costly refining, and greatly increases the yield (e.g. most modern copper ores yield only about 3% of their mass in copper; a 500t asteroid could correspond to 15kt of copper ore in the ground). Aluminium would save a lot of energy on refining - if it isn't one of those that's frequently found oxidized even in asteroids.
It's hard to say if it's going to be good enough in 50 years. The economy is complicated, and what seemed like a great venture might dissipate to a low-margin trade very quickly. The initial investment required is very large, and we don't really have the technology to do this right now - either for human-manned or robotic-based miners. Any attempts will probably come hand in hand with larger presence in space in general - that's where the real savings are.
The main problem with mining asteroids is that they're pretty far from the Earth, and perhaps more importantly, from each other. If you happen upon the right kind of asteroid, you might be looking at hundreds of billions of dollars of worth. If you happen upon the boring kind, it might mean a few months spend looking for and travelling to the next one. Some sorts of automated probes would help, but again, we don't really have the tech now. Would it be plausible in 50 years? Possibly.
There's some asteroids that are more accessible than the Moon's surface even. One typical mining candidate is 4660 Nereus - it is thought to be magnesium rich, but it's mainly of interest because of it's approach-ability (if you time things right). It might serve as a pilot proof-of-concept operation sometime in the future, before we head on to the more distant belt.
For story purposes, it might help to have some good reason why the initial investment got started. Something that forces people out of the well. There's relatively little interest in space exploration and exploitation among the public right now, and you could even imagine people fighting hard to prevent that (e.g. imagine you find the entire stock of gold on Earth in just one asteroid - that's not going to make gold-holders happy). How do you change that? Making people want things to happen is usually a good start. If people don't care about space economy (or worse, find it competitive to their own job), you won't get asteroid miners in 500 years :P
I'm going to go against the naysayers here and say yes.
Economically speaking, the greatest cost to mining asteroids is the fact that there's no established pipeline. The assumption here is that every rocket must take off from earth, capture it's load and return to earth.
With regards to the reduction in leaving atmosphere costs, there's always the approach of using a so called "space elevator"
A Nasa article with regards to that.
Once that's established, you'd need to establish a system of craft built specifically for floating through the asteroid belt. They wouldn't need to be that large as they wouldn't need to carry enough fuel to take off from anything with a real gravitational pull.
With regards to the economics, the initial cost would have to be offset by large potential gains in the future. So the minerals pulled in would have to be incredibly scarce, or conversely, so incredibly cheap to pull down but be so incredibly abundant and be more so than on earth. Again, the second is a little more plausible if the established pipeline is already built and cheap to maintain.
You wouldn't even need there to be an economically viable reason to establish the initial pipeline, just someone with disregards to econ. In "The Man in The High Castle" by P.Dick, his timeline allowed for the Nazi's to establish efficient rockets for international travel. His Logic for such a situation was that the Nazi's were mad with a craving for doing the unthinkable, regardless of the consequences to themselves in the end.
Here's a link to the scene where 2 characters are aboard the lufthansa Rocket
Once anything is established and working, it doesn't need to prove it's theoretical worth to potential backers, as it's already generating visible wealth. If a madman in a dictatorship were to waste his resources on such a thing, You wouldn't have to worry about they why. If the profits of using such a system were to outweigh the costs of maintaining it, then it wouldn't be difficult to get potential investors for the continued use and expansion.
It all ultimately boils down to how your timeline's constructed (50 Years is a long time) and how much you really want to mine asteroids.
Asteroid mining would be expensive, but the materials brought back would be worth it. Find a big enough asteroid and you can get tons of ore like iron, gold, platinum etc. I also suggest you automate the process using robots to do all the leg work.
It's the year 2068, humanity has managed to get a space elevator working about twenty years ago. Now, they need more metals and rare materials which are found in asteroids.
Ships with specialized equipment bring asteroids towards Earth and set them in a very specific orbit, which passes close by the space elevator but does not collide with any other asteroids. Miners work on these asteroids and they get to work and deliver materials using the space elevator.
A gigantic construction is underway to complete a self sustaining refinery so that asteroids can be mined and processed in place instead of having them brought to Earth.
So one thing that I didn't see anyone talking about is sure you get an asteroid, but how are you going to refine it. out in space there's no to low gravity, that means that even if you are able to heat metals to boiling, that you're not going to be able to pour them. They would need to be forced through some type of piston into workable shapes, ingots or what not that can then be tools and or rolled and compressed. This Piston type forge would have to be make of some material that could handle the heat and not get clogged by cooling metals, it would need to be easily repaired and replaced. ferrous metals could be manipulated by magnetism, but heated to molten, you find that magnets work differently on the metals. Sure it can be done on a no gravity environ, but the expense and process is going to be much more difficult. Extruded metals would be the easiest to process. If you had a large amount of dense mass you could actually create your own pseudo gravity well. But centrifugal force gravity is be far the cheapest, and could handle the things that gravity assists with such as pouring metals from crucibles. It just adds to the size of your operation(ship) though bringing a mass onboard a rotating ship also has it's issues.
