I was reading this question and realized that I didn't actually know enough to give the answer that I wanted.

Obviously in the near term, all our raw materials come from the Earth. The only other place we've been is the Moon, and we haven't been there lately. So if we built a space station with gravitational rotation, we'd have to build it with Earth materials at the moment. The thing is though that in the long term, I don't believe it makes sense to lift materials from Earth.

Lifting materials out of the Earth's gravity well is energy expensive. It seems like it would be much easier to get materials that are already in space and redirect them to where we want. For example, we could collect materials from the asteroid belt and direct them to the Earth/Sun Lagrange-5 point. Starting to do this would be expensive, as it requires flying out to the asteroid belt. But it seems like it should be easier to maintain once started. Also, this would save mining and other costs on Earth.

I would think that we'd mainly do this with self-replicating miner robots controlled (loosely) from Earth. I'm assuming that we'd make similar robots for large scale space construction regardless, so the only difference is in energy costs. Energy is plentiful in space, as you can build arbitrarily large solar panels. So I'm figuring that the asteroid project will be self-sustaining once started.

The question remains: how much stuff could we get into Earth orbit for the start-up cost of initiating the asteroid project? Ideally the answer should be referenced in terms of population capacity. For example, "we could either build space stations for 10,000 people or build an asteroid harvester" would be an example of the kind of answer that I'd like to see.

Feel free to neglect the cost of providing atmosphere, water, and food. I'm going to assume that all those things come from the same place in either scenario. This will probably be the Earth initially but may be someplace more exotic later (Venus, Saturn's rings, a Jovian moon, etc.).

  • $\begingroup$ Actually there is a lot of water ice out there for the taking (planetary rings for example) which gives you hydrogen and oxygen. $\endgroup$
    – Tim B
    Commented Nov 11, 2014 at 10:21
  • $\begingroup$ @TimB Planetary rings meaning what Saturn has? Are you saying that that's far enough out not to be considered part of the gravity well? It seems that xkcd says it's inside the gravity well. $\endgroup$
    – Brythan
    Commented Nov 11, 2014 at 10:32
  • $\begingroup$ It's already in orbit though, so you have orbital velocity which gives you most of the energy you need. Additionally water makes good reaction mass so you can actually use some of what you harvest to propel the rest. $\endgroup$
    – Tim B
    Commented Nov 11, 2014 at 10:42
  • $\begingroup$ To answer the title question: when you're building a Death Star ;-) $\endgroup$
    – Shokhet
    Commented Nov 11, 2014 at 22:10
  • $\begingroup$ Ok for gathering material but what about transforming them. Chemistry (especially flames) don't work the same way without gravity or without unlimited supply of oxygene. It can be overcome, but it is definitely a pain in the neck. $\endgroup$
    – Madlozoz
    Commented Feb 25, 2016 at 14:36

3 Answers 3


When will it be economical to harvest the resources you need in space rather than lift them from the surface?

Well, that of course depends on several factors:

  1. The cost per kilo of lifting the resource (obviously)
  2. The cost per kilo of bringing the resource in from where you found it in space
  3. The cost/value of the resource.

The first two are pretty obvious. If it costs \$5000 per kilo to lift a chunk of whatever from the surface, and \$500 to bring that same chunk over from the asteroid belt, that's a cost saving of \$4500 per kilo.

But that doesn't tell the whole story. The cost of extracting that material on the surface is likely a lot lower than the cost of extracting it in say the asteroid belt, at least initially (only once the initial investment has been paid off will you possibly be competitive, and that might take a while).

Also keep in mind that if large deposits of something that's very expensive on earth now are found out in space, the value of that material is likely to plummet, unless the people finding it are very careful in piping it into the economy only in small amounts.

Say the price of platinum is now \$10000 per kilo (just a figure, no clue about the actual price), with a world wide production of 10 tons per year.

Now say I find me an asteroid that has 500 tons of the stuff in it, and I decide to mine the thing. I can mine it at a rate of 100 tons a year. If I dump all that 100 tons a year in the world economy, the price of platinum is going to drop and drop hard. Instead of the \$10000 per kilo I expect to get I might after a few days of it only get \$500 per kilo.

So I have to make sure I feed that platinum in in small amounts only, say 10 tons a year, which might not even cover the cost of installing and maintaining my mining operation...

All this assuming there's a healthy on-orbit society already from which to draw manpower and support infrastructure. If you need to build that as well, the cost goes up far higher, making the whole venture into a loss leader from the outset (which btw is one reason there's never yet been put in place things like solar power stations in orbit, the initial investment to get the permanent settlements in space up that are needed to maintain and support such industry is too high for interested parties to bear).

  • $\begingroup$ Another thing I would add in the same lines: the cost of maintaining a space-mining culture. That culture may allow more flexibility in the prices (i.e. shifting to different export materials as prices shift). This also means cost of things like feeding miners (which is not cheap) $\endgroup$
    – Cort Ammon
    Commented Nov 21, 2014 at 14:52
  • $\begingroup$ @CortAmmon short term, yes. Long term, they'd quite likely be more than self sufficient. Which might well lead to war as the colonies (because that's what they'd be) will want independence rather than be eternal profit machines for "old home earth"... $\endgroup$
    – jwenting
    Commented Nov 21, 2014 at 20:38
  • $\begingroup$ But this doesn't answer the question. I'm not asking about the cost of mining in space versus Earth. I'm asking about the startup cost of mining in space versus the amount of space-based infrastructure that could be lifted from Earth. This is an interesting answer to an entirely different question. $\endgroup$
    – Brythan
    Commented Mar 28, 2016 at 17:23
  • $\begingroup$ Another thing to consider is that if the price of platinum were to drop to \$5000/kg, it may open up new market possibilities with much larger demand, that couldn't exist at \$10,000/kg. So, sure, you won't be making the higher price per kg but you might be able to sell 10x the platinum at the lower price. (And I see we have MathJax in the comments now!) $\endgroup$
    – Green
    Commented Sep 3, 2017 at 12:43

Well, maybe not so much raw materials for building projects in space, but for other more essential things, like life support and fuel, there are already plans for that with In-Situ Resource Utilization(ISRU)


Asteroid mining? Hmmm. If want to go out and grab a near-Earth asteroid, it is doable right now. A single Saturn V style F-1 engine can introduce delta-v of about 7km/sec change to near-Earth asteroid of 1000 tons (about ten meters across) if supplied with 40% of the Saturn V first stage fuel and firing for about 5 minutes. If the asteroid is rich in ammonia and other volatile materials, it could be directed to orbit about the Moon and then 'mined' for Moon use. So, we could use existing technology to do this which makes for good, 'hard-science' science fiction. There are many near-Earth asteroids that are in this size range and come to within 10 Lunar diameters of the Earth-Moon system at relative speeds of well under 7 kilometers per second. Slow it to Moon orbital velocity at 100 kilometers orbital height (about 1.6 kilometers per second) and enjoy. Go up anytime and pick a piece off from the Moon. Nice. So, to answer your question: one F-1 engine and enough fuel to fire it for five minutes as stated. Of course, we also need to get that engine and fuel into position and that takes another engine and some fuel, but that would be easily worked out and mining would be thus initiated...at a very small scale, of course. So, the start-up cost would be, say, one Apollo style mission to get the 'tug-boat' into position and then the F-1 tug-boat itself. The target object need not go into orbit about the Moon, but there really is not point in asteroid mining if you're going to bring the material to the Earth. The Earth is full. It is time to spread out. Build a colony on the Moon first and then do asteroid mining.


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