If we could mine asteroids, how would we get the stuff mined from said asteroid back to earth?

Question

I was thinking of some contraption that would suck up the material from said asteroid and put it in some type of container thingy that would then be transported to a shuttle that would then get sent back to Earth. But after a while, I figured out that my design is wrong and doesn't make sense at and complicated. Is there a way to extract resources and get them back to Earth efficiently?

Answer 1

We probably do not, at least not at scale.

There are some minerals (platinum and friends) where 100 tonnes would be meaningful, but for most you need millions of tonnes to be achieve much, and at this scale a number of problems show up. Further it is unclear if you can purify many desirable materials in space at any useful scale, the precious metals in particular appear likely to be dissolved evenly into bulk rock rather than concentrated by millions of years of geology as they are on Earth.) So you may be shipping raw or minimally processed ore rather than pure metal pushing our delivered mass to billions of tonnes.

Getting a payload back from an asteroid requires changing orbit enough to get an earth intercept. For Earth crossing asteroids that may be arbitrarily small, but for asteroids in the main belt beyond mars the Delta V costs will be above 2 kilometers a second, which mean we need to burn between 25% and 50% off our payload mass in fuel, depending on how good the fuel and rocket is for the return.

Then we get to the little problem of landing payload.

You could put the payload inside a winged lander, but that means you dragged a winged lander out to the asteroid, and with travel times in years you will need a lot of them at around 100 tonnes per vehicle. Flying from earth to intercept an incoming payload to load needs less vehicles, but is very very expensive in fuel, since payload will be moving fast as it falls in towards earth forcing vehicle to do a high energy maneuver to match with it.

We could just send the payload, let it much of it burn up and impact, then strip mine the hopefully worthwhile crater, but this is wasteful, politically problematic and if done at useful scale have global effects.

Possibly the least unreasonable is to try to use waste material from mining to build an ablative heat shield, with payload formed to have a reasonable cross section/mass to get a minimally cratering terminal velocity. This still means we are firing large flocks of guided building killer weapons at earth, producing a fair amount of pollution and dealing with the payloads that break up and miss the landing area.

The boring answer is that stuff mined in space is most useful in space.

Answer 2

Getting the minerals from an asteroid to Earth would be relatively easy. For starters, because asteroids have no real discernable gravity, taking off from one would require hardly any rocket fuel. Energy wise, travelling from one asteroid to another would be as easy as travelling between continents and islands on Earth. After leaving the asteroid, the shuttle could use its remaining fuel to head back to low-earth-orbit. After the return to Earth orbit, a parachute system could deliver a capsule containing the mined asteroid material to land in the ocean, where some rescue party would retrieve it. Also, not everything mined on an asteroid would be bound for Earth, a lot of it would remain in outer space to be used for manufacturing, habitat construction, etc.