Miners earn a living by digging useful materials from Asteroids and hauling the resulting materials back to civilization where someone else can turn them into useful raw materials.
There are several possible mining techniques:
- Nickel-iron asteroids: you need a heavy cutting laser to lop bits off then magnetic grapples to grab the bits and stuff them into the hold. Purity matters - rare metallic deposits are also worth money.
- Icy asteroids: you need to liquify the thing so you can pump it into the tanks.
- Dirty-snowballs: are difficult to mine for that reason - and impurities in the water make it less valuable.
- Carbonaceous chondrites: ...??? (useful for synthetic foodstuffs).
- Ammonia ice asteroids: have to be liquified. (useful for fertilizer and nitrogen in air factories).
Liquified materials (water, ammonia) need liquid tanks to hold them. Solid materials (nickel-iron or chondrite) require a solid ore hold. Nickel-iron can be held using magnetic grapples without a hold at all.
Mining solids requires a high power laser and a grapple of some kind.
Mining liquids can be done by setting up a large curved mirror to concentrate sunlight onto the asteroid to melt it - or you can dump a running nuclear reactor onto the surface and wait for the waste heat to melt the water. This is much faster but results in radioactive water that's only good for making hydrogen/oxygen fuel - not for drinking water or air.
Rare deposits of unusual metals or other materials are always considered super-valuable.