Asteroid mining is the exploitation of raw materials from asteroids and other minor planets, including near-Earth objects. Minerals and volatiles could be mined from an asteroid or spent comet then used in space for in-situ utilization (e.g. construction materials and rocket propellant) or taken back to Earth.
These include gold, iridium, silver, osmium, palladium, platinum, rhenium, rhodium, ruthenium and tungsten for transport back to Earth; iron, cobalt, manganese, molybdenum, nickel, aluminium, and titanium for construction; water and oxygen to sustain astronauts; as well as hydrogen, ammonia, and oxygen for use as rocket propellant.
Due to the high launch and transportation costs of spaceflight, inaccurate identification of asteroids suitable for mining, and in-situ ore extraction challenges, terrestrial mining remains the only means of raw mineral acquisition today. This situation is likely to change in the future as resources on Earth are becoming increasingly scarce and the full potentials of asteroid mining—and space exploration in general—are researched in greater detail.:47f However, it is yet uncertain whether asteroid mining will develop to attain the volume needed in due time to fully compensate for dwindling terrestrial reserves.
Based on known terrestrial reserves, and growing consumption in both developed and developing countries, key elements needed for modern industry and food production could be exhausted on Earth within 50–60 years. These include phosphorus, antimony, zinc, tin, lead, indium, silver, gold and copper. In response, it has been suggested that platinum, cobalt and other valuable elements from asteroids may be mined and sent to Earth for profit, used to build solar-power satellites and space habitats, and water processed from ice to refuel orbiting propellant depots
Multiple types of asteroids have been identified but the three main types would include the C-type, S-type, and M-type asteroids:
- C-type asteroids have a high abundance of water which is not currently of use for mining but could be used in an exploration effort beyond the asteroid. Mission costs could be reduced by using the available water from the asteroid. C-type asteroids also have a lot of organic carbon, phosphorus, and other key ingredients for fertilizer which could be used to grow food.
- S-type asteroids carry little water but look more attractive because they contain numerous metals including nickel, cobalt and more valuable metals such as gold, platinum, and rhodium. A small 10-meter S-type asteroid contains about 650,000 kg (1,433,000 lb) of metal with 50 kg (110 lb) in the form of rare metals like platinum and gold.
- M-type asteroids are rare but contain up to 10 times more metal than S-types.
There are three options for mining:
- Bring raw asteroidal material to Earth for use.
- Process it on-site to bring back only processed materials, and perhaps produce propellant for the return trip.
- Transport the asteroid to a safe orbit around the Moon, Earth or to the ISS. This can hypothetically allow for most materials to be used and not wasted. Along these lines, NASA has proposed a potential future space mission known as the Asteroid Redirect Mission, although the primary focus of this mission is on retrieval. The House of Representatives deleted a line item for the ARP budget from NASA's FY 2017 budget request.