In 2012, Planetary Resources announced a plan to mine asteroids for resources and return those resources to Earth. As futuristic as this sounds, the capability may well exist. Unfortunately, what may not exist is profitability. Therefore it makes sense to examine the economics of this intriguing proposition.
Capability
Near-term capability needs consist of the ability to identify resources, extract the resources, and return the resources to Earth for sale. The first capability appears to already have been achieved as, according to Planetary Resources, potential resource nodes have been identified by the company on near-earth asteroids and targeted for exploitation. The second capability, extraction using robotic vehicles, on the surface appears to be achievable using current or derivative technologies. The third capability, returning the resources to Earth for sale, also appears to be achievable as NASA has announced a plan to capture an asteroid and return it to orbit (albeit lunar orbit in this case) (1). Returning resources to the surface from orbit could rely on existing technical capabilities such as those demonstrated by the Space Shuttle or, more relevantly, SpacePlaneOne, the X-37, or the SpaceX Dragon.
Economics
But can it be done economically? Payload costs to low earth orbit (LEO) range from $800 to $2100 per pound using existing commercial systems (2), while launching and returning payload to earth costs around $20,000 per pound (3). According to news reports, Planetary Resources is targeting precious metals such as gold and platinum for extraction and recovery. Based upon a spot price of around $1,200 per ounce (4) for the refined metal, the estimated value of a single return could be around $19,000 per pound, or a 5% loss over payload costs, assuming the returned mass is equivalent to the launched mass.
Not a promising number given current commodity prices, and it does not account for R&D and operating costs of the resource extraction vehicles or the cost of rockets and propellant to move the extraction vehicles from earth orbit to the asteroid and the extracted material from the asteroid back to earth orbit. It also does not account for the fact that the extracted material will be ore, not refined metal, meaning that the returning payload will be substantially less valuable. (Gold and platinum ore of earth origin sells for $0.50 per pound.)
Economizing
So, how does this proposition become economically feasible? First, we must minimize the cost of getting materials from the Earth's surface into orbit. Secondly, we must minimize the cost of moving mass from Earth orbit to the target node, and back again. Lastly, we must maximize the value of the payload being returned to Earth.
There are a number of tested and validated means of launching payloads into LOE. Economies resulting from using different launch mechanisms (such as vertical ground launch, horizontal ground launch, and air launch) as well as from locating the launches in equatorial regions, result in incremental changes in payload costs per pound, but the reality is that 75-80% of the launch mass is the propellant required to get the payload from the surface into orbit, and more than 90% is the cost of the disposable launch vehicle. The good news here is that SpaceX is experimenting with a recoverable first stage that, when successful, will reduce the launch cost per pound by an order of magnitude.
The most expensive commodities in space are the consumables: propellant, air, water, and food. Relying on unmanned missions eliminates the need for the last three allowing the outbound payloads to concentrate on propellant and vehicles. Unmanned missions also significantly reduce the cost and weight of the launch and recovery vehicles as equipment needs and safety parameters can be significantly relaxed when human lives are not at risk. Once the vehicles are up, the critical component is propellant which can be launched separately from the vehicle payload and rendezvoused with as necessary to either fuel the trip to the resource node, or to propel the extracted material back to Earth.
Which brings up the second means of improving the economics of space exploitation: developing space-based means of propulsion. If the consumables are the most expensive commodities in space, arguably the most valuable commodity in space is not gold or platinum, it is water ice. Using solar power, water ice, if retrievable from asteroids or from the lunar surface, can be broken into its component parts and then used as a propellant (LOX/LH2) and as an oxygen and purified water source for manned missions. Propellant extracted from these space-based water sources would be more expensive to develop in the short term than its earthbound counterpart (which costs a few dollars per pound), but would require far less cost to move to Earth orbit, even if launched from the lunar surface, thereby reducing the cost of fueling and propelling space vehicles.
An alternative to traditional propulsion means, the Planetary Society's LightSail (4), although in its infancy, is currently in the experimental stages. The light sail concept, while providing relatively slow acceleration compared to chemical propulsion and therefore not likely suitable for manned missions due to the necessary increase in consumables, has a number of intriguing benefits for unmanned vehicles. First, the payload weight, while increased by the mass of the sail, is decreased by the mass of the propellant required to move the vehicle to and from the target using traditional propulsion. Assuming the mass of the sail is lower than the required mass of propellant for the mission, this results in a considerable decrease in launch costs. Second, as with a sailboat, the propulsion is unlimited for as long as the wind holds, and barring a supernova, the solar wind's duration is continuous, and its force and direction calculable. This provides the solar sail vehicle with a greatly increased operational life over a vehicle reliant on expendable propellant.
Which brings us to maximizing the return payload. Given the high cost of returning payload to the surface (ten or more times the cost required to get the equivalent mass into orbit), the extracted material will have to be either extremely valuable in its extracted form, or will have to be refined before being returned. The latter case, will require technologies, such as solar smelters, that do not exist today. If developed, these technologies would be a precursor to an orbital or space-based manufacturing capability that could be used to sustain further exploitation efforts without incurring the cost of bringing all materials from the Earth's surface.
The Big Question
Given these factors, the question we should be asking isn't whether we can profitably mine gold and platinum in space and return it to the surface, but whether these are the most profitable commodities available to us. As noted previously, the most valuable commodities in space are the consumables: propellant, water, oxygen, and food. While we are unlikely to profitably produce food on an asteroid; propellant, oxygen, and water are certainly within the realm of possibility. A bonus to trading in these commodities is that they don't have to be returned to the Earth's surface for their value to be realized; in fact, they are far more valuable if they remain in space or in Earth orbit, thus significantly reducing the production cost.
(1) (http://www.nasa.gov/content/what-is-nasa-s-asteroid-redirect-mission)
(2) based upon launch costs of the SpaceX Falcon 9 and Falcon Heavy (http://www.spacex.com)
(3) based upon NASA contract costs utilizing the SpaceX Dragon reentry vehicle. ($1.6B contract/12 flights/3000kg down payload)
(4) as of May 19. 2015 (Gold $1208/oz, Platinum $1152/oz)
(5) (http://sail.planetary.org)
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