Volatiles for propulsion and life support only scratch the surface of what we might extract once viable mining communities begin tapping the asteroids. Metals like platinum remind us how readily available some resources will be in space as opposed to trying to dig them out from the depths of our planet. Centauri Dreams regular Alex Tolley continues to explore these matters in today’s essay, which looks at how companies will turn a profit and what kinds of targets most justify early efforts. Key to our hopes for asteroid mining is reducing the costs of getting payloads into space. That’s a driver for an infrastructure whose demands may well produce the propulsion solutions we’ll need as we push outside the Solar System.
by Alex Tolley
“There’s gold in them thar hills” – M. F. Stephenson
In 1848, James Marshall discovered gold at Sutter’s Mill, on the American River, in foothills of the Sierra Nevada mountains of California. The California gold rush ensued. Science fiction stories have been replete with such miners eking out a living in the asteroid belt, hoping for that lucky strike and the discovery of the gold asteroid. While gold is no longer used to back the value of fiat currencies, other metals have arisen to take their place as valuable elements, from platinum to the so-called rare earth elements. John Lewis  estimated that the asteroid resources of the solar system vastly exceeded the potential supplies on Earth and that reserves were far more accessible than those deep within the Earth’s crust or even below it.
Despite this, there is not a single mining company currently extracting such vast wealth. One reason is the same as the absence of seabed mining for manganese nodules – the legal position of those resources. Those legal restrictions are now being actively changed as the possibility of being able to mine these bodies becomes more feasible. Yet so far, only startups have formed with distant plans to extract those vast riches.
So assuming that those resources are legally owned by the prospectors, just how viable is the space mining business?
The possible approaches to mining include the classic platinum group metals, Fe-Ni metals, carbon, rocks for radiation shielding, and most recently, volatiles, especially water, for propulsion and life support. The question is what to target, and how to do it profitably.
Approaching the Economics of Financial Return
A business must generate positive value. Traditionally, this is estimated by requiring a positive value for discounted cash flows, where the initial capital cost is recovered by a stream of net cash flows suitably reduced by the required risk-adjusted rate of return.
Sonter  derived the equation below as a baseline for determining the net present value of an asteroid mining business.
Figure 1 – the value of a an asteroid mining program.
The Sonter Equation
Sonter’s equation is a nice simplification, although it suffers from some operational assumptions. The terms describe the present value of the material returned to an Earth orbit and the costs associated with that operation. The equation explicitly assumes that the value is the orbital mass value by launch cost, for example for volatiles and commodity metals, but excludes precious metals that could be returned to earth. The mass returned is adjusted by delta V costs for propellant for solar-thermal propulsion, mined concurrently. Mass returned must be 250-500x the mass of the miner to be viable. Higher isp rockets would increase the fraction of mined payload returned to earth orbit. The discounted value is adjusted with a time value based on orbital mechanics, which assumes a one-shot operation of a single vehicle prospecting and returning to Earth orbit. This is decoupled from the number of years of the operation. The mining “season” was assumed to be short compared to the transfer time to and from the asteroid. Launch costs of the mining craft appear to be excluded too, which is a rather major component of the business cost. This might be explained by reference to Oxnevad who, using NASA launch costs believed that launch costs were not a critical issue, although it is now thought that the drive to lower launch costs by the New Space companies does make this a relevant factor.
Sonter assumed that launch costs would decline to at least $200-500/Kg, a cost necessary for developing space assets probably driven by space tourism. Without that driver, there is little need for large mass space infrastructure and asteroid mining would probably be still-born. 1000 MT developments was Sonter’s tipping point for favorable asteroid mining conditions.
The best targets have low delta V and short return intervals. The earth-approaching bodies such as the Apollo, Amor, or Aten asteroids, and possibly Mars’ moons, Phobos and Deimos. Sonter goes into some detail on target selection based on orbits, although also allowing less delta V-favorable dead comets are suitable.
Sonter states as a conclusion:
Thus there will potentially exist a profit-rnaking opportunity for a resource developer who could develop a capability to recover space-based materials and return them for sale in low-Earth orbit to capture the developing in-orbit market at its inception.
Mining for platinum group metals
Let’s start by looking at those more high value elements, the platinum group metals. Platinum is currently priced at around $30k/Kg. But to extract such elements requires handling a lot of asteroidal rock. Even the best concentrations are in the tens of parts per million (ppm), although higher concentrations may be found.
Gerlach  published work on his NEOMiner – a fairly extensive analysis of a large mining craft that would extract platinum group metals [PGM]. The craft was to be about 4.5 MT in size and return 14-35 MT of platinum using a chemical extraction method. The cost of the craft was to be around $150MM
Ross  looked at various mining options, and estimated that the craft must return more than 100x its mass in valuable resources.
Andrews  also went big, with a plan returning $10s bn over 12 years, although positive cumulative cash flows were only appearing by year 10, a very long and risky time horizon. The size of the operation required mining 5 million MT of regolith, equivalent to an open cast mine pit 250m in diameter and 125m deep.
Over long time horizons, the business faces forecast risks. In 2003, Gerlach  assumed a doubling of the demand for platinum in a decade based on the hyped hydrogen economy and need for platinum in fuel cells. However, platinum demand declined over that period as fuel cells used less platinum, and also switched to cheaper alternatives, a classic economics response that had largely invalidated resource shortage doom-saying in the 1970s. A similar fate befell Dennis Wingo’s  hopes for recovering platinum from lunar impact sites.
Mining for Water
The simplest resource to extract from stony and carbonaceous asteroids are volatiles, including water. Unobe  showed that common minerals in asteroids might contain water and hydrated minerals up to 25% by mass. Lab experiments on various simulated asteroid materials showed that volatiles, primarily water, could be recovered by heating the rocks up to 800°C and condensing the emitted gases in a cold trap for recovery.
The higher the capital cost, the higher the return risk. This has led to smaller, lower cost, designs for mining craft. At the 2017 IAC meeting, Calla et al  described a mining craft mission architecture to extract water using microwave heaters to extract and collect water. Their baseline craft was less than 500 kg. Their targets were NEAs with very low delta Vs, a short season for mining of less than a month while the NEA was close enough (less than 0.1 AU) to be teleoperated from Earth, and the returned payload just 100 kg of water. Total mission time was about 1 year. For simplicity, microwave heating was assumed for extracting the water, with an average of about 8.5% content by mass of suitable asteroids. Mined water was to be used for propulsion, using an off-the-shelf electrolysis unit to separate the gases prior to combustion.
Their particular innovation was to use many copies to reduce unit costs. The R&D costs of a single unit would be amortized, and scale economies would further drive down costs. The value of water delivered to various orbits was simply their launch costs to certain earth orbits by mass.
Figure 2. Cost analysis and economic return for one spacecraft.
Figure 3. Cost analysis and economic return for two hundred and fifty spacecraft.
Figure 2 shows the payback from one spacecraft, and figure 3 shows the payback from 250 craft. For a single craft, profitability is never attained, even for high cost, cis-lunar orbits. With 250 craft, the reduced unit costs allow for profitability when delivering water to cis-lunar space at $35k/Kg. However, breakeven is not for 5 years. Any reduction in transport costs would push out the payback period, perhaps disastrously.
Calla’s analysis failed to learn the lessons from earlier analyses that profitability requires high mass payload multipliers, of 2 orders of magnitude or more. Clearly, the higher the return payload, the larger the craft to deliver mining energy, or the longer the mining operation. By adapting the craft for autonomous operation, the craft could mine for 1 ½ orbits rather than just a 1/10th of an orbit, allowing for at least a 20 to 40x increase in payload.
High demand requires low launch costs = low commodity value
While delivering platinum and other precious metals to earth has been studied, most analyses assume that demand will be in space. Water for propulsion and life support, metals for structures and even regolith as meteor and radiation shielding. As noted earlier, this demand requires much lower costs for access to space, reducing the value of these resources.
“A cost delivered into LEO of probably $200/kg or so will be necessary for space raw materials resources recovery to be a viable competitor against Earth-launch cost in the first few decades of the next century.”
With launch costs to orbit reduced 10-fold, plugging is suitable values to the Sonter equation shows that the value of water return to cis-lunar space becomes negative, only recoverable by a commensurate increase in the returned payload. This implies more powerful mining equipment, higher rates and efficiency of processing material, and more powerful engines to make the return journey. This may become a vicious cycle of adding spacecraft mass and cost, undermining the low cost, low risk, small mining craft approach.
Multiple lines of income?
It has been suggested that multiple lines of revenue might be needed, beyond the returned resources – scientific data and media broadcast rights might help defray the costs. For example, SpaceFab has suggested that scientific information may be more valuable per kg than the resource itself. Media rights are often sold for interesting projects that would attract viewers. The Interplanetary Society’s failed Cosmos solar sail experiment was partially financed in return for media rights. A proposed reality show of [doomed] Mars colonists was a brief sensation a few years ago. These alternative revenue streams might be possible in the early stages of the mining business, but once the business becomes established, the novelty wears off and the value of these revenue streams decline.
A key issue is how to increase demand of space resourced materials by reducing the cost of access to space, while maintaining the relative value of these resources acquired from extraterrestrial bodies. Clearly, one issue is reducing the capital cost of the mining craft. Calla’s use of multiple copies of the craft makes a lot of sense as it leverages the economic drivers of mass production. Coupled with reduced launch costs as currently being pursued by New Space companies, capital costs and financial risks are reduced. The CubeSat approach using off-the-shelf components and software shows the way. Spacecraft need to manufactured like automobiles – scale economies reducing costs, rather than highly expensive, custom vehicles for specific missions. The craft need to use common components and just adapt their equipment for the asteroid type and target resource.
Reduced launch costs are also needed to increase demand. Launch costs of 5-10% of current costs, largely due to launch vehicle reusability are expected to drive increased use of space, of which tourism is a much hoped for business.
As we can see from the Sonter equation, once the NEAs are used up, the higher delta Vs and longer mission times of the main belt asteroids requires better propulsion systems. Ideally, propellantless propulsion like solar sails would be very useful to reduce costs, although the cost may incur increased delivery times and therefore higher discounts on the returned resources. None of the published work on asteroid mining economics considers solar sails. The reason may be because these sails would need to be very large. Returning payloads of even 100 MT would require sails with millions of square meters of area, implying sails with sides or diameters of a kilometer and more, with a mass perhaps 10% of the payload. These sails are currently beyond our experience to manufacture and deploy. Nevertheless, such sails might be the most economical means of transporting asteroid material as their costs can be amortized over many missions and they are robust in terms of flexibility of asteroid types as they need no ISRU for propellant.
I leave the final say to Jerome Wright :
“What if we build such things, give them robotic brains, and turn them loose to accomplish thousands of tasks throughout our solar system? What if those gossamer robots carry other robots: crawlers, diggers, crushers, and carriers, and distribute those around the solar system with instructions to support a bold, dynamic civilization spanning across the solar system, with thoughts of going to the stars?”
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Calla, P., Fries, D., Welch, C. “Analysis of an Asteroid Mining Architecture utilizing Small Spacecraft”, IAC 2017
Erickson, Ken. “Optimal Architecture for an Asteroid Mining Mission: Equipment Details and Integration.” Space 2006, 2006, doi:10.2514/6.2006-7504.
Gerlach C. L. “Profitably Exploiting Near-Earth Object Resources”. 2005 International Space Development Conference. National Space Society, Washington, DC, May 19-22, 2005
Lewis, John S. Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Addison-Wesley, 1998.
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Unobe,E.C., “Mining asteroids for volatile resources: an experimental demonstration of extraction and recovery” (2017).Masters Theses. 7688. http://scholarsmine.mst.edu/masters_theses/7688
Wingo, Dennis. Moonrush Improving Life on Earth with the Moon’s Resources. Apogee Books, 2004.
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