M. J. Sonter presented a paper at the 49th International Astronautical Federation Congress, Sept 28 - Oct 2, 1998, Melbourne, Australia. titled: "An Overview of the Technologies to be Employed in the Recovery of Asteroidal Resources and the Economics Behind the Planning."
Future large scale commercial activities in space will require raw materials obtained from in-space sources rather than from Earth, to overcome the high cost of Earth launch. This paper reviews the prospectiveness of non-terrestrial resources and notes the competitiveness of Near-Earth-Asteroids c.f. the Moon and Phobos or Deimos in terms of accessibility and likely resources. Astronomical work over the last fifteen years has increased the number of known Near Earth Asteroids (NEAs) from about 30 to about 400. Discovery rate of NEAs is now about 50 per year.
Asteroid geography: NEAs are classified by orbital parameters into Apollos, Amors, and Atens; in addition, the “Arjunas” are the group of small objects in very Earth-like, and therefore very accessible, orbits. Accessibility is defined in terms of velocity requirements (delta-v) for outbound and for return trajectories. Approximately 10% of NEAs are more accessible than the Moon, and maybe 50% of these are likely to be potential orebodies.
Asteroid “geology” has advanced dramatically in the last decade, via spectroscopic and dynamical studies of asteroids and comets, and meteorite studies; reasonable inferences can now be made from asteroid types defined by spectral properties to probable surface mineralogy. Many asteroids may be “volatiles bearing”, containing clays, hydrated salts, and hydrocarbons. It also now seems that there are dormant cometary bodies within the population of NEAs. These are likely to contain remnant primordial ices within their cores, making them possible sources of volatiles for future space industry. Resources which would appear to be readily recoverable are thus water and other volatiles, for manufacture of propellant in orbit; and nickel-iron metal, for construction in orbit.
There have been various concepts proposed for mining and retrieval to low-earth-orbit of materials from NEAs, but methods of comparison of the economic feasibility of competing mission concepts are not well-developed. In-situ production at the asteroid of the propellant needed for materials return is an important “enabling” concept. This paper develops methods for comparison of different asteroid mining concepts, and for choosing between various product, process, mission, and engineering alternatives, so as to maximize likely project economic feasibility.
Application of celestial mechanics shows that (i) simple estimates of “global minimum” delta-v can be made; (ii) low-energy opportunities occur at approx 2-yearly intervals, for many NEAs; (iii) long synodic periods militate against multiple-return mining missions; (iv) Earth-return hyperbolic velocity should be kept low; (v) high-eccentricity targets require Hohmann transfers, and a short mining season at aphelion; (vi) low-eccentricity targets may use continuous-thrusting propulsion, and extended mining season. There is a growing subset of targets that are intermittently accessible for an outbound delta-v of under 6 km/s, and offering return departure delta-v under 2 km/sec.
Mining and processing system choices depend on the assumed regolith mineralogy and bulk handling properties, and on the assumed subsurface composition and properties. Process options are (i) in-situ fluidization; (ii) mechanical collection and thermal or magnetic separation; (iii) carbonyl process. Equipment mass estimations for volatiles extraction suggest total processing system mass of less than 5 tonnes for a teleoperated / autonomous miner mission to return 1000 tonnes to LEO.
Sensible and politically achievable propulsion and power system choices are restricted to (i) solar thermal steam rocket; (ii) solar photovoltaic arcjet; (iii) solar photovoltaic massdriver.
In terrestrial mining projects, the Expectation (probabilistic) value of the Net Present Value is a crucial unifying concept for evaluating competing mission options. By testing system choices for their effect on NPV, one can arrive at project design choices that are optimized. The NPV formula can readily be expanded in terms of the astrodynamic and rocket equation parameters, and the parameters describing the mining and processing equipment and performance.
Conclusions: Advances in asteroid astronomy and discovery rates give confidence that there are many accessible potential orebodies among the Near-Earth Asteroids. Mining and metallurgical options exist that are simple and robust. The use of NPV is crucial in project concept development. A teleoperated miner for return of volatiles from NEAs is economically feasible, using present technology, with an initial market of about 1,000 tonnes per year. — Asteroid mining is very close to technical and economic feasibility. Further, the technology needed to avert comet or asteroid impact is similar to that needed to recover the essentially unlimited resources contained in these bodies. Thus it is desirable to develop asteroidal resources, both to achieve wanted outcomes (namely space industrialisation, species security, and long term prosperity) and to build the capacity to avert disaster.
This paper reviews concepts for mining the Near-Earth Asteroids for supply of resources to future in-space industrial activities. It discusses a standard approach for carrying out Technical and Economic Feasibility Studies on proposals for asteroid resource recovery projects.
Potential Commercial ‘Drivers’ for Space Industrialisation: The industrialisation and settlement and of space is likely to be brought about primarily by increasing commercial activities in space, including the following:
- Expansion of trunkline communications, direct broadcast TV, navigation, remote sensing, and meteorological services worth several billion dollars per year from an in-space satellite assets investment estimated to be about 50 billion dollars. LEO satellite constellations will roughly double the annual income of these services, over the next decade.
- Commercial space-based production of high value pharmaceuticals, semiconductors, ultra-pure crystals, and exotic alloys. Although research work has been done on Mir (in orbit since 1986), commercialisation has been severely delayed by the loss of access to the Space Shuttle, after the Challenger disaster.
- The concept of satellite solar power stations ( SSPS) is again receiving active consideration, after a decade of disinterest: the Japanese are planning an equatorial orbit SSPS pilot plant, titled SPS2000, orbiting at 1100km altitude, of mass 200 tonnes.
- The feasibility of space tourism is being promoted by Patrick Collins and colleagues in Japan. Their projections show that at a launch cost of $200/kg the space tourism market will grow rapidly to several billion dollars per year. Hotels in orbit will be needed, to cater for 10,000 person accommodation after some years. Shimizu Corp has developed a plan for such an orbiting hotel, of mass 6000 tonnes.
The future market for mass-in-orbit: As a result of the activities described above, we can hypothesise a conceptual future market for mass in low-earth-orbit (i.e. metals for construction, volatiles to make propellants for stationkeeping and for deorbit burn, and unprocessed mass for ballast and shielding against cosmic radiation). The size and rate of development of this future in-orbit market for materials could easily exceed 1000 tonnes per year by 2010, growing exponentially to tens of thousands of tonnes per year if any of the larger-scale activities “take off”. The large reductions in launch cost promised by new launcher concepts (from the present $10,000/kg down to something like $500/kg) will prompt a huge growth in the launch market, probably driven initially by tourism.
The Accessibility and Competitiveness of Non-Terrestrial Resources: The natural resources in space include metallic nickel-iron alloy, silicate minerals, hydrated minerals, bituminous material, and various volatiles, including water, ammonia, carbon dioxide, methane, and others. These have all been identified either in meteorites, or spectroscopically in asteroids and comets. Any industrial development in space requiring more than about a thousand tonnes of structural mass or propellant per year will direct attention to these materials as ores, in the true mining engineering sense.
Raw materials retrieved from non terrestrial sources need not attract the high “airfreight” costs referred to above. This is because the energy requirement to return material from many of the possible target near-earth asteroids is much less than the energy requirement to launch from Earth. In addition, the freedom to deliver the velocity change non-impulsively, means that low power propulsion systems may be considered, and this allows a system that uses solar power and derives its return-journey propellant from the target body, such as asteroidal volatiles.
In-Situ Propellant Production: The mission velocity delta-v needed to reach selected “near earth” low delta-v target asteroids is not much greater than that needed to place a communications satellite in geosynchronous orbit (GEO). The delta-v required to return material from these targets is very much less than that required to lift mass into orbit from the surface of the Earth, and can be imparted gradually, over several weeks, thus very substantially reducing the demands on the propulsion / power system. If the return transfer can be accomplished using part of the retrieved non-terrestrial mass as reaction mass, such as asteroid-derived volatiles, and solar energy for the power source, or onboard nuclear power, then it becomes possible to return to earth orbit very much more mass than the outbound-leg earth-orbit-departure mass of the mining-processing spacecraft. This in situ propellant production then allows a high Mass Payback Ratio (mass multiplication). Mass multiplication factors above 100 are the initial aim.
The effect of the above concepts is that some asteroidal material may be able to be delivered into Earth orbit for a cost which is very much less than Earth-launch cost. Thus, there will potentially exist a profit-making 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.
Orebodies in Space: It is necessary to identify the requirements that must be satisfied by an Earth-approaching asteroid or short-period comet to make it an “orebody” in the mining engineering sense: that is, to identify it as a resource source that can support an economic materials retrieval project.
These economic and technical requirements are:
- there needs to be a market for the products,
- need adequate spectral data indicating presence of the desired materials,
- check that orbital parameters give reasonable accessibility and mission duration,
- development of feasible concepts for mining & processing,
- development of feasible retrieval concepts,
- require positive economic Net Present Value, using the chosen engineering concepts.
Like terrestrial mining projects, we find that each asteroidal resource project will have its own idiosyncrasies, reflected here in the alternative mission trajectory profiles to be considered.
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Original URL: http://space.nss.org/the-technical-and-economic-feasibility-of-mining-the-near-earth-asteroids/
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