Visions, Ventures, Escape Velocities: A Collection of Space Futures

by Ed Finn

  The short story “The Use of Things” by Ramez Naam deals precisely with the dawn of the asteroid mining era. In 2035, humankind has managed to create a system for extracting water from asteroids (and the Moon) in order to support human habitats and to produce in-space hydrogen and oxygen. Storing these rocket propellants in a near-Earth refueling station greatly alleviates the financial and logistical burden of sending them from the Earth’s surface. Though this vision of a global project of future asteroid mining seems quite plausible, such a future will not dawn for us as soon as 2035. An operation like the one Naam describes would require complex in-space infrastructure like a permanent Moon base, or a medium-to-high-output power generator in space, which is unlikely to be constructed and operational in a mere 20 years. Still, a roadmap to this possible future can be established even now.

  The Target

  First, we have to locate a likely prospect. Due to their proximity, near-Earth asteroids (NEAs) seem to be a particularly accessible subclass of solar system small bodies. Such bodies are currently under particular scrutiny thanks to increased awareness of the potential long-term threat they represent. As of 2016, around 15,000 NEAs are known,[1] most of them discovered via ground-based surveys looking for bodies that might hit Earth. This catalogue must be completed: we have accounted for only approximately 1% of NEAs with a diameter of less than 50-100 meters, as their small size makes them difficult to spot with our current technologies. The B612 Foundation, a private nonprofit group dedicated to protecting the Earth from dangerous asteroid strikes, is currently designing and building the Sentinel Space Telescope, with the goal of locating nearly 90% of NEAs larger than 140 meters within a decade of its operation.

  But simply improving our knowledge of asteroid spatial distribution is not enough to determine which objects offer the most accessible targets for mining resources to support space exploration, colonization, or industrialization. We must find asteroids that are not only within accessible distance from Earth and large enough to warrant further investigation, but which also rotate along a simple axis at a slow rate to facilitate surface operations. Further, we will need to acquire detailed information on NEA geology (structure, density, porosity, composition) to decide which are the best targets: mining and processing system choices depend on the assumed regolith mineralogy, bulk handling properties, and subsurface composition.

  This kind of information is very difficult to accurately determine using Earth-based surveys; it will require physical sampling. Luckily, the growing interest in NEAs has translated into an increasing number of missions to these objects, such as the sample return missions Hayabusa 2 (from JAXA, the Japan aerospace exploration agency) and OSIRIS-REx (an ongoing NASA mission), impactor missions such as Deep Impact (from NASA), and possible deflector demonstrator missions such as Don Quijote (a mission concept from ESA). These projects offer a template for future investigations of NEA composition, which can help us determine whether objects are realistic mining possibilities.

  Motivations for Asteroid Mining

  Any industrial development in space requiring more than about a thousand tonnes of structural mass or propellant per year will necessitate the use of NEA materials, as the cost of launching that mass from the Earth’s surface would likely exceed $20 billion. Retrieving raw materials from non-terrestrial sources could alleviate this high freight cost, as it would require significantly less energy to return material from many of the possible NEA targets to a space-centered outpost than to launch similar quantities of those materials from the surface of the Earth or the Moon. Velocity delta-v required to go from Low Earth Orbit to an NEA is in the range of 4-6 kilometers per second, while it is only necessary to reach 1 kilometer per second to move from an NEA to Earth transfer orbit (compare these values with the 8.5 kilometers per second needed to go from Earth surface to LEO). Thus, mined resources could in principle be placed in Earth orbit for a lower energy cost than material delivered from the surface of the Earth or Moon. In addition, velocity change can be delivered gradually, over several weeks, meaning that low-power propulsion systems are a viable option (though for any crewed mission, the use of exclusively electric propulsion will certainly be discarded due to the lengthy flight time). This would allow the return transfer to be accomplished using part of the target body (such as volatiles) as reaction mass, and solar energy or onboard nuclear power for the power source.

  Many materials that are useful for propulsion, construction of life support, metallurgy, and semiconductors could be extracted and processed from NEAs. Volatiles such as hydrogen and methane could be used to produce rocket propellant to transport spacecraft between space habitats, Earth, the Moon, and asteroids. Metallic nickel-iron alloy could be used to manufacture structural materials. Rare earth metals will allow the production of solar photovoltaic arrays, which could be used to power space or lunar habitats. These solar cells could also be used in space solar power systems in orbit around the Earth in order to provide electrical power for their inhabitants. Precious metals such as platinum, platinum-group metals, and gold are also available. These materials have all been identified either directly in meteorites, or spectroscopically in asteroids and comets. But the main material could be water, which can be split into (liquid) hydrogen and oxygen to produce rocket fuel. Moreover, water and oxygen can be used to feed space habitats. These materials are of major concern for people living in the asteroid belt in The Expanse, a series of science fiction stories by James S. A. Corey in which humanity has colonized much of the solar system.[2] Indeed, the company Planetary Resources plans to create a fuel depot in space by 2020, using water from asteroids. Water is also at the core of a similar venture named Deep Space Industries. As they write on their website, “Water is the first resource we will harvest, and the first product we will sell.”[3] Such ambitious plans may seem like the mirage of a far-distant future, but the groundwork for a realistic implementation of asteroid mining is already being laid. In 2012, NASA’s Institute for Advanced Concepts announced the Robotic Asteroid Prospector project, which will examine and evaluate the feasibility of asteroid mining in terms of means, methods, and systems.

  Mining on an Asteroid

  Once mining operations have been established, there are two ways to get the material back to Earth. The first is to attempt mining an NEA in its existing orbit, dropping off a payload every time it passes by Earth. This is the reason for the search for asteroids with appropriate orbits. In this situation, real-time teleoperation is not possible due to the large round-trip time of the command signals. Thus, robotic probes must be largely autonomous during the exploration and mining process, and they must rely on some kind of trained machine intelligence, such as deep learning. The other way, which would allow for real-time operation but which offers its own distinct challenges, is to retrieve smaller asteroids from their own orbits and place them in orbit around the Earth or the Moon, and then mine them at will.

  However we ultimately choose to access NEAs, the mining process itself must be tested and perfected. Maneuvering around a small asteroid with a highly inhomogeneous microgravity could be quite tricky. Thus, mining machinery must first be anchored to the asteroid surface, and the released material efficiently contained and recovered. Collecting and handling ejecta and volatiles in microgravity (where electrostatic charge becomes a dominant force on dust particles, causing them to adhere to anything) will be an important issue, considering that the escape velocity for small asteroids is in the range of 10-20 centimeters per second. Mining approaches will depend on the material: frozen volatiles may be cut, mechanically mined, melted, or vaporized for extraction. Solid metal must be cut or melted at high temperature. This will require a large amount of energy, either collected by large mirrors focusing the sun’s light on the asteroid surface (in order to vaporize volatiles) or provided by a nuclear source (see the “Energy Supply” section of this essay, below).

  Once asteroid raw materials are extracted, they must be separated into usable materials b
efore being used in manufacturing. Manufacturing in microgravity and in a vacuum offers both opportunities and challenges. The upside of making things in space is that we can create very large structures that would never fit into a launch vehicle’s payload fairing. Huge solar arrays to meet Earth’s energy demands and enormous antennae to enhance the range of communications satellites are among the possibilities. The downside is that surface forces (surface tension, friction, electrostatic charge, etc.) exert increased influence and necessarily modify all the processes we have developed for use in Earth’s gravity.

  Before we put them into use on asteroids, all of the essential technologies must be identified and tested in real conditions. The Moon could be a good place to perform this task. Compared to asteroids, the lunar surface is volatile-poor and metal-poor—not the best resources deposit in space. Although its gravity is greater than that of small bodies, the Moon is within relatively easy reach of Earth, and offers a harsh environment (dust, UV, cosmic rays) appropriate for testing in situ resource utilization. Any potential robotic or human activity on asteroids must operate on rough surfaces and contend with vacuum, dust, thermal constraints, and extreme radiation. Moreover, the constraints for human mission success and safety are even more stringent than those for automated missions. Research and development on radiation countermeasures are necessary (space dosimeter and radiation shielding), together with habitation and life support (effect of dust on space suits and airlocks), astronaut mobility systems around NEAs, human-robot interaction, and more. Due to its proximity, the Moon could be the best place to install a test bench to prepare for future robotic and crewed missions in real conditions.

  As the largest body in the main asteroid belt and a place rich in water, the dwarf planet Ceres could also be a base for exploring and exploiting asteroidal resources, in support of development throughout the solar system, as depicted in The Expanse. Because of the dwarf planet’s very low escape velocity (.51 kilometers per second), the large amount of water on Ceres would not only be a valuable resource for in situ use, but would also be an exportable resource, supplying fuel, oxygen, and water for ships going through and beyond the main belt.

  Energy Supply

  The feasibility of asteroid mining relies heavily on the availability of huge amounts of electrical power in space. To operate a plant transforming and manufacturing thousands of tonnes per year could require power in the range of 10-100 megawatts (MW). Below 100 kilowatts (kW) and in the vicinity of Earth, solar panels are appropriate, although they present other drawbacks. Reaching higher power could be difficult: a 100 MW solar power plant in space must have a large collecting area on the order of 1 million square meters (with 10% energy conversion efficiency) facing the sun. The cost to launch such a mass from Earth’s surface could be too high to make an orbital plant economically viable. Radioisotope thermoelectric generators, which are very useful for Mars, planetary, and deep space exploration, are able to deliver few hundred watts at best. However, these systems are not good solutions for missions with higher (multi-kW or MW) electrical power needs because the amount of plutonium fuel you would need becomes unwieldy and difficult to produce.

  The most efficient option could be a small fission nuclear reactor, such as those used in nuclear marine propulsion, which produces power in the 30-100 MW range and could also be used for propulsion purposes. A tug powered with 1 MW of electricity produced by a nuclear reactor could execute a wide range of missions, including deterring inbound asteroids like Apophis and moving them off course or moving tons of payload from Earth orbit to the moons of Europa or Titan. But the task of launching such a nuclear reactor in space and operating it safely would prove a significant challenge. As in a classical heat engine, energy is produced thanks to the temperature gradient between a hot source and a cold source. In space, cooling is achieved by evacuating extra heat into space using radiant panels. Thus, the temperature of the cooling source cannot be as low as it would be on Earth but rather around 400 kelvin (400 K). This implies that the temperature of the heat source must be well above 1,200 K in order to achieve a good energy conversion efficiency. This high temperature, even higher than what we anticipate in generation IV fission reactors, would be the main challenge for the reactor. There are also issues with the manufacturing and transportation of the shield (it can weigh as much as the reactor) and its thermal environment (deformation has to be limited), in safety systems, and thermal control. Developing 30-50 kW and 100-300 kW nuclear reactors in space could be a milestone toward NEA exploration and mining, and more generally to the exploration of the solar system. But overcoming people’s reluctance to put a nuclear reactor in space will be a significant challenge.

  Another Path to Space Industrialization?

  As we have already established, future large-scale commercial activities in space will require raw materials obtained from in-space sources to bypass the high cost of Earth launch. Another way to resolve issues around the availability of large quantities of materials in space is to dramatically reduce this cost by developing easier access to Low Earth Orbit. Building a space elevator is one way such access could be achieved. In a space elevator, a vast cable anchored to the surface is extended into space. Vehicles travel along the cable directly into space or orbit, without the use of large rockets. Carbon nanotubes have been identified as meeting the very high specific strength requirements for the cable of an Earth-based space elevator. But no one has yet managed to manufacture a perfectly formed carbon nanotube strand longer than a few centimeters. The design of a space elevator also relies on the use of an orbiting counterweight to stretch the cable, using centrifugal force. This counterweight must be positioned past geostationary orbit; it could be a captured NEA in the range of 105-106 tonnes, and/or the spaceport where raw material collected from asteroids is stored and transformed. Thus, even if we plan to solve the problem of countering the high cost of launching materials for in-space construction by using of a space elevator, rather than “docking” at targeted asteroids, the blueprint begins with successfully exploring a near-Earth asteroid.

  To conclude, in my opinion, the best way to attain asteroid mining is twofold: tackle the asteroid deviation problem (which leads to retrieving small NEAs to put into Earth or Moon orbit) and develop an in-space high power generator (which will help solve the asteroid deviation issue). Developing our capabilities to protect humankind from an NEA impact could provide the social and political momentum that is necessary if we are to proceed further. And it is that social and political momentum in which science fiction’s speculative futures, too, play an important part.

  Science fiction writers, in depicting these futuristic projects in their stories, make them more concrete and more human. Thus, they can play a key role in the way the public will perceive these futuristic projects, and boost the social and political acceptability of such missions. As Ramez Naam’s story elegantly asks: how can people dream of space, if we only send robots to explore it?[4]

  [1] “Discovery Statistics,” Center for Near Earth Object Studies, NASA, http://neo.jpl.nasa.gov/stats. [back]

  [2] Other notable fictional portrayals of asteroid mining include Alien, a 1979 film directed by Ridley Scott, which follows the crew of the Nostromo, a commercially operated spaceship returning to Earth with 20 million tonnes of mineral ore mined from an asteroid; Outland, a 1981 film directed by Peter Hyams, which takes place in the titanium ore mining outpost Con-Am 27, operated by the company Conglomerates Amalgamated on Io, a moon of Jupiter; EVE Online, a massively multiplayer online space game where asteroid mining is a popular career for players; and Devil to the Belt, a two-novel omnibus written by C. J. Cherryh—the first of the two novels, Heavy Time, describes economic disputes over asteroid mining for minerals. [back]

  [3] See https://deepspaceindustries.com. [back]

  [4] The following studies provided important background information for this essay, and appear in the bibliography for this collection: Jonathan F. C. Herman, et al., “Human Ex
ploration of Near-Earth Asteroids”; J. P. Sanchez and C. R. McInnes, “Assessment on the Feasibility of Future Shepherding of Asteroid Resources”; John Brophy, et al., Asteroid Retrieval Feasibility Study; Didier Massonet and Benoît Meyssignac, “A Captured Asteroid”; Edward T. Lu and Stanley G. Love, “A Gravitational Tractor for Towing Asteroids”; Bret G. Drake, “Strategic Considerations of Human Exploration of Near-Earth Asteroids”; Shane D. Ross, “Near-Earth Asteroid Mining,” John S. Lewis, Mining the Sky; Mark J. Sonter, “The Technical and Economic Feasibility of Mining the Near-Earth Asteroids”; and Bradley Carl Edwards, The Space Elevator. [back]

  Night Shift

  by Eileen Gunn

  2032: An interplanetary gold rush has begun, and the prize is water, not gold. The miners are robots, with human intelligence and superhuman survivability. All over Earth, corporations and governments are using AI robots to assay the closest asteroids and prioritize them for exploitation. A small automated colony on the Moon, directed by a private company in India, is building a materials processing plant near its north pole, using lunar regolith as a building material. It’s fueling the work with solar cells and with hydrogen extracted from lunar water. The Mongolian government has claimed an area near the south pole where it believes there is water, and is deploying hydrophilic nanobots.