Resources

Natural resources are abundant throughout the solar system, off Earth, but harvesting them is quite difficult and expensive.

Water for Propellent

Water has been discovered in the permanently shadowed polar craters of the Moon ¹. This water can be melted and electrolyzed into hydrogen and oxygen, which can be used as rocket fuel ². Several studies have examined the feasibility of doing this, relative to resupplying fuel from Earth.

In general, propellent from lunar ice is more likely to be economically feasible for geosynchronous satellites and deep space missions, and less so for low-Earth orbit satellites.

As of 2021, Masten Space Systems, Lunar Outpost, and Honeybee Robotics are working on lunar ice mining ¹².

Water can also be recovered from near-Earth asteroids, from which water may be more abundant ¹³ and the economics of making fuel and propellant more favorable ¹⁴¹⁵. However, it should be remembered that asteroid mining remains challenging, with two recent prominent companies--Planetary Resources and Deep Space Industries--having failed ¹⁶.

Methane on Mars

The Sabatier process is a method of producing methane and water from carbon dioxide and hydrogen. The process is as follows.

The Sabatier process is an endothermic process, requires 165 kilojoules of heat for each mole of reaction. On Mars, the CO₂-rich atmosphere is a source of carbon dioxide, while the water produced can be electrolyzed as a source of hydrogen. Source: Wikipedia.

The Sabatier process is of interest to allow fuel on a return rocket flight from Mars and is envisioned for a Mars sample return ¹⁷ or for SpaceX's Starship ¹⁸. The process is used currently on the International Space Station to recycle oxygen, but on Earth, it is not currently competitive with natural gas ¹⁹. Improving process catalysts is an active area of research ²⁰.

Asteroid Mining

There are several proposals to mine asteroids and other celestial bodies for raw materials, but nothing that will come to fruition soon.

Although asteroid mining has received considerable attention in the press, there are relatively few studies that analyze the economics rigorously. Above are results from some select analyses. Asteroid mining is likely to be economically viable only for high value minerals, such as platinum-group minerals ²¹. Sources: Busch ²², Hein et al. ²¹, Kleinschneider et al. ²³, Lu ²⁴.

Harvesting resources for use in space, such as water to make rocket fuel, is more likely to be economically viable than bringing resources back to Earth ²⁵,²¹.

Launch costs would have to be below about $330 per kilogram to low-earth orbit (2020 dollars) ²⁶ for asteroid mining to be economically viable, figures that SpaceX hopes to achieve with the under-development Starship. Near-earth asteroids, or those whose orbits come close to intersecting that of Earth, are most likely to be economical ²⁷.

Solar Satellites

Space-based solar power (SBSP) is a proposed system that harvests solar energy from satellites in geosynchronous orbit. The satellites transit the power to a ground rectanna in the form of microwaves. While SPSP is probably technically possible ²⁸, the economics are highly uncertain ²⁹,³⁰. Self-replicating factories on the Moon, which would launch components via a mass driver for arrangement in geosynchronous Earth orbit, have also been proposed ³¹.

Lacking reliable figures specifically for space-based solar, we take the cost of a full research program to be $65 billion, the same as the ITER project for fusion ³², and the time frame to be 40 years. We estimate the benefit to be about $9 billion, with an ultimately achievable cost of electricity of 7 ¢/kWh and otherwise the same greenhouse gas and other external costs of other forms of solar. See our research and development analysis for more details.

As the ultimate cost of SBSP is highly uncertain, and the appropriate discount rate is debatable, the benefit/cost ratio could vary widely.

Helium-3 Mining

Helium-3, a possible candidate for fusion fuel, accumulates on the lunar surface from solar wind. Mining this fuel and bringing it back to Earth would be an extensive operation, with several estimates of the feasibility of doing so.

For lunar helium-3 mining to be sensible, the following must hold:

• fusion power is economical,
• the deuterium-helium-3 route is superior to the deuterium-tritium or the proton-boron-11 routes, and
• lunar mining is more economical than harvesting helium-3 as a decay product of tritium.

We see no reason to expect the second point, nor are we aware of a reliable analysis on the third.

Th, U, Pu, Li, T, D, and 3He are thorium, uranium, plutonium, lithium, tritium, deuterium, and helium-3 respectively. Lunar and imported deuterium indicated whether the D is to be harvested from the lunar surface or imported from Earth, where it is much more abundant. Source: ³⁵.

The 163 million TWh of helium-3 available for D3He reactions would last 1400 years at present world energy demand ³⁵. This assumes that the entire surface of the moon is strip-mined of helium-3 to three meters. If we assume that world energy demand grows by a factor of 5 for a civilization capable of such a mining operation, that only a fifth of lunar helium-3 is recoverable, and the overall efficiency (including heat losses in the power plant and the energy cost of strip mining and transportation) of the mining operation is 25%, then there are only 14 years of He3 reserves available.

It is also proposed to mine helium-3 from gas giants ³⁶, including Uranus ³⁷, though this is even more logistically difficult than mining the moon.

Aside from possible use for fusion, helium-3 is used as a neutron detector to screen for fissile materials. Fearing commercial shortage, the Department of Homeland Security has developed a detector using boron-10 instead of helium-3 and identifies the commercial supply of boron-10 to be sufficient ³⁸. Helium-3 is also use for medical imaging of lungs ³⁹ and for other purposes ⁴⁰. Today, helium-3 is generated from the radioactive decay of tritium from nuclear reactors and nuclear weapons, and there is a commercial shortage mainly due to the post-September 11 spike in demand from security applications ⁴⁰.