Water is the key to the Solar System. In space, water provides benefits beyond its critical role in hydration. It can protect from solar radiation, be used as propellant, provide a source of oxygen, and sustain food supplies. To date, all water and water-derived resources necessary for spaceflight have been brought from the surface of the Earth at exorbitant expense. Of all constraints to the expansion of humanity off the Earth, this is the most limiting. What is needed for real, sustained growth is a plentiful supply of water already in space, available at the required point of use. Unchained from the Earth as our single source, humanity could use this in-space resource to further expand beyond Earth orbit and into the Solar System. Fortunately, a plentiful source of in-space water has already been found and is waiting to be claimed – the near-Earth asteroids.
Water: Unlocking the Solar System
Water from asteroids can be both converted to and used directly as propellant, then shipped and stored at strategic locations set up as fuel depots. This fuel – supplied and sold to NASA or other in-space customers – will dramatically accelerate the pace of human spaceflight.
Asteroid water can sharply reduce the cost of human spaceflight missions because the mass of most deep space missions is primarily comprised of propellant. For example, it is more energetically efficient to carry a liter of water or propellant from a near-Earth asteroid to an Earth orbit destination than it would be to carry that same liter of water from the Earth’s surface.
In Earth orbit, water from asteroids can also be converted and used to refuel satellites, increase the payload capacity of rockets by refueling their upper stages, reboost space stations, supply propellant needed to boost satellites from Low Earth Orbit to Geostationary Orbit, provide radiation shielding for spaceships, and provide fuel to space tugs that could clean up space debris.
A 500 meter diameter water rich asteroid has $50B (billion) worth of water deliverable to a deep space fuel depot, even if one makes the conservative assumptions that: 1) only 1% of the water is extracted; 2) half of each load of water is consumed en route for propulsion; and 3) the success of commercial spaceflight causes the cost of Earth-originating launches to drop by a factor of 100. Of course, less conservative assumptions would raise the value of the asteroid to many trillions, or even tens of trillions, of dollars.
The economics of an asteroid mining operation can also be enhanced by the use of in-situ propellant. Mining spacecraft can travel across interplanetary space using water reclaimed from the very asteroid it is mining, leading to a high “mass payback ratio” where a single ton of mining equipment can be used to obtain hundreds of tons of mined resources.
Moving from Water to Metals
Once water mining operations are successful, the economics of space travel will have changed such that the reclamation of other asteroid resources becomes more feasible. In a very real sense, mining water ultimately enables the mining of metals.
Platinum group metals are extremely rare on Earth and these metals, and others like them, have special chemical properties that make them incredibly valuable for important industrial processes in the 21st century economy. An increase in abundance of rare metal resources could also enable new, unforeseen applications that exploit the properties of rare metals beyond the current state of practice.
Using Asteroid Metals in Space
In addition to being brought back to Earth, metals from asteroids can also be used directly in space. Metals like iron or aluminum can be moved to collection points in space for purposes such as space construction materials, spacecraft shielding, and raw material for industrial processes at, for example, a future NASA deep space L2 space station.