Asteroid Mining, Belt Mining

The process of extracting useful minerals and other substances from asteroids

Wrapped asteroid
Image from Alex Mulvey
A neumann swarm envelopes an asteroid-sized object within a planet's rings
Despite their small size and comparatively sparse distribution, asteroids are the most common source of raw material within Terragen civilization. Readily accessed and with negligible gravity, they can be mined and transported more easily than a similar volume of mass extracted from a planetary body. While asteroids can be found freely orbiting almost anywhere, gravitational interactions tend to collect them into denser groupings such as asteroid belts or planetary rings. The nature of any general group of asteroids, including but not limited to their location, orbit, consistency, density, and mass, along with the inhabiting civilizations' potential intentions, desires, culture, and technology, leads to innumerable ways that the material might be extracted and utilized. Despite this, there are several general methods which deal with the advantages and disadvantages that asteroids offer.

One main advantage of asteroids is their inherent orbital momentum and low mass, making extracting their resources or moving them to a different orbit a trivial feat for even midtech civilizations. The main disadvantages of asteroid mining are the challenges associated with the debris which collects naturally on their surface as well as that generated by the mining process. Even small asteroids possess layers of loose surface material ranging from particulate dust to large boulders, held together delicately in an otherwise undisturbed micro-gravity environment. The escape velocity of these bodies can be fractions of a kilometer per hour, meaning any contact with their surface, or any changes to their rotational momentum, will result in clouds of debris which can escape and float away, enter orbit, or fall back to the surface. Asteroids also tend to have irregular rotation, tumbling through space about random axes. This rotation must be stopped or matched in order to have easy access to their material, however the process of slowing down the rotation may result in parts of the surface flying off into space.

This issue is usually solved by enveloping the asteroid before material extraction, a method inherent to the process regardless of surface debris as it can ensure no desired material is lost to space. If the target is located initially in an area intended to receive regular traffic, such as a waypoint for a larger mining operation, it is likely to be completely enclosed prior to mining operations. Mid-tech mining units suited to this task utilize a bag which opens and closes mechanically, while higher-tech versions consist of utility fog able to form surface-area efficient sealed environments around the body and perform the material extraction itself. The debris issue can also simply be ignored; for asteroids far from other infrastructure, it may not be detrimental to lose the debris within a localized area, as it will continue more or less in the same orbit it always had. If the asteroid is to be sent to another location, the debris may be intentionally cast off before departure.

For larger bodies, extraction may be done from the inside out. Small access ports are drilled within small bubbles on the surface, leading to the interior where the asteroid is hollowed from the inside out. Inhabitants may live on their surface, or utilize the interior to create numerous types of enclosed habitats. The material on the surface will still be disturbed and must be collected or cast off.

The actual processing methods themselves can take many forms, any of which may be most desirable for a given logistical system. Asteroids may be collected and moved as a whole towards central processing locations within the field. Gravity tugs can be used to pull them. Small seedships may land on the surface and construct small thrusters and processors on the surface from material mined there, turning the asteroid itself into a ship which flies to its destination. Asteroids can also act as radiation shields, keeping a cool shadow over orbital infrastructure.

Mass Driver
Image from Jack Harper
A mass driver attached to an asteroid can be used to deliver mined materials to a distant location, and may also be used to accelerate the asteroid itself.
Because of their small and easily manageable size, individual asteroids are very valuable. They have negligible gravity wells, making it relatively easy to move materials to habitat constructions in orbit. Even a small asteroid of a few hundred meters diameter can contain billions of tons of raw material. For this reason, individual prospectors (the so-called belters) are willing to gamble life-savings against the cost of relativistic transport, mining rights, and so on, and quite a few do make it rich. Both small and large development corporations are also very keen to get their hands on asteroids. Many asteroids, most particularly nickel-iron rocks, contain varying amounts minerals: platinum, iridium, and sometimes radioactives, while carbonaceous chondrites are prized for being a rich source of volatiles and very occasionally fullerenes and amino acids). Water ice and ammonia are also very useful.

The main challenges in Asteroid Mining

The main difficulties facing an asteroid miner include
  1. A lack of atmosphere for aerobraking; landing on Earth is made easier because of this useful deceleration aid.
  2. Minimal Oberth Effect making it expensive in delta-vee to decelerate into orbit round an asteroid,
  3. Irregular shape, making any orbit around an asteroid chaotic and potentially dangerous ( try plotting a close orbit around Kleopatra without hitting one or other of the protuding ends).
  4. Rapid rotation- for asteroids smaller than 100m the rotation may be fast enough that you could be thrown off the surface.
  5. Tumbling- many asteroids have unstable rotation (i.e. their period and axis of rotation vary over time), which also makes it difficult to land.

    Envelope Mining

Image from Steve Bowers
A Pacman miner manoeuvring around an asteroid, after matching its rotation. The spherical bag will envelop the object and will become an enclosed environment allowing mining activities to be carried out with minimal losses
The small gravity field of an asteroid also causes problems, as mined material may drift away and volatiles can be lost to evaporation. For this reason most mining occurs inside flexible, sealed domes or in sealed tunnels inside the object. Very small asteroids can be entirely enclosed by an envelope miner vessel, known for historical reasons as a Pacman Miner or Pacminer. The rapid rotation of small asteroids also causes problems when they need to be moved or deflected - various kinds of gravity tug can be used for this purpose without contact with the rotating object.
Envelope miner
Image from Steve Bowers
This envelope miner system encases the asteroid in smart gel, which refines the ores and contains any volatile gases

Optical Mining

Another process which is often used is optical mining: using concentrated sunlight to break up asteroids. This begins with enclosing a target asteroid in a bag attached to the mining ship. Next, sunlight is concentrated onto the asteroid using a system of mirrors, fracturing it and releasing volatiles such as water. The volatiles are then collected and frozen for storage. The remaining solid slag may be discarded or retained for further processing, depending on the capabilities of the individual mining ship.

Not all asteroids are amenable to optical mining: this technique is best used on asteroids that are relatively small and have a high water content.
Neumann at Dactyl
Image from Steve Bowers
Neumann vecs replicating near Dactyl. Many von Neumann self-replicating systems replicate by producing miniature copies of themselves which then grow larger over time
Many individual asteroids and whole asteroid belts have been exploited by self-replicating von Neumann devices, which sometimes develop various degrees of autonomy or sentience (becoming Neumann vecs) and establish civilisations of their own.

Occasionally an asteroid or asteroid belt will be discovered with an unusual composition that makes it valuable for scientific or even aesthetic purposes. Even more rare, the hulk of an ancient ship or a neumann may be recovered, often centuries or millenia old, drifting in a belt. The salvage rights of such a find can make a belter rich for a life. Rarest and most prized of all are alien artifacts, although the possibility of such a find is more a part of myth and legend than pragmatic reality.

Pacman Miner
Image from Todd Drashner

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Development Notes
Text by Alex Mulvey, M. Alan Kazlev, Tardigrade and Steve Bowers
Initially published on 08 October 2001.

Revised Feb 2021