OVERVIEW

The thinking upon the possibilities of extracting useful and economic amounts of pure metals and other useful materials from asteroids, either as Near Earth Asteroids (NEAs), also know as NEOs (Near Earth Objects), or those asteroids beyond the orbit of Mars, is linked to discussions with Ueli Scheuermeier of The NEA Mines Group:

http://www.asteroidmines.net/

In response to Ueli's suggestion, the possibilities of my producing technology concepts and illustrating them, to throw into the pot for further discussion, I thought would be a very productive addition to the EOS Program.

The current ideas represented here are the proposals of how this could be embodied in some technology for mining a variety of materials for extraction of common and rare metals, raw organic compounds, solid gases and water ice.

ASTEROID ATTACHMENT

The problem that has taken most thought has been attachment, maintenance and release of hold from a suitable asteroidal host body. A mosquito comes to mind here. With only a carbonaceous host, pairs of legs fitted with opposing counter-rotating augers may be enough to gain a foothold. For solid metal bodies, a thermal welding solution seems inevitable. Then there is the action/reaction problem when attempting to drive into the host under zero G.

This has necessitated thinking about decoupling the driving-in attachment from the drill head main body by a floating suspension system, and powering each leg with its own thruster to give the necessary momentum, and without endangering the integrity of the processing body. Each leg, therefore can attach at its own speed and in its own time.

A pair of parallel arms can push out each leg, with hydraulic rams, to an appropriate distance from the main body, so setting the radius of the rig's placement according to terrain conditions.

Releasing a ferro-liquid magnetic brake allows the driven leg shaft to move freely forward under thruster force.

For a largely metallic surface, a small charge fires off a consumable thermite lance at the end of the leg that melts the surface metal of the asteroid, creating a metal pool. The thruster drives this forward and down, until melt anchors on the leg enter the pool, and maintains pressure until the pool solidifies by heat dissipation through the asteroid body, thereby bedding in the anchors. The heat shield foot can be then moved into contact with the cooling surface, and the in-leg hydraulic rams adjusted to balance the orientation and equilibrium of the whole rig.

On moving the rig out and away, clamps disengage from the anchor axle, releasing it for moving the rig to another site or maintenance. If further work on an established bore is required, it would be easy to relocate and re-engage with the anchor points.

The hydraulic legs, magnetic brakes and thruster motors all combine to create a flexible suspension system to smooth out stresses induced by the mining operations, as well as partially controlling the proximity of the drill-head to the working surface.

METAL EXTRACTION

Previously, I had been looking at plasma smelting for use in melting pure nickel-iron from asteroid sources, which is a well-understood technology in current industrial practice, but was unhappy about using lots of scarce gases in space, and was yet unable to discover whether metal vapour itself could form a plasma cloud in vacuum that could be controllable.

From previous readings, I recovered articles on using microwaves for ore mining (some of which I have previously cited at Mars Homestead) and extended this to include smelting. It is clear that microwaves are being applied extensively in standard mining operations to recover ore, which have a splintering effect, producing evenly divided particles of selectable dimensions. Applied to smelting, they can be used to create large melt pools, where previously electric arc processes were used to melt metals. The advantage here is none, or less, oxidative byproducts when used in atmosphere, but obviously highly suitable to applications in the vacuum of space.

However, with more time spent on research, it is perceived to be more likely to find a mixture of materials bound together, and extraction with post-processing will be involved to refine and separate the various components of the mix. So a combination of microwave shattering and mechanical scraping is probably more suitable.

DRILL HEAD

Although this looks like a conventional grinding head, the rotating parts are not the primary tool for breaking into the regolith. Steerable apertures are microwave guides limited in size by the frequency of the waveforms and proportions of their cavity magnetrons, so have to be ganged for total energy output.

The drill head magnetrons should draw proportionally very little power compared to conventional grinding drill systems.

The outer set are tunnel excavators backed up by scraping blades, to allow access for the drill head into the bore and to cause the bore wall to slump into the centre. The central ring of variable focusable guides generate a central concentrated fragmented area of grits shattered from the regolith floor itself. To balance the impact of overall heating on the equipment, according to the material being mined, the guides could also be powered in a rotated sequence, almost as if it were a conventional grinder, in pairs or triples etc, to optimise the heating/cooling balance of the head.

Scrapers in the head base drag shards up a helical ramp into a vestibule in near zero gee. Applied momentum would bounce the grits upward in slow motion. Helical screw elevators would then move the material up the main conveyor tube for collection in the detachable hopper drone.

The drill head tube can be moved up and down through the body shell, so accommodating a fairly deep bore. This works interactively with vertical control from the leg assemblies. Cylinders would carry thruster fuel, flight fuel for tractoring around the sites, and control equipment. Mining tools power could be accessed from several sources, in-house fuel cells tanked from these cylinders, solar panels (risky on rotating hosts that have nightsides), or probably best, microwave reception (very efficient conversion) of energy from wider orbiting solar power stations (that may also double as ingot smelters) that never eclipse.

COLLECTION AND REMOVAL OF METAL

At any depth of bore, the drillhead tube can be moved out and up to expose the storage ring and allow bulk transfer to take place. A filled hopper can be ejected from the excavator by rapidly moving the conveyor tube up through the surrounding geodesic gallery, and releasing the hopper latches at the top of its travel. Once accelerated from the minimal gravity field, the hopper and its cargo can be guided automatically towards the processing hub, in parallel orbit to the asteroid. These cargo drones may well be powered by perhaps ceramic thrusters, using water as the working fuel to produce microwave-induced superheated steam.

What one does NOT want is a local environment littered with mining debris of various scales, all as hard as bullets, oscillating about in wild unpredictable orbits and causing a major traffic hazard for mobile craft at any delta vee. I would suspect much trash would return slowly to ground under the influence of gravity after mining disturbance. Once mined material has been processed to extract its useful content, tailings could be returned to the surface to maintain the rotational equilibrium of the asteroid, or even stabilise its rolling by redistribution at key points on the axis (like balancing a car wheel).

This material could be used to act as radiation shielding at the crew habitat, or even build concrete spaceships, with the same end in view.

SUMMATION:

Having passed through several stages of consideration in the design of a mobile excavator, for use in remote control drilling operations, several questions have arisen which are more to do with human presence and survivability in an extreme environment.

The use of intense microwave energy to shatter rock is a key technology, that reduces wear and tear on moving parts. It also allows frequency tuning for different minerals.

Projecting power by microwave energy derived from solar photovoltaic sources helps to keep the mass of the whole vehicle down.

A more complex requirement is a healthful manned habitat that maintains a low level of induced gravity, and adequate radiation shielding for safe long term occupation. This seems unavoidable given the complexity of the different processes required, and their consequent regular maintenance.

© Jan Kaliciak 12-05-2007   NeoMiner v. 3.9