NEEP 602 Lecture #21

NEEP602 Course Notes (Fall 1996)
Resources from Space

Extraction Techniques for Minerals in Space

Mining:

3-D workplace that must be: safe, well drained and ventilated with necessary power and transportation
also must be able to produce ore at steady rate and quality

Extraction Methods
Orebody shape is function of its mode of formation:

Mining depends on:

Blasting

an individual explosion removes cone of material
more explosives lead to smaller rock but not more excavation
amount of breakage should be controlled or keyed to requirements of subsequent treatment
timed blasting:
- to remove material from an open pit bench
- to advance a face underground

Open Pit/ Quarry

Underground

details depend strongly on geometry and grade of ore and the nature of the gangue
usually need to leave ore behind as pillars
gravity is commonly used to help reduce handling
must start with access system of drifts and shafts (usually in footwall)
extraction done in rooms (stopes) connected by drifts, raises
artificial supports commonly needed

Broken ore occupies 30-50% more volume than parent material

Cut and Fill: fill mined area with waste rock or cemented tailings

Sublevel or Block Caving

Mining either by advancing from or retreating to the point of access

In-situ recovery: possible for oil shale (burn front)
Borehole Extraction; Heap Leaching

Milling: "bust it up and classify it"

breaking method depends on tensile and compressional strengths
classifying depends on size, shape, density, magnetic properties, ...
various types of crushers: gyratory, cone, jaw, ball/rod mill
sorters: grizzlies, screens, cyclones, flotation, settling velocity, shaker table
hydrometallurgy, pyrometallurgy

Resource Recovery in Space

Unconsolidated material at the Surface: Lunar regolith

Mobile Slusher
able to move from site to site as needed
Stationary Slusher
simpler, lighter
would need help getting around
Both are 3-drum cable tools which can reach any area defined by the location of the power unit and the 2 anchor pylons
Scraper fills because of combination of in-haul forces and weight of the scraper
Looks like a simple operation but at present this would probably have to be run by people either on site or by teleoperation. We still couldn't automate even this simple process.
Ability to change from scraper to rake to ripper to plow.
Lower levels of regolith will probably need to be broken up.
Explosives? Design of ripper or plow?

Before going any further consider weight, mass, inertia, friction, traction

On earth loading equipment operates near its traction limit
Reduced gravity creates a less favorable inertia: traction ratio
Can increase traction by increasing mass (which makes for inertia problems)
Once anchored, the slusher fills basically in response to the in-haul force which is traction independent. The bucket will have to be more massive but this may be accomplished by using onsite rocks.

Asteroidal Mining:

Probably start with a near-earth Amor, Apollo, or Aten asteroid
Some asteroidal material is very easily crushed and may be processed easily
Long lead time increases expenses
long duration manned mission
automated or teleoperated mission
slow long low DeltaV equipment arrival combined with faster high DeltaV manned portion
Problems with manned mission:
long exposure to zero gravity
solar radiation
life support
manned deep space vehicle

Problems with automation or teleoperation

slow progress on doing this on Earth
so many unknowns which might require a human touch to overcome
time lag of teleoperation may make it impossible to respond soon enough to keep disaster at bay

Mining in zero gravity

Inertia not weight is the real problem and as this is a function of mass not weight, the lack of gravity is not a real bonus
Fracturing and evacuation equipment on Earth uses gravity as the hold-down mechanism. Something else will have to take its place.
Fracturing provides initial velocity to rock particles/pieces. On Earth these pieces rapidly loose their V and accumulate; at zero gravity you have an out-of-control 3-D billiard game.

Possible solution:

Cable the mining equipment to the small asteroid.
The cable holds both the fracturing/removal equipment and the collecting `bag' to the surface of the asteroid. The bag maintains its shape because the asteroid is spinning; this spinning also helps collect the broken material into the bag.
Material needs to be boosted with enough energy to pass the synchronous orbit limit so that centripetal force collects it into the bag.
Blasting could be an alternative but would have to be done very carefully.

Extraterrestrial Mining Problems for Research:

How should mechanical equipment be modified for operation in reduced gravity? (excavation, loading, moving)
Remote and automated mining. What progress has been made on Earth?
Environmental effects: extremes of heat and cold
Applicability of terrestrial techniques to low gravity, no atmosphere situations.
Rock drilling:
conventional drilling: drilling mud? friction?
melting and vaporization; chemical reaction; heat induced spalling; mechanical stress; spark cratering
Changes in traction and how to compensate:
traction is function of gravity and friction
Changing role of blasting in low gravity settings; vacuum will also affect blast
Wear resistant materials
Particle size reduction in low gravity settings
design of crushers; substitute for wet grinding and separating?
classifiers

References:

W. H. Dennen and B. Moore (1986) Geology and Engineering

W. H. Dennen (1989) Mineral Resources: Geology, Exploration, and Development

University of Wisconsin Fusion Technology Institute · 439 Engineering Research Building · 1500 Engineering Drive · Madison WI 53706-1609 · Telephone: (608) 263-2352 · Fax: (608) 263-4499 · Email: fti@engr.wisc.edu