NEEP602 Course Notes (Fall 1996)
Resources from Space
Extraction Techniques for Minerals in SpaceMining:
- 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
Orebody shape is function of its mode of formation:
- 2-D sheetlike or tabular bodies
- linear or rod-like bodies
- irregular 3-D masses
- thickness, attitude, depth, strength of ore and host materials
- 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
- f(overburden thickness, topography, nature of ore)
- pit wall angle: 45o for rock; 30o for unconsolidated material
- pit vs underground: f(geometry of ore body; grade of the ore)
- pits may lead up to underground operations (or the reverse) over time
- originally too expensive, now infrastructure in place and paid for
- postpone the ecological day of reckoning
- 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
- shrinkage stope method uses this fact
- keep minimum headroom by drawing down the muck pile
- very versatile, commonly used
- development costs relatively low
- pillars can be recovered
- takes care of some of the waste disposal problem
Sublevel or Block Caving
- used in weak ore, may not be safe to mine in other ways
- low cost
- LOTS of premining development needed
- problems with ore dilution and surface disturbance
- advance more common because quicker return on investment
- retreat common in some coal mines
- may lead to surface subsidence
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.
- 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
- 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
- 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.
- 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?
W. H. Dennen and B. Moore (1986) Geology and Engineering
W. H. Dennen (1989) Mineral Resources: Geology, Exploration, and Development
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