String-Shooter Light Gravity Mining

Mining asteroids, dwarf planets and small moons, have some inherent issues. Chief among which are:

• Weight
• Parts replacement
• Programming

The issue with weight is obvious, any mass you bring with you is going to cost a lot, so a mining vehicle has to be very lightweight compared to the mass it can mine in its lifetime. A major issue here is that only a tiny  fraction of the machine is actually “wore down” once the machine finally becomes useless, because so many individual parts are used in normal operation. Once one out of three motors in the digging arm is broken, you can’t dig anymore. Once two out of four wheels are broken, you can’t move. Once the camera no longer functions, you don’t know what you should program it to do. Etc.

Parts replacement is an obvious problem as well, you can’t replace that which your machine can’t make where it is. Even if it can make the parts it then also has to be able to replace them by itself, without human help.

And the entire mining operation has to be programmed from afar, with the issues of light-speed lag that involves. If you order your machine to perform a certain digging operation and the ground turns out to be harder than expected, or that an unexpected rock means said operation can not be done, you may find that you get a picture after the operation was supposed to be complete, that shows your mining equipment has toppled over or stopped mid-operation because sensors detected something was about to go wrong.

Therefore I suggest a new mining vehicle design especially for low gravity worlds (asteroids and dwarf planets like Ceres, and possibly as heavy as our Moon). It is basically a string-shooter:

You shoot a wire out across the landscape, and the bit that rubs the ground on the way back then brings dust with it. This dust is then collected and sorted by density in a centrifuge, then refined in another machine or simply piled up sorted by density.

Some advantages of this design:

• The wire is wore down gradually, very evenly. So you can run this until the wire is worn extremely thin before replacing said wire. Whereas a shovel-based excavator design will not be able to function as soon as the shovel is partly worn, or when the wheels or tracks are worn enough to risk the links breaking.
• It relies on only one motor, with a free-spinning wheel opposite the driven wheel. Whereas other designs rely on at least two or three motors, which wear unevenly (note your machine with three motors then stops functioning if one motor fails, it does not run on 2/3 efficiency). So this string-shooter design can have multiple motors driving the wheel, thus only reducing the performance as motors fail and are discarded.
• The wire mechanism can double as the mechanism that moves the vehicle. Several methods can be employed to do this, depending on the gravity level. In very light gravity the kinetic energy of the wire itself can be used to lift the vehicle in bounds and leaps in one direction or another. Simply stop the wire, aim the string-shooter, then start it, then stop it. You can also lay out wires in one direction and tug on them all at once to get pulled in said direction. Assuming of course you designed the proportions of your wire and machine to fit your gravity.
• To anchor the vehicle you only need some spare mining wires and a mechanism that allows you to switch which wire is being shot out of the string-shooter. The anchoring wires are shot out by the string-shooter on low power when you arrive. Each time you shoot out a wire in more directions you can increase the power, eventually you have cycled through them enough to have many wires laid out at full length across the surface. The friction of these wires keep your machine from toppling over when mining at full power with the last wire. As wires are worn out you simply use them as anchoring wires instead of mining wires. To move you pull them back a little at a time to reduce the length of each one across the landscape, otherwise you may topple over when you try to pull back the last wire.
• To program this is very easy in day-to-day running operation. The wire will deflect off anything solid so you can pretty much just tell it to run continuously in one direction for days at a time. Meanwhile with a traditional digging mechanism each action has to be thought-out and programmed from Earth, and then some portion of those actions will be cancelled by sensors detecting something unexpected (such as an unexpected amount of force on the digging arm). The only human interaction it really needs in daily operation is that the wire occasionally has to be used in reverse to clean the solar power panels.
• I have an hypothesis that it may be best to use a heat-based energy system, heat-exchangers that heat some gas up that is run through gas turbines, because that will provide mechanical force to the wheel even if a solar flare fries the entire computer system. So even if there is a complete systems failure the machine will collect and sort dust until the wire fails or gas turbine fails. There are some mechanical methods you could use to make the machine change to the next wire if a wire fails, even if the computer is fried (A mechanical RPM sensor that latches onto the next wire once the RPM exceeds that of normal operation). The main reason why I think this might be better, even though photovoltaics is probably more reliable, is because once the machine is utterly broken you end up with pipes, heat-exchangers and gas-turbine parts left over, not a heap of broken photovoltaic cells which are no use to anyone who might be based around said broken mining vehicle. So if you use the same standard parts in this mining vehicle as your habitat module and refinery vehicle and so forth, from easily recycled alloys and plastics, then you get more use from the mass you paid to get off planet Earth.
• The machine can also cut through big boulders if there happens to be any (explaining how is a bit too messy for this short intro to the concept). Not to mine them itself, but it can certainly make cuts that gives access for other machines to sample the contents of the boulder. I would only do this once you can make wires in-situ however.

So there you have it, probably the simplest, cheapest method to mine remotely in space. One moving part under constant use, while the motor that turns the string-shooter in a 360 degree arc will practically never fail because its not used continuously, and the mechanism that switches wires will also never wear compared to the constantly running one moving part.

Of course this can’t mine huge rocks, but as you make more wire-material where you mine, you can simply make the wire larger with more surface roughness to begin picking up larger pebbles. This can be achieved by simply winding the smaller gauge wires you begin with, into larger wires. So you only ever need the machinery to make really thin wire in-situ with the elements you mine (for example magnesium). And the tool to wind wires around each other.