Methods and Feasibility of Antimatter Mining?

Question

Say 200-300 years in the future, humankind has colonized much of the solar system, using a combination of laser thermal drives and solid-core nuclear rockets (fusion never really panned out). Suddenly, astronomers spot an odd object entering the solar system. The object turns out to be a kilotonne-scale chunk of rock, ordinary in every way except for the fact that the thing is made entirely of antimatter. Collisions with the interplanetary medium, and the energy they give off, slow down the object sufficiently for it to be captured by the solar gravity field and enter a slowly-decaying orbit somewhere in the region of Neptune. Obviously, this rock is a potentially enormous fuel source for both antimatter drives and commercial power reactors. The question is, how exactly is one going to get antimatter out of this thing? You can't exactly land equipment on it and start mining, and it's not like you can just start chipping off pieces of it. So, how exactly would one go about mining an asteroid made of antimatter? Also, for extra points, how plausible is the scenario laid out in the question, where an antimatter asteroid enters a slowly decaying orbit in the near edge of the Kuiper belt, and how long could such an orbit last.

Note: It has been brought to my attention that collisions with the interstellar medium may not be sufficient to slow the asteroid. As a result, a gravity assist from Neptune or a Kuiper Belt Object may be involved to make the capture of this asteroid more feasible.

Answer 1

One thing which other posters have not mentioned is the effects of the interplanetary medium on the asteroid and mining operation.

Before you can do anything, it would be very wise to "clear" the area around the asteroid. A massive "wake shield" in an orbit slightly ahead of the antimatter asteroid will create a zone of extremely hard vacuum behind it, and the antimatter will be safely secured from further unwanted contact with the interplanetary medium.

Since you want to manipulate the antimatter without touching it, using a high energy laser to vapourize small sections is a good start. As each bit of antimatter is "puffed" away from the asteroid like a puff of smoke, another laser can supply the energy to ionize it, allowing for suitable electrostatic and magnetic fields to guide the plasma into a Penning trap for storage and later use.

Proposed antimatter harvester. The ionized antimatter is collected here and funneled into a Penning Trap

Answer 2

Similar question but with a moon made up of antimatter. Is it realistic to have a moon made of antimatter?

My proposition there:

1. Cut some chunks off. You can do this using a laser. In the linked moon scenario you would have to blast stuff up and away from the moon because it would be too dangerous to approach. Your smaller chunk is more tractable in that respect.

2. Confine small chunk using no-touch vacuum maglev jar. Magnetic levitation would be ideal. If a strong enough magnetic field can levitate a frog, you should be able to magnetically levitate and confine your antimatter chunk within a magnetic coil. Just about everything is diamagnetic or paramagnetic to some degree and magnets don't care what kind of matter you are.

3. Keep jars someplace safe. The moon would be good.

Answer 3

How exactly would one go about mining an asteroid made of antimatter?

In short:

1. Laser ablation to blow off parts of the object. The laser can be put in orbit around the body, without physical contact with it.
2. Channel the plasma to the "box". The produced plasma can be channeled via a suitable magnetic field into a magnetic storage. Again, no physical contact.
3. Ship the "box". The magnetic storage can be sent to the following user.

Obviously you need a layer of safety: you don't want any interaction between any matter particle and the antimatter, so you need to provide an adequate shielding.

Answer 4

You're not really mining, more like controlled exploding.

There is no real extraction just cutting off usable chunks. to do that you just throwing normal particles at it, a superfine stream of low pressure hydrogen will cut this thing like a high power laser through styrofoam. An electron gun or ion gun will cut better than any laser for very little energy input, switching between the two works even better and as others have pointed out you can use this to give the antimatter a charge thus making containment easier.

Just don't use anything powerful you don't want an industrial cutting electron gun, you want something closer to one used in a vacuum tube. You also don't want anything near it, Thucydides idea of a wake shield is great, breaking this thing up would be very very bad for the solar system. As it plows into the solar wind you will have issues with pieces breaking off as it is. you have to worry about anything coming near it hitting these near invisible particles.

As much as diverting to a more convenient location is, the problem is the flecks of matter you will hit doing a pass, steering will be near impossible when every scrap of dust hitting it produces huge amounts of thrust, you have this problem anyway but it gets worst the closer you get to a planet. you want this thing as far from other objects in the solar system as possible then you try to catch it.

The containment vessel will be massively expensive, (likely wiping out any gains for fuel, but for science it is worth doing) you need a magnetic bottle of ludicrous proportions. On the upside as long as you can keep it as a solid containment is fairly easy, expensive but easy. It may be worth refrigerating the entire contraption to prevent heat transfer, radiative heat transfer will still work after all, if it starts outgassing it becomes much harder to deal with. A cold solid lump of antimatter is a lot easier to deal with than a hot gas cloud of antimatter, to the point that putting a sunshade in front of the containment vessel would be a good idea.

The idea is to store it far away form everything then cut off tiny chunks for transport, you will not generate power at its location (not more than to run its containment systems) you transport less dangerous chunks to places to generate power for other purposes. This thing is far too dangerous even bring inside the asteroid belt no matter what safeties you have.

Answer 5

Unfeasible due to frame challenge

If the thing is coming into the solar system, it is in a flyby trajectory. Deceleration due to contact with the interplanetary medium will reduce its velocity in two directions:

• Radial out: this will rotate the orbital path, but not change it enough to have an apoapsis (and therefore cause a capture);

• Retrograde: this can decellerate the object enough for a capture - but if a capture happens, this decelleration will never stop due to the object being made of antimatter. It will end up causing the object to go suborbital and eventually crash into the sun.

In either case, you won't have enough time to assemble a mining operation before it either exits the solar system or crashes into the sun.

Answer 6

Manipulate dust with electric field

First, shield the asteroid from further interaction from interplanetary matter as explained by other answers. Then, make it electrically charged using positrons. We can make positrons (anti-electrons) even with today's technology because they are product of one type of radioactive decay. Then, if there is any surface dust, it will start levitating because of electric repulsion, as it happens sometimes with the Moon regolith. The dust can be created artificially too with laser pulses.

Next, a computers will track all dust particles and use electric field to carefully guide one away and transport it to final destination, all the time by applying electric force (high voltage electrodes). If it detects the particle is moving toward one wall of container, it will put positive voltage on that wall and negative on the other side to stop or reverse the movement.

I believe managing charged antimatter dust particles will be much more efficient than taking care of antimatter plasma, because plasma particles must be moving at high velocities.

Answer 7

This really doesn't seem feasible.

I don't have hard numbers, but matter/antimatter annihilation is so incredibly energetic that this object wouldn't really have its own trajectory. any deviation in speed from the background medium would immediately be corrected by the increase in collisions on the front side. that means the object almost certainly wouldn't enter the heliopause, and if it did, it would immediately be repulsed by the solar wind. obviously if it were large enough, it could overcome those forces, but in that case, it would probably be so large that its surface reactions would probably give off more energy than the sun. good luck mining that.

Answer 8

Magnetic confinement seems to be a fairly common suggestion and would work in the technical sense, but the amount of energy actually required to magnetically confine an asteroid worth (over the lifetime of the "mine") would be extraordinary. This is particularly concerning given that the containment field would not only have to contain the antimatter under constant acceleration, but would also have to have to account for the acceleration/deceleration of the transport device.

Keep in mind that the frog example mentioned above required a 16 Tesla magnetic field using a bitter magnet requiring ~20 kiloamperes of current. That's the electrical draw of 130-200 modern households to levitate the mass of a frog under constant acceleration. Add to that additional mass imparted through acceleration and you very quickly get to energy levels that are not reasonable (not even going to go into dealing with angular momentum). While technically the antimatter would produce substantially more energy than what is needed to cover this, transportation this way just feels like an inefficient/overly technical response to a problem.

A better option would be to build a power plant directly around the asteroid, and to perform the energy generation activities within relatively close proximity. The antimatter could be moved through short term containment, or even better, could be directly blasted into the reaction chambers (requiring only a short containment for sealing etc). The energy produced can then be converted into far more "docile" states which can be transported with much less complication (For example as Ultra-compressed gases/liquids etc etc).

I know you have disqualified fusion energy as an option, but I think it's important to consider that such a discovery would substantially improve the feasibility of fusion energy production as a means of energy production. One of the primary hurdles to fusion energy is generating enough energy to initiate the fusion reaction to begin with. Current technologies operate using a similar magnetic containment principle, only in this case we are containing ionized plasma either with external or intrinsic magnetic fields. A major hurdle in the process is the mind numbing amount of energy require to initialize a fusion reaction (something on the order of 100 million degrees kelvin). Short of discovering the miracle of cold fusion, the next best option of achieving such incredible temperatures would be antimatter. In this regard, using antimatter as the seed to fusion reactions, this asteroid could effectively generate unlimited energy so long as the fusion reactors have a steady supply of fuel.

Answer 9

The IPM near Earth is 5 particles/cm^3. If we assumes this is 5 hyrdogen atoms we won't be far wrong.

First, lets do some Feynman math to see how plausible this is.

Everything is about as dense as water, give or take an order of magnitude. A water-density object that weights 1000 tonnes (or $10^6$ kg) is going to be about 10 meters on a side.

Solar escape velocity at Earth Orbit is about 40 km/s. So your asteroid will pass over a volume of 10 m * 10 m * 40 km / s or 4 * 10^6 m^3/s.

There are 100^3 cm^3 in a m^3, so this is 10^6 * 4 * 10^6 * 5 hydrogen atoms/second, or 4*10^12 hydrogen atoms/second.

There are 6*10^26 hydrogen atoms per kg, so this is 0.7 * $10^{-14}$ kg/s of hydrogen swept up.

Times two, times c^2, gives us about 1.25 kwatts.

The kinetic energy of a 1 kilotonne object moving at 40 km/s is 8*10^20 J. The gravitational binding energy of such an object is 8 J. This is a problem.

Assuming the energy released is 100% efficient at slowing the asteroid, it would take about a million light years at that speed to reduce the kinetic energy of this asteroid by 50%. Collisions with the ISM won't, on average, do anything detectible other than make the asteroid glow with high-energy photons (and deposit some heat).

If the asteroid hit something more substantial (say, a mote of dust or whatever), the first problem is that anything that can slow it down from solar escape velocity will also blow it apart.

The problem is that the binding energy of any natural asteroid is going to be tiny, and the KE of a comet is huge; any impact that is enough to soak the KE in a short period of time is going to shatter the asteroid.

Can chemically bound might survive such an impact? A pure anti-Tugsten has a chemical binding energy of 850 kJ/mol. That mol has a weight of a bit under 200 g. 1/2 (40km/s)^2 * 200 g is 160,000,000 J. So an impact that would slag the asteroid would shave off half-a-percent of the KE of the asteroid.

So no impact/ism based energy deposit is going to do anything useful.

For the asteroid to be captured, it will have to get extremely lucky with orbital mechanics. It falls inward, does a close pass by a gas giant that "slingshots" it. That might be enough to kick it into a long elipitical orbit. If the slighshot (through insane luck) then swung by another large planet "just right", it could shed more KE and have a less elongated orbit.

A traditional capture would involve doing this dozens of times over millions of years, where a a few failures results in the asteroid being ejected from the system or hitting a planet.

In your situation, the best you could hope for is losing 5-10 km/s from a gas giant flyby. It has to get lucky and avoid hitting anything larger than a mote of dust (even a mote of dust will create an explosion, but maybe not enough to destroy the asteroid).

Then you might be able to use a gravity tug, over decades, to move it into a better orbit.

Once you have it reachable...

To cut is, fire a stream of electricaly neutral particles (to avoid giving it a net charge; any electron you shoot at it will cause a random proton to be attracted to the object as it seeks to become electrically neutral). As even a ghostly amount of such particles hit, it will produce an extremely vigorous energy emission; far more than anything you could generate for anywhere near the same amount of effort. I might fire separate proton and electron beams to cut different spots, or have them merge into a neutral beam.

Once you have defeated whatever chemical bonds are keeping the asteroid together, they'll drift apart easily.

You won't want to get anywhere near the object. Even rocket exhaust should be avoided near the target; it will be insanely more dense than the ISM. So you might want solar sails, avoid being either up or down "wind" of it (downwind, because it will shed antimatter; upwind, because you'll shed matter). You'd cut a piece off, then can move that piece by hitting it very gently with a beam.

Capturing an isolated piece becomes extremely tricky. Tricks with magnetic bottles etc are fine, but probably the easiest is to throw near-vacuum matter at it and let it glow and move itself.

You'd maintain some kind of defence system around the anti-asteroid, to avoid even dust particles from hitting it. As noted, a few microgram dust particle is enough to give it a kick enough to utterly change orbits; a defence system powerful enough to detect [b]every little bit[/b] of microgram dust and deflect it would be an extreme challenge.