Solutions for near-term antimatter fusion propulsion using isotope breeding cycle

The world only produces a nanogram of antimatter every year but we cannot store any of it for any length of time.

Positron Dynamics has solutions to all of the huge problems to use the immense power of antimatter.

Positrons are 2000 times easier to produce than antiprotons. The positron or antielectron is the antiparticle or the antimatter counterpart of the electron.

Positrons are produced constantly from various isotopes. Isotopes are variants of a particular chemical element which differ in neutron number.

They get around the problem of generating and storing antimatter by breeding Krypton 79 isotope to constantly generate more and more positrons.

They will breed Krypton 78 to Krypton 79 by capturing neutrons from D-D fusion. Deuterium is one of two stable isotopes of hydrogen.

Surround a source of D-D fusion with 1 meter thick ten atmospheric pressure Krypton 78 gas will capture almost all of the neutrons from D-D fusion.

The D-D fusion will be triggered using positrons. Thus the positron triggers the fusion which produces neutrons to breed more isotope, the isotope produces the positrons.

NASA has provided funding for Positron Dynamics with a Phase I NASA Innovative Advanced Concepts study.

100 micrograms of Krypton 79 can the start and in 3-4 months, the 10 kilograms of Krypton 78 would breed to Krypton 79. This would be able a proposed system to produce 60 newtons of thrust. This would enable the system of antimattered trigger fusion to propel a spacecraft to about 10% of the speed of light and enable a 50 year trip time to Proxima Centauri.

The fuel breeding cycle is shown above.

Krypton isotopes to generate hot positrons.
Use their system to moderate the positrons so they can be used.

They need to efficiently create more isotope to get more positrons instead of using magnetic storage.

Details of how the positron triggered fusion reaction produces thrust

Diverting, or directing, the trapped energy from the annihilation process to propel the rocket. To achieve this, Weed, CEO of Positron Dynamics, and his team use fusion reactions to transfer the kinetic energy of the gamma-ray producing positron beam into charged particles. Because charged particles “like” to follow magnetic field lines, Weed and his team employ magnets to direct the energy and produce the holy grail of thrust.

Timelines and the Future

Positron Dynamics proposed milestones which have had some slippage:

— Laboratory demonstration of “scalable” thrust using positrons. Six to eight months.

— Positron-powered launch of small “cubesat” satellite into low-Earth orbit, demonstrating orbital change from positron propulsion. Eighteen months to two years.

This propulsion system could be used in satellite constellations, for example — as part of a global network of broad-band internet, enabling virtually anyone on the planet access to the internet.

— Launch of another rocket to further demonstrate the feasibility of positrons to power a spacecraft. Two-and-a-half years (probably followed by a succession of other unmanned spacecraft over a period of years).

— Launch of a positron-propelled spacecraft to Mars. In the 2030s.

Degrading materials limits the scaling of the propulsion system.

Previous discussion of cubesat demonstration and Sodium 22 isotope

* Sodium 22 isotope (which they get in liquid form) will produce positrons which will be moderated with semiconductor structures

Liquid Sodium 22

The Moderator structure

Cold positrons instead of 1 million times hotter than the sun

* moderated cold positrons produced in a gamma ray beam
* The beam hits the dense film of deuterium which produces fusion products
* the fusion products are now charged particles which can be then guided as propulsive thrust with magnets

positron emission: ²²Na → ²²Ne + 1 e⁺ + 0.94 MeV of kinetic energy
positron annihilation: e⁺ + matter → pion (5%) or kaon (95%)
kaon decay: kaon → muon (80%) in 20 nsec
muon capture: muon + D or T → mD or mT
fusion (1): mD + T → ⁴He + ¹n + muon (non-consumed) (0.01 – 0.1 nsec)
fusion (2): mT + D → ⁴He + ¹n + muon (non-consumed) (0.01 – 0.1 nsec)
fusion (3): mD + D → ³He + ¹n + muon (non-consumed) (0.07 – 1.5 nsec)
muon decay: muon + time → electron + neutrinos (2,200 nsec)

²²Na (sodium missing one neutron) is almost perfect. Halflife of 2.6 years.

Each gram of the stuff:

1 g • ( 6.023×10²³ atom/mol ÷ 22 AMU ) = 2.74×10²² atoms per gram
= 434,400,000,000,000 decays per second.
× 1.6×10⁻¹⁹ J/eV × 1,000,000 eV/MeV × 2.843 MeV/decay
= 197 joules per gram

Muon Catalyzed Fusion

Muons are unstable subatomic particles. They are similar to electrons, but are about 207 times more massive.

The α-sticking problem is the approximately 1% probability of the muon “sticking” to the alpha particle that results from deuteron-triton nuclear fusion, thereby effectively removing the muon from the muon-catalysis process altogether. Recent measurements seem to point to more encouraging values for the α-sticking probability, finding the α-sticking probability to be about 0.5% (or perhaps even about 0.4% or 0.3%), which could mean as many as about 200 (or perhaps even about 250 or about 333) muon-catalyzed d-t fusions per muon. Indeed, the team led by Steven E. Jones achieved 150 d-t fusions per muon (average) at the Los Alamos Meson Physics Facility. Unfortunately, 200 (or 250 or even 333) muon-catalyzed d-t fusions per muon is still not enough to reach break-even. Even with break-even, the conversion efficiency from thermal energy to electrical energy is only about 40% or so, further limiting viability.

However Muon Catalyzed fusion from antimatter would multiply the energy production from the antimatter.

Each muon catalyzing d-d muon-catalyzed fusion reactions in pure deuterium is only able to catalyze about one-tenth of the number of d-t muon-catalyzed fusion reactions that each muon is able to catalyze in a mixture of equal amounts of deuterium and tritium, and each d-d fusion only yields about one-fifth of the yield of each d-t fusion, thereby making the prospects for useful energy release from d-d muon-catalyzed fusion at least 50 times worse than the already dim prospects for useful energy release from d-t muon-catalyzed fusion.

However, Positron Dynamics is looking at the fusion for propulsion and not energy production. The fusion rate for d-d muon-catalyzed fusion has been estimated to be only about 1% of the fusion rate for d-t muon-catalyzed fusion, but this still gives about one d-d nuclear fusion every 10 to 100 picoseconds or so

Description of a pellet based antimatter catalyzed fusion system but gives an idea of performance based on percent of material that is fused

* the 6U cubesat that they will use to test the propulsion in space will be generating 100s of watts
* the propulsion will have delta V of 1 to 10 km/second
* Later systems will have more delta V and enable cubesats and small satellites to stay in orbit for years instead of days

* the cubesats with propulsion will enable very low orbit internet satellites

* in the 2020s if things go well they will be able to scale to 10 km/second to 100 km/second with 10-100 kilogram payloads for small probe exploration of the solar system
* Later beyond 2030, they will have regenerative isotopes for a lot more power and achieve ten million ISP and several kilonewtons of propulsive force. This would seem to require multiple propulsion units as the more recent discussion limited propulsion to 60 newtons.
* could enable 1G acceleration and deceleration propulsion which would 3.5 weeks to Pluto

57 thoughts on “Solutions for near-term antimatter fusion propulsion using isotope breeding cycle”

  1. I have to think the fraction of energy going into waste heat for this process would be horrific. Antimatter is primarily useful as a dense way to *store* energy, not as an intermediate step in producing fusion. But positrons have a relatively high ratio of charge to rest mass, making it difficult to store them densely. My personal opinion? Antimatter won’t have much use in space propulsion until we can manufacture anti-protons, too, so that we can store it as condensed anti-hydrogen.

    Reply
  2. I have to think the fraction of energy going into waste heat for this process would be horrific.Antimatter is primarily useful as a dense way to *store* energy not as an intermediate step in producing fusion. But positrons have a relatively high ratio of charge to rest mass making it difficult to store them densely.My personal opinion? Antimatter won’t have much use in space propulsion until we can manufacture anti-protons too so that we can store it as condensed anti-hydrogen.

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  3. Once we learn how to store antimeter someone will likely use it to literally blow up the planet. We need to focus on learning to use fission better in space to generate electricity. It has enough energy for all our needs in space in the coming future.

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  4. Once we learn how to store antimeter someone will likely use it to literally blow up the planet. We need to focus on learning to use fission better in space to generate electricity. It has enough energy for all our needs in space in the coming future.

    Reply
  5. The whole attractiveness of this proposal is that you never need to store any antimatter at all. You are breeding a radioisotope which gives off a positron when it decays, this positron is then immediately used to initiate a deuterium-deuterium fusion which produces the neutrons needed to breed more of the radioisotope you were using in the first place. Since there is never any accumulation of antimatter, there is no great hazard. Also, antimatter is a *really* expensive way to blow up the planet (I once did the math, it turns out that you would need an amount equal to the mass of a really big, we’re talking dinosaur killer class, asteroid of pure antimatter to blow up the Earth). Of course, if all you want to do is exterminate humanity, you wouldn’t need anywhere near that much, but you’d still need tons of the stuff. I just happened to be watching a video today where there was a quote from a scientist in 2006 of $250 million for 10 milligrams of positrons and a NASA quote in 1999 of $62.5 trillion (with a “T”) for a single gram of antihydrogen. Fission technology, what you are pushing as an alternative, is and always has been a far less economically costly way for humans to commit collective suicide were we of a mind to do so.

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  6. Would you care to elaborate on how nuclear pulse would be *safer*. If you look at what the article actually says, they start off with 100 micrograms of Kr79. Even if this were pure antimatter (which it isn’t) the energy yield of .1 milligram would be smaller than the smallest plausible nuclear device and at least a couple of orders of magnitude smaller than the 1 kiloton devices that Orion was talking about using. But wait, I can give an approximate energy yield for the trivial portion of the Kr79 that does end up as antimatter. A positron is ~1800 times less massive than a nucleon, of which Kr79 has… 79 (see how that works). So 79 * 1800 = 142,200 (I’m omitting the electrons, each of which are the same mass as the positron you get, but if you want to include them, the number is closer to 142,300). So the antimatter yield of the Kr79 is of the order of 1 nanogram of positrons, which has an energy equivalent about equal to a single stick of TNT and I remind you that this energy is NOT all being given off at once, the half life of Kr79 is 35 hours, according to Wikipedia. The cute idea here is that the positron initiates deuterium-deuterium fusion which gives off neutrons needed to “breed” Kr79 out of Kr78, so there is never a huge amount of the Kr79 around at any one time. Compared to the nuclear pulse proposals which would have a spacecraft with thousands of devices, each scarcely distinguishable from a nuclear bomb out in space, this is massively safer.

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  7. Hold your panic. Storing antimatter is not the same as producing it, which is a separate, very difficult problem of its own. Even when we solve both problems, we’d need an enormous amount of antimatter to blow up the planet. A single gram of antimatter has 2 * 1e-3 kg * (3e8 m/s)^2 = 18e13 J of energy (the famous E = mc^2, times 2 to account for the regular matter mass that has to react with the antimatter). This is equivalent to a 43 kiloton atomic bomb, about 3 times more than the bomb dropped on Hiroshima. The one dropped on Hiroshima is considered a rather small atomic bomb. The Earth’s gravitational binding energy is 2.2e32 J, so one would need 1.2e15 kg or 1.2 trillion tons of antimatter to blow it up. That’s equivalent to 52 trillion gigatons of explosive power. For comparison, the world’s total nuclear arsenal is estimated at ~14000 warheads of ~0.5 a megaton on average, so ~7 gigatons total. Right now we’re only producing one billionth of a gram of antimatter per year, according to this article. Our total global energy production is just shy of 20 terawatts. If we spent all of it on producing antimatter at 100% efficiency, we’d only be able to produce about 3.5 tons of antimatter per year. All that energy has to come from somewhere. So we are very very far from blowing up the planet. Even when both storage and production of antimatter are solved, it will likely be regulated at least as much as nuclear materials, and producing even single tons of antimatter would be extremely difficult. So this isn’t something you need to worry about. As for space uses, the problem with fission is that current reactor designs are very heavy. We need much better energy per mass for space applications.

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  8. The whole attractiveness of this proposal is that you never need to store any antimatter at all. You are breeding a radioisotope which gives off a positron when it decays this positron is then immediately used to initiate a deuterium-deuterium fusion which produces the neutrons needed to breed more of the radioisotope you were using in the first place. Since there is never any accumulation of antimatter there is no great hazard. Also antimatter is a *really* expensive way to blow up the planet (I once did the math it turns out that you would need an amount equal to the mass of a really big we’re talking dinosaur killer class asteroid of pure antimatter to blow up the Earth). Of course if all you want to do is exterminate humanity you wouldn’t need anywhere near that much but you’d still need tons of the stuff. I just happened to be watching a video today where there was a quote from a scientist in 2006 of $250 million for 10 milligrams of positrons and a NASA quote in 1999 of $62.5 trillion (with a T””) for a single gram of antihydrogen. Fission technology”” what you are pushing as an alternative”” is and always has been a far less economically costly way for humans to commit collective suicide were we of a mind to do so.”””

    Reply
  9. Would you care to elaborate on how nuclear pulse would be *safer*. If you look at what the article actually says they start off with 100 micrograms of Kr79. Even if this were pure antimatter (which it isn’t) the energy yield of .1 milligram would be smaller than the smallest plausible nuclear device and at least a couple of orders of magnitude smaller than the 1 kiloton devices that Orion was talking about using. But wait I can give an approximate energy yield for the trivial portion of the Kr79 that does end up as antimatter. A positron is ~1800 times less massive than a nucleon of which Kr79 has… 79 (see how that works). So 79 * 1800 = 142200 (I’m omitting the electrons each of which are the same mass as the positron you get but if you want to include them the number is closer to 142300). So the antimatter yield of the Kr79 is of the order of 1 nanogram of positrons which has an energy equivalent about equal to a single stick of TNT and I remind you that this energy is NOT all being given off at once the half life of Kr79 is 35 hours according to Wikipedia.The cute idea here is that the positron initiates deuterium-deuterium fusion which gives off neutrons needed to breed”” Kr79 out of Kr78″” so there is never a huge amount of the Kr79 around at any one time. Compared to the nuclear pulse proposals which would have a spacecraft with thousands of devices each scarcely distinguishable from a nuclear bomb out in space”” this is massively safer.”””

    Reply
  10. Hold your panic. Storing antimatter is not the same as producing it which is a separate very difficult problem of its own. Even when we solve both problems we’d need an enormous amount of antimatter to blow up the planet.A single gram of antimatter has 2 * 1e-3 kg * (3e8 m/s)^2 = 18e13 J of energy (the famous E = mc^2 times 2 to account for the regular matter mass that has to react with the antimatter). This is equivalent to a 43 kiloton atomic bomb about 3 times more than the bomb dropped on Hiroshima. The one dropped on Hiroshima is considered a rather small atomic bomb.The Earth’s gravitational binding energy is 2.2e32 J so one would need 1.2e15 kg or 1.2 trillion tons of antimatter to blow it up. That’s equivalent to 52 trillion gigatons of explosive power. For comparison the world’s total nuclear arsenal is estimated at ~14000 warheads of ~0.5 a megaton on average so ~7 gigatons total.Right now we’re only producing one billionth of a gram of antimatter per year according to this article. Our total global energy production is just shy of 20 terawatts. If we spent all of it on producing antimatter at 100{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} efficiency we’d only be able to produce about 3.5 tons of antimatter per year. All that energy has to come from somewhere.So we are very very far from blowing up the planet. Even when both storage and production of antimatter are solved it will likely be regulated at least as much as nuclear materials and producing even single tons of antimatter would be extremely difficult. So this isn’t something you need to worry about.As for space uses the problem with fission is that current reactor designs are very heavy. We need much better energy per mass for space applications.

    Reply
  11. I think Dave was assuming that the antimatter would be accumulated in significant amounts, rather than being used as it was generated.

    Reply
  12. My detailed comment didn’t go through, but here are the main points: – Even when storage of antimatter is solved, production of it is still a separate and very difficult problem. – The Earth’s gravitational binding energy is so large that one would need 1.2 trillion tons of antimatter to blow it up. – That’s equivalent to 52 trillion gigatons of explosive power, compared to “only” ~7 gigaton of the total global nuclear arsenal. – Even if we spent all of our energy production on making antimatter with 100% efficiency, we would only be able to make about 3.5 tons/year. – Antimatter will likely be regulated at least as much as nuclear materials. – So no need to worry about blowing up Earth. That said, causing mass extinction would be much easier. But it would be much easier still with traditional nuclear weapons.

    Reply
  13. I found video in the article very enlightening, worth watching if you haven’t already. Ryan Weed essentially suggests that their approach is the counterpart of trying to bring the National Ignition Facility into space with a tiny fraction of the mass that the actually bringing the NIF would entail. The thing is that the power that you need to actually produce the fusion is only the amount you need for doing the separation, collimation, etc. for the positrons and enriching the Kr79, so sustaining the fusion would seem, in principle, much easier then with say 192 uber powerful lasers. The D-D fusion itself is going to produce a lot of waste heat, but it seems to me that that this is going to be true for virtually any high Isp rocket motor. A Ve that is a fraction of c is going to need a massive amount of energy and that is going to mean a good bit of waste heat unless you have engines that are efficient to an unrealistic degree. I mean if we had some *other* way of sustaining fusion in something that isn’t unreasonably massive, I might be inclined to agree. But currently we don’t have any kind of controlled fusion that is self-sustaining whatever the mass budget. Until there is an alternative method of producing fusion propulsion that we know works, I’m inclined to give the “breed a positron emitter as an intermediate step” approach a shot at it.

    Reply
  14. I think Dave was assuming that the antimatter would be accumulated in significant amounts rather than being used as it was generated.

    Reply
  15. My detailed comment didn’t go through but here are the main points:- Even when storage of antimatter is solved production of it is still a separate and very difficult problem.- The Earth’s gravitational binding energy is so large that one would need 1.2 trillion tons of antimatter to blow it up.- That’s equivalent to 52 trillion gigatons of explosive power compared to only”” ~7 gigaton of the total global nuclear arsenal.- Even if we spent all of our energy production on making antimatter with 100{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} efficiency”” we would only be able to make about 3.5 tons/year.- Antimatter will likely be regulated at least as much as nuclear materials.- So no need to worry about blowing up Earth.That said”” causing mass extinction would be much easier. But it would be much easier still with traditional nuclear weapons.”””

    Reply
  16. I found video in the article very enlightening worth watching if you haven’t already. Ryan Weed essentially suggests that their approach is the counterpart of trying to bring the National Ignition Facility into space with a tiny fraction of the mass that the actually bringing the NIF would entail. The thing is that the power that you need to actually produce the fusion is only the amount you need for doing the separation collimation etc. for the positrons and enriching the Kr79 so sustaining the fusion would seem in principle much easier then with say 192 uber powerful lasers. The D-D fusion itself is going to produce a lot of waste heat but it seems to me that that this is going to be true for virtually any high Isp rocket motor. A Ve that is a fraction of c is going to need a massive amount of energy and that is going to mean a good bit of waste heat unless you have engines that are efficient to an unrealistic degree.I mean if we had some *other* way of sustaining fusion in something that isn’t unreasonably massive I might be inclined to agree. But currently we don’t have any kind of controlled fusion that is self-sustaining whatever the mass budget. Until there is an alternative method of producing fusion propulsion that we know works I’m inclined to give the breed a positron emitter as an intermediate step”” approach a shot at it.”””

    Reply
  17. It cant be used to literally blow up the planet. It stores energy and releases it at once. nobody can generate enough energy to store in antimatter to blow up the planet.

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  18. WOW. I’ve skeptical about their claims a long time. Now that they showed us details I’m impressed! We really might make it!

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  19. It cant be used to literally blow up the planet. It stores energy and releases it at once. nobody can generate enough energy to store in antimatter to blow up the planet.

    Reply
  20. WOW. I’ve skeptical about their claims a long time. Now that they showed us details I’m impressed! We really might make it!

    Reply
  21. Don’t positrons and electrons annihilate into two photons? Aren’t kaons ORDERS OF MAGNITUDE more massive than a positron and an electron combined, how can a positron possible annihilate and produce a kaon? How is this supposed to work?

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  22. Don’t positrons and electrons annihilate into two photons? Aren’t kaons ORDERS OF MAGNITUDE more massive than a positron and an electron combined how can a positron possible annihilate and produce a kaon? How is this supposed to work?

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  23. can’t some of that waste heat be channeled to thermally power other devices like additional ion drives on board systems and charging backup batteries ect… using A integrated thermoelectric generators

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  24. can’t some of that waste heat be channeled to thermally power other devices like additional ion drives on board systems and charging backup batteries ect… using A integrated thermoelectric generators

    Reply
  25. I’m pretty sure the decay energy of Kr79 is orders of magnitude less than the mass of a kaon, and these positrons are being moderated so their energy should be even less right?

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  26. I’m pretty sure the decay energy of Kr79 is orders of magnitude less than the mass of a kaon and these positrons are being moderated so their energy should be even less right?

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  27. The magnetic field of Saturn is the best local location to harvest antimatter in space. At any one time, it contains about a hundred mg of antimatter. Collecting such a small amount of material over such a large distance (from Saturn, no less) would be quite a challenge. We could collect smaller amounts from Earth’s magnetic field.

    Reply
  28. The magnetic field of Saturn is the best local location to harvest antimatter in space. At any one time it contains about a hundred mg of antimatter. Collecting such a small amount of material over such a large distance (from Saturn no less) would be quite a challenge. We could collect smaller amounts from Earth’s magnetic field.

    Reply
  29. Positrons and electrons that have little relative kinetic energy are most likely to annihilate into two photons. They could, with lower probability, annihilate into neutrinos. If the positron and electron have combined kinetic energy that is equal to or greater than the rest energy of heavier particles, the annihilation could produce those heavier particles. Thanks to Wikipedia article, “Electron–positron annihilation” for describing the annihilation mechanisms of positrons and electrons. The website, “The Particle Adventure” graphically illustrates the annihilation process, showing how at high energies, it produces charm quarks that then separate into D+ and D- mesons.

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  30. Positrons and electrons that have little relative kinetic energy are most likely to annihilate into two photons. They could with lower probability annihilate into neutrinos. If the positron and electron have combined kinetic energy that is equal to or greater than the rest energy of heavier particles the annihilation could produce those heavier particles. Thanks to Wikipedia article Electron–positron annihilation”” for describing the annihilation mechanisms of positrons and electrons. The website”””” “”””The Particle Adventure”””” graphically illustrates the annihilation process”” showing how at high energies”” it produces charm quarks that then separate into D+ and D- mesons.”””””””

    Reply
  31. The magnetic field of Saturn is the best local location to harvest antimatter in space. At any one time, it contains about a hundred mg of antimatter. Collecting such a small amount of material over such a large distance (from Saturn, no less) would be quite a challenge. We could collect smaller amounts from Earth’s magnetic field.

    Reply
  32. Positrons and electrons that have little relative kinetic energy are most likely to annihilate into two photons. They could, with lower probability, annihilate into neutrinos.

    If the positron and electron have combined kinetic energy that is equal to or greater than the rest energy of heavier particles, the annihilation could produce those heavier particles.

    Thanks to Wikipedia article, “Electron–positron annihilation” for describing the annihilation mechanisms of positrons and electrons. The website, “The Particle Adventure” graphically illustrates the annihilation process, showing how at high energies, it produces charm quarks that then separate into D+ and D- mesons.

    Reply
  33. can’t some of that waste heat be channeled to thermally power other devices like additional ion drives on board systems and charging backup batteries ect… using A integrated thermoelectric generators

    Reply
  34. Don’t positrons and electrons annihilate into two photons? Aren’t kaons ORDERS OF MAGNITUDE more massive than a positron and an electron combined, how can a positron possible annihilate and produce a kaon? How is this supposed to work?

    Reply
  35. It cant be used to literally blow up the planet. It stores energy and releases it at once. nobody can generate enough energy to store in antimatter to blow up the planet.

    Reply
  36. My detailed comment didn’t go through, but here are the main points:
    – Even when storage of antimatter is solved, production of it is still a separate and very difficult problem.
    – The Earth’s gravitational binding energy is so large that one would need 1.2 trillion tons of antimatter to blow it up.
    – That’s equivalent to 52 trillion gigatons of explosive power, compared to “only” ~7 gigaton of the total global nuclear arsenal.
    – Even if we spent all of our energy production on making antimatter with 100% efficiency, we would only be able to make about 3.5 tons/year.
    – Antimatter will likely be regulated at least as much as nuclear materials.
    – So no need to worry about blowing up Earth.

    That said, causing mass extinction would be much easier. But it would be much easier still with traditional nuclear weapons.

    Reply
  37. I found video in the article very enlightening, worth watching if you haven’t already. Ryan Weed essentially suggests that their approach is the counterpart of trying to bring the National Ignition Facility into space with a tiny fraction of the mass that the actually bringing the NIF would entail. The thing is that the power that you need to actually produce the fusion is only the amount you need for doing the separation, collimation, etc. for the positrons and enriching the Kr79, so sustaining the fusion would seem, in principle, much easier then with say 192 uber powerful lasers. The D-D fusion itself is going to produce a lot of waste heat, but it seems to me that that this is going to be true for virtually any high Isp rocket motor. A Ve that is a fraction of c is going to need a massive amount of energy and that is going to mean a good bit of waste heat unless you have engines that are efficient to an unrealistic degree.

    I mean if we had some *other* way of sustaining fusion in something that isn’t unreasonably massive, I might be inclined to agree. But currently we don’t have any kind of controlled fusion that is self-sustaining whatever the mass budget. Until there is an alternative method of producing fusion propulsion that we know works, I’m inclined to give the “breed a positron emitter as an intermediate step” approach a shot at it.

    Reply
  38. The whole attractiveness of this proposal is that you never need to store any antimatter at all. You are breeding a radioisotope which gives off a positron when it decays, this positron is then immediately used to initiate a deuterium-deuterium fusion which produces the neutrons needed to breed more of the radioisotope you were using in the first place. Since there is never any accumulation of antimatter, there is no great hazard.

    Also, antimatter is a *really* expensive way to blow up the planet (I once did the math, it turns out that you would need an amount equal to the mass of a really big, we’re talking dinosaur killer class, asteroid of pure antimatter to blow up the Earth). Of course, if all you want to do is exterminate humanity, you wouldn’t need anywhere near that much, but you’d still need tons of the stuff. I just happened to be watching a video today where there was a quote from a scientist in 2006 of $250 million for 10 milligrams of positrons and a NASA quote in 1999 of $62.5 trillion (with a “T”) for a single gram of antihydrogen. Fission technology, what you are pushing as an alternative, is and always has been a far less economically costly way for humans to commit collective suicide were we of a mind to do so.

    Reply
  39. Would you care to elaborate on how nuclear pulse would be *safer*. If you look at what the article actually says, they start off with 100 micrograms of Kr79. Even if this were pure antimatter (which it isn’t) the energy yield of .1 milligram would be smaller than the smallest plausible nuclear device and at least a couple of orders of magnitude smaller than the 1 kiloton devices that Orion was talking about using. But wait, I can give an approximate energy yield for the trivial portion of the Kr79 that does end up as antimatter. A positron is ~1800 times less massive than a nucleon, of which Kr79 has… 79 (see how that works). So 79 * 1800 = 142,200 (I’m omitting the electrons, each of which are the same mass as the positron you get, but if you want to include them, the number is closer to 142,300). So the antimatter yield of the Kr79 is of the order of 1 nanogram of positrons, which has an energy equivalent about equal to a single stick of TNT and I remind you that this energy is NOT all being given off at once, the half life of Kr79 is 35 hours, according to Wikipedia.

    The cute idea here is that the positron initiates deuterium-deuterium fusion which gives off neutrons needed to “breed” Kr79 out of Kr78, so there is never a huge amount of the Kr79 around at any one time. Compared to the nuclear pulse proposals which would have a spacecraft with thousands of devices, each scarcely distinguishable from a nuclear bomb out in space, this is massively safer.

    Reply
  40. Hold your panic. Storing antimatter is not the same as producing it, which is a separate, very difficult problem of its own. Even when we solve both problems, we’d need an enormous amount of antimatter to blow up the planet.

    A single gram of antimatter has 2 * 1e-3 kg * (3e8 m/s)^2 = 18e13 J of energy (the famous E = mc^2, times 2 to account for the regular matter mass that has to react with the antimatter). This is equivalent to a 43 kiloton atomic bomb, about 3 times more than the bomb dropped on Hiroshima. The one dropped on Hiroshima is considered a rather small atomic bomb.

    The Earth’s gravitational binding energy is 2.2e32 J, so one would need 1.2e15 kg or 1.2 trillion tons of antimatter to blow it up. That’s equivalent to 52 trillion gigatons of explosive power. For comparison, the world’s total nuclear arsenal is estimated at ~14000 warheads of ~0.5 a megaton on average, so ~7 gigatons total.

    Right now we’re only producing one billionth of a gram of antimatter per year, according to this article. Our total global energy production is just shy of 20 terawatts. If we spent all of it on producing antimatter at 100% efficiency, we’d only be able to produce about 3.5 tons of antimatter per year. All that energy has to come from somewhere.

    So we are very very far from blowing up the planet. Even when both storage and production of antimatter are solved, it will likely be regulated at least as much as nuclear materials, and producing even single tons of antimatter would be extremely difficult. So this isn’t something you need to worry about.

    As for space uses, the problem with fission is that current reactor designs are very heavy. We need much better energy per mass for space applications.

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  41. Once we learn how to store antimeter someone will likely use it to literally blow up the planet. We need to focus on learning to use fission better in space to generate electricity. It has enough energy for all our needs in space in the coming future.

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  42. I have to think the fraction of energy going into waste heat for this process would be horrific.

    Antimatter is primarily useful as a dense way to *store* energy, not as an intermediate step in producing fusion. But positrons have a relatively high ratio of charge to rest mass, making it difficult to store them densely.

    My personal opinion? Antimatter won’t have much use in space propulsion until we can manufacture anti-protons, too, so that we can store it as condensed anti-hydrogen.

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