Author Topic: new M-AM propulsion technique?  (Read 5464 times)

Offline rdheld

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new M-AM propulsion technique?
« on: 09/29/2016 11:34 AM »
has this been discussed before?

Offline Nilof

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Re: new M-AM propulsion technique?
« Reply #1 on: 09/30/2016 09:15 PM »
I'd call it an antimatter production technique, certainly not a propulsion technique. Antimatter is a method of storing energy, not an energy source. Making antimatter on board of a spacecraft makes as much sense as making hydrogen on board of a hydrogen car while on the highway. If you have the energy to do that, you can use it directly.

With that said, lasers approaching the Schwinger limit is a very real thing, and is definitely of interest for the experimental physics community right now. It might become a viable way of producing positrons eventually, but I'm very sceptical about photon-photon scattering ever being more efficient than scattering between charged particles for antimatter production.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #2 on: 10/26/2016 08:17 AM »
Positron dynamics has had some sort of milestone passed in the proof of concept/prototype department if a couple of new Next Big Future articles are not hype. if they continue on track with their cubesat it will eventually lead to antimatter catalyzed fusion with a top end of ten percent c.

http://www.nextbigfuture.com/2016/10/positron-dynamics-vision-of-antimatter.html

http://www.nextbigfuture.com/2016/10/positron-dynamics-near-term-work-to.html



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Offline rdheld

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Re: new M-AM propulsion technique?
« Reply #3 on: 10/26/2016 11:47 AM »
Stormbringer, how believable is the information in those links?

Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #4 on: 10/26/2016 05:43 PM »
well the technical stuff seems believable to me but the thing is that they have to rely on money not yet in evidence in order to get to the cube sat let alone a fieldable craft of some sort after that.
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Online meberbs

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Re: new M-AM propulsion technique?
« Reply #5 on: 10/26/2016 06:11 PM »
I don't have a very thorough background in particle physics, but it is enough to show that their technical stuff is very, very wrong.

In the past I saw information from them that looked promising, but the main question I had was how does antimatter catalyze fusion. My research turned up no mechanism for this. Now that they have more details of the fusion mechanism I can clearly say that their idea is nonsense.

The issues start with this formula:
positron annihilation: e⁺ + matter → pion (5%) or kaon (95%)

First of all "matter" is not a particle, and putting it in a reaction formula like that is just silly.

Breaking it down, the reasonable things that could be "matter" in this context are a proton, a neutron, or an electron. (Anything else is unstable particles we can't store)

Proton: I know of no interactions between protons and positrons, and since they have "moderated" (slowed down) their positrons, then no annihilation type interaction would result because electrostatic repulsion would keep them apart.

Neutron: This is unlikely again because neutrons would be in a nucleus, and electromagnetic repulsion would keep slow positrons away. If they did get through, the interaction would be turning the neutron into a proton, the reverse of the decay that created the positron (an anti-? neutrino would also be involved) This is only energetically possible in some atoms, and doesn't do what they claim anyway.

Electron: This is what would happen essentially all of the time, and would just produce gamma radiation. The energy involved (2 electron masses with minimal kinetic energy) This is nowhere near the energy required for a kaon, which is made of 2 quarks, and is much more massive (~490 MeV) than the energy available in this situation (~1MeV)

I have some doubts about the muon catalyzed fusion bit as well, but there is no way they are turning positrons into muons to begin with, by any imaginable mechanism.

Offline as58

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Re: new M-AM propulsion technique?
« Reply #6 on: 10/26/2016 07:39 PM »
Apparently a magical step has been omitted where a positron turns into an antiproton which then annihilates and produces mesons. The people behind the company seem to have at least some education in physics, so I'm sure they haven't made such an elementary error. I guess the website is responsible for the bungled explanation.

Offline rdheld

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Re: new M-AM propulsion technique?
« Reply #7 on: 10/26/2016 10:56 PM »
i thought that electron positron annihilation gives only two or three photons, depending on the momentum?

Offline ChrisWilson68

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Re: new M-AM propulsion technique?
« Reply #8 on: 10/27/2016 12:04 AM »
Only the original post and first response in this thread are actually about the original topic, which is the paper posted in the original post.

Then there was an off-topic post about a company doing anti-matter-catalyzed fusion.  Great, but it should be in a different thread.  It's a very different technology idea.

Is there any chance we could get this split into two different threads?
« Last Edit: 10/27/2016 12:04 AM by ChrisWilson68 »

Offline Rei

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Re: new M-AM propulsion technique?
« Reply #9 on: 03/25/2017 12:19 PM »
Just found this old thread.

Reviewing the Positron Dynamics videos, I see nothing about kaons and muons. I see that mentioned on this Next Big Future article:

http://www.nextbigfuture.com/2016/10/positron-dynamics-vision-of-antimatter.html

But that doesn't correspond with what's shown even the screenshots that they link. I have to wonder if that's their own speculation.

The Positron Dynamics videos - eg:



... state that the process is:

22Na -> 22Ne + e+
e+ moderation
e+ e- annihilation on a "dense deuterium" target -> gamma (that would be 2 γ (0.511 + 0.511 = 1.022 MeV) or potentially 1 γ = 1.022 MeV in the presence of a third body)
γ -> trigger fusion -> hot ions
hot ions -> magnetic nozzle -> thrust

I'm curious as to the mean free path of 0.511 MeV gamma in deuterium... I went to the NNDC sigma server, but they don't seem to have anything like that.  I'm thinking somewhere in the ballpark of 5-10cm.  But they can't afford to thermalize the 3He or T + p reaction products. So they're probably constrained to the same sort of geometric issues affecting fission fragment rockets. Makes me wonder if they're likewise looking at having the fuel as a suspended dust for cooling. But then again, how do you keep D2 frozen in the middle of a nuclear reactor?  Maybe it's bound as a hydride. Or sealed inside ultra-thin shells that have a low absorption cross section for the reaction products and positrons.  But if it's a gas inside a shell, that wouldn't be "dense".

Let's see... 0.511 yields up to ~1eV in γ + p -> γ' + p, 1.022 up to ~2eV.  Hmm... would that really be enough for a meaningful fusion yield?

I have to wonder what they mean by "dense deuterium" on their diagram. I really wish they'd gone more into detail on the gamma conversion aspects... another thing about their diagram, maybe it's just how they drew it, but it looks like the positron is hitting some sort of miniscule pellet. Which makes me wonder if the energy from the gamma is supposed to be for compression...  Could random gammas really give you enough heat and compression to ignite tiny pellets?  Hmm...

And more to the point, if the whole goal is to set off fusion reactions with gamma, why not just have gamma emitters onboard instead of going through the whole positron generation / moderation process?  Handling difficulties?  They could start with parent isotopes that decay to gamma emitters, so they wouldn't be so hazardous in the beginning...
« Last Edit: 03/25/2017 02:34 PM by Rei »

Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #10 on: 04/23/2017 09:28 PM »
I didn't want to start another thread for this but i found an old article on the casimir effect possibly being of use for repelling or levitating certain materials and wondered if this could be tinkered with to make better antimatter storage?

https://phys.org/news/2012-04-prospects-quantum-levitation.html#nRlv

And speaking of casimir force there was this on my feeds this morning:

https://phys.org/news/2017-04-harness-mysterious-casimir-tiny-devices.html

Woohoo!
« Last Edit: 04/23/2017 09:31 PM by Stormbringer »
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Offline as58

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Re: new M-AM propulsion technique?
« Reply #11 on: 04/24/2017 09:08 AM »
Just found this old thread.

Reviewing the Positron Dynamics videos, I see nothing about kaons and muons. I see that mentioned on this Next Big Future article:

http://www.nextbigfuture.com/2016/10/positron-dynamics-vision-of-antimatter.html

But that doesn't correspond with what's shown even the screenshots that they link. I have to wonder if that's their own speculation.

Sorry for being off topic, but this has turned mostly into a Positron Dynamics thread anyway.

With nextbigfuture it's a pretty sure bet that it's their own speculation, hype and misunderstanding (such as confusing antiprotons and positrons).

It seems that what Positron Dynamics have developed is a more efficient method for cooling positrons. The cooled positrons are then used in ways that are not really explained and IMO seem to be close to 'and then magic happens'. There seems to be a lot of inspirational talk about going to stars but little about how all that is actually done.

Quote
And more to the point, if the whole goal is to set off fusion reactions with gamma, why not just have gamma emitters onboard instead of going through the whole positron generation / moderation process?  Handling difficulties?  They could start with parent isotopes that decay to gamma emitters, so they wouldn't be so hazardous in the beginning...

Yeah, if high-energy photons are what you want, there are other ways to do that (even without any radioactive isotopes at all).

Offline Star One

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new M-AM propulsion technique?
« Reply #12 on: 04/24/2017 09:55 AM »
I didn't want to start another thread for this but i found an old article on the casimir effect possibly being of use for repelling or levitating certain materials and wondered if this could be tinkered with to make better antimatter storage?

https://phys.org/news/2012-04-prospects-quantum-levitation.html#nRlv

And speaking of casimir force there was this on my feeds this morning:

https://phys.org/news/2017-04-harness-mysterious-casimir-tiny-devices.html

Woohoo!

I posted a related article on the EM drive thread last week trying to get a feel for its validity but didn't get any response to it.

Here it is.

https://m.phys.org/news/2017-04-physicist-strange-nanoparticles.html

Here's the paper.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.133605

I also found this recent piece.

https://m.phys.org/news/2017-04-harness-mysterious-casimir-tiny-devices.html

Related papers.

https://www.nature.com/nphoton/journal/v11/n2/full/nphoton.2016.254.html

https://www.nature.com/nphoton/journal/v11/n2/full/nphoton.2016.277.html
« Last Edit: 04/24/2017 10:05 AM by Star One »

Offline Stormbringer

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Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #14 on: 11/02/2017 02:47 AM »
also a funding update. they are 80 percent there for their latest financing attempts:

https://www.nextbigfuture.com/2017/11/positron-dynamics-1-5-million-bridge-round-fund-is-still-open.html
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Offline as58

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Re: new M-AM propulsion technique?
« Reply #15 on: 11/02/2017 02:42 PM »
I still have no idea how their technique for cooling positrons is supposed to help in generating thrust.

Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #16 on: 11/03/2017 02:11 AM »
using positron annihilation for propulsion is fairly sketchy compared to antiprotons anyway but one old school idea was using the  released energies and light to heat another medium that is used for exhaust either through ablation of something like tungsten or using the heated tungsten or whatever to heat a working medium. This new method seems to bypass a lot of those steps in the Rube Goldberg style of the older positron schemes.
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Online meberbs

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Re: new M-AM propulsion technique?
« Reply #17 on: 11/03/2017 02:37 AM »
using positron annihilation for propulsion is fairly sketchy compared to antiprotons anyway but one old school idea was using the  released energies and light to heat another medium that is used for exhaust either through ablation of something like tungsten or using the heated tungsten or whatever to heat a working medium. This new method seems to bypass a lot of those steps in the Rube Goldberg style of the older positron schemes.
I am not sure how you think it "bypasses a lot of steps" it is extreme Rube Goldberg.
First they throw out most of the energy from the nuclear decay process in their "moderation device" They apparently just let this all go to waste. They then somehow catalyze fusion, apparently by positron annihilation generating muons or something despite being orders of magnitude short on the required energy, and the charge not working out. After they magically do this, they have to somehow extract energetic charged particles from the fusion when energetic charged particles are not a result of hydrogen fusion.

Their whole point is to capitalize on the energy density of antimatter, but really are getting energy from nuclear decay and fusion, and being very inefficient about it on top of the magic impossible steps.
« Last Edit: 11/03/2017 04:33 AM by meberbs »

Offline rdheld

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Re: new M-AM propulsion technique?
« Reply #18 on: 11/03/2017 10:25 AM »
what link or reference tells me how thrust is produced?

Offline Stormbringer

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Re: new M-AM propulsion technique?
« Reply #19 on: 11/03/2017 10:45 AM »
what link or reference tells me how thrust is produced?
a quick look leads to this older article which explains it in more detail than my recent link

https://www.nextbigfuture.com/2016/10/positron-dynamics-vision-of-antimatter.html

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