Best Antimatter Rocket Fuel

[Tommygun]

Then it would not be a Bussard Ramjet, it would be a Ram-Augmented Interstellar Rocket (RAIR)

http://www.projectrho.com/public_html/rocket/slowerlight.php#id--Bussard_Ramjet_Derivatives

The difference being that while it may not be subject to the drag effect of a Ramjet, the drawback is that it no longer has infinite fuel, when the on-board supply of antimatter runs out, so does the thrust.

Oh well, I thought I was being clever, I guess it's hard to have an original idea when there are seven billion other people on a planet.

So are there any theories on how dark matter reacts to antimatter?

Edited May 13, 2013 by Tommygun

[Fractal_UK]

If the confinement of anti-hydrogen is going to be a problem, then use ionized anti-hydrogen.

You can't really store antimatter as anti-protons, the charge is a real problem. It's great if you want to store one single anti-proton, that's really easy, you can stick it in a magnetic trap but if you want to store fuel at anything like a reasonable density then you need to ensure that your fuel doesn't strongly repel the rest of your fuel or you'll quickly find you're using more energy storing it than you can actually extract out of using it in your reactor/engines. That is why it's a requirement for any practical application of antimatter drives/reactors to have neutral antimatter.

[K^2]

Can the Mössbauer Effect produce collimated photons, even in principle? If so, then you're right that that would be the ideal photon drive.

I only understand the effect qualitatively, so I can't tell for sure. But dimensions of the lattice might make a difference. The biggest problem is that I don't know how you'd get rid of all the other emission modes, so it's kind of hard to tell what sort of side effects the non-existing technique would have.

[architeuthis]

Yes, got it in one. As long as there are no antimatter mines, antimatter is not a fuel, it is an energy transport mechanism.

http://www.projectrho.com/public_html/rocket/basicdesign.php#id--Power_Plant--Exotic_power_sources--Antimatter_Power

It seems there may be naturally occurring sources of anti-protons albeit in minuscule quantities. I read a blog post over at Centauri Dreams which mentioned the possibility of strong natural magnetic fields (such as Earth's) trapping anti-protons created through pair production when energetic cosmic rays interact with our atmosphere. New ones are trapped at the same rate as they decay so there is an equilibrium storage of up to 160 ng of the stuff up in the van Allen belt.

You can't really store antimatter as anti-protons, the charge is a real problem. It's great if you want to store one single anti-proton, that's really easy, you can stick it in a magnetic trap but if you want to store fuel at anything like a reasonable density then you need to ensure that your fuel doesn't strongly repel the rest of your fuel or you'll quickly find you're using more energy storing it than you can actually extract out of using it in your reactor/engines. That is why it's a requirement for any practical application of antimatter drives/reactors to have neutral antimatter.

To roughly quote my pre-crash self: there are trade offs. On the one hand with a positron photon drive you are essentially riding a Death Star class gamma-ray laser to the stars, and how awesome is that? But as you noted, storing practical amounts positrons for interstellar missions is problematic. There are limits to the density of positrons that can be stored in an electromagnetic bottle like a Penning or Paul trap, after all you are trying to fight truly colossal Coulombic forces by storing charged particles in high densities. The Brillouin density limit is n=(e_0*B^2)/(2m_e) (where n is the number of positrons, B is the magnetic field in Tesla, e_0 is the permittivity constant, and m_e is an electron mass). In what is probably an optimistic case you would need 225 million 1m^3 Penning traps each with a 1000 T magnetic field in total to store a single ton of positrons. In so many ways does this easily fulfill Clarke's 'sufficiently advanced technology' axiom. On the bright side though, if you are able to create fields of these strengths, you can probably use them to produce antimatter very efficiently.

On the other hand you can avoid the these neutron-star-esque strength magnetic fields by using anti-hydrogen as fuel instead. Charged pi-mesons are funneled out of a super-conducting magnetic nozzle with exhaust velocities anywhere between .3c and .94c. But there is a problem: try keeping an anti-hydrogen Bose-Einstein condensate snowball close to >0.1 K anywhere within a thousand kilometers of an engine with thermal power on the order of 9E15 W (assuming say a 10,000 ton wet mass seedship accelerating at a max of 1 g). It is kind of like trying to keep a beer cold while it sits under a SSME at main engine start. Here it's the plumbing that's 'indistinguishable from magic'.

Edited May 13, 2013 by architeuthis

[nyrath]

It seems there may be naturally occurring sources of anti-protons albeit in minuscule quantities. I read a blog post over at Centauri Dreams which mentioned the possibility of strong natural magnetic fields (such as Earth's) trapping anti-protons created through pair production when energetic cosmic rays interact with our atmosphere. New ones are trapped at the same rate as they decay so there is an equilibrium storage of up to 160 ng of the stuff up in the van Allen belt.

Yes, I do mention that in what I wrote at the link I gave you. However since 110 nanograms has the energy content of half a fluid ounce of gasoline, you probably cannot use this as the source of energy for your Death Star class photon drive. The best you can do is use the antiprotons to catalyze fission or fusion or something.

[Fractal_UK]

In what is probably an optimistic case you would need 225 million 1m^3 Penning traps each with a 1000 T magnetic field in total to store a single ton of positrons. In so many ways does this easily fulfill Clarke's 'sufficiently advanced technology' axiom. On the bright side though, if you are able to create fields of these strengths, you can probably use them to produce antimatter very efficiently.

On the other hand you can avoid the these neutron-star-esque strength magnetic fields by using anti-hydrogen as fuel instead. Charged pi-mesons are funneled out of a super-conducting magnetic nozzle with exhaust velocities anywhere between .3c and .94c. But there is a problem: try keeping an anti-hydrogen Bose-Einstein condensate snowball close to >0.1 K anywhere within a thousand kilometers of an engine with thermal power on the order of 9E15 W (assuming say a 10,000 ton wet mass seedship accelerating at a max of 1 g). It is kind of like trying to keep a beer cold while it sits under a SSME at main engine start. Here it's the plumbing that's 'indistinguishable from magic'.

Solving the problems with anti-hydrogen storage seem far more plausible than what you are suggesting would be required to store positrons. Producing such a ludicrous magnetic field would require both an incredible amount of current as well as some remarkable superconducting material capable of remaining superconducting at orders of magnitude higher magnetic fields than we are aware of. That's before we even consider the fact that one ton of positrons (combined with one ton of electrons) would produce around 1.8x10^21J, that might seem like a lot but that is only a power output of about 60TW for 1 year. Any civilisation capable of such engineering would not utilise it for such a miniscule amount of power output, especially when you consider that you if your 225 million penning traps require more than about 250KW each to generate their 1000T magnetic fields (which they almost certainly would) you're actually consuming energy by storing your antimatter in that form.

There is not a strict requirement to utilise anti-hydrogen in a pi-meson type drive and indeed there are many reasons why you might not want to. A pi-meson drive sure has great specific impulse thanks to the relativistic exhaust but try maintaining a reasonable acceleration with it... 1G would be a pipe dream.

Utilising an antimatter reactor as a generator of both electricity and heat seems like a more plausible mechanism to me, that way you could use it to either directly heat exhaust gases or use the power for electromagnetic thrusters of some kind - something like an MPD thruster and it eliminates the problem of excessive piping of antimatter around.

It is, incidently, not neccessary to store your anti-hydrogen as a BEC. Keeping an atom cloud at relatively low temperature (<=1K) is relatively easy since it's still well above the doppler cooling limit while typically getting down to BEC temperatures requires discarding many of your atoms to achieve a far less numerous but colder cloud via evaporative cooling.