# Anti-matter Vs. Fusion power Rockets



## Velocius quam lucem (Jun 4, 2013)

If You write science fiction, this might be a topic that should garner some consideration. Many modern SF writers use Anti-matter/matter (controlled) as a source of power, and for the kilometer per micro-gram it certainly would out-do fusion. 

The problem is, with our current state of affairs, fusion is more likely to be feasible in the next two to five hundred years. Why? Anti matter is to endothermic, and expensive. 

Here's a discussion from space.com:

Anti-matter vs. Fusion

They are actually suggesting using antimatter to get the fusion reactions going, but then fusion would take over. 

Thoughts anyone?


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## chrispenycate (Jun 4, 2013)

Unless we can mine anti-matter somewhere (doubtful) it's a way of storing energy rather than generating it. That is, at least as much energy goes into creating it as can ever be pulled out, sort of like a chargeable battery. So, Hamilton in his "Night's dawn" trilogy used solar energy to manufacture antimatter, or Haldiman (Worlds enough and time) found a convenient source close enough to the solar system to mine from.

Obviously, as an energy source antimatter is several orders of magnitude more efficient than fusion, but containment is a serious challenge; it obviously can't be held in anything material, and the space in which it is kept has to be a rather spectacularly good vacuum, manipulating it must be done with fields, magnetic, electrostatic, gravitational, whatever. Well shock mounted, too.

And it is not purely Mvsquared (energy) that is our limitation in high velocity travel; Mv, reaction mass will make up the principal inertial limitation, and even with a perfect photon drive we can't get up to the 90%c needed for economic star travel; we absolutely need new physics (well, actually we could get up to speed; we just wouldn't be able to slow down again). That's with unlimited energy. 

Whereas hydrogen is the commonest substance in the universe, and sticking a couple of molecules of it together to make a helium nucleus gives a very reasonable amount of energy; pushing it a bit harder to get oxygen or carbon is even better. Yes, it gets a bit warm for material barriers, but that's only while it's actually fusing; you can store it on Earth, without worrying about stray magnetic fields.

All right, we can't do it yet; but we've managed an uncontrolled close equivalent (which might be a primitive propulsion system if done right; a series of hydrogen bombs thrown out of the back of a spaceship, exploding right behind it, give a serious acceleration), so it's safe to bet it's possible, while the antimatter created until now has had a lifetime measured in serious negative exponentials of a second.


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## Velocius quam lucem (Jun 4, 2013)

You make some good points. I suppose I should have selected these excerpts from the article to show what propelled me in the direction of my current opinion:

"Perhaps the biggest challenge (in creating antimatter) is obtaining enough antiprotons — which can be produced in particle accelerators — and storing them for long enough to make a far-flung space journey feasible.

According to the "Technology Frontiers" report, about 1.16 grams of antiprotons would be required for a trip to Jupiter. That may not sound like much, but production levels are currently measured in the billionths of a gram.

Antiprotons are extremely expensive; a few grams would cost multi-trillions of dollars," Hay said. "I believe the total production so far since the 1950s is on the order of like 10 nanograms.""


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## chrispenycate (Jun 4, 2013)

Yea, I went round to CERN and asked my contact there delivery delays on enough antimatter to power my starship – less than a kilogram – and he said 'come back in ten thousand years'. Not encouraging.


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## Mirannan (Jun 4, 2013)

There are a couple of points not so far made that I think are worth mentioning. First, storing either antiprotons or positrons is going to be very difficult; for storage of any useful amount of the stuff, the antimatter is going to have to be neutral. Storing neutral hydrogen with the use of magnetic fields isn't easy; anti-iron or some such might be easier to deal with but how the heck does one make that?

The other point is a bit more subtle. Fusion can be arranged to put out most of its energy in forms that actually do some good because they either can be manipulated (alpha particles) or just dump their momentum into something solid (gamma rays and neutrons). There is some loss in neutrinos, but it isn't all that much.

However, IIRC proton/antiproton annihilation creates quite a lot of its energy in exotic neutral particles such as various mesons, and also in high-energy neutrinos. Both of these will zip right through anything that you're trying to extract their momentum with, and are emitted isotropically - with a resultant thrust of zero, natch.

In other words, a far amount of the much higher energy density of antimatter is going to be negated by the fact that the energy generated is in completely useless forms.


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## Velocius quam lucem (Jun 4, 2013)

Mirannan said:


> The other point is a bit more subtle. Fusion can be arranged to put out most of its energy in forms that actually do some good because they either can be manipulated (alpha particles) or just dump their momentum into something solid (gamma rays and neutrons). There is some loss in neutrinos, but it isn't all that much.



I may be reading this wrong, but I suspect you may be confusing "fusion" with "fission".

We've been using fission in "nuclear reactors" for quite some time, but there is no commercial fusion reactor available as of this writing. France is working on one. (ITER) The good thing about fusion is it isn't outwardly radioactive, but it requires immense energy input to start the reactions. Basically, you are taking two protons, two neutrons, and two electrons into a state of plasma (breaking the weak nuclear force) and then allowing them to re-combine into helium. That reaction is exothermic so it produces more energy than it takes in.


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## Velocius quam lucem (Jun 4, 2013)

chrispenycate said:


> Yea, I went round to CERN and asked my contact there delivery delays on enough antimatter to power my starship – less than a kilogram – and he said 'come back in ten thousand years'. Not encouraging.



You have a contact at CERN???!!!   I'm envious.


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## Bowler1 (Jun 5, 2013)

chrispenycate said:


> Yea, I went round to CERN and asked my contact there delivery delays on enough antimatter to power my starship – less than a kilogram – and he said 'come back in ten thousand years'. Not encouraging.


 
To hell with the CERN contact - _you have a starship?_ I suspect it's on blocks in your driveway as the fuel tank seems to be empty, _but still!_


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## Harpo (Jun 6, 2013)

Bowler1 said:


> To hell with the CERN contact - _you have a starship?_ I suspect it's on blocks in your driveway as the fuel tank seems to be empty, _but still!_


 
We _all _have a starship - it's an oblate spheroid with oceans, (mostly) breathable atmosphere, plants & animals.  Travels through space at a far old lick.


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## Vertigo (Jun 6, 2013)

I seem to recall that there is a theory that mining anti-matter might be a possibility. I'm sure I read that it is thought most of the Trojan points around the solar system may 'gathered' signigficant collections of anti-matter. I just don't recall what 'significant' means in this context.


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## Mirannan (Jun 6, 2013)

Velocius quam lucem said:


> I may be reading this wrong, but I suspect you may be confusing "fusion" with "fission".
> 
> We've been using fission in "nuclear reactors" for quite some time, but there is no commercial fusion reactor available as of this writing. France is working on one. (ITER) The good thing about fusion is it isn't outwardly radioactive, but it requires immense energy input to start the reactions. Basically, you are taking two protons, two neutrons, and two electrons into a state of plasma (breaking the weak nuclear force) and then allowing them to re-combine into helium. That reaction is exothermic so it produces more energy than it takes in.



Maybe I should have added "when we can do it at all". There are basically four reactions being studied AFAIK; D/D, D/T. D/He3 and P/11B. What I said, I believe, applies to all those reactions in varying degree.


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