Antimatter - More viable than fusion?

Trebuchet · 2004-12-02 00:33:08

NASA estimated the price of antimatter, with $20 million in adjustments and enhancements to the Fermi National Accelerator Laboratory, at $6.4 million per nanogram.

on Tuesday Harold P. Gerrish Jr. of Marshall Space Flight Center's Propulsion Laboratory discussed American work in antimatter propulsion.
"Future spacecraft won't be designed around the propellant tank," Gerrish predicted, since it would take only a few billionths of a gram of antimatter to propel a 400-ton spacecraft to Mars and back in four months

Actually, some searching showed that NASA's ICAN-II design requires 140 nanograms of antimatter for its proposed mission, or $910 million dollars per mission. The trick to the engine is that NASA discovered that antimatter can cause fission in uranium without needing any particular critical mass of uranium, meaning that instead of needing to build Orion style pulse bombs, you could use antimatter striking a uranium mass as a sort of solid rocket engine with an ISP of 13,000 or so. Not bad....

Personally, I think it's worth the cost. 400 tons with a quicker transit definitely works for me, especially as NASA thinks that the next generation of the engine might put Alpha Centauri within unmanned-probe range. Of course, that's only if the storage problem is conquered...

Trebuchet · 2004-12-02 00:35:47

BTW, same engine would allow manned missions to Jupiter, with the same time scale that Mars Direct gives for chemically propelled missions to Mars.

MarsDog · 2004-12-02 03:37:20

How would it work ?

Antiproton beam and charged Uranium beam attracting each other ?
Something like an enhanced ion drive ?

Trebuchet · 2004-12-02 14:06:58

It works sort of like a mini-Orion; small pellets of uranium wrapped around lithium deuteride are fired backwards and are detonated by antimatter. NASA refers to this as ACMF (antimatter catalyzed microfusion). The antimatter allows you to detonate very small pellets (no critical mass) this way. I believe that you can use plain uranium as well, no need for refinement.

NASA and PSU apparently also looked at two other antimatter concepts; one involved a 'solar sail' of uranium which would be hit by antiprotons to create thrust, and the other, which NASA believes is the more logical followon to ICAN, would contain a diffuse cloud of antiprotons elecromagnetically and shoot droplets of deuterium/He3 through the cloud to create what amounts to a fusion pulsejet. That engine (AIM - Antimatter Initiated Microfusion) would be capable of missions up to about ~1% the speed of light. However, it's not a near term technology, ICAN is. All ICAN needs is the ability to store the nanograms of antimatter we make long enough to make it into orbit.

Once that is accomplished, the solar system is ours - the ISP of ICAN is vastly higher than chemical propulsion, or nuclear thermal It beats out ion engines as well, at a better thrust/weight ratio.

Grypd · 2004-12-02 17:02:20

There was also the proposal that small pellets of Antimatter and uranium are collided and the incredible heat created is used to heat water to its plasma stage and this is used as propellant. This was supposed to give a propellant fraction in the 17000s, not bad at all.

Trebuchet · 2004-12-02 17:59:57

Yeah, however, ICAN performs as well or better even with first-generation technology, and the other design (AIM) is even better (1% lightspeed, hurrah!) in its first-generation version.

GCNRevenger · 2004-12-02 18:35:37

It sounds promising, but I think its a far-farish future concept. Storage will be a huge issue, the only practical way to do it now is to bascially cycle the antiprotons around an loop like a particle accelerator, and carry that loop with you. How much of that 400 tons is the storage ring?

And say it can be done, it is not a scaleable solution. The rate which antimatter can be produced is probobly not very big, and the device to create it... a national lab particle accelerator with huge energy costs... is not going to be a viable source for more then exploration purposes.

As far as getting around the inner solar system, and perhaps out further, plain old nuclear fission still has a ways to go before reaching its limits... Gas core nuclear, vapor core electric, and Doc Zubrin's personal invention - the salt water rocket - are all capable of providing very high performance (>5,000sec Isp) and thrusts.

Shaun Barrett · 2004-12-02 22:26:25

I wasn't aware of this hybrid antimatter-fission and antimatter-fusion propulsion idea until now. It sounds very promising indeed.
I found information about it on Wikipedia, which says:-

The current antimatter production rate is between 1 and 10 nanograms per year, and this is expected to increase dramatically with new facilities at CERN and Fermilab. With current technology, it is considered possible to attain antimatter for $25 billion per gram ...

Isn't that $25 per nanogram?
And it's supposed to take only a few nanograms to propel a 400 ton spaceship to Mars and back(! ), in only 4 months?!

Trebuchet · 2004-12-02 22:37:12

Yeah... actually, what NASA needs is a recycling ring at Fermilab (they produce lots of antiparticles for immediate use right now, and what NASA proposes is to siphon some off) and a better Penning trap capable of holding a few nanograms of material without needing a huge holding ring. The latter is the only real stumbling block. BTW, NASA estimates the cost at a few million per nanogram, there's a bit of discrepency in the prices here...

The only part that isn't currently available is the trap. And a trap of the size and weight necessary is considered feasible; there's just not been a need to move that many antiprotons around before. Current NASA/PSU research on the engine apparently revolves entirely around the trap.

I personally wouldn't be surprised if this engine ends up being the one used in the Mars missions, given the timeframe for that (2020 or threabouts)

GCNRevenger · 2004-12-02 23:00:11

Thats a pretty big hurdle though... if chemical or solid-core NTR engines can do the job, the mess of antimatter might be overkill. Hard to make antimatter in bulk for large-scale shipping too.

I also wonder what would happen if a storage ring were to fail... would it be the total destruction of cape canaveral?

Antimatter doesn't help the limitations of launching into orbit either... I wonder if the money would be better spent on Scramjets or somthing.

GraemeSkinner · 2004-12-02 23:30:23

Unless they come up with a safe containment system I don't think many are going to want to fly with even the smallest amounts of antimatter strapped behind them. They'd also have to have an antimatter production and containment unit at the launch site because you don't want to be moving the stuff all over the place.

Graeme

GCNRevenger · 2004-12-02 23:46:28

Depends on how much destruction there would be if it leaked. If the antiprotons are just used to initiate other nuclear reactions, then you may not need that much.

Trucking it all over the country probobly isn't going to happen, or at the least won't be easy, since the storage ring would have to either have a constant energy supply or be a cryogenicly cooled superconductor.

Trebuchet · 2004-12-03 00:18:11

Um...
The catalyzed system uses NANOGRAMS of antimatter. For purposes of comparison, this is about as strong as a firecracker; the antimatter's usefulness is because it can be used in such vanishingly tiny amounts to initiate nuclear reactions controllably without a lot of dangerous hardware like.

Because it's not a destructive threat in such minute quantities, NASA can and apparently has shipped it around the country in portable traps. They had one such portable trap in a photo somewhere on the PSU page; it was, IIRC, being pushed by two guys on a floor dolley. They were talking about using the larger capacity trap NASA was developing to deliver antimatter for medical research around the nation, so apparently they're quite sure about the reliability of the traps (although the small amounts are not really a health problem, if they're considering making the stuff available for timely medical research they must have a low failure rate).

When talking about this technology - please, PLEASE remember the truly tiny amounts being talked about. The antimatter is used like the spark from an automobile spark plug. It's the nuclear fuel which provides the thrust; the antimatter just lets you use it with efficiency far higher than even gas-core NTR's, and the efficiency even beats out nuclear-electric and with a higher thrust to boot.

GraemeSkinner · 2004-12-03 03:11:52

When talking about this technology - please, PLEASE remember the truly tiny amounts being talked about. The antimatter is used like the spark from an automobile spark plug. It's the nuclear fuel which provides the thrust; the antimatter just lets you use it with efficiency far higher than even gas-core NTR's, and the efficiency even beats out nuclear-electric and with a higher thrust to boot.

I realize that one propulsion system on its own would use a tiny amount, but they'll not store tiny amounts if the systems work. There would be little sense having an efficient means of powering our way around the solar system only to have to limit the number of flights through lack of antimatter.
As a theory I like the sound of the 'more power from less materials' but its got a long way to go

Graeme

GCNRevenger · 2004-12-03 08:57:20

When talking about this technology - please, PLEASE remember the truly tiny amounts being talked about. The antimatter is used like the spark from an automobile spark plug. It's the nuclear fuel which provides the thrust; the antimatter just lets you use it with efficiency far higher than even gas-core NTR's, and the efficiency even beats out nuclear-electric and with a higher thrust to boot.

Yes I know that the antimatter reaction itself won't cause much of a boom, but that isn't the only reaction that goes on... If the antiprotons can induce nuclear fission in Uranium, what else could it induce fission in? Would the antiprotons cause the trap to initiate limited fission? That would cause a pretty big bang or at least a thermal/radiation surge...

I am also not yet convinced of the high efficency and thrust claims. The quantity of uranium and/or fusion fuel would probobly be pretty high if this system is to achieve signifigant thrusts; this is just a consequence of thermodynamics and not anything to do with the engine. Plenty of theoretical research groups (*cough* plasma beam sail rider?) love to issue press releases that herald somewhat... optimistic performance assumptions. Frankly, if it were this good, I imagine that it would be getting more attention from NASA.

Euler · 2004-12-03 14:18:27

Even if you solve all of the antimatter production and storage obstacles, there is still a long way to go before you have a practical engine. I think that we will see ordinary fusion engines become successful before we get antimatter catalyzed fusion working.

Trebuchet · 2004-12-03 14:36:13

Even if you solve all of the antimatter production and storage obstacles, there is still a long way to go before you have a practical engine. I think that we will see ordinary fusion engines become successful before we get antimatter catalyzed fusion working.

Wha~? The engine is like Orion with an antimatter sparkplug. Pingpong-ball sized spheres of uranium and lithium deuteride. We've been able to manufacture fusion devices of that kind for decades - the problem for space travel is the monumentally huge size of the spacecraft you'd need to build if you're going to use normal, chemically-imploded nuclear bomb fuel. This one has no minimum size requirement, so you can use microbombs. (As an aside, the Pentagon might want to fund this NASA research, now that I think about it).

GCN Revenger:

Yes I know that the antimatter reaction itself won't cause much of a boom, but that isn't the only reaction that goes on... If the antiprotons can induce nuclear fission in Uranium, what else could it induce fission in? Would the antiprotons cause the trap to initiate limited fission? That would cause a pretty big bang or at least a thermal/radiation surge...

It could induce fission in other fissile materials. Seriously, if you ran a nanogram of material into most stuff, you might create a few more nanograms of radioactive stuff. The reason it works on uranium is because if you blow up a uranium atom into a spray of neutrons and protons, this will cause a chain reaction. The chain reaction won't go far in a subcritical mass, but that's OK - just add more antiprotons. With ordinary materials, there's more danger from the firecracker-like explosive power of that much antimatter than any radiation concerns.

As far as efficiency, the ship is basically propelled by pulsed nuclear detonations. Small ones, to be sure, but nuclear detonations. That's a rather lot of power and thust per unit mass there... yes, you will need to carry along a significant mass of propellant. But significant mass does not equal significant volume when a lot of it is uranium. If you're wondering why the fuel magazine is so smallish looking in the drawings, that's why.

Euler · 2004-12-03 15:13:23

If you want to get an efficient reaction, then your antimatter will have to hit the Uranium/Lithium Deuteride spheres from all directions in a small fraction of a second. You can't just point a beam of antimatter at a block of Uranium and Lithium Deuteride and expect it to produce a worthwhile fusion reaction.

Shaun Barrett · 2004-12-03 19:05:16

It still sounds to me like a particularly promising line of development. I tend to be more optimistic than some about how long such concepts might take to reach fruition and, considering our prowess at the precision engineering involved in today's nuclear bombs, I don't see any insuperable obstacles to getting this engine up and running sooner rather than later. And the potential payoff is very attractive, which is the greatest spur to swift development.

This idea can give us most of the advantages of Orion, without most of the disadvantages. I'm even wondering whether a scaled-down craft, less than the 400 tons mentioned for the Mars trip, might actually be launched from the ground?
When sober assessments of radioactive pollution from Orion were made, it turned out that a ground launch would add only a relatively insignificant amount of radioactive material to Earth's atmosphere. It was enough, though, as our environment became an ever more important political factor in the calculations, to put a stop to such ideas.
Assuming we can manufacture small, light, reliable antimatter containment systems, could we use this suggested antimatter/fission, or better yet antimatter/fusion, to achieve LEO in an SSTO vehicle?
If the amount of radioactive pollution can be shown to be truly negligible, might we not have an answer to the problem of getting stuff off the ground and into orbit cheaply?

[NOTE: Only affirmative and optimistic replies will be considered by the editor.]

John Creighton · 2004-12-03 19:22:58

I wonder if this can be made small enough for airplanes. Here comes fusion powered scram jets.

Trebuchet · 2004-12-03 19:32:08

No.

Problem with use in-atmosphere: the atmosphere. It does you no good to fry some innocent nitrogen and oxygen with antimatter and have the fuel spheres drop on the ground like so many hailstones.

It's purely deep space. Besides, that would be a hideous waste of antimatter.

John Creighton · 2004-12-03 19:41:41

Use the reaction to heat the air passing though the scram jet. The flow of the of air should naturally create an evacuated chamber where antimatter fusion reactions could be set off. The blast after it dissipates should partly clear the chamber as well.

Shaun Barrett · 2004-12-03 20:04:13

For use in the atmosphere, could you use a more conventional explosion initially to create a vacuum in the combustion chamber, followed quickly by a 'machine-gun' succession of antimatter/fusion explosions. The frequency of the detonations might keep the chamber clear of atmospheric gases until orbit is achieved(?).
Just a thought.

Euler · 2004-12-03 20:17:10

For use in the atmosphere, could you use a more conventional explosion initially to create a vacuum in the combustion chamber, followed quickly by a 'machine-gun' succession of antimatter/fusion explosions. The frequency of the detonations might keep the chamber clear of atmospheric gases until orbit is achieved(?).

I don't think that you can create a good vacuum through explosions. You might get rid of the atmospheric gasses, but you introduce new gasses with each explosion.

Euler · 2004-12-03 20:19:29

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#1 2004-12-02 00:33:08

Re: Antimatter - More viable than fusion?

#2 2004-12-02 00:35:47

Re: Antimatter - More viable than fusion?

#3 2004-12-02 03:37:20

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