Spacescifi

Antimatter Bombs VS Nuclear Bombs For Project Orion

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Antimatter bombs are arguably more efficient than nukes (assuming you already have enough safely stored away for use).

 

What is the fallout of antimatter bombs compared to nuclear bombs?

I remember reading somewhere that it left less fallout than a nuke, which I found surprising.

 

I guess if you wanted to you could make only nuclear size blasts using small amounts of antimatter to reduce the fallout.

Is this correct about antimatter or did I misread?

Since from what I read, antimatter/matter annihilation releases mostly gamma rays, whic plain air absorbs as a horrific fireball anyway.

 

What do you say?

Edited by Spacescifi

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One gram of antimatter costs about one billion dollars to produce. Wanna shell the bill for couple hundreds of AM bombs?

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A pure AM bomb, depending on what type of EM, produces only gamma rays and neutrinos. That doesn't make any fallout per se. However, it will result in temperatures that cause Fusion, which makes neutrons, which makes radioactive isotopes. I'd guess it would be cleaner than a pure fusion bomb of the same yield. All of our fusion bombs have fission triggers, so...

Most fallout concerns are the byproducts of heavy element fission and decay.

To be much more economical, ones could use a "antimater catalysed" fusion bomb. Its not really catalysed, but triggered. Replace the fission trigger of a thermonuclear bomb with a small amount of antimatter, for the same yield there would be much less fallout. Also, you'd use much less AM that way.

If you want a powerful rocket, you have access to AM, but not that much, using the AM to trigger fusion seems like a good idea.

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And if the AM ship gets out of power for a while, the AM will inevitably annihilate in one exponentially growing explosion.

Then if the rocket is pure AM, you get a nice desert area to build a new spaceport, and spread around all fission materials contained.
If the rocket is AM-triggered, you get a smaller desert, but still spread around all fission materials contained.

Without AM, it just gets hot.

Edited by kerbiloid

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Antimatter is insanely dangerous stuff in the quantities required for a bomb. The slightest imperfection in containment and you get a premature detonation. 

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The point of the Orion pusher plate design is to find a way to unlock the extremely power density and energy density of nuclear chain reactions for propulsion. Because the energies are too high to be nominally contained, a "pulsed" approach is the only way to do it.

The smallest unboosted nuclear fission warheads have a minimum yield of around 10-20 tonne TNT equivalent and the largest have a maximum yield of about 500 kiloton TNT equivalent.

The smallest thermonuclear warheads have a minimum yield of around 5-10 kiloton TNT equivalent and the largest have no theoretical maximum. 

The smallest possible antimatter bomb is...just one positron.

Antimatter will blow up at ANY concentration or quantity if exposed to mass. For that reason, you don't need a pusher-plate approach at all. You can just build a big engine and pump exactly as little antimatter into it as you need in order to run it. Throttle it, vector it, whatever you want to do.

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5 hours ago, KerikBalm said:

All of our fusion bombs have fission triggers, so...

I know "trigger" is the accepted word, but it actually kind of understates it. Fusion bombs are really fission bombs that use some of the energy released by the fission to start a fusion reaction that greatly amplifies the total energy release.

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1 hour ago, sevenperforce said:

Antimatter will blow up at ANY concentration or quantity if exposed to mass. For that reason, you don't need a pusher-plate approach at all. You can just build a big engine and pump exactly as little antimatter into it as you need in order to run it. Throttle it, vector it, whatever you want to do.

An AM-heated moped.

Spoiler

800px-Honda_Hobbit.jpg

 

5 minutes ago, mikegarrison said:

I know "trigger" is the accepted word, but it actually kind of understates it. Fusion bombs are really fission bombs that use some of the energy released by the fission to start a fusion reaction that greatly amplifies the total energy release.

If heat a fusion pellet with AM, there will be no fission.
Say, a frozen pellet with some amount of AM frozen into the fusion fuel.
Or a pellet heated by a positron beam.

Edited by kerbiloid

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This is called antimatter-initiated microfusion:
http://ffden-2.phys.uaf.edu/213.web.stuff/scott kircher/microfusion.html

One thing to keep in mind that an Orion drive is a really crude device. It's appealing because of its simplicity and good performance, but it's not all that great when it comes to energy efficiency. If you can make and store antimatter, you can afford to use something more sophisticated.

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3 hours ago, sevenperforce said:

The point of the Orion pusher plate design is to find a way to unlock the extremely power density and energy density of nuclear chain reactions for propulsion. Because the energies are too high to be nominally contained, a "pulsed" approach is the only way to do it.

The smallest unboosted nuclear fission warheads have a minimum yield of around 10-20 tonne TNT equivalent and the largest have a maximum yield of about 500 kiloton TNT equivalent.

The smallest thermonuclear warheads have a minimum yield of around 5-10 kiloton TNT equivalent and the largest have no theoretical maximum. 

The smallest possible antimatter bomb is...just one positron.

Antimatter will blow up at ANY concentration or quantity if exposed to mass. For that reason, you don't need a pusher-plate approach at all. You can just build a big engine and pump exactly as little antimatter into it as you need in order to run it. Throttle it, vector it, whatever you want to do.

I think the main benefit of the pusher plate isn’t actually the pulse aspect. Yes it exists but consider the waste heat of an internal drive. At high power you need immense radiators. Even mini-mag Orion (which I think is worth developing), an internal pulsed drive, needs radiators for the drive. The biggest advantage of a pusher plate is to avoid the need for dealing with the engine’s waste heat. This lets you run engines with immense power and no need to physically contain anything and no need to reject waste heat. Of course a Medusa style sail approach should have a similar benefit.

Edited by Bill Phil

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Medusa's advantages are that it should be somewhat lighter (due to energy being spread over a larger area), more efficient (larger angle, a larger percentage of total energy captured) and that it allows near elimination of the jerky acceleration inherent in normal Orion (just design the cable winch to pull with the same force no matter what's happening). The downside is that it's hard, though perhaps not impossible, to make it usable in atmosphere (it's an "inverse parachute" of sorts).

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24 minutes ago, Dragon01 said:

Medusa's advantages are that it should be somewhat lighter (due to energy being spread over a larger area), more efficient (larger angle, a larger percentage of total energy captured) and that it allows near elimination of the jerky acceleration inherent in normal Orion (just design the cable winch to pull with the same force no matter what's happening). The downside is that it's hard, though perhaps not impossible, to make it usable in atmosphere (it's an "inverse parachute" of sorts).

 

It is theoretically possible to do a combination of both!

 

Use boosters to get Orion away from the launch facility, drop first stage boosters, engage Orion pusher plate to orbit.

 

Once in orbit unfurl the nuclear sail and start flinging and detonating nukes against a massive taut sail of thermal resistant fabric.

 

The real engineering challenge here is that for this to work, the ship will be loaded with bombs both in the rear and the front. It will arguably be lighter in the middle than the ends, which will mean RCS had better be beefy ( not weak thrust).

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Nobody has ever built an antimatter bomb, for the simple reason that actually making antimatter at all is exorbitantly expensive, requires some form of large particle collider and the antimatter that gets produced will literally turn into nothing (apart from a burst of energy) if it touches regular matter so requires lots of energy to run magnets that keep it away from all that matter. Storing it long-term is impossible with current technologies, and even if it becomes possible in the future there's no point in doing it.

If you're making a rocket engine that literally runs on nuclear explosions, radiation clearly isn't a particularly big consideration so a regular fission-fusion system is a far better bet: it's decades-old and well-proven technology that has an existing skills base with a fairly large number of people who already work with nuclear reactors/weapons/materials and the technology to make more; the raw materials are easier to get hold of (plenty of old nuclear warheads around waiting to be decommissioned!); it's far less likely to blow up in your face, as actually getting a nuclear explosion going takes some effort and a leak of the fissile material will actually make it less likely to blow up whereas antimatter will go off the moment it touches matter and so any leak at all could be catastrophic; and when you're in space, it doesn't matter that you're flying along leaving a cloud of heavy radioactive isotopes in your wake. Antimatter is hideously expensive, hideously volatile and quite frankly over-hyped.

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40 minutes ago, Spacescifi said:

Use boosters to get Orion away from the launch facility, drop first stage boosters, engage Orion pusher plate to orbit.

This is incredibly wasteful. An Orion pusher plate is massive. If you're boosting with rockets, you may as well launch to a sufficient altitude to engage the Medusa directly. 

39 minutes ago, jimmymcgoochie said:

Nobody has ever built an antimatter bomb, for the simple reason that actually making antimatter at all is exorbitantly expensive, requires some form of large particle collider and the antimatter that gets produced will literally turn into nothing (apart from a burst of energy) if it touches regular matter so requires lots of energy to run magnets that keep it away from all that matter. Storing it long-term is impossible with current technologies, and even if it becomes possible in the future there's no point in doing it.

Actually, accelerator storage would be sufficient for some antimatter-based designs. They can do long term storage, too. The nice thing about antimatter is that unless you're going relativistic, you don't need all that much of it.

I'll tell you why antimatter is so great: it gives the tyranny of rocket equation a good kick. The math is quite long winded, but you can check it out here:
http://www.projectrho.com/public_html/rocket/enginelist2.php#antirocket
Antimatter requirements would be in miligrams, and that's a lot. Some proposals lower this amounts, at the cost of having to haul around more propellant. Antimatter is expensive because there's nobody making it, if even a single accelerator optimizing for producing it was built, we could, in a few years, make and stockpile sufficient antimatter to fly one of those. It'd still be expensive, but it's very much possible.

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As others pointed out, and to paraphrase John Clark: nuclear fuel has only one advantage, but it's a truly magnificent one: it's available in usable quantities.

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5 hours ago, Dragon01 said:

Actually, accelerator storage would be sufficient for some antimatter-based designs.

To store 1 g of antihydrogen per "1000 t" of the storage and electric plant.

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22 hours ago, Spacescifi said:

assuming you already have enough safely stored away for use

Everybody keeps pointing to the production/storage problems and ignores the fact that we've used scifi magic to handwave these away.

 

22 hours ago, Spacescifi said:

What do you say?

I'd say that if we're going to ignore the reality of the issues: "Woo hoo, antimatter drives are a thing! Let's pretend they can make wormholes so we can have FTL travel to make interesting stories, too!".

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6 minutes ago, razark said:

Everybody keeps pointing to the production/storage problems and ignores the fact that we've used scifi magic to handwave these away.

 

I'd say that if we're going to ignore the reality of the issues: "Woo hoo, antimatter drives are a thing! Let's pretend they can make wormholes so we can have FTL travel to make interesting stories, too!".

 

 

Where the science is understood I do not go against unless absolutely necessary

 

 

Antimatter could theoretically provide the power for warp and wormholes, but the amount required would likely be enough to crater Earth really good.

Besides, in addition to antimatter we would need 'exotic matter' and  probably some control over 'dark matter', which are both terms scientists use that imply they simply do not know what it would take and would like to know.

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11 minutes ago, Spacescifi said:

Antimatter could theoretically <insert damn near anything scifi has proposed>, but the amount required would <be covered under the initial assumption>.

In you OP, you just assume that A exists. If we're going to ignore <X arbitrary parts of reality>, why don't we just ignore <(X+1) arbitrary parts of reality>?

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2 hours ago, razark said:

"Woo hoo, antimatter drives are a thing! Let's pretend they can make wormholes so we can have FTL travel to make interesting stories, too!".

So, you suggest to travel between stars on back of antimatter worms crawling through the holes in reality they can make?

That's interesting.

Edited by kerbiloid

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18 hours ago, mikegarrison said:

I know "trigger" is the accepted word, but it actually kind of understates it. Fusion bombs are really fission bombs that use some of the energy released by the fission to start a fusion reaction that greatly amplifies the total energy release.

That depends entirely on the design of the bomb that uses fusion.

A boosted fission weapon might as well be a pure fission bomb as far as radiactive particle production is concerned:

https://en.wikipedia.org/wiki/Boosted_fission_weapon - this type of weapon uses some fusion fuel to produce more neutrons and increase the fission yield.

When a "trigger" is mentioned, it normally refers to the first stage of a multistage weapon, in which the 2nd stage is fusion. In a 2 stage design, such as a tellar ullam design

https://en.wikipedia.org/wiki/Nuclear_weapon_design#Two-stage_thermonuclear_weapons

https://en.wikipedia.org/wiki/Thermonuclear_weapon

The bomb can be mainly a fusion weapon. such as the Tsar bomba, in which 97% of the energy came from fusion

https://en.wikipedia.org/wiki/Tsar_Bomba#Genesis

Then there are "layer cake" cake designs, with additional stages. The Tsar bomba would have had a 3rd stage, roughly doubling its power. I'm not sure how much power would increase due to fission, or due to fusion, but worst case scenario, the bomb would be roughly 50-50 fusion vs fission energy.

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6 hours ago, razark said:

In you OP, you just assume that A exists. If we're going to ignore <X arbitrary parts of reality>, why don't we just ignore <(X+1) arbitrary parts of reality>?

Because, surprise surprise, antimatter is a part of reality. Wormholes are disputable, but antimatter can exist, can be stored in a number of physical devices and so on. He's not writing an engineering proposal, if the exact methods of storage and production don't matter. Those are, in essence, engineering problems, which are most certainly solvable with the right infrastructure. 

6 hours ago, kerbiloid said:

To store 1 g of antihydrogen per "1000 t" of the storage and electric plant.

Maybe, now go do the calculations and see how far those numbers take you. Unless you want your 2000T torchship to fly all the way to Pluto and back, you don't need a whole gram. :) Oh, and you can use antimatter to produce electricity, too, which is great if you manage to combine it with the storage chamber.

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8 minutes ago, Dragon01 said:

 Unless you want your 2000T torchship to fly all the way to Pluto and back, you don't need a whole gram. :) 

Omitting the ISP, just talking about the energy.
Energy = 1*10-3 kg * 2 (because "anti") * (3*108 m/s)2 ~= 1.8*1014 J.
Max. speed = (1.8*1014 J / (2*106 kg) * 2)1/2 ~= 13.4 km/s

Happy 40 year long journey to Pluto.

Oh, no... Wait... Some part of energy becomes waste radiation.

Edited by kerbiloid

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11 minutes ago, kerbiloid said:

Max. speed = (1.8*1014 J / (2*106 kg) * 2)1/2 ~= 13.4 km/s

Wrong. You forgot that it's still a rocket. A "2000T" ship will mass about 1000T once it expands the propellant (and no, we're not talking beam core, equations for that are awful). I linked a page with equations for a reason. Use it.

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1 hour ago, Dragon01 said:

Wrong. You forgot that it's still a rocket. A "2000T" ship will mass about 1000T once it expands the propellant (and no, we're not talking beam core, equations for that are awful). I linked a page with equations for a reason. Use it.

(Silently opens "Energy conservation law". Reads. Closes.)

***

If someone is interested, one microgram of antiprotons is considered enough to replace the fission trigger for a pure fusion device.

P.S.
Same good in the single-use Xray lasers to burn the @Dragon01's fleet of space fighters armored with tungsten-lithium, like the Roman infantry.
Confirmed by professionals. <snip>

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