Nuclear Fusion Achives Milestone

[Warhorse]

optimism:

fusion will become available sooner than expected, unfortunately the first reactors will be installed as part of the american war machine before being built and sold for domestic and international use.

polywells <3

Well, but that actually makes perfect sense. Military applications are a lot more forgiving of poor efficiency than commercial products can ever be, as long as the item in question works fairly reliably and gives an improved capability. Also, the way trends in science are going these days, there's a substantial possibility that this will be part of the Chinese war machine, rather than the American ...

[Stargate525]

What the HELL kind of weapon would you need a fusion reactor to power? It would be immobile, as the equipment to lug that stuff around... Laser artillery? EMP defense system? What?

[TheDarkStar]

Laser artillery? EMP defense system? What?

Possibly a rail gun. I can't think of much else.

[Stargate525]

Possibly a rail gun. I can't think of much else.

So... an immobile, massively powerful projectile artillery.

You'd get six or seven shots before every enemy source zeroes in on that location.

[TheDarkStar]

So... an immobile, massively powerful projectile artillery.

You'd get six or seven shots before every enemy source zeroes in on that location.

AFAIK, they're usually on boats.

[Aghanim]

With laser point defenses installed. If you have a lot of energy you could do nearly things that are impractical before

[Scotius]

That's what i thought. "Lasers and railguns? How will they power them up?" Answer: Polywells.

[Seret]

What the HELL kind of weapon would you need a fusion reactor to power? It would be immobile, as the equipment to lug that stuff around... Laser artillery? EMP defense system? What?

Same stuff they use fission reactors for, mostly naval propulsion.

[Tex]

You'd get six or seven shots before every enemy source zeroes in on that location.

True, but six or seven well-placed railgun shots could completely annihilate the enemy force! Railguns are friggin' powerful.

[drakesdoom]

As long as we are confining the discussion to terrestrial artillery the only thing that matters for it's destructive capability is bore size. Ground and naval artillery fire high explosive shells. it doesn't matter how fast they go out the barrel they will slow down before they hit the target. The only improvement a rail-gun brings is ammo storage, and maybe down the line a little more range and accuracy.

Now if you could power a rail gun on a tank that would be a big improvement. Tank guns fire direct and against other tanks mainly use armor piercing rounds, which would benefit from a higher launch speed.

[Stargate525]

As long as we are confining the discussion to terrestrial artillery the only thing that matters for it's destructive capability is bore size.

But muzzle velocity does affect range. With a railgun, I could conceivably see an orbital artillery; something that has a range most easily measured in percents of the earth's surface.

[Sillychris]

the only thing that matters for it's destructive capability is bore size. Ground and naval artillery fire high explosive shells. it doesn't matter how fast they go out the barrel they will slow down before they hit the target.

That is so untrue in the case of a railgun... Kinetic energy of the projectile is what does the damage. For example, a rifle round and a rimfire cartridge both with the same bore size the rifle round is going to do a lot more damage to the target because it has a lot more powder and a lot higher muzzle velocity.

Specific example: I hunt deer with .223 remington cartridges and grouse with .22 rimfire cartridges. Both bullets have the same bore size, but the .22 rimfire round wouldn't even slow down a deer and the .223 rifle round would make a grouse explode. The difference is that the rifle round has magnitude of order more gunpowder behind it and thus goes waaaaay faster. When it strikes the target, that energy has to go somewhere, and most of it goes into putting a crater in the deer.

What makes railguns so powerful is the absurd muzzle velocity you can pack into them. It's true that they slow down before they get to their target 100 km away, but they are still going ridiculously fast when they get there.

[Stargate525]

That is so untrue in the case of a railgun... Kinetic energy of the projectile is what does the damage. For example, a rifle round and a rimfire cartridge both with the same bore size the rifle round is going to do a lot more damage to the target because it has a lot more powder and a lot higher muzzle velocity.

Specific example: I hunt deer with .223 remington cartridges and grouse with .22 rimfire cartridges. Both bullets have the same bore size, but the .22 rimfire round wouldn't even slow down a deer and the .223 rifle round would make a grouse explode. The difference is that the rifle round has magnitude of order more gunpowder behind it and thus goes waaaaay faster. When it strikes the target, that energy has to go somewhere, and most of it goes into putting a crater in the deer.

What makes railguns so powerful is the absurd muzzle velocity you can pack into them. It's true that they slow down before they get to their target 100 km away, but they are still going ridiculously fast when they get there.

You're talking direct fire, where you're only accounting for a little bit of drop when aiming. He's talking parabolic firing. In that case, your shell is going to be doing about terminal velocity no matter how its sliced.

[Kryten]

You're talking direct fire, where you're only accounting for a little bit of drop when aiming. He's talking parabolic firing. In that case, your shell is going to be doing about terminal velocity no matter how its sliced.

Then why do mortars and guns of similar bore sizes have such radically differing ranges? And how would something like the Paris Gun be possible, given it used pretty much conventional shells?

[Scotius]

And range does matter. 16 inch shells used by Iowa-class battleships could reach about 32 kilometers. Range of precise fire was of course much shorter. And this huge 45 000 capship carried only about 800 rounds for its 9 main cannons. Only couple percents of all fired shells was expected to hit the target. Now imagine 10 000 ton destroyer/cruiser armed with railgun, able to deliver its projectiles over four times further than Iowa - with almost the same destructive power, since modern warships are not armored. I sincerely doubt anything short of aircraft carrier (only due to their sheer size) can take more than 2-3 railgun shells and stay afloat. Railgun fire will be even more dangerous against "soft" land targets. Such as industrial centers, communication hubs, airfields etc. And consider this: cruise missiles can be detected and shot down with CIWS point defence - hipersonic slug from a railgun would be almost impossible to take out in flight.

[Seret]

You're talking direct fire, where you're only accounting for a little bit of drop when aiming. He's talking parabolic firing. In that case, your shell is going to be doing about terminal velocity no matter how its sliced.

Gravity only supplies the vertical component of the shell's downwars trajectory. Even weapons like howitzers will still have a considerable horizontal component. That's why the characteristic shape of shell impacts is like this:

Incidentally, if you can spot it on the round you can use this shape to know what direction the fire was coming from. Handy if you want to know which side's artillery you should send a thank you note to.

This is a bit of a stupid argument though, as most people commenting are at least partly right. Rail guns are KE weapons, and they would be expected to be effective in direct fire, where they would function very like tank guns firing sabots. Like sabots, they would be devastating against some targets, of questionable utility against soft ones, and almost entirely useless as anti-personnel weapons. Ever tank out there carries a flavour of high explosive round for use against troops, structures, softskins and light armoured vehicles. The sabots are only used on the tough nuts. Hitting lighter stuff with them tend to just increase their ventilation without necessarily doing a lot of damage.

Even in indirect fire railguns would have enough muzzle velocity to use a pretty flat trajectory, which means they'd be able to throw considerable kinetic energy a long way down range. However, they'd be limited in their ability to damage soft targets, and their low trajectory would mean a lot of stuff would be behind terrain.

[astropapi1]

This is how I feel when coming to the Science Labs:

Guess I'll just go back to General Discussion...

[Stargate525]

Then why do mortars and guns of similar bore sizes have such radically differing ranges? And how would something like the Paris Gun be possible, given it used pretty much conventional shells?

muzzle velocity. When you're doing trigonometry to get your target, a lot of the kinetic energy you're putting into the shell is used to get it to the target.

[Nuke]

there is another thing the railgun does for you: the ammo is just a hunk of metal, it doesn't need a warhead. how many ships in ww2 were sunk because their magazine got hit? lots, hms hood being the prime example. you get hit in your railgun magazine, its going to ruin some your ammo, but its not going to sink you. fusion reactors also mean you dont need to carry fuel so there is less risk of fire (except on carriers that need to carry jet fuel and air ordinance). from that point i wonder how long it will be till they cram a polywell into an aircraft and eliminate the need to carry fuel (or have carriers for that matter). you should be able to do that because the optimal radius for a polywell is ~3 meters (somewhere between break even and magnetic forces so high that the reactor blows itself to bits).

Edited March 7, 2014 by Nuke

[Stargate525]

there is another thing the railgun does for you: the ammo is just a hunk of metal, it doesn't need a warhead. how many ships in ww2 were sunk because their magazine got hit? lots, hms hood being the prime example. you get hit in your railgun magazine, its going to ruin some your ammo, but its not going to sink you. fusion reactors also mean you dont need to carry fuel so there is less risk of fire (except on carriers that need to carry jet fuel and air ordinance). from that point i wonder how long it will be till they cram a polywell into an aircraft and eliminate the need to carry fuel (or have carriers for that matter). you should be able to do that because the optimal radius for a polywell is ~3 meters (somewhere between break even and magnetic forces so high that the reactor blows itself to bits).

You'll still need a place to store and regulate that amount of energy, and a source of fuel. The beauty of the fusion reactor is that when it fails catastrophically it doesn't explode like internal combustion or meltdown, it just... stops.

[Nuke]

im just saying you will have less. one of the big problems with reactors will be the start up power requirements. so you will need some kind of generator to charge a capacitor bank to start up the reactor. this might just be a deisel generator, but i could imagine large naval ships also keeping a small fission reactor as a startup device. i think in practice we will simply have more than one polywell on a ship, and keep at minimum one running at all times. you will need to carry fuel for the start up system, and you will also have your hydrogen and boron, but only small quantities. compare this to thousands to millions of gallons of fuel oil.

Edited March 8, 2014 by Nuke

[Aghanim]

there is another thing the railgun does for you: the ammo is just a hunk of metal, it doesn't need a warhead. how many ships in ww2 were sunk because their magazine got hit? lots, hms hood being the prime example. you get hit in your railgun magazine, its going to ruin some your ammo, but its not going to sink you. fusion reactors also mean you dont need to carry fuel so there is less risk of fire (except on carriers that need to carry jet fuel and air ordinance). from that point i wonder how long it will be till they cram a polywell into an aircraft and eliminate the need to carry fuel (or have carriers for that matter). you should be able to do that because the optimal radius for a polywell is ~3 meters (somewhere between break even and magnetic forces so high that the reactor blows itself to bits).

I think polywell is only suitable on ships or spacecraft that could afford that 3m radius, excluding all those necessary lead shielding... Fusion reactor that is suitable for fighter jet is dense plasma focus/focus fusion as it could be miniaturized further. And it will use helium-3 for fuel as it provides 207.5 TJ/kg instead of p-B11 69.97 TJ/kg

Then it will be only matter of time before someone invents fusion powered car

But still, there's still a huge hurdle before we could put a fusion reactor in a aircraft. There isn't any way to convert huge amount of electricity to huge kN of thrust, its either ducted fan that have low top speed or ion/plasma/whatever propulsion that couldn't even blow a paper...

Edited March 8, 2014 by Aghanim

[Stargate525]

But still, there's still a huge hurdle before we could put a fusion reactor in a aircraft. There isn't any way to convert huge amount of electricity to huge kN of thrust, its either ducted fan that have low top speed or ion/plasma/whatever propulsion that couldn't even blow a paper...

Welcome back to the age of the zeppelin. That much energy, you can easily support the creation of a commercial hot air envelope. OR... Since the product of fusion is helium...

And if you want to go somewhere fast... hyperloop.

[Aghanim]

But... Fusion SSTO!

[Nuke]

I think polywell is only suitable on ships or spacecraft that could afford that 3m radius, excluding all those necessary lead shielding... Fusion reactor that is suitable for fighter jet is dense plasma focus/focus fusion as it could be miniaturized further. And it will use helium-3 for fuel as it provides 207.5 TJ/kg instead of p-B11 69.97 TJ/kg

Then it will be only matter of time before someone invented fusion powered car

But still, there's still a huge hurdle before we could put a fusion reactor in a aircraft. There isn't any way to convert huge amount of electricity to huge kN of thrust, its either ducted fan that have low top speed or ion/plasma/whatever propulsion that couldn't even blow a paper...

dpf is an interesting idea, and i think that it would produce the smallest fusion reactor possible to construct. the only problem is it seems to attract all the environmentalist nutjobs and make the whole concept appear to be bogus. but that may just be an attempt to get funding. from what ive seen its enough to make it worth keeping my eye on.

i personally think the he3 reactions are overrated. i dont think you can do direct conversion with it. going the thermodynamic route will work well here on earth just fine, and for naval applications. for space applications direct conversion is especially useful because of how hard it is to get rid of heat. you would need a brayton cycle with the reactor being the heat source, and huge, bulky radiators, and the coolant in the loop as the sink. its a lot of heavy hardware. i believe one of the problems we had with space fission reactors was the limits of the heat dissipation systems needed for power generation. direct conversion gets around that entirely. you get these helium ions being flung out of electron cloud and high velocities, it picks up an electron and gets decelerated by a negative grid, creating electricity in the process (or something like this, its a little over my head). theoretically were talking an efficiency of around 80-90%, and getting breakeven is all about efficiency.