Explosive propulsion

[impwarhamer]

You guy's renember the orion project? Not the new space capsule, but the idea of using nuclear bombs to propell spacecraft.

There is a mod for it in ksp that was released a while back

Anyway, I renember when I first found out about it, I came up with an idea for some sort of sci-fi explosive manoeuvring system using conventional explosives that would be used on space fighter craft. The idea being it could be used to for a sudden boost in acceleration to dodge things like missiles.

I was actually about to do some concept art to post here when it occurred to me, how does an explosion push the spacecraft? There's no shockwave since it's in space, but somehow it must work for nuclear explosives.

Anyone got any idea?

[Rakaydos]

Orion doesnt just use nukes, it uses "shaped charge" nukes that deliver 50% of the explosive power of an atomic bomb in a relatively narrow beam. This beam is an extremely dense particle beam that bounces off the plate to push the craft foreward.

The problem with doing this with conventional explosives is that it suks. You''re losing 50% of your potential thrust, that would be better spent in a rocket. The reason it works for nukes is because it's the -only- way to use high-supercritical fission (as opposed to controlled supercriticality, like NERVA) without blowing yourself apart- all the efficency is in the fuel, not the drive.

[impwarhamer]

I see. So, would conventional explosives produce next to no propulsion?

My original idea was that the use of using conventional explosives to get a large amount of acceleration in a short burst, rather than efficiency.

I guess what I'm trying to say is, would you get a better TWR using conventional explosives than using a rocket?

Edited March 4, 2015 by impwarhamer

[AngelLestat]

50% of efficiency is not bad (if is possible to achieve that), but I am agree that this propulsion method suks due many others drawbacks.

I have my money on Solar Sails taking into account how much they can benefit from carbon base nanotechnology and 3d printing.

[KerbalEssences]

I don't know if its allready answered but the "push" comes from the hot accelerated plasma which strikes at the plate. An atom bomb consist of nuclear active material which has a certain mass. The explosion occurs if you go beyond a certain critical mass. A bomb consists of multiple masses which are spatially split. If you want to make it detonate you fire up little bombs which smash all the masses together. The matter does not annihilate like when using antimatter. Only a small fraction of the mass is converted to energy. This energy heats up the "reaction mass" which reaches the hottest state of matter. A plasma! You may know that heat is nothing but movement of the particles. This insane plasma heat creates an enourmous pressure on the plasma which expands in all directions. You can shape the nuclear bomb (shape charge) in a way so the plasma does not expand in all direction but mostly two. To the front and to the back. 50% of the plasma smashes into your absorber while the other 50% are gone.

The stresses of the sudden acceleration would be too much I guess on a plane. A plane looks sturdy but it's really just paper. It has to be as light as possible! A full turn using their joystick would allready be too much at high speeds. This means they can't turn more quickly than they allready can due to structural limitations.

Edited March 4, 2015 by KerbalEssences

[Rakaydos]

I see. So, would conventional explosives produce next to no propulsion?

My original idea was that the use of using conventional explosives to get a large amount of acceleration in a short burst, rather than efficiency.

I guess what I'm trying to say is, would you get a better TWR using conventional explosives than using a rocket?

Given an equal sized rocket, no. That's true for the nuke as well.

[impwarhamer]

oh well that's a shame. Glad I realised this and asked you guys before drawing anything, just gonna have to think of something more crazy!

[magnemoe]

oh well that's a shame. Glad I realised this and asked you guys before drawing anything, just gonna have to think of something more crazy!

Nukes works as they have an high ISP compared to anything chemical, even thermal rockets. They have an insane trust.

Chemical explosives has much lower ISP than chemical rocket, its basically solid fuel who burn very fast

[andrewas]

Couldn't antimatter catalysed nuclear pulse propulsion scale down to fighter size?

[impwarhamer]

Couldn't antimatter catalysed nuclear pulse propulsion scale down to fighter size?

I'm listening

[Rakaydos]

I'm listening

At which point, the question is how much armor do you have, and how much G force and radiation your crew can take.

EDIT: and wether the solution is worse than the problem.

[PB666]

At which point, the question is how much armor do you have, and how much G force and radiation your crew can take.

EDIT: and wether the solution is worse than the problem.

A nuclear drive would only be economical on a very large ship, like this:

More so effective considering its task.

[Aanker]

I just want to point out that to my knowledge, for most (atmospheric flight) fighter jets, the limiting factor nowadays isn't structural strength but crew squishiness in the face of G forces.

Of course if your craft is a drone you could do a bunch of interesting things without worrying about that.

[Rakaydos]

A nuclear drive would only be economical on a very large ship, like this:

http://media-cache-ak0.pinimg.com/736x/36/b0/5a/36b05a7dac11815f6313826688b3205c.jpg

More so effective considering its task.

Military craft dont care about economy, only effectiveness. The us army is one of the least efficent, but most effective, bureaucracy in the world.

[Tommygun]

There have been some non-nuclear Pulse detonation engines, although they were all meant to be used within the atmosphere.

http://en.wikipedia.org/wiki/Pulse_detonation_engine#First_PDE_powered_flight

[Newt]

Military craft dont care about economy, only effectiveness. The us army is one of the least efficent, but most effective, bureaucracy in the world.

Well, the US military has the luxury to be well funded and powerful, not all militaries do. I think perhaps more what PB666 was getting at was that it would be absurd to make one that small to fit on a vehicle the size of a fighter, like trying to put a nuclear powerplant of the sort on aircraft carriers into a wristwatch. It is not about economic efficiency, but technological efficiency. Even the US military cares about doing things well.

@Rakaydos: Of course, at that point you need not worry about armament, only armor and acceleration. To fight someone, you merely fly past the fleet with your engine going, and sit back .

[impwarhamer]

Just to clarify, this wouldn't even be used as a main source of forward propulsion, It would be side mounted for short bursts of horizontal acceleration.

[magnemoe]

There have been some non-nuclear Pulse detonation engines, although they were all meant to be used within the atmosphere.

http://en.wikipedia.org/wiki/Pulse_detonation_engine#First_PDE_powered_flight

This is another type of ramjet engine, pulsed but detonates the fuel like in an IC engine rather than burning it.

As for the fighter, it would be better to use high powered chemical vernier engines. Optionally you could heat the monopropelant or other fuel to increase trust, say use an laser instead of the nerva reactor.

You are after high TWR engines to do evasive action if I understand you right. Here TWR is more important than ISP.

[StrandedonEarth]

Orion designs also use the intense radiation of a nuke to vaporize a thin layer of the ablative pusher plate, generating some more thrust.

Rocket engines, solid or liquid, are essentially continuous, controlled, directed explosions. Put an explosive charge in a tube and you'll create thrust. But for evasive maneuvers, I'd suggest something like sepratrons pointed sideways

[PB666]

There have been some non-nuclear Pulse detonation engines, although they were all meant to be used within the atmosphere.

http://en.wikipedia.org/wiki/Pulse_detonation_engine#First_PDE_powered_flight

Pulse Jet - So called V-1 rocket "Buzz bomb".

- - - Updated - - -

Exactly. No need to launch a weather satellite with a nuclear bombs, definitely you would not win a popularity contest and probably instantly become public enemy #1.

But even moreso, if you had say a VCF sized ship you could make a bowl at one end and detonate the bomb and the focal point of the bowl, it would be more efficient. But if you tried to do the same on the booster engine of a saturn-V rocket, you would simply blow off the engine and the other 4 engines, and the end of the rocket.

This was getting at something I mentioned in the other thread.

The types of reactions that will generate the most energy per given starting mass are also the most difficult to control. For example recreating a supernova reaction would generate a hell of alot of energy and in particular, if it could be directed, momentum (the players involved are heavier than tritium). The problem is that initatiing the reaction is more difficult than simple fusion, and once you have created that force, then how do you control it.

The problem with a pulse charge is that if the impulse is say for 5 seconds (generous) and you are limited to 8 g of force, then the maximum acceleration you can get from a blast is around 400 m/s.

A nuclear bomb is not simply nuclear material. The hydrogen bomb is made of explosive lenses than electrons, there are outer layers of fissile materials, there is a neutron generator and layers of other material that include inate material such as lithium, and the fissile/fussile material are not completely or efficiently utilized. So to make this viable one would have to find a way of

1. Making a more efficient bomb with no inert reactants (Since you have to carry the weight of bombs just like fuel)

2. Scale down the size of the bomb so it does not blow of the end of your ship

3. And use isotopes bomb that maximally translate in classical work better than heat.

[PB666]

I just want to point out that to my knowledge, for most (atmospheric flight) fighter jets, the limiting factor nowadays isn't structural strength but crew squishiness in the face of G forces.

Of course if your craft is a drone you could do a bunch of interesting things without worrying about that.

You put all your delicate scientific equipment like gravity and seismic sensors and diffraction gradient spectrophotomenter on the end of a bomb that accelerates the craft to 30g.

The egg test, place the egg in a compatible bowl and cover it. If you can get the egg into space and hatch it, you are probably safe, if the egg comes out smashed or hard-boiled, or sizable percentage of its atoms all rearranged into free-radicals, then you prolly should rethink your go-to-space-today strategy.

[Rakaydos]

Orion designs also use the intense radiation of a nuke to vaporize a thin layer of the ablative pusher plate, generating some more thrust.

The effect is inconsiquential, though, compared to the main pruplusion. If they could get rid of it entirely without losing efficency, they would, because it cuts into the drive's operating life.