Orion drive and related physics

[sevenperforce]

Yeah, if a fully-loaded Orion starts to crash, you kinda want to detonate the whole damn thing long before it hits the ground, rather than waiting for the massive radiological dispersal event that will happen when it hits.

[DerekL1963]

1 hour ago, sevenperforce said:

Yeah, if a fully-loaded Orion starts to crash, you kinda want to detonate the whole damn thing long before it hits the ground, rather than waiting for the massive radiological dispersal event that will happen when it hits.

I'm not sure that massive radiological dispersal in the atmosphere is much better...  at least not below the stratosphere anyhow.

[sevenperforce]

8 minutes ago, DerekL1963 said:

I'm not sure that massive radiological dispersal in the atmosphere is much better...  at least not below the stratosphere anyhow.

If they're thermonuclear then presumably most of the energy will come from fusion, not fission, resulting in very little fallout.

[DerekL1963]

1 hour ago, sevenperforce said:

If they're thermonuclear then presumably most of the energy will come from fusion, not fission, resulting in very little fallout.

There's only "very little fallout" by comparison to a fission weapon of the same yield.   By any rational standard, there's still considerable fallout.   Doubly so considering the huge number of weapons and significant mass available to be contaminated.

[damerell]

I think the least-worst approach is for the bomb magazine to, in KSP terms, have a high crash resistance and to be equipped with decouplers, chutes, and heatshields such that (in a failsafe dead-kerbal's-handle arrangement) if the craft fails the magazine itself will return safely, leaving only the immediately ready bombs to strew themselves all over the landscape.

I mean, I don't think Orion is by any means safe; it's attractive because it's so much better otherwise than anything we can build with today's technology - or Cold War technology.

[lobe]

Speaking of atmospheric Orion usage, would it work better in atmosphere? If the propellant charges are designed with propellant to shoot at the propulsion plate, I think it could be thought the rapid heating of air would also provide an additional propulsion force in atmosphere.

[HebaruSan]

Just now, lobe said:

Speaking of atmospheric Orion usage, would it work better in atmosphere? If the propellant charges are designed with propellant to shoot at the propulsion plate, I think it could be thought the rapid heating of air would also provide an additional propulsion force in atmosphere.

Based on previous comments and threads, I believe the consensus is that yes, that's correct.

[DerekL1963]

2 hours ago, lobe said:

Speaking of atmospheric Orion usage, would it work better in atmosphere? If the propellant charges are designed with propellant to shoot at the propulsion plate, I think it could be thought the rapid heating of air would also provide an additional propulsion force in atmosphere.

I suspect not, the additional mass of heated air is very minimal compared to the mass of the propellant charge.

[fredinno]

2 hours ago, lobe said:

Speaking of atmospheric Orion usage, would it work better in atmosphere? If the propellant charges are designed with propellant to shoot at the propulsion plate, I think it could be thought the rapid heating of air would also provide an additional propulsion force in atmosphere.

You would never do that anyways- Orion is limited in that you need it to be kept out of the magneosphere so that radiation doesn't hit Earth.

[HebaruSan]

13 minutes ago, fredinno said:

You would never do that anyways- Orion is limited in that you need it to be kept out of the magneosphere so that radiation doesn't hit Earth.

Well, if aliens were bombarding us and our only hope was to get the Michael (Project Archangel) into orbit as quickly as possible, some exceptions might be made.

Spoiler

 

[steve_v]

12 minutes ago, fredinno said:

You would never do that anyways- Orion is limited in that you need it to be kept out of the magneosphere so that radiation doesn't hit Earth.

It's not really the radiation that's the problem for atmospheric usage... it's the difficulty of producing a compact 'fallout-free' fission device, 'cause too many radioactive particles in the atmosphere is a Bad Thing.
Attenuating the gamma to safe levels requires a large-ish exclusion zone, but it's not too far-fetched... after all, atmospheric fission devices have been tested before.
I guess it all depends on your "acceptable losses". If diverting an extinction level asteroid means 2 people get cancer from fallout... yeah, ok. Not so good for replacing chemical boosters on LEO runs though.

[Bill Phil]

http://www.projectrho.com/public_html/rocket/realdesigns.php#id--Project_Orion

Here's a good source. Albeit not necessarily 100% accurate.

[K^2]

14 hours ago, Buster Charlie said:

Actually I think shaped charge is 1000% the right word. In warheads,  the explosive itself isn't what penetrates the armor of armor tank, iirc it's something like a copper plate that is vaporized and propelled at high speeds in a controlled fashion.  So in essence, the explosive energy efficency is not important to the idea of a shaped charge, only that the explosive force is used to do work in a controlled fashion.  What made me feel this is a perfect analogy,  is the reading I did on why tungsten  is used, and what would happen if you used a different  material with the exact same setup.

Regardless of what actually does penetration, the term "shaped charge" refers to the shape of high explosive in the warhead, which focuses the detonation wave and produces a directed explosion. This is fundamentally impossible with nuclear weapons.

[magnemoe]

22 minutes ago, K^2 said:

Regardless of what actually does penetration, the term "shaped charge" refers to the shape of high explosive in the warhead, which focuses the detonation wave and produces a directed explosion. This is fundamentally impossible with nuclear weapons.

Its quite possible to do with with nuclear bombs. Yes its weird but its how hydrogen bombs works. 

[K^2]

It really, really isn't.

[kerbiloid]

1 hour ago, K^2 said:

It really, really isn't.

Rapatronic photos.

Edited February 19, 2016 by kerbiloid

[Bill Phil]

7 hours ago, K^2 said:

Regardless of what actually does penetration, the term "shaped charge" refers to the shape of high explosive in the warhead, which focuses the detonation wave and produces a directed explosion. This is fundamentally impossible with nuclear weapons.

The initial explosion is mostly radiation, particularly X-Rays. This can be absorbed by materiaks opaque to X-Rays. In Orion they're using depleted uranium in the case. 

This only blocks the radiation, though. And it gets vaporized. Idk how it effectively focuses the blast. Even so, only 85% of the blast is focused.

[DerekL1963]

53 minutes ago, Bill Phil said:

8 hours ago, K^2 said:

Regardless of what actually does penetration, the term "shaped charge" refers to the shape of high explosive in the warhead, which focuses the detonation wave and produces a directed explosion. This is fundamentally impossible with nuclear weapons.

The initial explosion is mostly radiation, particularly X-Rays. This can be absorbed by materiaks opaque to X-Rays. In Orion they're using depleted uranium in the case. 

This only blocks the radiation, though. And it gets vaporized. Idk how it effectively focuses the blast. Even so, only 85% of the blast is focused.

The initial energy release is mostly X-rays, which 'flows' much like water at those densities.   This energy is redirected by the radiation case towards the channel filler (in a thermonuclear weapon the energy is redirected to the secondary).

So while it's not a "shaped charge" in the picky sense that K^2 is using the term, and the physical mechanisms are different, the effect is the same - energy released by the explosion is used to vaporize and accelerate mass in a given direction.  In a high explosive charge it's used to accelerate a copper liner, in a thermonuclear weapon the pusher/tamper of the secondary, in an Orion pulse unit the propellant.

Edited February 19, 2016 by DerekL1963

[PB666]

On 2/17/2016 at 0:34 AM, Temstar said:

This is not a huge problem, because the only type of Orion that need that kind of Isp are interstellar ships, and those have plenty of time for thrusting anyway. Dyson's "energy limited" Orion takes this into consideration and it has 0.00003g of acceleration. This ship by the way is 20km in diameter and has a 5 million ton copper pusher plate.

The alternative is to use open cycle cooling where you accept that each bomb will cause some material to ablate away and you design the ship so the pusher plate or whatever ablation system it use can just survive all the bombs. The ship will be useless when it reaches its destination (as in, it can't be refueled with more bombs) but can achieve 1g acceleration for 10 days and so reach 3.3% c.

How does it stop. IIRC a hydrogen bomb is compose of hydrogen isotopes and lithium, lithium deuteride, lithium tritide. So only about a third of the weight of the core undergoes fusion. If we then argue that 0.1% mass energy conversion that is 0.03% of the bomb, much less (assuming an efficiency of 100%). If the bomb mass is say 1/10th of the ship then that is 0.003% or a proportion of 0.00003 which means the best you could do is reach 0.5% of the speed of light. To reach 3.3% the bombs would have to be something like 90% and only a flyby.

10 hours ago, K^2 said:

Regardless of what actually does penetration, the term "shaped charge" refers to the shape of high explosive in the warhead, which focuses the detonation wave and produces a directed explosion. This is fundamentally impossible with nuclear weapons.

Yep, the explosives in a hydrogen bomb are in the shape of shallow pyrimdial triangles, hundreds of them each wired to an electronic detonater that precisely times the detonation charge.

 

It is possible by very very muscular confinement of metals to direct the flow of energy, while it maybe true there is alot of xrays, these xrays are ionizing and that energy undergoes conversion, however, muscular confinement by metallic structures is not suitable for space craft as these structures increase the mass and are potentially catastropic projectiles. Orion anyway I think is not a feasible propulsion system because wear and tear, and many engineers will tell you, is not flat, and degradation starts in pits and tends to grow from there.

Edited February 19, 2016 by PB666

[Nothalogh]

1 hour ago, PB666 said:

How does it stop. IIRC a hydrogen bomb is compose of hydrogen isotopes and lithium, lithium deuteride, lithium tritide. So only about a third of the weight of the core undergoes fusion. If we then argue that 0.1% mass energy conversion that is 0.03% of the bomb, much less (assuming an efficiency of 100%). If the bomb mass is say 1/10th of the ship then that is 0.003% or a proportion of 0.00003 which means the best you could do is reach 0.5% of the speed of light. To reach 3.3% the bombs would have to be something like 90% and only a flyby.

Yep, the explosives in a hydrogen bomb are in the shape of shallow pyrimdial triangles, hundreds of them each wired to an electronic detonater that precisely times the detonation charge.

 

It is possible by very very muscular confinement of metals to direct the flow of energy, while it maybe true there is alot of xrays, these xrays are ionizing and that energy undergoes conversion, however, muscular confinement by metallic structures is not suitable for space craft as these structures increase the mass and are potentially catastropic projectiles. Orion anyway I think is not a feasible propulsion system because wear and tear, and many engineers will tell you, is not flat, and degradation starts in pits and tends to grow from there.

So just change the plates out on a schedule 

[sevenperforce]

Yikes. So much misinformation. Where to begin...

Yes, there are a bunch of pyramidal chemical charges with detonators inside nuclear weapons. At least, there were in the earliest spherical implosion warheads. Later designs used more advanced two-point implosion. But in all these cases, the role of the chemical explosive was to precisely implode the fissile mass with enough inertial confinement to allow supercriticality to be reached. Once the actual nuclear chain reaction was triggered, the chemical explosives were utterly useless.

Chemical shaped charges and nuclear shaped charges serve the same function, to a degree, but they use completely different and unrelated mechanisms. A chemical shaped charge uses an explosive material molded into the form of a concave lens. When the explosive is detonated the combustion takes place on the surface of lens so that the supersonic, superheated gases from the explosive are inertially focused into a thin, penetrating stream that cuts through pretty much anything. 

In contrast, you cannot really shape or mold a nuclear explosive to produce a comparable effect, because the nuclear explosive depends on a particular geometry in order to achieve criticality. A nuclear device can only be spherical, as in the case of a fission warhead, or cylindrical, as in the case of a Teller-Ullam thermonuclear fusion bomb. In either case, the explosion is so viciously energetic that it will smooth out any inhomogeneities into a gigantic spherical plasma death ball every time. No way to shape that.

However, it is possible to use a portion of the energy from the exploding nuke - usually the xrays - to redirect momentum in a particular way. That is how a Teller-Ullam device works, after all. Something very dense, like tungsten, will be able to absorb a large portion of the x-ray spectrum energy even though it isn't going to be able to physically confine the explosion. It's like being on a trampoline and getting a bounce from a really really fat kid: you are going to get launched, but you can control what direction you'll be launched in if you know what you're doing. By giving the tungsten plate a particular shape, you can cause its momentum to have a particular vector.

[Nothalogh]

2 hours ago, sevenperforce said:

Yikes. So much misinformation. Where to begin...

Yes, there are a bunch of pyramidal chemical charges with detonators inside nuclear weapons. At least, there were in the earliest spherical implosion warheads. Later designs used more advanced two-point implosion. But in all these cases, the role of the chemical explosive was to precisely implode the fissile mass with enough inertial confinement to allow supercriticality to be reached. Once the actual nuclear chain reaction was triggered, the chemical explosives were utterly useless.

Chemical shaped charges and nuclear shaped charges serve the same function, to a degree, but they use completely different and unrelated mechanisms. A chemical shaped charge uses an explosive material molded into the form of a concave lens. When the explosive is detonated the combustion takes place on the surface of lens so that the supersonic, superheated gases from the explosive are inertially focused into a thin, penetrating stream that cuts through pretty much anything. 

In contrast, you cannot really shape or mold a nuclear explosive to produce a comparable effect, because the nuclear explosive depends on a particular geometry in order to achieve criticality. A nuclear device can only be spherical, as in the case of a fission warhead, or cylindrical, as in the case of a Teller-Ullam thermonuclear fusion bomb. In either case, the explosion is so viciously energetic that it will smooth out any inhomogeneities into a gigantic spherical plasma death ball every time. No way to shape that.

However, it is possible to use a portion of the energy from the exploding nuke - usually the xrays - to redirect momentum in a particular way. That is how a Teller-Ullam device works, after all. Something very dense, like tungsten, will be able to absorb a large portion of the x-ray spectrum energy even though it isn't going to be able to physically confine the explosion. It's like being on a trampoline and getting a bounce from a really really fat kid: you are going to get launched, but you can control what direction you'll be launched in if you know what you're doing. By giving the tungsten plate a particular shape, you can cause its momentum to have a particular vector.

I was under the impression that the beryllium absorbed the xrays, got turned into plasma, and which in turn vaporized and drove the tungsten 

[PB666]

2 hours ago, sevenperforce said:

Yikes. So much misinformation. Where to begin...

Yes, there are a bunch of pyramidal chemical charges with detonators inside nuclear weapons. At least, there were in the earliest spherical implosion warheads. Later designs used more advanced two-point implosion. But in all these cases, the role of the chemical explosive was to precisely implode the fissile mass with enough inertial confinement to allow supercriticality to be reached. Once the actual nuclear chain reaction was triggered, the chemical explosives were utterly useless.

Chemical shaped charges and nuclear shaped charges serve the same function, to a degree, but they use completely different and unrelated mechanisms. A chemical shaped charge uses an explosive material molded into the form of a concave lens. When the explosive is detonated the combustion takes place on the surface of lens so that the supersonic, superheated gases from the explosive are inertially focused into a thin, penetrating stream that cuts through pretty much anything. 

In contrast, you cannot really shape or mold a nuclear explosive to produce a comparable effect, because the nuclear explosive depends on a particular geometry in order to achieve criticality. A nuclear device can only be spherical, as in the case of a fission warhead, or cylindrical, as in the case of a Teller-Ullam thermonuclear fusion bomb. In either case, the explosion is so viciously energetic that it will smooth out any inhomogeneities into a gigantic spherical plasma death ball every time. No way to shape that.

However, it is possible to use a portion of the energy from the exploding nuke - usually the xrays - to redirect momentum in a particular way. That is how a Teller-Ullam device works, after all. Something very dense, like tungsten, will be able to absorb a large portion of the x-ray spectrum energy even though it isn't going to be able to physically confine the explosion. It's like being on a trampoline and getting a bounce from a really really fat kid: you are going to get launched, but you can control what direction you'll be launched in if you know what you're doing. By giving the tungsten plate a particular shape, you can cause its momentum to have a particular vector.

YOu can shape are reaction if you can alter the momentum early in the reaction, thats were the muscular structures come in, the problem is that these structures will eventually accelerate out of the way. Nuclear reactions don't stop the moment the fusion reaction reach thier peak, they continue on depending on pressure and temperature and also neutron density. So the area of the reaction where this is the highest will push out in the direction where it is lowest. The idea of shaping nuclear weapons came about for he following reason, as the pictures show a nuclear explosion occur in largely a three dimensional space, but all the targets lie essentially on a two dimensional plane, therefore have a 100 megaton bomb is not 5 times more useful than a 20 megaton. So the basic idea was to steer the explosion so that the blast wave moved primarily in the X,Z directions and not in the Y. The problem has basically been solved by other methods, namely just making more smaller weapons and clustering their detonations. This is not to say it has not been done or no-one is doing it, its just that have a Tsar Bomb in your arsenal affords certain bragging rights, but the Russian have tended to focus more on multiwarhead missiles than on making directional super bombs. Moreover, with the smart weapons in the US arsenal, nuclear weapons per say are for nothing more than show and detent. GIven the cleanup cost of nuclear weapons and likely suits that would follow now, they are not a wise choice.

In space you prolly want the smallest possible warhead, which means you are prolly going after a spherical device (two plate fission devices are rather inefficient), just because of the mass energy issues. unless of course you are using structure as an accelerant to push the bombs ejecta onto the blast plate.  I have not thought about it that much because I think Orion is a really really bad idea, the use of TNEDs to propel a ship introduces so many more variables that TNRs do not have, namely the uncontrollability of the heat and forces involved. Any deviation of the bombs explosion can cause turning forces on the rest of the rocket, or potentially breaking the standout which the plates set. The impulse of the bomb, no matter how well buffered will likely degrade the structural integrity of the ship after a while, particularly where the thruster and rest of craft join.

[Nothalogh]

1 hour ago, PB666 said:

YOu can shape are reaction if you can alter the momentum early in the reaction, thats were the muscular structures come in, the problem is that these structures will eventually accelerate out of the way. Nuclear reactions don't stop the moment the fusion reaction reach thier peak, they continue on depending on pressure and temperature and also neutron density. So the area of the reaction where this is the highest will push out in the direction where it is lowest. The idea of shaping nuclear weapons came about for he following reason, as the pictures show a nuclear explosion occur in largely a three dimensional space, but all the targets lie essentially on a two dimensional plane, therefore have a 100 megaton bomb is not 5 times more useful than a 20 megaton. So the basic idea was to steer the explosion so that the blast wave moved primarily in the X,Z directions and not in the Y. The problem has basically been solved by other methods, namely just making more smaller weapons and clustering their detonations. This is not to say it has not been done or no-one is doing it, its just that have a Tsar Bomb in your arsenal affords certain bragging rights, but the Russian have tended to focus more on multiwarhead missiles than on making directional super bombs. Moreover, with the smart weapons in the US arsenal, nuclear weapons per say are for nothing more than show and detent. GIven the cleanup cost of nuclear weapons and likely suits that would follow now, they are not a wise choice.

In space you prolly want the smallest possible warhead, which means you are prolly going after a spherical device (two plate fission devices are rather inefficient), just because of the mass energy issues. unless of course you are using structure as an accelerant to push the bombs ejecta onto the blast plate.  I have not thought about it that much because I think Orion is a really really bad idea, the use of TNEDs to propel a ship introduces so many more variables that TNRs do not have, namely the uncontrollability of the heat and forces involved. Any deviation of the bombs explosion can cause turning forces on the rest of the rocket, or potentially breaking the standout which the plates set. The impulse of the bomb, no matter how well buffered will likely degrade the structural integrity of the ship after a while, particularly where the thruster and rest of craft join.

You know, the best way to prove it right or wrong, is to sack up and build it.

Unmanned, of course, for the proof of concept mission.

This would be the perfect way to get a massive amount of scientific gear to the outer solar system.

This is the only piece of machinery that can get you a sample return from Pluto.

 

Also, a question for those who might know.

Is the fission-fusion-fission design called a Sakharov device in Russia, in line with how we named it after Teller and Ullam? 

Edited February 19, 2016 by Nothalogh

[sevenperforce]

24 minutes ago, Nothalogh said:

Also, a question for those who might know.

Is the fission-fusion-fission design called a Sakharov device in Russia, in line with how we named it after Teller and Ullam? 

They didn't name it after Sakharaov. Sakharaov proposed First Idea, Second Idea, and Third Idea. First Idea, nicknamed sloika, was a layer-cake design which was fusion-boosted fission. Second Idea involved the use of lithium deuteride as the fusion booster. Third Idea, developed by Sakharaov, Zeldovich, and Davidenko, separated the primary and secondary and use x-rays from the primary to compress the secondary; this was equivalent of the Teller-Ullam design. Third Idea was first tested in the RDS-37 shot.

Teller-Ullam is technically still classified, and although the basic principle is fairly clear, there seem to be critical details enabling the actual process which remain secret. The US didn't share any of the details with the UK until after UK's Grapple X test demonstrated that they had unlocked the secret.