Sunday 21 May 2017

Nuclear EFP and HEAT

A follow-up to the popular Casaba Howitzer post, we now look more closely at the concept of nuclear shaped charges in both Explosively Formed Projectile and High-Explosive Anti-Tank (Monroe effect) forms. 
The concept

An explosive produces hot gasses that expand in all directions. A shaped charge focuses the energy of an explosive into a narrow cone. How effectively it does this is called 'directivity'.

The energy of a shaped charge can be used to accelerate a projectile. This projectile absorbs some of the gasses' kinetic energy and some of its thermal energy.

To maximize the amount of kinetic energy gained by the projectile and to reduce how much heat it absorbs, the projectiles are made as thin sheets of metal resting on a layer of explosive filler. The filler detonates and expands in only direction - into the projectile.
Cross-section of a HEAT warhead.

The projectile henceforth will be referred to as the 'metal plate' or the 'liner'. You can find it called the 'flyer plate' or simply 'flyer' in literature.

The angle the metal plate forms with the explosive filler determines how much of the Monroe effect it uses. At shallow angles, we produce an Explosively Formed Projectile. At sharp angles, the Monroe effect is used to pinch together the walls of the cone and squirt out a very fast jet. The latter is used today in High Explosive Anti-Tank projectiles.
Modern weapons use chemical energy. The explosive filler is also a chemical compound, so the maximum velocity of the metal plate is proportionate to the energy density and the amount of explosive filler being used.

In this post, we will consider inert fillers being heated by nuclear shaped charges. For more information on, read the Casaba Howitzers post.

Existing performance

Chemical explosives today energy densities measured in megajoules per kg. TNT contains 4.184 MJ/kg. HMX contains 6.27 MJ/kg. Some chemical compounds such as some solid rocket propellants contain even higher energy densities, but do not produce the supersonic shockwave necessary in shaped charges.

These explosives create gasses reaching 3000 to 4000 Kelvin. The rate of expansion of a gas, and therefore its kinetic energy, is strongly dependent on its temperature. Therefore, a hotter gas contains more energy and can accelerate a metal plate even faster.

Modern EFPs manage to propel their metal plates at velocities ranging from 2000 to 3000 m/s. Attempting even higher velocities quickly requires huge amounts of explosive filler. 
Velocity distribution in a HEAT jet. Numbers in m/s. Jet tip 5000 m/s, body 1500 m/s, rearmost slug immobile.

HEAT weapons manage to accelerate the tip of their jets to velocities ranging from 7 to 14 km/s. The remainder of the metal lining reaches much slower 1 to 2 km/s velocities, with the deepest segment not being accelerated at all. This velocity differential stretches out the jet until it fragments into ineffective pieces, which severely limits the effective range.

Nuclear Explosive Formed Projectiles

The idea here is weaponize the nuclear pulse propulsion units designed for use in the Orion drive. 
Orion pulse sequence.

From the original project, we know that 85% of the nuclear yield can be directed into a narrow cone of 22 degrees or less. Instead of allowing beryllium filler particles to fly out into space, we place a thick metal plate on top.

In a NEFP, the metal plate is at a very shallow angle. 

Research has already put into the concept, as published by Science and Global Security 1990.

NEFP velocity

The main requirement of a NEFP is that the energy deposited into the metal lining is not sufficient to vaporize it. 

Copper's melting point is about 1400 K. Refractory materials such as tungsten can stay semi-solid at 3600 K. Some materials can stay solid at even higher temperatures, but would not exhibit the plastic behavior of metals. This limits the maximum metal plate temperatures to about 3500 K.

We can use the contemporary performance of Explosively Formed Penetrators to estimate the maximum temperature of the filler in a nuclear design. 

This study from Thermal Science 2016 tracked the temperatures and pressures in a copper plate being driven by Octol, a mix of TNT and HMX. Octol has a detonation velocity of 8480 m/s and a specific energy of 6.3 MJ/kg.

We observe that the copper reaches temperatures around 622 K if we average between the 545 and 698 K in the last frame. The gases driving it reach 4010 K. In the experiment, the copper is 10 mm thick, masses 12.5 kg and is shaped as a hemisphere 150 mm in radius, for an 'exposed' area of 0.14 m^2. 

Copper's heat capacity is 385 kJ/kg/K and its heat conductivity is 385 W/mK. 

Tungsten's heat capacity is 133 kJ/kg/K and its heat conductivity is 100 W/mK. 

If we substituted copper for tungsten, the metal plate would survive 3500K, a temperature 5.83 times higher, but requires only 2.04 times more energy due to the lower heat capacity. 

Heat transfer by conduction is linear with the temperature difference. In the Thermal Science test, the copper started at 300 K and ended up at 622 K, averaging a 3548 K temperature difference between the hot gasses and the metal plate.

A tungsten plate would heat up from 300 K to 3500 K, averaging 1900 K. Its heat conductivity is 3.85 times lower than that of copper, so the temperature difference can be allowed to become 3.85 times higher for the same heating effect.

Considering all these factors, tungsten can survive a temperature difference 3.85 * 2.04 : 7.85 times higher. 

This works out to a  tungsten plate would average 1900 K if it is accelerated by a gas of temperature just under 30000 K. 

This gas contains 7.42 times more energy than high explosive gas. It would accelerate a tungsten plate to a velocity 2.7 times faster.

We can safely say that Explosively Formed Projectiles can be propelled about three times faster using nuclear energy than using chemical explosives. This suggests velocities of about 6 to 9 km/s.

Higher velocities can be achieved if we accept the fragmentation of the metal plate. These fragments have a theoretical velocity of 100 km/s.

Even higher velocities, such as those cited in the Science & Global Security article, are the result of explosive fillers being heated to millions of Kelvins. They allow for velocities of up to 3% of the speed of light, as fast as the particles in a Casaba Howitzer. However, heating a metal liner and an explosive filler to those temperatures turn them into a plasma, and plasma-plasma interactions do not allow for much of the nuclear weapon's yield to be converted into kinetic energy. 

NEFP efficiency
Relevant section underlined in red.

According to Friedwardt Winterberg, 50% of the nuclear blast is converted into the kinetic motion of the particles in the shaped charge's explosive filler. The rest goes into heating the filler. 
M the metal place, C the explosive filler.

Since the nuclear blast also destroys everything aft of the explosive filler, the configuration is assumed to be an 'open-faced sandwich'. Roughly 50% of the filler's kinetic energy is used to accelerate the metal plate in the target's direction. 

Using the 85% efficiency for the nuclear blast, 50% for the filler and 50% for the metal plate, about 21% of the nuclear yield ends up in the projectile.

This is better than the 5% efficiency listed in experimental studies. 

In a NEFP, this means that a 1 kiloton yield warhead could propel more than 21.7 tons of metal at the target at 9 km/s. 

This literal boulder would be immune to most forms of anti-missile defenses, such as Whipple shields, lasers, missile interceptors or even wide-angle defensive Casaba Howitzers. 

A 2 m wide, 21.7 ton tungsten projectile would be 352mm thick. Using the hydrodynamic penetration model, this projectile would penetrate 947mm of aluminum. Armor materials suited to resisting laser fire would be less dense and suffer greater penetration. This isn't an exceptional penetration depth for the mass invested in the weapon.

Instead, the metal has incredible momentum. Striking a 10000 ton target would knock the target back at 19.5 m/s. In practice, this would break the target in half through sheer mechanical stress. The relatively size of the projectile makes the impact resemble a cannonball ploughing through a building.  

Spaced NEFP

In the Orion drive, the nuclear pulsed propulsion charges are detonated at a distance of 25 meters from the pusher plate. This spacing allows for the hot plasma (67000 K) ejected by the nuclear charge to expand and cool down to 14000 K. This greatly reduced the erosion and heating of the pusher plate. 
USAF 10m Orion
A similar concept can be used to allow nuclear EFPs to both use high-temperature gasses and the high kinetic efficiency of solid metal plates.

By spacing the explosive filler from the metal plate, an initially very hot plasma can be accelerate a solid plate without vaporizing the latter. 

The advantage is that a very hot plasma allows for very fast EFPs and much lighter weapons. The disadvantage is that they will become much larger and there will be some efficiency losses from the metal plate not intercepting the entirety of the filler gasses.

Let us assume a 1 kt yield nuclear shaped charge with 85% directivity. We want the gasses arriving to accelerate a tungsten plate to be no hotter than 30000K, as calculated in our example above.

How hot can the initial filler get?

If we use the original 22.5 degree cone, and state that the filler starts out 1m wide (surface area 3.14 m^2), then in 10 meters spacing it will have spread out to a disk 5m wide (19.47 m^2). This linear expansion would cool the plasma by a factor 6.2. The initial plasma temperature can be 186000 K and allow velocities (186000/4010)^0.5 about 7 times higher than with chemical explosives.

If we increase the spacing to 20 meters, the plasma would cool by a factor 20. The initial plasma temperature can be 602400 K and velocities 12.25 higher.

We could instead reduce the radius of the filler down to 10 cm and increase the propellant cone's angle to 45 degrees to achieve an expansion and cooling ratio within 10 meters of 7,022x, within 20 meters of 27,755x, each allowing velocities 83 and 477 times faster!

Here is a simple equation to determine how the spacing and spread angle cools the plasma and allows for higher projectile velocities, based on the results from the experiment cited above. 
  • Velocity factor = ((tanA * Spacing + Ri) / Ri ) ^ 2 * (Ts / Tc ))^0.5
Velocity factor is how much faster the NEFP projectile can be compared to a chemical EFP. Typical velocities for chemical EFPs at 2 to 3 km/s. 

A is half the spread angle. For the Orion drive, this is 11.25 degrees.
Spacing is the distance between the filler and the metal plate, in meters.
Ri is the initial radius of the filler, in meters.
Ts is the survivable temperature of the metal plate. For tungsten, it should be 30000 Kelvin.
Tc is the chemical gas temperature we are using as a reference. For our example, this is 4000 Kelvin.

Using this equation, we determine that a 1 kt yield shaped charge with 85% directivity, spreading by 60 degrees (30 degree half-angle), Ri 15cm, and placed 10 meters away from a 16.7kg tungsten plate could reach velocities of up to 324 km/s. 

The same warhead with the same spread at 25 meters distance would be able to accelerate a 2.75 kg plate to 798km/s. 

A problem with very high spread angles is that some of the gas particle's kinetic energy is not perpendicular to the plate and therefore does not contribute to its acceleration. Great separation distances increases losses from gasses expanding laterally and not being intercepted by the plate. Overall efficiency would be lower in these cases.

Nuclear HEAT or Nuclear Munroe Projectile

Using the Monroe effect on metal cones angled sharply inwards allows for jets with tip velocities 7 to 10 times greater than the velocity of the explosive gasses driving them.
Method of operation
Modern HEAT weapons generate tip velocities of up to 14km/s using gasses that travel no faster than 2 or 3km/s. 

A 'Nuclear Monroe Projectile' would therefore produce metal jets of 60 to 90km/s. 

If the maximum particle velocity in a fusion shaped charge is 3% of the speed of light, then the Monroe effect can increase this velocity to 30%. 

However, there are severe limitations that reduce the effectiveness of this type of weapon.

The first is the standoff distance.
HEAT warhead testing for the correct standoff distance. 

While the tip of the jet can reach astounding velocities, the main body of the projectile reaches much lower velocity, with the rearmost 'slug' remaining mostly stationary relative to the warhead. 

The large velocity differential stretches out the jet to the point of fragmentation and uselessness. Tip velocities of several tens of kilometers per second would disrupt a jet in milliseconds, meaning that it has to be fired close enough to its target to penetrate with an intact jet. 

The standoff distance would be measured in single meters. 

The second is efficiency.

In a NEFP, 21% of the nuclear yield ends up as the kinetic energy of the projectile. In a NMP, the kinetic energy is shared between a small fast tip, a slow moving body and a mostly stationary slug concentrating most of the mass. This reduces the overall efficiency of the weapon to a few percent. 

In a realistic space setting, getting an intact warhead close to the target before it detonates is a difficult task. In most cases, factors which make this easier (massed missile attacks, high velocity warheads) reduce the usefulness of nuclear warheads (high per-unit costs, waste of missile's kinetic energy). 

Performance compared to lasers and Casaba Howitzers

Lasers are generally taken to be low-efficiency, long-ranged weapons which require so many high-mass components that spaceships are built around them. Their extreme effective range can further be extended by relatively cheap methods (larger focusing mirror, laser webs) once the initial investment in radiators, reactors, cooling systems, electrical generators and so on, is made. 

Casaba Howitzers unlock the potential of nuclear energy at long distances. Conventional nuclear warheads waste their energy in spherical explosions that cannot harm spaceships beyond a few kilometers. A Casaba Howitzer focuses this nuclear energy into particle beams that can vaporize targets at close range and cover large swathes of space in burning plasma for only a few hundred kilograms per warhead.

At an average 1 kW/kg from reactor to radiator through all the components required for a laser weapon, a gigawatt beam would require an investment of 1000 tons. 

This 1000 ton weapon would maintain a 10mm/s penetration rate in aluminum at about 25000km, using a 40m wide mirror and 400nm wavelength. 

In comparison, a much less complex spaceship could arms itself with 285 Casaba Howitzers with 10 megaton yield and 0.001 radian directivity, with the 10000km effective range. The lack of huge radiators and power requirements means that some stealth tactics are possible, wherein the spaceship unloads its missiles and overwhelms its targets with multiple particle beams each. 

However, if the Casaba Howitzer-equipped spaceship is detected and intercepted, it will lose to the laser. The laser can fire indefinitely and stay outside of the range of the particle beams. 

Increase the yield of the nuclear warheads to reduce the range gap quickly reduces the mass advantage they have over a reusable laser. A 150 megaton yield warhead would be effective out to 25000km, but would mass more than 52 tons each. 

The solution is the spaced NEFP. Its effective range is practically infinite. A 1 megaton warhead could propel a 2.7 ton projectile to 800km/s, while massing only about 6 tons. This projectile crosses the laser's effective range in about 30 seconds, gouges out a crater nearly a 100 meters deep and/or cracks the target in half with 2160 kN.m of momentum concentrated on a spot less than a meter wide.


The consequences of mature NEFP technology in a setting are similar to those of Casaba Howitzers. 

Devastating effects, able to be projected at extreme ranges, requiring only small investments in terms of propulsion, energy and mass to be used. The smallest freighter can take down the largest warship in a surprise attack. Large specialized warships such as laser battleships would not be able to compete with swarms of NEFP-equipped fighters. 

On the flip side, widespread use of shaped charges means that the Orion propulsion concept is viable. Spaceships would be able to sustain heavy-g burns for long periods, either for travel or for dodging projectiles. 

Combat might evolve into a cross between a chess board and a pinball machine. Chess, when it comes to intercepting your target and setting up a cross-fire they cannot dodge, and pinball, for when the nuclear warheads detonate and you have 30 seconds to outsmart your opponent and out-maneuver their projectiles.

A secondary consequence is that widespread use of nuclear energy requires either inordinate amounts of fissile fuels (with proliferation and unconventional warfare effects) or a cheap way to ignite fusion fuels.


  1. Is there a limit on how light the plate on the spaced NEFP can be? I am thinking about 27kg plates which would reach 2,7% of C with a megaton device behind. They can cross a gigameter in 125 seconds / 2 Minutes. Instead of 1250s / 21~ Minutes. And decreasing the weapon weight to around 500kg.
    The strength of such a device is enormous, aluminium (300MPa) would be excavated to nearly 60m depth, and nearly a million cubic meters of volume, a 100x100x100 Cube. Or 7,8m of Graphene.

    1. Well, the maximum velocity the spaced NEFP can reach is determined by the temperature of the explosive gasses, so using a lighter plate just means you are wasting the kinetic energy of the gasses.

      Instead, you should just increase the mass of the plate until you reach the efficiency limits of the warhead.


      First restriction: gas velocity

      Second restriction: warhead efficiency (available energy)

    2. I thought the efficiency equals area instead of mass, why is that? Does that mean NEFP plate have to be heavy to be efficient?

    3. The only efficiency I calculated was kinetic, in other words, how many joules from the nuclear warhead are captured by an ideal plate under ideal conditions.

      The plate cannot travel faster than the explosive gasses. An extremely lightweight plate will be carried up the gasses' velocity and stay at that velocity.

      A heavy plate reaches the same velocity, but it stops all the gasses behind it.

      Its the difference between an elastic and inelastic collision. A lightweight plate and the gasses is inelastic: the gasses continue moving after impact. The heavy plate allows for a more inelastic collision where more kinetic energy is absorbed.

    4. So, is the 800km/s the peak velocity? And If not, how high could it get in your opinion

    5. I really think it depends on how good you are at catching gas leaking from the sides of the plate.

      If you oversize the plate and use some sort of ultra-high temperature resistant metal... probably 3% lightspeed, the maximum velocity of the filler particles themselves.

      The weapon would probably have to detach the plate and wait for it to drift into the right spot before it can detonate though.

    6. Well ok, whats the diameter of the 2,75kg/ton plate? Is there any reason to use megaton NEFPs? The kiloton device can overkill every possible space craft. Even super-materials that are 500x stronger than steel need nearly a whole meter of the stuff to survive the impact. And it's unknown if graphene/nanodiamonds keep their properties when in mass, the strongest mass produced carbon fiber will be penetrated 2,13m deep!

    7. Well, if we use the spaced NEFP example, the plate would be about 29 meters wide and mass about 4 grams per m^2. Thankfully, a slight curve in the plate can be used to shape it into a long, narrow penetrator about 15m long.

      The megaton NEFP allows for extreme velocities. These might be important when the target has an Orion drive and can accelerate very quickly.

    8. A 29m wide plate for a kiloton device? How wide is the 15m long penetrator?
      At the same area around 17m? What you mean with "high velocities" 1% of C? Is your crater equation usable for objects such high area?

    9. It should be about 8mm thick.

      Extreme velocities: the 300 to 800km/s figures calculated as examples in this post.

    10. I still like to know the Diameter, not the thickness of the long penetrator.
      But Kiloton devices can also reach velocities up to 800km/s. Megaton devices are exactly the same as kiloton ones, but they have 1000x heavier plate/1000x the damage, but the force of 210 tons of TNT directly coupled into a target is enough to destroy any spaceship.

    11. The plate would fold up into a cylinder roughly 8mm in diameter and 15m long.

      The problem with using kiloton devices to push small masses to high velocities is that the projectiles end up becoming vulnerable to defenses such as interceptor drones or reactive armor.

      A heavier projectile can punch through or resist impacts through ablation, and still deliver a certain kill.

    12. So the long rod penetrator can have very low cross-sections compared to ordinary plates?
      Wouldn't heavy plates have the same problems? A 1kg Kirklin mine would have the energy of 320GJ when impacting the 2750kg plate, enough to completely vaporize it/pulverize it. Instead of 1 Megaton /2,75ton NEFP you could use 25x 1kt/2,75kg and still have a weight advantage, up to 100x 1kt/1MT ratio. If we say the Pulse unit weights 25kg. And roughly 2kg rest mass.

    13. Nevermind the long rod part, I understand now. The plate is angled and will be formed into a long and narrow cylinder. At 754 cubic cm shouldn't it weight around 15kg when its made out of tungsten?

    14. The long-rod shape is the result of having the nuclear blast unequally accelerating the edges and the center of the metal plate. The plate folds up on itself.

      I'm guessing that thicker plates don't deform as much as become something ranging from a bowel to a dart in shape.

      Smaller nuclear warheads are less efficient with the fissile fuels, unless you suppose using fusion energy. The specific details on how you want to balance projectile velocity, destructive power, defence penetration and nuclear efficiency is up to you mostly.

    15. Yes, the megaton NPU weights 200kg, the kiloton NPU weights 25kg, 1kg/5kT - 1kg/0.04kT, My small nuclear warhead is 125x worse in mass efficiency. Specific details are up to my estimations what would be realistic? Alright, 5kg Tungsten formed into a 1,5m long and 1,45cm wide rod, travelling at 1000km/s.
      the plate had a efficiency of 70% instead of 25%, achieving a total efficiency of 60% for NEFP.
      Is there a limit for how efficient can a plate be at absorbing kinetic energy? Using plate ranging from 10-30m in diameter.

    16. I meant that as you get closer to the minimum critical mass, it becomes harder and harder to achieve high burnup rates. Even with the 1.15 ton pulse units in the original Orion study, they assumed burnup rates of only 10%.

      The 21% I gave for the overall efficiency is the hard upper limit. Practical versions will have lower efficiency, down to 10 or even 5%, as experimentally reported.

    17. The SADM had a max yield of 1kT at 23kg weight, and it was developed 50 years ago.
      What limits the efficiency of the NEFP? Can the 20% efficiency be reached with "futuristic" tech-levels comparable with the "futuristic" Casaba Howitzer?

    18. The main limitation on the NEFP efficiency is how the nuclear energy is split between heating and moving the filler gasses. They need a nozzle to properly cool down and expand... the problem is that no nozzle will withstand nuclear temperatures.

      The other question is an engineering problem I can't give a solid answer to.

    19. Magnetic nozzles? It's a bit over the top but a possibility. When the setting already have magnetic focused lances you could use the tech.

      Casabas and NEFP are currently Velocity vs ranges as it seems like. I also believe NEFP have better target coupling making them more efficient than a casaba with the same energy.
      Yours sincerely.

    20. The electric energy and the magnetic force required to contain and direct a nuclear pulse unit would be horrendous.... but not technologically impossible. It would double the energy available.

      I agree with your assessment, but in my opinion, Casaba Howitzers are best used as missile warheads for slow missiles or mines, or defensive anti-missile weapons. NEFP are long range warheads.

      Combined with railguns and lasers, we'd have an interesting variety of weapons for any setting.

    21. As I said over the top, why does it have to be contained? Just use some high angle NPU, and let the magnetic fields form a nozzle. (Sounds way more easy than it actually is if I explain ot that way)

      The "new" variety of weaponry already needs a post on its own.
      Missiles vs Laser (Green vs purple) vs coilguns.
      You brought it to new extremes thanks to your posts.

    22. Is there a way to use the nuclear explosion itself to generate a magnetic field for the nozzle?

    23. @Eth
      Hello, yes there are some ways, the magnetic focused casaba powers its magnetic funnel through the heat of the explosion, the problem is we need way higher magnetic fields to make it work. Thermocouples uses heat to generate electricity.

    24. @Matter Beam
      Quick question. Does the magnetic nozzle increases the efficiency to 40% (Quote: "It would double the energy available".)?

    25. The current efficiency goes: 85% * 50% * 50%
      A magnetic nozzle will help with the middle value.

    26. To get back to Eth question, could you use the yield of the bomb to generate the magnetic field? If thermocouples absorb 10% of 0,1% of the yield you still be getting nearly 420MJ of energy, which can be perfectly converted into magnetic energy through superconducting coils. the actual question is if you can produce enough energy to power a magnetic nozzle without some extremely complicated design.

    27. Well, an electromagnet only needs to run long enough to hold the plasma as it moves through the nozzle's neck.

      This only takes about 1 millisecond.

      The problem is that in a deLaval nozzle, you need to 'choke' the gasses down to their subsonic velocity so that they expand properly. Compressing a gas raises the pressure. The magnetic strength required to hold the pressure of a nuclear bomb might not be realistically achievable.

    28. Accelerating gas from multiple thousand kilometers per second to under 343m/s? Yes that is realistically impossible in a warhead, sounds like 21,25% will stay the peak of NEFP efficiency.
      Thanks for your response.

  2. Instead of one single massive, one-hit-to-annihilate projectile, it could be fragmented in order to spray a circle of still-deadly fragments. This would require more complex projectiles, though I don't know by how much.
    It would require the target to accelerate harder in order to escape, or several warheads could be used to blanket a larger circle than the target can escape even at maximum acceleration.
    On the other hand, individual fragments would be more prone to counter-measures.

    1. I think there are many problems with fragmenting the metal plate. The biggest problem is the forces involved.

      Accelerating a metal plate to several km/s over the course of a a hundred microseconds or less involved incredible forces (10 million G for 10km/s, 815 million G for 800km/s). Semi-fluid metals can handle these pressures, and the thinner they are the better. A metal plate with pre-cut lines along its length for the fragments to form, like those around a grenade, would prevent the plate from remaining intact long enough to be fully accelerated.

      It's a big waste of energy.

    2. You could conceivably use a pair of devices. One that fires off a large projectile and another that fragments it, either by catching up to it or be being in the big one's way after acceleration. This might combine well with a high velocity pellet gun barrage, each missile would pick pellets in between it and the target for fragmentation. A two stage missile is probably simpler. The second stage can be as slow as you like, so long as it doesn't make it super easy to forecast the coming shot. I'm thinking a solid rocket tip that fires off the top of the device and clears to whatever distance you need/want for optimum scatter.

    3. I find it hard to picture what you are describing. Shouldn't the second missile be faster than the first one to catch up? How does a solid rocket operate at the same velocities and energies as a nuclear device?

    4. The solid rocket is a submunition of the nuke. It's mounted on the nose of the nuclear missile and launches just before the nuke fires. It carries enough matter to reliably fragment your penetrator. You time the detonation of the nuke so that your solid rocket/target is at the right standoff distance to get the degree of fragmentation you desire. This lets your high speed penetrator form normally and then collide with a solid object for fragmentation afterwards. Does that make sense? I chose a solid rocket because it's cheap, durable and capable of sudden high accelerations.

      You might be able to fine tune fragmentation by having a variable size target that can eject chunks of its target plate before or after the submunition launches or by firing the penetrator off angle to the plate.

      Whether that's feasible and desirable is another question. Standoff distances might be unreasonably long (and therefore let the enemy predict the vector of attack from the line formed by the rocket and the nuke) or fragmentation might waste too much velocity and defeat the point of using these devices As you stated elsewhere, fragmentation may be undesirable for ship-to-ship attacks. Perhaps as a longer range antimissile attack?

    5. I see an immediate problem with the 'collide' part. The high speed penetrator will achieve velocities ranging from tens to hundreds of kilometers per second. Smacking against a slow-moving object won't fragment it, it would vaporize most of it.

      You could solve this problem by using a slower NEFP... but that cuts massively into its effective range even with fragmentation increasing the area it can cover. Or, you could use a faster submunition to reduce the relative velocity at impact... but the velocity difference has to lower than 1km/s for solid-body interactions to occur, and at that point you'd need to justify equipping your missile with a second, smaller NEFP just to achieve fragmentation. Remember that nuclear pulse devices lose effectiveness and efficiency very quickly as you make them smaller.

      I can propose a solution to achieve the effects you want.

      A nuclear device can heat up very large quantities of inert propellant. You place the casaba howitzer behind a funnel half-filled with a something like lithium or water. The nuclear device is detonated and its energy goes into heating the fluid.

      The tube is on the wide end capped by a pre-fragmented grid of projectiles. The fluid vaporizes and expands spherically. If the funnel is big enough and strong enough, it can act as a nozzle and direct most of the plasma in the direction of the fragments. But the time the plasma has expanded and converted its thermal energy into kinetic motion, it would have cooled down enough to hit the fragments and accelerate them without destroying them.

      Instead of sharp spike of energy from the energetic plasma directly from a casaba howitzer, they will be accelerated by a slower, cooler wave of propellant instead.

      The advantage of this system is that it allows for large quantities of fragments, perhaps even with electronics onboard, to be accelerated to cover a vast fraction of the sky. The downside is extremely low system efficiency, limited maximum fragment velocity and extreme mass requirements for a one-shot weapon. I'm talking about a device in the hundreds of tons shooting a few kilos of projectile with an overall efficiency of a handful of percent to velocities of about 10-100km/s.

      If any of the fragments hit a target, they'll be delivering less than a millionth of a percent of the nuclear device's energy.

  3. Hello,
    I have a question, is there place for Orion-style missiles? I worked some numbers out.
    Wet mass: 25t
    Dry mass: 15t
    Delta-v: 2108km/s
    Burn-time: 100s at 1Hz
    Warhead: 100x 1kT NEFP (50kg each)
    60% Fuel, 20% Warheads, 16% Pusher-plate, 4% Electronics etc.
    It uses 250kT pulse units which weight 150kg.
    Each NEFP has 2912km/s Vmax, 2,7kT of energy on impact. Although you might want to not use the NEFP, the 50kg warhead at 2108km/s has a yield of 26,6kT KE.
    These missiles can cover extreme distances over 2,5x times faster than NEFPs.
    Are they plausible and would they fit in a setting where Casabas/NEFPs, X-ray FEL, Laser Webs, Pellet guns, Stealth and Orion-drives are the agenda?

    1. Well, there might be three complications:

      -Target performance. Your missile uses an Orion drive, but so can your target. If your target is a big warship, it might be able to use more efficient externally-ignited fusion pulses and capture more of the pulses' energy than a small missile. In other words, because Orion drives become less and less efficient as you make them smaller, it is entirely possible that the missiles end up being slower than their targets.

      -Cost effectiveness. You are loading up big amount of expensive nuclear fuels and sending off into the enemy as a bright, shoot-on-sight target. Only a fraction of the missile's total energy ends up in the target, even if it hits with every single warhead. What if I added the total mass of your stock of Orion missiles to my warship's armor, as dumb plating, to allow me to get closer and strike you down with much smaller NEFPs or even a big reusable laser?

      -Energy effectiveness. Compare the mass of the missile, especially the mass of its nuclear fuel, to a NEFP of similar mass. What can a 25 ton NEFP do in this setting? How small can you make a single NEFP that can shoot a projectile at 2108km/s?

      These are the questions a sane weapons designer will ask in your setting. Just like today, we don't have fleets of thousands of supersonic stealth bombers because even if they're cool and exciting, they're less effective than the same number of ballistic missiles.

      I'm not saying you should rule out the Orion missile. I think you should try be able to talk to someone who lives inside the setting about these weapons and have them answer you back their reasoning and solutions in a satisfactory manner.

    2. The Orion-missile was born out of interest to get a anti-orion-torship weapon, It's very likely that a big warship has more delta-v, but it probably won't have high acceleration because it has a human screw on board, sub-G or 1 G acceleration are the norm, humans can survive at 8G and higher , but living at that acceleration for months?
      It was already clear to me that such a missile is too big and over the top.
      The orion part was rather optional, I searched for a system can cover one astronomical unit in less than 24h.
      And the orion drive was the best candidate in my perspective.
      -Target Performance: Nearly every warship has higher delta-v than the missiles, but missiles have the acceleration advantage. At 1Hz NPU ignition rate the orion missile has a acceleration of of 21500G.
      The sweetness of the Orion-missile is: You can kill multiple targets at once, the 100x NEFP warhead are dismounted probably at 50-100 million km away. Every NEFP has 20kg engine and fuel. Each can select a individual target, able to kill fleets. Or extremely valuable targets with extreme defenses.
      -Cost Effectiveness: In a setting where Orion drives are the common warship drive, wouldn't the prices drastically sink due to mass production? They would still be expensive as hell, but probably more economical than it would be with our current tech.
      As said, the individual warheads are supposed to detach at range way outside any realistic laser etc.
      The Orion-missile would be a terrible stock weapon, the same goes for 150Mt casabas and alike, they are just too heavy. I thinked about max 5 of them one a very big warship and one one average 100-200m warships.
      But If a warhsip carried 100 of them, 5kT for armor aren't that much. Considering that every single one of the hundred Boosted NEFP's can "penetrate" 4,14m of graphene. At that thickness your +100m spaceship would have nearly a megaton of armor.
      Energy effectiveness: Wait.... you can make NEFP's that are over 800km/s? I got the impression that such NEFP's were way to impractical to be ever weaponized.
      I am a little confused at the last two segments of your post. I Should I immerse in the setting and create a mental situation where I talk to some one who lives in that setting?
      Any suggestions for missile designs which allow for around 1% c? Because it seems like they are getting more and more obsolete with time, NEFP's, Casabas, X-ray FEL death rays.
      I liked your Stealth bomber analogy except that "cool and exciting" part. I imagined Orion-missiles just as what stealth bombers are in real life, rare and expensive, but they fulfill a very specific niche.

    3. If the warships' primary weakness is their inability to accelerate as fast as missiles due to a human crew... it wouldn't make sense to make them manned fighters. It would doom them to being chased down and destroyed by much smaller missiles.

      Instead, if you need a human crew around, it would stay very far back, maybe in the long-ranged laser platforms and not the front-line high-acceleration dogfights between NEFPs and Orion missiles.

      Once the human crew is out of the way, the only difference between the missiles and the warships is how well the missiles are positioned (initial relative velocity, initial distance) and how much extra propellant the warships are willing to burn to increase their thrust.

      One major distinction between a missile and a warship is that the warship has a lot of on-board power and defenses to shoot down the incoming missiles. If you are using lasers for defense, the biggest factor in whether you shoot down the missile or not is how long you can keep the laser on its targets. Accelerating away from the missile increases the time on target. This means, in practice, that you don't really need to match the acceleration of a missile - you only need to accelerate hard enough to keep this time on target at acceptable levels...

      One AU in 24 hours is incredible performance. You need an average velocity of 1736km/s. If you want to stop at the other end, you'd need a total of about 3500km/s.

      The original Orion proposals could deliver this level of performance... but you'd need quadrillions of tons of fissionables per ton of payload. Not realistic. You'd have to use pure fusion variants with exhaust velocities of 3000km/s to bring down the mass ratio to something like 3.2

      Warships can use less or no propellant around the fusion pellet. This allows them to move their exhaust velocity, and total deltaV, up and down according to thrust requirements. Missiles would want maximum thrust to reduce the time they spend under laser fire.

      Yes, NEFPs can reach a theoretical maximum velocity of 9000km/s. This is apparently the maximum velocity of the plasma generated by a fusion warhead, so the metal plate can't travel faster than that. However, the ratio between energy input and energy reaching the target is very poor.

      For the last segment of my post, I was just describing the level of explaining you'd have to do to create a 'tough sf' setting. I wasn't asking you to really do a thought experiment, but to develop your setting to the point where you would be able to imagine having all the answers for such a situation.

    4. -Level of performance: I modelled the Orion-missile after the NEFP, just with lower yields, heavier plate and multiple bursts. the isp has to be 235k, that's nearly a fourth of the Orion MAX specific impulse. At 25MT (100x 250kT) I achieved 2108km/s velocity at the usual 21,25% efficiency with a 10t Spacecraft.
      -NEFP: That was exactly what i meant, they exchange energy for velocity. Making them pretty much impractical at some point, and a Orion-missile boost allows for velocities up to 1% c and 2,7kT of NMP yield, from a 1kT NEFP which on itself only produces 0.21kT NMP.
      -Acceleration: Still, there are not many orion-warships which could even reach 1k-G, short of 21,5k-G. Or maybe there are, correct me if I am wrong.
      -AU in 1 day: Yes, I searched for a system that can reach this velocity in "short" time, considering that this is a missile we speak of you don't want it to stop. That is what the torch missile will most likely be, scaled down Warship drives which don't need fuel to slow down.
      Again, do you have some ideas how to reach such speeds with missiles, at
      the sizes/weight of roughly a Trident-II missiles?

    5. -Laser fire: The missile isn't supposed to be anywhere near laser range, It was designed to be launched from across the solar system (10-20Au) When it reaches is peak velocity it can the detach the warheads, which also can immediately fire, now you have 100x 8mm wide rods travelling at 2912km/s. Each strong enough to crack your spacecraft wide open. I don't know how a long-ranged laser platform/star can defend against something like this. Except some reactive armor/interceptor drones designs.

    6. Orion propulsion doesn't work the same way as an EFP in one critical way: the pusher plate is relatively immobile before, during and after the pulse detonation.

      A propellant/plasma cloud colliding against a solid, immobile object achieves much better energy coupling than an object being swept away by the gasses. This doubles the overall efficiency, from 0.85*0.5*0.5: 0.21 to 0.85*0.5: 0.42.

      Also, a propulsion system can afford to have a very high propellant to fission fuel ratio. This cools down the plasma, meaning the portion of its energy contained as kinetic energy approaches 100%.

      Overall efficiency of a propulsion unit can approach 85% or more.

      I doubt the delicate explosive lenses and/or the fusion ignition systems used to detonate the nuclear devices will survive such accelerations. Its not even an engineering problem, but hard limits caused by material strengths.

      Missiles that need to reach extreme velocities can use external propulsion, such as particle beams, macro-matter beams or ride tracks of kinetic impactors. They could use gaseous-core fission rockets that burn fission fuels more efficiently.

      The problem with extreme ranges, such as those measured in astronomical units, is that it becomes exceedingly hard to find and track your target. It becomes even more of a problem if your target can accelerate hard in any direction.

      Laser platforms will see the hot jets of metal from the moment they are fired. They will be bright on radar and cannot dodge any interceptors. An EFP has to take all defenses head-on and survive them through sheer mass and momentum. Its strength comes from being too thin for lasers to track and hit accurately, mostly immune to laser damage (if melted, it'll stay roughly the same shape) and big enough to punch through interceptor plates. At a certain point, it is better to start shooting heavier NEFPs than simply faster and faster versions with lower and lower masses.

    7. Thanks for clearing this up.
      I looked up the NSWR MAX, and wow, thats is extremely impressive, Scaling it down to like 50-150ks will be enough for the fastest torch missiles.
      Re Extreme ranges: I have to agree on that, the NEFP could rotate after detaching but then the warships could further accelerate out of the way.
      Re Laser Platforms: The NEFP is proposed was your average 1kT 2,75kg 804km/s NEFP, it just had 2108km/s velocity before it was detonated. If we replace my 100x 1kT NEFP with 1x 3t 1MT NEFP you could achieve a Vmax of 3161km/s, the 2750kg which now folded into a long rod penetrator, It will hit with the force of 3285kT, compared to 212kT of a normal 1MT NEFP. A Hyper-torch-missile or whatever you call missiles with circa. 1% of c Dv. Can give you faster NEFP's without reducing mass and energy of the NEFP. But let's just increase the max of the NMP from 2750kg to 5t,
      I kept the efficiency the same, I got 596km/s, plus 2083km/s from the missile, gives me 2670km/s, It will hit with the force of 4.3MT now.

    8. Why use a NEFP payload at all why not use thousands light penetrators (10g-500g) or hundreds of heavier (5kg-50kg) rockets. Even a 10g projectile traveling at 2100km/s has 22GJ of KE.

  4. Sorry if you already wrote answer in the article, but I can't read it whole now, but are you going to make a post about particle beam that further focuses the jet from Casaba Howitzer? Could it help making the efficiency higher? And could be there a magnetic bottle mounted around the charge, to help directing energy forward, into the forming jet, and not waste it? That starts to look like real life, ultimate, Plasma Cannon (tm).
    Now when I think about it, the strenght of the Casaba Howitzer is in jet not being plasma, so not expanding quickly, but on the other hand, would expanding matter at a few percents of c? The target is reached really fast, so maybe the width of the beam would acceptable

    1. I need a bit more information on how exactly particle beams are focused before I can write on that subject. I would include the Casaba Howitzer option inside a more general look at particle beams.

      The usefulness of magnetic focusing is that it reduces the spread of the particles. Less spread means they do the same damage at longer distances. There is a point where a small increase in focusing ability, using magnets, is more effective at increasing the weapon's range than simple increasing the warhead's yield.

      The magnetic focusing would work like a funnel.

      The plasma produced by a Casaba Howitzer is modelled as a cone. The cone has an angle at its peak - the better the warhead is focused, the narrower the angle.

    2. @MrAnderson
      Actually,a Casaba which uses magnetic fields to further focus the beam is already described in the Casaba Howitzer blog. I am unsure what you meant with "efficiency", the actual efficiency is mostly unaffected through the magnetic focus, but the combat effectiveness/efficiency is increased because of the extended range.
      You are suggesting a gigantic Inertial confinement fusion device? (You'll need a lot of handwavium for that) You can take a nuke, completely cover it with propellant and you have nearly 100% efficiency but no directivity, the magnetic field now focuses the plasma into a beam. Ultimate Plasma cannon™.
      The casaba jet is plasma, but for some reasons it don't happen to expend like a normal plasma would. I already talked about this thing with Matter Beam, but the radiant beam includes everything, Electrostatic bloom, thermal expansion, etc.
      The futuristic Casaba reaches it effective range in one second. The Futuristic Magneto Casaba Howitzer™ had a range of qoute" 10 million kilometers" that is 1000s travel time for the plasma jet, but somehow it stays focuses at that time.

    3. @Matter Beam Thanks for answer!
      The function of magnetic field to focus the cone is clear to me, but I think more about using the magnets to use higher percentage of energy from detonation to propel the jet, from this 20% or something to 80% let's say. I am not sure if that could work, because I don't know if the plasma made from channel filler, liner etc would absorb enough energy.
      @OMG its WTF
      Thanks, you explained a lot to me, I want a hybrid between inertial confinement and long funnel it seems now.
      The lack of expansion seems a bit weird to me, maybe the jet isn't really the plasma? Or scientists didn't know much about plasma expansion back when the Casaba Howitzer project was going? It all seems a bit weird, and makes commonly met statement "plasma weapons can't be made because plasma would expand into all directions" somewhat not true

    4. Well, the way I now see the plasma expansion subject is, it stretches itself instead of expanding in all directions, imagine it like a water hose (Casaba), they stay focused for some time, now imagine a water balloon without the balloon, will fall apart instantly (Your average plasma cannon).One the other side, how such plasma can stay focused even after 1000s is beyond me. I asked the same question as you did with the plasma expansion.
      And because I am bored I will also answer the first question, there might be a design that would make it possible for you to have a Magneto-Casaba. First of you need energy, a heck ton of it. Using superconductive coils you can just round up the efficiency to 100%, so 1J magnetic energy = 1J Kinetic energy. But how can you use the energy of the Nuclear charge? You put the bomb inside a gas bubble, upon detonation the radiation flux will superheat the gas and turn it into plasma which will start radiating the energy as heat. Using Thermocouples with let's say 5-10% efficiency you can use a sphere, but you need a giant area to use the energy without the T-couples getting damaged and destroyed, I am thinking about maybe 1-2 km distance. Now you have your giant sphere and you can absorb the energy, this adds 5-10% efficiency to 20% efficient casaba weapons, 50% power increase (30% eff. max) for only few kilotons of thermocouples and structural material, a cooling system for the superconductors etc. Mostly it isn't a question about if it's possible but if it's practical. And If you want a ICF with a magnetic nozzle and funnel, but sorry, the energy amount you’ll need to capture and direct a megaton explosion are probably as high as a megaton itself. Or if it is somehow possible without enormous energy demands and creating several thousand tesla strong magnetic fields without problems, why not use the these magnets for a giant coilgun?

    5. @MrAnderson:

      Using magnetic fields to focus the plasma in an EFP weapon would only help in the spaced NEFP design by increasing the percentage of plasma that reaches the plate. In the Orion designs, between 5 and 50% of the plasma could be lost because it was not intercepted by the plate. Increasing the focusing ability of the shaped charge reduces losses. Increasing the diameter of the plate reduces losses. Both are simpler options that integrating large magnetic loops and focusing mechanisms.

      The plasma I refer to in a NEFP is the super-hot propellant contained in the shaped charge. This propellant in the original Orion design was tungsten that absorbs the heat in the beryllium filler, itself heated by X-rays from the nuclear device.

      The propellant can be anything though, as long as it can be efficiently heated by the beryllium filler and does not itself reach too high temperatures. Lighter propellants, such as polyethylene (Project Prometheus) or even frozen hydrogen can reach very high velocities but their lower heat capacity means that they also reach very high temperatures. High temperatures would melt or vaporize the metal plate into uselessness.

      The plate in NEFP needs to stay solid.

      The plasma 'jet' only needs to travel the dozen or so meters of spacing between the shaped charge and the plate in a spaced NEFP. Low velocity NEFPs have the plate in direct contact with the propellant, so this isn't an issue.

      You might have been confused by references to the HEAT 'jet'. That is semi-molten metal, not plasma.

      The plasma weapons usually referenced in science fiction try to directly damage the target with plasma. Here, it is being used to drive a projectile.

  5. @Matter Beam
    Quick question: Can the engine mass of the 90% NSWR be scaled down to 10-11,5 metric tons?

    1. Very unlikely.
      NSWR needs to achieve a critical concentration of nuclear salt in the water at the choke point. The only way to reduce the engine mass is to increase the concentration of the uranium... which makes random explosions more likely...

    2. Hm, then only AM Beam core drives are left for Torch missiles, or external propulsion methods.
      Actually what makes the 20% UTB engine so heavy?

    3. I wrote this on the Children of a Dead Earth forum, but the amount of water you need necessarily makes for a large propulsion unit. There's plenty of bright ideas suggested on the thread you started :)

  6. Hello, I read the post but there was something that wasn't clear that I would like to ask about here. What would the weapon system look like? Is it like a gun where slugs are loaded and fired, spent casings being replaced with new rounds? Or is it like a missile, shooting off until detonating at a safe distance to launch/shoot the "slug"?

    1. Google "EFP" then you get a idea how this system will work.
      The NEFP is a one-shot weapon, the nuke explodes, superheats propellant into a plasma cone, this plasma cone accelerates a big metal plate to several hundred kilometers per second, your missile will be dust/plasma after firing off the NEFP.

    2. There are three versions of the weapon: NEFP, spaced NEFP and HEAT (NMEs).

      The NEFP is a hemisphere of metal sitting on top of a propellant cone. The cone is truncated and merges into a cylinder. The cylinder contains the nuclear charge.

      The spaced NEFP is a wide disk of metal on top of a cone-and-cylinder nuclear shaped charge. Springs or explosive bolts push the disk away slowly. At the correct distance between the plate and the charge, the weapon is detonated.

      The NME is just a big cone. At one end is the nuclear shaped charge, at the other is an inverted cone of metal and in between is propellant filled with bubbles. The bubbles rotate the detonation wave inwards onto itself to converge at the metal cone.

      All of these weapons end up with a cloud of swirling plasma and a metal object flying away at high speed. They can be launched like large, fragile shells or equipped as missile warheads.

  7. A few comments:

    EFPs and shaped charge weapons can be designed to have interesting effects. "Dimpling" the cone, for example, can create a cloud of small shaped charge projectiles rather than a singular one, an effect that was experimented with to create anti aircraft shells. Something similar could be done to create a cloud of fast moving projectiles to strip away enemy missile clouds or expose a missile from its cloud of decoys.

    While multi ton projectiles would be devastating, I'm not sure if the equivalent of a nuclear carronade is really the answer. Given the velocity of the firing platform, the target and the ranges that "real" space combat would take place, speed might be far more important to prevent the target from being able to dodge the shot. After all, once you get a hit, then the enemy ship becomes progressively less able to dodge subsequent shots.

    A final point, powering plethoras of nuclear devices to drive the Orion ships and their weapons could be done by initiating the fusion reaction with antimatter. Antiprotons are reported to exist trapped in the Earth's magnetic field and can be harvested in orbit, gas giant planets like Saturn with far larger fields could reasonably be expected to have correspondingly larger zones where antimatter could be harvested. This gives the setting a definite reason for conflict (Saturn is a desirable piece of real estate already, with hydrocarbons and nitrogen available on Titan and plenty of water ice on the various moons and rings, and 3He in the atmosphere; being the locus of antimatter mining in the Solar System is icing on the cake).

    With little or no need for fissile material to initiate fusion reactions, nuclear devices to drive weapons systems can be far smaller and more robust. The antimatter "triggers" will be quite touchy, however.

    1. The reason for multi ton projectiles isn't because their "devastating" effects, it's the smallest practical and effective mass for a plate, you could use lighter, waaaay bigger and way thinner plates to reach very high velocities, but that would make them very impractical weapons and probably way less efficient. The solution for the velocity problem is probably a Long-range Strategic Missile (LRSM). Weighing 25 tons wet mass, having 2300km/s Dv, and 3-4t payload. It's drive is a Medusa concept which uses 0,1-1kg LiDT charges which are struck by one microgram of antihydrogen fired from a small particle gun from the missile. It's average acceleration is 25G. Needing a total of 10mg Antimatter.

    2. @Thucydides:

      Nuclear carronade. Nice image :)

      A plate dimpled like a frag grenade to produce a cloud of shrapnel was actually the original proposal in Project Prometheus' shaped charge weapon.

      The advantage is that one warhead could sweep a vast swathe of space. The disadvantages are multiple. From an energetic point of view, it is complete murder on your efficiency. Very little of the nuclear yield ends up at the target - for the velocities expected, you are better served by a coilgun shooting 'corridors of projectiles' as described in my Electric cannons post.

      Efficiency is also the reason why the projectile is so big in a direct contact NEFP. There is a speed limit imposed by the projectile's melting point. You cannot exceed it without increasing the propellant's temperature, and this melts the projectile. A molten projectile has no cohesion and is blow apart like a bubble instead of riding the blast wave. So, if you are limited on one hand by the maximum achievable velocity, and on the other by a minimum size of a nuclear warhead, you maximize instead the percentage of energy extracted from the warhead. This leads to a very massive projectile reaching close to the maximum velocity and containing nearly all of the nuclear yield as kinetic energy.

      Back to the frag NEFP.

      As noted in the Prometheus documents, it would be necessary to fragment the projectile into uniformly sized and distributed pieces. As the nominal range increases, the pieces have to be finer and finer to make sure a spaceship or missile does not slip through the gaps. Considering the semi-chaotic turbulence in a blast wave, there might be a minimum size for the divisions.

      Another problem is that the frag plate has competing objectives. One objective is to separate into pieces. The other objective is to hold together while riding the blast wave. Reconciling the two leads to less energy extracted from the blast wave, so lower velocity.

      Antimatter are a great solution! They allow for micro-fusion devices with incredible power, achieving perhaps the 25TJ/kg limit for energy density. However, many 'hard sf' settings try to forgo antimatter as the miracle solution for energy and propulsion problems as large-scale production might stretch the limits of plausibility within their future history.

      Another problem is the antimatter will likely be precious for a very long time, even if technology advances. If spaceships burn through several grams of it per interplanetary trip, you'll need to vastly scale up the output... maybe several tons per year for human civilisation? If these quantities are not available, then it is extremely likely that more productive uses for antimatter will be found.

      @OMG its WTF:

      Remember the distinction between direct contact and spaced NEFP. Direct contact is velocity limited, so using a heavier projectile allows you to extract more energy from the nuclear warhead. Spaced NEFP spreads out the blast wave across a large thin disk to achieve higher velocities.

    3. @Matter Beam

      I completely ignore the contact nefp because of their low velocities and high plates masses. If I say NEFP I always mean the spaced one.
      Also Project Prometheus is more akin to a shotgun, what Thucydides meant was probably a MEFP, a plate using multiple small cones on a plate instead of one large cone. Which don't really cover a big area but instead strikes with multiple projectiles at once.

  8. The "dimpled" cone is actually more of a modification of a shaped charge warhead than a shotgun shell, but OMG its WTF is correct in the end result is a swarm of small, high speed projectiles. I can't remember where I read this, but the initial idea was to give a present day tank something which would allow it to fire at enemy helicopters. The modified HEAT shell would be detonated by a time fuse or radar proximity fuse and spray a cone of high velocity fragments (each individual one going far faster than the already considerable velocity of a 120mm tank round).

    Since tanks only carry about 40 rounds, substituting HEAT or APDSFS for "Flack" rounds was a losing proposition, and helicopters have a considerable edge over anti aircraft cannon rounds fired from a tank. Using a gatling gun or a SAM is a much different proposition, however.......

    This bring s up another point: a ship can only carry so many rounds, so the large numbers of effects that can be created using various nuclear driven rounds (from the shotgun rounds to CASABA Howitzer rounds) need to be considered in the context of what is the most versatile rounds, given the limited amount of mass a ship can reasonably carry. Even a giant "Arsenal ship" based on the USN proposal carries 500 VLS cells; when target 501 shows up you're done. Once again, by analogy, modern tanks carry two types of rounds for the main cannon: APDSFS to fight other tanks, and HEAT-MP to attack everything else (HEAT goes through armour, walls, bunkers etc, and the fragmentation effects built into the shell take care of exposed infantry and other soft targets).

    I suspect that at least some space navies might prefer the CASABA howitzer, and maybe have "fly along" particle accelerators driven in part by the blast to shape and accelerate the plasma spindle into a very tight beam moving far faster than "just" 10% of the speed of light......

    1. A technologically advanced nuclear shaped charge could use micro-electromachines to modify the angle and dimpling of the projectile plate. This could allow the weapon to configure the projectile for each situation and produce flank, EFPs or Monroe jets.

      A particle beam focusing mechanism would not make the particle beams faster, only more effective at longer ranges... a particle accelerator would only realistically add a tiny amount of energy to a particle beam generated by a nuclear weapon. For example, a 100m long particle accelerator with a 1TJ Casaba Howitzer beam entering at one end would need to deliver power at petawatt rates or higher to add any appreciable amount of energy to the beam...

    2. The tradeoff of having a more expensive and complex round vs having only one type of round in your magazine would be an interesting calculation for the owning space navy. This might make an interesting plot point too: the gunnery officer or turret captain needing to make a quick decision as to how the warhead will be configured (especially if it is the last round or a last ditch shot at a distant enemy).

      As for the use of a fly along accelerator to increase the efficiency of a CASABA howitzer, wouldn't some of the extra energy come from the beam itself, as it is compressed and shaped by the external magnetic fields of the accelerator? The energy already contained in the particle beam is being forced from a reasonably wide cone into a much narrower stream, and it has to go *somewhere*. I'd think this would result in much more energetic beam coming out the muzzle end, although this might be expressed as a much "brighter" beam moving at the same speed, rather than a much faster one.

    3. That would be an interesting decision indeed.

      Sorry, I was confused about the Casaba/accelerator question. I thought you wanted to use the accelerator to increase the velocity of the particles in the particle beam produced by the Casaba Howitzer... would have been problematic. Using a focusing ring of magnets is a much less energy intensive task that only has to cancel the lateral motion of the particles within the beam.

      Using quadrupole magnets in series, you can apply a magnetic force to the particles. The specifics of how to focus particle beams requires a bit of research to understand and worthy of a post on its own :)

  9. Hi!

    I don't get the stuff about using a nuclear head as a locomotion. It's almost like using an enormous shotgun to push your way riding a bicycle. You know this is possible to make it, but is there someone who believe this is a viable method for travelling into space?

    1. Hello!
      The Nuclear Pulse propulsion unit uses it's high energy radiation to heat it's channel filler to hundred of millions of degrees, the material expands at multiple thousand kilometers per second. this material has mass, this means it also has thrust. Imagine it like a giant gun, without a barrel. Which shots a bullet (spacecraft) in a specific direction. Well, the NASA and USAF thought that this might be an viable way of exploring the solar system, even today a similar concept is still researched, although it has way it's using fusion, is more efficient, uses pellets with a thousand of the yield. Being overall more effective than just throwing nukes/firecrackers under a spacecraft/tin can.

    2. More details on using shaped nuclear charges for propulsion can be found here:

      A full explanations of the method can be found here:

      NASA's Orion project very nearly got funded, and it was a design that depended on nuclear pulse propulsion.

  10. I'm trying to imagine space combat using these weapons, and coming to some interesting, if somewhat contradictory conclusions.

    If you are being shot at by jets of plasma moving at a significant fraction of *c*, or multi ton metal slugs coming at super high velocities, you either need to nave a platform with the sort of performance of an F-22 Raptor, or be coming at the enemy encased in a gigantic asteroid.

    You can see the issues with either solution. The "Raptor" will be stripped down to the point where it is a single, deadly instrument of death, but have little staying power, carry a very limited load of missiles and could be made obsolete quickly by some unexpected development (practical RBoDs are probably the greatest threat to this sort of spacecraft, but a significant upgrade to nuclear lances and NEFP weapons that exceed the sinking ability of the Raptor might also spell doom to the craft).

    Gigantic battlestars built around asteroids or engineered materials consuming the bulk of an asteroid will be so slow and unwieldy that just getting them to speed and into the combat zone will be exceedingly difficult. And of course, if you see something like that coming, you can ramp up production of nuclear lances, or even simply fill the sky with SCoDs and strip away every surface fixture, sensor and other fitting, before carving it into bite sized pieces with the nuclear lances.

    In essence, we have discovered a way to get to RBoD level combat without the mass and expense of kilometre long electron beam accelerators, wiggler magnets optimized to harvest hard, coherent x-rays and gigantic diffraction arrays. If using nuclear energy to drive weapons effects is common, then there will be a corresponding drive to create a true RBoD, since vapourizing your enemies one light second away is about the only true defence you wold have against nuclear driven weapons.

    Of course wags will now say we have set up the conditions for squadrons of "X-wings" to dive towards the Death Star, which was't really the outcome I was expecting.....

    1. In either case, what would those warships bring, compared to interplanetary missiles directly serviced at rear bases?
      Those missiles would probably have one or more bus stages carrying one or many terminal vehicles, not unlike current MIRV nuclear ICBM.
      What is the advantage of those X-Wings or Death Stars compared to simpler missile busses?

    2. From a worldbuilding perspective, my issue with nuclear shaped charges is that they approach another level of stale compared to even RBoDs. Stealthy weapons that would set every city ablaze within milliseconds.

      I do not think any lightweight, stripped down craft resembling a jet fighter would survive a battlefield where lasers are used. Casaba Howitzers can have impressive range, but lasers still out-range them. A lightweight launcher will be detected and hosed down by gigawatts of short wavelength energy.

      On the flip side, incredible armor that can shrug off small impactors and lasers for days on end can be cracked open by a single sufficiently big nuclear warhead. Remember the multi-ton 'slow' nuclear EFP that was termed the 'nuclear cannonball'? That is an ideal weapon for cracking open large defenses. You'd lose the entire investment in one strike.

      What I do think will happen in a full-on shaped charge setting is actually quite familiar. Submarine warfare.

      The warships are all vulnerable to utter devastation by a single strike. They are far less manoeuvrable than the missiles and point defenses, decoys and EW jamming are all just last ditch efforts to turn a sure kill into a pretty sure one.

      What is their defense? Stealth. You stay cold and silent and you hunt each other's intermittent fuzzy pings. You can move around using ECCNs but you do not have the tactical mobility to outpace non-stealth warships without compromising your stealth.

      Now, there is a lot that can be done with stealth/submarine warfare. A lot of good fiction has come out of it. But its a matter of tastes, it might not be suitable for everyone.

    3. @ eth

      Missile busses violate the "Zeroeth" law, which is readers want to read about characters, not missile busses.

      I suppose you could write a story set inside a missile base where tensions are rising and perhaps the crew believe their communications systems have been compromised (do they obey the launch order or not?), which would be a good psych-drama, but not classic space opera or lending itself to wider settings.

      The ultimate answer of course is that most polities will insist on a manned presence to make the critical"shoot/don't shoot" decisions before turning the aiming and firing over to the AI and expert systems. I am pretty sure that any poliity which openly violates this "rule" against turning killer AI loose will suffer pretty severe consequences (although this could make for another plant point, how far do you have to have your back to the wall before you make the decision to go rogue?).

      Much of world building rests on the initial assumptions you make, and working out the consequences of these decisions (unless you throw in weird stuff like "The Force", but that's not what this blog is about). The depressing reality is that factors like economics will probably be far more important in the basic setup than how much "cool factor" you can giove your fleet. Even then, you do have lots of room to work. The Imperial Japanese Navy was well aware that the United States outmatched the Japanese Empire in such things as steel production by a ridiculous margin (something like 8 or 10 to 1), and would be able to crush the Japanese Empire in a prolonged war, so made the desperate calculation they could knock the United States out of contention with a surprise attack instead. Will the alliance make the same gamble and push lots of nuclear lances forward to destroy Imperial bases and ships in a single surprise attack?

    4. While that it true, ToughSF is coming up with a good plausible explanation for why you don't just have interplanetary missile busses.

      One explanation I would personally use is that of marginal utility. If a human crew costs a 10% loss in performance compared to a purely robotic fleet, they better have a benefit that allows more than 10% victories or 10% less losses compared to purely robotic vs robotic engagements. Another explanation is that the humans manage the battle like an RTS game or a general at the back of the army. They give commands but they are not within arrow range. The story still has opening where the human crew is directly threatened, however, like if the robotic fleet got circumvented and the enemy goes straight for the command ship...

      Shoot/don't shoot can be the least important argument in that case!

      Human crew benefits can come in the form of performing repairs to recover parts or allow billion dollar spaceships to limp back home... they spot patterns in their automated opponents or device on-the-spot strategies like a game of speed chess. They can be failsafe against hacking: they are given a master shutdown switch to deactivate a drone they fear is under enemy control, because a machine certainly doesn't know if it has been hacked.

    5. I will agree with being able to spot patterns, do damage control and so on, and 100% in the fact that human crews are more resistant to "hacking" (Although the use of PSYOPS like Russian "Hybrid Warfare" in Crimea and Ukraine shows it is possible to sap the will of you opponents and make them less or unwilling to fight).

      Shoot/Don't shoot is more a political thing, the Admiral in charge of the constellation can choose to make a demonstration rather than simply vapourizing everything in range.

      At the tactical level, I think things will be going far to quickly (closing speeds measured in kilometres per second, weapons moving at velocities ranging from metres per second to the speed of light) for humans to truly be in the loop, once the signal is given for "weapons free" then the crewed ships have to hope they are protected by active defences, ECM and armour sufficient to ride out the storm.

    6. I doubt that PSYOPS will work on tactical timescales, like with spacemen on their spaceships on their way to space war.

      As for the closing velocities and rate of engagement... there might still be room for human rates of decision making. If we use the ranges dictated by laser weaponry, we are easily talking about hundreds of thousands of kilometers. Lasers might take hours to go through thick armor when the opponents stay at extreme range. Kinetics take several minutes to hours to cross long distances. Ship manoeuvring takes days and the exact angle of intercept and relative velocity could be decided after weeks of reactive thrusting.

    7. PSYOPS can be used on a tactical level (there are thousands of examples out there, for example General Brock scaring General Hull into surrendering Fort Detroit in the war of 1812).

      Crews locked aboard spacecraft on prolonged cruises will be more susceptible to various sorts of PSYOPS, because there will be more time for it to work. The German High Seas Fleet and the Imperial Russian Fleets both mutinied near the end of WWI because the crews had bee left in port and exposed to Communist agitprop, as one example..

      As for the time for human decision making, I'm mostly in agreement (you can imagine something like a battle in Italy during the 1400's, where the commanders look at the layout of the battlefield and agree as to who won and who lost without actually fighting, much to the fury of the city states who hired them....), but once the shooting starts, I'm going to be hunkered down in the hardened bunker and letting the expert systems and AI's battle it out.

      There might be one interesting fail safe: every weapons platform like a Laserstar or Kineticstar will be a "zero g" construct, while maned platforms will have large and conspicuous "Hamster wheels" to provide artificial gravity for the crew. The AI's will be programmed never to fire at anything with a "Hamster wheel", since they know the surrender order will need to come from one of those ships in the enemy constellation.

    8. It would be an impressive breach of communications security if enemy propaganda filtered down to the crew members while they are sitting in emissions-controlled spaceships. It could be done, but that's probably some sort of spy drama.

      If the crew makes decisions and reacts to developments up until the encounter and they can only sit tight while weapons fire and armor gets ablated... they might end up recreating a very familiar theme of timed turn-based gameplay. Like, chess but you have less and less time to make each move.

      Your failsafe is even more interesting if we consider the fact that reasonable fleets will have a clear distinction between heavily armed drone warships and a human-occupied 'drone minder' at the back.

    9. Propaganda can be passed through multiple means. Based on my employment, I am aware of what RT pushes out, and am constantly amazed that local media uncritically passes on RT messaging and themes. We are literally getting Russian propaganda in our news feeds, generally without attribution ("sources say") and often without countervailing messaging either.

      I can only imagine what the Chinese are doing, given their vastly greater resources.

    10. Ah, but that case you were listening in to a busy radio environment composed of local media and commercial telecommunications. You are bound to pick up enemy attempts at spreading propaganda.

      In space, the environment is much cleaner and anyone trying to contact a specific spaceship will have to focus a radio or laser beam on them and achieve a much brighter signal than background communications.

      My point above was that if the crew in combat conditions refused to pick up such a signal, they wouldn't accept propaganda pointed at them. If they choose to survey all radio communications, they will pick up background media.

      But, thinking again about this... listening in to everything you can will always be the wise decision, as you cannot know if that faint radio signal is a soap opera, a propaganda message or the inter-swarm communications of a sensor array. So in practise, propaganda will always leak through.

  11. Hello, is there anything that limits the velocity of a RAIR/Bussard Scramjet? Besides the very minor drag from scoop/cosmic radiation. Considering an 100t spacecraft with a 10km² scoop scooping 1mg of hydrogen per second. Being Z-pinched by one gigawatt of power. If Something like this would be launched from a system like trappist-1 it would accelerate up to 0.76c with an constant acceleration of 0.35m/s. Ending up with 12MT per every kilogram.

    1. Actually, drag from the interstellar medium is the number one limiter for Bussard rockets.

      Your spaceship, for example, would have 150kN of drag at 50% of the speed of light. You need to generate that much thrust out of your engine. A Bussard's exhaust is necessarily faster than the gasses at the intake, so you'd need to have a rocket that produces at least 0.5C*150kN/2: 11.25TW of power.

      You'd need to made 11.25TW of engine power out of 1 milligram of fuel. That's before any inefficiencies or exhaust velocity above 0.5C increases your power requirement. For comparison, pure antimatter annihilation will give you 0.18TW per milligram.

      Now, you mentioned a scramjet. This drive attempts to ignite fusion in a propellant stream travelling at the same speed as the craft, instead of completely stopping the hydrogen. This greatly reduces drag... but also massively reduces how long you can interact with the hydrogen. For example, a 10km long reaction chamber would have only 67 microseconds to focus, confine and ignite the hydrogen.

      The RAIR solves both problems. The hydrogen being scooped doesn't have to be completely stopped, and the fusion can happen inside a nice, slow reactor... you'd only have to solve the problem of accelerating the hydrogen collected by an appreciable amount within the microseconds it stays within the ship. This precludes heating: that is far too slow. Electromagnetic acceleration might work. You'd have ions enter a particle accelerator at 0.5C and exit at 0.6C...

      Another problem would be creating enough electrical power to feed the particle accelerator without running out of fusion fuel.

      Personally, I believe that all Bussard variants are much too difficult for what they are worth. Pre-seeded trajectories make all their problems go away.

    2. I thought about a Hydrogen fusion Z-Pinch Scramjet/RAIR, the feasibility might be a bit limited. Other than that, What about Antimatter catalyzed fusion? I believe a 6000x higher AMAT/Fusion fuel ratio compared to D-T Should be enough to initiate hydrogen fusion. Means I can accelerate an the ship to 0.76c with only 100g Antihydrogen. Pre-seeded are nice and all for routes. But you need to have a first fuel-track ship to lay seeded routes, also what if you want to reach another solar system?

    3. You can shoot the seeds out of your home system at low speed, continuously, and have spaceships ride them like rails at much higher speeds.

      I might dedicate a new post to seeded interstellar travel, but I covered a lot of this on Interstellar Trade part II.

  12. Late to this party, and since this stuff makes my head explode, my observations may be a bit ... scattered. But two complications occur to me:

    1) If you are accelerating the slug (plate?) to 800 km/s over a distance of a few tens of meters, the acceleration will be about a zillion g. I suspect that this will melt/vaporize the slug, not from heat transfer but from sheer mechanical crushing forces. Similarly, even very slight turbulence in the accelerant plasma will shred any material substance. The energy imparted is about 10,000x the binding strength of any material.

    (Ueber powerful coilguns have a similar challenge.)

    2) This is a single shot weapon, so you can't correct any initial aiming error - no 'walking' your fire into the target. Hitting a target at 10,000 km is tough; hitting on the first and only shot is REALLY tough.

    1. 1) MatterBeam mentioned in a earlier reply that the acceleration for a 800km/s NEFP will 815 million G.
      2) The lack of guidance really is what makes this weapons lack of. At 10,000km this device should hit any object bigger than 125m and having 1G of Acceleration.

      (Überpowered Kinetics)
      Using Laser-Kinetics might be an better alternative, using current technology an Photonic thruster can produce as much newtons per watt as an Ion engine.

    2. The beauty of the device is you are not carrying around heat rejection equipment, generators or any other mass, your "X wing" potentially has the firepower of a Death Star mounting a RBoD.

      To get around the aiming problem you can "dimple" the plate so it forms multiple projectiles, and the projectiles can be driven in an expanding cone. This trades a greater probability of a hit against less of the devices energy being transferred to the target (the energy is spread amongst a number of smaller projectiles, many of which might miss the target entirely).

      Of course, even a small sub projectile moving at that sort of velocity (plus whatever initial velocity the firing craft had, +/- the velocity of the target spacecraft) equals metric crap tons of kinetic energy, so this will still be a crippling shot at worst, and potentially a killing shot against smaller spacecraft or if it hit a critical part like the radiator or reactor containment vessel.

      If there are multiple "smart" warheads in play, the first one will be configured to fire a shotgun spread to strike and cripple the spacecraft. Follow up rounds will examine the drop in performance and either continue to fire shotgun spreads (maybe changing up to "00 magnum" shot) to continue to strip away critical parts and cause deteriorating performance, until the ship has been immobilized for the kill shot using a singular "nuclear carronade" round. Matter beam has suggested that small MEMS devices could be embedded in the plate to create or configure the dimples and shape of the plate for various effects. I suppose this might also be accomplished by creating or filling voids in the filler medium between the plate and the "physics package" to shape the blast wave and create the desired effects.

    3. @Thucydides An MEMS wouldn't be that great. With 10m distance between each MEM at 10,000km and an area of 1km² you need 10,000 projectiles, with a 1kT bomb behind each will pack only the energy of 20kg of TNT. And only 10 or 20 will hit an enemy ship.

    4. @Rick:

      Such incredible g-forces are already achieved in laboratories today, such as in Voitenko Compressors. I infer from this study ( that 40km/s in 20 microseconds means the disk survived about 200 million g's.

      This is very much greater than binding strength of solids... but in which direction? The disk is nearly tangent to the shockwave front. No lateral forces are imposed. While irregularities in the plasma might bubble or depress the plate in the first few microseconds, their effect is dwarfed by the entire plate folding up on itself into a stretched pole.

      It is an explosively FORMED projectile, so deformation is expected. I concede, however, that imperfect plasma waves might cause the projectile to tumble and twist after it becomes a noodle.

      Aiming: Let's say the effective range of your enemy's lasers are 25000km. You want to stay out of this range, otherwise your armor will be whittled down at no cost to your opponent. Your opponent can reach 1m/s^2 acceleration. You load up a NEFP and fire at this distance.

      The NEFP has a megaton warhead designed to accelerate a 2.7 ton projectile to 800km/s. It reaches the target in 31.25 seconds. The target will have moved by about 500m in this time. If the ship is more than 500m long, you'll catch it and slap it with a 864GJ plasma explosion upon impact. This will destroy the target even if it so much as clips a radiator.

      You can drive your NEFP closer to hit smaller targets or faster, or simply pump up your velocity at the cost of efficiency. A very large spacing allows you to push a NEFP plate to extreme velocities without melting the plate material. Multiples of thousands of km/s are achievable. You have such a considerable mass advantage over your target that you can afford to cover possible escape venues with multiple warheads.

    5. @Thucydides, OMG its WTF:

      Dimpled 'fragmentation' NEFPs work best when trying to catch small targets that even the fragments will be able to destroy. Missiles, for example. Its a terrible way of trying to catch large ships, not because it can't, but because it would be a very expensive projectile compared to its destructive effect.

      If you really want fragmentation warheads in an offensive role, load them up on a missile and fire them at relatively close range. Like, 100km.

      The shotgun blast will pepper the entire target's length with penetrating fragments, which is arguable a more effective way of neutralising targets than one big, localized explosion.

    6. @OMG its WTF: I'll dive into weaponized kinetic swarms in a future post, but the idea was already floated in Stealth in Space and How to Live on other planets: Jupiter.

      A quick note for now would be that if you don't care about re-using the projectile, then laser-ablative would provide both excellent Isp and thrust per watt compared to ion or photonic.

    7. Pure photonic are still better. Calculate how many newtons a 1GW Beam would produce in a Laser ablative drive. And then compare it to 67nN/W or 67/MW. That was highest bounce value that was achieved to this point.

    8. @Matter Beam
      I was responding to the idea that beyond a certain distance, the ship has the possibility of moving enough to cause the warhead to miss. If the combination of ship manoeuvrability and stand off distance due to RBoDs, CIWS ro other defensive systems makes it difficult to catch a ship in the past of a nuclear carronade, then pulling out the nuclear shotgun and at least clipping the vehicle may be enough to allow a successful follow up engagement. (your own examples showing ships able to move between 125 &500 m between the blast and the warhead arriving provide the parameters of the problem).

      If the enemy ships are "X-wings" or Raptors, then using shotguns makes sense. If you are fighting the HMS Victory or a Deathstar, then a nuclear careened is the best tool for the job.

    9. @Thucydides: Absolutely. A common weakness of all unguided projectiles is that targets can move out of the way.

      In a world where NEFPs are the main weapon, small manoeuvrable ships, basically space fighters, would have the highest survivability. By the same token, they would be the most vulnerable to frag-NEFPs.

      This reminds me of the human vs AI debate: in a case where traditional warships must fire multiple NEFPs at a target if they want to catch them, then reducing your number of NEFPs fired per kill would lead to victory. This is especially critical when space fighters would have limited ammo. Both humans and AI would prefer to use predictive technology and use firing patterns to catch targets with much fewer NEFPs than a wasteful all-axis-covered barrage.

  13. @Matter Beam
    Voitenko Compressors ... 40km/s in 20 microseconds means the disk survived about 200 million g's.

    That's kind of awesome! But I still have to rain a bit on the parade, because the proposed NEFP requires 800 km/s in 20 microseconds (or thereabouts), so acceleration would be 4 billion G. (!) And in the compressor the plate probably could become molten or even vaporized and still do its job - you have a heavy mass moving a fairly short distance through a confined space, pushing air ahead of it. Not needing to hold together for 12 seconds on its way to the target.

    Generally, I'm uneasy about scaling from chemical explosive energies, on the same order as chemical bonds, to nuke energies that are ~6 orders of magnitude higher. Having said that, this is way above my physics pay grade.

    On aiming, my concern isn't target evasion, but the challenge of initial aim precision; for a 100 meter diameter target, permissible angular error is 1 arcsecond. With a one shot weapon you don't get to tweak the aim! You will at least need to mount the aiming optics on the weapon; offset aiming from the launching ship would multiply the mechanical aiming errors.

    1. This is excellent reading:

      Chemical shaped charges deform the plate at a rate of dozens of millions of gravities. The material acts like a fluid and as long as it forms a cohesive surface for the gasses to push against for the critical microseconds the blast wave is present, then we do not really care about what happens afterwards. You'll have a mass of metal in an elongated shape rushing at the target at a suitably incredible velocity.

      Fragmentation or particularization of the NEFP plate as it travels to the target isn't such a big deal either, I think, because even a kilometer spacing between the tip and tail of the projectile means the kinetic energy is delivered within milliseconds.

      In comparison, high velocity tank rounds (1500m/s) about 1m long deliver their energy within a millisecond.

      Another point is that penetrator integrity is not a big concern for high velocity NEFPs because we use crater depth penetration.

      With regards to scaling: the total gas energies and the initial temperatures are nuclear. However, the blast wave reaching the plate are well within the confines of chemical detonations.

      Aiming: quite a reasonable concern, but I think it might be improved over time, just like gun accuracy. Which reminds me, the gasses would cool down enough to be confined by an actual gun barrel like structure, which would vastly increase accuracy.

  14. Interesting link, indeed! Apparently the physics remain puzzling, even for 'ordinary' chemical devices.

    Fragmentation into a spray might be more effective, so long as the thing does not disperse too much and the droplets mostly hit the target.

    If it works, it would certainly be a motivator to develop laserstar zapping range, because the only good way to stop it would be to zap it before it reaches detonation range.

  15. Interesting!

    Given how devastating these weapons are, is it possible to use an NEFP for defense purposes against an incoming strike from the same type of weapon?

    It would make battles between ships dependent on who carries the most number of these weapons if they can cancel each other out.

    1. I don't think there is any need to have your interceptor be accelerated to velocities similar to those of the target projectiles.

      If your target projectile is a NEFP incoming at 800km/s, and you manage to get a good target lock on it early enough to give yourself time to react, all you have to do it place a thick metal plate in its path. The energy from the collision between the projectile and the interceptor plate will be enough to vaporize all parties involved. Having the collision velocity be 1600km/s instead of 800km/s would not benefit you much.

      For each NEFP, you could deploy hundreds of interceptor plates for the same mass budget. Normally, this would make defending against NEFPs quite easy... but the real battle is decided by who can detect the NEFP warheads the earliest, and get a lock on the projectiles the fastest.

      If you cannot detect the NEFP warheads before they fire, then the attacker can shoot from unexpected angles or set up a multi-strike from multiple directions. If you take too long to target the NEFP projectiles after they fire, then you won't be able to deploy the interceptor plates or you won't be able to intercept the projectiles at enough distance from yourself to prevent secondary damage.

      Even if a NEFP projectile is intercepted by a plate, you'll have a wave of plasma from the collision that resembles a small nuclear explosion. You'll also have the projectile particles continuing to move in the same direction due to their momentum, at practically the same velocity. You need to leave some room for these particles to disperse into harmlessness, otherwise they'll just bore through the ship.

    2. Hmm, so instead of a battleship having layers upon layers of thick armor, it would instead project its armor outwards, sort of like a porcupine?

      Instead of energy shields a la Star Trek, shields would in fact be solid masses like extendable Whipple shields to defend against this type of attack? Did I understand this correctly?

      (Please forgive my layman type questions, I dont have much of a background in science.)

    3. I would suggest reading the Space Warship Design series parts 1 to 3 and Innovating In Armor to get a good idea of how spaceships can defend themselves from high speed impacts.

      A space warship will have four hulls in practice.

      The innermost hull is the pressure hull. This is where the crew and sensitive equipment is held.

      After that is the internal armored bulkheads. They don't completely enclose the pressure hull. They are made to capture fragments from projectiles that got through the other hulls and smashed against internal components like your laser generator or capacitor banks.

      The outer hull is a big whipple shield with the inner section made to withstand fragments and the outer section containing reactive armor bricks, like on tanks. These fling out interceptor plates at the last second to make a virtual whipple shield with several meters of spacing.

      The outermost 'hull' is your anti-laser shielding. It is not very strong against projectiles, but is difficult for lasers to burn through quickly.

      This configuration is the most mass efficient way to maximize protection for your crew.

      I answer all questions here, and the whole point of the blog is to bring hard SF to the otherwise 'layman' science fiction fan without alienating them with 'you can't do this' or 'the maths say otherwise'.

    4. Thanks for the clarification. I listed this blog in the acknowledgements page of my newest release as a form of thanks for all the research you've done. :)

    5. You are quite welcome. Again, feel free to contact me for questions or discussions on other topics.

    6. A bit farther up John asks about using NEFP charge as defensive weapons.

      I totally agree, and think that "fighter" or "Torpedo boat" analogues would absolutely be possible. (Using the naming terminology that comes from Rocketpunk Manefesto, these would probably be named "Gunstars" as a compliment to Laserstars and Kineticstars). The general idea would be to largely dispense with the power hungry laser and associated hardware and mass, and be able to (violently) slew the ship to point launch cells in the direction of incoming kinetic energy threats like missile busses, SCoDs (Soda Cans of Death), railgun projectiles and other assorted items. You could almost picture a truss structure with Vertical Launch missile cells sticking out in multiple directions peppered with AESA and optical sensor arrays to pick up incoming threats.

      While a pure Gunstar is possible, having an on board laser provides several advantages. The laser can engage farther out and much faster at "scorch" range, where the beam does not physically destroy the incoming round, but burns sensors and may cause internal damage. The primary benefit would be to pump enough energy into the incoming round(s) to make them shine more brilliantly against the cold background of space, allowing better target solutions to be developed for the outgoing NEFP weapons which attack at "medium" ranges (hundreds to thousands of kilometres, depending on what sorts of weapons and assumptions you are using). The laser's final use is "close in" like a CIWS, where it has sufficient energy to burn through enemy rounds that made to through the nuclear gauntlet.

      Gunstars as part of a constellation, provide a wall of firepower intermediate to the massive Laserstars (with their incredible lethal zone reaching out to one light second) and faster response than Kineticstars (covering the same one light second range could take several hours using railguns or rockets). The nature of NEFP type rounds is they provide a means of fending off mass attacks, where waves of Kinetic energy weapons or SCoDs are used to overwhelm Laserstars. They would also be the weapons of choice for poor polities which cannot afford dedicated constellations, and can also serve as more "general duty" ships on their own (they can be used offensively as well as defensively).

      Given the economics and technical difficulties of building true RBoD (Ravening Beams of Death) laser weapons and competing demands of the Rocket equation (every gram counts) and the need for high performance military spacecraft, Gunstars may well be the first true military spacecraft, with specialized Laserstar and Kineticstars following as technical abilities improve.

    7. Personally, I'd reserve 'Gunstars' for spaceships hauling large electromagnetic cannons and launchers. Maybe 'Nukestars'?

      The details of how they are used and whether there are special warships dedicated to carrying them depends again on the availability of the fissile materials and the maturity of the technology.

      If they are rare or special weapons, then a dedicated launcher is plausible. They would be best used as warheads on missiles. These missiles cannot be launched in massive swarms like SCoDs due to their cost, so the 'Nukestar' might actually be a dedicated drone launcher and handler, with the drones being miniature warships that position the NEFP warhead at the correct distance and vector to the target for a killing blow. I think the Rocketpunk Manifesto terminology for this would be a torpedo.

      If however NEFPs are plentiful, then it is likely that they would be included as a last-ditch last-layer-of-defense device against an incoming missile or kinetic swarm. Every laserstar would have several of these mounted on multiple hardpoints, facing every possible direction, ready to fire. It's a last-ditch attempt because it would fry sensors and crack the main lens, but it might be a better alternative to your laser point defenses being overwhelmed.

      Offensively, the cheap NEFPs would be mixed in with identical mass and signature dumb kinetic warheads. They can engage the targets before the missile swarms close in, making target prioritization more complicated, or even fire backwards after the swarm has passed, like a nuclear Parthian shot.

      I can see a plausible midfuture setting where the current balance between the USA supercarrier groups and the cheap Russian/Chinese carrier killers can be recreated.

      The CVs would be the massive laserstars - multi-role, high performance and at the heart of a fleet dedicated to finding targets for the lasers and defending it against attacks.

      On the other side, we'd have lightweight, cheap ships loaded with RBoD-killing NEFP rounds. They don't try to close in or try to overwhelm the massed defenses surrounding the laserstar. They just stun the sensors with Casaba Howitzers and follow through multiple NEFPs per ship.

  16. Terminology wise maybe "Firestar" to reflect the nuclear energy source of the weapons.

    The availability of fissile material would be a huge issue in how NEFP is used, although my handwave is to postulate that harvesting antiprotons trapped in the planetary magnetic field provides non fission triggers for fusion devices to power the NEFP. This means Earth will be about the only practical source of anti protons in the inner system, while you would have to move out to Saturn for large scale harvesting in the outer system (going even farther to Uranus and Neptune is possible, but the time/distance factors make this uneconomical, at least in the short to medium term Jupiter's gravity and radiation environment makes harvesting antimatter in the Jovian magnetosphere problematic).

    So now we have both the solution, and a means of setting up conflict. After all, Saturn and Earth will have every reason to want to control the harvesting of antimatter, while other polities (Mars, space habitats, asteroids) will not be very keen on being placed at a large disadvantage. Saturn in particular may become a battleground as factions fight over the multitude of resources available (water ice, hydrocarbons, nitrogen, antimatter), and a fairly spectacular setting for demi operatic space battles (see "Ring Raiders" in Atomic Rockets, for example:

    As always, YMMV

    1. I haven't looked into antimatter harvesting much, but what about the Sun itself? It might be a better source of antimatter than even the gas giants.

      I personally tend to handwave antimatter out of my settings. Even tiny quantities of the stuff allows for antimatter-catalyzed fusion ships that can jet around the solar system with impunity owing to the combination of 'cheap' low-energy fusion ignition and fantastically powerful yet clean aneutronic reactions.

      On the other hand, such a capability would make it very sought after if you don't go down the path I did, also for the reasons you mentioned.

      Fun fact: I could rename the whole blog from 'ToughSF' to 'YMMV-SF' and the title wouldn't lose meaning ;)

  17. "'YMMV-SF'" Hah! I am so stealing that.....

    I tend to think about things like antimatter harvesting or ORION nuclear pulse drive and analogues precisely because "jetting around" the Solar System is so much better for both story purposes and real life. Who would seriously head out to homestead on one of the Jovian Moons if a one way ticket involves waiting for the proper synodic period to come up *and* a six year, one way journey using a low thrust/high ISP drive like dusty fission fragment (with the exhaust velocity of 1% of c, we're not talking about a wimpy high ISP drive either).

    The economics are bad for this sort of thing for a multitude of reasons, most especially the compound interest equations. Would any investor be willing to put up a considerable sum of money with no prospect of return for years or possibly decades if the same sum can be invested in something else which has either a guaranteed rate of return, or a speculative shorter term ROI?

    Even in my imagined setting, bulk cargo is shot out of mass drivers in unpowered cargo pods (think of ISO containers), but futures markets accept this because there is essentially a "pipeline" of cargo pods following ballistic trajectories across the solar system. This also tends to make the setups go the shortest distances with the lowest synodic periods possible; the Neos will be mined out before the Asteroid belt becomes profitable, and the Asteroids will be heavily exploited before Jupiter becomes a profit centre. Mercury works because they can use sunlight and solar sails to "brute force" the problem away.

    Maybe at some point there should be a post about the "dismal science" and its effects on PMF settings.

    1. The Laser Problem.
      Jetting around the solar system with terawatt thrusters sounds nice, and fixes the problem of having to wait months between ports, but just exacerbates the fact that high drive power equals nightmarish lasers.

      I'm a finance student so the dismal science is kind of my thing. I explored some economics and finance in the Interstellar Trade posts, but I must admit that most people do not find this sort of thing interesting.

      With regards to travel times and asteroid mining, it is critical to develop local markets and basically break down the production chain of the products from ore to product into small, individually profitable steps.

  18. It is sad that people are not more interested in things like economics, since understanding of these sciences provides a much broader perspective of the underlying forces that cause changes in society, demographics, political structures, bureaucracies and so much more.

    Of course it is much easier to "see" the Firestars making their attack runs than to "see" all the factors which led up to them appearing in orbit in the first place. Story wise you might need a Christopher Nolan tour de force like "Dunkirk", with multiple story lines on sliding timelines....

    1. There are quite a few SF works which have economic or financial theory as a central plot point, and were excellent reads, that make me confidently say that the audience's interest in a matter is subject only to how well it is introduced and how engaging the writing is.

      For example, we have Neptune's Brood by Charles Stross, which deals with interstellar crypto-currency banking systems. There's The Diamond Age by Neal Stephenson in which the economics of a nano-technology dependent society is core to the plot.

      I find the post-singularity settings, such as Ian M. Bank's Culture, or free trader games such as the Traveller RPG, all have economics at heart, just better hidden.

  19. New on Atomic Rockets is a ship design which comes pretty close to the concept of a "Firestar", even being powered by a fusion pulse drive and mounting multiple VL missile cells:


    1. I like the tactical reasoning very much: forcing missiles to drop their boosters is very 'ToughSF' and reminiscent of WWII interceptors forcing P-51 Mustangs to drop their tanks and engage in combat - whether the interceptors win or not does not matter, as without the tanks the Mustangs cannot escort the bombers anymore.

      However, the design smacks the 'Laser Problem' face-first. Hundred-terawatt drives might be fun because they allow the author to draw up spaceships that both burn at multiple G yet don't really have to care about deltaV... but also mean that if even a fraction of that drive power can be converted into a laser beam, then the interceptors are better off just lasing down the missiles.

    2. Well that is indeed the issue, how do you convert that energy into a laser beam? The other issue has been brought up in Rocketpunk Manifesto, the problem of isolating the optical train of the laser to allow for extreme range engagements (the classical RBoD engages in "killing strokes" at a light second, and can scorch targets at a light minute and is even dangerous to unshielded targets at a light hour. Illuminating targets that far away makes them shine even more against the cold background). Of course with such extreme power outputs, you might simply have a very massive mirror and enjoy the advantage of a giant laser spot with the power to burn through metal, ceramics and carbon fibre at a light second's range.

      This might also make for the basis of a "Gunstar" mounting multiple rail or coilguns, since it can manoeuvre quickly to aim anyplace the shots.

      Assuming the drive is halfway plausible, this turns demi operatic space battles into more classical "space opera" engagements than the stately mobile Vaubin fortress like constellations sometime envisioned.

    3. Quite easy!

      All the methods proposed for collecting enough energy to ignite the next fusion pulse in a fusion rocket can be harnessed to power a laser.

      The least efficient methods use waste heat reclamation: even the cleanest fusion reaction produces some neutrons. These neutrons must be absorbed by a radiation shield, which heats up as a result. This heat can be converted in electricity.

      The heat from gamma rays or un-absorbed x-rays can also be used.

      A hole can be created in the magnetic nozzle of a fusion rocket to allow plasma to bleed out. This plasma is run through an MHD generator for power.

      Or, most efficient of all, you can slow down the charged particles from the vaporized and ionized propellant by a tiny amount and extract power directly from the magnetic coils in the nozzle - like regenerative braking in an electric car.

      Once you are in the Terawatt domain of propulsion, all propellants are extremely hot, ionized and moving quickly. This makes it easy to extract energy from the drive.

      I'm not sure what 'isolating the optical train' means, sorry.

      With such high power output available, you can get away with using small mirrors and just blasting the entire sector of the sky the targets could be located in.

  20. Tony in Rocketpunk Manifesto has commented numerous times that the optical train on a laserstar wold be subjected to vibrations from the spacecraft itself and thus less likely to be able to engage at classical RBoD ranges.

    I tend to believe that up to a certain level, you can isolate the optical train of the laser from vibrations much like you isolate the machinery on a submarine on a "raft", but terawatt level pulse drives are probably far beyond where that sort of technology would work. My conception would be to use the ship in a "sprint and drift" mode, unfurling the laser mirror or diffraction array once the drive has been shut down so you only have residual vibrations to deal with and can make light second engagements possible.

    The other ways of dealing with this would be your (Matter beam's) idea of just blasting the laser in the direction of the target (much like WWII era British warplanes used 8 X .303 machine guns rather than smaller numbers of heavy machine guns or 20mm cannons, because they were using the idea of the Lanchester equations favouring large numbers of bullets in the air to achieve both hist and enough hits to do killing damage.

    Finally you could simply decree that the various factors in play make laser weapons ineffective beyond "x" distance, putting a hard limit on cutting or vapourizing the enemy, although scorch damage and long range illumination still is possible.

    1. Tony makes an interesting point, but the conclusion requires many assumptions that do not fit with real-world achievements.

      Modern spy telescopes can track moving objects on the ground to within a meter from altitude of about 200km. That works out to 5 microradian accuracy. They are moving across the ground at roughly 7800m/s, so the slew rate should be about 39 milliradians/sec. This is accomplished with a satellite that has a very small dampening mass and has many moving parts, such as adjusting dishes and rotating solar panels to track the sun.

      The key to such performance seems to be adaptive optics and as you mentioned, free-floating optics within the satellite.

  21. Either I miss something, or your estimation of maximum velocity achievable by Spaced NEFP is missing the real problem.

    The metallic pusher plate is heated up by shock wave inflicted by impacting plasma. You cannot have acceleration 10^6 Gees without such shock-waves. These shock waves lead to considerable entropic heating (which is dominant source of heating as heat conductance is slow, and metal is opaque for most of EM radiation) (well described here

    Therefore I think you cannot achieve much more than few tens km/s (say 20-30km/s?) by any abrupt impulse, without evaporation of pusher plate. Only way how to avoid this entropic heating would be accelerate it over longer time/path, but than we are not talking about bomb.

    Beside that you would need guarantie very homogenous distrubution of plasma pressure and density and match it with area-density of pusher plate, otherwise some parts of pusher plate would be accelerated to higher velocity and the whole pusher plate would fragment (tensile strengh is negligigle with respect to accelerating pressure)

    1. Sorry for the late reply.
      I will look into the heating caused by compression shockwaves, but for now, I will stick with the conclusions of this Science and Global Security report, which mentions molten metal being shot at 10,000km/s from nuclear devices:

      If anything, my calculations are conservative!

      The homogenous distribution here is expected to be achieved from nuclear devices for the Orion project back in the 60s, so it is reasonable to assume that it will be achieved again in the future.

  22. With 285, 10 megatons casaba howitzer 10 000km range, if you detonate them at the same time again't the same target, you could increase the range of the attack to (10000x285^0.5)to 169000km. With 285, 150 megatons casaba howitzer, the range of the attack would be 422000km. So a casaba howitzer ship could detroy the laser star before the laser could engage or detect it.

  23. incredibly late i know but i was wondering if a 1-2m diameter spaced NEFP would be possible/practical, or if the concept demands a larger plate