As you should know, there are two types of nuclear weapons. An "atomic bomb" is a weapon with a war-head powered by nuclear fission. An "H-bomb" or "hydrogen bomb" is a weapon with more powerful warhead powered by nuclear fusion. In some military documents they will refer to the nuclear warhead as the "physics package."
You can read all about the (unclassified) details of their internal construction and mechanism here.
Occasionally you will find a fusion weapon referred to as a "Solar-Phoenix" or a "Bethe-cycle" weapon. This is a reference to the nuclear scientist Hans Bethe and the Bethe-Weizsäcker or carbon-nitrogen cycle which powers the fusion reaction in the heart of stars heavier than Sol.
As far as warhead mass goes, Anthony Jackson says the theoretical limit on mass for a fusion warhead is about 1 kilogram per megaton. No real-world system will come anywhere close to that, The US W87 thermonuclear warhead has a density of about 500 kilograms per megaton. Presumably a futuristic warhead would have a density between 500 and 1 kg/Mt. Calculating the explosive yield of a weapon is a little tricky.
For missiles, consider the US Trident missile. Approximately a cylinder 13.41 m in length by 1.055 m in radius, which makes it about 47 cubic meters. Mass of 58,500 kg, giving it a density of 1250 kg/m3. The mass includes eight warheads of approximately 160 kg each.
Wildly extrapolating far beyond the available data, one could naively divide the missile mass by the number of warheads, and divide the result by the mass of an individual warhead. The bottom line would be that a warhead of mass X kilograms would require a missile of mass 45 * X kilograms, and a volume of 0.036 * X cubic meters (0.036 = 45 / 1250). Again futuristic technology would reduce this somewhat.
Nuclear weapons will destroy a ship if they detonate exceedingly close to it. But if it is further away than about a kilometer, it won't do much more than singe the paint job and blind a few sensors. And in space a kilometer is pretty close range.
Please understand: I am NOT saying that nuclear warheads are ineffective. I am saying that the amount of damage they inflict falls off very rapidly with increasing range. At least much more rapidly than with the same sized warhead detonated in an atmosphere.
But if the nuke goes off one meter from your ship, your ship will probably be vaporized. Atmosphere or no.
George William Herbert says a nuke going off on Terra has most of the x-ray emission absorbed by the atmosphere, and transformed into the first fireball and the blast wave. There ain't no atmosphere in space so the nuclear explosion is light on blast and heavy on x-rays. In fact, almost 90% of the bomb energy will appear as x-rays behaving as if they are from a point source (specifically 80% soft X-rays and 10% gamma), and subject to the good old inverse square law (i.e., the intensity will fall off very quickly with range). The remaining 10% will be neutrons.
The fireball and blast wave is why nuclear warheads detonating in the atmosphere will flatten buildings for tens of kilometers, but detonations in space have a damage range under one kilometer.
For an enhanced radiation weapon (AKA "Neutron Bomb") figures are harder to come by. The best guess figure I've managed to find was up to a maximum of 80% neutrons and 20% x-rays.
If you want to get more bang for your buck, there is a possibility of making nuclear shaped charges. Instead of wasting their blast on a spherical surface, it can be directed at the target spacecraft. This will reduce the surface area of the blast, thus increasing the value for kiloJoules per square meter.
According to John Schilling, with current technology, the smallest nuclear warhead would probably be under a kiloton, and mass about twenty kilograms. A one-megaton warhead would be about a metric ton, though that could be reduced by about half with advanced technology.
Eric Rozier has an on-line calculator for nuclear weapons. Eric Henry has a spreadsheet that does nuclear blast calculations, including shaped charges, on his website. For bomb blasts on the surface of the Earth or other planet with an atmosphere, you can use the handy-dandy Nuclear Bomb Effects Computer. But if you really want to do it in 1950's Atomic Rocket Retro style, make your own do-it-yourself Nuclear Bomb Slide Rule!
A "neutron bomb" is a nuclear warhead design that has been tweaked so it is much better at killing soldiers and civilians while doing much less damage to military vehicles and civilian buildings. It makes it easier to kill off the enemy soldiers so you can steal their stuff. Neutron bombs are also good to use if the enemy is invading your country. No sense in blowing huge holes in your own cities when all you want to do is exterminate enemy soldiers.
This weapons is what you call an "enhanced radiation bomb". They are specially constructed so more of the bomb's energy is emitted as neutrons instead of x-rays. This means there is far less blast to damage the buildings, but far more lethal neutron radiation to kill the enemy troops. Conventional nuclear warheads typically release 5% of the energy as neutrons, but in neutron bombs it is a whopping 40%. Neutron energy is higher as well: 14 MeV instead of the conventional 1 to 2 MeV.
A 1 kiloton neutron bomb will irradiate anybody unfortunate enough to be at a range of 900 meters with 80 Grays of neutrons. According to dosages set by the US military, this is high enough to instantly send the victim into a coma, with certain death to follow within 24 hours due to damage to the central nervous system. The LD50 dose is at a range of between 1350 and 1400 meters (almost a mile).
- Neutron activation of the steel girders of buildings would render them unsafe. Which was one of the selling points of neutron bombs: the buildings could be immediately used by an advancing army, once you removed all the dead enemy soliders.
- Armored fighting vehicles provide enemy soldiers with a surprisingly high protection of neutron radiation, and can be easily increased. Since all spacecraft include radiation shielding from solar storms and galactic cosmic rays, this will drastically reduce the effect of neutron bombs used as anti-spacecraft weapons. Spacecraft with nuclear propulsion will try to aim their shadow shields at the neutron bomb for added protection.
- Enemy ground soldiers can also find high amounts of protection by sheltering inside buildings with 12 inch concrete walls and ceiling, or in a cellar under 24 inches of damp soil. Both will reduce the radiation exposure by a factor of 10.
- Neutron bomb ordinance requires maintenance, since one of the components is Tritium with its annoyingly short half-life of 12.32 years. This means that every few years the neutron bombs will have to be opened up and have their tritium replaced.
Energy distribution of weapon Energy type Proportion of total energy (%) Fission Enhanced Blast 50 40 to minimum 30 Thermal energy 35 25 to minimum 20 Prompt radiation 5 45 to minimum 30 Residual radiation 10 5
A neutron bomb, officially defined as a type of enhanced radiation weapon (ERW), is a low-yield thermonuclear weapon designed to maximize lethal neutron radiation in the immediate vicinity of the blast while minimizing the physical power of the blast itself. The neutron release generated by a nuclear fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components. The neutron burst, which is used as the primary destructive action of the warhead, is able to penetrate enemy armor more effectively than a conventional warhead, thus making it more lethal as a tactical weapon.
The concept was originally developed by the US in the late 1950s and early 1960s. It was seen as a "cleaner" bomb for use against massed Soviet armored divisions. As these would be used over allied nations, notably West Germany, the reduced blast damage was seen as an important advantage.
ERWs were first operationally deployed for anti-ballistic missiles (ABM). In this role the burst of neutrons would cause nearby warheads to undergo partial fission, preventing them from exploding properly. For this to work, the ABM would have to explode within approximately 100 metres (300 ft) of its target. The first example of such a system was the W66, used on the Sprint missile used in the US's Nike-X system. It is believed the Soviet equivalent, the A-135's 53T6 missile, uses a similar design.
The weapon was once again proposed for tactical use by the US in the 1970s and 1980s, and production of the W70 began for the MGM-52 Lance in 1981. This time it experienced a firestorm of protest as the growing anti-nuclear movement gained strength through this period. Opposition was so intense that European leaders refused to accept it on their territory. President Ronald Reagan built examples of the W70-3 which remained stockpiled in the US until they were retired in 1992. The last W70 was dismantled in 2011.
In a standard thermonuclear design, a small fission bomb is placed close to a larger mass of thermonuclear fuel. The two components are then placed within a thick radiation case, usually made from uranium, lead or steel. The case traps the energy from the fission bomb for a brief period, allowing it to heat and compress the main thermonuclear fuel. The case is normally made of depleted uranium or natural uranium metal, because the thermonuclear reactions give off massive numbers of high-energy neutrons that can cause fission reactions in the casing material. These can add considerable energy to the reaction; in a typical design as much as 50% of the total energy comes from fission events in the casing. For this reason, these weapons are technically known as fission-fusion-fission designs.
In a neutron bomb, the casing material is selected either to be transparent to neutrons or to actively enhance their production. The burst of neutrons created in the thermonuclear reaction is then free to escape the bomb, outpacing the physical explosion. By designing the thermonuclear stage of the weapon carefully, the neutron burst can be maximized while minimizing the blast itself. This makes the lethal radius of the neutron burst greater than that of the explosion itself. Since the neutrons disappear from the environment rapidly, such a burst over an enemy column would kill the crews and leave the area able to be quickly reoccupied.
Compared to a pure fission bomb with an identical explosive yield, a neutron bomb would emit about ten times the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of both gamma rays and neutrons is approximately 5% of the entire energy released; in neutron bombs it would be closer to 40%, with the percentage increase coming from the higher production of neutrons. Furthermore, the neutrons emitted by a neutron bomb have a much higher average energy level (close to 14 MeV) than those released during a fission reaction (1–2 MeV).
Technically speaking, every low yield nuclear weapon is a radiation weapon, including non-enhanced variants. All nuclear weapons up to about 10 kilotons in yield have prompt neutron radiation as their furthest-reaching lethal component. For standard weapons above about 10 kilotons of yield, the lethal blast and thermal effects radius begins to exceed the lethal ionizing radiation radius. Enhanced radiation weapons also fall into this same yield range and simply enhance the intensity and range of the neutron dose for a given yield.
History and deployment to present
The conception of neutron bombs is generally credited to Samuel T. Cohen of the Lawrence Livermore National Laboratory, who developed the concept in 1958. Initial development was carried out as part of projects Dove and Starling, and an early device was tested underground in early 1962. Designs of a "weaponized" version were carried out in 1963.
Development of two production designs for the army's MGM-52 Lance short-range missile began in July 1964, the W63 at Livermore and the W64 at Los Alamos. Both entered phase three testing in July 1964, and the W64 was cancelled in favor of the W63 in September 1964. The W63 was in turn cancelled in November 1965 in favor of the W70 (Mod 0), a conventional design. By this time, the same concepts were being used to develop warheads for the Sprint missile, an anti-ballistic missile (ABM), with Livermore designing the W65 and Los Alamos the W66. Both entered phase three testing in October 1965, but the W65 was cancelled in favor of the W66 in November 1968. Testing of the W66 was carried out in the late 1960s, and it entered production in June 1974, the first neutron bomb to do so. Approximately 120 were built, with about 70 of these being on active duty during 1975 and 1976 as part of the Safeguard Program. When that program was shut down they were placed in storage, and eventually decommissioned in the early 1980s.
Development of ER warheads for Lance continued, but in the early 1970s attention had turned to using modified versions of the W70, the W70 Mod 3. Development was subsequently postponed by President Jimmy Carter in 1978 following protests against his administration's plans to deploy neutron warheads to ground forces in Europe. On November 17, 1978, in a test the USSR detonated its first similar-type bomb. President Ronald Reagan restarted production in 1981. The Soviet Union renewed a propaganda campaign against the US's neutron bomb in 1981 following Reagan's announcement. In 1983 Reagan then announced the Strategic Defense Initiative, which surpassed neutron bomb production in ambition and vision and with that, neutron bombs quickly faded from the center of the public's attention.
Three types of enhanced radiation weapons (ERW) were deployed by the United States. The W66 warhead, for the anti-ICBM Sprint missile system, was deployed in 1975 and retired the next year, along with the missile system. The W70 Mod 3 warhead was developed for the short-range, tactical MGM-52 Lance missile, and the W79 Mod 0 was developed for nuclear artillery shells. The latter two types were retired by President George H. W. Bush in 1992, following the end of the Cold War. The last W70 Mod 3 warhead was dismantled in 1996, and the last W79 Mod 0 was dismantled by 2003, when the dismantling of all W79 variants was completed.
According to the Cox Report, as of 1999 the United States had never deployed a neutron weapon. The nature of this statement is not clear; it reads "The stolen information also includes classified design information for an enhanced radiation weapon (commonly known as the "neutron bomb"), which neither the United States, nor any other nation, has ever deployed." However, the fact that neutron bombs had been produced by the US was well known at this time and part of the public record. Cohen suggests the report is playing with the definitions; while the US bombs were never deployed to Europe, they remained stockpiled in the US.
In addition to the two superpowers, France and China are known to have tested neutron or enhanced radiation bombs. France conducted an early test of the technology in 1967 and tested an "actual" neutron bomb in 1980. China conducted a successful test of neutron bomb principles in 1984 and a successful test of a neutron bomb in 1988. However, neither of those countries chose to deploy neutron bombs. Chinese nuclear scientists stated before the 1988 test that China had no need for neutron bombs, but it was developed to serve as a "technology reserve", in case the need arose in the future.
In August 1999, the Indian government disclosed that India was capable of producing a neutron bomb.
Although no country is currently known to deploy them in an offensive manner, all thermonuclear dial-a-yield warheads that have about 10 kiloton and lower as one dial option, with a considerable fraction of that yield derived from fusion reactions, can be considered able to be neutron bombs in use, if not in name. The only country definitely known to deploy dedicated (that is, not dial-a-yield) neutron warheads for any length of time is the Soviet Union/Russia, which inherited the USSR's neutron warhead equipped ABM-3 Gazelle missile program. This ABM system contains at least 68 neutron warheads with a 10 kiloton yield each and it has been in service since 1995, with inert missile testing approximately every other year since then (2014). The system is designed to destroy incoming endoatmospheric nuclear warheads aimed at Moscow and other targets and is the lower-tier/last umbrella of the A-135 anti-ballistic missile system (NATO reporting name: ABM-3).
By 1984, according to Mordechai Vanunu, Israel was mass-producing neutron bombs.
Considerable controversy arose in the US and Western Europe following a June 1977 Washington Post exposé describing US government plans to equip US Armed Forces with neutron bombs. The article focused on the fact that it was the first weapon specifically intended to kill humans with radiation. Lawrence Livermore National Laboratory director Harold Brown and Soviet General Secretary Leonid Brezhnev both described neutron bombs as a "capitalist bomb", because it was designed to destroy people while preserving property.
Neutron bombs are purposely designed with explosive yields lower than other nuclear weapons. Since neutrons are scattered and absorbed by air, neutron radiation effects drop off rapidly with distance in air. As such, there is a sharper distinction, relative to thermal effects, between areas of high lethality and areas with minimal radiation doses. All high yield (more than c. 10 kiloton) nuclear bombs, such as the extreme example of a device that derived 97% of its energy from fusion, the 50 megaton Tsar Bomba, are not able to radiate sufficient neutrons beyond their lethal blast range when detonated as a surface burst or low altitude air burst and so are no longer classified as neutron bombs, thus limiting the yield of neutron bombs to a maximum of about 10 kilotons. The intense pulse of high-energy neutrons generated by a neutron bomb is the principal killing mechanism, not the fallout, heat or blast.
The inventor of the neutron bomb, Sam Cohen, criticized the description of the W70 as a neutron bomb since it could be configured to yield 100 kilotons:
the W-70 ... is not even remotely a "neutron bomb." Instead of being the type of weapon that, in the popular mind, "kills people and spares buildings" it is one that both kills and physically destroys on a massive scale. The W-70 is not a discriminate weapon, like the neutron bomb—which, incidentally, should be considered a weapon that "kills enemy personnel while sparing the physical fabric of the attacked populace, and even the populace too."
Although neutron bombs are commonly believed to "leave the infrastructure intact", with current designs that have explosive yields in the low kiloton range, detonation in (or above) a built-up area would still cause a sizable degree of building destruction, through blast and heat effects out to a moderate radius, albeit considerably less destruction, than when compared to a standard nuclear bomb of the exact same total energy release or "yield".
The Warsaw Pact tank strength was over twice that of NATO, and Soviet deep battle doctrine was likely to be to use this numerical advantage to rapidly sweep across continental Europe if the Cold War ever turned hot. Any weapon that could break up their intended mass tank formation deployments and force them to deploy their tanks in a thinner, more easily dividable manner, would aid ground forces in the task of hunting down solitary tanks and using anti-tank missiles against them, such as the contemporary M47 Dragon and BGM-71 TOW missiles, of which NATO had hundreds of thousands.
Rather than making extensive preparations for battlefield nuclear combat in Central Europe, "The Soviet military leadership believed that conventional superiority provided the Warsaw Pact with the means to approximate the effects of nuclear weapons and achieve victory in Europe without resort to those weapons."
Neutron bombs, or more precisely, enhanced [neutron] radiation weapons were also to find use as strategic anti-ballistic missile weapons, and in this role they are believed to remain in active service within Russia's Gazelle missile.
Upon detonation, a near-ground airburst of a 1 kiloton neutron bomb would produce a large blast wave and a powerful pulse of both thermal radiation and ionizing radiation in the form of fast (14.1 MeV) neutrons. The thermal pulse would cause third degree burns to unprotected skin out to approximately 500 meters. The blast would create pressures of at least 4.6 psi out to a radius of 600 meters, which would severely damage all non-reinforced concrete structures. At the conventional effective combat range against modern main battle tanks and armored personnel carriers (< 690–900 m), the blast from a 1 kt neutron bomb would destroy or damage to the point of nonusability almost all un-reinforced civilian buildings.
Using neutron bombs to stop an enemy armored attack by rapidly incapacitating crews with a dose of 80+ Gy of radiation would require exploding large numbers of them to blanket the enemy forces, destroying all normal civilian buildings within c. 600 meters of the immediate area. Neutron activation from the explosions could make many building materials in the city radioactive, such as galvanized steel (see area denial use below).
Because liquid-filled objects like the human body are resistant to gross overpressure, the 4–5 psi blast overpressure would cause very few direct casualties at a range of c. 600 m. The powerful winds produced by this overpressure, however, could throw bodies into objects or throw debris at high velocity, including window glass, both with potentially lethal results. Casualties would be highly variable depending on surroundings, including potential building collapses.
The pulse of neutron radiation would cause immediate and permanent incapacitation to unprotected outdoor humans in the open out to 900 meters, with death occurring in one or two days. The median lethal dose (LD50) of 6 Gray would extend to between 1350 and 1400 meters for those unprotected and outdoors, where approximately half of those exposed would die of radiation sickness after several weeks.
A human residing within, or simply shielded by, at least one concrete building with walls and ceilings 30 cm (12 in) thick, or alternatively of damp soil 24 inches thick, would receive a neutron radiation exposure reduced by a factor of 10. Even near ground zero, basement sheltering or buildings with similar radiation shielding characteristics would drastically reduce the radiation dose.
Furthermore, the neutron absorption spectrum of air is disputed by some authorities, and depends in part on absorption by hydrogen from water vapor. Thus, absorption might vary exponentially with humidity, making neutron bombs far more deadly in desert climates than in humid ones.
Effectiveness in modern anti-tank role
The questionable effectiveness of ER weapons against modern tanks is cited as one of the main reasons that these weapons are no longer fielded or stockpiled. With the increase in average tank armor thickness since the first ER weapons were fielded, it was argued in the March 13, 1986, New Scientist magazine that tank armor protection was approaching the level where tank crews would be almost fully protected from radiation effects. Thus, for an ER weapon to incapacitate a modern tank crew through irradiation, the weapon must be detonated at such proximity to the tank that the nuclear explosion's blast would now be equally effective at incapacitating it and its crew. However this assertion was regarded as dubious in the June 12, 1986, New Scientist reply by C.S. Grace, a member of the Royal Military College of Science, as neutron radiation from a 1 kiloton neutron bomb would incapacitate the crew of a tank with a protection factor of 35 out to a range of 280 meters, but the incapacitating blast range, depending on the exact weight of the tank, is much less, from 70 to 130 meters.
However although the author did note that effective neutron absorbers and neutron poisons such as boron carbide can be incorporated into conventional armor and strap-on neutron moderating hydrogenous material (substances containing hydrogen atoms), such as explosive reactive armor, can both increase the protection factor, the author holds that in practice combined with neutron scattering, the actual average total tank area protection factor is rarely higher than 15.5 to 35. According to the Federation of American Scientists, the neutron protection factor of a "tank" can be as low as 2, without qualifying whether the statement implies a light tank, medium tank, or main battle tank.
A composite high density concrete, or alternatively, a laminated graded-Z shield, 24 units thick of which 16 units are iron and 8 units are polyethylene containing boron (BPE), and additional mass behind it to attenuate neutron capture gamma rays, is more effective than just 24 units of pure iron or BPE alone, due to the advantages of both iron and BPE in combination. During Neutron transport Iron is effective in slowing down/scattering high-energy neutrons in the 14-MeV energy range and attenuating gamma rays, while the hydrogen in polyethylene is effective in slowing down these now slower fast neutrons in the few MeV range, and boron 10 has a high absorption cross section for thermal neutrons and a low production yield of gamma rays when it absorbs a neutron. The Soviet T72 tank, in response to the neutron bomb threat, is cited as having fitted a boronated polyethylene liner, which has had its neutron shielding properties simulated.
However, some tank armor material contains depleted uranium (DU), common in the US's M1A1 Abrams tank, which incorporates steel-encased depleted uranium armor, a substance that will fast fission when it captures a fast, fusion-generated neutron, and thus on fissioning will produce fission neutrons and fission products embedded within the armor, products which emit among other things, penetrating gamma rays. Although the neutrons emitted by the neutron bomb may not penetrate to the tank crew in lethal quantities, the fast fission of DU within the armor could still ensure a lethal environment for the crew and maintenance personnel by fission neutron and gamma ray exposure, largely depending on the exact thickness and elemental composition of the armor—information usually hard to attain. Despite this, Ducrete—which has an elemental composition similar (but not identical) to the ceramic second generation heavy metal Chobham armor of the Abrams tank—is an effective radiation shield, to both fission neutrons and gamma rays due to it being a graded Z material. Uranium, being about twice as dense as lead, is thus nearly twice as effective at shielding gamma ray radiation per unit thickness.
Use against ballistic missiles
As an anti-ballistic missile weapon, the first fielded ER warhead, the W66, was developed for the Sprint missile system as part of the Safeguard Program to protect United States cities and missile silos from incoming Soviet warheads.
A problem faced by Sprint and similar ABMs was that the blast effects of their warheads change greatly as they climb and the atmosphere thins out. At higher altitudes, starting around 60,000 feet (18,000 m) and above, the blast effects begin to drop off rapidly as the air density becomes very low. This can be countered by using a larger warhead, but then it becomes too powerful when used at lower altitudes. An ideal system would use a mechanism that was less sensitive to changes in air density.
Neutron-based attacks offer one solution to this problem. The burst of neutrons released by an ER weapon can induce fission in the fissile materials of primary in the target warhead. The energy released by these reactions may be enough to melt the warhead, but even at lower fission rates the "burning up" of some of the fuel in the primary can cause it to fail to explode properly, or "fizzle". Thus a small ER warhead can be effective across a wide altitude band, using blast effects at lower altitudes and the increasingly long-ranged neutrons as the engagement rises.
The use of neutron-based attacks was discussed as early as the 1950s, with the US Atomic Energy Commission mentioning weapons with a "clean, enhanced neutron output" for use as "antimissile defensive warheads." Studying, improving and defending against such attacks was a major area of research during the 1950s and 60s. A particular example of this is the US Polaris A-3 missile, which delivered three warheads travelling on roughly the same trajectory, and thus with a short distance between them. A single ABM could conceivably destroy all three through neutron flux. Developing warheads that were less sensitive to these attacks was a major area of research in the US and UK during the 1960s.
GAR-11/AIM-26 was primarily a weapon-killer. The bomber(s, if any) was collateral damage. The weapon was proximity-fused to ensure detonation close enough so an intense flood of neutrons would result in an instantaneous nuclear reaction (NOT full-scale) in the enemy weapon’s pit; rendering it incapable of functioning as designed...[O]ur first “neutron bombs” were the GAR-11 and MB-1 Genie.
It has also been suggested that neutron flux's effects on the warhead electronics are another attack vector for ER warheads in the ABM role. Ionization greater than 50 Gray in silicon chips delivered over seconds to minutes will degrade the function of semiconductors for long periods. However, while such attacks might be useful against guidance systems which used relatively advanced electronics, in the ABM role these components have long ago separated from the warheads by the time they come within range of the interceptors. The electronics in the warheads themselves tend to be very simple, and hardening them was one of the many issues studied in the 1960s.
Lithium-6 hydride (Li6H) is cited as being used as a countermeasure to reduce the vulnerability and "harden" nuclear warheads from the effects of externally generated neutrons. Radiation hardening of the warhead's electronic components as a countermeasure to high altitude neutron warheads somewhat reduces the range that a neutron warhead could successfully cause an unrecoverable glitch by the transient radiation effects on electronics (TREE) effects.
At very high altitudes, at the edge of the atmosphere and above it, another effect comes into play. At lower altitudes, the x-rays generated by the bomb are absorbed by the air and have mean free paths on the order of meters. But as the air thins out, the x-rays can travel further, eventually outpacing the area of effect of the neutrons. In exoatmospheric explosions, this can be on the order of 10 kilometres (6.2 mi) in radius. In this sort of attack, it is the x-rays promptly delivering energy on the warhead surface that is the active mechanism; the rapid ablation (or "blow off") of the surface creates shock waves that can break up the warhead.
Use as an area denial weapon
In November 2012, during the planning stages of Operation Hammer of God, British Labour peer Lord Gilbert suggested that multiple enhanced radiation reduced blast (ERRB) warheads could be detonated in the mountain region of the Afghanistan-Pakistan border to prevent infiltration. He proposed to warn the inhabitants to evacuate, then irradiate the area, making it unusable and impassable. Used in this manner, the neutron bomb(s), regardless of burst height, would release neutron activated casing materials used in the bomb, and depending on burst height, create radioactive soil activation products.
In much the same fashion as the area denial effect resulting from fission product (the substances that make up most fallout) contamination in an area following a conventional surface burst nuclear explosion, as considered in the Korean War by Douglas MacArthur, it would thus be a form of radiological warfare—with the difference that neutron bombs produce half, or less, of the quantity of fission products relative to the same-yield pure fission bomb. Radiological warfare with neutron bombs that rely on fission primaries would thus still produce fission fallout, albeit a comparatively cleaner and shorter lasting version of it in the area than if air bursts were used, as little to no fission products would be deposited on the direct immediate area, instead becoming diluted global fallout.
However the most effective use of a neutron bomb with respect to area denial would be to encase it in a thick shell of material that could be neutron activated, and use a surface burst. In this manner the neutron bomb would be turned into a salted bomb; a case of zinc-64, produced as a byproduct of depleted zinc oxide enrichment, would for example probably be the most attractive for military use, as when activated, the zinc-65 so formed is a gamma emitter, with a half life of 244 days.
Hypothetical effects of a pure fusion bomb
With considerable overlap between the two devices, the prompt radiation effects of a pure fusion weapon would similarly be much higher than that of a pure-fission device: approximately twice the initial radiation output of current standard fission-fusion-based weapons. In common with all neutron bombs that must presently derive a small percentage of trigger energy from fission, in any given yield a 100% pure fusion bomb would likewise generate a more diminutive atmospheric blast wave than a pure-fission bomb. The latter fission device has a higher kinetic energy-ratio per unit of reaction energy released, which is most notable in the comparison with the D-T fusion reaction. A larger percentage of the energy from a D-T fusion reaction, is inherently put into uncharged neutron generation as opposed to charged particles, such as the alpha particle of the D-T reaction, the primary species, that is most responsible for the coulomb explosion/fireball.
You will also occasionally find references to a nasty weapon called a "cobalt bomb". This is technically termed a "salted bomb". It is not used for spacecraft to spacecraft combat, it is only used for planetary bombardment. The purpose is to render the land downwind of ground-zero so radioactive that it will be unsafe to enter for the next few thousand years. They are spiteful weapons, sending the message that if the attacker cannot have the land, then nobody can have it.
They are enhanced-fallout weapons, with jackets of cobalt or zinc to generate large quantities of deadly radioactive cobalt or zinc isotope dust. The warhead proper will probably be a neutron bomb: since the more neutrons emitted by the warhead, the more of the jacket will be neutron-activated into radioactive isotopes.
Suggested elements include cobalt, gold, tantalum, zinc, and sodium. The idea is to use as a jacket some element that will neutron activate into an isotope which is a high intensity gamma ray emitter with a long half-life.
Please note the difference between a "salted bomb" and a "dirty bomb".
A dirty bomb is an ordinary chemical explosive in a small bag of ground-up radioactive material. The chemical explosion merely sprays the powdered plutonium or whatever all over the city block. Strictly a terrorist weapon, it is pretty worthless as a military weapon.
A salted bomb is a nuclear warhead designed to make a nuclear explosion that will spread millions of bagfulls of fallout that is thousands of times more radioactive that mere powdered plutonium over a quarter of a continent.
Term comes from metaphor "sowing the Earth with salt".
Thermonuclear weapons are typically a mass of fusion fuel (with some other items) that are ignited to fusion temperatures by a fission bomb "match." The requirement of an atom bomb to light off your h-bomb is a bit inefficient. In science fiction one occasionally encounters fusion weapons that contain unobtainium capacitors powering honking huge lasers to ignite fusion. You might save on plutonium, but this is hardly cheaper than conventional fusion warheads.
Finn van Donkelaar has been playing around with another concept. It might be barely possible to ignite a small fusion reaction using chemical explosives. Maybe. Not out of the question. Possibly. Not impossible. Sort of.
His initial write up is very interesting reading, abet loaded with nasty equations. He notes it has a lower yield-to-weight ratio compared to conventional fusion warheads (which is bad), but has a couple of advantages. Which you can read about in the report.
He calculate the device in the diagram above is at the low end of possible yields. Mass of 20 kilograms, length of 45 centimeters, diameter of 8 centimeters, and a yield of 250 kg of TNT. Scaled up to largest reasonably portable size the same design would have a mass of 1.6 metric tons, length of 2.5 meters, diameter of 40 centimeters, and a yield of 2 kilotons of TNT.
Most SF fans have a somewhat superficial understanding of EMP: an evil foreign nation launches an ICBM at the United States, the nuke detonates in the upper atmosphere over the Midwest, an EMP is generated, the EMP causes all stateside computers to explode, all the TVs melt, all the automobile electrical systems short out, all the cell phones catch fire, basically anything that uses electricity is destroyed.
This is true as far as it goes, but when you start talking about deep space warfare, certain things change. Thanks to Andrew Presby for setting me straight on this matter.
First off, the EMP I just described is High Altitude EMP (HEMP). This EMP can only be generated if there is a Terra strength magnetic field and a tenuous atmosphere present. A nuke going off in deep space will not generate HEMP. Please be aware, however, if a nuke over Iowa generates a HEMP event, the EMP will travel through the airless vacuum of space just fine and fry any spacecraft that are too close.
Secondly, EMP can also be generated in airless space by an e-Bomb, which uses chemical explosives and an armature. No magnetic field nor atmosphere required. This is called a Non-nuclear electromagnetic pulse (NNEMP). As with all EMPs, once generated they will travel through space and kill spacecraft.
Thirdly, there is System Generated EMP (SGEMP) to consider. HEMP is created when the gamma rays from the nuclear detonation produce Compton electrons in air molecules, and the electrons interact with a magnetic field to produce EMP. But with SGEMP, gamma rays penetrating the body of the spacecraft accelerated electrons, creating electromagnetic transients.
A one kiloton nuclear detonation produces 4.19e12 joules of energy. One kilometer away from the detonation point defines a sphere with a surface area of about 12,600,000 square meters (the increase in surface area with the radius of the sphere is another way of stating the Inverse Square law). Dividing reveals that at this range the energy density is approximately 300 kilojoules per square meter. Under ideal conditions this would be enough energy to vaporize 25 grams or 10 cubic centimeters of aluminum (in reality it won't be this much due to conduction and other factors).
1e8 watts per square centimeter for about a microsecond will melt part of the surface of a sheet of aluminum. 1e9 W/cm2 for a microsecond will vaporize the surface, and 1e11 W/cm2 for a microsecond will cause enough vaporization to create impulsive shock damage (i.e., the surface layer of the material is vaporized at a rate exceeding the speed of sound). The one kiloton bomb at one kilometer only does about 3.3e7 W/cm2 for a microsecond.
One megaton at one kilometer will do 3.3e10 W/cm2, enough to vaporize but not quite enough for impulsive shock. At 100 meters our one meg bomb will do 3.3e12 W/cm2, or about 33 times more energy than is required for impulsive shock. The maximum range for impulsive shock is about 570 meters.
Luke Campbell wonders if 1e11 W/cm2 is a bit high as the minimum irradiation to create impulsive shock damage. With lasers in the visible light and infrared range, 1e9 W/cm2 to 1e10 W/cm2 is enough. But he allows that matters might be different for x-rays and gamma rays due to their extra penetration.
As to the effects of impulsive damage, Luke Campbell had this to say:
Dr. John Schilling describes the visual appearance of a nuclear strike on a spacecraft.
Crew members are not as durable as spacecraft, since they are vulnerable to neutron radiation. A one megaton Enhanced-Radiation warhead (AKA "neutron bomb") will deliver a threshold fatal neutron dose to an unshielded human at 300 kilometers. There are also reports that ER warheads can transmute the structure of the spacecraft into deadly radioactive isotopes by the toxic magic of neutron activation. Details are hard to come by, but it was mentioned that a main battle tank irradiated by an ER weapon would be transmuted into isotopes that would inflict lethal radiation doses for up to 48 hours after the irradiation. So if you want to re-crew a spacecraft depopulated by a neutron bomb, better let it cool off for a week or so.
For a conventional nuclear weapon (i.e., NOT a neutron bomb), the x-ray and neutron flux is approximately:
Fx = 2.6 x 1027 * (Y/R2)
Fn = 1.8 x 1023 * (Y/R2)
- Fx = X-ray fluence (x-rays/m2)
- Fn = Neutron fluence (neutrons/m2)
- Y = weapon yield (kilotons TNT)
- R = range from ground zero (meters)
There are notes on the effects of radiation on crew and electronics here.
Back in the 1960's, rocket scientist came up with the infamous "Orion Drive." This was basically a firecracker under a tin can. Except the tin can is a spacecraft, and the firecracker is a nuclear warhead.
Anyway, they realized that about 99% of the nuclear energy of an unmodified nuclear device would be wasted. The blast is radiated isotropically, only a small amount actually hits the pusher-plate and does useful work. So they tried to figure out how to channel all the blast in the desired direction. A nuclear shaped charge.
Propulsion Shaped Charge
Remember that in the vacuum of space, most of the energy of a nuclear warhead is in the form of x-rays. The nuclear device is encased in a radiation case of x-ray opaque material (uranium) with a hole in the top. This forces the x-rays to to exit only from the hole. Whereupon they run full tilt into a large mass of beryllium oxide (channel filler).
The beryllium transforms the nuclear fury of x-rays into a nuclear fury of heat. Perched on top of the beryllium is the propellant: a thick plate of tungsten. The nuclear fury of heat turns the tungsten plate into a star-core-hot spindle-shaped-plume of ionized tungsten plasma. The x-ray opaque material and the beryllium oxide also vaporize a few microseconds later, but that's OK, their job is done.
The tungsten plasma jet hits square on the Orion drive pusher plate, said plate is designed to be large enough to catch all of the plasma. With the reference design of nuclear pulse unit, the plume is confined to a cone of about 22.5 degrees. About 85% of the nuclear device's energy is directed into the desired direction, which I think you'd agree is a vast improvement over 1%.
Weapon Shaped Charge
About this time the representatives of the military (who were funding this project) noticed that if you could make the plume a little faster and with a narrower cone, it would no longer be a propulsion system component. It would be a nuclear directed energy weapon. Thus was born Project Casaba-Howitzer.
Details are scarce since the project is still classified after all these years. Tungsten has an atomic number (Z) of 74. When the tungsten plate is vaporized, the resulting plasma jet has a relatively low velocity and diverges at a wide angle (22.5 degrees). Now, if you replace the tungsten with a material with a low Z, the plasma jet will instead have a high velocity at a narrow angle ("high velocity" meaning "a recognizable fraction of the speed of light"). The jet angle also grows narrower as the thickness of the plate is reduced. This is undesirable for a propulsion system component (because it will destroy the pusher plate), but just perfect for a weapon (because it will destroy the enemy ship).
The report below suggests that the practical minimum half angle the jet can be focused to is 5.7° (0.1 radians).
They would also be perfect as an anti-ballistic missile defence. One hit by a Casaba Howitzer and a Soviet ICBM would be instantly vaporized. Which is why project Casaba-Howitzer's name came up a few times in the 1983 Strategic Defense Initiative.
Casaba Howitzers fired from orbit at ground targets on Terra would be inefficient, which is not the same as "does no damage." A nuclear warhead fired at a ground target would do far more damage, but the Casaba Howitzer bolt is instantaneous, non-interceptable, and would still do massive damage to an aircraft carrier.
Scott Lowther has done some research into a 1960's design for an Orion-drive battleship. It was to be armed with naval gun turrets, minuteman missiles with city-killing 20 megatons warheads, and Casaba-Howitzer weapons. It appears that the Casaba-Howitzer charges would be from subkiloton to several kilotons in yield, be launched on pancake booster rockets until they were far enough from the battleship to prevent damage (several hundred yards), whereupon they would explode and skewer the hapless target with a spear of nuclear flame. The battleship would probably carry a stockpile of Casaba-Howitzer weapons in the low hundreds.
Mr. Lowther estimates that each Casaba-Howitzer round would have a yield "up to a few kilotons" and could deliver close to 50% of that energy in the spear of nuclear flame. Three kiltons is 1.256 × 1013 joules, 50% of that is 6.276 × 1012 joules per bolt.
This is thirty-five times as powerful as a GBU-43/B Massive Ordnance Air Blast bomb, the second most powerful non-nuclear weapon ever designed. Per bolt.
Get a copy of the report for more details, including a reconstruction of a Casaba-Howitzer charge.
What is the mass and volume of a Casaba-Howitzer charge? Apparently this also is still classified.
An Orion Drive nuclear pulse unit would be about 1,150 kg, have a blast yield of about 29 kilotons, and be a cylinder with a radius of 0.4 meters and a height of 0.87 meters. The volume would therefore be about 0.4 cubic meters. As previously mentioned a Casaba-Howitzer charge would have a yield ranging from sub-kiloton to a few kilotons, so presumably it would be smaller and of lower mass than a pulse unit. I just got the lastest inside scoop from Scott Lowther. He estimates each Casaba Howitzer charge is about 115 kg and 0.14 m3, with a probable yield of 5 kilotons. See details below:
Mass Schedule System Mass
Optics 9.1 Primary ACS 9.1 Secondary ACS 2.7 Communication 2.7 Warhead 90.7 TOTAL 114.3
The story is fictional, an alternate history novel. But the details about the Orion nuclear pulse drive and the casaba howitzer are meticulously researched and extrapolated where the details are classified.
Warhead has a length of 0.676 meters, infrared telescope has a length of 0.552 meters. Length when folded, about 1.23 meters. It is mostly a cylinder with a diameter of 0.387 meters, but there are four bumps near the top of the warhead that increase the diameter to 0.412 meters. I calculate the volume to be approximately 0.14 m3.
Nuclear device yield is 5 kilotons. Weapon jet velocity is 280,000 meters per second, containing a whopping 8,700 Ricks.
The first generation of operational Casaba Howtizer units was first deployed in 1972 aboard the USSF Hornet. The units were composed of four primary assemblie… the modified small Orion pulse unit, a high-thrust, short-burn solid rocket booster, a 13-inch infrared telescope and a deployable communications module. All are stored and launched as a 15.25" (0.412 m) diameter cylinder. During the short boost phase, the freon fluid-injection TVC system directs the unit towards the target and roughly aims it using internally stored data obtained from the warship at the moment of launch. After booster separation the unit deploys the sensor and communication systems. A high-thrust monopropellant thruster system aims the weapon to within half a degree of the target. The infrared scope detects the target, using reflected laser light (projected from the warship); the cold gas thruster perform final aiming. Weapons initiation is commanded from the warship after confirmation of target lock.
From author's afterword:
Discussion of Casaba-Howitzer
The Casaba-Howitzer was a real concept: a modified pulse unit that fired a jet of plasma. But instead of a jet of fairly dense plasma at a fairly wide angle, Casaba-Howitzer was to fire a lower density jet at a much tighter angle in order to serve as a weapon. Work continued well after the Orion program was terminated. And that, sadly, is about the sum total of the publicly available information on Casaba-Howitzer. Everything else about it is speculative. So, I speculated.
My first generation Casaba-Howitzer weapon is a modification of the pulse unit designed for the small 10-meter Orion. Exactly how a tight “beam” of nuclear death was to be generated, what sort of range could be expected… these are concepts about which I simply cannot speculate. But other areas sort of fall into place on their own. Was Casaba-Howitzer a weapon that would be fired from the ship, like a massive cannon? Given that the yield for a small pulse unit was a good fraction of a kiloton, trying to contain that energy in any sort of cannon-like object seems futile. So the pulse unit would be fired in free space. And likely you’d want to fire it at some distance from the ship. Therefore the pulse unit would need to be projected from the ship. This could be done via either gun or rocket; I’ve chosen rocket. In this case, a fast-burning, high-thrust booster similar to a Sprint motor, using Freon injection in the nozzle for thrust vectoring. The rocket would burn for only a second or so, tossing the projectile some considerable distance from the ship. After burnout, the projectile would unfold. I’ve given the projectile a sizable telescope with an IR scanner and a communications system. The presumption is that the weapon would be used to take out enemies at ranges of hundreds of kilometers, so it would need precise aim. If it was hundreds of yards from the ship, the only way to be sure of precise orientation with early 1970’s tech would be if the projectile could see what it was aiming at. The projectile would be aided by a laser on the warship; this would illuminate the target, making it stand out from the background, shining as a bright point in the distance. Computer aiming would be needed; even with a jet velocity of 2.8×107 cm/sec (~174 miles/sec) — slightly less than twice that of the pulse unit — it will still take several seconds to hit a target. In that time the jet will have radiated away much of its heat as well as spreading out some distance, so the target will be hit with a shotgun blast of tiny particles. A thin cloud of dust moving at one tenth of one percent the speed of light.
The weapon has three attitude control systems. The first is the thrust vector control system on the booster; this is enough to get the unit within a few degrees of the target. The second system is a hydrazine monoprop thruster system which, once the system is properly deployed, quickly gets the weapon within a fraction of a degree of the target. The third is a simple cold gas (helium) system that has very low but precise thrust, used for getting the system precisely on target. Once the weapon has locked onto the target, the command to fire is issued by the warship. The weapon is initially launched with the telescope and radio communications system folded against the front of the system, but you wouldn’t want “stuff” immediately in front of the beam, as that would disrupt the blast.
The Casaba Howitzer yield is here given as 5 kilotons, about ten times the yield of a comparable pulse unit. The pulse units were at the low end of what was feasible for repeatable nukes; dialing one up to five kilotons would only be a matter of letting the base nuke be what it wants to be, rather than intentionally throttling it.
DIRECTED THERMONUCLEAR EXPLOSIVES
Another device being investigated by both SDI architects and weapon designers is "a kind of nuclear shotgun with little pellets" named Prometheus. According to a Congressional report that was otherwise quite pessimistic about SDI, Prometheus "may have nearer-term applications for picking out warheads from decoys" (in the midcourse phase of ballistic-missile flight) than the Neutral Particle Beam (NPB), a leading contender for that role. Encouraged by experiments already conducted, SDI officials in 1987 ordered an acceleration of the Prometheus project for "concept verification," using funds from that year's $500 million supplemental SDI request.
One research engineer familiar with the project described the device as operating much like a rifle, using a polystyrene-filled barrel to help couple a plate to the "gunpowder-like" blast of a directed nuclear charge. After the impulse from the explosion generates an intense shock wave, the plate "fractionates" into millions of tiny particles. Of course, these would vaporize if in direct contact with the bomb, but as configured, the pellets have reportedly achieved speeds of 100 kilometers per second without vaporization.‡
Thermonuclear shaped charges, one of the better understood third-generation concepts§, have much in common with conventional shaped-charge explosives already used extensively in military and commercial applications. Both conventional and thermonuclear shaped charges tailor an explosive burn-wave using a detonation front that releases energy along a prescribed path. Both can produce jets of molten metal having velocities greatly in excess of the detonation velocity.*
For thermonuclear fuels such as deuterium plus tritium, the burn-wave can be directed by placing hollow bubbles or inert solids in the path of the detonation front in order to alter its velocity. Of course, ignition of a thermonuclear burn in a warhead requires a fission trigger to achieve the necessary compression and temperature (about 100 million K), but even with such a (nondirected) trigger, the overall directivity of a thermonuclear shaped charge can still be significant. †
Velocities achievable with thermonuclear shaped charges are impressive. Unlike molten jets produced by conventional shaped charges, which are limited to about 10 kilometers per second (about four times the velocities of the gases resulting from chemical explosions), thermonuclear shaped charges can in principle propel matter more than two orders of magnitude faster. Since fusion temperatures reach 100 million K, the detonation front of a thermonuclear explosive travels at speeds in excess of 1,000 kilometers per second. Using a convergent conical thermonuclear bum-wave with a suitable liner, one could theoretically create a jet traveling at 10,000 kilometers per second, or 3 percent of the speed of light.‡
Up to 5 percent of the energy of a small nuclear device reportedly can be converted into kinetic energy of a plate, presumably by employing some combination of explosive wave-shaping and "gun-barrel" design, and produce velocities of 100 kilometers per second and beam angles of 10-3 radians*. (The Chamita test of 17 August 1985, reportedly accelerated a 1-kilogram tungsten/molybdenum plate to 70 kilometers per second.† ) If one chooses to power 10 beams by a single explosion, engaging targets at a range of 2,000 kilometers with a kill energy of 40 kilojoules per pellet (one pellet per square meter), then such a device would require an 8-kiloton explosive and could tolerate random accelerations in the target, such as a maneuvering RV or satellite, of up to 0.5 g (5 m/s2).‡
The initial plate for each beam in this Casaba-like device would weigh only 32 kilograms but would have to fractionate into tiny particles to be an effective weapon—4 million evenly spaced pellets to produce one per square meter at 2,000 kilometers range. If such pellets could be created uniformly, which is highly questionable, then, at a velocity of 100 kilometers per second, they would each weigh 8 milligrams, carry 40 kilojoules of energy (the amount of energy in 10 grams of high explosive), and travel 2,000 kilometers in 20 seconds. Such hypervelocity fragments could easily punch through and vaporize a thin metal plate and could cause structural damage in large soft targets such as satellites and space-based sensors, but they would have little probability of striking a smaller RV, or even disabling it if a collision did occur.§
10-kiloton ASAT Nuclear yield 10 kilotons Number of beams 10 Mass per plate 32 kg Mechanism 50 kilojoules per pellet impact kill Assumptions 4 × 106 particles per beam
uniformly spaced 1 per m2
at 2,000 kilometers
Range 2,000 kilometers
‡ SPARTA, Inc., Workshop on Interactive Discrimination, 1986, unclassified. The velocity of 100 kilometers per second falls between the goal of 50 kilometers per second in the 1960s, only a fraction of which was achieved, and the 1,000 kilometers per second velocities possible with the plasma howitzer concept. The latter allegedly operates at 10 percent efficiency up to about 1 megaton, although with only about 10-2 radian beam directivity. Speeds of 1,000 kilometers per second are inevitably accompanied by ionization, and because charged particles curve in the earth's magnetic field, they would not be useful for long-range applications. Velocities up to 200 kilometers per second, however, are believed possible without vaporization.
§ See, for example, the detailed analysis of nuclear shaped-charges by R. Schall, "Detonation Physics," in P. Caldirola and H. Knoepfel, eds., Physics of High Energy Density, (New York: Academic Press, 1971), pp.230-244.
* Friedwardt Winterberg, The Physical Principles of Thermonuclear Explosive Devices, (New York: Fusion Energy Foundation, 1981), p.117. Conventional shaped charges have been applied to demolition, antisubmarine weapons, and advanced ordnance antitank munitions—all being further developed at Livermore—as well as for igniting the fission triggers in thermonuclear warheads. Cf. Energy & Technology Review, Lawrence Livermore National Lab, (June-July 1986), pp.I4-15.
† Devices based on this principle were pursued in the 1960s. Project Orion examined their potential for space propulsion. Casaba and "nuclear howitzer" were names for weapon applications.
‡ The detonation front shock-wave velocity is (32 kT/3M)½, where M is the average mass per ion of the thermonuclear fuel. Suitable geometries can propel matter at many times the detonation front velocity. Using cone geometry, the jet speed is v/sinθ, where v is the detonation-front velocity and θ is the cone's half-angle. A practical minimum for θ has reportedly been found to be θ ≈ 0.1. See Winterberg, Thermonuclear Physics, p.41,122
* SPARTA Workshop, 1986. This scaling presumably holds up to about 50 kilotons but, due to blackbody x-ray emission, decreases to about 1 percent for larger yields.
† Robert S. Norris, Thomas B. Cochran, and William M. Arkin, "Known U.S. Nuclear Tests July 1945 to 31 December 1987," Nuclear Weapons Databook Working Paper NWD 86-2, Natural Resources Defense Council, September 1988.
‡ The energy fluence per beam, E in J/m2, is approximately ηY/(NbR2θ2), where η is the fraction of overall yield transferred to the pellets, Y is the bomb yield (1 kiloton is equivalent to 4.2 × 1012 joules), Nb is the number of individual beams being driven by one bomb, R is the distance to the target, and θ is the individual full-beam divergence angle. A maneuvering target could accelerate out of the path of the beam if amR/vf2 > θ, where am is the magnitude of the target's average acceleration, vf is the particle velocity, and τ = R/vf is the particle fly-out time. (For comparison, the average acceleration of ICBMs is about 40 m/s2.) To deliver this energy requires a total mass per beam of Mb = 2E(Rθ)2/vf2.
§ For instance, even if an RV were coated with aluminum, a more volatile material than might be expected, the resulting vapor blow-off would only push a 350-kilogram RV off course by about 15 meters in 20 minutes of flight (about five times the amount if there were no ablation), thus failing to degrade significantly the ≈150 meter accuracy of a modern ICBM. Of course, if the collision caused the RV to tumble upon re-entry, the results would be less predictable
There are a few more crumbs of information in the report Fourth Generation Nuclear Weapons: Military effectiveness and collateral effects. They note that harnessing the x-rays from a nuclear blast is not only good for making deadly jets of atomic fire, but can also be used to pump x-ray lasers and energize EMP weapons. Not to mention accelerating projectiles to very high velocities by means of x-ray ablation, or by means of neutrons from the nuclear explosion (see report for cites on this).
So the report points out that the x-rays and neutrons can be used to drive or self-forge several projectiles or fragments (a "nuclear gun" or "nuclear grenade"). X-rays and neutrons can also be used to heat a working fluid and form hot jets (the above-described "nuclear shaped charge").
Thirdly, the forwards and backwards flux of x-rays and neutrons from a single nuclear device can be used to drive a multi-warhead weapon, e.g., a single weapon that fires a self-forging penetrator followed a few microseconds later by a jet of hot plasma. Talk about a one-two punch! The penetrator cracks the armor, allowing the hot jet to enter the target's interior and vaporize the soft chewy center.
The report also estimates, that for the use in military conflicts on the surface of the Earth, these weapons will probably be powered by nuclear devices in the 1 to 100 tons of TNT range (subkiloton range). Whether this will also hold true in the space environment is a question above my pay grade.
A propellant plate in the form of a pancake expands into a plume shaped like a cigar. And the reverse is true: a propellant plate in the form of a cigar/cylinder would expand into a plume shaped like a pancake. Specifically:
(Dplume / Lplume) = 1 / sqrt(Dplate / Lplate)
- Dplume = plume diameter (perpendicular to direction of travel)
- Lplume = plume length (in direction of travel)
- Dplate = plate diameter (perpendicular to direction of travel)
- Lplate = plate length (in direction of travel)
So if the plate had a diameter of 4 and a length of 1 (diameter to length ratio of 4/1 or 4), the plume would have a diameter to length ratio of 1/2, or a diameter of 1 and a length of 2. Equation is from Nuclear and Plasma Space Propulsion by M. Ragheb.
Kinetic Kill weapons are unguided missiles that have no warheads. Bullets and artillery shells in other words. They can be a simple as a bucket of rocks dumped in the ship's wake. Since they are basically solid lumps of matter they are much cheaper than a missile. They cannot be jammed, but by the same token they do not home in on the target. The damage they do depends upon the relative velocity between the kinetic lump and the target ship.
A sort of hybrid would be a missile which explodes into a cloud of deadly shrapnel that the enemy ship plows through, screaming.
In case it is not obvious, if the weapon projectile has no rocket engine strapped to it (as do missiles), the weapon is not recoiless. Cannons, coil guns, and rail guns all have recoil due to Newton's third law. The weapon will kick your warship like a mule every time you fire it, just like when a soldier fires a heavy calibre firearm.
In fact, the propulsion system know as a mass driver is basically a coil gun optimized as a propulsion system rather than optimzed as a weapon. This means that kinetic weapons can be used as crude propulsion systems in an emergency.
Kinetic kill weapons give you the tactical option to create terrain in the void of space in order to herd your opponent. Find the trajectories you want to deny to your opponent and fill them with cheap kinetic energy projectiles, thus forcing them to use trajectories advantageous to you.
The damage inflicted can be calculated by the equation below. The same equations will also apply when one ship rams another, of course with added damage from exploding missile magazines, unstable fuel supplies, and out of control power plants. In a ramming, you will have to calculate the equation twice, once to figure damage inflicted on the rammed ship, the second time to calculate damage inflicted on the ramming ship.
To get some idea of the amount of damage represented by a given amount of Joules, refer to the Boom Table.
Eric Rozier has an on-line calculator for kinetic kill weapons.
Please note that it is relative velocity that is important. If your ship is quote "standing still" unquote, and if the enemy is tearing past you at seven kilometers per second, and if you leisurely toss an empty beer can into the path of the enemy, the relative velocity will be 7 km/s and the beer can will do severe damage to the enemy ship (if the beer can masses 0.1 kilogram, it will do 2,450,000 Joules of damage). So even though the beer can has practically zero velocity from your standpoint, from the standpoint of the soon-to-be-noseless ship the can has the velocity of a bat out of you-know-where.
Ke = 0.5 * M * V2
- Ke = kinetic energy (Joules)
- M = mass of projectile (kg)
- V = velocity of projectile relative to target (m/s)
Wp = Ke * (1 / We)
- Wp = power required by weapon to fire one projectile (Joules)
- Ke = kinetic energy of one weapon projectile (Joules)
- We = efficiency of the weapon (0.0 = 0%, 1.0 = 100%)
Rick Robinson's First Law of Space Combat states that:
In other words there are 4,500,000 joules in one kilogram of TNT (3,0002m/s * 0.5 = 4.5e6). This means a stupid bolder traveling at 2,000 km/sec relative has about 400 kilo-Ricks of damage (i.e., each ton of rock will do the damage equivalent of 2e12 / 4.5e6 = 400 kilotons of TNT or about 20 Hiroshima bombs combined).
Ricks = (0.5 * V2) / 4.5e6
- V = velocity of projectile relative to target (m/s)
- Ricks = kilograms of TNT worth of kinetic energy per kilogram of projectile
So a projectile moving at 200 km/sec (20,000 m/s) would have about 4,000 Ricks (4 kilo-Ricks) of damage, approximately the same as a standard one-kiloton-yield nuclear weapon. By that I mean it has the same damage per kilogram as a nuke, counting all the nuke's framework, electronics, fissionable material, and whatnot. (for the projectile to do the same damage as a standard nuke, it would need to be the same mass as a standard nuke, about 250 kilograms) A projectile moving at 3,500 km/sec would have about one mega-Rick, which is the same damage per kilogram as the ultra-compact 475-kiloton-yield W-88 nuclear warhead.
As a general rule, anything with more than 100 Ricks (i.e., over 30 km/sec relative) does weapons-grade levels of damage. As an even more shaky general rule, anything with more than 4,000 Ricks (i.e., over 190 km/sec relative) does nuclear warhead levels of damage. This is based on the assumption that a nuclear weapon has about a 4,000 fold increase in energy per kg released versus TNT.
And if you are thinking in terms of bombarding your enemy with asteroids, as a general rule an asteroid's mass will be:
Ma = 1.47e4 * (Ra3)
- Ma = mass of asteroid (kg)
- Ra = radius of asteroid (m)
In AV:T are kinetic weapons called "Kirklin mines" (invented by Kirk Spencer). They are dirt cheap chemical fueled anti-missile weapons, specifically anti-Torch missile weapons. The ideas is that they cost a fraction of the price of a fantastically expensive torch missile, yet can scrag it. Using the magic of relative velocity, all they have to do is get in the way (this is why they are used against torch missiles, if the relative velocity isn't large enough the mine might not do enough damage to mission-kill the missile).
Launched at the proper time a Kirklin mine can either take out the incoming missile while it is too far away to damage the targeted ship, or force the missile to miss the ship entirely in the process of avoiding the mine (if the mine is launched too soon the missile has enough time to zig-zag around it and still kill the ship). Since they are cheaper, a given spacecraft can carry several mines for every missile their equivalent opponent ship has.
The current thinking is the only way a torch missile can avoid being neutralized by Kirklin mines is by becoming a bus carrying sub-missiles and decoys. Of course for a modest increase in cost the mines can become buses as well...
However, once the speed of the projectile surpasses about 14% the speed of light (42,000 kilometers per second), it is no longer a strict hypervelocity weapon, it has become a relativistic weapon.
A railgun is two highly charged rails. When a conducting projectile is introduced into the breech, it strikes an arc between the rails, and is accelerated down the barrel by Lorentz force. The projectile can be composed of anything, as long as the base will conduct electricity. Sometimes a non-conducting projectile is accelerated using a conducting base plate called a sabot or armature. The maximum velocity of the projectile is about six kilometers per second, which is pretty freaking fast. This would give the projectile about 3.8 Ricks worth of damage, e.g., a ten kilogram projectile would have as much striking power as thirty-eight kilograms of TNT.
And when we say "strike an arc", we don't mean "make a tiny spark like scuffing your shoes on the carpet and touching the doorknob." It is more like "incredibly powerful continuous electrical explosion." Those rails are carrying pleny of juice, and quite a bit of it is wasted.
Advantages are simple construction, disadvantage is the severe rail erosion each projectile causes, requiring frequent replacement of rails (some prototypes required replacement after each use). The rails need massive braces, since they are under tremendous force trying to repel the rails from each other.
Remember, since the projectiles are not rocket-propelled, railguns are not recoiless.
On Jul 20 2019, Amazon Prime released the trailer for season 4 of RocketCat's favorite show: The Expanse (see above).
Matter Beam (author of the indispensable Tough SF blog) and noted polymath Sevoris Doe watched the trailer and found some interesting details. The scene opens with the good ship Rocinante with its tail pointed at the destination planet in preparation for deceleration, as it should be. This is the sort of quality attention to hard-SF details currently only found in The Expanse and in a couple of movies. But I digress.
Apparently the good ship Rocinante has been equipped with a railgun. They test it on a hapless asteroid.
Sevoris spotted some hard numbers. In the first screencap the control panel displays that the railgun round is one kilogram of tungsten, and the railgun launches the little monster at 9.98 kilometers per second.
Matter Beam and Sevoris did some calculating. 1 kg at 9.98 km/sec is packing 50 megajoules of energy. Five times the energy of a 120mm tank gun or the equivalent of 12 kilograms of TNT. Blasted thing will explode into plasma upon impact. Since the hulls of most ships in The Expanse are little more than sheet metal, the round will probably punch right through the entire ship while spraying everything inside with star-core-hot plasma. Unless the round hits something substantial, like the ship's thrust-frame spine, the nuclear reactor, or the Epstein fusion drive. Then things get real exciting for the crew, assuming they are not instantly killed.
Yep, that's weapons-grade levels of damage, no doubt about it. The legendary Scott Manley points out that while 50 MJ is weapons grade, it is nowhere near enough to split an asteroid. Personally I'm willing to cut The Expanse some slack here, since they get so much else correct.
Secondly, the recoil from firing that round will nudge the Rocinante backwards with about 10 kilo-Newtons of thrust. This is roughly the equivalent of a Toyota Prius running into a brick wall at a mild 27 km/hr. The fact that the crew got a fairly good jolt may indicate that the Rocinate is a pretty low mass spacecraft.
Thirdly, according to the control panels, firing the round only drained half the capacitors ("primary" bar graph reduced by half). Since the round took 50 MJ of energy (assuming 100% efficiency), this implies that the capacitors can hold about 100 MJ.
Fourth, the firing rate of the railgun (after the first two shots drain the capacitors dry) will give us the recharge rate of the capacitors. E.g., firing rate of 1 shot/sec = recharge of 50 megawatts, 2 shots/sec = recharge of 100 megawatts, etc.
Artist Fluorescent Wolf had the thought that the Rocinante would have to do a small thruster burn to zero out the recoil from the railgun firing. A quick re-watch of the trailer showed that The Expanse's showrunner had thought of that. As you can see in the second screencap above the blue flare from the engines signified a thruster burn. Fluorescent Wolf then noted: "...I love my show."
The Strategic Defense Initiative was an anti-nuclear ballistic missile defense program announced in 1984, and finally dissolved in 1993. It was immediately dubbed "Star Wars" by the news media. It produced lots of classified images of high-tech orbital weapons, and spent lots of money, but no deployed systems. At least none that have been declassified.
Coil guns, magnetic linear accelerator, or mass drivers are a series of donut shaped electromagnetic coils (Philip Eklund calls it a "centipede gun", in the Traveler role playing game they are called "gauss guns"). Gauss rifle is technically incorrect because the weapon barrel has no rifling, but then again that is also true of a laser rifle.
A projectile composed of some ferromagnetic or conducting material (or encased in a ferromagnetic or conducting sabot) is placed just behind the first coil. The coil is energized so it attracts the projectile. When the projectile reaches the coil, the coil is turned off while the next coil in line is energized. The first coil no longer has any effect on the projectile, but the next coil attracts it. The projectile continues to accelerate. The procedure is repeated until the projectile emerges from the last coil at an incredibly high velocity.
Advantages are a much lower power consumption than an equivalent rail gun. Also the coils are not eroded with each projectile fired, unlike the severe rail erosion suffered by railguns. Disadvantages are the massive power switches required. In addition, each individual coil needs stronge bracing, as they are under tremendous force trying to expand the coil (actually for "expand" read "explode").
When these weapons are armed they will be carrying plenty of electricity. If they are damaged by enemy weapons fire, there will probably be plenty of high-voltage fireworks, at least inside of the ship. I am unsure if there will be much arcing outside of the ship unless the ship is venting gas by accident (atmosphere through a hull breach) or design (open-cycle cooling gas).
Like most projectile weapons as the guns get more powerful, the more recoil they will have (Newton's third law, of course). Indeed, they will approach being auxiliary propulsion systems. If such a gun was optimized as a propulsion system it is called a "mass driver".
Note that one can use the kinetic energy equation above to see how much power the railgun or coilgun will require for each shot. Since these weapons are nowhere near 100% efficient, you will quickly discover that these weapons are power hogs.
There are some examples of the problems with coilguns at the LS-DYNA Examples website.
To calculate parameters of your coilguns, Eric Henry has an Excel Spreadsheet. Or you can use Luke Campbell's method:
Ken Burnside notes how difficult it is to calculate the damage caused by a solid shell:
Isaac Kuo is of the opinion that hypervelocity weapons will have limited penetration. He notes that a projectile has both kinetic energy and momentum. Momentum is what keeps the projectile moving in its direction of motion.
Now, if you look at the equations for kinetic energy and momentum, you will note that as the velocity rises the kinetic energy goes up much faster than momentum (1/2 velocity squared vs just plain velocity).
Ke = 0.5 * M * V2
p = M * V
So Mr. Kuo figures that the greater your ratio of kinetic energy to momentum, the more spherical the resulting explosion and the less penetration into the interior you will get. This means hypervelocity weapons can be stopped (for a while) by a Whipple shield (until it is shot full of holes). Whipple shields are set at some distance from the hull, if the spacing is larger than the radius of the explosion, the shield takes damage but the hull does not.
I'm still looking for more details on this, especially the mathematical relationship between the ratio and the explosion sphericality.
Missiles are small drone spacecraft that chase enemy ships and attack them with their warheads. It can have its own propulsion unit, or be launched by a coilgun and just use small guidance jets. It can carry a single warhead, or be a "bus" carrying multiple warheads. Or multiple mini-missiles. Go to The Tough Guide to the Known Galaxy and read the entry "MISSILE".
One of the big advantages of missiles over directed energy weapons is that missiles do not generate huge amounts of waste heat on the firing ship. A missile can be pushed off with springs or cold gas. Once clear of the ship, the missile's propulsion system ignites. But then all the waste heat is the missile's problem, not the ships.
By the same token, the disadvantage is that missiles are expendables, unlike laser bolts (as Anthony Jackson puts it: "If you're willing to have expendables, you can also have expendable coolant."). When the missile magazine runs dry, the launcher will just make clicking noises. But a laser cannon can fire as long as it has electricity.
The second advantage of missiles over directed energy weapons is that (depending upon the warhead) most missiles are not subject to the inverse square law. Laser bolts grow weaker with distance but a nuclear warhead has the same strength no matter how far the missile travels. However, laser bolts cannot be neutralized by point defense.
The warhead is generally a nuclear weapon but others are possible. One possibility is a single-shot coilgun firing a kinetic weapon. Another type of warhead is an explosive charge coated with shrapnel, designed to deliver a cloud of kinetic kill masses into the path of the target spacecraft. A third type is the "submunition".
Of course the simplest is no warhead at all, making the structure of the missile an impromptu kinetic kill weapon. According to the first law of space combat, above about a three km/s relative velocity difference a chemical explosive warhead is superfluous. Rick Robinson says that at these speeds the only reason for conventional explosives is for the bursting charge on a shrapnel cloud.
Rick Robinson suggested that the term "torpedo" be used for a missile that has acceleration capacities comparable to a spacecraft, while the term "missile" or "torch missile" be used for those that have somewhat more acceleration than spacecraft. In GURPS: Transhuman Space they use the term "Autonomous Kill Vehicle" (AKV) instead of torpedo.
To be an effective weapon, missiles have to have acceleration abilities at least as good as the target ship. Rick Robinson says "Basically you have to make your ship drive, or something comparable to your ship drive, small enough and cheap enough for a one-shot weapon." Some drive technologies cannot be squeezed down since they have a minimum size.
Rick also notes that missiles have stupendous range. If your spacecraft can cross the solar system, so can your missiles.
Ken Burnside did the math and found that it is worse than Rick realized.
There is some convergent evolution going on here. If you take a conventional fighter aircraft and replace the pilot with remote-control gear, you have an unmanned combat aerial vehicle or combat drone. If you replace the remote-control gear with a computer AI you have an autonomous combat drone.
In the same way, if you take a space fighter and replace the pilot with remote control you will have an unmanned combat space vehicle. Replace the pilot with an AI and you have a smart missile.
Of course this raises some sticky moral questions about creating a computerized self-aware intelligence whose purpose in life is to commit suicide.