We've already established that war in space will encompass vast distances never before encountered by any military force. Spacegoing warships will have to hunt for each other across vast expanses of nothingness and be forced to engage the enemy at distances of many thousands or even millions of kilometers. But what kind of weapons can travel, much less hit and do damage to a target, from such immense ranges?
The oldest space technology may well prove to be the most effective space weapons. Essentially small spaceships in and of themselves, these advanced rockets would swarm across the void to attack an enemy ship en masse.
Missiles have a definitive advantage over beam weapons, in that they can track and home in on an enemy vessel no matter how the other ship maneuvers. Most beam weapons lose effectiveness and accuracy with range; a missile's warhead can get in close to a ship and have a far greater potential for hitting and doing damage.
Missiles also need not be launched directly from the main ship. They can be "dropped off" into space while the main vessel maneuvers away, so that when their engines are ignited they will not give away the position of the ship.
The type of missile warhead most effective for space combat is still open to debate. Because of the vast scale involved, the presumed "slipperiness" of an enemy ship maneuvering at high velocity in three-dimensional space, and other defensive measures the foe can take, direct-impact weapons are not a very practical consideration. The missile should instead carry a warhead that can damage the enemy from a moderate distance, which in space can range from several dozen to several hundred kilometers.
One obvious candidate is a nuclear warhead, the more powerful the better, to propel thousands of high-density, high-speed shrapnel fragments from a specially designed casing. Assuming at least a 1-megaton blast, the nuke's heat and radiation flash, electromagnetic pulse, and hypervelocity projectiles could prove a very deadly combination for any spaceship even dozens of kilometers away. Far more powerful warheads with much larger danger zones may be desirable, and research has shown that it is possible to tamp nukes to direct over half of the bomb's energy in the enemy's general direction.
It should be noted that one thing a nuke in space will not produce is a significantly powerful shockwave. Shockwaves on the surface of Earth are propagated by the atmosphere; in space the only shockwave felt would be that produced by the vaporized bomb casing, and at typical space-engagement distances its impact on a ship would be negligible. However, without the atmosphere to absorb all that excess energy, both the heat and radiation flash of the bomb would prove much more lethal at much greater distances.
Another possibility is to use a nuclear detonation to propagate one or more powerful X-ray lasers at a target. This technique was researched extensively as part of the Reagan administration's Strategic Defense Initiative in the 1980s, and though it proved unworkable with contemporaneous technology, the theory is still sound and could lead to practical weaponry in the future. Unlike shrapnel-propelling warheads, nuclearly propagated X-ray lasers would be able to deliver far more of the warhead's energy to the target. Depending on how powerful the originating blast is, they could also be effective from much farther away, perhaps up to several thousand kilometers distant.
Explosions using matter/antimatter annihilation should also be considered. This is the base technology behind Star Trek's famed photon torpedoes. Matter/antimatter explosions can deliver far more potent detonations per gram of reaction mass than any conventional or nuclear explosive. Nuclear explosions release less than five percent of the energy potential in matter; antimatter annihilations release one hundred percent.
Of course, given the presumed velocity differences of the missile and its target, an explosive warhead may be superfluous. A missile may be assumed to be able to overtake its target with sheer velocity, as vessels with human crews would be limited to accelerations humans could tolerate, whereas missiles would have no such limitations. Once close enough the missile could use a conventional explosion to break itself apart and hit the enemy ship with a spray of hypervelocity shrapnel much like an enormous shotgun blast. At typical relative space velocities of dozens of miles per second or greater, that would be more than enough to shred most hull materials.
Highly advanced civilizations may also use missiles to deliver payloads of nanotech weaponry, particularly self-replicating microbe-sized robots called nanites that could disassemble enemy ships molecule by molecule. In Charles Stross's novel Singularity Sky, advanced AI missiles launch billions of such nanites at enemy ships in a wide-angled spray, each nanite protected from the extreme velocity and impact by a sheath of artificial diamond a molecule thick.
In space combat, the main difference between a missile and a drone is that missiles are expendable, while drones are meant to be recovered and reused if they survive a battle. General-purpose combat drones would basically be miniature automated battleships in their own right.
Drones have an obvious advantage in stealth-dependent combat such as space warfare. Prior to attacking a target, a ship may drop off one or more drones that can approach a suspected target from different angles, allowing a ship to initiate an attack remotely without giving away its position. Drones can also be used as supplementary scanners, sweeping a suspected area at angles the main ship can't cover by itself. And if the ship needs to engage active sensors, it might be far safer to have a remote drone do so.
Missiles, lasers, and particle accelerators would probably be the preferred offensive weapons for a drone for much the same reason they're preferable for a main warship. However, drones could also be used to employ moderate-ranged weapons such as plasma guns and electromagnetic launchers against an enemy ship without having to risk the main ship getting in close to the target.
A laser's main advantage as an offensive weapon in space is its speed—moving at the velocity of light, it can reach a target much faster than any other weapon. But lasers also have a major problem that's rarely addressed in space operas: beam focusing. Though they are more tightly focused than any conventional beam of light, lasers suffer from the same phenomenon of beam spreading as any flashlight, only elongated over much larger distances.
How far a beam can travel before it spreads too far to be effective depends on its focusing diameter. The larger the focusing element, the easier it will be to concentrate a large amount of the laser's energy at a target from longer distances. Think of differently sized magnifying glasses used to burn materials under a hot sun; the smaller magnifying glasses must be brought much closer to the surface to be burned than the larger ones, because the larger ones have a longer focal length.
An advanced laser with a beam diameter of a few centimeters will have a maximum effective range of a few kilometers. Lasers with beam diameters measured in meters (such as those researched for SDI applications) will have effective ranges of hundreds of kilometers. In order to reach a distance of, say, ten thousand kilometers—"close" range for typical space combat—the aperture on a visible-light laser would have to measure thousands of meters across. This would preclude their use as offensive weapons by any but the most immense ships.
One way around the focusing aperture limitation is to employ very-high-frequency lasers, such as X-ray and gamma-ray lasers, which would require much smaller focusing elements. These present other problems, such as much larger power requirements and finding materials that can not only handle precision focusing of such ultra-high frequency light, but that can also withstand the intense energies flowing through them.
Regardless of frequency, offensive deep-space lasers will prove to be enormous. One can imagine these huge laser systems being integrated exclusively as spinal-mount weapons. Spinal-mount weapons are a type of armament that runs the entire length of a ship; the rest of the vessel is literally built around the weapon system. The best known example in science fiction is probably the Yamato and its "wave motion gun" from Space Battleship Yamato (a.k.a. Star Blazers in the U.S.). In this case, however, the diameter of the beam-focusing elements would probably exceed the length of the rest of the weapon system, resulting in large disk-shaped ships. Think of vessels resembling large spacegoing spotlights and you'll have an idea of what a ship with a spinal-mount laser weapon might look like.
Another way to extend the focusing range of a laser is to use a very special type of submunition—a drone or missile that can deploy a large focusing mirror. The drone would position itself between the ship and its target at an oblique angle, then deploy a quick-assembling mirror. The originating ship would then aim its laser at the mirror, which reflects incoming laser energy, refocusing it at the target. To keep an enemy from using this system in reverse, the mirror can be made monochromatic to reflect just the one specific frequency of light employed by its makers. Given the extreme fluidity of space combat, chances are these reflecting mirrors could only be used once or twice before the target maneuvered out of the mirror's effective focusing range.
Lasers would also have a secondary offensive use of being able to blind an enemy's visual sensors, even at very long ranges where they can no longer be used to inflict physical damage.
Particle accelerators are sophisticated scientific instruments designed to plumb the depths of the quantum world; however, it has long been theorized that they could be used for offensive capabilities. Particle accelerators do not have to be ring-shaped, as they are in laboratories. They can be made linear and open at one end, allowing the particles to be accelerated to near-light speed along their length, then shot out the open aperture. This is the basis for particle-beam weaponry found in a great many science fiction sources, including the phasers from Star Trek and the disintegrators from Forbidden Planet.
As with lasers, their main advantage in a space battle is speed—particle beams typically would travel just below the velocity of light.
Particle beams come in two broad varieties: charged and neutral. Charged particle beams work well for operations within an atmosphere where the charged particles moving in a single direction will create a loose current through the air, generating a magnetic field which "pinches" the beam together. Lightning, which is composed of electrons, works on loosely the same principle. But in space this represents a very serious problem, as without this air-circuit effect to hold them together, the like-charged particles will repel each other, so the beam quickly flies apart.
In space, neutral particle beams would be necessary to reach beyond a few kilometers. It's much easier to accelerate charged particles via magnetic and electrical fields rather than neutral particles, which suggests the need for a charged-particle accelerator with a "neutralizer" on its open end. This might take the form of a screen, a layer of gas, or an intersecting electron beam to render the charged particles neutral.
Because they are essentially firing physical objects, albeit very, very tiny ones, particle beams do not quite have the same problem of beam spreading that lasers do. Ranges of hundreds of thousands of kilometers are achievable with foreseeably advanced technology. Particle velocity is a much more substantial factor for delivering damage to a target. The closer to lightspeed the weapon can push the particles in the beam, the more energy they will have and the more damage they will cause upon striking the target. For a particle accelerator, this means a longer barrel length for increased electromagnetic acceleration, with spinal-mount weapons being a natural outgrowth of such a progression. Whereas spinal-mount laser weapon ships would resemble huge, wide spotlights, a spinal-mount particle accelerator ship would be long and thin, resembling an enormous rifle barrel.
A specialized type of particle beam first postulated in the Traveller RPG universe is the meson gun. Pi-neutral mesons (created by the collision of an electron and a positron) are subatomic particles that pass through normal matter with very little interaction, similar to neutrinos. However, they also have a very short life, decaying with a burst of gamma rays, which react strongly with material substances. A meson gun accelerates pi-neutral meson particles to near-light speeds, where time dilation slows their rate of decay. If done with precision, the mesons can be timed to decay at a predetermined spot and, if packed densely enough in the beam, they can unleash a tremendous amount of energy upon decay, approaching the level of a nuclear bomb.
Meson guns are a very sophisticated technology, as they must accelerate the pi-neutral mesons to within the right tiny window of near-lightspeed to delay their decay until they are passing near or through the desired target. They do have the unique property of being able to be fired through physical objects without harming or even interacting with them in any way—that is, until they decay. They can easily bypass defenses such as sandcaster clouds (explained below), magnetic fields, and armor. In fact, a ship equipped with a sufficiently powerful meson gun could theoretically fire right through a planet to hit a target on the other side.
With missiles, drones, and shrapnel from explosions being such a major factor in most space battles, the need to intercept and destroy these potential threats before they reach the ship becomes paramount. This is a part of space combat the Star Wars film series, which I may have disparaged a bit unfairly in Part One of this article, did get right—the need for large arrays of medium- and short-range weapons to deflect incoming threats.
However, even "close" range in space combat—the minimal distance for missiles to detonate with a decent chance that their shrapnel will hit the target—can be measured in dozens of kilometers, meaning that the target will still be well beyond visual range. Add to this the fact that the targets will be moving at relative speeds of at least dozens of miles per second, and one can see how useless human-controlled gunnery like that on the Millennium Falcon would be. Almost all defensive gunnery would have to be handled by a computer, which could track and target much faster and much more effectively than any flesh-and-blood gunner. Specialized officers may still be needed to oversee the system as a whole in order to make broad tactical decisions.
At medium ranges, defensive tactics would use targeted weapons as much as possible, to take out incoming missiles and drones. Close in, tactics would change to be dominated by dispersed particle throwers, beams, and fields to throw off incoming shrapnel from detonated warheads or weaken beam weapons.
Close-in defensive tactics would be aimed much more at deflecting rather than destroying outright any incoming shrapnel. As any boxer or martial artist can tell you, deflecting an incoming punch away from you takes far less effort than stopping it dead; the same principle applies in deep space. Because of the distances involved and the speed the ship is travelling, even a tiny change in the direction or velocity of incoming shrapnel will likely prevent a hit altogether.
Defensive missiles are an already known if underdeveloped technology, the most famous being the Patriot antimissile system used during Gulf War I. A defensive missile would scream into the void, max out its velocity in relation to its target, then explode, meeting the incoming threat with a high-velocity, rapidly expanding shower of shrapnel.
Nuclear weapons, even small ones, would likely not be used in defensive missiles, not because of the potential damage to the ship (typical distances to target and tamped detonations would prevent that) but because nearby nuclear explosions would temporarily blind sensors.
Defensive drones would most likely be decoys, deployed alongside and copying the sensor signature of the main ship to draw fire at critical moments. At the technological level required for routine deep-space travel, an AI missile would easily be able to distinguish between a real ship and a "dumb" decoy like a flare. A defensive drone would not only have to mimic the main ship's electromagnetic signature but also be able to maneuver and put up at least some defensive fire to mimic a real ship.
Lasers truly come into their own when used defensively. Like in Star Wars, ships may have large batteries of laser turrets. Remember that realistic combat lasers won't be the pencil-thin beams of science fiction. Beams up to several meters wide, like large spotlights, could quickly pan across broad swaths of the sky, using their energies not only to target incoming bogeys but also to deflect much closer dangerous shrapnel.
Relatively low-powered lasers can also be used to ionize threatening debris, allowing it to be more readily deflected by a defensive magnetic field (see below).
Scaled-down, turreted particle beams can be used as defensive weapons to target incoming missiles and drones. However, unlike lasers, their use very close in is dubious, as they require more power than lasers to accomplish the same tasks at a close range.
Plasma weapons can be devastating short-range weapons, with effective ranges of several hundred kilometers in the larger guns.
Take a volume of hydrogen, superheat it to a plasma state in a magnetic bottle, then collapse the containing field rapidly so the plasma is compressed into a high-pressure jet that's expelled from the weapon at high velocity. The energy weapons in the Star Wars movies, despite various descriptions down through the years as lasers and particle beams and "photonic bursts," most closely resemble plasma guns in look and effect.
At effective ranges, plasma weapons can deliver both thermal damage measured in tens of thousands of degrees as well as kinetic-energy damage as the high-velocity plasma impacts the enemy's hull.
These weapons do have drawbacks, however. Plasma is very energetic and chaotic, and despite leaving the weapon as a tight stream, it spreads out quickly and flies apart. There's also the problem of entropic heat loss of the plasma stream as it moves through hundreds of miles of vacuum.
To offset these problems and maximize its potential range, the velocity of the plasma as it leaves the weapon is crucial. The higher a plasma bolt's speed, the farther it can travel before the chaotic dynamics of the plasma make it ineffective. Both ultra-high pressures used to collapse the plasma as well as an array of accelerating electromagnets along the barrel can maximize a plasma bolt's velocity and potential damage.
Electromagnetic launchers (EMLs) accelerate a projectile using magnetic field generators arrayed along the length of a barrel. The two most popular schemes involve either using a powerful current running along two charged rails with a projectile between them, or a series of coil magnets to propel a suspended bullet. In real-world tests, the railgun configuration has proven problematic, as the rails tend to deform after only a few shots, and the coil-gun configuration, while much more dependable, is harder to engineer. Today, research is continuing on both types of weapons.
As they have very little friction, EMLs are capable of launching many small projectiles at very high speeds in rapid succession. EMLs can cover large areas with disabling shrapnel in only a few seconds in order to take out incoming missiles and drones.
Large EMLs can also double as missile launchers, to give missiles an extra boost of velocity leaving the ship.
Unfortunately, though effective against short-range targets, EML projectiles would lack a missile's maneuverability and would be far too slow to be effective as long-range weapons.
These defensive weapons have had numerous incarnations in many different sources, but the principle is basically the same. Sandcasters throw out large clouds of some kind of particulate around the ship. Actual sand has been quoted because of its assumed plenitude and cheapness, but tiny ball bearings, water droplets, and dust have also been mentioned as possible materials. Because of the huge relative velocity differences in space combat, even small grains of sand would impact incoming threats like high-powered bullets.
Sandcaster magazines would basically be large canisters filled with particulate, whose contents are shot out into space and immediately dispersed in an outward-bound cloud. As these are relatively low-velocity, low-range weapons, sandcasters are usually the defensive measure of last resort, a Hail-Mary cloud of particles used to stop or deflect incoming shrapnel. They're also of some use against beam weapons as they create an obscuring cloud that can weaken or perhaps even deflect an incoming beam. A sandcaster's cloud of expanding particles can also help obscure a ship's sensor signature, helping to prevent precise target locks.
Some sources have also suggested making the "sand" magnetically charged and using a small drone subunit with a powerful magnetic field to shape the sand into different configurations for different purposes. If trying to deflect incoming shrapnel, for instance, particulate matter arranged into expanding layers would be more effective than just a random cloud. Also, if one can anticipate having to defend against laser weapons, the particles in the cloud could be made light-reflective.
Powerful magnetic fields were the original concept behind the term "force field," i.e., a field of electromagnetic force. Basically, the ship generates a very powerful field around itself, which helps to deflect incoming objects and beam weapons. The simplest way of doing this would be with large amounts of superconductive wire arrayed in a grid around the outer hull.
Unfortunately, in order to be effective, such a field would have to be many, many times the strength of Earth's magnetic field, so much so that exposing humans to it would be fatal. The ship would need heavy shielding, not so much for combat but to protect its human operators from the effects of its own defensive field.
Electrostatic Defense Field
A defense originally conceived for armored ground vehicles, a scaled-up version could also help a spaceship defeat incoming physical threats. Large capacitors on board would build up and store a tremendous amount of electrical charge, which can be routed to conductive grids on the outer hull of the spacecraft. The ship projects a weak electromagnetic field around itself. Any physical object entering this field would become instantly charged, allowing an open circuit to form with the ship's capacitors. From an observer's perspective, it would look very much as if a bolt of lightning lanced outward from the ship to incinerate the incoming threat.
The system would be set up so that it would activate automatically to intercept anything of significant size entering the triggering field. Even though in typical space combat the ship would be expected to be hit by hypervelocity shrapnel as opposed to large projectiles, given the enormous scale of the battlefield, even a ship a kilometer across would typically not encounter more than a handful of shrapnel fragments from any one explosion. (That's right—all those sandcasters and defensive missiles and whatnot would be trying to stop a handful of fragments at most—but remember, even one impact at those velocities could severely damage the entire ship.) A ship would typically carry multiple high-power capacitors to handle multiple incoming threats, each being activated in quick succession as needed.
As we've seen in both parts of this article, battles in deep space will be like nothing we've yet seen on screen. They will, in fact, be far more terrifying. Imagine crews huddling around sensor readouts and poring over computer analyses for days, trying to find that near-inconsequential anomaly that could indicate an enemy ship. Their deaths may have already been launched days ago, streaking through the void to detonate at any second. To kill their mighty warship and end their lives with a single hypervelocity missile fragment that may be no larger than a penny.
On such small things, the fate of freedoms, peoples, worlds, and even entire civilizations may rest in the future.
Perhaps the coming centuries of space travel will be ones of peaceful exploration and settlement. But really, given human nature, how likely is that? The real question is not if war in space is inevitable, but only who will reap its terrible consequences.
Fire, Fusion, & Steel: Technical Architecture (Traveller: The New Era) by Frank Chadwick and Dave Nilsen
On the Web
Nuclear Weapon Effects In Space [nasa.gov]
Space Weapons Earth Wars, by Bob Preston, Dana J. Johnson, Sean Edwards, Michael Miller, Calvin Shipbaugh
Meson Gun [Traveller RPG]
Introducing the Particle-Beam Weapon, by Dr. Richard M. Roberds
Magnetic shielding for spacecraft, by Nancy Atkinson