On X-Wing Laser Cannons

Which are not, in fact, lasers. That they are not lasers is a point that has been made over and over by anyone claiming to study Star Wars technical systems: They travel slower than light, the beam glows (real-life lasers in a vacuum are not visible from the side), and nobody has attempted to use mirrors or shiny surfaces to simply reflect the lasers.

Starfighters from Naboo are an exception in that they are shiny, but that’s for aesthetic purposes, not defensive.

Estimates for the amount of energy that an X-Wing’s cannon can put out are around 60 GJ per shot, derived from when he strafed the Death Star in A New Hope.

For reference, I’m getting my numbers from: http://www.stardestroyer.net/tlc/Power/, which is presumably reputable (I mean, who would lie about that?). Also, its estimate for the power output of the Death Star’s main beam (lower limit 2.2×10^32) is around the same as another site gives (https://medium.com/starts-with-a-bang/the-physics-of-the-death-star-c21ccc58ade9#.8mqzyc93l, 2.24×10^32).

The second site claims that antimatter is how the Death Star does what it does. In other words, launches a 1.24 trillion ton chunk of antimatter at Alderaan, which is enough to explode a planet. This is the size of an asteroid ~4km across, which is large but not impossibly large. The Death Star is certainly large enough to store a rock this size. Most cutaways show a large “hypermatter reactor” at the center of the Death Star. Hypermatter could just as well be antimatter – a small amount of matter that stores a relatively large amount of energy.

In the modern-day U.S., antimatter production costs are quoted at around $62.5 trillion per gram of antihydrogen (citing Wikipedia), “because production is difficult, and because there is higher demand for other uses of particle accelerators.” Conceivably, either or both barriers could be broken: production could become more efficient (which it is doing), or specialized particle accelerators could be constructed (which is what would happen if the military found a practical use for antimatter). So it’s not inconceivable that a far more technologically advanced civilization would be able to produce large quantities of it from raw materials.

Another way to get it is to mine it. Antimatter occurs naturally in small amounts in our galaxy, but conceivably (I like this word) antimatter in the Star Wars universe could be relatively common: Common to the extent that oil is common on Earth today, but existing in stars or planets or dust clouds composed entirely of antimatter. Like today on Earth, with a few distant countries (Russia and OPEC) that seem to produce a significant amount of the world’s oil, there could be a few outer-rim territories that control most of the antimatter production in the galaxy. It’s been established that while the Empire controls the majority of the galaxy, it only tenuously reaches many of the outer-rim territories like Tatooine. Storm troopers only appeared on every corner after Imperial troops track the Tantive IV there. In this scenario it would be possible for the Rebellion to obtain antimatter without the Empire cutting off their supply, since they both buy it from outside agencies.

The alternative to buying antimatter at an antimatter gas station is producing it on the Death Star, perhaps using a large onboard particle reactor. However, it would need to get an equivalent amount of energy in order to make that much antimatter, and so the question is where does it get that energy?

In the case of (the poorly named) Starkiller Base, it clearly produces its own onboard antimatter using the energy it consumes from eating a star. But the Death Star is not depicted as eating stars, so we have to assume it gets its energy from somewhere else. I posit that it is refueled periodically with antimatter. It being smaller than Starkiller Base also supports that the Death Star is lacking some internal machinery that Starkiller has, like a high-throughput particle accelerator.

Containment is, of course, a big issue with antimatter. If it interacts with normal matter, there’s a violent explosion, like there was on Alderaan. So antimatter is kept in place using magnets (beam weapons in Star Wars are already theorized to interact with magnetic fields, which makes antimatter a good fit). At the center of the Death Star we have a large fuel tank, which holds potentially a hundred trillion tons of antimatter in a massive magnetically-sealed container. The mechanics behind containing (and periodically siphoning off) so much antimatter requires occasionally venting gasses to space, in the form of a thermal exhaust port. The system is necessarily delicate, because it’s the first edition of such an antimatter-containment system on anything near this scale. Thus, a pair of proton torpedoes could easily wreck the magnetic containment system, causing the Death Star to catastrophically fail, as happened in A New Hope.

And as happened again in Return of the Jedi, where the exhaust port flaw was resolved and they had to actually fly ships to the reactor, which could have been an antimatter-containment system.

So that’s my case that the Death Star uses antimatter. Now let’s get back to X-Wings, and starfighters in general.

An X-Wing laser cannon puts out 60 GJ per shot. This is equivalent to 1/3rd of a gram of antimatter, an amount that is quite easy to store and shoot. Using the same arguments as above, X-Wings probably carry a fuel tank of antimatter, possibly around 1kg (a few thousand shots worth, plus extra for the engines). However, 1kg of antimatter would release as much energy as the Tsar Bomba (which made a fireball 8km wide) if it all exploded at once, but X-Wings are destroyed all the time in relatively minuscule explosions. It’d be pretty terrible if X-Wings blew up like the Tsar Bomba. You could argue that it’d be bad for your enemies, because then when you explode you do serious damage to the enemies. But the same goes if you accidentally crash near the friendlies. In the Yavin battle sequence, the X-Wings are shown all stored in a cramped underground hanger. If some line technician screwed up the refueling sequence, the entire Rebel base would become a crater, and the Empire wouldn’t have to go destroy it.

Clearly antimatter is typically stored (in small quantities) in a relatively safe way. In the real world, a lot of things are easier to do when they’re small. It’s easier to build a small bridge than a large one. It’s presumably easier to build a small deflector shield than a large one. So for small amounts of antimatter, say around 1kg, the antimatter could be stored in a small self-powered deflector shield that can absorb vast amounts of energy without breaking, by virtue of being small. The shield could have a small break/valve in it to allow antimatter to be siphoned off. Then if a small spaceship is destroyed, the nuclear explosion is averted, because the fuel tank will survive anything that could happen to it (unless something very large happens to it, in which case everything’s destroyed anyway).

In the case of capital ships and the Death Star, the containment deflector shield would be so large, to encompass so much antimatter, that it’s not as strong anymore. Ion cannons and small ships are frequently seen to pass through Star Destroyer deflector shields, so larger shields are ostensibly vulnerable to small attacks.

One alternative would be to store the large quantities of antimatter in many small tough antimatter tanks. This would be both vastly more complicated and prohibitively costly – storing a trillion tons in 1kg bottles would require trillions of small deflector shields, which would stretch the resources of even the Empire, which has only ever procured on the order of between millions and billions. If small shields were cheap, every storm trooper and TIE fighter would have a deflector shield.

Not to mention that there’s no point to toughening the fuel tanks in capital ships: in order to breach the containment unit, one would have to breach the rest of the Death Star/Star Destroyer, which is hard anyway. That there was a convenient way to do it was a design flaw (or maybe a backdoor placed on purpose). If someone is able to breach enough of the Death Star to get to the containment unit, they clearly have the resources to destroy it anyway, and the Death Star is large enough that it doesn’t spend time near important strategic targets. If the antimatter tank goes, the Death Star’s splash zone won’t damage anything else the Empire owns that wasn’t destroyed in the attack anyway.

Same rationale goes for capital ships. If somebody has the resources to carve up a Star Destroyer to the containment unit at the center, it doesn’t matter if they breach it – the Star Destroyer is far away from other Imperial ships, and if the containment unit is lost then the ship is lost anyway.

This contrasts with smaller ships, like X-Wings and TIE fighters. These are both easy to destroy, and are commonly in close formation with other ships/sitting in hangers where a large explosion would be problematic.

On the exhaust port being a purposeful backdoor – it’s generally considered that the second Death Star was largely built after the first was destroyed, and the exhaust port was fixed. Either the technology improved to the point where they didn’t need the port anymore the second time around, or they didn’t need it either time. The first point seems unlikely. The first Death Star was the one where all of the technology was developed – for the second one the Emperor probably went to Amazon and clicked “re-order,” it was built so fast there was clearly no major re-engineering. My guess is that a lot of the parts were made in parallel, but the second one was simply assembled later. Regardless, a lack of good design review and constantly changing specifications means that a designer would have been able to slip something in without the flaw being caught:

Saboteur: “Hey Bob, I can’t find your boss, but we need to add an exhaust port running from the core to the surface.”

Hapless worker: “But won’t that create a giant security hole that the Rebellion could manipulate?”

Saboteur: “No, I thought about that, but I talked to some guys and I think it’ll be fine.”

Hapless worker: “Okay, sure thing, I’ll add it to the design.”

10 years later:

Death Star: “Kaboom”

Hapless worker: “Wow, I have a lot of accrued vacation time, I think I’ll go spend it on Tatooine.”

Hapless worker’s boss: <choking noises>

Darth Vader: “You have failed me for the last time.”

That’s how I think that’d go.

Anyway, here are the antimatter masses for a few other things:

Anti-personnel blaster: 2 MJ is an inconsequential amount of matter (order of micrograms).

Large cannons on a Star Destroyer: lower-limit 6,000 TJ is just over 33 grams of antimatter, 20,000 TJ is around 110 grams, a veritable slug.

Another point that supports antimatter is that beam weapons are seemingly range-limited on planets. Most handheld blasters are rated for only a few hundred meters before the beam dissipates. During the Battle of Hoth, AT-AT walkers had to close the distance to the shield generators before they could destroy them. An antimatter bolt would interact with a planet’s atmosphere, but an appropriately shaped bolt could be shaped so that it ablates slowly as it goes through the atmosphere, or it could be wrapped in a small ferrous sheath (think cheap magnetic containment field).

On the subject of appropriately-shaped bolts, some bolts are seen in the trilogy to behave like flak, where they explode at a fixed range. An antimatter bolt could be shaped to break apart after some time ablating, thus exposing more area and exploding against the atmosphere. This only explains how that works in planetary atmospheres, but the other place where fixed-duration bolts are seen are in an asteroid field (correct me if I missed a scene), where cosmic dust is abundant and bolts could ablate against that.

Another related topic is, why the S-foils? Why do X-Wing’s wings famously split in two to form an X? Spacecraft with cannons have done this for as long as time itself (at least since the Actis-class intercept and the ARC-170 starfighter). One source I read said that this has to do with giving the X-Wing’s guns a bigger spread, which is possible, except that neither the ARC-170 nor the Actis put guns on the tips of the wings that spread out. It could be Incom’s signature move, except that it isn’t (they didn’t produce the Actis). It’s not decorative, presumably, because the Actis’ fins block a substantial portion of the pilot’s view, so it’s not just a hood ornament. In every case the fins are stowed during normal flight but deployed during battle, so they aren’t some sort of foldable solar panel.

Consider the above system I described, where cannons shoot antimatter. It’s difficult to carefully siphon antimatter out of a fuel cell, assemble the anti-plasma in a specific shape, and fire it at high velocity out of the nozzle. All of this trickery causes heat to be generated, and in space heat is the worst. There’s no way to get rid of it. In an atmosphere we can use things like heat sinks and fans to wick heat into the atmosphere, but in space we don’t have these things. Our only hope is radiative heat transfer – we have to radiate any excess heat.

However, the armor covering the exterior of the ship, while metal, is thermally isolated from the mechanics by virtue of being physically isolated (if the armor is hit, you don’t want the guts of the ship to be damaged by the shock). So these interceptor ships, in order to sustain a high rate of fire, expose special radiator panels to radiate excess heat from the laser cannons. But, you ask, these radiator panels are on the inside of the S-foils, so they point at each other, and thus radiate heat at each other. Yes, I say, but that’s engineering tradeoffs for you. They also have to be protected, so they aren’t as efficient as they could be. They do radiate some heat.

But, you say, Naboo’s fighters, A-Wings, Y-Wings, and TIE fighters don’t have folding wings. Well, yes, but those ships don’t need them. Naboo’s fighters were largely a decorative army – they were commissioned and built in a time of peace, and spent their time flying in parades and escorting officials. They have no need to fire lasers continuously. A-Wings are analogous to torpedo boats. Yes, they have laser cannons, but more importantly they carry up to twelve concussion missiles, more than any other Rebellion spaceship. They fly in quickly, fire missiles, then leave. No need for continuous laser fire. Same with Y-Wings – they’re the bombers of the Rebellion, their weapons are missiles and the ion cannon. For all of these fighters, they can shoot a certain number of laser bolts continuously (on the order of dozens?) before the equipment has to cool off. This isn’t normally a problem, because pilots fire in short bursts, so the cannons have time to cool off. In the case of the X-Wing, however, continuous fire is an important feature: It allows the pilot to lay down consistent fire on fixed targets, on the ground or on capital ships, where the other fighters wouldn’t be able to maintain such continuous fire and cause so much havoc (reference: Luke’s strafing run on the Death Star).

In a planet’s atmosphere, the radiative panels are even more effective, because now the heat is wicked directly into the atmosphere. A sufficiently quick-moving X-Wing pilot on a cold day (or a warm day on Hoth) should be able to hold down the trigger indefinitely without the cannon overheating.

TIE fighters are built with the same radiative panels as X-Wings are, but they don’t fold – they’re the giant fins on each side. A folding mechanism would be useless, since it would be prohibitively expensive and TIE fighters don’t travel. They’re deployed at the scene of battle, and are picked up at the scene of battle. There’s no need to fold for landing or protection from micrometeorites during travel. At any rate, they’re cheap enough that the Empire can just replace them if/when the fins wear out.

The radiative panels on TIE fighters are so large that I theorize (I don’t have access to Imperial design documents, so I don’t know for certain) that they can maintain continuous fire in space forever, surpassing even the X-Wing’s continuous fire capabilities.

Another note is lasers come in different colors, namely red and green (which is appropriate, with Christmas around the corner). Traditionally, Rebellion ships have fired red beams and Imperial ships have fired green beams. The Imperial color comes from the colors that the Republic used before it became the Empire (spoiler alert if you’ve been living under a rock for 10 years), and presumably the Rebellion’s colors come from leftover Trade Federation technology that they scavenged (maybe we’ll find out in Rogue One). Hand-held blasters are red for both sides, though.

With antimatter, one could pick a color based on what type of antimatter you have. If you have antineon, you get red, but if you have anticopper you get green, as the antimatter travels through and reacts with the medium. Different materials could give off different colors of light. This would explain why there are no orange laser bolts or yellow laser bolts: those types of antimatter are not produced like the red and green antimatters. Perhaps these two colors come from two distinct anti-mines, one which produces red antimatter and sells primarily to civilians and the Rebellion, and one which the Empire controls and produces green antimatter.

This doesn’t explain why they have colors in space, but there could be some sort of slow-burn tracer system going on.

The bolts clearly have mass. In many scenes, turbolasers are shown to have recoil effects. Launching antimatter would cause some recoil, but not as much as is typically depicted. It has been hypothesized that this is to prevent flashback damage, which while this idea is refuted on The Turbolaser Commentaries, makes a lot of sense with antimatter. Large artillery emplacements are expensive, and difficult to maintain (because you have to wear spacesuits to replace barrels). When the antimatter leaves the magnetic containment of the barrel accelerator, particles near the edge of the bolt are liable to spread once they leave the barrel. Retracting the barrel as the bolt fires may help reduce damage to the barrel (it’s cheaper to build a recoil mechanism on a system where weight doesn’t matter than it is to replace the barrels all the time).

The Turbolaser Commentaries also makes a lot of noise about “damage before contact”: That is, bolts occasionally appear to cause damage in the asteroid-shooting scene before they actually make contact with the asteroid. I chalk this up to special-effects (purposeful or accidental): It presumably looks better that way, or it was hard to synchronize the laser film and the asteroid film, or something, and the differences are usually only on the order of a frame or two – it’s also entirely conceivable that burst shots were fired, but the first one incinerated an asteroid before the camera could capture it. Also they mention pulses in beams, but this appears to be an optical illusion in the images they cite. This is how conspiracies are made.

They do mention the shape of the bolt, though, which is somewhat like a comet’s tail. This makes sense with antimatter as well, as the head of the bolt is the antimatter and the tail is made up of particles that are sloughed off of the main bullet.

One significant problem with the antimatter theory is that bolts don’t appear to be affected by gravity, as much as one would expect. For this I have no good explanation for antimatter, I’m sorry. The antimatter theory works so very well on every other point, even explaining away spaceship systems (S-foils) in ways that I haven’t seen any convincing explanations for. (The explanation that they radiate engine heat doesn’t explain why some ships need the radiative panels but not others. Wouldn’t all combat ships need that? Why don’t A-Wings, which are small, fast, and maneuverable, need radiating panels?)

We can hand-wave away gravity because neon gas floats, so if a red (neon) bolt were suspended in midair we might expect it to rise. If we move a red bolt through the air horizontally, we might expect it to at least not drop as much as a normal bullet would. This would explain why, while Imperial starships shoot green bolts, Imperial stormtroopers shoot red bolts – because they aren’t subject to gravity like the green (copper?) bolts are. That can at least hand-wave away the gravity problem, but I’m not certain it’s a perfect solution.

Another question, that’s more relevant to my current interests at hand, is how is all of this presented to a spacecraft pilot? The movies don’t give us much detail about this, beyond “trigger is shoot,” but the game X-Wing vs. TIE Fighter (which is not canon) does.

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In XWVT, each system (laser, ion, shield) has a current charge. For laser and ion cannons, these are shown above the targeting computer in the screenshot above. For shields they’re the dim red indicator around the ship icon to the left of the targeting computer (the shields are mostly down in this image). As systems get used, they lose charge, but they can be charged gradually by configuring the blue, red, and green slides to the right of the targeting screen.

I won’t talk about how the deflector shields work, but this system makes sense for antimatter laser cannons. The central fuel tank is centrally located, so it’s difficult to move antimatter from the tank to the laser cannons on short enough notice to shoot effectively. The latency is high, because the pipes are long, but the throughput is built to be fast enough to sustain fire once the pipes start flowing. So small shielded caches are built on each wingtip, which are long enough to sustain the cannon for the dozen or so shots before the antimatter starts flowing from the main tank.

The bottleneck in throughput is extracting the antimatter from the central tank. By virtue of being heavily shielded, the opening is as small as is required to support the ship. If the pilot is pointing the full firehose from the central tank to the laser cannons, there is necessarily less antimatter available for the engines and the shields. So the pilot has to choose where to commit the ship’s antimatter. The engines and the shields may also have their own builtin antimatter caches, depending on how they’re designed. If the pilot decides to send all of the antimatter to the engines, then the lasers will still have some antimatter, so the pilot can still fire the shots left in the cannons.

Anyway, that’s how I think Star Wars cannons work. Maybe we’ll learn some more when Rogue One comes out tomorrow, Friday, December 16th. Except that theaters are showing it today, so maybe it’s a typo and they meant to say it comes out today, Thursday, December 15th? I’ve never understood how movies are released.

 

 

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