Making a lightsaber (in theory)
Ever dreamed of being a Jedi? Armed with an elegant weapon for a more civilized era, many of us have fantasized about cutting a bright green (or blue) sliver through a galaxy far, far away. Disney even has one patent in 2018 for such a device, though “Sword device with retractable, internally lit blade” doesn’t quite conjure up images of slicing through blast doors or droid armor.
That begs the question about this Star Wars Day: is it really possible to build a lightsaber, and if so, how far away from holding it in our hands and whistling ‘Duel of Fate’ are we? The answer may surprise you, but first we need to explain exactly what we mean when we say lightsaber and learn some science along the way.
So what do you need to make a lightsaber as we know it?
There are six fundamental boxes that a lightsaber must meet: it must light up and glow when in use, it must be able to cut through an object, it must be retractable, it must make a distinctive whooshing sound, you must be able to cross them in a combat, and most importantly, it must obey the rule of cool. The bad news is that not all of these are possible yet, but the good news is that they are all possible individually, at least in theory.
While we don’t have access to Kyber crystals in our galaxy, the laws of physics are more than a fine substitute. The first problem to be addressed is the light and advanced one, and for that we can use the physical principle of laminar flow. This is when all the components in a gas or liquid move in exactly the same direction without bumping into each other, a bit like when you use a shower head.
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This then allows us to use any kind of liquid fuel-oxidizer mixture to make a single, high-intensity beam of cutting power. While we may be tempted to use rocket-grade propellant and fuel, the reality is that something as simple as the liquid propane used in barbecue grills is more than enough. With these ingredients; BBQ fuel, and a laminar flow jet, the job simply becomes one of tuning the fuel mix and valves to get a retractable blade. For the iconic whoosh, it’s a matter of building a circuit with a speaker and accelerometer to make the famous sounds of a lightsaber when swung.
The finishing touch is the famous coloring of the blade. While Wien’s displacement law states that the temperature of an object is directly related to its color, this does not give us the intense color we usually associate with this aspect of the object Star Wars universe. Instead, we can influence the color by adding small amounts of specific chemical compounds to the end of the handle. We can achieve that by burning strontium metal, for example iconic Sith red or potassium chloride for the Mace Windu purple. The lightsaber’s intense glow comes from the heat of the plasma generated by the mixture of fuel and oxidizer.
This still leaves us with the question of being able to cross them in a duel, which requires resistance to temperatures high enough to melt a blast door. At present, the material with the highest melting temperature is the alloy Tantalum hafnium carbide (Ta4HfC5), which melts at a whopping 3990 °C. Unfortunately, this is the approximate temperature of burning liquid propane. When you make something retractable, you also introduce small weaknesses into a metal, making breaks and failures more likely. Therefore, even when working with ultra-heat-resistant materials, proper care is needed to prevent the material from collapsing due to stress.
This means that any plan to build a lightsaber that you can duel with should include not only a heat-resistant material, but also a robust one.
How close are we to wielding the Jedi’s weapon of choice?
There are two major stumbling blocks for us swinging around a screen-accurate lightsaber: the fuel and the duel. Assuming we still follow the principle of laminar flow mentioned above, we can achieve a steel-melting glowing jet by finding a fuel with a high density and a high combustion temperature. The former we want so we can store the fuel in a nice little rechargeable cylinder, like a battery, and the latter so we can melt through the blast doors of any Rebels.
Rocket grade acetylene or kerosene could be good candidates, with acetylene being used in plasma cutters and kerosene having put people on the moon in the Apollo program. Yet these still don’t quite fit the bill. Acetylene isn’t compact enough to be stored in a battery, and you’d need a large tank of it to power a lightsaber for any amount of time. Kerosene, on the other hand, has a relatively low flame temperature, meaning it would struggle to cut through metal.
Then comes the problem of being able to cross the blade, because you need a sturdy material that can withstand the stress of high temperatures and fight with a deadly enemy at the same time. My guess for realizing this design would be a central core of a high-melting point material, such as a tantalum-hafnium carbide alloy, that can be telescopically extended with the high-temperature flame of the propellant and fuel mixture.
The good news is that modern science is making great strides in this area. Ongoing research into high-density, high-energy fuels and stress-resistant materials means we are now closer than ever to producing a lifelike lightsaber. The only question left to ask is, what color do you want yours in?
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