Space battles are an exciting part of SciFi stories. Canons are the staple of any military platform. For cannons, most stories use energy weapons, but some use projectiles. In this post, I’ll talk about the practicality of projectiles in space.
Lasers
Laser weapons are still not practical for our military. There are news stories about new lasers being mounted on aircraft and ships, but they are still in their infancy. Lasers suffer from two major problems: Power and scattering. To create a laser beam powerful enough to do damage, the military platform must have a power source that is large. That works if you’re mounting a laser on a nuclear-powered aircraft carrier. The ship can be designed to have a larger nuclear power plant that can provide the necessary energy for the beam. One downside is that if war breaks out, lasers will drain the power plant faster and a nuclear plant cannot be reloaded while at sea.
Jets can carry lasers, but a power plant would need to be light and compact to power a laser. Maybe some of the energy from the jet engines can be siphoned off to power the lasers. This will certainly drain the aircraft fuel supply much quicker if used. Fortunately, for aircraft, in-flight refueling is a normal process. Energy weapons could be considered positive for such a situation because guns and missiles can only be reloaded after the aircraft lands.
One reason lasers are probably never going to replace guns on ships and aircraft is that the beam will scatter or be absorbed by dust and moisture in the atmosphere. Cannons can fire in foggy weather and be directed by radar. This problem will be reduced by a laser fired in space.
Shells
Shells are still the standard munition for ship-borne artillery. They are usually cheap and can be large. In space, the same will be true. Large guns can be mounted on a platform that can fire shells. Shells will work similarly to how they work on Earth, except there are some differences.
First, all shells fired on Earth follow a parabolic arc. This goes out the window when a shell is fired in various directions in space. Gravity will affect the trajectory of the shell and the further the shell travels, the more it will deviate from a straight-line course.
Second, all shells fired on Earth land. In space, a shell could be on a course that will take it on a journey forever. It might get caught in a gravity well of a planet or star and plunge to its death, or it could just travel for millions of years. Sometime in the distant future, that shell could be a hazard for a ship passing through space. Unlikely, since the size of a shell is small and space is so vast, but I could imagine a volley of free-flying shells fired close to Earth that might obtain an orbit and become a hazard for satellites.
Shells fired on Earth are usually fired with a casing that contains gunpowder. Some shells are self-contained units and use a brass casing. When a ship fires the shell, the brass is ejected onto the deck of the ship. In a war situation, those casings can be kicked over the side. During peacetime, they are usually collected and sent back to be recycled. Watch the 5″ U.S. Navy guns fire (notice the shell casings kicked out after it fires a shot):
The three-inch guns are liquid-cooled (the ones with a domed cover). You can see water streaming out of the barrel. That’s because they can fire at a more rapid rate. On a spacecraft, cooling will probably be performed using another technique (maybe liquid oxygen?).
Back to those brass shells. If the shell is kicked out someplace inside the spacecraft, they can be collected and returned when the ship is re-armed. That is one option. Another option is to use bags of powder like the Iowa class battleships, the bag burns up with the powder. Auto-loaders could be difficult to design for such a system. Another technique that has been researched is the liquid system. Basically, a liquid propellant is pumped into the chamber after the shell is loaded and the breech closed. The liquid burns and there is nothing to eject.
Railguns
Railguns are another option. These require a lot of energy, like a laser, but they fire a projectile. Here is a video of railguns that the Navy is currently testing:
Railguns can accelerate a projectile much faster than gunpowder. Such a weapon isn’t limited to a round shell either. They can propel a shuttle that may contain something heavy, like rock or metal. The book Ark Royal used railguns that could propel rocks. The rocks would need to be shaped to fit in the gun barrel, or at least inside a shuttle. That would make it more convenient for reloading since projectiles could be mined on an asteroid. The energy of the ship would be the limiting factor for this weapon.
Any military spacecraft that are built in the near future is going to be lightly armored. The more massive a spacecraft is, the more fuel it will require to move around. Thinner ships can be destroyed with smaller guns, like 20mm Gatling guns. This is the scenario used in the TV show (and the books) The Expanse. If a large-scale war breaks out in space or between planets, larger artillery could become the dominant weapon. In such a scenario, shielding could increase to protect a ship from such weapons.
Here’s a chart that lists the armor penetration of different shells used in World War II, starting with the 16″ shell and working down to a 5″ shell:
World War II Naval Gun Armor Penetration Tables
These charts are based on the fact that a shell flying through an atmosphere will lose velocity as it travels. In space, that momentum will be conserved until it strikes the enemy. In other words, a 16″ shell fired from almost any distance would be able to penetrate approximately 33 inches of armor. The PP designation means partial penetration. Here’s the list of abbreviations for the above list:
Do you have any favorite artillery technology you’ve seen in a SciFi story or movie? Be sure and leave a comment!