Pros and Cons of Laser and Projectile Weaponry

Question

I am working on building a somewhat-near-future(500 years, but after near-total-annihilation and then induction into a more advanced galactic society) in which infantry-based wars are fought throughout the galaxy, mainly by humans. Due to the inherent danger of fighting in a world where FTL ships and nuclear fusion reactors exist in large quantities, wars will be strictly regulated by a super-advanced autonomous group. This group ensures that opposing armies are relatively equal in power, and with the kind of technology that will lead to an interesting fight. The best army, then, is not the one with the most money, soldiers, or technology, but the one that's able to accurately predict what tools work best in the context of the location of the battle and the equipment being used by the enemy.

Thus, I want to know what pros and cons laser and projectile weaponry bring to the table. The kinds of things I'm mostly interested in is what planetary conditions or tactical situations each would excel or be hindered, and what kinds of armor or fortifications soldiers would use to protect themselves from such weapons. Perhaps also the expected size, shape, maintenance of the weapons. Basically, why would you use one over the other, and why you would later use the other over the one.

By 'projectile weapons', I mean the somewhat-distant-future of modern guns, with some sort of explosion in the barrel delivering force to a small bit of metal that then flies out of the barrel and into the enemy. By 'laser weapons', I mean something that fires a beam of energy with the capability of causing fatal harm to someone. I'm hoping for an explanation of modern laser technology, but with the size, weight, and usefulness of a modern rifle. This is something I don't have much knowledge on, so an explanation of exactly what would happen to a laser-shot victim and in what timeframe would also be appreciated.

Bonus points for a scientific explanation of plasma weaponry, if that's different than laser weaponry.

Answer 1

Laser Weapons

Pros:

1. Flexibility. Presumably you can make a laser that's extremely adjustable on it's intensity, meaning you can literally dial your weapon for exactly what it is you're facing - no point in using the anti-tank laser vs puny humanoids. You could double it as a strobe-type light attack weapon to blind your enemies, or focus for sustained output as a cutting tool.
2. Stealth - it's likely that there's no way to say that a specific Laser created a specific wound - there's nothing like the current pattern-matching police can use to match bullets, there's less physical evidence. This can be important in warfare too because you can hit someone and they have fewer ways to figure out where the attack came from (assuming you use non-visible light and things like that). And lasers are quieter.
3. Accuracy - it's likely that with computer-aided support lasers are much more accurate than projectiles at short to medium ranges in ideal conditions, since you can ignore things like gravity (keep in mind that ideal conditions though, add in a storm and projectiles pull back ahead).

Cons:

1. Countermeasures. There are a lot of additional countermeasures you can take against lasers that don't do anything against bullets. Mirrored armor (include non-visual light here), or armor that adjusts it's color to precisely match laser frequencies for maximum deflection. Both of those degrade the amount of power a laser weapon can deliver. Lasers are vulnerable to anything that impacts light, which includes atmospheric effects or water vapor - defending forces could create a screen of steam which would defract any lasers that fired through it. And it would be very iffy to use lasers in the rain at any significant distance. Or think about scattering light-weight mirrored chaff to deflect part of a laser beam and reduce the power it can hit you with.
2. Line-of-sight. For close in combat this is important for things like tossing a grenade around a corner, but it's also significant for medium or long range combat too - indirect artillery fire is something you need projectiles for, or shooting around moons/planets.
3. Time-on-target. You have to hold a laser on an exact spot for it to have effect. This will be extremely difficult against fast-moving targets. Realistic lasers aren't lightsabers, you can't just wave them through people - doing so likely won't even significantly impact decent armor.

Projectile Weapons

Pros:

1. Countermeasures - It's harder to stop bullets. I mean sure you can add armor, but a big enough gun and those things just become another part of the losing end of the mass * velocity equation. It's up to you where your tech ends up, but traditionally there's really no defense against a big enough gun - it will plow through anything you put up against it, and at a high enough speed that dodging isn't a realistic option. And armor works against lasers too.
2. Specialty rounds - exploding, self-guided, penetrating, non-lethal... possible to do a lot with rounds and switch between them. The downside (why lasers are better at this) is with a gun you only have the ammo you have with you, and taking more of Ammo B subtracts from Ammo A. With a laser it's all the same power source.

Cons:

1. Logistics - I suspect carting around bullets is harder than a power supply and/or batteries, but I could be wrong. Theoretically a self-powered laser could work for weeks at some sort of output, but a gun can always run out of bullets.
2. Guns are loud. Break the speed of sound and you're making a ton of noise, really no way around this (unless you want to have stealth rounds that "magically" smooth the air to prevent that... but I think that's stretching). There's really no way to hide that you're using them, and sufficiently advanced technology should be able to track bullets back to their originating point.

Answer 2

For projectile weapons, modern-style explosion shoots a bullet guns probably won't have much on an advanced laser system. However, there are other projectile weapons that are much more likely to stay relevant. Grenade launchers, rocket launchers, and rail guns, for example, all have some significant advantages over lasers, as well as some weaknesses.

Projectile Weapons

Projectile weapons essentially break down into two categories: weapons that shoot something that does something (in the case of a grenade that 'something' they do is exploding), and weapons that shoot something really fast.

The first category of weapons has a whole range of capabilities that lasers don't have. It's possible to shoot a rocket around a corner or a mortar over a building, and a grenade can be launched through a window. Most of these projectiles then explode, so precise aiming isn't required. They call also be packed with chemical agents, smoke or incendiaries, giving them lots of tactical uses.

The second category of projectile weapons, ones that shoot things really fast, works a bit differently. A rail gun effectively fires something in a line, unless you're shooting it over distances of tens or hundreds of miles, so it can't go around an obstacle. What it can do it place a huge amount of energy in a very small area, leading to lots of destruction. A rifle-sized rail gun is likely going to need to charge capacitors, and will make lots of sound and light, since the projectile will be moving fast enough to turn the air to a glowing plasma behind it. It's also likely to make an explosion when it hits. Basically, the rail gun will be the future version of the bazooka.

Laser Weapons

Laser weapons are a bit different. They're quiet, tunable, and hit their targets instantly. The navy is looking at using laser weaponry as a deterrent against asymmetric threats, such as small, fast boats and UAVs. It's harder to get the power in a laser required to blow through the side of a building, but they're much more effective against small, fast moving targets. They also suffer far less damage and degredation than projectile systems, so they can be used to pick off swarms of weaker enemies.

So what's the difference?

Essentially, the laser will take the place of modern sniper rifles and assault rifles. It's not as great of a weapon against an armored target, but it shoots fast, far, and accurately.

Explosive launchers will continue to do what they do today, with the exception of taking out hardened targets. Nothing else can attack someone on the other side of a building or launch nerve gas.

Rail guns will be the go-to weapon for hardened targets. They do lots of damage to a singe thing, and are difficult to defend against.

Both rail guns and lasers will require huge amounts of power, though. This is the biggest change in technology that will be needed to get them to a point where they can replace modern weaponry. If power is limited to what could be stored in a next generation supercapacitor, a laser or rail gun may be limited to only a few shots, making them good weapons for sniping or attacking an armored target, but suboptimal at close ranges when compared to modern conventional weapons.

Answer 3

It hasn't been properly addressed, but the biggest constraint of a laser weapon is the power source.
The power source in traditional, explosion based weapons is a chemical reaction and the expansion of gases from that reaction - this is used directly.
With laser weapons, we need a power source that has larger power density than the above explosion method (due to power loss on converting to optical and power loss over distance), but I am assuming we need that power source not to explode on first use as it would kill the operator, not the target. On the other hand, if we're OK with it exploding, we just have a a grenade that can be tossed.
Basically as such power density, an energy release would be so powerful that no metal or alloy or composite can physically hold it together, so we're talking some sort of magnetic or optical or gravitational method to hold the power source in place.
Pretty much like any fusion reactor holding plasma in place with supercooled, superconducting magnets.
And since such tech must be available for lasers to work in the first place, this unlocks a whole class of weapons where projectiles are propelled by the same tech that holds the power source together.
In other words: railguns, which are my favourite sci-fi weapons.
They can propel anything from tiny metal particles, to create a deadly cloud of 'metal storm' all the way to launching whole big rockets and even whole ships, where the 'rail' can stretch half the planet...

Answer 4

Adding to the existing answers and as it has not been brought up so far: Frank Herbert's Dune offers a "technological scenario" with quite a major drawback of laser weapons. A shield (so called Holtzmann Effect) is invented that blocks physical attacks (or to be more precisely to prevent penetration by fast objects like bullets, mortar rounds, you name it). Furthermore a violent reaction of said shield with laser weapons is postulated - killing both the attacker and the attacked.

So the tactical situation being: Bring your lasgun to a fight with shields and die horribly. There is of course another catch to the idea - as a single suicide attacker with a lasgun could wipe out entire battalions of the enemy it is stipulated that the resulting explosion would be similar to an atomic explosion with rules of conduct (the Great Convention) banning the use of atomics.

Answer 5

I don't want to repeat things that others mentioned. Here are two new points which you could just mentally add to the winning answer:

Lasers are quite inefficient today. Roughly half the energy is lost in the machine, the other half is transported to the target. This means that they overheat faster and need more kg of ammo or fuel than a comparably strong projectile weapon. There are chemical lasers which use the burning of some material as power source. Those will generate more vapor than comparable projectile weapons, and today the vapors are also toxic but of course you can change that in your book.

Second point is about projectile weapons in a singularity tech context. Today most projectile weapons are slugs of metal, as heavy as you can get them, which are passive once they are on the way. The maximum you do is having an explosive or splintering head. But already today, the big artillery grenades can extend little wings and correct their course with an internal GPS during their 30km or 40km flight. That's today. One sensor (gps), basic steering, done.

Just minify this and amplify the tech capability in sci-fi context. They can have more and better sensors, intelligence, control over their flight path.

Rifle rounds may correct for inaccurate shooting and wind/coriolis deviation. They may choose the weakest point of the target to fly in. If you shoot a salvo of three or four, they may communicate and choose a different target soldier each, if the targets are near each other. They may have a hollow shape charge head they trigger once they are close enough, 50cm before they impact. They may communicate with your rifle so that it shoots one, two or three rounds on a single pull of the trigger, just as it estimates tactically best fitting. And so on. In short, forget bullets and rifles of today. Rather think of them as active participants of the battle, with a certain degree of intelligence and some sensory on board. With this, I guess the balance leans quite to the bullet side.

Back to the lasers. If the lasers are directed by an electronic without moving parts, (which is being developed today for LIDAR) they might be fast enough to blind the bullet sensors, and if their resolution is high enough they might transfer the impression of targets to the sensors where there are none. Holography is done with lasers - so if you could project an image into the sensor of an approaching bullet, you can derail it. So the role of lasers could be an active and intelligent defense, without which the squad would die in a tenth of a second.

Answer 6

lasers are good for attacking people with no armor since its quiet and it has faster fire rate and more ammo while while bullets are better for armored things like tanks since bullets can break metal while lasers take more time to melt it and it also heats up

short, laser: good for attacking people like. bullets: good for attacking armored things and people but needs more ammo

Answer 7

The big cons of projectile weapons are

1) they reached their peak about 100 years ago.

2) the ability to mass produce graphene would render them obsolete.

EDIT

Laser weapons offer the following benefits

1) Range in space: Lasers travel at the speed of light, allowing

2) Power: as far as I can tell there's theoretically no limit on how much power can be added to a laser, barring finding a source for it.

3) Logistics: any good source of electricity could be used to charge a laser's batteries.

Projectiles have the following benefits

1) Indirect Fire: being affected by gravity means that projectiles can be launched over an obstacle and hit something behind them. This potentially offers increased range from the ground.

2) Versatility: a laser is just a laser, but projectiles could produce smoke, fire, gas, or any number of other effects.

3) Reliability: laser's may end up being finicky weapons that are prone to breaking a lot, or at least they're frequently depicted.

There's one other issue that's much harder to take a side on: Atmospheric Interference, which could cause the laser to become to diffuse to be effective, or it could cause too much drag for the projectiles to be effective.