Laser pistols, laser turrets, turbo lasers, laser bombs – Science Fiction is in love with lasers. I get it. They’re cooooool. They’re Space Opera. But lasers in hard SF? Don’t make me laugh.
Lasers, as anything other than a close-range weapon, are completely useless.
1. Lasers disperse.
Lasers today have a dispersion of around 3 mrads, meaning that for ever 1000 units of distance, the dispersion is 3 units of width, meaning that the energy delivered to the target is spread out over a 9 times as large area.
Put this in the context of even very moderate space distances, of say, 1 000 km, and even if you increase the coherence of the laser by a thousand-fold compared to today, you get a 3^2 square meter dispersion for every 1000 km.
2. Lasers are instantaneous.
Yes, this is a negative factor, since you have no way of stacking the laser bursts. With missiles or a rail gun, you can adjust the velocity of the payload in order to make sure they all arrive at the same time, this is important because the distances to target means that your target will have moved during the time you fire. So even a target as close to the firing ship as the moon is to Earth (yes, in astronomical terms that’s close) will have 2.5 seconds to alter its velocity.
Which doesn’t sound like much, but if you’ve got a small ship and a powerful engine, you can move it out of the way of the beam. At 5g of acceleration, you’re changing your velocity by 49 m/s^2, meaning that you accelerate from 0 to 100 (or 0 to 60 for you Americans) in half a second.
3. Lasers are a point-of-fire target weapon.
That means that once you fire your laser, you can’t change its trajectory. It just goes straight.
With missiles, you could fire a volley to cover a large area of space, and have it turn on active targeting when close to where you expect your enemy to be, and then alter its course to hit them. Can’t do that with lasers.
4. Lasers aren’t 100% efficient.
That is, you can’t convert all the energy you put into the laser into the laser beam. Some of it will be lost as heat, meaning your laser will heat up. Combine this with the dispersion in point 1, and you’ll melt your own ship before you do any damage to your enemy.
5. Lasers are visible. Very visible.
I don’t mean to our eyes, but they scatter across the electromagnetic spectrum. When you fire a rail gun, you can do it fairly quietly – that is, passive scanners won’t pick it up all that easily. Fire a laser, and the bleed in terms of waste radiation, or even scattered radiation from any particles the laser beam hits en route, will be like a big, fat arrow towards your firing ship. You might as well play martial music on a broad-spectrum radio transmitter.
6. Lasers can’t loiter.
This goes hand-in-hand with the instantaneous part. You can’t fire your laser, and then have it hang around to suicide into any enemy ships that turn up like a missile can. Loitering munitions are a big thing already, and are likely to become a bigger thing as they increase the time you can suppress or destroy the enemy in the target area, effectively denying your enemy the space.
Ok, end of soap box speech. Let me know what you think, and keep writing!
Luck and Persistence!