Why wouldn't a space fleet use their lasers for a precision strike?

Question

You are the admiral of a fleet of warships in orbit around Saturn (EDIT: the individual ships can be anywhere in the Saturnian system, including into Titan's orbit), tasked with performing a precision strike on an aerial target in Titan's atmosphere (for more context, check Orbital Bombardment of Airships).

For the sake of an interesting story, I don't want the fleet to take the obvious action, using the laser arrays present on most of its ships to take out the target.

What I need is a plausible and satisfying explanation for why you don't use your lasers.

Your answer should not be:

• That the lasers are broken or inadequate (they're not).
• Handwavium or technobabble. I need a hard, logical reason why lasers are tactically the wrong choice because of some scientific or logical reason that makes sense under our current understanding of the universe.
• Evaluation of an alternate option from lasers. I already have that (see the referenced question). What I need is why not lasers, not why another option might be better.

You may, if necessary, add minor amounts of background information to the situation to contextualize your answer.

If you have any questions, just ask.

Answer 1

The lasers aren't designed to be used against targets in an atmosphere

If the wavelength happens to be one that Titan's nitrogen atmosphere isn't very transparent to, your lasers are going to lose energy heating up all the air in the way instead of your target (if your laser is strong enough to just punch through, scattering can result in significant collateral damage). Titan can also have other obstacles to transmission in its methane haze and clouds. If your force if pressed for time, waiting for the weather to change to give you a clear shot may not be a usable option. This would mostly apply to higher-frequency sources, but a weapon optimized for space-to-space combat could plausibly be using them for their higher energy density. Changing a laser's frequency usually requires some extra equipment, which could be unavailable for whatever reason.

(side note: this could be an intentional choice to protect places on Earth from rogue elements or stray shots)

Answer 2

Wild Weasels

Lasers can only move in a straight line. That means any automated defenses of the enemy will immediately know exactly where to find your ships. As a matter of training, your forces may have been taught to avoid using lasers unless strictly necessary in order to avoid giving away their exact location. Even in a situation where a laser might make sense, Standard Operating Procedure prevails and the crew acts as they've been taught.

In the real world, the United States Air Force has used special attack aircraft to locate Surface to Air Missile sites by their radar signature. The so-called "Wild Weasels" then attack the missile site. Wikipedia has a good description:

In brief, the task of a Wild Weasel aircraft is to bait enemy anti-aircraft defenses into targeting it with their radars, whereupon the radar waves are traced back to their source, allowing the Weasel or its teammates to precisely target it for destruction. A simple analogy is playing the game of "flashlight tag" in the dark; a flashlight is usually the only reliable means of identifying someone in order to "tag" (destroy) them, but the light immediately renders the bearer able to be identified and attacked as well. The result is a hectic game of cat-and-mouse in which the radar "flashlights" are rapidly cycled on and off in an attempt to identify and kill the target before the target is able to home in on the emitted radar "light" and destroy the site.

If combat lasers became common, a similar tactic might develop where defenses are built that automatically return fire to any laser attack.

Answer 3

The thick atmosphere provides both concealment and cover

The report "Navy Lasers, Railgun, and Gun-Launched Guided Projectile: Background and Issues for Congress" by the Congressional Research Service tells us that

lasers might not work well, or at all, in rain or fog

This is a problem, because Titan is covered by a 600km thick atmosphere, consisting of a dense haze in the upper layers, and over 200km of even thicker orange smog in the lower layers; Also, it's the only other place in the solar system where it can rain.

From the orbit, the entire moon looks like a hazy brown-orange sphere:

(Image made by Cassini space probe, joint NASA/ESA mission)

On the surface, it looks like Silent Hill in sepia:

(Image made by Huygens, joint ESA/NASA mission)

It took decades of orbiting the moon to obtain even a low resolution map of the moon's surface. If your targets are actively hiding, or even just drifting in the strong winds, they might be very difficult to detect.

The absorption spectrum shows that the atmosphere happens to absorb the ~3μm light of your IR-laser cannons very well, so that most of the energy will simply dissipate in the air.

Translated into military-babble, it means that Titan's atmosphere provides both

• concealment (because your adversary is difficult to detect in the thick clouds), and
• cover from your laser-weapons (because the atmosphere is impenetrable for lasers),

therefore lasers are of limited use in this situation.

Answer 4

It's a weapons test.

I have a new, experimental weapon and want to find out how it fares against aerial targets in a real-life combat situation. This battle is rather low-stakes and easy to win, so it is the perfect opportunity for a field-test.

It's practice.

I have a squadron of green atmospheric fighter pilots. I don't know yet which of them have the guts for real combat and which of them will pee their pants when someone actually fires back at them. I would like to find out before I send them into a battle that actually matters. This is the perfect opportunity to let them collect some real combat experience. So I send them to take out the target using short-range strafing runs. Should they screw it up, I can still fire the lasers and do their job for them.

I want to humiliate my enemies.

I am intentionally using inefficient weapons against them just to show them that I can beat them even if I handicap myself. This should both demoralize the enemy and bolster the morale of my own troops.

It's a bet.

Admiral Jackass wagered a bottle of 20 year old Olympus Mons Brandy that I can't take out that target without lasers. I am going to prove him wrong.

Answer 5

Stealth concerns! Lasers have a unique signature that identifies the ship and reveals your location.

If you attack the planet using your lasers, then there will be the occasional reflected and refracted photons that can be viewed by anyone in the solar system with line of sight. The attack will be captured on dozens of satellites and security cameras and anything else with a camera happening to look in the direction of the target.

Those refracted photons can be analysed - the frequency distribution of those photons are a product of tiny imperfections within the laser itself or power generator.

If every gun had a muzzle flash that was a unique colour, and any high fidelity security camera could distinguish that colour from all others, and the flash was so bright half the solar system could see both the impact and you, youd keep it in reserve.

Answer 6

Lasers are expensive

You could take out the targets with lasers, but there’s a cheaper option. After all, you’re in a war. One laser used now is going to cost a lot of energy, and if there’s a cheaper option, you want to do it, cause you’re faction is running low on energy, so you shouldn’t waste it. Alternatively, if your faction isn’t running low on energy, the admiral might just hate being wasteful

Lasers are limited

In the comments of the linked question, you mention reinforcements. Use your lasers now, and you might not have them when the enemy fleet comes rolling in, and that’s going to put you in a bad spot for the coming battle. Some ideas to limit lasers (as helpfully pointed out by @Hobbamok in the comments) is that they could run off a coolant, which can only be replenished at a home base, or they might require an exotic type of energy which the ships reactors cannot replenish.

Too many casualties

Lasers disperse, and maybe these lasers would damage the enemy ships so much everybody on board dies, and in the linked question, you stated you want to avoid too many casualties. (This one might be a bit sketchy science wise as I’m not sure how much lasers actually disperse)

The admiral forgot lasers existed

This one requires a fairly incompetent admiral (perhaps a political appointee?), who also doesn’t like getting corrected by the crew. The admiral then forgets lasers exist and thinks of something else to do (which might be a bit Wierd to write with an incompetent admiral)

Answer 7

The target is underground

(Edit: I missed the part where they're firing on airships. Oops. Perhaps the ideas can be adapted.)

Lasers are neat and all, but they can only "drill" so deep before...

• the walls of the hole collapse
• the laser overheats
• the laser runs out of power
• collateral damage
• they fire back

Take your pick. A few need further explanation.

Collateral damage

Maybe the target is under a civilian area. Firing risks heat from the laser and vaporizing material causing collateral damage on the surface. Or maybe there's vital underground civilian infrastructure in the way.

They fire back

It's incredibly difficult to find and target an object the size of a spaceship at 1.2 million km, especially when staring into the "glare" of Saturn. Space is big. Space is really, really, really, really big. Compared to space ships are very small. You didn't say how big your spaceships are, but let's make them a pretty big 1 km. A 1 km wide spaceship around Saturn from Titan has an angular diameter of 1 microradian. This is like trying to find a very small flea (1mm) from 1 km away while looking into the Sun. By comparison the International Space Station is about 100 m wide and at 400 km away appears to be 250 times larger with lots of big, shiny surfaces to reflect light and doesn't have a bright gas giant behind it.

Unless they're shining a high power laser at you, then its very easy.

Titan is three light-seconds from Saturn, it will take three seconds for the laser to reach Titan, and another three seconds before their return fire reaches you. So long as you keep your laser pulses short and random and maneuver defensively you have six seconds to get out of the way of laser counter-fire down your laser's bearing. But a precision continuous drilling laser might have to be on for more than six seconds, and might require precise station-keeping. This allows the enemy to fire back down your laser's bearing, and (despite Star Trek tropes) a planet can generate a lot more power than a spaceship.

Answer 8

The target is on the opposite side of Titan

Lasers are a perfectly wonderful weapon but they do not work very well when a planet is in the way.

Indirect fire offers numerous tactical advantages, not the least of which is the ability to fire on a target that cannot see you and may not be aware of your precise location, or even that you are present at all.

In reference to the linked scenario, in which you wish to force surrender with minimal casualties, demonstrating force when the enemy cannot see you could be sufficient to force a surrender even without casualties or even damage - all you have to do is demonstrate that you're capable of delivering deadly force to their location without exposing yourself to counterattack, and you've got them.

Answer 9

Is what you're attacking shiny? Lasers will be reflected and not damage the craft (to the significant amount required for a kill shot).

You could say it was hardened for such an attack and therefore ballistics or missiles are the only alternative.

Answer 10

I'm going to borrow an idea out of the Dune universe: laser + shield = adverse reaction in the form of big BIG boom

Adverse reactions

If you have "lasers" there's a strong possibility of "energy shields". If we are using high tech to create lasers? Then high tech also has defenses. Maybe even multiple types of defenses - against energy (lasers), high energy (plasma), physical (bullets), explosive (nuclear), etc.

Well lasers of a certain type + shields of a certain type have a high chance (or guaranteed chance) of causing a high energy explosion - an explosion large enough to destroy the target and the surrounding areas - including your ships. The right combination of lasers + certain types of defenses will lead to such negative reactions at the physical/molecular level that the resulting explosion will destroy and cause so much collateral damage as to be Very Bad.

The last thing The Commander wants to do is kill innocents and cause an intergalactic incident.

Plausibility

The "handwavy"ness of this shouldn't be much more than any other "high tech" hand waving. Laser guns exist? So do shields... so must the interactions between various forms of weapons & shields. So must the chance of Big Bad Uncontrollable Boom.

Are there times where you'd want to make the BBUB? Sure... but not this commander and not this mission.

Reference:

https://dune.fandom.com/wiki/Shield

Answer 11

The target is too far away to use a laser

Your ship is in orbit around Enceladus, Saturn's second moon. It aims its lasers at the airship on Titan. The laser shoots across the million kilometers (3.3 light seconds) of empty space between the two moons and hits the top of the atmosphere in an area a kilometer wide. Only a fraction of laser hits the airship, the rest misses and is absorbed by the atmosphere. It is not the precision strike that you promised High Command.

You ask your engineers and scientists if they can do better. No, they say. Not without making bigger lasers, bigger than the 10cm beam they make now, or going to a smaller wavelength, as well as improving the precision manufacturing of huge ship-mounted space lasers. As it is, the beam divergence is only a little above the theoretical minimum. This is why lasers like this are designed for point defense and perhaps close-range (less than 1000 kilometers, where the beam is only a meter wide) combat. They wisely stop just short of saying "I told you so".

Answer 12

You can't obtain sufficient precision because of atmosphere refraction

The path taken by light is only real straight line in a uniform environment (e.g. space, air with uniform pressure/temperature, etc.), as demonstrated when you look at an object that's in a swimming pool, or (more closely related to your problem) by mirages. Similarly, the laser beams will be deviated from course when traversing the different layers of Titan's atmosphere and any other perturbations (clouds, etc.).

Your ships, being designed for interstellar use, do not have the tools to take that into account while aiming, and as such just can not strike with sufficient precision.

Answer 13

Politics

The use of laser weapons is a contentious issue in politics. You may be able and willing to use them, but you may debatably be violating some peace treaties. Either way, it's going to be a whole international incident if you fire that thing. Better to avoid if at all possible.

Answer 14

You can't, without adding some external factor. As you said, lasers are adequate.

I'm assuming that by adequete you mean they have the proper frequency to deal the required damage despite Titan's atmosphere density and absorption.

The reasons could have little to do with the weapon used and more to do with the mission. You DON'T want to slag the entire habitat due to political repercussions, or because you want to be absolutely two hundred percent sure that someone is killed, which would warrant the insertion of a special team onboard for assassination.

Or maybe the settlers of Titan have some utterly massive ground to space coilgun hidden under the ice, with little risk of actually hitting but extreme consequences if they do so. You may then want to park your fleet far enough out of their effective range that laser can't focus accurately anymore, and may want to rely on kinetics travelling more slowly to target, but having longer range (and may even use some laser powered rocket engine to accelerate faster, since these lasers are freed from the direct fire role)

It would help a lot if you explained how your writing evolved to end up in this specific situation, yet do not want to bring it to its logical conclusion. If you work under the hard sci-fi logic of bringing your basic postulate to its logical conclusion, you need to rework the postulate, or you can soften your sci-fi and handwave space clouds or hyperspatial interference.

Answer 15

Tactics

Unless your laser can dump all its energy in a small pulse, you will likely need to hold the beam on target. Even if the laser is in non visible spectrum, there is a good chance the planet has equipment to detect multiple spectrums. Which means that the defenders now have the most accurate description of the attacker's position they could hope for, right where the beam starts.

Projectiles might be low tech, but by the time they arrive the attacker will have moved. Missiles can change trajectory to further add complexity to tracing.

Answer 16

One thing to remember is that warships specialize in function and work together. If the only thing a fleet can do is blow up other space ships, then it's only useful when fighting other ships. Seems cool, but imagine the D-Day invasions if the only thing the allies had available were battleships - there wouldn't have been an invasion. Below I've listed a couple reasons why lasers might not be optimal for this situation, but you might want to ask yourself if there really isn't a good reason why none of the fleet in this scenario is equipped to launch scout vehicles and trans-atmospheric missiles.

You want precision? Get eyes on target and guide your shot in. After all, what's the point of parking a fleet over a target if the only two options are to either annihilate it or do nothing? There's no point in spending all the time, money, and effort involved with building a battleship if there aren't other ships for it to protect.

Okay, fun reasons why just shooting a laser at an airship in Titan's atmosphere might not work: A. The balloons have a fairly reflective coating. A laser could burn through them, but it would require a lot of time focused on an exact spot, which with the distances involved is kind of difficult.

B. The airships have confetti cannons. Not even kidding. They have decided to go with some of the most vulnerable possible vehicles available, they're going to plan ahead. Lasers don't punch holes, they ablate material which takes time. If you simply monitor for someone shooting you with one, then you should have time (especially with a protective coating on the targeted surface) to launch counter-measures. Launch a bit of chaff in the path of the beam, and the beam will scatter too much to do anything.

Edit: spelling

Answer 17

As other have said, not only do lasers scatter in atmosphere (so reducing power or increasing collateral damage), they can also be deflected by changes in heat (think mirages and how they bend light).

The fast moving nature of the targets is not so much of an issue (space fights can be held with fast speeds), its the targets ability to change direction that is a factor.

Answer 18

To make the lasers powerful enough to be useful weapons they have to big. Not bigger than your ships but the kinda of size where you have to point the ship rather than the laser.

As there so big and your ships are comparably slow at turning, then trying to track small fast moving object in Titans atmosphere is hard. Your lasers where designed for strikes against big slow moving capital ships not small fast objects.

Answer 19

Laser beams have a tendency to wander a bit. Continuous adjustments can easily compensate for the drift, but not until after the lasers and associated equipment have warmed up. Ever tried to spear a fish in a pond? The constantly changing refractivity of the atmosphere around the target, due to changing winds and condensates, means the lasers rarely hit the target initially, and tend to drift off target quickly.

Add that your enemy has rapid counter-strike capabilities, that you must completely eliminate on the first strike, or reserve your laser capacity for incoming projectiles during the battle.

You have a more stealthy weapon, that can eliminate the target before a counter-strike can be launched. Lasers in reserve, in case of total or partial failure.

Answer 20

Heat dissipation Lasers are used as a defensive measure against incoming missiles. It is well known that it is difficult to get rid of heat in a vacuum. Therefore the time required to get rid of the heat between shots would make them vulnerable.

Answer 21

The enemy has anti-laser cover: Let’s say that your laser works by firing a concentrated stream of radiation at a target that causes it to rapidly heat up and take damage. The first step to reducing laser damage is having a high albedo, which can be done with a shiny coat that’s white or pale. Next, there’s using materials with a high specific heat capacity, which means that it takes longer to heat it up, and a high thermal conductivity, which will dissipate the heat, which will mean that it will take even longer for the laser to deal significant damage. Also, a small and mobile target would be hard to hit, and you’d need your laser to be focused on a certain point on the target, which is especially hard if they’re far away and constantly moving about.

And we don’t need any made-up materials for that. Diamond, while brittle, has the highest thermal conductivity of any known material, with values as high as 2100 W/mK, and hydrogen gas has the highest known specific heat capacity of any substance, at 14304 J/(kgK). Tungsten has an really high melting point of 3695 K, so if you have a small, mobile bunker with an outer shell of diamond painted white, with an inner shell of tungsten, and between them, a layer of hydrogen gas, unless the laser is really powerful, it will take a very long time to burn a hole in your bunker. And by then, it’ll be far easier and less time-consuming to use explosives to shatter the bunker.

Answer 22

Any high-energy weapon lights them up for the entire system to watch and post or aim at, thanks to waste heat.

Lasers are notoriously power-hungry. Every power generator has to dump waste heat, and in space the only way to do so is radiation with the help of through Avatar-like "red fin" radiators or fancy Mass Effect-like droplet coolers. The power demands of lasers capable of dealing reasonable damage right through the atmosphere (scattering and opaquity are a laser's hardest counters) take that to obscene.

This means that while ships launching missiles or firing chemical guns can do away with small and nearly-invisible (compared to the overall multispectral signature of an orbital bomber) heat radiators, a ship firing a bombardment-capable laser will immediately have to make it's radiators become yellow-hot or melt itself on the spot.

This has the obvious military and media repercussions.

First, a firing lasership shines enough to be aimed at even with a cellphone's camera, let alone military-grade guidance systems. If your Titaneans have (or have had) reasonable access to orbit, they've already spammed Titan orbit with dirt cheap mine fields made out of dormant missiles, ready to activate and strike anything that is hot enough to be considered an enemy lasership.

Second, and that works even if the Titaneans have no mass access to orbit, they've already made friends with factions elsewhere in the system. Laserships on full power are target-painted for free by their own radiators for half the system to shoot at their leisure; even if there are no friendly guns/launchers in range, they are bright enough for thousands of eyes, from local space tourists to space telescopes of Earth or Mars, to be captured on video destroying civilians. Anyone half-competent in journalism can whip up a media disaster for the bombarding party if they manage to catch the bombers on tape. Kinetic weapons have a much lower media profile, because space is big and missiles/cannon shells are small. This will allow the bombing party to at least remotely plausibly deny involvement and say that they were on a routine patrol, and airships going down below is a coincidental malfunction. Or photoshop the presence of a rogue terrorist warship and say that it was terrorists who shot the airships, and the orbital force was an attempt to intercept and destroy the terrorists.

Answer 23

There has already been an answer about Titan's atmosphere interfering. I'm going to take that a bit farther:

How accurately you can focus a beam is a function of the frequency of the photons (A simple illustration of this: Note how low resolution radio telescope images are despite radio telescopes being far bigger than optical telescopes) and the size of the object doing the focusing.

Since the purpose of your laser is to deliver destructive energy on target you are going to build your laser to use as high a frequency as you can efficiently use as this will deliver more concentrated energy to the target. Lasers in the UVC spectrum already exist, I don't know if we can go farther and who knows how far they've gone by the time of your story.

UVC basically doesn't make it through even Earth's atmosphere and Titan has [b]far[/b] more atmosphere than we do.

Thus, unless your ships specifically have lasers meant for engaging ground targets your fleet probably can't even light a candle on the surface of Titan--and even ground attack lasers meant for other worlds are likely stopped by the haze in Titan's atmosphere.