Maximum (Effective) Laser Range

When I began writing, The Huralon Incident, I wanted to figure what would be a plausible “effective range” of future military lasers. I dug into Google and started researching. The number of different, and often contradictory answers, I found were legion. Nobody seems to know for sure, and even those who should know, say the end result depends on a huge number of factors. Safe to say, I didn’t get any really hard, useful information after reading so many articles my eyes turned red and they began to creak in a distressingly loud way.

Maximum Effective Laser Range

Having found no definitive data I, somewhat arbitrarily, decided that any distance within one light-second is point blank range. “That’s really close, E.A.” you might say. Actually, it isn’t. The distance from Earth to the Moon is 238,900 miles, and that is 1.28 light-seconds. So, here is the ISS space station, a large installation looking a bit diminutive, in orbit around the Earth:

We’re already some distance from the ISS, but you still cannot see the whole Earth. We’re too close. Now for comparison, here’s an Apollo 11 shot taken from the Moon, 1.28 light seconds away.

Now we can see the whole Earth, but where would the ISS be? Well, it would be a tiny little speck too small to see. And this distance would amount to a knife fight in a phone booth during futuristic space combat.

The reason I consider this point-blank range is because the information directing a firing a laser at this range is “only” two seconds old. One second for a light-speed radar range finder to reach the target, one second for the range information to come back and tell you how far away it is. Considering that a ship could move hundreds (instead of thousands) of kilometers from the location a radar tells you the target is located at, that’s not too incredibly awful. Futuristic computers, I wager, could work out where a target might be at that range. You’ll have a snowball’s chance in hell of actually hitting something, with a sophisticated AI.

At five light-seconds away, you’ve got little hope of hitting a maneuvering target. The enemy would be dodging his/her butt off because that’s a ship full of people who very much don’t want to die. Your information would be ten seconds old and when you fire your laser this beam of superheating destruction it will take a further five seconds to arrive on target. That’s a fifteen second lag time! Adding to the thinking is that every time you release the immense energies of your laser, you create heat in your own ship. Getting rid of heat in space is very difficult because there is no atmosphere to transfer the heat to. So, you want to fire your lasers when you can make the shots count. That means, at a range where you’ve got a hope of hitting.

And thus, is the logic for how I determined maximum effective range for a futuristic laser. What say you? Any thoughts to add? Let me know in the comments.

About EagleAye

I like looking at the serious subjects in the news and seeking the lighter side of the issue. I love satire and spoofs. I see the ridiculous side of things all the time, and my goal is to share that light-hearted view.
This entry was posted in Essay, Uncategorized and tagged , , , , , . Bookmark the permalink.

15 Responses to Maximum (Effective) Laser Range

  1. Lyn says:

    Absolutely…couldn’t agree more! (what did he say, Albert?)
    😀

    Liked by 1 person

  2. List of X says:

    Actually, at one light second away, you might have an excellent chance of hitting a spaceship with a laser. It doesn’t actually matter at what speed the ship is traveling (assuming it’s not some near-light speed at which time and space are no longer work with basic physics and geometric formulas). Basically, knowing the speed and direction of the target ship, and a distance to it, the targeting computer will just have to aim the blast to where the center of the target ship will be. The target, to avoid being hit, have to get away as far as possible from the place where the laser is going to intersect with the target ship’s trajectory at the time the laser is fired, so it will have to change speed and direction. For convenience, let’s assume the ship’s location is determined on the system of coordinates that are moving in the same direction and same speed as the target ship at the time of the radar reading, and remain fixed, so at this time the ship is not moving, but can change direction and speed and thus move from the original position. Within 2 second, the target can move away no farther than 2 x it’s maximum acceleration amount from that point (the formula is distance = 1/2 x acceleration x time squared – that’s if the target begins acceleration right after the radar signal is reflected towards the attacker. In reality, since the target doesn’t know when the attacker is firing, it to maneuver more often than once every two seconds, otherwise if it’s not changing direction and speed for just a second before and a second after the blast is fired, it will travel in a straight line and fixed speed (and remain fixed in that system of coordinates) and will be the easiest to hit. So, in best case scenario, a ship accelerating at 20g will get at most 400 meters away from the expected position, but in reality, much less. So if a target ship has a diameter of 500 meters, and the laser is aimed at where the ship’s center is expected to arrive based on the radar reading, then the best case scenario for the target is the laser passing 150 meters away from the hull. So this would mean maybe a 50/50, if not better, chance of a direct hit.

    Liked by 1 person

  3. List of X says:

    And now the part 2 (sorry for the long comment, I find this a really fascinating question 🙂
    The problems… All above works only if the radars and targeting all work absolutely perfectly with zero error. In reality (yes, even in sci-fi reality:), the radars will not be 100% accurate – if a radar misjudges the ship’s speed by 0.1% (because the target is 300,000km away, and it is trying to vary it’s speed), and the target is moving at 1000km/second, it will be around 2km away from where the laser hits. So that makes a hit maybe about 5% likely. The targeting system is not going to be 100% precise either, and unlike a missile, a laser can’t adjust the direction, so the probability of a hit decreases even further. And finally – and, potentially, the biggest problem, is that the laser rays will dissipate over longer distance (and I think you’ve mentioned that in your book). If the laser ray gets wider by a just a millimeter over 10km, it will spread over the area of 30 meters wide after traveling 1 light-second. That will spread the impact of the laser over the area a 1000 times larger (assuming the original ray was a meter wide), so it would be like trying to stab someone with a handle of the knife instead of the pointy end – not technically impossible, but much harder.
    Maybe a solution would be try to attack a ship with missiles armed with lasers instead of explosive materials – a laser 10 times less powerful than a battleship’s laser, but having the same precision, and attacking from 1/10 of a distance may actually have a more powerful impact since ray divergence will spread to the area 100 times smaller. And, of course, you could have a few of those missiles attacking at once, maybe even getting a few shots each, and definitely able to aim much better from a closer distance. (As an added bonus, these missiles might either still carry explosives, or fitted to return back to the mothership and reused over and over again. Of course, unless the target ship managed to also deploy such missiles (should I call them interceptors, maybe?), and there’s a mothership still left to go back to. 🙂
    ….and here I am back to small ship vs large ships discussion. 🙂

    Liked by 1 person

    • EagleAye says:

      No worries about the comment length. I love it. In the Huralon Incident, I usually present acceleration values just to keep things simple, but actual velocity is a big factor in space combat. I assume, perhaps wrongly that the velocities of space combat within a solar system won’t be really high as compared to the speed of light. Relativistic velocities would in a space full of planets, asteroids, rogue comets and assorted debris would be a “bad thing” I wager. Still, combat speeds would still be pretty high. I’m assuming the highest would be around 1/10 of 0.01c. That’s 300,000m/s. That’s still freaking fast. If your target is 1 light-second away, that means your data is two seconds old, and then you fire, you add another second for the laser to arrive on target. That amounts to the target being 900,000m from the last range and bearing. That’s a pretty huge error potential. If the target maintains a steady course, this is easily doable. Future computers should hit 99% of the time. Trouble is a maneuvering target should be changing course at least one time per second, so you can only guess at where it will be the time your shot arrives. I’m thinking highly advanced computers might “guess” pretty well (even accounting for your very good point regarding range finder error) and managing to hit 10-30% of the time. At five light seconds, I’m thinking getting a good targeting solution is nigh on hopeless. You’re lucky to hit 1% of the time and building up heat in your ship with every shot for little return. Also, in the Huralon Incident, Springbok can accelerate at about 417 gravities forward of backward; she can accelerate laterally/up/down (not covered in the book) at about 40 gees. This amounts to a maximum change (delta) in velocity, and it doesn’t have to be a consistent acceleration, and that means a ship could be thousands of kilometers away from a point where it would be if it held a steady course. Shooting lasers as McCray puts it, is a crap shoot. And you make an excellent point about laser collimation. They cannot be perfectly collimated, so they will slowly disperse over distance. To me shooting a laser (intending to damage it) much further than 5 light-seconds is an exercise in futility. Lasers fired from Earth to measure the distance to the Moon have a footprint of about 1000 kilometers when they hit it. That doesn’t matter if all you want is a range, but for military applications is almost useless. And that’s just over one light-second away. I’m guessing military lasers in the future will be better collimated by that, but long ranges will still affect laser power. And, you make another point about missiles. In The Huralon Incident, warships also carry missiles and these do most of the destruction because they can fire their lasers from much closer, dispersing the power less, and enjoy far more accurate targeting data. Missiles are firing from about 5,000 kilometers which is akin to trying to hit a barn door with a pistol from two meters away. Can’t miss! The downside for missiles is, they must survive a fusillade of anti-missile lasers and anti-missile missiles to get to that range. At such a close range, it’s not hard at all for these weapons to their target, even if it is maneuvering.

      Like

      • List of X says:

        Yes, if a target ship is moving at a fast but fixed speed and direction, it would be just as easy to hit as a ship that’s not moving (technically, there’s no such thing as “not moving” in space, since all speed and direction is always determined in relation to an observer).
        And I think you overestimate the effect of even 417G acceleration 🙂 A ship moving at 300km/s will be 600km away in 2 seconds. A ship starting at 300km/s and accelerating at 417G will be 608km away, so just 8 km farther. However, what I think would really be useful if that ship could rotate away from the direction its traveling (and I’m sure the Springbok should be able to). Assuming that the ship is spherical with a 500m diameter, can take the equivalent of 40G acceleration from the centrifugal force instead of the regular acceleration, and can do such an angular acceleration at the same 40G equivalent, and assuming my math is right, it should be able to make a 45% angle turn in one second. In that case, at a 300km/s speed, the profile of the ship represents around 0.0003% or so of the possible area where it could travel, which means trying to shoot lasers from 1 light second away is just a waste of time and energy. it would be like trying to shoot a fast and randomly moving cockroach on a wall 100 yards away after turning off the light and then counting to 4 before pulling the trigger.
        And I don’t think any computer could be able to guess a position of the target in two seconds if the target can change speed and direction randomly. I’m not sure how AI can beat a game of chance which doesn’t use any rules of logic.

        Liked by 1 person

      • EagleAye says:

        You are quite right that Springbok can simply rotate to another direction and use its primary acceleration in the new direction. The lateral acceleration numbers provide for a maneuver that aircraft can do called a “skid.” It just adds another dimension to possible evasions. And I think a computer couldn’t make reliable guesses about the future position of a target, educated guesses at best. No way would you be hitting every time, in fact probably a low percentage. Then again, this reflects what ship to ship combat with guns was like during ww2. The vast majority of shots fired were misses. So the winner of a laser engagement amounts to the one who closed enough to ensure he was getting hits while his enemy was still missing. War is almost always a balancing act like this.

        Like

      • List of X says:

        I think in the WWII they had an advantage (or a disadvantage, if you’re being shot at :)) of actually seeing the enemy ship and its movement in real time. And although it may still take a couple of seconds for a shell to hit the target, it was impossible for the ship to evade it.

        Like

  4. Benjamin Scherrey says:

    Physics prevents you from focusing a laser at any such distance without it being a HUGE HUGE mirror. Low millisecond distances will be top maximum effective range.

    Liked by 1 person

  5. Fascinating discussion! To me the issue of hitting a randomly moving target with (say) a 1-second lightspeed lag is coupled with the problem of laser-spread and the duration of the beam. Much depends on what assumptions are made about the energy delivered and the likely collimation of the beam.

    Unless I’ve dropped a decimal point, Springbok’s up to 40g acceleration laterally would produce a maximum displacement of 67.8 km up or down, coupled with up to 608.3 km displacement horizontally at 417g from the point of origin. I’m ignoring any sideways displacement (range increase) because at light-second distances it’s negligible; the possible location of the ship from a firing-solution perspective is two dimensional over the two-second period. The resulting shape in space is essentially a Reuleaux triangle with the apex at the point of origin, defining the maximum possible range of positions the target could occupy. I’m assuming here that the ship accelerates rather than flipping and decelerating with main drive; the issue of how quickly Springbok can rotate enters the calculation and might take two seconds (we’re talking significant angular momentum to first induce and then damp).

    The question is how to then hit the target within that defined area of possible positions. To me it comes down to the length of time the laser beam can be sustained and the degree of spread. It’s possible to envisage a focusable laser; but of course diffusing it reduces the net total energy delivered to a target. This is generated by (a) the actual energy of the beam for a given surface area at a specified distance, and (b) time that this energy is then delivered. The time factor is important; a beam able to be sustained for two seconds could be made to sweep the whole of the potential target area, guaranteeing a hit; but the question is how much energy would such a brush-past hit actually deliver?

    I suspect the main problem for a laser able to fire for a multi-second duration, and to produce militarily usable energies out to 1 light-second, would be cooling the cannon so the inevitable thermodynamic transfers at that end don’t damage the cannon or the firing vessel. To keep that within bounds of ‘suspension of disbelief’ for readers, that implies something closer to a ‘burst’ fire than a continuous beam.

    There’s also the point that a powerful enough laser will produce measurable thrust. (As an aside, I think Niven & Pournelle came up with that in ‘Mote in God’s Eye’, although their laser portray was wildly silly because they imagined the beams were visible in space – I still don’t know whether that was authors’ license or just a mistake both of them missed.)

    So to me, a lot of it comes down to author judgement in terms of how powerful the laser is; but to keep the sense of disbelief going I think a realistic limit to the laser power would have to be established. As a final note, this was a crucial plot-point in Stanislaw Lem’s ‘The Invincible’, where the key weapons were anti-proton cannons, but where the problem of energy transmitted back to the weapon was a significant issue. (There was a sequence involving a monster robot tank armed with such a cannon, which cut loose with it at ground level – I blogged about it, way back when: https://mjwrightnz.wordpress.com/2013/10/15/omg-the-baddest-sci-fi-mega-mech-e-v-a-h/ )

    It’s all interesting stuff for which the answer is ‘a discussion’ – and that’s great.

    Liked by 1 person

    • EagleAye says:

      Hey, I will get back to this and reply at length. For now, New Years is coming in about 40 mins. I’ll be popping corks shortly and will respond “next year” in the morning. Cheers and Happy New Year!

      Liked by 1 person

    • EagleAye says:

      It’s the diffusion of a laser that gave me a lot of trouble. How much happens now, and how much is likely (per kilometer) in the future. Well, when it comes to military lasers that sort of data is difficult to find. I think that’s by design of course. Enemy nations would like to know that too. To me, I felt that roughly 400 years in the future (with 250yrs development time) a laser should retain 90% of power within the firing bore diameter at 1 light second. By 5 light-seconds that might be down to 50-60% where firing the laser isn’t worth the heat it is creating in the firing ship. Add to it, the data is so old and the volume of space where the ship might be is so large, its a waste of effort to even fire. Another factor is how many lasers are available to fire. If you’ve only got one, you’ve got to fire when you have the best chance of hitting. If you had a battleship and could fire eight lasers simultaneously, then you could use the salvo technique, sending each laser into a different high-probability location. This could help for any ship with two or more lasers to fire at once. Still, heat is the enemy and that needs to be managed by firing lasers in the most productive way possible. I could imagine a scenario where both sides “take a break,” not firing and trying to dump waste heat. Wouldn’t that be interesting?

      Liked by 1 person

  6. texsoroban says:

    Space ad you have determined is really really unimaginably big. Because it’s so big battles in “deep space” will probably never happen. The detection ranges are too small, the ability to project power too slow. It’s even highly unlikely that engagements will happen within a solar system. It’s too big and too easy to hide if you want to avoid a fight. No. Space battles will happen within or near gravity wells. Because that’s where the only stuff worth fighting for will be. Yes I include asteroids and space stations in that group.

    Liked by 1 person

    • EagleAye says:

      Agree. Space battles at any appreciable distance from a star system are unlikely. What’s there to fight for? So, yes the space battles in my book all occur within a gravity well, around some strategic target within a star system. There shipping will concentrate and that’s where you find the predators of ship…warships.

      Liked by 1 person

      • texsoroban says:

        In such a case, Orbital mechanics become paramount. If we take the earth as an example it’s a sphere of radius 12,500 miles (or there bouts I’m not researching this on my phone and writing this). That means the lower you are in orbit the more constrained your detection range is for other objects in orbit. The higher you are the more vision you have, conversely, you are faster when lower and slower when high, also a properly camoed ship in low orbit can hide against the planet while a high ship just has the backdrop of space. Ground based and microsat based detectors could give globe wide coverage to whoever controls the well. You are still looking at engagement ranges of less than 100k in most cases. Less than a second for lasers and particle beams barely a minute for hyperV missiles, but still a long time for rail guns. I would think that orbital smart mines and barrage nets would be used a lot. It would be more like “run silent run deep” than ” battle of midway.”

        Like

  7. joetwo says:

    The inverse square law will put down any attempt to use lasers at anything more than a few hundred kilometers. At appreciable distances I would imagine that missiles would be far more effective. I would imagine that lasers will be more use as point defence systems.

    Liked by 1 person

Don't be shy. Say something!

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s