What's The Max Effective Range...

Fixed the spelling for you Greg.

First, the short answer:
X-rays can go pretty much as far as you need them to, electrons are less useful, as are the charged mesons, uncharged mesons can go pretty far but are less damaging. Also, the issue is not how far you can shoot, but how far you can see, and how accurately you can aim.


The long version:
Technically you can shoot as far as you like in space, with pretty much any weapon, because there's nothing to stop it. Your x-rays will be gradually lost to beam attenuation, but it'll be a huge distance before that'll take the punch out of it. Your electrons and mesons will fly until they hit something, which will be quite a long time. There are bits of matter floating in the void - interplanetary space actually has a few hydrogen atoms, dust particles and stuff like that drifting about in it; it's not a perfect vacuum, but the stuff you're firing is so small that the chances of hitting a passing hydrogen atom is tiny.

The real limiting factor on range is not what you're firing, but how you're firing it. Let's take a look:
X-rays and other EM radiation
Attenuation will weaken the beam, but very gradually in a vacuum. The main loss of damaging capability will be beam spread. The better you can focus the beam, the further you can hit stuff - and that's just simple trigonometry to work out how wide the beam will be given a certain angle of spread and a certain range to target.

Electrons, mesons and other particles
The main thing to consider with particles is their charge. The problem with firing charged particles (like electrons, for example) is that because they all have the same charge, they'll repel each other, which will spread the beam pretty quickly, giving charged-particle beams a very short range. Of course, you could fire neutral particles. This is tricky, because the lack of charge makes them harder to accelerate, but it can be done, usually by accelerating charged particles and then removing or neutralising their charge as they leave the weapon. The problem is that their lack of charge also makes them very light on damage. Neutron beams are pretty nasty at high intensity, but they're also pretty hard to produce in enough intensity to cause serious damage, and usually their damage is to living tissue. On spaceship armour, they do very little. (Technically they do very little to tissue too, but with DNA being so delicate it doesn't take much).

The BIG problem
There is one other really major thing you need to consider when fighting in space: space is BIG. Like, seriously huge, in a way your mind isn't built to handle. Say you were orbiting the Earth, and you saw an enemy ship floating over near the sun. First, you're not seeing where it is - you're seeing it where it was eight and a half minutes ago, because that's how long light takes to get here from the sun. So, you'd have to hope that it hasn't changed course in the last eight and a half minutes and try to work out where it would be by now. Then, you fire a laser at it. That laser will take another eight and a half minutes to get to them, so they have a total of seventeen minutes in which the tiniest nudge in their course will cause you to miss - and because they're so far away, if your laser's aim is off by even a fraction of a degree, you'll miss by kilometres at the other end.

And if you're firing a particle beam, or something more old-fashioned like a missile, then they'll have even longer to dodge, and they might even be able to see it coming. There's pretty much no way to hide in space, so anything large like a missile will be seen. Of course, you can give it guidance systems so it can home in, but that means it needs fuel and engines to manoeuvre, which means it's heavier. That means less in space than on a planet, but more mass will still give it more momentum, which means it will be harder to steer quickly - and you'll be able to carry less, because they're bigger and heavier.

If you want a really good look at space combat, I suggest you head over to Project Rho's excellent website and check out the 'Space War' pages (use the drop-down menu at the top).

The Range of a laser depends pretty much only on the divergence angle in space. (you would avoid lens diameters that make diffraction a problem)
The divergence angle depends on the laser wavelength (shorter is better) and the size of the mirror/lens.
For a bomb-pumped laser, the divergence angle (in radians) is 2*w/l where w is the width and l the length of the rod. The minimum possible width depends on the wavelength of the laser, it's in the same ballpark as the wavelength (don't remember right now). There's also a maximum practical lenght for lasing rods.
Now, how much actual range that gets you depends on a lot of other factors. You need to figure out how much output energy you get out of the lasing rods, and over how big an area that can be spread and still count as "effective". Then you can calculate backwards, at what distance the lasing rods can be. To give a general figure: when using x-ray lasers, and lasing rods a few meters long, the divergence angle would around a few microradians, i.e. your beam diameter will increase by a few meters for every kilometer. (Just noticed i mixed up my SI prefixes. The beam divergence at 1 microradian is 1 meter for every megameter, not every kilometre) Because the spread radius is proportional to the distance, the area is proportional to the square of the distance (being an area) which means the inverse square law applies. I.e. 9 times the power output will only give you three times the range.
Reusable lasers can get much more practical range, since they can use large (and expensive) lenses. Lens diamter is directly proportional to divergence angle.
Addendum: More practical range means MUCH MUCH MORE. Many orders of magnitude more, with a just a few meters mirror diameter. (There are no known lenses for x-rays)
On another note, 80% efficiency for bomb pumped lasers is extremely hard to make work, since lasing rods lase out of both ends when hit perpendicular by the nukes radiation. To make them lase all the energy out of one end, they'd need to be hit end-on, which means the shaped charge has to be a lot more tightly focused. Another approach would be to use x-ray mirrors on one end of the rod, which however would be extremely difficult. The amount of energy dumped into the mirror by the nuke AND the x-rays it reflects (there can be no perfect mirror) means the mirror will vaporize even faster than the lasing rod. It could however boost the laser output somewhat, depending on how much energy it manages to reflect before.


Electron and other charged particle beams are next to useless compared to the range of lasers, since their charged nature makes them dissipate extremely quickly. They're weapons for knife-fights. Really suited to that end however, since they are much more deadly than a laser.

While neutral particle beams do not suffer from the dissipation problem so much, they are still harder to focus than a simple laser, and since they don't generate bremsstrahlung at the target not nearly as deadly as a charged particle beam. In other words, there's not much point using them, they're less efficient than a laser.

I think because this thread is asking for speculation, for a work of fiction, it belongs in either the main SF/F forum, or perhaps in the Sandbox forum. Greg,I think you'll get more results in the main SF/F forum, so I'm moving it down there.

FOTSGreg said:

I need a light speed weapon, obviously a beam weapon, that has an impact energy of 20kt at 150k km.

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The question really is, how wide that energy can be spread. A laser doesn't lose any energy in space, so the range is determined by the the distance at which it becomes so unfocussed that it no longer heats up the target.At 150 Million meters distance, a bomb-pumped laser would spread the energy over an area a few kilometres wide. Wether that still does damage, depends on the amount of output energy of the laser, and on the hardness of the target.
For comparison: Let's say we have a divergence of 20 microradians, which gives a nice round figure of 3km diameter of the laser at 150Mm. Which is an area of ~14km². Now, if we want to compare that to a spherical nuke, the distance at which we get the same energy per m² is about 1.05 km. So, the lasing rods produce the same energy/m² at 150Mm, as the unfocused nuke would at 1.05km. At perfect efficiency. At 50% efficiency, it'd be comparable to 1.48km (inverse square law).

I have 20kt of mass and 20kt of cubic volume for the "projector" and as much generating power as I really need to get the job done (in fact, the projector, when fired, generates 46% of the energy of the beam as heat - which is a HUGE problem with my internal consistency and which brings up the next question),

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If the laser uses a mirror with a couple of meters in radius to focus, it'll have an effective range well in the lightseconds.

Obviously, heat is generated by the weapon's firing. How do you dump that heat safely so it doesn't affect your ship or friendlies in th near vicinity? I don't know of a single material, including superconductors that can reasonably handle that kind of energy load in a 30-second cycle time (that's the sustained rate-of-fire of the beam weapon without all kinds of fancy tech upgrades).

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Yes, heat dumping is a big problem in space. There are basically two way to do it: either use a temporary heat sink. A spaceships superstructure would serve this purpose for example. Basically, just keep absorbing the heat until reaches dangerous levels, then wait for the heat radiator panels to get rid of it. This would means that one can keep firing a laser rapidly, until heat storage capacity is used up, after which the firing rate depends on the capacity of the heat radiators. Or one could break of the engagement, and wait for the radiators to cool the sink down again.
Alternatively, use a chemical laser. The heat is generated in the lasing medium, which could be quickly dumped into space after each shot, to get rid of it before the heat transfers.

Maximum range for really, really, long-ranged beam weapons is 250k km. Rates-of-fire can go up, but that requires a lot of R&D work. Most species have opted for long-ranged projectile "buses" that can be maneuvered after launch and which do not engage until they are within the effective range of beam weapons (most don't actually engage until well inside this range).

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A laser with a big mirror will pretty much only be limited in range by targeting accuracy.

In one scene in the WIP I'm working on, an enemy commander launches a salvo of projectile buses early in the opening maneuvers of a battle. He programs the weapons to diverge from his course, fly to a gas giant's vicinity, then "pop up" and intercept the enemy as they close with his own force. The commander's forces are driving ahead with their drives (very bright, very fast) lit full up. The projectile's maneuver requires hours of time (it's space opera so bear with me here). Is this vaguely possible or would the salvo be spotted almost "instantly" (given the realspace time lag between the opposing forces given that the projectile buses are moving at the same speed as the engaginf force, have to make a few course corrections to veer off and then maneuver, etc.)?

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Without magical stealth, there's no way no way to hide anything hot in space. A missile drive would definitly be hot. But one solution could be to supercool the projectile bus, and launch it as an inert projectile from a mass driver on a ship. It would be much harder to detect until it engages its own drive. Still not impossible, since a lot of sensors would be focused on the fleet that launches it, but pretty damn hard.

In another scene, a weapon is deployed which, essentially, fires a sustained beam of X-rays, using the heat generated by the weapon's own systems, at a populated world 3 light hours distant. The weapon is supposed to be able to track the planet's path and maneuver itself to sustain a continual bombardment of the enemy world (through a jump point, which passes energy in both directions) until the population on the world is, basically, fried. The weapon's yield is about the same 20kt at the projector, but can an object as big as a planet or even a section of a planet 3 light hours away be reasonably tracked well enough to rast it (as I think about it I think the answer is a definite Yes as we can track the ioneer spacecraft well beyond even that range and send and receive signals)?

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Yes, the tracking isn't a problem. The range isn't much of a problem either, the laser mirror would need to be a couple of hundreds, possibly only dozens of meters in radius, which is technically diffcult, but possible. (We build pretty big telescopes today already. And in gravity)
Kilotons would be a useless measure for the weapon though, as it's a measure of energy (joules), while for a continuously functioning weapon, you need power (watts). Not sure what you mean by using the heat generated by the weapons own systems.

Finally, how would you go about deflecting an X-ray laser without wasting a huge amount of resources? Would a "sandcaster" work reasonably well to do it? How about a reflecting sail of some sort?

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Reflective sand can work relatively well, though it's more of a temporary measure, it's only better than an actual mirror in that it's easier to deploy.
A mirror should work, depending on the energy of the laser. Since it's supposed to fry a planet over time, i'll assume the energy isn't high enough to vaporize a mirror (or it wouldn't need long to fry the planet), not to mention that deploying a mirror to stop it implies one has the time to do that,
Anyway, any surface reflective to the wavelength will do, a "sail" would just be one that's built to be pretty thin. Reasonable choice, no need to waste material for a thick mirror.

Lhun seems to have it all covered there!

I'll just add that there is one fancy way to dump heat besides massive heatsinks and massive radiators: cooling laser. The basic idea is that you excite the lasing medium to just below the correct energy level for laser emission, and by various quirks of physics, it takes the remainder from its own heat. So, if you can transfer the heat of the various hot systems to the lasing medium, then you can shed the excess energy into the laser beam. This has the advantage of veeeeery slightly reducing the energy requirements for the laser, and also being the only undetectable way of losing heat in space, because you can only see it if the beam hits you, or is scattered off something (like dust in its path). Unfortunately, it doesn't shed heat nearly fast enough to cool a whole ship, and it's basically impossible to make sure that all the heat goes to the lasing medium rather than out into space, so you can't make a stealth spacecraft by using loads of cooling lasers. Also, you need to dope the lasing medium with specific chemicals to make it work, which I presume means it won't work with certain types of laser. If you want a more detailed explanation, I'm pretty sure they're discussed on Project Rho as well. The summary is basically that they take advanced tech to be worthwhile, and even then they're not brilliant. It just occurred to me that if you're going to have a huge beam weapon operating continuously for a while, then you might as well make it an x-ray laser and see if you can't get it to help you out a little with the heat issue - every little helps.

As for the stealthy projectile buses, I'm afraid they're going to be really easy to spot, what with the nice hot engines. I remember reading somewhere that the Space Shuttle's engines could theoretically be seen from the other side of Mars orbit. However, if there's a gas giant in the general vicinity then you have an option there: if the buses can get behind it, then the enemy won't be able to see any course alterations they make, so they could change course so that they come whipping round the planet on a fast slingshot right when the enemy is close to the planet, which would give the enemy very little time to react. Of course, the enemy would have seen them go behind the planet in the first place, so they'd probably be watching for it, and would probably avoid going that near the planet... It'd be better to launch them while the entire ship was behind the planet, so they enemy doesn't know they've been launched.

Anaximander said:

I'll just add that there is one fancy way to dump heat besides massive heatsinks and massive radiators: cooling laser. The basic idea is that you excite the lasing medium to just below the correct energy level for laser emission, and by various quirks of physics, it takes the remainder from its own heat. So, if you can transfer the heat of the various hot systems to the lasing medium, then you can shed the excess energy into the laser beam. This has the advantage of veeeeery slightly reducing the energy requirements for the laser, and also being the only undetectable way of losing heat in space, because you can only see it if the beam hits you, or is scattered off something (like dust in its path). Unfortunately, it doesn't shed heat nearly fast enough to cool a whole ship, and it's basically impossible to make sure that all the heat goes to the lasing medium rather than out into space, so you can't make a stealth spacecraft by using loads of cooling lasers.

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Well, making sure the heat all goes into the lasing medium is technically possible. Unfortunately, the process generates more heat than it can move around. (2LOT strikes again)
However, cooling lasers are a theoretically interesting way to keep the heat generated by certain solid state lasers down. A phased array laser for example might be able to run with very low excess heat using this effect.

Actually, one thing just occurred to me: when you talk about the enemy entering the system, do you mean literally crossing the line dividing 'solar system' from 'interstellar space', or do you mean via some sort of hyperspace flight or jump gate? Because if those missile buses are important plot-wise, you could always say that the jump messes with sensors in some way because hyperspace is weird - maybe sensors have to be shut down for the jump and take a few moments to come back online. That would give a short window in which the buses could launch, give a short boost towards the gas giant and dump heat as fast as they can, and then be cold and relatively hard to spot, especially if the enemy isn't looking for them. At those ranges it'd take about 5 hours before they'd be seen by the enemy, and depending on which way you and the enemy are moving it's possible that you'll have entered combat by then, which would kinda distract them from searching for the buses. Anything the buses do behind the gas giant would be undetectable, so then they'd be surprised when the buses slingshot round the gas giant and open fire.

If you really need the missile buses to be vaguely effective for the sake of plot, then that's how I'd do it.

I am impressed by this discussion (about whose subject I know nothing), given that writers of medieval fantasy cannot usually reach agreement, or even, after a few exchanges, talk very politely, about the effective range of an arrow.

Vomaxx said:

I am impressed by this discussion (about whose subject I know nothing), given that writers of medieval fantasy cannot usually reach agreement, or even, after a few exchanges, talk very politely, about the effective range of an arrow.

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Oh, there're older threads where the heat sink's been overloaded quite a few times.

FOTSGreg said:

Liosse, Oh, yeah - and I will admit I was part of the heat a few more times than I'm comfortable with (yes, I can be an asshole at times and was).

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Consensus seeking can lead to groupthink, which is dangerous. There's nothing wrong with some informed "debate".

All right, I've got a couple of questions to add too.

How large a role will deception play in space combat?

(just a late night example) Say a missile that's designed to get half way there and then sputter and go out like it was defective, but kicks back in when it gets close enough to the target?

Or (I think this one might be a bit out there) an inert projectile weapon that launches a few in short order, but one is a drone with a laser battery and a couple of shots in it. Like it looks like the rest of them from the receiving end but shoots you as it passes by?

I'm interested in this. I came to the realization that space warfare would really be about costs in the end. destroying a ship or a planet would be very difficult, so you would try to do things that make the war too expensive for your enemy continue fighting before you run out of funds yourself.

And making the enemy paranoid would drive costs up greatly. if you have them wasting their shots on every dumb projectile you fire in fear one might be a drone you have them wasting money. And you'll only be able to use each strategy once. Then the word is out.

I know about RKVs but if you can accelerate them to that point, I'm pretty sure I can slow them down.

FOTSGreg said:

While it might be easy to see and detect a drive flare from a fusion source from a long ways away, how difficult is it to determine the course of the object emitting the fkare? Is it a matter of analyzing the flare's spectrum and thus determining if it's red-or blue-shifted and what percentage of a 100% red-or blue-shift it is to determine the object's exact course? Given modern computers and an actively emitting source, what's the time frame for such an analysis?

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Short enough to count as instant. At least the calculating time is. Depending on the accuracy of the sensors, a few seconds of observation to get an accurate vector might be required, though if we assume sensors built for the purpose, "instant" applies here as well.

Seeing the flare allows a good measurement of it's thrust. (And also to determine which class of ship/missile is generating it, and possibly a good guess as to which ship of a certain class it is, if it's been seen before.)
Measuring the acceleration of the object will allow one to calculate its mass. Measuring the current vector can be done directly anyway, whether one tracks the position of the object "itself" or just of the start of the flare doesn't make any difference. Red/Blueshift isn't really necessary, having at least two sensors spaced a bit apart (the wider the better though) allows simple geometric calculations of the position of the target. Do that twice with a bit of time in between and you have a precise vector. Do it thrice and you have a vector and an acceleration.

Nivarion said:

How large a role will deception play in space combat?

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As large a role as in any combat. Everybody tries to do it as best as they can. The combat environment just changes how you have to be deceptive. Space pretty much prevents hiding, or most forms of electronic warfare, it doesn't prevent you from outsmarting the other guy.

(just a late night example) Say a missile that's designed to get half way there and then sputter and go out like it was defective, but kicks back in when it gets close enough to the target?

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Well, that works exactly like you described it. So it looks like it's defective. Now it depends on the other guy what he does about it. He could ignore it or he could shoot it just to be safe.

Or (I think this one might be a bit out there) an inert projectile weapon that launches a few in short order, but one is a drone with a laser battery and a couple of shots in it. Like it looks like the rest of them from the receiving end but shoots you as it passes by?

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A Mass driver launching bomb-pumped nukes would be an example of this. A Problem with this would be that inert projectiles would normally be a lot smaller than a laser, but in general there's nothing wrong with this idea. Though you would probably want to supercool the laser before launching it, to make it practically invisible, instead of hiding it in a swarm of projectiles. Any projectiles this big would probably be shot down just to be on the safe side.

I'm interested in this. I came to the realization that space warfare would really be about costs in the end. destroying a ship or a planet would be very difficult, so you would try to do things that make the war too expensive for your enemy continue fighting before you run out of funds yourself.

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Every war is about costs. It's just a little more obvious in a realistic SF setting since there's more technology and less humans doing the fighting.

I know about RKVs but if you can accelerate them to that point, I'm pretty sure I can slow them down.

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Or just take them out with another RKV.

Have a look at the anime Banner of the Stars. Although it still has some characteristics often discounted in the discussio on AW, they do use "debris" that is really mines to achieve some fairly large casualty rates at some points.

FOTSGreg said:

Can you differentiate very bright drive flares in a group where the individuals are several seconds acceleration time away from each other from one another and thus obtain a count of the ships in the enemy group?

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Since there is no atmosphere in space, there is nothing interfering with sensors. You resolution is as high as your lens can manage. I can only mention again that we, today, can take shots of extrasolar planets. Compared to that, observing anything within a solar system is a piece of cake.

My thinking in this regard is based on the idea that ships with very fast accelerations would tend to space themselves far enough apart so that an accident or act of fate (say a lucky hit knocking out a ship's navigational sensors) would not cause the ship to ram a nearby friendly. In my case, maximum acceleration for warships has them up around 60kps so fleets tend to string themselves out over a long distance or a wide area.

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What would mostly determine fleet formation are the characteristics of weapons. I.e. keep enough distance so that one weapon won't take out two ships but keep close enough so that they can cover each other. Given the ranges in space, tens, or even hundreds of kilometres distance between ships aren't a problem.
Another important characteristic is whether ships can block each others field of fire. This is pretty much the reason why sailships were fighting in lines of battle, while during WWII ships did not really use formations at all. Now, spaceships don't need to adhere to formations to keep covering each other, the range of point defence is far greater than the size of any ship, and missiles will not be blocked by other ships. However, laser need line of sight, so it's reasonable to have no two ships obstructing each others line of sight to the enemy. A really paranoid fleet commander could even place his ships so that they get nearly 360° coverage. (I'd have to look up what is geometrically the maximum possible.)
Anyway, point being: unless a ship is being obstructed by any other object, it would be visible. And it'd be in the interest of any fleet commander only suspecting to be within missile/projectile range to keep his ships unobstructed.
While a ship could hide behind another ship/another ships drive flare, that would be enough to prevent proper identification, but not enough to prevent the other side from noticing that there's something hiding. For that, the complete drive flare of the hiding ship would need to be hidden as well, and that is much, much bigger than the ship generating it (and any similar ships it tries to hide behind)
Another problem is the sheer size of space. Unless the ships line up perfectly to hide from a sensor, they're still visible, since one ship only obstructs a very tiny portion of the sky. If they don't know exactly where the sensor is, lining up won't work. And if there's more sensors out there it can't work. Even when many ships, flying close together in a plane, provide cover for a few ships, they can only hide them from 180° of sky. Sensor drones are probably the most important drones to use in any kind of space warfare, and deploying a few for 360° coverage on any remotely interesting point would be the start of any engagement (in addition to the more conventional sphere around the fleet, serving as scouts). Whoever "owns" the solar system would probably place a few bigger and more permanent sensor installation wide above and below the ecliptic. While they'd be too far away for useful real-time data, they'd provide 360° coverage of the entire solar system, without blind spots. No-one hiding close to or landing on any planet unnoticed, ever.