Effective Combat Range in Space

[doom3607]

What factors affect it? And why, and how so?

Ah, sorry. To elaborate, I'd like to try my hand at writing an original fic, and I'm trying to get advice on how to make combat at a certain range reasonable in space. so, where better to ask than SDN?

The factors I could think of are ECM, point-defense, and the vulnerability of the weapon system to dodging as compared to the target's ability to dodge. Anything else anyone can think of?

[KlavoHunter]

Sensors: Are they limited by the speed of light, or do you have FTL sensors of some form?

[doom3607]

I'm thinking there are FTL sensors, but that just means they sense FTL. They can see the enemy coming in, but the instant they go STL, that sensor is useless.

[Ahriman238]

Sensors are huge, as with any laser, particle beam or projectile weapon you have effectively unlimited range. They will keep moving until they hit something.

However, absolute range is not the same thing as effective range. Effective range being defined as the point where you can hit them more often than you miss. There can be a huge gap between the two numbers, in archery or with firearms, but especially in space, where distances are commonly measured in the millions of miles.

This gets even worse when you are far enough away to count as multiple light-seconds, or even light-minutes because (barring magic FTL sensors) you aren't seeing where your enemy is, but he was. Plus at those ranges it will take several seconds or minutes for even lasers to reach the target, throwing off your aim even more, to say nothing of what happens if your weapons are actually slower than light.

[doom3607]

That's why the tread name specified effective range as, in theory, any kinetic weapon has a nigh-infinite theoretical range. I'm interested in it being useful. And I just said no magic FTL sensors for STL, and combat is impossible in FTL.

[Elheru Aran]

Well. The point is, you need to establish parameters. How close can an object be before x weapon can hit it more than 50 percent of the time? How close can said object be before x weapon can hit a specific target upon that object more than 50 percent of the time?

More to the point, how good are your sensors and aiming systems?

There are fictional universes where 'effective range' is positively Napoleonic wet-fleet (hundreds of feet), and then there are universes where range is routinely in the light-minutes. It's all in knowing where your target is and whether you can hit it. Without knowing more about the capabilities of your fictional technology, we can't do anything other than go "well if you throw a rock at x velocity it'll go y distance in z seconds, adjust for windage", et cetera.

[Ahriman238]

Ah, sorry. Was in a similar conversation in ST V SW and sort of carried it over. Mea culpa.

Well, if you have an FTL comm you can cheat a bit by having fighters, remote probes, or stealthy observation craft draw close and relay targeting information. You'll still have to lead the target by a generous margin and pray he doesn't alter course, but there will be less guess work involved.

Failing that, you could still still acheive kills at very long range by either mounting so many weapons you can still probably acheive a hit with old location data and only a general estimate of where they are, or having multiple ships fire on it's most probable locations for both altering and holding course. The latter has the additional advantage of allowing ships to coordinate their sensor data and triangluate on the enemy's position. However, there a comes a point where neither option is really feasible, even in a best-case scenario it's inefficient.

So the further you get, the greater the delay of your information, the older your intel is, the worse your aim becomes. At a range of a few light-seconds, you should be able to compensate alright. Maybe up to a full light minute, though a lot can happen in a minute, and your enemy should have two before your shots reach.

[Ahriman238]

Ah, sorry. Was in a similar conversation in ST V SW and sort of carried it over. Mea culpa.

Well, if you have an FTL comm you can cheat a bit by having fighters, remote probes, or stealthy observation craft draw close and relay targeting information. You'll still have to lead the target by a generous margin and pray he doesn't alter course, but there will be less guess work involved.

Failing that, you could still still acheive kills at very long range by either mounting so many weapons you can still probably acheive a hit with old location data and only a general estimate of where they are, or having multiple ships fire on it's most probable locations for both altering and holding course. The latter has the additional advantage of allowing ships to coordinate their sensor data and triangluate on the enemy's position. However, there a comes a point where neither option is really feasible, even in a best-case scenario it's inefficient.

So the further you get, the greater the delay of your information, the older your intel is, the worse your aim becomes. At a range of a few light-seconds, you should be able to compensate alright. Maybe up to a full light minute, though a lot can happen in a minute, and your enemy should have two before your shots reach.

[Ariphaos]

Interferometry sensors around a spacecraft in theory could have an angular resolution roughly equal to

R = l/D

R = radians, l = wavelength, D = distance between two sensors.

So if D is ten meters and l is 200 nanometers (near-UV), you can resolve such wavelengths at about 4 milliarcseconds. But if the wavelength was 1,000 nanometers (near infrared), the limit would be 20 milliarcseconds.

This can be important - stealth may be no easy feat in space, but that isn't the end of the story. If you can eliminate high-frequency emissions, you'll be that much harder to target.

That said, there really isn't a range limit. It's not out of the question for a dyson swarm to focus planet-baking energy on a target several hundred light-years away. They'll miss due to light-lag and gravitational perturbations, not an inability to focus.

[avatarxprime]

I'm thinking there are FTL sensors, but that just means they sense FTL. They can see the enemy coming in, but the instant they go STL, that sensor is useless.

What is the nature of your FTL drive? Can it be outfitted on a missile and be cost effective? How about a semi-sacrificable torpedo boat? These things matter in regards to how you engage in combat when lightspeed lag matters. If the former, FTL missile spam time. If the latter, you do your best Tom and Jerry impersonation during combat as your ships switch from missile destroyers to carriers that launch attack craft at the enemy while running away from that enemy's similar craft.

Well, if you have an FTL comm you can cheat a bit by having fighters, remote probes, or stealthy observation craft draw close and relay targeting information. You'll still have to lead the target by a generous margin and pray he doesn't alter course, but there will be less guess work involved.

Even without an FTL comm that system can still work, look at Andromeda. You send a bunch of remote targeting drones out and then withdraw to a safer distance and launch missiles. The drones handle final targeting of the missiles once they reach communications range.

[doom3607]

...Which sounds remarkably similar to Honorverse Apollo when being run by ships that can't run them directly from their own computers. Like the battlecruisers in the latest book, blowing up that Solie task force.

OK, exposition time- it's the (late) twenty-first century, and humanity's got small colonies going on mars and Jupiter's larger moons, and scientific bases elsewhere, as we finally got fusion working so Orion drives became viable again. But fusion this time. Someone finally got something along the lines of a quantum 'entaglement' com going -it isn't really, because it has 'frequencies' which aren't really frequencies, but close enough- and is cruising the 'frequencies' as a form of SETI. And lo and behold, he hears a signal on one of them.

Cut forward a few years. It's a Contact-style message, basically a huge engineering diagram. We can build it, but we really don't know what it does. Fortunately, once we suceed in decoding a certain bit that looks like an explanation, we find out. Simply put, it says, more or less, "This is an FTL drive. Here's how to use it." Cue massive skepticism... until a ship winds up flying from the Earth/Moon L1 point to Jupiter at ~1000 C.

Skip forward a few decades. Humanity's got a few interstellar colonies going, we've met an alien race on one of our scouting missions, and all is going pretty well. The FTL drive lent itself quite nicely to modification to an FTL detector, so we can see stuff coming in. Then a scouting fleet stops sending back messages. And that's where the thing starts.

Ok, back to the tech- FTL drive is about twice the size of a school bus and requires about 1 GW of power while operating. FTL sensors, the best we can build see about five light-years out. And our FTL comm is similar to our radio now, as in, we can do short range- in this case Earth can talk to Alpha Centauri, but nothing else, at least for a shipboard transmitter- but we can recieve from much farther. Depending on the size of the reciever. So messages from ships back to Earth are usually sent back by (very large) messenger drones. They're basically an FTL drive, a hard drive, a radio, a fusion generator, and the stuff you need to use some of that output for thrust. Basically venting a bit of the explosion behind the drone. That's how ships do it too, at this point.

I'm hoping to find a reasonable way to get very short effective range, I.E. a thousand kilometers being a long-range engagement. Any ideas on that? And thanks for all the help so far.

[someone_else]

Sensors are huge, as with any laser, particle beam or projectile weapon you have effectively unlimited range. They will keep moving until they hit something.

Uhm, no. Unguided projectiles are basically useless beyond a few dozens of Km. Lasers and particle beams do have a max range. The former is in practice a kid focusing light with a lens to burn ants. You stay too far from the focus point and you do nothing. The latter dissipates early due to the fact it must follow the inverse-square law (lasers do not), and other things like temperature and atomic mass of the ions you are shooting.

Guided projectiles are a waste of mass if your enemy can FTL around with ease.

[doom3607]

That they can't, usually. unless you're stupid enough to start a fiught outside the jump limit, in which case, yes they can. But jumps are only accurate to within ~1000 km.

[Hawkwings]

Effective range should be something like inverse-square proportional to how well ships can maneuver. If you can't change direction very fast, then you can predict trajectories a lot better and fill space with kinetic penetrators. If you can change direction quickly, then light-second range is probably the farthest out you can reliably hit someone.

If you want to get within thousands of kilometers, go for good maneuverability, good ECM, weak lasers (that are good at shooting down missiles), and the preferred weapons being dumb KE bricks and guided missiles. If you've got 10km/sec railguns the best you can probably do is 300km effective range if you stack them in batteries and fire a lot. For reference, the US Navy's current railgun that they're testing is supposed to have a muzzle velocity of 5.8 km/sec.

[bz249]

If jumps are accurate within 1000 km, well than having weapons and targeting ability above that range is pretty much an overkill. The enemy can jump to direct proximity of our assets, so the combat should focus on attacking/defending those instead of doing stunts in the deep space. Anyway this also means that ship to ship combat is very likely happen in the orbit where planetary mass, magnetic field, background radiation etc. might play a significant role. Thus a very noisy environment, it is better to have sensor platforms which excel under those circumstances.

[doom3607]

Yeah, that's where I thought combat would be happening too. Considering that gravity needs to be under a certain net field strength that I'm still working out, if you're close to a planet, you can't jump, and all is well. But that's the only condition on entering a jump, and you can exit anywhere. Like, say, inside the atmosphere of a planet- if you're jumping crazy close in. And if you don't just burn from doing that.

That's.. pretty much what I thought I'd need, hawkwings. Although the laser angle didn't occur to me, thanks. Bolo-style fusion guns (nuke in a barrel) work, maybe?

[Hawkwings]

Does it propagate at lightspeed, or a significant fraction thereof? The advantage of lasers is that they're fast, so even said bolo gun fired at 1% of lightspeed, it's still covering 3000km in a single second. That's plenty damn fast for the sub-1000km range we're discussing, and would be a game-changer.

And if you're jumping into atmosphere then you're crazy. What if you miss by 100km and end up underground?

[doom3607]

That's why you'd aim for ~1010 km above the surface. Or a gas giant. Or you're desperate.

And I have no idea how fast Bolo shots are, but as I recall, even with insane Bolo aiming, they can miss at ranges of a few kilometers.

[Eternal_Freedom]

And if you're jumping into atmosphere then you're crazy. What if you miss by 100km and end up underground?

Or...you fly on a tangent to the planet's surface, so if you overshoot byt a hundred m you just end up a bit further away.

[doom3607]

Umm... you end up anywhere within about 1000 km of where you were aiming for, any direction. Flying on a tangent doesn't help.

[Eternal_Freedom]

Oh...well in that case..aim for high orbit and pray you don't miss

[doom3607]

Exactly. Fortunately, if you do wind up in the surface you can still survive as long as you can survive smashing through it. Or just open fire the instant you begin to exit FTL.

[Eternal_Freedom]

That second option sounds devastating if you exit over a city

[doom3607]

That would be... fun...

But seriously, a superdreadnought could probably make it through half a kilometer of crust if it went to maximum-rate fire with all weapons the instant it started to leave FTL. And a supermonitor... Lemme put it this way. At the start of the story, the biggest ship are the SDs, which are maybe 5 kilometers long and armed and armored to an insane extent. They kill small fleets for target practice. A monitor is maybe 15 kilometers long and proportionately broad and tall, is even better armed and armord proportionately, and is centered around a mass driver that accelerates a 20 kg slug to .2c for a yield of about nine megatons. Once. Per. Second. And I refuse to say how badass supermonitors are.

[Jawawithagun]

How precise are the servos for your rayguns? How quick react the shock absorbers in their mountings?
The further away a target is the smaller the angle that covers it and more problems you get from unwanted vibrations due to say, people running around.