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So, why are lasers missing?

Carlobrand

SOC-14 1K
Marquis
We've talked about this before, I think. Take a ship laser, aim it at a target as big as an office building at a range of about a light-second. In the two seconds it takes for the light from the target to reach you and your own shot to reach him, a target doing 6G can move 120 meters on the axis of its engines (or 30 meters perpendicular to that if you like MT Starship Operator's Manual's look on things and port that over here). At a half light-second range, we're talking 30 meters on the engine axis (or 7.5 meters perpendicular).

At a light-second, an object 1.5 kilometers long covers a bit more than an arc-second. An Azhanti High Lightning's shortest dimension is about 1/40th of that, it's longest dimension is a bit under 1/4 of that (4/15ths, actually). Takes 3.65 seconds for an AHL sized ship doing 6G to change its vector by its entire length. I'm not sure how accurate our modern tools are at centering something on a target at that fine an angle, whether they can move quickly enough or accurately enough to track an object changing vectors at a quarter arc-second per second, but when we're talking ships at TL9-15, I'm pretty sure somewhere along that line they acquire that level of accuracy.

So you aim your one laser, you shoot ... and you miss. With no agility, you miss 58% of the time. With full agility, you may have no chance at all. How did you miss?

Well, maybe you didn't.

Let's say a laser hits pretty much whatever they're pointed at within a light-second or so, at least on the scale of a ship. Overall, you miss 58% of the time, but when you hit, you get a surface damage result: a weapon, a bit of fuel, maybe some drive damage. You don't penetrate, you can't reach the computer, can't hit the power plant or the jump drive (which are fairly large targets within the ship), can't hit stuff within the hull. Basically, sometimes you get lucky and hit a weapons port or turret ring, or the exposed portion of the maneuver drive, or a hit over a fuel tank will radiate heat from the hull into the tank and force the tank to vent fuel to keep from rupturing, but you're not burning through the hull even on an unarmored ship.

The ship's moving as you hit it - as much as 30 meters during a one-second burn - and it might also be spinning to distribute any hit over a larger area, and your ability to penetrate depends on your ability to track his changes with fraction-of-an-arc-second adjustments over the course of the burn. So, most of the time you're hitting, but the ship's hull disperses the beam without effect. You only get an effect when you're lucky enough to hit something exposed, like that weapons port, or hit over a fuel tank. In that paradigm, agility is less about dodging the hit entirely and more about making it harder for them to get a bead on the vulnerable parts of your ship's surface. With a one-second delay, holding a beam accurately on something as small as a turret is a lot trickier than holding it on something the size of a ship.

Why would a computer rating affect that? I don't know. Maybe the computer controls some sort of camouflage pattern on the ship's surface intended to make it more difficult for those targeting the ship to discriminate between turret and flat surface, but that shouldn't save the maneuver drive or fuel tanks.

On the subject of lasers, I'm about set to say that that shipboard lasers are x-ray lasers at TL7 and gamma lasers at TL13, at least IMTU. We're doing x-ray lasers now, though in an experimental way and at vastly lower power levels, so TL7 might be pushing it but they'd certainly be a possibility for TL9. I figure I can justify a 2 cubic meter 250 Mw ship-mounted laser to be able to achieve it, and it makes the range thing easier.

Yes, I'm a bit too compulsive about verisimilitude; that's my curse, though it does offer some interesting educational benefits. Yes, there've been suggestions about accomplishing light-second ranges at lower wavelengths with gravity lenses, but I can't see where the power for that comes from when it's delivering 250 MwS at the target.

A useful side effect is that it gives me a handy explanation for why lasers aren't useful for attacking surface targets from orbit: x-ray is blocked by atmosphere. (I have enough trouble keeping those minor colonies alive without worrying about them getting carved up by orbiting pirates trying to pry a ransom out of them.) It also limits the application of ship's lasers groundside, if you have players inclined to indulge in such things: half-value layer in air for photons at 100 KeV is about 35 meters, which I think means you've got a 125 million joule flash of heat and light going off on a line 35 meters out from the laser turret, hot enough to cause lethal burns out to 14 meters perpendicular to that line (and out to 10 meters for the next 35, and out to 7 meters for another 35, ...), but you're not actually likely to do damage to something you aim at unless it's within about a football field's length of you, and it's probably hot enough at the point of emission to damage the laser emitter. That last one is likely to discourage players from trying to carve up the starport from their ground berth: you might fry a boarding party at close range but you won't do a lot more than that, and you'll kill the weapon in the process.
 
That's the deal from my perspective- most shots are a hit, but many don't effectively penetrate to do meaningful damage.

I think a lot of evasion going on has to do with thrusters pushing the ship a few meters one way or another to present a deflection shot, i.e. along the edge of the ship where the hull becomes a lot tougher to punch through.

Not quite like kinetic penetration issues, but assuming hulls have some sort of reflec/heat dissipation built in, more thickness should work out to better.
armorangles.jpg


Agility would be firing about altering the axes of the ship and randomly accel in differing directions from the main inertial course, giving a larger targeting volume the laser has to cover and potentially generating less concentrated fire for again effective penetration.

Also, for something like the AHL, there would be lots of rolling and presenting different aspects.

I've always figured the computer differential is more about EW, especially performance between tech levels (unless there is something like Evade-10/Predict-10).
 
I know it's not CT, but in TNE that was indeed the official answer, you smack the beam on target a lot more but most of the time it doesn't really do any damage.

In addition to the angle changing the effective distance a laser beam would have to drill through the armour, it also changes the 'footprint' of the beam. So if you hit square on, you have a circle beam, but if you hit at the 50 degree slope shown above, that beam is no longer a circle, it's smeared out into a long ellipse, and the power is dissipated across the whole footprint. If you ever played with a flashlight in the dark as a kid, tilting the thing, you've seen the effect.
 
So you aim your one laser, you shoot ... and you miss.
A combat round is long. You don't just fire once, but several times.

You know roughly where the enemy is, but you don't know exactly he is or will be when your weapon intercept, so you fire a spread or pattern, something like depth charges against a submarine.
 
See that all you say here would also apply to PAs and Mesons, as we can asume they have laser designators...

Maybe all I say is crap, as I'm not an expert (to say the least) with laser designators, but:

  • Ship combat is fought over visual range, being based on sensors readings instead.
  • Electronic noise is going to be quite strong (radars, ladars, ECMs, many laser designators pointing eveywhere, sand covering everything at irregualar intervales, etc...)
  • Your own ship is not static, being assumed to also be using its own agility

Of course, improved computers may compensate for all of this, hende the computers modifiers to to hit rolls...
 
See that all you say here would also apply to PAs and Mesons, as we can asume they have laser designators...

For Meson guns, I don't think the angle would affect it as much - if the relativistic particles are decaying and releasing energy at point X inside the ship, I don't think the relative angle matters as much. The 'boom' bypasses the armour any way the target is tilted.

It could be that way for PAs, I don't recall if the 'official' source of damage is strict energy density, or if it was supposed to have some sort of Star Wars "Ion Cannon" effect that takes out a target that way.

I don't think it would matter that much for a target designator - if you can see the dot, you're good on aiming, it doesn't matter much if the dot is perfectly round or smeared out a bit.
 
Why would lasers always hit?

All measurements have limited precision. The sensor reading of the enemy position is a measurement.


Current radar seems to be limited to a precision of about 0.05°. If we assume the Imperium can build ten times better sensors with a precision of 0.005° that is still an uncertainty of 26 km at 300000 km range. The only thing we know is that the target is likely somewhere inside a circle with a 26 km radius, but possibly a bit outside.


Our ability to aim the laser weapon also has a limited precision. A turret must be able to turn and elevate the weapon to within 0.0000002° to have a precision of 1 m at a range of 300000 km. That means positioning the tip of the weapon with a precision of 3 nm as you are tracking a manoeuvring target. As a comparison a human hair is 20000 - 200000 nm thick.


In conclusion: Hitting a target at 300000 km is not trivial, much less a manoeuvring target...
 
For Meson guns...
You need a full 3D target solution, not just the 2D that lasers can use. A blast that is slightly off for distance, and keep in mind that's not a very large number in meters even for the "big" ships of Traveller, will be encountering the armor instead of the soft interior.
 
Once again looking at the EPs transferred to a black globe indicates what a hit actually represents energy wise.

The elephant in the room is and always has been, how does a ship hull cope with all of those incident EPs without magic heat sinks?

Even if the ship is spinning to avoid spot hits, it is still going to be heated - rather a lot by a factor 9 laser battery.
 
You need a full 3D target solution, not just the 2D that lasers can use. A blast that is slightly off for distance, and keep in mind that's not a very large number in meters even for the "big" ships of Traveller, will be encountering the armor instead of the soft interior.

If no one has spotted you yet, a (relatively) low-powered laser rangefinder pulse would work nicely for that.

If everyone knows you're there and you don't care if they see you, radar is great for ranges.

In the middle of combat, there will be a whole lot of usable data to give ranges to target.
 
The elephant in the room is and always has been, how does a ship hull cope with all of those incident EPs without magic heat sinks?
How does Traveller starships do anything without "magical" heat radiators?

Even if the ship is spinning to avoid spot hits, it is still going to be heated - rather a lot by a factor 9 laser battery.
One EP is 250 MW for twenty minutes so 300 GJ.
A factor-9 Laser does 9 × 1 EP or 2.7 TJ.
A 1000 dT ship with armour 5 has a hull of about 310 × 123 × 0.26 ≈ 10000 tonnes (according to MT).
A 1000 dT ship is a sphere of 14000 m³, so radius 15 m, so surface area ~2800 m². Armour 5 is about 113 / 7 ≈ 16 cm thick so 2800 m² × 0.16 m = 448 m³ at 15 tonnes/m³ is 6720 tonnes (according to Striker). Close enough i guess...
Steel has a specific heat of about 0.5 kJ/kgK.
It would take 8000000 × 0.5 = 4000000 kJ = 4 GJ to heat a 8000 tonne hull 1 K. 2.7 TJ would heat the hull 2700 / 4 = 675 K.
A hull with a surface of 2800 m² would radiate σT⁴ or about 5.67 × 10⁻⁸ × (950 K)⁴ × 2800 m² ≈ 130 MW so would take hours to cool down.

But then the waste heat from the power generation and use would melt the ship quicker than enemy fire...
 
If everyone knows you're there and you don't care if they see you, radar is great for ranges.
Radar has a problem with very long ranges. The reflected signal is proportional to (among other things) Power × Aperture / Range⁴, if I have understood it correctly.

To make a radar that can detect small spacecraft at 300 000 km range would take prodigious amounts of power and/or huge antennas.
 
A combat round is long. You don't just fire once, but several times.

You know roughly where the enemy is, but you don't know exactly he is or will be when your weapon intercept, so you fire a spread or pattern, something like depth charges against a submarine.

I've heard that claim. It's hard to play agility any other way since otherwise you'd only need to divert power from engines for a second or two every 20 minutes or so and there'd be no reason to subtract the ship's weapons power to calculate agility, not given their battery tech. The thing is, I know exactly where he is. He's hanging out in the middle of space glowing in infrared like a glowbug in the night. That being said, there's something about hitting 40 times and getting only one damage result out of it that bugs me.

The black globe makes an interesting case. A ship under full globe is a pretty simple Newtonian firing solution if you had eyes on before it went under globe, so you ought to be able to saturate the globe pretty quickly, and that doesn't seem to happen. On the other hand, the jump drives need two full turns output to work, and if that's coming off the black globe, that does indeed suggest the EP it gets from that laser counts for many, many hits during that turn, essentially the laser's full input for 20 minutes, rather than one short blast. However, that makes the HE missile a rather wicked warhead, putting out as much power as a laser in 20 minutes of operation, 36,000 gigajoules - unless we're saying that it represents something like 72,000 missiles. That's a point where you just sort of sigh and move on, because there's no making sense of that piece.

Still, whether it's once or a hundred, you're still ending up with only one really effective hit, and that's what I'm focused on at the moment. The rest of them just seem to be warming the hull up a bit.
 
Once again looking at the EPs transferred to a black globe indicates what a hit actually represents energy wise.

The elephant in the room is and always has been, how does a ship hull cope with all of those incident EPs without magic heat sinks?

Even if the ship is spinning to avoid spot hits, it is still going to be heated - rather a lot by a factor 9 laser battery.

How much is fuel tanks just underneath the hull, beyond that black globe (shpere!)?
 
The thing is, I know exactly where he is. He's hanging out in the middle of space glowing in infrared like a glowbug in the night.
Quite, but you do not know EXACTLY where he is, only almost exactly where he is. Everything has limited precision. That almost is a severe problem at a range of 300 000 km.

E.g. good human visual acuity is about 0.025°. That means that at 1 km range the smallest detail you can see is about 0.5 m. You can see smaller objects if they are bright enough, but you cannot see the difference between a 0.1 m and a 0.2 m object. In the same manner you can't see the difference between a 0.1 m object and the same 0.1 m object displaced 0.1 m to the side. So, even if you can see the object if you fired a laser beam directly at it you might miss.


The black globe makes an interesting case. A ship under full globe is a pretty simple Newtonian firing solution if you had eyes on before it went under globe, so you ought to be able to saturate the globe pretty quickly, and that doesn't seem to happen.
Agreed, and that is exactly what happens.
 
...E.g. good human visual acuity is about 0.025°. That means that at 1 km range the smallest detail you can see is about 0.5 m. ...

Except that we're not dealing with human vision. We're dealing with technology. Specifically, we're dealing with the ability of sensors to determine a target's position to fractions of an arc-second, and of weapons systems to aim weapons with the same degree of accuracy, within a period of time short enough to hit the target before it can alter its position enough to avoid the hit.

Now, I will be the first to admit I don't know the present state of technology with respect to such abilities. I know Hubble can pick items out at a tenth of an arc-second, but that doesn't mean something similar to a Hubble could deliver the information quickly enough to be useful in battle, nor do I know how accurately things can be aimed with current technology. However, for the most part we are not dealing with current technology - we're dealing with a speculative future technology where people are successfully aiming laser communicators across similar distances. While similarly targeting an evasive hostile would present different challenges, that does at least tell me the tools can be aimed with extreme precision. That only leaves the question of whether sensors at TL 9, 10, 11, 12, 13, 14 or 15 are able to deliver precise enough information quickly enough to be able to take advantage of that precision. Frankly, I don't see any reason that they wouldn't be.

I remain uncomfortable with the view of ships scoring dozens of hits in a turn. There are very good arguments for the scoring-dozens-of-hits-in-a-turn paradigm - including the argument I just now made, that it should be no great challenge for future ships to do exactly that. Certainly it is strongly implied in the way the black globe operates. However, there are some quirky problems with that paradigm. As you point out, things get very hot very quickly. Also, missiles become a real puzzle: either the HE missile is delivering a fantastic quantity of energy, or there are enough HE missiles flying around in a turn to seriously challenge the notion that matter cannot be created from nothing, because those ships just don't have storage for missiles on that scale.

I can't help thinking we are compelled to turn to the one-shot-per-turn paradigm simply for the sake of practicality, however illogical it might otherwise be. That or amend things a bit so the HE missile doesn't do anything of consequence to a black globe - and come up with a really fantastic way of dumping waste heat quickly so we don't turn our ships to slag after one round under a dreadnought's laser batteries.
 
I just recently looked up Hubble's angular resolution on the CCD. 0° 0' 0.1"

https://www.spacetelescope.org/about/faq/

I've seen mention that the scope has a potential for 0.05" mathematically, but the CCD isn't up to matching the diffraction limit of the mirror-set.

That's around 77 kAU per pixel at Andromeda...
Math inside the spoiler:
0.1" = 4.8481e-7 radians
Distance to Andromeda: 2.5e6 LY
convert to AU × 63241.1 = 1.5810269e+11 AU
1.5810269e11 × 4.8481e-7 = (1.581269× 4.8481)e(11-7) = 7.66497651389e4
= 76649.7651389 AU.

Keck runs "0.04 to 0.4 arcseconds for individual telescopes, depending on target and instruments used" (per the wikipedia entry).
That's only dividing the spot area by 2.5 or so...
 
I'm reminded of an SF novel I read many moons ago. It mentioned the reason that all their equipment was high gloss shiny and brightly colored, rather than drab camouflage, was that reflecting beam weapons was more effective than hiding.
 
I'm not digging into the numbers now, but I have been assuming that the average ship has an array of small transmitters, antennae and passive sensors located all over the hull, so you get a VLA effect AND hull hits from combat or environmental damage does not blind the ship.

As such, I am assuming the ship size itself represents a general capability for sensor precision, coupled with computing power.

I've also taken a cue from the TNE ship rules and consider the possibility of deploying a separate folded antennae, something like a spacegoing towed array sonar.

Of course such an array is fragile and would reflect a larger size, making the deploying ship much more detectable. A deployable sensor array that drops from the ship might help, but it would definitely point interest in the general area, or any signal traffic coming to/from such an array.

Another point is that radar is not the only EM frequency in play here. IR emissions from power generation, engine and/or weapons use would be sure beacons to detection and ranging. The various gravitic and neutrino sensors would also be a data point, along with active laser which would presumably be in play in battle.

Optics may or may not be an issue, depending on whether a VLA approach would actually work. I don't have enough expertise to say one way or another, the principle should work conceptually. Hubble can pick up 194 foot wide objects at UV and 300 foot for visible light on the moon, effectively 1 LS for our purposes and good enough for larger ships.

But the potential 'signal return' may just be too little for practical reliable use against ship sized objects at 1 LS in all situations (outer planet space with less stellar reflection, excessive background like a nebula or planet, blacking out of the ship, etc.).

In any event, there are no doubt similar issues with resolution with each one of these- however the combination should make for a lot more information to stitch together an accurate fire solution much more then any one sensor package would provide.
 
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