What is the CEP of traveller beam weapons?

[warwizard]

Regardless of computer if I fire a weapon (lightspeed
) at a target and the CEP (circular error probable) of the weapon stays entirely on the enemie's hull even after calculating reaction time and target evasion, that shot will hit. (think fighter diving on the deathstar, every shot hits the deathstar, and makes little char marks on the surface)

This begs the question of what is the CEP of a Traveller beam weapon?
Let's start with IRL, a sniper rifle, fired from a machine rest with the best match grade ammo we can make, might have a 5 shot group of 3 inches at 1000 yards, or 4 cm at 1 Km. take that rifle and mount it on a spaceship with a boresight and aiming system as good as the machine rest on the ground, and we get a 40 meter CEP at 1000 Km and 1.2Km at 30,000 Km (1 hex) and at 80 hexes, that's a whopping 96 Km.

So now for some handwavium, lets try a rule:
Each TL advance halves the CEP of the previous TL
80 hexes:
TL7 = 96000m
TL8 = 48,000m
TL9 = 24,000m
TL10 = 12,000m
TL11 = 6,000m
TL12 = 3,000m
TL13 = 1,500m
TL14 = 750m
TL15 = 375m
TL16 = 185m
so even TL 16 can't hit a fighter at 80 hexes, and concidering that's a 16 second command loop at 80 hexes, the evading fighter is entirely outside of the CEP, now that Tigress at 80 hexes has a problem, it's hull is measured in km.

 

[HG_B]

Your starting analogy is flawed. Bullets flying through an atmosphere are acted upon by internal & external forces that don't exist and/or don't effect beam weapons in space. All of which affects its accuracy.

 

[warwizard]

flawed analogy or not

There is also crew members moving about the ship and fluids shoshing in tanks, and weapons impacting the hull to throw off your space accuracy.
In the TL 8 sniping task we use lasers to measure the total vectors of the wind along the bullet path by getting the returns off of dust particles and integerating the result, And I suppose the calculation will take into account evelation change and I guess that at TL 9 we'll map and use the local variances in the gravity field.

So let's discuss what would be reasonable assumptions. will a TL 15 beam weapon be able to place it's shot within a 1 meter CEP at eight light seconds? What would be reasonable?

I'm assumming a beam pointer is used that is coaxial with the weapon and exactly aligned and boresighted with the weapon, you shine the beam pointer and when you get a reflection off of the target you fire the weapon. Adjusting the aim point for your ship's movements and vibrations, and the target's radial vector and perhaps rate of change of that vector (1st and 2nd deriative) to give you your final aim point for the shot. Given an 8 second light speed delay for that 80 hex shot, how accruately can we point the beam weapon when making these adjustments? Should there be - DM's or + DM's for the firing ship's own evasions or lack thereof?

 

[HG_B]

So let's discuss what would be reasonable assumptions. will a TL 15 beam weapon be able to place it's shot within a 1 meter CEP at eight light seconds? What would be reasonable?

Yes, considering that the ships have inertial dampers & artificial grav so ship movement is not really a factor. Also, there aren't really any unknown external factors, as with a bullet. Even measuring wind along the entire path is imprecise.

The random die roll to hit takes into account any variables. IF the ship were totally motionless & given the computer systems (fire control) at the Trav TL's, it would probably be an almost automatic hit.

 

[sabredog]

The only increase in CEP there might be in a beam energy weapon is the way light spreads as the distance from the source increases. But given that these are lasers of extreme energy and not generally passing through any dispersant I doubt even that applies enough to make a difference.

As for any "jiggling" around the beam would do it doesn't matter - firstly, the agility factor (and computer) of the ship takes that into account since that is what supposedly makes gigantic warships in space defy the forces of inertia and mass so they can dodge lightspeed weapons.

Secondly, the weapon only has to impact the target for a microsecond to do damage and the energy imparted is great enough that even if your CEP was 100 feet is wouldn't matter because the imprecision of an abstract system like HG only makes the issue worse anyway.

You can't worry about CEP and such types of precision in a game that says if you have more than one battery you destroy each battery at a time, but if only one battery then only one part of it at a time, or that if the crew gets reduced by 1 point then all the rest of the crew can't use any weapons or perform damage control anymore (that's because a one non-critical factor hit could mean a crew of 9000 knocked them all the way down to 999 or less).

With so much slop who cares if you hit the left end of the barn's side - all that seems to count is that you hit it all.

 

[warwizard]

Yes HG_B I realize you do not want to deal with this level of detail and that's fine, I'm posting this to get a discussion going on the hard physics of these tasks.
There needs to be some weapon stabilazation system in place that maintains the weapon alignment on a target at least as long as the weapon can still bear.
Just how good are these systems, and their moment of inertia, and response times?
Are the calculations for the firing soloution made on the weapon mount, in the turret, in the nearby Master fire director or in the combat infomation center?
These systems don't just have to maintain the same alignment but also have to be offset for the target's predicted movement, so their moment of inertia and response times are part of your control loop delay, the more delay, the more time the target has to clear out of your CEP on their predicted location.

a crew member accelerating himself by 2 m/s to cross the compartment also accelerates the ship's hull in the oppsite direction by the ratio of his mass to the ship's, some of this acceleration will be spin, and some linear, and when the crewbeing decelerates the rotation and linear accelerations are reversed.

 

[warwizard]

The only increase in CEP there might be in a beam energy weapon is the way light spreads as the distance from the source increases. But given that these are lasers of extreme energy and not generally passing through any dispersant I doubt even that applies enough to make a difference.

As for any "jiggling" around the beam would do it doesn't matter - firstly, the agility factor (and computer) of the ship takes that into account since that is what supposedly makes gigantic warships in space defy the forces of inertia and mass so they can dodge lightspeed weapons.

Secondly, the weapon only has to impact the target for a microsecond to do damage and the energy imparted is great enough that even if your CEP was 100 feet is wouldn't matter because the imprecision of an abstract system like HG only makes the issue worse anyway.

You can't worry about CEP and such types of precision in a game that says if you have more than one battery you destroy each battery at a time, but if only one battery then only one part of it at a time, or that if the crew gets reduced by 1 point then all the rest of the crew can't use any weapons or perform damage control anymore (that's because a one non-critical factor hit could mean a crew of 9000 knocked them all the way down to 999 or less).

With so much slop who cares if you hit the left end of the barn's side - all that seems to count is that you hit it all.

It should be pretty clear by now that I'm way past the level of detail in HG, I'm using T4 and FF&S II, brilliant lances as the basis for this analysis, and am attempting to probe into the real physics involved in laying a beam on a target.
Back to the sniper anology, the sniper at 5km has opened fire on the tangos, and in the surprise round has downed 5 tangos with 5 shots, has reloaded and is engaging a fully alerted tango that is doing his best to dodge the fire. The bullet flight time is 5 seconds, and unless the tango makes a mistake and becomes predictable, he can dodge till he can reach cover or concealment, and has very little chance of being hit. In this instance the sniper's CEP is irrevalant, the time to target allows the target enough time to remove himself completely from the CEP. The sniper's buddy with the AR opens up on the tango and has a CEP of 20 meters, and sends 30 rounds downrange. The tango cannot remove himself from the CEP of the AR, and thus CAN be hit, with the hit chance being the exposed area of the tango's body compared to the area of the CEP times the number of shots fired. (Actually you should calculate the chances of each bullet NOT hitting for the true analysis).

 

[sabredog]

It should be pretty clear by now that I'm way past the level of detail in HG, I'm using T4 and FF&S II, brilliant lances as the basis for this analysis, and am attempting to probe into the real physics involved in laying a beam on a target.

I never played either of those so I can't form an opinion on those systems or their accuracy with far future weaponry. But I do think its reasonable to postulate that if you are advanced enough to make a meson T gun you can find a way to make it accurate over the distances involved in space combat without having to worry about being off "target" by a bit. Unless for some reason pinpoint accuracy is required?

Back to the sniper anology, the sniper at 5km has opened fire on the tangos, and in the surprise round has downed 5 tangos with 5 shots, has reloaded and is engaging a fully alerted tango that is doing his best to dodge the fire. The bullet flight time is 5 seconds, and unless the tango makes a mistake and becomes predictable, he can dodge till he can reach cover or concealment, and has very little chance of being hit. In this instance the sniper's CEP is irrevalant, the time to target allows the target enough time to remove himself completely from the CEP. The sniper's buddy with the AR opens up on the tango and has a CEP of 20 meters, and sends 30 rounds downrange. The tango cannot remove himself from the CEP of the AR, and thus CAN be hit, with the hit chance being the exposed area of the tango's body compared to the area of the CEP times the number of shots fired. (Actually you should calculate the chances of each bullet NOT hitting for the true analysis).

First...5km is too far for ANY shooter to try to hit even one target, let alone hit 5, reload, and then try to hit a 6ht ducking around. He wouldn't even hit the first guy unless he was very, very, very lucky with some sort of wonder weapon. And an operator with an AR at the same range will have a heck of a lot more CEP than 20m...more like, well, forget the whole thing....the bullets won't even land near the target.

To use a better analogy - if I'm reading you right - you're trying to figure out if the beams in HG are firing a lot in a turn or just once and you're actually rolling to see what that one hit does. That is the case, yes.

As for the fire control systems...well, they are centrally controlled batteries (that's why they all use one computer for the DM's and are organized in batteries even if one "battery" is a single weapon). There are no locally controlled fire control systems in HG unless the ship is 1000tons or less because the rules will then allow turrets to be used individually. And since they then have to be individually manned they are locally controlled with each having their own fire control....BUT...they still use the ship's one computer for the to hit DM's. It makes no sense at all but whatever - it's HG.

I think that the game as a whole is just too abstract for what you are trying to do without gutting it and starting from scratch.

As for the whole tiny crewman affecting the rotational mass of a multi-ton ship...well, that is impossible. Mass and inertia means the greater mass will not be affected by the lesser one to the degree you are describing. Besides, Traveller postulates reaction-less drives that propel gigantic ships of unimaginable mass through ridiculous maneuvers to dodge lasers while an inertial damper inside keeps the crew from splattering all over the bulkhead every time the computer says it's time to dodge another laser salvo. So your hypothetical crewman's mass effect would be negated by the damper system even if it could affect the mass of a ship. It's not like every time somebody bounces around the ISS in orbit they have to recalculate it's inertia.

 

[HG_B]

Yes HG_B I realize you do not want to deal with this level of detail and that's fine,

I just dealt with it. I realize that you don't have the level of physics EDU to deal with it or, you would have realized that your examples (crewmen bouncing around a Trav Starship) would have zero effect on gunnery.

that's fine.

 

[whartung]

He's not talking about the abstract game. He wants to have a better understanding of what is "supposed" to be happening.

But CEP is only part of the problem.

Another issue is simply being able to track the object, and that the gimbals, gears, and turrets have a fine enough granularity to track the object.

For example, a Scout Ship is 35 meters long. So, for argument we'll call it a 35m X 35m box. A dead center hit puts the beam at 17.5m X 17.5m.

So, put that ship at 30K km. Imagine a triangle. One end in the firing ship, the other is the Scout ship, and the final, itty bitty line is that 17.5 meter margin.

The opposite angle ends up being 0.0000334 degrees. And that's at one hex range.

That means when the turret/mirror/gimbal/whatever is tracking that object needs to be able to move with that kind of precision. It's obvious worse as ranges grow.

CEP has an affect on this. If you have a particularly large CEP, then you can have less precise tracking, assuming you're delivering enough power to the big dot. With our Scout ship, you're not poking holes in it, you're simply roasting it wholesale.

But that's clearly not the intent of the effect as described in TNE, where laser have a special exception to the normal rules for damage, being far far better penetrators, and less on if the actual large explosions meme.

This also implies millisecond burst of power, rather than "lightsaber" like cutting. That is, there's no description of a laser hit tearing long gashes in to the hull. Rather it's poking long deep holes, which implies a small CEP.

GDW came up with a nice handwave to explain how to make lasers useful at combat ranges, via the "gravitic focusing", and I think it's fair that if they can use gravity to focus the laser, they can use gravity to fine tune the targeting. That means that there are mechanical elements in the mount to point the weapon in the "general" direction (for assorted definitions and precision of "general"), and the grav focus mechanism handles the fine tuning, including acting as a dynamic lens to ensure that the laser CEP is the same throughout the effective range of the system.

So, in that sense, CEP "doesn't matter", the mount handles that problem for us. But also helps show basically how difficult deep space targeting etc. is going to be.

 

[warwizard]

thank you Whartung. Exactly the kind of discussion I'm try to garner.

I have thought about the problem of vibration and micro motion and it's effect on the end point of where that beam goes at the distance of 1.2 Million Km, and have concluded that they have to isolate the weapon from these effects. Whatever handwavium you want aside, (inertial dampers, anti grav or tractor the guns next to the ship) it only takes a very very small change at the firing end to make the shot miss by many KM.

The lasers could have a lot of power put into them but there is a TL cap to the energy so there is no chance of having the weapon spot be several Km in diameter AND have enough intensity to do damage. The beam pointers would be the one to de-focus to pick up the target then tighten the focus to localize the target. The bomb pumped lasers go the route of having hundreds of thousands of .1cm or shorter lasing rods to try to get just a few beams to hit the target, (and should be concidered for group hits by autofire if ships are reasonably close to each other, as in trying to dock.) If you want a kill shot just program your bomb pumped laser heads to hold off detonating till less than a KM from the target... 10,000 bomb pumped beam hits should ruin anybody's day.

Yes I grant the AR is not that accurate and does not have a sighting system capable of engaging targets at that distance, it was used as an example of the situation I think would be the case for the 80 hex beam shots. The pointing accuracy is just not there to put the beams on such a small CEP today. Using today's sensors, we can't even resolve the luner lander decent stages that were left on the moon, and that's only .5 light seconds.
I have proposed that the accuracy of beam pointing vary as a function of tech level and proposed an arbitary accuracy table and rate of improvement.

Others have stated that they want to see the TL 15 CEP at 80 hexes to be 1 meter at 1.2 million Km (80 hexes). OK, use that as one endpoint, how accurate should we concider today's TL-8 beam pointing to be?
The USAF airborne laser program can put a laser spot on a leading edge of a wing at 16Km, call it a CEP of .1cm at 16Km.

 

[mike wightman]

Emm - the Earth's moon is over 1 light second away.

You really are seeking the impossible. You can't use real world physics to explain the combat parameters used in Traveller because the distances involved are just too great.

 

[fusor]

You really are seeking the impossible. You can't use real world physics to explain the combat parameters used in Traveller because the distances involved are just too great.

Then I guess that means Traveller combat needs to be done at much shorter ranges if it's to be remotely feasible .

 

[sabredog]

Then I guess that means Traveller combat needs to be done at much shorter ranges if it's to be remotely feasible .

My players usually just jump out the locks with blades in their teeth and a laser pistol in each hand. They find that's just about short enough.

 

[Matt123]

If your beam laser had no error, you still have a problem.

Given you are targeting using information that by the time 'impact' occurs is several seconds old, pin-point accuracy on this old information will guarantee a miss.

To get a hit at lightsecond ranges you need to cover the area the target could be in at the time of impact. A better firearm analogy is a squad machine-gun. Although at high tech levels I'd accept that the area coverage would be calculated and computer controlled, not random.

 

[aramis]

your CEP needs to be less than (Accel in m/s/s)*((2 * distance in LS)^2) m simply to track the target, as your tracking data is (distance in LS) old, and your beam takes the same time to hit. Note that, at the ranges we're talking, ca 90k km, a 20x20m cros section is a tiny fraction of a degree... 1 second of arc is 4.3km or so...

1 arc-second (1/360 degree) accuracy at 1 BL hex is an error of up to 1454 meters. To hit a scout at that range, you need an accuracy of around 14 meters... 0.01 second accuracy. And to cous a beam at that range, a similar but tighter level of accuracy from a moving mirror. And you then also need to predict 0.2 sec ahead of your data to hit. (but at that range, a 6G ship is only 2.4 meters from your data..., and at 3 hexes, only 5.4m).

Agility is a crock.

 

[HG_B]

Agility is a crock.

Did this calc years ago and laughed. The spherical area in which even a 6G ship "lives in" in small time segments is VERY tiny. Especially for a star ship.

 

[warwizard]

Agree, the 6 g ship gets nailed 100% of the time at short range, but concider if you will the point defense task of shooting down a laser head missile that is evading at 30 g's and is a .2m diameter target at 2 hexes.

Time delay between the sense data and beam arrival is .4 seconds +fire control delay + turret movement delay. I'll take a guess and call it .41 seconds.
300m/s *.41s/2 = 61 meters. That's a 122 meter diameter of target probability. Looks like you need to fill the skys with beams and try to get lucky.

You might use a fusion gun and de focus it, (fusion guns are NOT lightspeed, so they have to be fired using even older data) all we need is 1 DV to kill the missile, they are not usually armoured. For lasers dial the power down and up the ROF to one or more shots per second, you have about 10 seconds to nail it before it gets to 1 hex and goes boom, and that's going to need thousands if not tens of thousands of shots to get a decent chance of nailing the thing.

Ok next task is final protective fire against the KK missile at 3000 km. Here the missile is 40 g, but is using 24 g to negate your 6 G evasion, leaving 16g for it's own evasion. lightspeed delay is .02s + the .01s for your fire controls as before.
160m/s *.03s/2 =2.4 meters, target diameter is .2m in a 4.8 meter diameter target prossiable area. This task is 3 orders of magnitude easier than shooting down the laser head, only needing about one hundred shots to give a good chance to nail it, and a fusion gun comes into it's own here, defocus to 10m or so and it's 50% lightspeed beam scores an auto hit. The KK missile is going to still hit at this point but in small bits that may be defeated by your armour. Some number of .1-10 Kg chunks instead of a 250 Kg piece, each chunk DV is in the order of 100 DV, (in the order of, means the DV of any given chunk might be as low as 10 DV or as high as 1000 DV).

One nod to cannon here, the final protective fire against the 1/2 dton 8 g HE missile of cannon is damn near an auto hit.

 

[Dragoner]

One should take into account that ships would have active and passive systems to avoid weapons targeting. Aircraft have it now, it's largely unexplored in Traveller, but to assume it isn't there would be illogical. Ships aren't firing at a visual target, they are firing by their sensor readings beyond visual range. Firepower would assume that enough shots would hit to be effective, thus there would be a calculated hit to miss ratio.

 

[warwizard]

One should take into account that ships would have active and passive systems to avoid weapons targeting. Aircraft have it now, it's largely unexplored in Traveller, but to assume it isn't there would be illogical. Ships aren't firing at a visual target, they are firing by their sensor readings beyond visual range. Firepower would assume that enough shots would hit to be effective, thus there would be a calculated hit to miss ratio.

Agreed, but that's a different discussion of sensors, jammers, decoys, and deception. Hop on over to the BITS site and look at their mayday and how they treat the sensors jammers and such.