One of the most annoying holes in GURPS Ultra-Tech is the comparison between armour-piercing or shaped charge warheads with both heavy battlesuits and tanks. The DR values given for either of these are woefully inadequate at stopping even the lightest shaped charge or HEMP round. I was reading through the entries for tanks, trying to find some justification for why the main battle tank doesn't have enough DR to stop being ripped to shreds by a shoulder-mounted HEMP round. Then I found it: the tank has a strike laser on the turret for point defence. This makes sense! If you can stop missiles and anti-tank weapons from even hitting you in the first place, you don't need to lug around armour heavy enough to stop the damage. Well, that's all well and good for tanks, but how does that help battlesuits?
As per usual, GURPS Ultra-Tech provides us with the tools to make what we want, it just doesn't put them together for us.
To make a laser point defence system, we need four things. First, a weapon that can reliably destroy or terminally damage missiles within one second. Second, a system that can hold the weapon, swivel it and fire it. Third, a targeting system that can detect and track incoming missiles or grenades. And finally, an AI targeting program that can reliably hit missiles travelling at 1,900mph up to the maximum range of the weapon. GURPS Ultra-Tech gives us all of these!
Weapon
There are a variety of laser weapons to choose from but the best is actually the Survival Laser (p. 116). This is basically the Heavy Laser Pistol with higher accuracy. It can hit out to 900 yards and does full damage out to 300. Average damage is 14 burn, which is enough to take the Hunter, Striker or Floater Missiles (p. 168) down to at least negative HP. Non-smart missiles, like the regular dumb rounds fired from 64mm or 100mm missile launchers, will have less HP. It also has RoF 6, allowing it to claim rapid fire bonuses for slightly higher chances to hit. So we've found our weapon that can reliably take down missiles.
Mount
The shoulder servomount (p. 151) allows you to hold a single weapon, firing it without using the hands. There are two main reasons for this: first, it lets soldiers without hands fire guns; second, it lets you fire more guns if your hands are full (with guns, probably). You need to use either a HUD link or an AI to fire it but either can use targeting information from other sensors. This will be the core of our point defence system. Weight and cost is dependent upon the weight of the weapon it's designed for – for the 3.3lbs laser, it costs $8,300 and weighs 9.9lbs.
Target Acquisition
A small tactical multi-mode radar (pp. 64-65) suits us just fine, with a 20-mile range in search mode and a 2-mile range in imaging mode. The radar can sweep its 120-degree arc across the battlefield to search for incoming projectiles, then focus on up to 10 within that arc for tracking. Slaving our weapon system to the sensor allows double base accuracy when firing, which is also very important.
AI
Dedicated AI is sufficient for our uses here. An IQ 10 dedicated AI is Complexity 6, costing $300 at TL10. But we need some extras: Altered Time Rate (Basic Set p. 38) will allow the AI to Aim and Fire in one round, and Gunner (Beams)-14 is necessary to keep the odds of intercepting a projectile high. This totals 112 character points, for a +560% increase in cost of the software. The final point defence software costs $1,980 and will likely be LC2, since it's military-grade.
Bringing It All Together
The grand totals of all this equipment is a cost of $17,680 and a weight of 14.2lbs. These aren't trivial but given this is designed for a TL10 Heavy Battlesuit, the price is a fraction of the cost of the battlesuit itself and the extra weight is negligible with Lifting ST +20. To demonstrate how everything works, we'll go with a worked example. A battlesuit soldier is walking through a city ruined by conflict. The AI in the point defence system is constantly taking Wait manoeuvres, waiting until it detects incoming fire. An enemy infrantryman in a building two blocks away (about 200 yards) catches sight of him. The infantryman hasn't been spotted by the battlesuit soldier, so he takes his time to load his rocket launcher with a 64mm HEMP missile, aims and fires.
The AI detects the flying missile immediately. It makes an Aim manoeuvre, getting +24 to hit from doubling the base accuracy. Since the missile is detected immediately after it is fired, it doesn't have much time to gain speed. As a rule of thumb, we'll halve it's maximum speed of 1,900mph to 950mph, which is Move 475. Looking up 200+475 = 675 on the speed/range table gives a penalty of -15. The missile is SM-4, giving a further -4 penalty. The AI fires, making an All-Out Attack (Determined) for +1 and firing six shots for a further +1. The AI is rolling at 14+24-15-4+1+1, for a total of Gunner (Beam Weapons)-21. The missile cannot dodge and the laserfire swats the it out of the air like a fly before it can even get halfway to the battlesuit, then the AI alerts the soldier to the direction of the fire.
If the missile was fired further away, the AI waits until it's within 300 yards before firing for maximum effect. An object 300 yards away travelling at 1,900mph (Move 950) gives a total speed/range penalty of -17, so the final target number in this case would be 14+24-17-4+1+1 = 19, which is still nearly an automatic success.
Counter-Countermeasures
This system isn't infallible. The most obvious solution is brute force – fire two missiles at once. The point defence system is only able to take down one missile per round, so one will get through. This requires some amount of co-ordination, which may be tricky either over long distances or in the heat of combat.
A more clever solution is to utilise the fact that anything that blocks either the laser or the radar will prevent the AI from either hitting or detecting incoming missiles. A shroud of either prismatic or electromagnetic smoke serves this purpose. EMPs are also capable of disabling either the AI, radar or motors on the servomount, preventing it from firing. The tricky part is that at a distance, the easiest way to deploy these countermeasures is by missile... which the system will intercept. Anti-battlesuit tactics should include traps that trigger either EMPs or smoke near the battlesuit, allowing another soldier to fire at the suit from a distance to take it out.
The shoulder servomount says it counts a gyrostablised weapon mount but self-targeting, which in turn counts as a articulated weapon mount without and attack penalties.
ReplyDeleteFirstly this means that even if the battlesuit is moving when it's trying to shoot down missiles there won't be an extra penalty, which doesn't affect your numbers above.
Secondly this means the gun counts as braced, which means an extra +1 to hit that you weren't counting for. It also means 2/3 minimum ST, but that's hardly a factor here.
I could be wrong with my reading of the results, so I'm interested to see if you view it differently.
A second query I have is that you seem to be treating Gunner as an IQ based skill for this (understandable given both the AI and mount don't have a defined DX), is this just your fix for the 'how do I work out the DX of something that doesn't have one) or is this an official rule somewhere?
In part I'm asking because I want to use your approach, but also I have other AI run no-defined-DX systems I want to build (for example, what is the DX of a spaceship or AI driven car?). Do I just assume 10, or do I base stuff off IQ?
I'm not clear on what results you mean. I had forgotten about the +1 from bracing but the worst-case scenario (the missile moving at full speed) still gives automatic success, barring critical failure, so the extra +1 isn't too important.
DeleteI think when I wrote this I was assuming Gunner was an IQ-based skill, which it isn't. In which case, the AI having IQ 10 isn't necessary! Can probably drop it down to the limit of "sapience": IQ 6 (Complexity 4). As for DX, unless something says otherwise, you should normally assume any mobile object/robot/vehicle has DX 10. An AI uses the DX of the hardware it has to move, which will normally be 10.
Results was me doing a typo on 'rules', so sorry about that.
DeleteI didn't think the bracing was all that important, but it's worth noting given you're including the RoF bonus, and unlike the RoF bonus doesn't have the minor risk that the PD system could end up hitting stuff it didn't mean to with excess shots. That risk is very unlikely though.
So just treat anything that doesn't otherwise have a defined DX and is animate as 10? That works fine as a rule of thumb, and it's not like it needs high DX given a) only one DX based skill, and b) Altered Time Rate. I do wonder if Gunslinger might also be a way to represent an advanced targeting module for an AI.
Do you think there is an argument for sensor related skills to make sure it spots incoming attacks or are you working on the assumption that a missile on terminal approach is going to be automatically visible?
One thing that occurs to me, and I just checked the book, is that Altered Time Rate does not increase reaction speed. It gives you an extra action once you do start moving, but doesn't let you react faster to start with, so you the build may need Enhanced Time Sense [45] as well to ensure that it will react in time to hit a missile that in theory could take well under a second to go from 'in the tube' to 'in your face'.
Also, do you see any reason, baring 'running out of shots/actions in a round' that the system couldn't also intercept shells, bullets, thrown grenades, and similar kinds of issues? In most cases they will be moving quite a bit slower than your example missile, Mach 2 is only move 750 after all.
One limiting factor, though I can see a 'universal shoulder mount' as a fix for that, is that the standard servo mount will only shoot stuff in front of the user, and the radar only has a 120 degree arc, so attacks from behind won't be stopped, so that would increase the cost and weight for a full coverage system. And if I was attacking a battlesuit with a missile, I'd want to wait till it's facing away to fire.
Sorry if I sound picky but it's because I like this idea a lot am going over it carefully before I use it in my own game. :)
Sorry for the delay in answering, I got a harsh bout of tonsillitis.
DeleteGunslinger's main utility is for allowing Acc on shots without having to aim. It serves the same purpose as having ATR and using the extra action to aim, but it's intended for a cinematic game. I feel like ATR is the better fit here.
With regard to sensors, that's a valid question so I went and double-checked the radars in Ultra-Tech. The quote is: "The GM can assume that most moving targets that fit the radar’s criteria are detected automatically." so I feel pretty confident letting the AI automatically detect missiles.
You're right about Altered Time Rate not increasing reaction speed. I assumed it had the same effect as Enhanced Time Sense in that regard. That's something I may have to go back and fix, along with the IQ and Complexity of the AI.
Regarding other projectiles? The limit is speed and size. Missiles go very fast and are fairly small. Bullets are much smaller and probably go at the same speed or faster - large rifle rounds might be SM-9 whereas tiny 4mm gauss rounds might be as small as SM-15. The general trend will probably be that smaller projectiles will go faster, so there will be a point where it'll become impractical to hit.
My thought is the radar would be the limit there. If this problem came up while I was GMing, I'd rule that detection of anything fist-sized or larger moving through the air is automatic - anything smaller requires a roll. Grenades should be easy to hit, since they're large (SM-6) and slow-moving, likely never over Move 20.
I admit I fudged a little on the angles. The shoulder servomount does say it can only fire in front of it, but the idea of having two servomounts just to cover one troop felt excessive, which was why I said it rotates around to sweet the area. I don't really have any smart responses to this. I would've used the powered tripod mount if it weren't so damn heavy (fifty pounds?!).
That does make sense on the Gunslinger thing, ATR + ETS makes more sense. Also a good point on the radar thing, though it could become an issue with more stealthy rounds (though that's more a higher tech issue) or ECM being thrown around (which seems likely in a combat environment).
DeleteI had underestimated how fast a bullet moves, I though it was around mach 2, not 3.5 for a rifle (move 1,300 so -17 for speed along) which leads to -26 to hit a rifle bullet on the way in and that isn't happening. Gauss rounds will be smaller and a lot faster, so this is going to be good against big slow slow projectiles (big and slow still covering supersonic missiles) but isn't going to be 'immunity to bullets'. I'm fairly happy with that to be honest, you want something that will stop missiles, but not stop somebody with a main sniper railgun or so forth.
The angles you'll just need to fudge I think ... probably add a bit of weight for 'wider attack angle' and similar for the sensors.
The powered tripod is probably a better model for a semi-portable local area defence system and what you'd model an ad-hock ultratech version a modern vehicle mounded Active Protection System.