Psi-Wars Electronics II - Sensors and Sensor Jamming

In the real world, we use sensors for two main purposes: to alert us to the presence of an enemy, and to guide our missiles. In Space Opera, including Psi-Wars, we also use sensors to analyze a target: scanning for life-scans, picking up the make and model of a target, etc. We also use counter-measures: in the real world, to buy ourselves a little time before the enemy picks us up, and to jam guidance systems to keep us from being hit by a missile.

The technology used for both is easy enough: we use Ultrascanners for all our sensory needs, and we use Distortion jammers to disrupt all uses of ultra-scanners. The interesting question is not what we use, but to what scale and what rules should govern their use.

Welcome to  part II of my giant post on electronics.  Again, I have a focus on things I might use for military vehicles, because my ultimate goal here is to start working on dogfighting 2.0, which means we need to get a sense of how our vehicles work.  Yesterday, I looked at comms, today, I look at sensors.

As before, this touches on some of my vehicles material.  Feel free to ignore that if you wish.

Ultra-Scanners

The core rules of how ultra-scanners work is simple enough and detailed on UT 66 (though I would skip the radscanner component). They can image and scan at their listed range, and “search” up to 10 times that; this farther range is also your “lock on” range with targeting systems.

Star Wars is a bit odd, in that, as depicted on screen, it relies on visual tracking of its targets, like in WW1 and WW2. Most space fighter sims I’ve played, by contrast (including X-wing vs TIE fighter) use radar to at least find your target, and often allow you to make “locks” on opponents and gain the benefit of a targeting system that automatically “leads” your target for you (similar to the targeting systems in the F-86 saber). This suggests that it makes sense to have fighters with solid sensor systems (and, in fact, the vehicle guides to Star Wars clearly indicate sensor systems).

GURPS Spaceships argues that active scanners, like radar, are essentially useless in space, suggesting that we should not bother with ultra-scanners. The logic of this is sound, but I don’t think it’s applicable. Imagine sending a light-speed ping (such as radar) to Jupiter: that would take something like 80 minutes to reach Jupiter and come back, and will have a very weak signal by then. If you can pick that signal up, you can also pick up light, and you have more than enough time to look for anything traveling at sublight speeds in space. A rocket trying to reach you from Jupiter, for example, will take months, so you can take your time to look. This advice is largely useless in Psi-Wars, though, because ships can move at light speeds between planets, they exit the universe when going into hyperspace, making them very difficult to detect except moments before arrival, and Ultrascanners could be FTL in nature. This makes them far more useful and they will serve as the basis of all non-visual detection, simply to make life easier and more similar to real-world combat.

But how much Ultrascanner do you need? We’ve been using the Dogfighting rules, and I think they offer some interesting insights into the scale of our combat. “Extreme” distances are as far as we might expect fighters to fire blasters at one another, and this maxes out at a range of 2000 yards (a bit over a single mile). In the real world, you’d need a 30 (TL 7) or 15 lb (TL 8) radar dish to pick up a target this far. A TL 9 radar dish would be able to image a target at this range with a 1 lb handheld device. An ultrascanner could do the same. For “Distant” distances, we need to reach 10,000 yards, which is about 5 miles. We would need a 100 lb radar dish at TL 7, 15 at TL 8, 1 lb (for search) or 10 lb (for imaging) at TL 9; An ultrascanner would need 1 lb for search mode and 100 for imaging mode. For “Beyond Visual” we need more than 10,000 yards. This likely covers up to 50,000 yards, or ~25 miles.. At TL 7, we need a 10 ton station, TL 8 needs a 50 lb dish, TL 9 needs 10 lbs for search mode, and almost gets all of it with a 100 lb one when imagine; the Ultrascanner matches these ranges.

In the real world, 200 miles is about as far as most ships scan (this is also why they tend to have sensor masts, so they can look farther “beyond the horizon”). Modern fighters seem to have radar ranges around about 75 miles. When it comes to ships in orbit, we need about 100 mile range to detect things on the planet; that seems your minimal distance if you want to be a major capital ship that engages in orbital bombardment. Even if we set aside interplanetary distances, orbits can get enormous. The moon is a quarter of a million miles away, and the earth itself is nearly 8000 miles across: if you were 100 miles above the Earth and you wanted to see another ship also in orbit, but about as far away from you as it can be and still not beyond the horizon, you’re probably looking at something on the order of 8,000 miles, which gets you above the inner Van Allen belts, but doesn’t get you into geostationary orbits or even high orbits. This is fine, most people don’t really know or care about that sort of thing, so our maximum limit is likely 10,000 miles, and such a distance is likely only for vessels that want total, absolute command of the sky with but a single vessel. The rest could easily network. This probably means that our important ranges are:

• 3 miles (ground vehicles searching for other ground vehicles)
  
  
• 5 miles (ground vehicles searching for aerial vehicles)
  
  
• 30 miles (maximum combat ranges)
  
  
• 100 miles (orbital artillery ranges)
  
  
• 10,000 miles (Absolute maximum strategic scan ranges)
  
  

We can arbitrarily calculate a value for the Ultrascanner using the following (though I warn you, it is not pretty):

weight = 10 ^ (log₃ R)

Where R = the scan (not search) range. A simpler way to handle this is to realize that every 3x range increases the mass 10 fold (so a 30 yard scan range would require 1,000 lbs of scanner, and so on).

Their arbitrary cost is, according to Ultra-Tech, $2,000 per lb, or $10,000 per lb for a tactical scanner; GURPS Spaceships sets it at $100 per lb, or $200 per lb for a tactical array.

Note that this only covers a 120 degree area in front of the vehicle. If the vehicle wants to integrate an AESA-style, full 360 scanner, it will need three such systems! Or it will need a rotating dish, on a mount or wrapped in a turret.

Options: Low-probability Intercept (See UT 63): x2 weight; Targeting (UT 63): x5 cost; UT 63 also discusses Vehicular Arrays: assume that fixed, body-mounted sensor systems are Vehicular Arrays, they have additional costs or concerns.

Note that ultrascanners will detect other ultrascanner signals directed at it at up to twice range (or 1.5 range for LPI arrays).

Missile Guidance Systems

These use Ultrascanners as well, as detailed in UT 146. How we’ll treat them in combat is beyond the scope of this article.

ESM

The ESM and tactical ESM (UT 62) will also detect an ultrascanner signal as though it was an ultrascanner, and a tactical ESM detector will do so quickly enough offer a bonus to a dodge roll. Double the listed price!

Passive Visual Sensors

Psi-Wars uses all the passive visual sensors listed on UT, but most people use either Elecro-optical viewers or Hyperspectral viewers; the latter are doubled in price from what is listed in UT 61. The specifics of the devices vary from their listed values to more closely match real-world expectations. See below.

Spaceships do not rely on scopes as their primary means of detection, as their ultrascanners are far quicker; vehicles tend to be close enough in battle to simply see through a window.

Electro-Optical Binoculars: Night Vision 9, 64x magnification, $500, 1.5 lbs, neg. LC 4

Electro-Optical Surveillance Camera: Night Vision 9, 4x magnification, $250, 0.6 lb, neg, LC 4

Electro-Optical Goggles or Visor: Night Vision 9, 4x magnification, $1,000, 0.3 lbs, neg, LC 4

Hyperspectral Binoculars: Hyperspectral Vision, 64x magnification, $20,000, 3 lbs, C/50 hr, LC4

Hyperspectral Surveillance Camera: Hyperspectral Vision, 4x magnification, $4,000, 1 lb, B/50 hr, LC 4

Hyperspectral Goggles or Visor: Hyperspectral Vision, 4x magnification, $4,000, 0.6 lb, B/50 hr, LC 4

Sensor Jamming

The Dogfighting rules allow fighters to have -2 to -3 to radar rolls. GURPS Spaceships allows a -1 “per ECM system.” GURPS Ultra-Tech allows a few different counter measures, with wildly superior values to those above.

A Distortion Jammer represents the typical modern ECM system, which responds to an active sensor ping by distorting the return of the ping to give a false impression. It can actively “Jam” or “Spoof” the signal, represented by a flat penalty of, according to GURPS Ultra-Tech, -8, which is quite substantial.

GURPS Ultra-Tech has no rules for it, but GURPS Spaceships suggests an area jammer, which allows the user to protect numerous vehicles within a particular radius. A more realistic area jammer projects the jamming signal forward towards a specific target, jamming their specific sensors. Both might work, though we need to work out the range (likely generous). This typically has half the effectiveness (thus -4).

GURPS Ultra-Tech also has “Radar Stealth.” This represents the sorts of delicate coatings and configurations necessary to present a very small radar profile. While Psi-Wars doesn’t use radar, the ultra-scanner is clearly meant as a radar-like stand-in, so a form of “Radar stealth” would also be perfectly appropriate. This applies a -8 to detection.

Taken together, we can expect to have a maximum of -16 to detection. If we use the Dogfighting Rules for missiles, noting that 160mm missiles have an acc of 3, assuming you were SM +5 and traveling at 500 yards per second and the pilot shooting you had Artillery 18, he’d have an effective skill of 3. This creates my primary problem with ECM as described here: it would make targeting someone with a missile effectively impossible (our critical hit chance is only possible because we have an 18 in skill!).

(If we look at the results across all size modifiers, it turns out that stealth is a better option with smaller vehicles, while jammers are better for larger vehicles. The break even point is SM +5, where they both cost the same).

For missile fire, I personally would find it more satisfying if one ECM system effectively canceled out the accuracy bonus of a missile, and two inverted the bonus. Assuming an accuracy of +4 rather than +3, in the same situation, against a target with no ECM (+4 from accuracy), we have an effective skill of 20; with one ECM system (-4 from ECM, +4 from accuracy), we have an effective skill of 16, and with two ECM systems (-8 from ECM and +4 from accuracy), we have an effective skill of 12. A more modestly skilled character at 15 would have a 17, 13 and 9 to hit. This +/- 4 suggests I should boost the base accuracy of missiles, and halve the penalties for ECM in a dogfight.

GURPS vehicles discusses decoys, things like chaff or flares that you can discharge to further confuse targeting systems. In space fighter sims, this is often carefully timed, requiring a skilled use of your decoy while you dodged out of the way. This sounds like a defense bonus used against missiles (it won’t help much against general detection that you’re there, though it might assist in spoofing). In GURPS Spaceships, decoy use is reflected by a bonus to dodge. We could use it similarly here: a decoy adds +4 to your dodge against a missile or you can make a “Parry” using Electronic Warfare with a similar bonus. These reflect using a decoy “at the right moment.”

Distortion Jammer stats

The distortion jammer is based on the diameter of the jamming area. This must equal or exceed the size of the vehicle for it to work. To determine the minimum necessary radius, take either the cube root of the vehicle’s volume or take the size modifier and find its length in yards.

Weight: 1.25 lbs x distortion field diameter

Cost: $4,000 x lbs

Energy: 0.0025 kw x distortion field diameter

Stealth stats

Weight: 0.1 lb x surface area

Cost: $500 x lb

Decoy Launcher

A decoy discharger is a fixed-mount, rear-facing 40mm EMGL loaded with 25 expendable jammers. Lighter versions are possible (base weight is 2.5 lb, base cost is $3500, etc)

Weight: 65 lbs

Cost: $4,000

Power: 60 kw

Chameleon surface

Psi-Wars sometimes makes use of Chameleon surfaces, which grant a +8 to avoid visual detection, or +4 to avoid detection by those using hyperspectral sensors. Halve this bonus if moving (thus in dogfights and such, it always provides no more than half-bonus). It provides no protection against an Ultrascanner. See UT 98 for more.

Weight: 0.4 lbs per square foot

Cost: $1000 per lb

Power: neg

Ultra-Scanners, Stealth and Detection Mechanics

So ultimately, all of this Electronic Warfare discussion boils down to two things: when can we detect you, and can we hit you with our missiles. The second half I’m going to leave for when I dive into dogfighting again, which will be soon! The first half, though, is tricky, and we can ask a second question: When do they know you’re carrying contraband?

If we go “by the book,” using GURPS Basic, the rules seem to be these: If you want to detect a target who is within your listed range (-2 per doubling beyond range), roll Electronics Operation (Sensors) to notice them. It doesn’t say what modifiers to add, but presumably superior tools might add a bonus, as might SM. Darkness and range penalties definitely don’t apply. Our jammers and stealth seem to apply a flat penalty: they are the equivalent to Obscure.

So, by these rules, our contest would look something like this: If I try to detect you, I roll Electronics Operations (Sensors) if you are in range to “notice” you, just as if I were a guard rolling Vision to spot you while you snuck past. If you are equipped with either Stealth or a Jammer, I am at -8; if you have both, I am at -16. This makes it virtually impossible to detect you.

That seems awfully difficult, and how often can I roll? Once a second? Once per encounter? How close can I get? Can we “actively” sneak? Is there some skill that we can master to improve our ability to slip in undetected?

If we follow the action philosophy, the answer to “how often do we roll” is “once per pertinent moment.” Say you want to sneak past my patrols: then we roll once to see if you do. If you decide halfway to stay in the area and monitor my traffic, then we roll again to see if I notice you doing that. And if you decide to ambush me, then we roll once more to see if you successfully do so. Simple enough. As for difficulty, that does indeed seem a bit high. I think a -4 and a -4 is fairer: if we stack our bonuses, you need to be skill 18 to break even.

We can use similar rules for checking your contraband. The Distortion Jammer works as noted, but stealth will not protect you from being analyzed. For that, we’ll use a “Shielded Cargo space,” which works similarly.

As for skills, you can contest the Electronics Operations (Sensors) roll to scan you for contraband with Smuggling. If you’re using a Distortion Jammer, you can roll against Electronics Operation (EW) to trick them into seeing something else, but you add half your Distortion Jammer bonus rather than the full value. For actively sneaking past a scanner, roll Stealth if on foot, Smuggling if in a vehicle, or Electronics Operation (EW) if you’re using a Distortion Jammer; if multiple are true, use your best roll. As always, apply BAD.