So, why are lasers missing?

[AnotherDilbert]

I don't know CT power ratings, but to mix systems a bit, a Beowulf can generate 990 MW in MT. If it gets to a point where the ship needs an extra MW or two in order to get a firing solution on the pirate that wants to kill them, in most cases it's available.

Besides, if a ship needs an exact range for a target because they don't want the meson blast to miss, it's a warship that has a lot more generation capacity than that.

Certainly spacecraft have a LOT of power available.

But the 1/R⁴ term is still problematical. It means that to get 10 times the range, we have to use 10000 times the power. If we take a hypothetical radar with 100 km range and a power consumption of 1 kW, then the same radar would need 10 MW to reach 1000 km, 100 GW to reach 10 000 km, 1 PW to reach 100 000 km, and 81 PW to reach 300 000 km.

Adding power to gain range gets impractical real soon...

 

[AnotherDilbert]

Now the question is, is that 250 MW constant or 250 MW per 1000-second turn?

Thus, as (for example) per Striker, we are looking at 250MW/s steady output from those space-combat-rated lasers.

A Joule [J = Ws] is a measurement of energy, done work. This is always measured over time.
A Watt [W = J/s] measures a flow of energy. This is power consumption. This is instantaneous.
A Watt/second [W/s] measures rate of change of power consumption. This mostly of importance to power stations.


With TNE we can say that a laser weapon consumes a steady 250 MW and either emits a steady beam or short pulses with a stronger intensity. Doing that it will have used 250 MW × 1000 s = 250 GJ energy over a 1000 s period.

 

[whartung]

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.

In TNE, the typical laser, with an an associated Master Fire Director, with a normal crew, shooting at a <1000 dTon ship, has a 95% chance to HIT that target at 600kkm. (For scale, the Moon orbits at an average of 385kkm).

So, whatever limits to precision in terms of tracking, aiming, etc., they've certainly overcome them.

 

[AnotherDilbert]

In TNE, the typical laser, with an an associated Master Fire Director, with a normal crew, shooting at a <1000 dTon ship, has a 95% chance to HIT that target at 600kkm. (For scale, the Moon orbits at an average of 385kkm).

For at least 10 shots during a 30 min period by a TL15 weapon... Doesn't really suggest that nearly all shots hit.

 

[jcrocker]

Certainly spacecraft have a LOT of power available.

But the 1/R⁴ term is still problematical. It means that to get 10 times the range, we have to use 10000 times the power. If we take a hypothetical radar with 100 km range and a power consumption of 1 kW, then the same radar would need 10 MW to reach 1000 km, 100 GW to reach 10 000 km, 1 PW to reach 100 000 km, and 81 PW to reach 300 000 km.

Adding power to gain range gets impractical real soon...

Again, I don't have CT construction rules handy, but I do have the MT ones.

"EMS Active Array combines radar, all weather radar, ladar, radar jammer, radio jammer, active IR and image enhancement into one integrated and optimized sensor array."

I'll skip the rest of the table, but there is no TL15 entry so I'll use TL14. The longest range on the table is Far Orbit, which as we all know, is 500 000 km. It weights 0.030 tons, costs 600,000 Credits, and requires 0.3 MW.

The next table down is the EMS Passive Array, longest range is Interstellar (2 parsecs) and again no TL-15, but the TL-14 set weighs 0.016 so the price is 320,000 Credits, and requires 0.16 MW power.

As far as ship construction rules, I have the most experience with MT - and while I find your real-world numbers interesting and pardon the pun illuminating, I guess either GDW hadn't run across that formula, or they decided to go their own way.

If you wanted a nod toward realism, of course, they already include ladar and IR sensors in the arrays - instead of radars that would suck all the power over a given range, you could rule that IR sensors give a general bearing, and ladars firm it up and give range.

 

[kilemall]

Neither LBB2 nor HG got into sensor rules beyond those already quoted. I do recall the sensor fit that went forward, including the NAS, in magazine articles of the era, but not the rulebooks themselves.

 

[kilemall]

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.

Going back to Striker, the 250 MW laser works out to something like 1 million km in space. With atmospheric effects, divide by 1000, so an atmosphere will force a bombardment ship to be much closer.

Depends on how you rule it, whether you count atmosphere depth as 1000x or total range is cut period no matter the depth. Orbital pass angle would count too, being located directly over the target town may minimize effects whereas coming in over the horizon on a low orbit may make a shot impossibly defracted- kind of an atmospheric equivalent of the armor penetration graphic I posted above.

 

[AnotherDilbert]

I'll skip the rest of the table, but there is no TL15 entry so I'll use TL14. The longest range on the table is Far Orbit, which as we all know, is 500 000 km. It weights 0.030 tons, costs 600,000 Credits, and requires 0.3 MW.

The given range is just a name, it has very little to do with the effective range of the sensor package. All sensors use (range / 25000 km) as a negative DM on their tasks, the better sensors just have a better base difficulty. At 500 000 km range, with a DM -20, it will have some difficulty detecting anything...

Note that really good passive sensors can have a better chance of success than active sensors.

 

[McPerth]

The given range is just a name, it has very little to do with the effective range of the sensor package. All sensors use (range / 25000 km) as a negative DM on their tasks, the better sensors just have a better base difficulty. At 500 000 km range, with a DM -20, it will have some difficulty detecting anything...

I'm afraid this is not exact:

• a good computer and user's skill, both used as + DM (in fact, skill is not listed on the UTP in page 92, but what else can it exist for?) may compensat for it (though at longer distances, they cannot, so your point stands then).
• in any case, DMs may not be over +8 or -8 (CT:RM, page 15), so you can always be successful in a simple task.
• For a routine task, you can try a cautious approach, so reducing it to simple (if you pass your determination task).

I guess that's how passive sensors can reach 2 Pc to detect some things. I guess computer operated sensors do not need to roll for determination.

But for tactical detection and lock on, your point mostly stands, as, being uncertain tasks (so needing to be twice successful, player's and referee's rolls), basing it in rolling 11+ (simple task with the maximum -8 DM) and needing to success twice (detecting and locking on), your chances are quite low...

 

[AnotherDilbert]

a good computer and user's skill, both used as + DM (in fact, skill is not listed on the UTP in page 92, but what else can it exist for?) may compensat for it (though at longer distances, they cannot, so your point stands then).

The task specifies Computer number or Sensor Op skill.

in any case, DMs may not be over +8 or -8 (CT:RM, page 15), so you can always be successful in a simple task.

I had missed this, thanks. In this case I would be very tempted to allow the full negative DM, to prevent sensors from having infinite range.

For a routine task, you can try a cautious approach, so reducing it to simple (if you pass your determination task).

It is further complicated by that you may need from Failure to Extreme Success to locate the target, depending on target size and/or emissions.

But for tactical detection and lock on, your point mostly stands, as, being uncertain tasks (so needing to be twice successful, player's and referee's rolls), basing it in rolling 11+ (simple task with the maximum -8 DM) and needing to success twice (detecting and locking on), your chances are quite low...

Only lock on is Uncertain, but I think only the player need to be successful for lock on to succeed, you just get more information about the target on Total Truth.


Since you can roll every round for each friendly ship, and it's enough for one friendly ship to lock on, you will detect and lock on at infinite range given enough time as long as you can achieve Simple difficulty. To prevent that I would allow the full negative DM, even if it's less than -8.

I assume fleets are not supposed to be able to engage each other at millions or billions of km.

 

[Straybow]

I don't think passive sensors can detect ships at 2 pc... or rather ships that were there six years ago. That's talking about system survey picking up GGs and perhaps larger planetesimals that aren't blocked by the glare of the star. And, of course, radio frequency noise if a developed planet is present.

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.

No, the half-value is in reference to normal radiative properties, not applicable to a coherent photon beam. A high density laser quickly "burns through" the air and creates a channel of partial vacuum surrounded by plasma. That soaks up energy, but doesn't do anything like that.

Alternatively, the laser is a low density beam. The ABL was only around 1 MW and had an effective range of tens of km. It's beam was about half a meter wide. It would cook the metal skin and portions of structural framing of the target to cause structural failure under aerodynamic load.

A modern electrically powered version light enough to go on a high altitude drone would have a higher density beam and an effective range of 100+ km. Again, only a few MW at most.

I'd expect a high density 250 MW laser to have a lightning-like plasma effect in atmosphere. It does give interesting area-effect usefulness against unarmored troops and unshielded electronics in vehicles. Might even cause petroleum/methane fuel tanks of vehicles near the target to explode.

An adaptive lens would have a low density beam focusing into a high density beam near the target, so there wouldn't be any effect near the ship.

 

[Straybow]

in any case, DMs may not be over +8 or -8 (CT:RM, page 15), so you can always be successful in a simple task.

I had missed this, thanks. In this case I would be very tempted to allow the full negative DM, to prevent sensors from having infinite range.

Since you can roll every round for each friendly ship, and it's enough for one friendly ship to lock on, you will detect and lock on at infinite range given enough time as long as you can achieve Simple difficulty. To prevent that I would allow the full negative DM, even if it's less than -8.

I assume fleets are not supposed to be able to engage each other at millions or billions of km.

Yes, that's why you change the rules to specify both detection difficulty level and base roll required, by range, instead of just a DM for range. That way the higher roll result isn't included in the DM limit.

Make the lock range a hard limit, too.

 

[Carlobrand]

...
No, the half-value is in reference to normal radiative properties, not applicable to a coherent photon beam. ...

Well, poop.

Oh well, thank you for the info. It's always an education playing this game.

 

[AnotherDilbert]

Which is why I am convinced the missing magic technology of Traveller is the gravitic heat sink - something built into the grav plate and inertial compensation system that keeps the ship cool by removing the waste heat as artificial gravity potential or some such handwave.

I agree we need, ahum, "sufficiently advanced technology" to remove heat from our ships.

The problem is to appease thermodynamics we have to not only conserve energy, but also increase entropy (disorder). Concentrating the heat into gravitational potential would be the opposite, it would decrease entropy. To increase entropy we have to diffuse, spread out energy to decrease concentration of ordered energy or matter.

Perhaps we could set up a vibration in the local gravity field that would be (mostly) absorbed by all mass in the local star system, making it very slightly warmer?

I assume we already have to push against the local gravity field (and hence celestial bodies) when we accelerate in order to conserve momentum.

 

[Soly]

If your firing at a moving target 58% is a very high chance of a hit, but who fires directly at a moving target, you allow for movement, that's what predict programs are for, or gunners instinct combined with computer predictions.

 

[Straybow]

The other factor that nobody had mentioned so far (kicking self for not mentioning initially) is that the firing ship is also maneuvering. Hubble gets its precision though gyroscopic station-keeping, otherwise it would be no better than an astronaut's hand-held 35mm pics from the space station.

So, whatever modifiers apply to someone targeting your ship would also apply to your targeting ability, maybe reduced by 1 since you can tell the targeting system your maneuver inputs and automatically move your turret to compensate, but however carefully you do it you are still introducing a destabilizing factor into the targeting solution.
_________

Somebody mentioned mesons... back in my day all that fancy stuff didn't exist, just LBB 77. Mesons don't work that way. They decay in a probabilistic fashion. So a meson weapon would project a beam of Pi meson decaying all along the path. The decay model (if I understand correctly) is Poisson with lambda = 1, so that means the highest decay occurs a short distance from the gun. Using dilation to time the peak at the position of the target means only a tiny portion of the gamma energy would be released inside the target.

https://www.umass.edu/wsp/images/poisson3.gif

The black line is lamba = 1, so picture the target at the peak, with the cross section of the ship being ship/range = very small. For a ship in the hundred meter neighborhood and range being 10k km, the area under the curve representing the ship would be 5000 times narrower than one pixel. Back-of-the-envelope calc says that would be about 1/250,000 of the total decay energy.

I think the crew of the targeted ship would say, "Hey, my radiation badge just lit up. Looks like I took a few millirems."

 

[kilemall]

The other factor that nobody had mentioned so far (kicking self for not mentioning initially) is that the firing ship is also maneuvering. Hubble gets its precision though gyroscopic station-keeping, otherwise it would be no better than an astronaut's hand-held 35mm pics from the space station.

So, whatever modifiers apply to someone targeting your ship would also apply to your targeting ability, maybe reduced by 1 since you can tell the targeting system your maneuver inputs and automatically move your turret to compensate, but however carefully you do it you are still introducing a destabilizing factor into the targeting solution.

Since the computer that is running your TARGET/PREDICT and whatnot is also running your MANEUVER/EVADE, it's all being updated simultaneously-and why you need a computer for combat.

The more interesting thing to do is highlight what happens when you don't have a computer. I'd say contrary to the rules you can shoot without your computer via that darn 1 ton fire control we paid for.

But you get a -4 DM just like changing targets, and your DM gets worse if someone is doing manual maneuvers down in engineering.

 

[Straybow]

My point is that it doesn't matter what the computer is doing, it matters what the physical ship is doing. No movements are going to be as smooth as pudding, and that lowers the precision available. You aren't merely moving the ship, you are inducing quasi-random shifts and turns at the highest accelerations possible into the ship's trajectory to be a harder target. That's doubling the problem. You're trying to move the gun and its turret to compensate for the gross motion of the ship, and more moving parts is again lowering the precision of the whole.

That makes having a stationary platform (even if just the first volley in a surprise attack) of great value.

 

[whartung]

The other factor that nobody had mentioned so far (kicking self for not mentioning initially) is that the firing ship is also maneuvering. Hubble gets its precision though gyroscopic station-keeping, otherwise it would be no better than an astronaut's hand-held 35mm pics from the space station.

The shooting ship is always "still", its the target that's always moving.

"Movement" by the shooting ship can be perceived as "erratic" movement of the target ship, but that's the beauty of it. The ship can "know" (outside of a random event) when and how it's going to move and compensate for it as part of its firing solution. For example the computer can compensate for motion that it "knows" the engines are adding to the net motion to isolate the ships behavior from the targets.

Consider the "Captain Phillips" story, when the military marksman on a navy ship shot some of the Somali Pirates that were on a lifeboat. Here, we have a moving shooting platform against a moving target (in this case both were subject to sea swells, I don't believe either vehicle was "moving" in terms of pushing through the water).

So, the marksman needed to compensate for both their ships motion and the targets.

But if simply take the point of view of the target through the scope, the shooter is NOT "moving" (his scope is "stationary"), but the target is "bobbing wildly". So, the shooters had to ascertain the patterns of the motion as viewed through their reticles to properly time the shots (plus they were timing to shoot simultaneously). From a technical aspect, these were spectacular feats of marksmanship under pressure.

But you can see, from the shooters POV, there weren't moving at all -- the target has all of the net motion manifest to the eye of the shooter.

In theory, the shooters may have had a spotter that could tell them when they were about to reach the top of a swell, giving them a bit more "stationary" time. But odds are they didn't need it, they simply compensated for the net motion they were viewing directly.

 

[infojunky]

Thus, as (for example) per Striker, we are looking at 250MW/s steady output from those space-combat-rated lasers./QUOTE]

Actually Output is a quarter of that 250mw, so 62.5mw.

Also note those rules assume a shot every 1.5 seconds over the course of a 30 second turn. Or 667 some odd shots per 1000 second turn in space combat.