Can you Design a Beam Weapon by power output?

[Malachite72]

I have been a fan of GURPS for a while but I have been flummoxed by the following:
With great enjoyment, I have been using David Pulver's excellent article "Blaster and Laser Design" in Pyr 3-37 Tech and Toys II. But my difficulty has been extrapolating Power Requirements versus Energy Output.

In Other Words, how many KWs does a beam weapon use per Kj of energy output? This should vary by beam type, but how can the number be found?

Many Thanks...
M.

[Varyon]

It’s a question of efficiency, and you’ll have to make your own decision there (I feel a decent progression is 30% at TL9, 50% at TL10, 70% at TL11, and functionally 100% at TL12). For something with 100% efficiency, (kJ output)*(RoF)=(kW input); lower efficiency calls for more energy input - 50% efficiency requires double the input (with my suggested progression, a 30 kJ, ROF 10 laser would require ~1000 kW at TL9, ~700 kW at TL10, ~500 kW at TL11, and ~300 kW at TL12; note I rounded most of these numbers to conform to the Size and Speed/Range Table).

As for energy per shot, a kWs is a kJ, but efficiency comes into play (above, energy required per shot is 100, 70, 50, and 30 kWs, respectively).

[Fred Brackin]

[QUOTE=Malachite72;2387241

In Other Words, how many KWs does a beam weapon use per Kj of energy output? This should vary by beam type, but how can the number be found?

[/QUOTE]

I'm afraid the answer is "By looking in Gurps Vehicles Second Edition." (which was a 3e book). The beam weapon design section in Ve2 dealt with things in the requisite level of detail. I don't think any thing in 4e does.

[trechriron]

Originally Posted by Varyon

It’s a question of efficiency, and you’ll have to make your own decision there ...

This reminds me of Star Trek V where Bones tells Spock - "he's saying he'll take your guess over most people's facts." Ditto Varyon.

This is a great answer, and if given the choice, I would choose to go this route vs. diving into vehicles. Simple, straightforward, and easy to figure out how big the backpack is going to be. :-)

[whswhs]

Originally Posted by Varyon

It’s a question of efficiency, and you’ll have to make your own decision there (I feel a decent progression is 30% at TL9, 50% at TL10, 70% at TL11, and functionally 100% at TL12). For something with 100% efficiency, (kJ output)*(RoF)=(kW input); lower efficiency calls for more energy input - 50% efficiency requires double the input (with my suggested progression, a 30 kJ, ROF 10 laser would require ~1000 kW at TL9, ~700 kW at TL10, ~500 kW at TL11, and ~300 kW at TL12; note I rounded most of these numbers to conform to the Size and Speed/Range Table).

As for energy per shot, a kWs is a kJ, but efficiency comes into play (above, energy required per shot is 100, 70, 50, and 30 kWs, respectively).

Figuring energy in = energy out/efficiency, I note that 30 kJ/50% = 60 kWs, and 30 kJ/70% = 43 kWs. So that's fairly drastic rounding.

If you want to use the speed/range table, why not say efficiency = energy in/energy out? Then 30 kJ/70 kWs = 43% efficiency at TL 10, and 30 kJ/50 kWs = 60% efficiency at TL 11.

[Varyon]

Originally Posted by whswhs

Figuring energy in = energy out/efficiency, I note that 30 kJ/50% = 60 kWs, and 30 kJ/70% = 43 kWs. So that's fairly drastic rounding.

If you want to use the speed/range table, why not say efficiency = energy in/energy out? Then 30 kJ/70 kWs = 43% efficiency at TL 10, and 30 kJ/50 kWs = 60% efficiency at TL 11.

If adhering to SSR, it's best to just keep in mind that everything is an approximation, including that 30%/50%/70%/100% progression. No constant % progression will work for all outputs - for 30 kJ it's 30%/43%/60%/100% (100 kWs, 70 kWs, 50 kWs, 30 kWs), while for 100 kJ it's 33%/50%/67%/100% (300 kWs, 200 kWs, 150 kWs, 100 kWs). I'd also be inclined to use SSR for determining how many shots you get out of a given power supply - a 1,000 kWs (1 MWs) power supply for a 30 kJ weapon supplies 10 shots at TL9, 15 shots at TL10, 20 shots at TL11, and 30 shots at TL12 (as opposed to 10, 14, 20, 33).

[Mysterious Dark Lord v3.2]

GURPS 3rd Edition Vehicles, pg 123-127 - detailed steps for designing a beam weapon by output in kj, from handheld to vehicular.

Just do that, then convert to 4th Edition.

Easy-peasey.

[the-red-scare]

According to David Pulver, the energy to damage formula for generic lasers is dice = 2 * cube root of kJ. This also approximately matches beam outputs in, for example, Spaceships, so it appears to be correct. Then you just pick your efficiency and you can calculate the energy per shot, etc. A TL9 C cell holds 90 kJ, so you can work out the rest from there if you want.

David also had the following useful bit of preliminary Vehicle Design info:

Originally Posted by David L Pulver

The switch is now a general assumption that most beams are about 25% efficient at TL of origin, 50% one TL later, and 80-99% efficient two TLs later. Weight is 1x at TL of origin, x0.2 one TL later, and x0.1 two TLs later.

On the other hand, I then multiplied the base weight by 5 and reduced the TL of origin of most of the beam weapons by one (e.g., blasters at TL10) - basically it means you can have big heavy inefficient vehicle-type systems one TL earlier at about 5x weight, you can get the standard system at the base TL, and you can either halve the weight or roughly multiply damage by 1.25 but keep the weight the same (by using 2x the energy) one TL later.

[Malachite72]

Thank you all! This is the type of feedback I was searching for.

My aim (no pun intended) is to be able to use Pulver's Beam Design article to construct spacecraft and installation cannon, and have them powered by larger power plants. I a mish-mash of design systems for spacecraft design, and weaponry can be powered by the spacecraft's power plant, or have an energy bank for independent power.

That's why I wanted to know how much power (in Kj per second, i.e. Kilowatts) a shot would use, based on kilojoules of energy of the energy blast. I am looking to be compatible with Ultratech, etc.

TY muchly, all!
M.