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In My Traveller Universe Detail what parts of Traveller you do (or don't) use in your campaign.

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  #121  
Old August 3rd, 2017, 02:39 PM
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Originally Posted by Adam Dray View Post
I'm willing to accept a handwave, but sandcasters are also made of handwavium.

See "Sandcasters" on Atomic Rockets: Warship Defenses. Stuff like:
Put simply, a layer of sand is no more effective at stopping a laser beam than a similar areal density of monolithic armor (in fact, it's a bit less effective due to structural issues); you can simply shoot holes in a cloud of sand, just like you can shoot holes in armor. As such, why spend X tons of your mass budget on temporary armor when you can just spend the same X tons on permanent armor?

In addition, a cloud of sand:

a) needs to be somewhat larger than the ship it shields (reducing areal density, and thus armor value)

b) cannot maneuver if the parent ship maneuvers (so if you deploy sand, you're stuck in your current position)

c) without some form of containment will simply disperse in a time frame that's comparable to the deployment time (if the cloud can cover the entire ship in 10 seconds, after 20 seconds it will have expanded to twice the size of the ship, reducing protection by a factor of 4. You can improve this time somewhat by using multiple projectors)
If you're already in a setting with reaction mass and important solid-to-liquid mass ratios for thrusters, the point about mass budget is especially salient.
I hadn't thought about the realism of sandcasters until now. Thanks for the hint.

Though I suppose some kind of active countermeasures will be available. Now, what that could be probably requires a bit more thought...
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  #122  
Old August 3rd, 2017, 03:00 PM
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The TNE model is how...

Sand is
  • reflective in the laser frequencies used in space combat
  • Not fired blindly, but to put that directly between by noting the targeting system ping and responding before the fire return (at several hundred G's)
  • Expended 1 canister per incoming laser.

The thing is, with laser at realistic ranges, it's not a great idea... but it's preferable to monolithic armor because Nyrath/Winchel overlooks one key point: The sand reduces the energy density more than monolithic armor of the same mass.

I don't have to stop the whole beam. I just have to make the beam drop below delivering more energy to my hull than the hull can dissipate. It doesn't matter if it does this by being a block (100%) or a 50% halftone screen - any energy spent on the sand reduces the energy on target as a unit density.

Also, the sand is MUCH easier to replace/repair than the monolithic hull armor is.
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  #123  
Old August 3rd, 2017, 03:32 PM
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At reasonable laser ranges (0.25 LS or less), a 6G ship can only change position 7.5m. How figured
D=0.5*A(2L)˛
D= distance in meters moved from predicted
L=distance in light seconds.
A=Acceleration in m/s˛
T=2L as your data is as old as your laser fire will be.
Yes I agree, it was TNE that first pointed the way to lasers being autohit under a certain range, in fact they had to nerf them for game balance.

However in this hard sci fi setting there is no grav focusing and no magic heat sinks - lasers will not be anywhere near as effective as in Traveller.
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  #124  
Old August 3rd, 2017, 03:44 PM
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Originally Posted by aramis View Post
The TNE model is how...

Sand is
  • reflective in the laser frequencies used in space combat
  • Not fired blindly, but to put that directly between by noting the targeting system ping and responding before the fire return (at several hundred G's)
  • Expended 1 canister per incoming laser.

The thing is, with laser at realistic ranges, it's not a great idea... but it's preferable to monolithic armor because Nyrath/Winchel overlooks one key point: The sand reduces the energy density more than monolithic armor of the same mass.

I don't have to stop the whole beam. I just have to make the beam drop below delivering more energy to my hull than the hull can dissipate. It doesn't matter if it does this by being a block (100%) or a 50% halftone screen - any energy spent on the sand reduces the energy on target as a unit density.

Also, the sand is MUCH easier to replace/repair than the monolithic hull armor is.
I agree with you.
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  #125  
Old August 3rd, 2017, 03:54 PM
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Sand is not special, and in fact it's probably less effective than armor, but it's sprayable.

So you have the ability to spray it right between you and the laser, and then there's the stuff about the targeting system ping, which is a whole lot of handwaving because you don't need to ping your target to hit it, so basically, you need to put up enough sand between your entire ship and the laser to serve as a shield.

Sand, once dispersed, is far less dense than equivalent armor. Let's say it's 1000 times less dense. So you need 1000x more sand than you have hull plating on the one side of your ship to be as effective as armor, and it needs to be placed and timed at laser speeds, and if you delta-V, your placement needs to account for that, too.

With reactionless M-drives, maybe this makes sense (probably not, but let's pretend). When you're worried about a 2:1 reaction mass ratio, hauling tons and tons of sand doesn't make much sense. Also, the thin-hulled torchships that Thot has been describing don't even want to run into a bunch of sand, I'd guess.
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  #126  
Old August 3rd, 2017, 04:26 PM
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Originally Posted by mike wightman View Post
Yes I agree, it was TNE that first pointed the way to lasers being autohit under a certain range, in fact they had to nerf them for game balance.

However in this hard sci fi setting there is no grav focusing and no magic heat sinks - lasers will not be anywhere near as effective as in Traveller.
Using the (relatively correct) formulae in FF&S, and not adding grav focusing, combat lasers can be made to about 60000 km.

Turret lasers far less. Still, lasers can be viable to about a quarter LS. And that's well within the "Can't miss the target ship" range.
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  #127  
Old August 3rd, 2017, 05:29 PM
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Originally Posted by aramis View Post
Using the (relatively correct) formulae in FF&S, and not adding grav focusing, combat lasers can be made to about 60000 km.

Turret lasers far less. Still, lasers can be viable to about a quarter LS. And that's well within the "Can't miss the target ship" range.
Whereas projectile weapons have - theoretically - unlimited range, but are going to be hideously inaccurate against even poorly maneuvering targets like spaceships outside far shorter ranges than laser.

Of course, immobile targets like space stations - or bases on a planetary surface - can be hit over far longer distances. Heck, with sufficient computer power to calculate the exact firing solution, you could probably hit a planet from a different star system.


As for the third weapon type, missiles... assuming missiles operate under the same "1400 seconds at 1 g" parameters as spaceships, a quick back-of-the-envelope calculation gives them a maximum range (at which they run out of fuel) of 9.8 million km, with a terminal velocity (assuming firing platform and target are at rest relative to each other) of 14 km/s - meaning a laser with 0.25 light-seconds maximum range would have about an hour and a half to destroy the missile if it comes in at maximum speed.

I don´t know what kind of rate-of-fire that laser is assumed to have, but to me this sounds like you´ll need a MASSIVE salvo of missiles to saturate any kind of point defense.
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  #128  
Old August 3rd, 2017, 06:37 PM
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The waste heat from such a laser would melt the ship that fires it.
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  #129  
Old August 3rd, 2017, 08:17 PM
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The waste heat from such a laser would melt the ship that fires it.
Hardly. The waste heat isn't any more an issue than the power source needed for it.

The ROF may be a bit low in order to avoid meltdown over time, but heat pumps are relatively functional, and while radiation isn't efficient, it works well enough to allow such a laser.
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  #130  
Old August 3rd, 2017, 09:53 PM
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Hardly. The waste heat isn't any more an issue than the power source needed for it.

The ROF may be a bit low in order to avoid meltdown over time, but heat pumps are relatively functional, and while radiation isn't efficient, it works well enough to allow such a laser.
True. In fact, it is exactly the same issue, as a significant portion of the reactor's 250 MW-per-dton-output will have to be dissipated. Without an enormous heat radiator tree, that's quite some achievement.
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