TA: The Kris Longknife series

[The Dark]

I've been reading David Drake's RCN series, and a friend recommended Mike Shepherd's Kris Longknife series as another low-miracle sci-fi setting. One "stupid factor" in the series is that the energy weapons are measured in inches instead of power output. However, the Battle of Wardhaven provides enough information to get a ballpark estimate of pulse laser firepower.

The scenario: Longknife and a squadron of 12 Fast Attack Boats are engaging what they initially believe to be 6 President-class Battleships, which are armored with 3 meters of ice. They believe their 18" pulse lasers can penetrate that armor utilizing paired shots, where two boats each hit the same spot at the same time. The ships end up being new Revenge-class Battleships, with 5 meters of ice, which the lasers do not penetrate using the double shot technique.

Assumption: 100% energy transfer, and the size of the lasers is also the size of the beam at impact.

Givens: The volume of a cylinder is pi*h*r^2. Ice has an average mass of 916.7 kilograms per cubic meters. The latent heat to melt ice is approximately 334 kilojoules per kilogram. Using just the latent heat will give a lowball estimate.

Calculations:
3 meters:
h = 3 meters
r = approximately 0.3 meters
volume = 3.46 m^3
mass of ice = 3,171.83 kilograms
energy to melt ice = 1.06 gigajoules
energy per shot = 0.53 gigajoules

5 meters
h = 5 meters
r = approximately 0.3 meters
volume = 5.77 m^3
mass of ice = 5,286.39 kilograms
energy to melt ice = 1.77 gigajoules
energy per shot = 0.88 gigajoules

Thus, it appears that an 18" pulse laser delivers more than 0.53 but less than 0.88 gigajoules per shot.

[JGregory32]

probably a very stupid question but why are you using the volume of a cylinder?

[Samuel]

probably a very stupid question but why are you using the volume of a cylinder?

The beams are fired from cylinders.

Isn't this the series with the main character being a rich girl and joining up with the marines? Is it worth reading?

[Questor]

She joins the navy, and at the very beginning is assigned to be the officer in charge of a bunch of Marines, for a single mission.

The supporting characters, especially after the first book can be funny, but I would imagine that like a great many things, your milage may vary based on what you are looking for.

I was worried that it was going to quickly Weber itself by bringing in politics, but those parts seem to be played mostly for interpersonal relationships or for laughs.

I was thinking about rereading them actually.

Has anyone read the books that come before the Kris Longknife ones? The Society of Humanity books by Mike Moscoe,

[Samuel]

Has anyone read the books that come before the Kris Longknife ones? The Society of Humanity books by Mike Moscoe,

And? Don't leave us hanging!

The supporting characters, especially after the first book can be funny, but I would imagine that like a great many things, your milage may vary based on what you are looking for.

I have 3 boxes full of books that are the dregs essentially. After going through about 7 before them. Decent is acceptable.

[Questor]

Has anyone read the books that come before the Kris Longknife ones? The Society of Humanity books by Mike Moscoe,

And? Don't leave us hanging!

I'm asking, as I can never find them. The events are alluded to in the Kris Longknife novels, and I want to know what happens.

Edit: Fixed quote.

[The Dark]

probably a very stupid question but why are you using the volume of a cylinder?

The beams are circular, so the "armor" (ice) they're melting would be roughly cylindrical (the curve of the hull would alter it slightly, but it wouldn't significantly alter the calculations.

I was worried that it was going to quickly Weber itself by bringing in politics, but those parts seem to be played mostly for interpersonal relationships or for laughs.

So far, the politics have mostly seemed to be excuses for the situations that happen.

[JGregory32]

The beams are circular, so the "armor" (ice) they're melting would be roughly cylindrical (the curve of the hull would alter it slightly, but it wouldn't significantly alter the calculations.

Wouldn't the area of effect be more like a half-sphere?

BTW Thanks for letting me know about the series, I'm trying to make it through the first book and it seems pretty decent so far.

[Drooling Iguana]

How the hell does ice work as armour? Does the ship just manage to magically teleport its excess heat away?

[Samuel]

How the hell does ice work as armour? Does the ship just manage to magically teleport its excess heat away?

I'm guessing ablative. When it vaporizes, it takes the heat with it.

[Drooling Iguana]

Yes, but it would also take the armour with it. How long is that stuff supposed to last?

[fgalkin]

Yes, but it would also take the armour with it. How long is that stuff supposed to last?

One combat engagement? if you have lasers vaporizing meters of it in every battle, how long do you think it would last? And ice is cheap and easy to replace.

Have a very nice day.
-fgalkin

[GrandMasterTerwynn]

Yes, but it would also take the armour with it. How long is that stuff supposed to last?

That's sortof the whole point behind ablative armor. It's supposed to dissipate weapon energy by ablating. As far as ablative armor materials go, ice actually isn't bad. It's easy to get, easy to work with, easy to replace, and is made from a substance which will soak up a lot of energy before changing phase.

[Drooling Iguana]

My point is that the excess heat of running the spaceship would most likely cause most of the armour to melt/boil off before it even arrives at the battle.

[Dave]

My point is that the excess heat of running the spaceship would most likely cause most of the armour to melt/boil off before it even arrives at the battle.

You could carry cryogenic coolants that you boil off to keep the heat down, or just have radiators. (I have no idea what timescales the engagements take place over.)

[white_rabbit]

Those President class battleships are supposed to have 100 gigawatt generators BTW.

[The Dark]

My point is that the excess heat of running the spaceship would most likely cause most of the armour to melt/boil off before it even arrives at the battle.

There are separate deployed radiators that are stowed during combat, when they dump heat into propellant. In this particular engagement, they actually did run coolant through plumbing to use the ice as a heat dump, and noted that it was weakening the armor, but that was considered an acceptable trade-off for increasing their rate of fire.

Wouldn't the area of effect be more like a half-sphere?

I don't think it would, because the beam should be equally intense through the entire area of the lased surface. You might get some hemispherical effect from the edge of the lased area radiating into the unlased area, making it slightly shallower, but it shouldn't be significant.