XKCD What If KEWs

Annachie wrote:I always thought that the Masadans wanted Grayson. Glassing the planet would be the last thing they wanted

They wanted Grayson. The stated plan was to bombard cities until the survivors surrendered. But it's pretty easy leap from there to well, we can't win, so we'll kill the heretics.

Daryl wrote:You weren't alone in pointing this out fly. Honorverse physics doesn't do Relativity well.
A high c fractional missile has gained a lot of mass from the "free energy" supplied by handwavium being converted in a reversal of E=MC2, which then converts back on impact.

Better check the relevant threads on who was pointing out the issue. KZT and this NAMELESSFLY who provoked such wailing, knashing of teeth, not to mention loss of bowel as well as bladder control were the chief instigators.

Don't get me started on the diffraction limitations of Grasers.

At .9 cee, the Lorentz factor is barely 2. One can ignore the relativistic mass for purposes of back of the envelope calculations.

At .9 cee, the Lorentz factor is barely 2. One can ignore the relativistic mass for purposes of back of the envelope calculations.

True, and thanks for that fly. However if shielding is only good up to 0.9c, I wonder if a very thick nose cap would suffice to get it up a bit more? Mind you even 2 means double, and when talking thousands of megatons that still means lots.

Daryl wrote:

At .9 cee, the Lorentz factor is barely 2. One can ignore the relativistic mass for purposes of back of the envelope calculations.

True, and thanks for that fly. However if shielding is only good up to 0.9c, I wonder if a very thick nose cap would suffice to get it up a bit more? Mind you even 2 means double, and when talking thousands of megatons that still means lots.

At .9 C, any gas much less dust impacts as energetically as Cosmic rays. I will have to look up the absorbtion factors, but I'm thinking that you might need a meter of lead. Weber's psudophysics dictated that his ships should have inpentrable "bow walls" to enable surviving velocities near Cee.

https://space.stackexchange.com/questio ... g-or-lower

Now that my memory has been refreshed, I realize that you need about 10 meters of liquid hydrogen.

TFLYTSNBN wrote:KZT and some NAMELESSFLY that was exiled from this forum were perhaps ungentle in pointing out that Mr Weber had FUBARed by not appreciating that the kinetic energy of a nuke impacting at .9 C is about a hundred times greater than the yield of the nuke. That nominal yield 20 Megaton shipkiller missile massing some 100 tons will do as much damage as about 1,000,000 Megatons. Just one missile is an ELY, Extinction Level Event.

Yeah, I've been saying this also--the warheads are mere firecrackers compared to the missile energy. I think any missiles that no longer have a purpose (dazzlers, Apollo control missiles, depending on the situation the jammers also) should be trying to ram.

The missiles still need the warheads because it gives them a standoff range they don't have otherwise--you're a lot more likely to get in range of your rods than to get an impact.

Loren Pechtel wrote:

TFLYTSNBN wrote:KZT and some NAMELESSFLY that was exiled from this forum were perhaps ungentle in pointing out that Mr Weber had FUBARed by not appreciating that the kinetic energy of a nuke impacting at .9 C is about a hundred times greater than the yield of the nuke. That nominal yield 20 Megaton shipkiller missile massing some 100 tons will do as much damage as about 1,000,000 Megatons. Just one missile is an ELY, Extinction Level Event.

Yeah, I've been saying this also--the warheads are mere firecrackers compared to the missile energy. I think any missiles that no longer have a purpose (dazzlers, Apollo control missiles, depending on the situation the jammers also) should be trying to ram.

The missiles still need the warheads because it gives them a standoff range they don't have otherwise--you're a lot more likely to get in range of your rods than to get an impact.

This was alluded to early in the series (and later, such as during the Yawata strike) that "old fashioned contact nukes" only went off if they couldn't hit the hull physically.

A better question is why haven't they reverted to contact nukes in mass launch situations? The original reason the laser head was so much more effective was that enemy point defense got much more effective as the warhead got closer, but with pod-launched MDMs that reason is no longer valid. The accuracy of the point defense is irrelevant if you can swamp it with far more targets than it can service in the time available.

Manty and GSN ships don't have to deal with that too much since they can fight with their wedge blocking contact hits, but Havenite and other navies are vulnerable to physical hits or nukes going off close aboard.

Galactic Sapper wrote:A better question is why haven't they reverted to contact nukes in mass launch situations? The original reason the laser head was so much more effective was that enemy point defense got much more effective as the warhead got closer, but with pod-launched MDMs that reason is no longer valid. The accuracy of the point defense is irrelevant if you can swamp it with far more targets than it can service in the time available.

Manty and GSN ships don't have to deal with that too much since they can fight with their wedge blocking contact hits, but Havenite and other navies are vulnerable to physical hits or nukes going off close aboard.

Certainly the MDMs are terminal approach are moving quickly enough that the improved PDLC hit percentages as they close that last 50,000 km are largely irrelevant because the PDLC clusters get only a shot or two off in the quarter second to so it takes to cover that distance; and in a mass launch there would usually be too many warheads per target to get more than an extra handful.

Certainly the warheads should be able to close to the point of using the directed nuclear blast sidewall "burn" mode. I can see a couple possible reasons they might not try for full contact nuke.

1) At closing speeds in excess of 0.7c the sidewall penetrator necessary to slip the warhead through the sidewall where it can do real damage may be unreliable

2) There may be so many warheads that attempting to go for the contact kill may result in many of them getting fried by friendly fire proximity kills as they all try to mob an area behind the sidewall of no more than, say, 2 km^3.

3) The risk that almost any last minutes rolling of the ship would cause the warheads to impact on the wedge rather than scream through the (relatively) tiny gap between the wedge planes to reach the sidewall.


If you just go for laserhead shots than your warheads only need to reach an area of 50,000 km or less with a view to the target - they can even try to pass ahead or astern of it (giving them shots not protected by sidewall) and so can keep relatively spread out.

Jonathan_S wrote:1) At closing speeds in excess of 0.7c the sidewall penetrator necessary to slip the warhead through the sidewall where it can do real damage may be unreliable

Very possible, although the kinetic energy hitting the sidewall would be significantly more than the warhead going off in "burn" mode, so it would still take down the sidewall.

2) There may be so many warheads that attempting to go for the contact kill may result in many of them getting fried by friendly fire proximity kills as they all try to mob an area behind the sidewall of no more than, say, 2 km^3.

That turns out not to matter much. Assuming they don't die to wedge fratricide (which is much more likely) they're moving so fast that the explosion of a warhead going off in proximity won't reach a neighboring warhead soon enough to disrupt the second warhead's detonation. And even if the detonation of one disrupts the detonation of another, that second one still has all the kinetic energy it needs to kill the ship if it was going to get a physical hit anyway.

3) The risk that almost any last minutes rolling of the ship would cause the warheads to impact on the wedge rather than scream through the (relatively) tiny gap between the wedge planes to reach the sidewall.

I've never seen specs on how wide the gap is or how much further open the front is than the back. Is there anything like an infodump on wedge geometry? Or sail geometry, which bugs me even more. Presumably they're annular, but how big is the hole around the hull? Does it project in the plane of the nodes or ahead/behind the ship?

If you just go for laserhead shots than your warheads only need to reach an area of 50,000 km or less with a view to the target - they can even try to pass ahead or astern of it (giving them shots not protected by sidewall) and so can keep relatively spread out.

Not to mention convenience for plot purposes. Laser heads can leave a beat up ship for survivors to struggle with as opposed to ships being contact killed with all hands or being basically fine with no middle ground.

So, I don't know the answer to this, but what is the effect of a planetary atmosphere on a projectile travelling at significant fractions of c?

We have problems with reentries, they have to be at the right angle and right speed, or they break up or bounce off.

Could this be a matter of being able to deliver the warhead to the surface?

Galactic Sapper wrote:I've never seen specs on how wide the gap is or how much further open the front is than the back. Is there anything like an infodump on wedge geometry? Or sail geometry, which bugs me even more. Presumably they're annular, but how big is the hole around the hull? Does it project in the plane of the nodes or ahead/behind the ship?

There is fact is an infodump on wedge geometry. There isn't one on sails, though the old SITS related Jayne's books include a diagram.

Wedge size varies somewhat with ship type, but for an SD each wedge plane is basically 300x300 km so the ship is still 150 km set back from the outer edge of the wedge and the opening near the center-point would be 100 km or so tall - with the sidewall just 10km or so out from the hull of the ship (but does appear to project forward and aft the length of the wedge). (And the ship itself being less than 1.5 km long and only at most a couple hundred meters high is a minnow inside the vast area within the wedge)

I don't have my copy of Jayne's handy but IIRC it gives size for a BC's wedge as well (in addition to the sails). IIRC the BC despite being 1/10th the size has a wedge that's about 65-70% the size of the SDs. Also IIRC the sails have a diameter roughly equal to the width of the wedge, so they're two parallel disks, stretching 150 KM in radius (for an SD) perpendicular from the hull -- one projecting from each Alpha node ring. So for an SD they'd be roughly 1070 meters apart (the nodes are about 150 meters from the ends of the ship - specifically looked a a Gryphon-class; but all should be similar. Obviously on a DD the hull is vastly shorter so the sails are correspondingly closer together)