XKCD What If KEWs

ThePlebicide wrote: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?

The effect is significant in some ways, almost trivial in others. Thirty metric tons of pretty solid construction moving near the speed of light is going to go through the atmosphere in about a thousandth of a second, hitting the ground a few milliseconds before a massive shock wave of superheated plasma generated by its collision with air molecules hits the ground. "Burning up" or not is nearly irrelevant; the energy still hits the ground whether it's in the form of the missile body hitting intact or the plasma wave that's basically a directional nuclear weapon by itself.

Jonathan_S wrote: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)

That's what I thought. It turns out that one of the significant story events in UH is geometrically impossible, or at least insanely lucky.

Galactic Sapper wrote:
That's what I thought. It turns out that one of the significant story events in UH is geometrically impossible, or at least insanely lucky.

That’s OK. Show me a drawing of how barricade works. Please include an explanation of how in your configuration every SLN missile has a view of the target and what the wedge clearance between the SLN missiles is and how it’s reasonable that the SLN missiles would asssume that formation without orders.

kzt wrote:

Galactic Sapper wrote:
That's what I thought. It turns out that one of the significant story events in UH is geometrically impossible, or at least insanely lucky.

That’s OK. Show me a drawing of how barricade works. Please include an explanation of how in your configuration every SLN missile has a view of the target and what the wedge clearance between the SLN missiles is and how it’s reasonable that the SLN missiles would asssume that formation without orders.

It doesn't work as described, as you allude to missile separation when the wedges shut down for the ballistic segment would be enough that an outbound attack missile even one with a slightly larger wedge (as Mk23s were described to be) can't hit many of them blowing straight through - maybe 2 or 3 per salvo. (Wedges being broader than they are tall you can stack impeller driving objects more closely vertically than horizontally, but the "barricade" missiles can roll to orient the width of their wedge as best they can)

And even if the "barricade" Mk23s are allowed to radically alter course they can't seem to get get many more. The cataphracts are going to be coasting at no more than about 84,000 KPS and the Mk23s were said to be at full power, 92,000 gees. Let's further assume they begin the intercept half way through their powered envelope, 90 seconds in, their base velocity would be up to about 81,000 KPS - so a closing speed of 165,000 KPS.

If the 500 Cataphracts were in a 25x20 array and we assume minimal spacing is probably 1.5 km lateral separation and 0.4 km vertical then they cover an area of 10 km tall and 30 km wide. At 92,000 gees it would take a Mk23 less than 0.3 seconds to fly across the 30km width of the array, so if it can swing wide then zip perpendicular across the path of the missile array it can seemingly kill at least one entire row of 20 missiles.

Except of course for that closing velocity! At 165,000 KPS that tiny 0.3 seconds means the base courses of the missiles brings them together another 49,500 km! So you still can't get more than a handful before they zip right past you, maybe you got 4-9 missiles instead of 2-3; maybe.

I actually started out thinking that this approach would work better until I ran the numbers. Darn.

Sorry, missile wedges are about 10 km wide. And they spin. Since the last stage is CM and they have bigger wedges the missiles have to be spaced over 15 KM apart minimum (body to body) so they don't all destroy each other then they initialize the next stage.

kzt wrote:

Galactic Sapper wrote:
That's what I thought. It turns out that one of the significant story events in UH is geometrically impossible, or at least insanely lucky.

That’s OK. Show me a drawing of how barricade works. Please include an explanation of how in your configuration every SLN missile has a view of the target and what the wedge clearance between the SLN missiles is and how it’s reasonable that the SLN missiles would asssume that formation without orders.

You forgot every missile needs rear LOS to the firing platform for targeting updates.

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.

You're a lot more likely to be able to get into laserhead range than to get to impact. Also, if a bunch of missiles try to ram they'll fratricide.

Thus I think ramming should mostly be a tactic for the otherwise spent missiles. However, let the Apollo control computers have ram as an option--by the time they reach laser range from a long burn there most likely won't be any point defense fire (the defenders will have shot everything, there won't be enough recharge time to get off another shot) and if the geometry permits a ram, let one missile try it.

ThePlebicide wrote: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?

What reaches the surface will not be a warhead. It will have been totally vaporized by it's passage through the atmosphere but still intact on a macro level. On the micro level, though, it's structure will be gone and there will have been a lot of transmutation.

The lack of a warhead is irrelevant, though--the biggest missile warheads are in the range of Tsar Bomba. A pod of ghost rider missiles at burnout is in the range of the dinosaur killer.