I'm not sure about that. Sorium is more abundant than anything else now (eg. Tritium for warheads) and mines faster than anything else.
And fuel is ridiculously energy dense; which can be packed into a high speed projectile by a high speed ship shooting a high delta-v missile, all without increasing the missile's weight.
Even if the missile turns into plasma in the upper atmosphere (I think you mentioned 50km?), the resulting nuclear fireball could be big enough to reach the ground.
I don't disagree with this. I was commenting on a proposal to allow the use of asteroids as weapons. And for that, you tend to go for mass over velocity. And it would break up well above 50 km. I just chose to find dynamic pressure there.
I would agree with byron that a relatively slow missile that can transit the atmsphere is going to be more effective that one that is basically trying to shove it out the way.
I'm now wondering if the best planetary defense would actually just be a bunch of terraformers that busily pumped up the atmosphere density to the maximum tolerances of my inhabitants.
Not a bad idea. However, it really wouldn't do much to mitigate the damage. All this does is make it impossible to physically hit ground-level targets.
At high velocities the atmosphere is largely treated as a solid. In reality compression would occur that would make a material with the number of atoms of the column of air equal to the missiles diameter. Essentially once the missile's transit time through the atmosphere is shorter than the ability of the air to move away from it the air is simply compressed. Pretty much as happens with a piston. The temperature rise is such the molecules disassociate into atoms. This heat is conducted into the missile body but again due to the short time involved...(at 0.1c 50 km requires 1.7 ms) only the upper fraction of the missile would convert into plasma but the plasma would have the same mass, and momentum (hence kinetic energy) of the original missile. The energy required to compress that air column would be lost to the missile but I suspect that it is not enough to slow the missile down significantly.
When the missile strikes the ground the entire mass of the missile (plus the air column) is then converted into kinetic energy and dispersed via the shock wave and in large part transferred to all the debris thrown up. In principle though everything within a reasonable distance of the missile strike would be converted into plasma by the energy contained in the missile and only once the fireball expanded and cooled would you start seeing debris thrown upwards.
Note the ground shock wave would be extremely powerful. But even the air shock would be considerable...the missile impact probably is causing an outward going pressure shock front that would meet the inbound atmosphere from the vacuum left by its passage with ugly results.
There is no need for warheads on missiles that can achieve even low fractional C velocities.
Really? The projectile will begin heating and suffering aerodynamic stresses somewhere above 150 km, which is three times what you estimated. Also, what's stopping it from breaking up under the load? Just curious.
The plasma is no less dangerous then a metal bar. It is fully capable of transmitting shock and energy to a material. HEAP rounds convert a titanium cone to a directed plasma jet to slice through armour, and plasma cutting is a standard way to cut thick metal. Any oxyacetylene torch is a plasma as well.
No, that's not how HEAT rounds work. The copper liner stays in metallic form the entire time, but behaves like a liquid under the pressure. And neither an oxyacetylene torch cuts by heating the metal, not by momentum transfer. So does a plasma torch for that matter.
A plasma strike is what does damage in a nuclear blast in space. It is the warhead/missile being converted into plasma that is doing the damage as there is no atmosphere to transmit the energy. All the other energy is contained in particles and photons...which are not negligible but follow a r2 law so they loss energy rapidly with range.
No, that's not what does the damage. The damage is done by the X-rays from the bomb itself. The casing is fairly negligible.