Depending on what kind of impact angle they can achieve they may not need to add high explosives to this. Mach 20 is 400 times the kinetic energy of mach 1 and 40,000x the kinetic energy of a 76mph collision. So, even a 100lb craft = 1,000 times the impact energy of a 4,000lb truck at highway speeds.
Mortars might, but not artillery, including Naval artillery. The gun fires a shell, not a bullet, which can be designed to cause different types of damage upon whatever it hits e.g. High Explosives to blow stuff up, Armor Piercing to penetrate through armor plating before detonating its minimal explosive load, etc.
The U.S. Navy had mostly moved away from Naval artillery due to the rise of guided missiles with their much longer range, but they are investigating railgun systems which may give advantages compared to missiles.
Kinetic Bombardment has been a sci-fi concept for decades, and it's interesting to see a real, possibly cost effective, technology that could make it real. At those speeds, you don't need explosives, just a lot of mass to slam into something.
According to project Thor, it would not be that cost efficient. The wikipedia page states that the rods would need to be at around 8 tons. A ton of tungsten is around 50k$ so 8 tons is rather negligible. What is very expensive is to get 8 tons of material to space. During the space shuttles era, bringing a kilogram of matter to space would cost around 20k$. A ton is 907 kilograms.
8 x 907 x 20 000 = 145M$ per payload.
I don't have the exact numbers for the cost of an ICMB with a nuclear warhead but I'm pretty sure that it is less than that. We also didn't factor in the cost of maintaining an orbital launcher, possibly manning that thing and other costs which being in space incur.
Maybe with newer launch methods bringing goods to space will be cheaper, but I don't think we'll see this kind of tech unless costs decrease to around 2000$/kg to space (1/10th of what it is now).
> As of March 2013, Falcon Heavy launch costs are below $1,000 per pound ($2,200/kg) to low-Earth orbit when the launch vehicle is transporting its maximum delivered cargo weight.
Well we are reaching an age (of asteroid mining) where it's probably more cost efficient to manufacture in space and ship (or railgun, I guess) the mass to earth. Probably not for a while, but I don't think it's science fiction anymore.
That gives me an interesting idea. Do you think it could be feasible to mine ore from space and then drop-ship it to some low-depth (a few hundred feet at most) part of the ocean? The heat from re-entry would likely turn the metal into a molten blob, and the sea water would rapidly cool it.
A Thor style pure kinetic weapon was supposed to impact at around Mach 10, but this is a scram jet and as such should be able to maintain a significantly higher speed. Granted it's unlikely to maintain that at sea level, but it sounds like it impacted the water reasonably intact and so could probably do a powered dive. Also, around mach 9 is the break-even point where high explosives have more kinetic energy than chemical energy so even if it hit's at say mach 12 that's still a lot of energy.
