The media is agog at hypersonic missiles and the difficulty in defending against them.
As a simple, back-of-envelop exercise, I calculated the mass of a projectile that was needed to impart the same kinetic energy as the 30X173mm ammo used in the Warthog A-10 cannon. My assumption is that a solid, axial shot with a 30x173mm round would eviscerate a hypersonic missile. Most of the armor on the missile would likely be ceramic, heat shields and ceramic is brittle.
At the muzzle, the 363 gram round is traveling 1020 meters per second, about three times the speed of sound. It boasts about 190kJ of energy.
Suppose one were able to fill the air with gravel with no forward velocity. How much would each stone have to weigh so that the imparted energy was the same as the 30x173mm round.
Spreadsheets are our friend. Assuming a forward velocity of the missile of Mach 10, each stone would have to weigh 32 grams, about one ounce.
What if the missile delivering the gravel had a velocity of Mach 5 and it was moving toward the hypersonic missile? Each subprojectile would have to weigh about 15 grams.
Hypersonic-to-hypersonic? 8 grams. Considering that a hypersonic missile is likely to be much more vulnerable to a kinetic energy strike than a Bradley fighting vehicle, it may prove that the most cost effective countermeasure would be a Patriot missile with a Claymore mine loaded into the nose.
Even knocking the hypersonic missile slightly akilter while it is traveling Mach 10 would likely cause it to spin and shred itself or rupture the heat shields and have it come apart like Space Shuttle Columbia.