https://web.archive.org/web/20080828221908/http://www.jerrypournelle.com/archives2/archives2mail/mail404.html#Thor https://infogalactic.com/info/Kinetic_bombardment An interesting thing happens when objects reach or exceed Mach 10. Their kinetic energy becomes roughly equal to the same explosive energy contained by an equal mass of high explosives. To try and put this into a context, the M829A3 depleted uranium rod penetrator fired from the 120mm L/44 M256A1 smoothbore gun on the M1 tank has a total mass of 22.3 kg (49 lb) and leaves the muzzle at a velocity of 1,555 m/s (5,100 ft/s). Not quite Mach 5. This still concentrates about 1,000,000 joules of kinetic energy onto an area about the size of a quarter. It's not a "death-ray", but it will do until the death-ray gets here. During the second Iraq war, we were guiding 500lb practice bombs that were essentially a big hollow steel case filled with concrete, with a laser guidance package installed. Dropped from 15,000 ft AGL, they could be guided to a precise impact on the top of the turret of a tank parked right next to a school or hospital, penetrate all the way through, killing the crew and destroying the vehicle, and the people in the building right next to it would hear a sound like the worlds biggest hammer hitting the worlds biggest anvil. And during it's landing approach the space shuttle would reach speeds in excess of Mach 25.