Russian President Putin just had to try out his new super-duper missile on Ukraine. While you’re bombing a country into the Stone Age, you might as while play with the new weapons in your arsenal.
The new missile is one that has stumped “military thinkers” for decades: how to make a weapon that that flies great distances at supersonic speeds and avoids detection by the enemy.
The dream is a hypersonic missile, essentially a glider released from a rocket or plane that can be manoeuvred. The initial speed is 20 times the speed of sound (Mach 20) but slows down as it glides to its target.
The U.S., China and Russia have been trying to make these things work for decades. The problem with them is physics.
Putin claims to have perfected hypersonic missiles as a demonstration of Russia’s superiority
A senior U.S. Defense official says their use in Ukraine is odd because the target is so close and conventional missiles are as effective and cheaper.
“It’s a bit of a head-scratcher. … Why you would need a hypersonic missile fired from not that far away to hit a building?” the official said.
The trouble with military thinkers is that they don’t think science. They come up with ideas and then hope that technology catch up.
Scientists David Wright and Cameron Tracy analyzed the physics of hypersonic missiles and found them wanting (Scientific American, August, 2021).
Hypersonic weapons promise more than they can deliver.
“Yet our studies indicate that hypersonic gliders encounter severe challenges,” say Wright and Cameron, “Physics gets in the way.”
A major problem is drag. Any object going through a fluid such as air has to plow through it, much like a boat through water. The amount of drag that a glider experiences is not directly proportional: drag increases as the square of the velocity. For example, a glider at Mach 5 is subjected to 25 times the drag force than when it flies at Mach 1. One at Mach 20 faces 400 times the drag of when it is at Mach 1.
Each turn in the glider also slows it down. Such manoeuvres can cost significant speed and range.
Another problem is heat. The leading edges of gliding missiles flying at Mach 10 or above can reach temperatures greater than 2,000 celsius. Not just the high temperatures threaten the integrity and stability of the glider but the air becomes ionized and scours away the surface of the missile.
Hypersonic missiles are supposed to reach their targets undetected by radar but even if the missile survives the roasting, the heat produces a bright infrared signal that satellites can see. They are not invisible as claimed.
Hypersonic missiles are supposed to travel faster than conventional ballistic weapons but that’s only true for high flying ballistic weapons. For those flying at lower altitudes (depressed trajectory), that’s not true.
“Our calculations show that a ballistic missile on a depressed trajectory can deliver a warhead with an equal or shorter flight time than a hypersonic weapon over the same range,” say Wright and Cameron.
Putin imagines that Russian superiority in hypersonic missiles will return the country to the glory years of Sputnik in 1957, when the Soviet Union dominated satellites.