What is behind the development of hypersonic weapons

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The supposed miracle weapon that China proudly presented to the public in October 2019 looks inconspicuous: a pointed white nose, a slim body painted matt green, and a pair of stub wings. Visually somehow a mixture of wind tunnel model and oversized paper airplane. But the weapon, brought up 16 times at the parade marking the 70th birthday of the People’s Republic, packs a punch. It should head for its targets at ten times the speed of sound, at more than 12,000 kilometers per hour: extremely fast, agile, invincible. At least that’s the promise.

This post is from Issue 4/2020 of the MIT Technology Review.

DF-ZF, as the Chinese called their arrow-shaped projectile, is a so-called hypersonic weapon – a new, supposedly revolutionary type of weapon. Not only the People’s Republic wants to be at the forefront in this field, Russia also added the first hypersonic projectile to its arsenal at the end of December 2019. Meanwhile, the USA is investing many billions of dollars in order to catch up with weapons technology. At least according to the announcements, the hypersonic triggered a new, expensive arms race.

Weapons that rush towards their target at hypersonic speed – i.e. more than five times the speed of sound – are basically nothing new. Every ICBM travels at a comparable speed. However, one thing distinguishes the new weapons from their conventional relatives: when they fall back to earth from space, the nuclear warheads of the ICBMs are on a so-called ballistic trajectory – similar to a stone that someone has thrown into the air.

This article is from Technology Review 4/2020. The magazine will be available from March 19, 2020 in stores and directly from the heise shop. Highlights from the magazine:

The further course of their flight can therefore be calculated in advance; the enemy missile defense has a good chance of shooting down the attackers. The new hypersonic weapons, on the other hand, can be controlled – at least to a limited extent. Similar to the much slower cruise missiles, they can change their course suddenly. Hyperbarrage weapons are therefore considered unpredictable. At the same time, they are so fast that enemy missile defenses cannot react to their maneuvers.

DF-ZF, China’s matte green flagship weapon, does this without its own engine – just like Avangard, the much larger Russian counterpart, which is said to have been officially delivered to the troops at the end of December 2019. “Like a meteorite, like a ball of fire,” the “weapon of the future” will soon fall on its targets, promises Russian President Vladimir Putin.

Avangard and DF-ZF belong to a category that military experts refer to as hypersonic gliders: In order to perform their tasks, the weapons must first be launched with a conventional rocket and brought up to altitude and speed – in the case of Avangard up to 27 times as much speed of sound. In this flight phase, the five-meter-long Russian glider hardly differs from the warhead of an ICBM. He, too, is initially traveling on a ballistic trajectory that takes him almost into space.

However, as soon as the aircraft separates from its rocket, falls back to earth and feels the end of the atmosphere, its behavior changes. Similar to a rock thrown into a lake at a low angle and bouncing on the surface of the water, the flattened Avangard can surf the Earth’s atmosphere. It regains altitude slightly, descends, reaches denser layers of the atmosphere, hops there again and finally, controlled by its small tail units, aims at the target. The glider remains invisible to enemy satellite and radar systems designed to detect and intercept ballistic missiles above the atmosphere. It is too fast and manoeuvrable for ground-based missile defense.

However, all this sounds easier than it is in practice. So far, none of the supposed magic bullets has proven their usefulness. Two problems in particular stand out: On the one hand, racing through the atmosphere at more than five times the speed of sound creates immense friction. The missiles inevitably heat up, their surfaces reaching temperatures of up to 2,000 degrees Celsius. Extremely resistant materials such as ceramics or alloys made of nickel and chromium are therefore necessary.

Nevertheless, the gliders expand, their shapes and thus their flight characteristics change. In addition, a bubble of plasma forms around the hypersonic weapons. While this hot, ionized gas absorbs some radar waves, making it harder to locate the gliders, it also changes their aerodynamics. The already small rudder surfaces find it even more difficult to initiate course changes.

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