What is a Hypersonic Missile? Why is it dangerous?

The hypersonic missile is one of the most dangerous weapons in the world. And the reason for this danger is not only because it is packed with explosives: these missiles can travel at between 5 and 25 times the speed of sound – about 1 to 5 miles per second (1.6 to 8 kilometers per second).

Surplus Navy Phoenix missiles like this one mounted on the centerline pylon of NASA’s F-15B research aircraft may be used to acquire hypersonic flight test data. Missiles of this model also exist in the military configuration. Credits: NASA Photo

The interest in hypersonic weapons and possible countermeasures spiked when Russia used a hypersonic missile against a Ukrainian arms depot in the western part of the country on March 18, 2022. Due to its fast velocity, it is difficult to track the flight of the missile. The other serious issue: it is difficult to counter such rockets before they hit their target because other types of armament simply do not act fast enough, and their projectiles do not achieve a comparable velocity.

At the present time, several countries claim to have fully developed hypersonic weapons, including China, India, Russia, and the U.S.

The hypersonic missile technology

Technically speaking, the word hypersonic describes anything that travels faster than the speed of sound. At 20 °C (68 °F), the speed of sound in air is about 343 meters per second (1,235 km/h; 767 mph), or one kilometer in 2.9 s or one mile in 4.7 s.

Hypersonic technology has existed for decades. Typical fighter jets can achieve velocities greater than the speed of sound. There was even a car that broke the so-called sound barrier. Rockets carrying humans to space also accelerate to hypersonic speeds shortly after the launch. And, of course, the infamous intercontinental ballistic missiles (ICBMs) carrying nuclear warheads reach about 15,000 mph (24,140 kph), or about 4 miles (6.4 km) per second at their maximum velocity, even though the first of them were developed right after the World War 2.

Compared to ICBMs, modern hypersonic missiles are smaller, and they do not need large platforms to launch them. They also do not fly that high – which is why their trajectory is more difficult to predict. If ICBM flies out of the atmosphere and then enters back, a hypersonic missile can be fired along a path in a straight line, unless the trajectory is modified electronically during the flight. 

A jet fighter carrying the Kinzhal missile. Image credit: Mil.ru via Wikimedia

Types of hypersonic missiles

There are three different types of non-ICBM hypersonic weapons: aero-ballistic, glide vehicles and cruise missiles.

• A hypersonic aero-ballistic missile is shot from an aircraft launcher, then accelerated to a hypersonic speed using a rocket engine. Then the missile follows a ballistic (unpowered) trajectory. Kinzhal, the Russian-made missile which they used during their invasion to Ukraine, belongs to the aero-ballistic type. This type of hypersonic technology is also the oldest.
• A hypersonic glide missile, similarly to the first type, is boosted using a rocket engine to a high altitude and then glides to its target, maneuvering along the way. There are several examples of hypersonic glide missiles: Dongfeng-17 (China), Avangard (Russia), and Conventional Prompt Strike (The United States).
• A hypersonic cruise missile is, like previous types, boosted by a rocket engine to hypersonic speed. Then, the missile uses an internal air-breathing secondary engine called a Scramjet to sustain that speed.

In all hypersonic missiles, their kinetic energy is exceptionally high. This means that even without an explosive warhead (conventional version), they generate a devastating impact power. However, these missiles can be easily modified to carry a warhead of any type – including nuclear.

The main danger of hypersonic missiles

Many nations seek to develop or purchase hypersonic missiles because of their main advantage: compared to conventional sub-sonic rockets, they are especially difficult to defend against. This means that nearly every shot lands on the target – if fired precisely.

Technologies to defend against hypersonic missiles already exist, but they are not widespread yet. One example is directed-energy weapons such as lasers (for example, Israel’s Iron Beam). The beam of light obviously propagates incomparably faster than any rocket in existence, and therefore high-power lasers may take different types of missiles relatively easily, sometimes in a matter of several seconds.

Detecting hypersonic missiles is another important issue because, in order to defend against one, you need to know when it was fired and where it is located at any instant. For this reason, some countries are developing sensor network technologies – either space-based or carried on specialized surveillance aircraft – which can be used to continuously observe large regions.

Of course, hypersonic missiles are also much more expensive compared to any conventional missile. That is why they are not produced in large numbers, and because for the same reason are not used often.

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