As the US, Russia, and China race to develop hypersonic weapons, misunderstandings about their speed and stealth persist. To be considered hypersonic, a missile must travel at five times the speed of sound (Mach 5). The defining characteristics also include the ability to maneuver throughout its flight.

What is Hypersonics?

The term hypersonic is used to describe objects that fly much faster than the speed of sound. This includes all speeds above 15,000 mph (24,140 kph), when the air molecules disassociate, forming a plasma that makes it very difficult to control or communicate with a craft.

The US and other countries are developing weapons and vehicles to reach hypersonic speeds. For instance, the intercontinental ballistic missiles in the world’s nuclear arsenal are hypersonic, traveling over 15,000 mph at maximum velocity. The military is also working on hypersonics to give the Pentagon the capabilities it needs to protect its forces and homeland, said White. These systems must be capable of flying long distances with unpredictable maneuverability to adversaries at high altitudes. 

Hypersonic Aerodynamics

Hypersonic flight represents a new level of complexity in aerodynamics, the branch of physics that deals with fluid motion. It involves speeds greater than the speed of sound, or Mach 5. This fast pace will cut commercial travel time and compress response times for military commanders.

At these speeds, air molecules near an aircraft vibrate and break apart. Their chemistry changes, influencing how much force is exerted on the aircraft. Moreover, shock waves and expansions generate large variations in air density and pressure around the aircraft, which can cause structural failure.

Hypersonic Materials

Objects that travel at hypersonic speeds must be built from materials that can withstand searing heat. They must also withstand hypersonic flight’s intense mechanical vibrations and shocks.

Structural problems primarily arise from the processes of oxidation and ablation, which cause scorching air and gas to remove surface layers of the metallic materials that comprise aircraft and rockets traveling at hypersonic speed. The resulting structural damage can severely impact the performance and life of such vehicles.

To withstand these extreme temperatures, materials must be both strong and light. Silicon nitride offers the ideal combination of strength and thermal resistance. It’s also lightweight, allowing for greater payloads. Engineers use silicon nitride in various aerospace and defense applications, including avionics and power systems. 

Hypersonic Weapons

The United States and Russia are developing weapons that travel at hypersonic speeds, including hypersonic glide vehicles and cruise missiles. These weapons are highly maneuverable and can change their target during flight. This makes them difficult to track and defend against.

One of the challenges engineers face is stabilizing a weapon at hypersonic speeds. When objects move at speeds faster than the speed of sound, they create a shock wave that can disrupt airflow around them. This can cause the weapon to lose control or even break apart. To overcome this challenge, engineers use aerodynamic surfaces to guide the weapon and to maneuver it. But, this can increase the missile’s thermal load and limit its maneuverability.