4 May 2023

Unique hypersonics facility: “From simulation to world-class experiments”

Armed forces around the world are following developments in hypersonic weapons. One of FOI’s main contributions to research in this field is the creation of a unique experimental facility for understanding scramjet propulsion of hypersonic cruise missiles.

The entrence of FOI's facility in Grindsjön.

The unique new facility will be located at FOI’s facility in Grindsjön. Photo: FOI.

Hypersonic vehicles and weapons travel at speeds of at least Mach 5 (1715 m/s). Their propulsion is primarily based on two different technologies:

  • scramjet engines that propel a cruise missile. Such engines are powered by burning a fuel (hydrogen) and the air’s oxygen, while competing technologies require tanked oxygen. The technology works first when it reaches Mach 5, which it attains with the help of traditional rocket propulsion.
  • gliding, which involves using a rocket to propel the craft upwards into the higher layers of the atmosphere, from where it subsequently glides towards its target. The craft launches at speeds of Mach 8–20 (approximately 2700–6900 m/sec). It is eventually slowed by the denser atmosphere at lower altitudes.

Hypersonic gliders, which in recent years have been liberally displayed in military parades in China and Russia, arouse great interest among defence researchers worldwide. FOI’s research into such gliders includes making advanced trajectory calculations to understand how and where they can travel.

Unique facility

FOI has chosen to place greater focus on research into scramjet engine propulsion and matters related to it. After ten years of working with theoretical simulations of the technology, FOI now has extensive knowledge of combustion physics, and thus extensive knowledge of the performance and fuel consumption of propulsion systems.

Now, the next step is being taken, through the construction of a unique new facility, CATLA (Clean Air High Temperature Laboratory).

“It is a completely new facility for conducting experiments. This is where we can recreate the conditions that these vehicles are exposed to, including extreme temperatures and high pressures. With CATLA, we are moving from world-class simulations to world-class experiments,” says Kristoffer Danèl, Senior Scientist at FOI.

The facility, which will be completed in 2024, will be one of the few in the world that can recreate real conditions in a scramjet combustion chamber. This will be attained with a pebble-bed system that heats the air up to a temperature of 1700 K.

“In the majority of the world’s facilities, air vitiators utilising combustion are used to produce these high temperatures. This process changes the air composition and pollutes the air fed into the experiment and hence affecting the experimental studies. In our facility, we can recreate the dry and clean air that is found at an altitude of 25 kilometers. The only alternative would be to build full-fledged vehicles for testing,” says Kristoffer Danèl.

High speeds create problems

FOI also conducts research into the effectiveness, defence and control of hypersonic weapons. The high speeds are a challenge, both for defenders and attackers.

“We are looking at several methods to defend ourselves. But these involve incredibly short reaction times. Because even if you know that a rocket has been launched, it is difficult to figure out where it is going. Therefore, we work with theoretical studies of which trajectories the hypersonic glide vehicles are capable of following and how tightly they can turn, as well as their drag and performance.

In order to assess what damage one can inflict on a hypersonic target we are carrying out studies in the FOI light-gas cannon that can fire projectiles at extremely high speeds,” says Kristoffer Danèl.

FOI’s main client is the Swedish Armed Forces, but foreign actors also use FOI’s knowledge and equipment. However, the development of knowledge in hypersonics is hampered by the fact that the number of research projects as well as the number of researchers in the field is limited.

According to Kristoffer Danèl, “NATO membership would mean that we could create cooperation with other countries in this area. We could contribute with simulation activities, our unique test facility and trial opportunities. In return, we could participate in other countries’ test methodology, results and diagnostics.”

A jet engine with few or no moving parts, and a theoretical maximum speed of Mach 10, about 12,240 km/h (3,430 m/s). It functions first at Mach 5, and therefore requires transport by another craft. It is powered by oxygen from the surrounding atmosphere via a hypersonic flow rate in the combustion chamber that prevents excessive temperatures and pressures when decelerating in the air. According to Kristoffer Danèl, a scramjet today has a maximum speed of 5-6 Mach.

There are those who claim to have scramjet vehicles that can travel at Mach 10. But our research shows that this will not work, at least not today. Too much fuel is consumed, and the craft becomes too heavy and hot.