Euronaval 2024 – Electromagnetic railgun technology from ISL
The French-German Research Institute of Saint-Louis (ISL) exhibited at Euronaval 2024 a model of a possible naval application of its electromagnetic railgun
Very long range and very high speed, these are the targets that the ISL is aiming at with the development of its electromagnetic railgun. As usual the Institute is busy generating cutting-edge technology and applying it to a demonstrator, while the task for bringing this up to product-level will be transferred to industry once the military will have analysed the potential application and issued requirements according to operational needs.
The current work being done by ISL is a continuation of the PILUM project, which was selected under the 2019 call for proposals for the EU Preparatory Action on Defence Research (PADR) managed by the European Defence Agency, and which was officially launched on 23 April 2021.
PILUM stands forProjectiles for Increased Long-range effects Using electroMagnetic railgun. This feasibility study lasted 30 months and was financed by the PADR for an amount of € 1.5 million. The consortium led by ISL, which has been working on the railgun technology since 1987, included 6 other partners Diehl Defence (Germany), Erdyn Consultants (France), Explomet Gałka (Poland), Naval Group (France), Nexter Systems (Now KNDS France, France) and Von Karman Research Institute (VKI) specialised in fluid dynamics and propulsion (Belgium), a total of four countries being involved.
The principle of the railgun is well known; it features two parallel rail-shaped conductors along which a sliding projectile, the armature, is accelerated exploiting the electromagnetic force generated by the electric current that flows down one rail, into the armature and then back along the other rail. That said switching from theory to a real gun that can be used on the battlefield, would it be at sea or on land, is a wholly different story.
The choice of a naval solution would seem more feasible since there is much higher electric power available on a combat ship than on a combat vehicle. ISL is the only research institute in Europe to master all the technologies relating to the three key components of the system – the electromagnetic railgun, the electric energy source, and the hypersonic projectile.
A follow-up project has been launched to increase the technological maturity of the three critical components developed by ISL. Known as THEMA, which stands for TecHnology for ElectroMagnetic Artillery, the project was awarded under the EDF call 2022, and activated in December 2023. Coordinated by KNDS France, THEMA corresponds to a budget of € 15 million and includes all the PILUM participants, plus others; ADDITESS (Cyprus), Bulgarian Defence Institute “Prof. Tsvetan Lazarov” (Bulgaria), Fraenhofer-Gesellschaft (Germany), Marduk Technologies (Estonia), MBDA Italy, Optimal Structural Solutions (Portugal), and Nexter Munitions (France) and Simmel Difesa (Italy), both part of KNDS France. THEMA is a new step towards the implementation of an electromagnetic railgun demonstrator on a firing range from 2028.
At Euronaval 2024 it was possible to talk to some of the programme subject matter experts from ISL. Depending on the operating mode the railgun “muzzle” velocity will be between 2,000 and 3,000 m/s. “Conventional kinetic energy ammunition used in tank guns and propelled by powder explosion will soon overcome the 2,000 m/s bar,” an ISL expert told, us, hence the railgun is moving towards much higher velocities, although indirect fire systems, namely 155 mm artillery guns, are still way beyond that V0. EDR On-Line understood that laboratory tests at ISL allowed the projectile to reach Mach 10, which means nearly 3,500 m/s, the starting velocity considered “hyper” being Mach 5.
Using the 6-metre long New Generation Launcher (NGL 60), with a square calibre of 60×60 mm2, muzzle velocities of up to 2,500 m/s can be obtained. The railgun calibre is clearly not the projectile calibre; the “C” shaped armature ensures the electric connection between the rails to allow the current to circulate, and carries the projectile, which has a maximum mass of 2 kg, and the sabot, the latter being discarded at launch as well as the armature. The sabot material is different from the one of conventional gun rounds, as it must not conduct electricity, or must be isolated from the armature. One of the remaining challenges seems to be the rail wear, caused both by the current and by the speed of the fire. Here tribology, the science understanding friction, lubrication, and wear phenomena for interacting surfaces in relative motion, comes into play. It takes a mere 5 ms for the projectile to reach a velocity of 2,500 m/s, the maximum current being 2.5 MA while breech voltage is short of 3,000 V, which explain well the aforementioned rail wear issues.
As for the projectile itself, the THEMA project aims at optimising its aerodynamics, as it flies at a speed which is much higher than previous kinetic energy rounds. The EDF-funded project is also considering guidance systems. One of the challenges here is the development of sufficiently hardened electronic components, capable to sustain accelerations between 25,000 and 50,000 g for rounds such as that of the railgun under development. Acceleration can reach 100,000 g for small rounds with a calibre of 25 mm. Internal ballistics, trying to provide higher acceleration for heavier rounds is also under study.
One of the key issues is the energy storage system, which must be capable of delivering an energy capacity of over 10 MJ in just a few milliseconds. Currently, ISL has developed a 1 MJ XRAM-Generator [1]; the demonstrator is a toroidal storage coil consisting in 20 identical segments. Each coil is energised by the same charging current in a series of connections. The pulsed current discharge is then generated by a parallel connection of those coil segments, which enable a x20 amplification of the charging current. Based on inductive energy storage and high current opening switches, it ensures very high energy density. The XRAM-Generator demonstrator has an outer diameter of around 1 metre with an inner diameter of 260 mm, it weighs 1,050 kg and has a volume of 220 litres. With a charging current of 50 kA, the maximum tested, it has an energy density of 5.7 MJ/m3 and a specific energy of 1.2 kJ/kg, these figures becoming 4.5 MJ/m3 and 1 kJ/kg when the charging current is 45 kA, maximum voltage being 5 kV. The demonstrator was used to power the 25 mm RAFIRA railgun, developed by ISL, which accelerated a 100 gramme projectile at 2,400 m/s. Permitting salvos of five rounds, the XRAM concept is being considered for the bigger 10 MJ PEGASUS facility at ISL. Other energy storage systems such as a capacitive bank are also being developed. EDR On-Line understood the inductive storage system, which is considered at TRL 4+, has a power density three times that of capacitive systems. A decision on the power source should be taken in the coming months, as the Institute aims to start its own preliminary field testing in 2025, a demonstrator being planned for 2028.
Long-range artillery for land strike and naval fire support is the priority for large calibre railguns. According to ISL sources, such railguns should be capable of firing a round at 200 km distance, reaching an altitude of 70 km. For medium-calibre railguns, the priority is antimissile air defence, especially against hypersonic weapons; fire rates of over 50 Hz are necessary for such missions, according to ISL, hence the need to be able to fire one round every 20 ms. Other roles such as close-in defence, anti-air warfare and anti-surface warfare could also be performed by future railguns.
Confronted with hyper-velocity or saturation threats, the ISL railgun concept provides more high-performance, low-cost artillery, thus contributing to the strategic autonomy of Europe.
[1] An XRAM generator works the opposite of a MARX generator, the latter taking the name from Erwin Otto Marx who first described it in the 1920s. In the MARX generator circuit, capacitors are charged in parallel and discharged in series to generate high-voltage pulses. By reversing the letters, the term XRAM indicates that the generator is the inductive counterpart to the MARX generator and its goal is to generate high-current pulses.
Images courtesy ISL, photos by ISL and P. Valpolini
