Beyond fighter jets: India is building a new family of engines for missiles and drones

On one hand, as India is taking steps to come up with a jet engine to power a fighter aircraft, on the other hand India is developing a family of small jet engines that can power cruise missiles as well as drones. Recently the Defence Research and Development Organisation's (DRDO) Gas Turbine Research Establishment (GTRE) has successfully announced the development of a 350kg class expendable turbo jet engine.Small powerplants such as this are used on platforms such as cruise missiles, drones and with the advent of jet powered loitering munitions. This class of jet engines have long been used on cruise missiles with the famed US Tomahawk using a 400kg or a 4 kilo-Newton (kN) class jet engine. India's Long Range Land Attack Cruise Missile (LR-LACM) too uses this type of a small jet engine, which is a 450kg class Small Turbofan Engine (STFE).From cruise missiles to jet-powered loitering munitionsMore than cruise missiles, jet powered loitering munitions too use this type of a powerplant. The army has recently ordered 106 Agniveg jet-powered loitering munitions that are designed to engage targets deep inside enemy territory and has a Circular Error Probable (CEP) of less than 5 metres. As this loitering munition is jet powered, it can fly at much faster speeds than the Shahed or Geran series of drones that Iran and Russia have been using and therefore can be used in a more effective way. This affords India the ability to hit targets deep inside enemy territory.The next leap: India's 5 kN rotating detonation engineIndia’s propulsion research ecosystem has now reached a turning point with the recent demonstration of a Rotating Detonation Engine (RDE) in the 5 kN thrust class by private firm D-Propulse. This achievement, carried out at a certified test facility, marks a significant departure from the sub-scale experiments that have dominated global RDE research.For decades, laboratories across the world have struggled to move beyond small air-breathing rigs producing thrust in the 1–2 kN range, often for only small periods of time. The ability to sustain a stable, mode-locked supersonic detonation wave with an integrated aerospike nozzle at a higher thrust level represents a leap in engineering maturity and places India in a select group of nations that have demonstrated this capability.Why RDEs could change the way missiles are poweredRemoving complex, multi-stage, high-temperature single-crystal turbine blades drastically drops manufacturing costs, making mass-producible, attrition-tolerant cruise missiles economically viable. The 15–25% gain in fuel efficiency directly converts to greater standoff range or longer loiter time without expanding the missile's cross-section or launch weight. The reduced launch platform footprint allows fighters to carry more precision standoff munitions per sortie.From an application standpoint, the most immediate utility of air-breathing RDEs lies in supersonic cruise missiles. Engines in the 5–10 kN thrust range are ideally suited for tactical missiles carrying warheads in the 100–200 kg bracket. These systems would be smaller, faster and more cost-effective than current powerplants. This would translate to longer ranged missiles. Looking ahead, rotating detonation rocket engines could replace conventional upper stages in launch vehicles, enhancing payload efficiency. In the medium term, high-altitude drones powered by RDEs are feasible, while the longer horizon could see combined-cycle drones integrating gas turbines with detonation stages.Rotating detonation engines promise efficiency gains over conventional combustion cycles, this translates directly to enabling lighter and faster platforms. This ability to indigenously develop such technology reduces dependence on external suppliers and signals parity with well established global players in the field.From laboratory experiment towards an operational engineThe demonstration of a proof motor designed with the aerodynamic and geometric constraints of a flight vehicle shows that the effort is not limited to laboratory curiosity but is aimed at operational relevance. The combustor diameter, annular flow channel, injector placement, ignition sequencing, and nozzle geometry have all been configured to mirror the requirements of a deployable weapon system.The major problem in developing this type of powerplant are that the engine wall faces cyclic pressure shocks along with heat fluxes, preventing wall melt requires aerospace grade materials. Another major challenge was preventing the high-pressure detonation wave from traveling upstream into the fuel and air manifolds. This has been overcome by precisely designing and engineering aerodynamic nozzles.The challenges of air-breathing RDEs are formidable. The most critical issue is preventing inlet unstart caused by backpressure, a phenomenon that can destabilise the entire propulsion system. The vibro-acoustic profile of detonation engines also demands advanced dampening solutions, similar to those used in scramjet vehicles. The program has achieved Technology Readiness Level (TRL) 5, this means that the advanced design has been validated in a relevant operational environment, moving beyond isolated benchtop setups.Why the 5 kN test is significant — and what it doesn't prove yetYet, the test was conducted on a static open-air rig with pre-conditioned feeds, which is still far removed from the dynamic conditions of flight. Angle-of-attack distortions, fluctuating pressures, and acoustic loads in real missions will pose additional hurdles.The decision to move directly to a 5 kN thrust class rather than remain confined to smaller demonstrators reflects confidence in scaling and thermal management. Successfully pairing a pressure-gain combustor with an aerospike nozzle demonstrates mastery over downstream expansion dynamics and flow-field choke management. This is not a trivial achievement, as the integration of detonation combustion with advanced nozzle geometries has been a persistent challenge worldwide.While several countries have invested heavily in this engine technology, most public demonstrations remain confined to rocket-based systems rather than in air-breathing variants. The ability to run a continuous-thrust air-breathing RDE at the 5 kN level on a certified facility is unprecedented. This positions India alongside a handful of nations that have crossed the threshold from theoretical exploration to hardware demonstration.With D-Propulse's successful hot-fire test of a 5 kN plus reaching Technology Readiness Level-5, India has vaulted into an elite tier of global detonation propulsion research. This has helped close the gap with global peers USA, Russia and China. Historically, the US and Russia have dominated high-thrust RD Rocket Engine testing, but much of their air-breathing liquid work remains highly classified or locked in TRL 3–4 laboratory rigs. Most disclosed work from China on the air-breathing side is restricted to 0.5 kN to 1 kN class systems. Achieving a 5 kN burn at TRL-5 places Indian private defense technology directly on par with advanced international programs.The difficult journey from test rig to flightThe current demonstration, while path breaking, is still a proof motor tested under controlled conditions. Transitioning to operational deployment will require extensive endurance testing, materials validation and integration with flight systems. The vibro-acoustic loads, thermal stresses and structural fatigue associated with detonation combustion are severe.Moreover, the complexity of integrating such engines into missiles, drones, or launch vehicles would also involve not just propulsion but also avionics, guidance and systems engineering. The path forward would focus on a lot of testing that would create tremendous amount of performance data, including thrust, efficiency and thermal loads. Durability testing over extended cycles is essential to quantify fatigue in this new type of powerplant.What comes nextMaterials research, particularly in coatings and cooling strategies, would also be critical to withstand detonation environments. System-level integration studies, including simulations and hardware-in-the-loop tests, will help bridge the gap between rig demonstrations and flight readiness.Indigenous RDE capability will help build expertise in advanced combustion, open avenues for new types of platform design and help strengthen the aviation linked industrial ecosystem. Sustained investment, rigorous testing, and collaboration with academic and research institutions will be necessary to translate these developments to reality.The demonstration of a 5 kN air-breathing rotating detonation engine marks a historic milestone, it signals the entry of the country in a select club of nations with demonstrated macro-scale capability.