Solid Fuel Ducted Ramjet

Solid Fuel Ducted Ramjet (SFDR) is a missile propulsion system currently being developed by the Defence Research and Development Organisation of India. The project aims to develop critical technologies required in the propulsion systems of future Indian long range air-to-air missiles.
Description.
The Solid Fuel Ducted Ramjet is a missile propulsion system that includes a thrust modulated ducted rocket with a reduced smoke nozzle-less missile booster. The thrust modulation in the system is achieved using a hot gas flow controller. The system utilises a solid fuelled air-breathing ramjet engine. As of 2017, the missile system has a range of about 120 kilometres at an altitude of 8 kilometres, with a speed of 2.3-2.5 Mach. As per International Institute for Strategic Studies (IISS), this kind of propulsion system drastically enhances the range with higher average speed. The missiles which use such system are also able to carry larger payload due to absence of an oxidiser. Unlike solid-propellant rocket, the Ramjet takes up oxygen from the atmosphere during flight.
Officially, the technology is being developed to power future Indian air-to-air missiles. However, the technology can also be applied to surface-to-air missiles.
In its current form, the SFDR-based missile first requires to be boosted into a high-altitude trajectory to simulate aircraft-launch conditions. Subsequently, the nozzle-less booster fires up and guides the missile through its desired trajectory.
Development.
The development of the SFDR started in 2013 and envisaged a five-year deadline to begin actual demonstrations. The missile is being developed primarily by the Defence Research and Development Laboratory (DRDL) and Research Centre Imarat (RCI) in Hyderabad. High Energy Material Research Laboratory (HEMRL) developed the nozzle-less booster while the ramjet engine is being developed with Russian assistance. Ground-based testing of the missile started in 2017.