What is Solid Fuel Ducted Ramjet System "Astra Mk3"

DRDO Astra Missile Technology  :- The Solid Fuel Ducted Ramjet (SFDR) stands out as an innovative missile propulsion system within the realm of advanced technology. Unlike conventional solid rockets, which lack the ability to adjust thrust once ignited, the SFDR introduces a revolutionary approach by utilizing controlled intake air for thrust adjustment during flight. This marks a departure from the traditional reliance on pumps for adjusting thrust in liquid-fueled rockets.

One distinctive feature of the SFDR is its self-sufficiency in terms of oxidization, as it draws atmospheric oxygen directly from the intake air, eliminating the need for an oxidizer mix. Developed by the Defense Research and Development Organization (DRDO), the SFDR is characterized by its low smoke, nozzleless solid rocket motor design.

Comprising four essential components, namely the Sustainer, Air Intake, Fuel Flow Controller, and Nozzleless Booster, the SFDR showcases a sophisticated engineering approach. Positioned at the aft section are the propulsion control unit electronics and fin actuation subsystem, enveloping the rear part of the Nozzleless Booster. The arrangement includes the Through Air Initiation Igniter behind the Fuel Flow Controller, followed by the combustor where the solid propellant nozzleless booster is seamlessly integrated. The design features two chin-mounted air intakes that supply ram air to ignite the solid fuel grain in the gas generator.

Critical to its functionality, the Nozzleless Booster adopts a conical shape at its end, optimizing the diameter for effective rocket propulsion. This design necessitates the careful optimization of the grain length to diameter ratio, achieving performance comparable to traditional nozzles.

In testing scenarios, the SFDR undergoes a high-altitude trajectory to simulate aircraft launch conditions. Subsequently, the Nozzleless Booster ignites, propelling the missile forward. This ignition process occurs seamlessly, whether during simulated aircraft launch conditions or the actual release from the launcher. The ram air triggers the gas generator action, and the Through Air Initiation Igniter employs an attainable pyrocartridge to initiate ignition. The continuous flow of ram air enhances the mixing of fuel and air, leading to the gradual outward burn of the solid propellant grain and the expulsion of hot gases through the Nozzleless Booster.