STAR - Supersonic TARget
DRDO has been carrying out Research and Development to develop missile based on LFRJ (Liquid Fuel Ramjet) Engine. STAR stands for Supersonic TARget. This will be surface launched (with a booster) and will serve as a supersonic target for A2A and S2A missiles capable to hit Mach 2.4 speed.
LFRJ motors more efficient when range and endurance are primary criterion rather than acceleration and storage. Thatís why Brahmos and now STAR-cruise-missile adapt the liquid fuel based ramjet motors. Both will use a booster to accelerate to the ramjet operating speed beyond which booster is ejected and the missile will carry on. The LFRJ design will allow us to reach smaller scale missiles than Brahmos, and more importantly autonomy in this crucial technology.
The STAR is designed to help Navy ship crews learn to defend themselves against modern anti-ship missiles like the French Exocet and Chinese Anti-ship missiles and also help in research in ship-defense systems and fleet training.
STAR has been going through wind tunnel testing by DRDO and design changes have been made accordingly and it is expected that it will be ready by 2023-24 for demonstration trials and speculation is also that once STAR Target drone is developed as a spin-off program an Anti-Ship Missile based on STAR Technology will also be developed for Aircraft and Ship-based platform.
A subsonic combustion ramjet operates best at supersonic flight speeds and, therefore, must be boosted to ramjet ignition speed by a first stage, usually a solid rocket. Practical upper flight limits for a subsonic combustion ramjet are usually between 500 and 8000 feet per second. If higher flight speeds are desired with ramjet propulsion, it is necessary to change from a subsonic combustion ramjet to a supersonic combustion ramjet. However, using the same basic ramjet requires effective geometry changes to the engine. Past and current efforts to develop dual-mode (i.e., subsonic-supersonic combustion) ramjets have required complicated mechanical geometry changes and/or complicated fuel injection location control with compromised performance. The major problem is to convert the geometry of the engine from a double-throat to a single-throat configuration. In practically all the studies, the conventional ramjet has been found to be the most promising propulsion option in the Mach 2-6 range. Beyond Mach 6, the supersonic combustion ramjet is an obvious choice.
Air-breathing propulsion, in the form of Liquid Fuel Ramjet (LFRJ) or Solid Fuel Ramjet (SFRJ) systems, is a highly competitive solution to tactical systems requiring long range and/or high speeds. While significant development has occurred, including development of several operational systems using traditional LFRJ technology and ducted rocket systems, few resources have been devoted to SFRJs despite the significant potential demonstrated in the programs that have been completed. SFRJ systems have a clear advantage over rocket-based systems due to their inherent high specific impulse values which greatly improve the range and kinematic performance of the system.
The use of high-speed air-breathing propulsion for tactical applications has a long history in the U.S. dating back to the Navaho, Bomarc, and Talos systems of the late 1950s and early 1960s. All variants of the Ramjet, e.g. SFRJ, Ducted Rocket, LFRJ, etc., allow significantly higher effective specific impulse (Isp>1200 seconds in the case of LFRJ and SFRJ cycles) compared with rocket propelled systems and can also possess design simplicity and safety advantages. For this reason, a large number of strategic and target development programs utilizing air-breathing propulsion have been conducted over the last 40 years including the Advanced Low Volume Ramjet (ALVRJ), Advanced Strategic Air Launched Missile (ASALM), Advanced Common Intercept Missile Demonstrator (ACIMD), Variable Flow Ducted Rocket (VFDR), and most recently, the Navy"s GQM-163A "Coyote" Supersonic Sea-Skimming Target (SSST) ducted rocket target drone.
The liquid fuel ramjet system employing a subsonic side-dump combustor was simulated, and the predictions are compared with the available experimental data. The complex combustion phenomenon in a ramjet combustor has been carried out at DRDO using probability density function (PDF) approach. The complexity arises because of the mixing of fuel and airstreams, and the burning of the resultant mixture, within the confined space of the combustion chamber. The predicted numerical results have been validated with the results available in open literature for a two-dimensional case and with in-house experimental data for a three-dimensional case. The methodology allows different designs to be evaluated quantitatively based on the performance metrics such as combustion efficiency, flame stability, etc.
The liquid fuel ramjet consists of an inlet, combustor and an exhaust nozzle. The inlet/diffuser admits free stream air to the engine, reduces the air velocity and thereby develops ram pressure. This air is mixed with fuel, burned in the combustor and the hot gases expelled through the nozzle to produce thrust. The heat release in the combustor should be carefully tailored to the flight speed and the appropriate nozzle opening or else it may lead to poor combustor or inlet performance, and in the extreme, lead even to an inlet unstart. Dump combustors are usually employed in volume limited ramjets. In addition to co-axial dump combustors, in some cases, the flight vehicle configuration would require that side dump combustors be employed. The free steam air would enter the combustor from the side through multiple inlets. The impingement of jets is an important feature of side dump combustor flow fields. Jet-on-jet impingement can sustain flow instabilities and this could in turn create a mechanism for unsteady heat release. The flow field in a dump combustor is extremely complex.
Complex vortex structures will exist between the dome head and the plane of the air inlets to the combustor. On entry to the combustor the air flow will follow a complex trajectory before finally turning in an axial direction. Control of flame stabilisation and flame propogation in such a complex turbulent flowfield represents a key element in combustion chamber design. Combustor configuration and the geometry of the fuel injector/flameholder and its location relative to the air entry points are basic design parameters that govern the performance of a particular combustor. A four-inlet side dump combustor configuration is frequently used. Clean aerodynamics is a characteristic feature of all high performance combustors and this is a definite goal to strive for.