Thermochemical Investigation of Di-Lead SQ-2 Propellant for RATO-UAV Operations

Rocket Assisted Takeoff (RATO) for Unmanned Aerial Vehicles (UAVs) is gaining traction due to its ability to power flight vehicles to be launched without the requirement of paved runways. RATO operation also enhances flight performance, especially during lift-off under high-payload or restricted terrain conditions. In RATO-UAVs the use of small rockets of 2 to 12 kN are best suited for sustaining high-tempo operations. These rockets can be powered with composite or chemically reacted solid propellants. These rockets are peculiar in terms of their small size, high chamber pressure, and ability to generate rapid thrust. This paper investigates the performance feasibility of using Di-Lead SQ-2 extruded double-base propellant vis-a-vis the Ammonium Perchlorate combined with conventional Hydroxyl-Terminated Polybutadiene i.e. AP-HTPB composite propellant. The comparison focuses on the variation of performance parameters including but not limited to specific impulse variations of both energetic materials for altitude, high chamber pressure, and adiabatic flame temperatures. Results show that SQ-2 stores a greater amount of energy as compared to HTPB—a fact established from thermochemical tests that are conducted using various design tools, including RPA®, ProPEP®, and SRM code. The Di-Lead SQ-2 propellant outperforms AP-HTPB in the specific altitude range of 0–50 km. It demonstrates superior performance with or without lead oxide additive due to the owing to the nitrocellulose–nitroglycerin matrix. A significant amount of energy is released from this matrix, making SQ-2 more energetic and reactive compared to the AP-HTPB formulation. It achieves a specific impulse of approximately 270 s, regardless of the presence of lead oxide. The superior performance of SQ-2 propellant, especially in high-thrust scenarios, makes it an ideal choice for RATO UAV application. The high specific impulse of SQ-2 also results in reliable and efficient thrust, which helps in supporting tactical rocket missions and including those needed for rapid medical and supply-drop operations. This evaluation therefore establishes SQ-2’s suitability for near-vertical takeoff roles, offering a reliable and high-performance alternative to conventional composite propellants.