Structural Loads for Crew Escape System (CES) of Gaganyaan Launch Vehicle During Abort 2024-26-0453

Abstract : In any human space flight program, safety of the crew is of utmost priority. In case of exigency during atmospheric flight, the crew is safely and quickly rescued from the launch vehicle using Crew escape system. Crew escape system is a crucial part of the Human Space flight vehicle which carries the crew module away from the ascending launch vehicle by firing its rocket motors (Pitch Motor (PM), Low altitude Escape Motor (LEM) and High altitude Escape Motor (HEM)). The structural loads experienced by the crew escape system during the mission abort are severe as the propulsive forces, aerodynamic forces and inertial forces on the vehicle are significantly high. Since the mission abort can occur at anytime during the ascent phase of the launch vehicle, trajectory profiles are generated for abort at every one second interval of ascent flight time considering several combinations of dispersions on various propulsive parameters of abort motors and aero parameters. Depending on the time of abort the ignition delay of LPM, HPM and HEM are adjusted in order to minimize the lateral acceleration on the vehicle, at the same time meeting the horizontal range requirement. Aerodynamic load distributions on the vehicle and aero forces and moments on the Grid fin are generated for various Mach No, AoA combinations for jet ON and jet OFF conditions of PM, LEM and HEM. In order to estimate the structural loads for Crew Escape System (CES) during abort, Static analyses are carried out on a free-free finite element model using inertia relief at all the time instances in the abort trajectory as a time sweep simulation considering the appropriate aerodynamic forces, propulsive parameters (mass consumption and thrust) and trajectory parameters (Mach No, Dynamic pressure and AoA) at each time instant in the trajectory. During abort at lower altitude along with LEM motor, Pitch motor is fired perpendicular to the axis of the vehicle to turn the vehicle towards the sea thereby increasing the angle of attack AoA and bending moment on the vehicle. The Pitch motor thrust acting perpendicular to the vehicle excites the first bending mode and augments the Bending moment. Similarly the LEM thrust and HEM thrust acting along the vehicle axis also can excite the axial modes of the vehicle. The aero dynamic forces on the vehicle excite the lateral dynamic of the vehicle whenever there is a sudden change in the AoA due to wind gust. To account for the dynamic forces, a load augmentation factor called Flexibility factor is multiplied on the static loads to arrive the limiting loads on the vehicle. This paper briefly explains the structural load estimation methodology for CES abort, various inputs required and different steps involved in it.