Dynamic Ascent Loads Estimation of Winged Reusable Launch Vehicle: Formulation, Analysis and Post Flight Studies

A structural load estimation methodology was developed for RLV-TD HEX-01 hypersonic experimental mission, the maiden winged body technology demonstrator vehicle of ISRO. Primarily the method evaluates time history of station loads considering effects of vehicle dynamics and structural flexibility. Station loads of critical structures are determined by superposition of quasi-static aerodynamic loads, dynamic inertia loads, control surface loads and propulsion loads based on actual physics of the system, improving upon statistical load combination approaches. The technique characterizes atmospheric regime of flight from vehicle loads perspective and ensures adequate structural margin considering atmospheric variations and system level perturbations. Features to estimate change in loads due to wind variability and atmospheric turbulence are incorporated into the load estimation methodology. Augmentation in loads due to structural flexibility is assessed along the trajectory using vehicle states calculated by a flexible vehicle response solver integrated to 6-DOF trajectory solver. This methodology was used to authorize the successful maiden launch of RLV-TD HEX-01 flight on May 23, 2016. The paper describes basic formulation of elastic load estimation technique, pertinent mission design simulation studies and comparison of estimated load with flight measured data. A close agreement between computed structural load and flight measured load throughout the atmospheric regime of flight demonstrates technological maturity of the methodology.