Structural Design, Development and Qualification Tests of Grid Fin

Crew Escape System (CES) is one of the most critical subsystems in a human-rated launch vehicle. It is an emergency escape module to rescue the Crew Module (CM) with the crew to a safe distance from the launch vehicle in an exigency at the launch pad or during atmospheric phase. Pad Abort Test (PAT) is a technology demonstration on the capability of CES to evacuate the crew in case of any exigency at the launch pad, the first in a series of tests to qualify a CES, which is a crucial technology relevant for human spaceflight. There is a wide range of altitude–Mach number regime over which CES is expected to operate and deliver the required performance. Most important among them is the requirement of aerodynamic stability for the entire Mach number regime. The configuration of CES called for an additional lift producing surfaces at its bottom to get the required stability conditions. Accordingly, four grid fins are located at the aft end of CES to move the centre of pressure down for better stability. Grid fin is a lattice structure of several aerodynamic surfaces supported by rectangular outer frames. It is designed for a variable pressure load acting on the fin elements and outer frames. Grid fins are designed and developed with composite material because of its high specific stiffness and specific strength. Composite grid fins are designed, developed, qualified and successfully flown in PAT flight. This article presents the design methodology, development, validation through structural acceptance and deployment tests of composite grid fins meant for the PAT of CES.