Grid fins are non-conventional aerodynamic lifting and control surfaces which are made of a frame supporting lifting surfaces positioned in the form of a lattice structure. Grid fins are also called as lattice fins and are used as control surfaces in launch vehicles, crew escape systems, missiles etc. to achieve static stability. Each panel of the grid fin acts as fin and it produces force which increases stability of the vehicle. For a crew escape system module, grid fins are used as a passive aerodynamic control surfaces to achieve static stability. Grid fins are positioned at the end of crew escape system module to provide required static margin by increasing moment arm. In contrast to conventional fins, grid fins incorporate a distinctive waffle-like pattern or grid pattern configuration, offering superior aerodynamic performance in supersonic regimes and enabling compact storage in stowed position during launch followed by deployment at the time of exigency.
In case of an emergency, crew escape system is activated and it will take crew escape module away from the launch vehicle during atmospheric regime. In this scenario, grid fins are deployed simultaneously along with firing of high-thrust, fast-acting solid rocket motors (SRMs) which provide the impulsive force needed for clean separation. Grid fins help to stabilize the crew escape system module by counteracting aerodynamic instabilities, especially when the module is moving through the atmosphere at high speeds.
The primary structural loads acting on grid fins include deployment forces (hinge forces, locking), aerodynamic, and inertial forces. Additionally, the exhaust plumes from the firing of SRMs impinge directly upon the grid fins, generating intense thermal loads characterized by rapid temperature gradients and localized heating. The simultaneous presence of thermal and structural loads influences displacements, stresses, interface joints integrity and maximum buckling loads. Furthermore, elevated temperatures degrade mechanical properties such as yield strength, ultimate strength, and Young’s modulus, therefore a thermo-structural analysis is carried out to study the effects of these combined loads on grid fins. This paper presents typical grid fin configuration, thermo-structural formulation, finite element model details, and thermo-structural analysis results including stress margins, deformations, buckling load factors and preload variations for the maximum design load case.