Grid fins are lattice structures employed as aerodynamic control surfaces to achieve the required static stability of re-entry modules during atmospheric descent. Grid fins help to stabilize the re-entry modules by counteracting aerodynamic instabilities, especially when the module is moving through the atmosphere at high speeds. Each panel within the grid fin functions as an individual fin, generating lift and drag forces that enhances the overall stability of the re-entry module. 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 through folding during launch followed by deployment at the time of exigency. The separation of re-entry modules from their launch vehicles is typically executed using high-thrust, fast-acting solid rocket motors (SRMs) which provide the impulsive force needed for clean detachment.
The primary structural loads 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 action of thermal and structural loads influences displacements, stresses, interface joints integrity and critical buckling loads. Furthermore, elevated temperatures degrade mechanical properties such as yield strength, ultimate strength, and Young’s modulus. Therefore, 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 critical design load case.