1 Estimating Minimum Inflation Pressure for Inflatable Aerodynamic Decelerators

The minimum inflation pressure and volume are key characteristics of an IAD design because the mass of the gas itself and the gassing system can constitute a large fraction of the total mass of the decelerator. In this paper, a method for estimating minimum inflation pressure is derived for each of three IAD types: tension cone (e.g. hypercone), trailing torus, and double-walled inflatables. Examples with the same ballistic coefficient are presented for each type of IAD, and comparisons are made of minimum inflation pressure, volume, and gas mass. Nomenclature c = Subscript referring to an “as-constructed ” or un-deflected dimension or angle d = Subscript referring to a deflected dimension or angle h = Subscript referring to heatshield or to the edge of the heatshield t = Subscript referring to the torus or to the intersection of the membrane and the torus IAD = Subscript referring to the total IAD c = Cord dimension across an arc D = Diameter d = Section diameter or double-wall spacing Fa = Axial aerodynamic force, drag m = mass P = Inflation pressure r = radius of curvature R = Component of the total tension in the radial straps, T, in the torus plane s = Arc length t = thickness T = Total tension summed over all radial straps w = Width dimension θ = Angle between spacecraft axis and a surface, half-cone angle σ = Stress. psi τ = Fabric or strip stress, lbf/in, All force variables are bold capital letters. The ambiguity between D (diameter) and D (drag) is avoided by using Fa. “Radial”, “circumferential ” and “gore ” are traditional parachute terminology and are used in that sense. The term “meridional ” is sometimes used in the literature to mean “radial ” in the present usage. The term “zonal ” is also seen for “circumferential”, but rarely. I