Spacecraft Launch Depressurization Loads

Abstract

The pressure variation inside the launch vehicle fairing during climb through the atmosphere induces structural loads on the walls of closed-type spacecrafts or equipment boxes. If the evacuation of the air is not fast enough, excessive pressure loading can result in damage of elements exposed to the rising pressure jump, which depends mainly on the geometry of venting holes, the effective volume of air to be evacuated, and the characteristic time of pressure variation under the fairing. A theoretical study of the reservoir discharge forced by the fairing timedependent pressure variation is presented. The basic mathematical model developed can yield both a numerical solution for the pressure jump and an asymptotic solution for the most relevant case, the small-pressure-jump limit, showing the dependence on a single nondimensional parameter: the ratio of the reservoir discharge to the fairing pressure pro le characteristic times. The asymptotic solution validity range upper limit, obtained by comparison with the numerical solution, is determined by the starting of choked operation. Very high sensitivity of the maximum pressure jump to the ratio of characteristic times has been observed. Another relevant nding is that the pressure pro les for different launchers can be considered similar when rewritten in appropriate form and only their characteristic times are required for the analysis. The simple expressions of the asymptotic solution are a useful tool for preliminarily sizing the reservoir discharge geometry and estimating depressurization loads. Nomenclaturea h = speed of sound at the output section, m/s K = ratio of characteristic times, t c t p M h = Mach number at the output section n = polytropic coef cient P = static pressure, Pa P b = value of P e for choking of the ow, Pa P e = static pressure under the fairing, Pa p = dimensionless pressure in the reservoir, P 0 P i p 1 = rst term in the series expansion of S = effective hole output section area, m 2 T = dimensionless time, t t c T max t max = values of T and t at which a reaches its maximum value t = time, s t c = characteristic venting time, 2 V S A i , s t p = characteristic fairing pressure variation time, s U h = ow mean speed through the hole at the output section, m/s V = reservoir effective volume of air to be evacuated, m 3 = ratio of speci c heats P = pressure jump, P 0 P e , Pa a n = dimensionless pressure jump, asymptotic solution, and numerical solution max = maximum value of a = small parameter of series expansions = total pressure loss coef cient through the hole = instantaneousdimensionless density inside the reservoir, 0 i x = uid density at position x, kg/m 3 Subscripts e = instantaneousconditions inside the fairing h = instantaneousconditions at the reservoir hole exit i = initial conditions in the reservoir 0 = instantaneousreservoir conditions

Experimental and Theoretical Study of Internal Pressure Loads on Boundary Walls under Gusty Wind Conditions

“…In the field of space vehicle design, payload assembly, and launch, we can find some studies relevant to the internal pressure loads under gusty flow conditions, namely, space vehicle compartment vent (NASA SP-8060) [11]. Sanz-Andres et al [12] analyzed the variation of the internal pressure loads during the climb of a spacecraft through the atmosphere. In the applications of payloads placed in fairing depressurization of spacecraft, Sanz-Andres and Navarro-Medina [13] proposed an analytical expression that can estimate the depressurization vent size.…”

Inverse venting problem for estimation of the discharge coefficient in a satellite launch vehicle

“…An earlier study was performed by Mironer and Regan [2] and Murri [3] to determine venting design criteria for space shuttle payloads, using a nominal ascent, payload bay pressure pro®le. A theoretical model of the discharge process of a reservoir into a decreasing time-dependent pressure environment has been published by Sanz-Andres et al [4]. They used numerical integration of the compressible¯ow equation to calculate the differential and compartment pressure during the ascent¯ight.…”

Thermal Systems

“…Otherwise, the blanket would billow out like a balloon and the dynamic pressure could detach it from the spacecraft. Thus, to allow proper venting of the blanket the sheets are perforated and/or sections of the edging are unsealed [19].…”