During the atmospheric flight of the Brazilian satellite launch vehicle the pressure inside the satellite compartment should be equalised with the atmospheric pressure. This becomes necessary due to the high pressure differences which result when the vehicle reaches high altitudes with decreasing atmospheric pressures, generating high loads acting on the internal surface of the fairing. The equalisation is achieved through venting holes placed around the fairing of the satellite compartment. The design of the venting orifices should be constrained to the restriction of constant evacuation of the compartment, so that, at any time of the trajectory, the pressure difference is minimal. Meeting this constraint becomes complex due to the flight environment of the vehicle which is characterised by very high acceleration levels. So, the flow around the fairing undergoes constant variation of the velocity field going from subsonic to hypersonic velocities. The position, size and number of venting orifices were determined using gas dynamic analysis and calculations and later validated through flight tests. The article describes the mean features of the design process, discusses the venting criterion, and shows the flight results.
compartment venting; pressure equalisation; launch vehicle; VLS
