Analysis of Pressure Oscillations during Ignition Transient and Steady-State of an Overloaded VEGA First Stage

The dynamic environment of a solid rocket motor may bring about severe impacts on the launch vehicle performance suited to the payload requirements, and therefore, especially in the early phase of its design, it has to be carefully evaluated in order to correctly assess the design configuration of the SRM and the launcher. This paper provides a first assessment of the ignition transient phase and the steady state phase of a tentative configuration of the VEGA upgraded first stage SRM, with particular attention on the characterization of the onset of pressure oscillations that are responsible for the dynamic environment experienced by the SRM during its operative life. This tentative configuration has been designed as a P80 XL stretched SRM, waiting for the VECEP first state configuration that will be consolidated in the summer of 2014. This first assessment is performed with the use of numerical models of the ignition transient (SPIT) and of the aeroacoustic phenomena in solid rocket motors (AGAR), which set-up is consolidated and validated against the P80 firings (DM and QM) and flights (VV01 and VV02) data. Results of this first assessment indicate that, as for the VEGA solid stages, the use of helium as pressurizing gas is mandatory in order to control the dynamic environment generated during the motor start-up by the P80 XL. For the pressure oscillations during the steady state of the P80 XL stretched, the first numerical simulations indicate that, as the P80, this motor is characterized by the presence of pressure oscillation blows, which maximum amplitude is slightly higher than P80 ones. The occurrence of the pressure blows appears during the steady state in similar motor phases, when compared to the P80 ones, and related to the activation of the first longitudinal acoustic mode of the combustion chamber.