Analysis & reconstruction of pressure oscillations during P80 steady-state of VEGA flights

Pressure oscillations can characterize the steady phase of large solid rocket motors, entailing dynamic loads on the launch vehicle structure and thrust oscillations. Both the modern large lower stage/booster configurations, segmented SRMs - e.g. Ariane 5 and Space Shuttle boosters - and monolithic finocyl SRMs - e.g. P80 of VEGA, are prone to pressure oscillations phenomena, at frequencies of the firsts longitudinal modes of the combustion chamber, with different characteristics time windows: during the second half of the SRM functioning, for the segmented SRMs; during the first half of the operative life, for the aft-finocyl configurations. This study is aimed at presenting the analysis of pressure oscillations of a real aft-finocyl SRM, addressing the following points: discuss and analyse the signature with the associated dispersion of the pressure oscillations phenomena (both in time and frequency domain) of the aft-finocyl first stage of the European launch vehicle VEGA, P80 SRM, exploiting the flight data from the first six flights over the nine successfully flown to date; provide a reconstruction and analysis of the pressure oscillation phenomena of the P80 SRM with the use of a Q1D aero-acoustic model of pressure oscillations in aft-finocyl SRMs, named AGAR, showing the capability of the model to represent with good correlation the whole experimental signature of the pressure oscillations experienced by P80 SRM during the flights.