Lessons learnt during the development of VEGA launcher solid rocket motors

VEGA is the new launcher developed by European Space Agency and qualified with its maiden flight on February, 13rd 2012. During the launcher development, a total of nine static firing tests (SFTs) have been performed for the 3 solid stages which compose the launcher: the 1 st stage P80, the 2 nd stage Zefiro 23 and the 3rd stage Zefiro 9A. Tailored for small payloads and low earth orbit missions, VEGA is a single-body four-staged launcher (three solid rocket motors – SRMs and one liquid upper stage), which completes the family of the European launchers, beside Soyuz and Ariane 5. This paper discusses and summarizes the activities performed during the last decade, for the development of the VEGA launcher SRMs, from the SPqR (Space Propulsion quasi Research) team at Sapienza University of Rome, as scientific consultant of the ESA ESRIN – VEGA Integrated Project Team. The paper will be focused, in particular, upon all the ”lessons learnt” during the solid stages development, describing the contributions given from the work-group to the launch vehicle: from Zefiro16, prototype of the VEGA family SRMs, to Zefiro9A, ”last born” of the solid stages, and flight version of the third stage. The research activities spanned all the relevant aspects in SRMs internal ballistics, from the SRM ignition to burn-out, as well as the external aerodynamic of the entire launch vehicle. Firstly, the use of the helium as pressurizing gas in order to reduce the pressure oscillations during the ignition transient (IT) of all the SRMs will be discussed from both ”historically”, during the project evolution, and technical point of views, from Zefiro 16 to P80 (DM fired with helium and QM, with nitrogen). Afterwards, the analyses performed during the design of Zefiro 9A, concerning the first phase of the ignition transient of the SRM, will be described, giving a description of the reasons behind the subsequent design modifications of Zefiro 9A with respect to the Zefiro 9 configuration. The description of the applied research activities performed will, then, consider the prediction and reconstruction methods and the consequent results, achieved in the analysis of all the VEGA SFTs: 0D post-static firing tests reconstruction, Q1D simulations of the internal ballistics and reconstruction of the P80 pressure oscillations. Finally, an analysis on the external aerodynamic of the complete launcher, performed in its full and detailed configuration (all protrusions included) will be resumed in its essential aspects. All these activities have been carried out with a series of numerical and analysis tools developed ”in-house” at Sapienza University of Rome – Propulsion Area of the Dept. of Mechanical and Aerospace Engineering, spanning from a 0D quasi-steady model of SRMs internal ballistics, to a full 3D unsteady CFD model of SRMs internal ballistics and launcher external aerodynamics.