A Parametric Study on Ignition Transient of Solid Rocket Boosters for Future European Launchers

The start-up of solid rocket motors represents a critical phase during their whole operational life, that may induce severe impact on the payload comfort and on the dynamic operational environment of the launch vehicle. This paper is aimed at providing a first assessment of the ignition transient with the SPIT code of the new large monolithic SRM foreseen in the future configuration of the VECEP upgraded first stage, that is based on the concept to be an over-loaded version of the current VEGA first stage P80. The SRM configuration selected is inspired to the P105, VECEP first stage, designed as a stretched version of the P80 SRM, with an aft-finocyl configuration and the same igniter and nozzle configuration of the P80. The parametric analysis considers the impact on the SRM behavior of different kinds of pressurizing gas, exploiting the experience and know-how achieved during the VEGA development phase, with a conservative assessment based on the outcomes of the P80 firings analysis. An accurate analysis of the P80 firings, in fact, indicates that a conservative assessment of the dynamic environment induced during the first phase of the SRM start-up can be obtained assuming a mixture of helium with a small percentage of nitrogen as pressurizing gas. Results for the P80 XL stretched tentative configuration indicates that the use of helium as pressurizing gas is mandatory for controlling the SRM behavior during the ignition transient.