Parametric study of SRMs design options affecting motor start-up and onset of pressure oscillations

The Ignition Transient (IT) of Solid Rocket Motors (SRMs) is characterized by strong unsteady phenomena occurring in a very short period of time. It starts at the first electric signal given to the igniter charge and ends just after the ignition of the entire grain surface, when the quasi steady state conditions in the bore are reached (usually after 0.2 to 1 seconds). In spite of the short period of time taken by this operative phase, its impact on the launch system design and operation can be relevant. In fact, the IT has significant implications not only from the point of view of the SRM start-up and performances, but also for the launch vehicle operational requirements and structural verifications. Therefore, the development of new SRMs requires to improve the understanding of the IT physical mechanisms and to clarify their origins and dependencies. Moreover, the availability of reliable and ecient IT simulation models to properly predict and analyze the SRM behavior will allow to lead the SRM design towards the accomplishment of system requirements already at the preliminary design phase. Many times unacceptable IT behaviors were detected at an advanced development stage (i.e. at the firsts Static Firing Tests), when remedies and/or design modifications could be very expensive and with a big impact on the project time schedule. Aim of the present study is to present a wide parametric analysis of the eects of the main SRM design options on the SRM start-up phase, with a particular attention on the onset of pressure oscillations during the ignition transient.