Early Detection of Solid Rocket Motor Case - Breach Failure ∗

This paper describes work on early detection of space launch vehicle failures that could lead to loss of control during ascent. The particular focus is on the Solid Rocket Motor (SRM) comprising First Stage of the Crew Launch Vehicle (CLV). Some of the most important failure modes leading to loss of vehicle control are caused by hot gases ejected from the SRM combustion chamber through a case breach, through a joint between SRM segments, through a nozzle joint, or through an igniter seal. These hot gases create lateral thrust augmentation, with the resulting tilting moment possibly leading to loss of control. By using Thrust Vector Control (TVC) gimballing of the main nozzle, the flight control system tries to counter any attitude disturbance, which could mask the moment augmentation till it overwhelms the TVC and the control authority is lost. The approach proposed and demonstrated in a medium-fidelity simulation of the rocket dynamics employs continuous model-based multivariable estimation and monitoring of the augmentation forces and moments for early detection of the failure. The computations are performed in two stages. First, a 6-degree-of-freedom model of vehicle dynamics is used to compute the predicted vehicle accelerations. Second, the differences with the observed accelerations – model prediction residuals – are used in optimal multivariable algorithms to estimate the thrust augmentation. A case breach failure may thus be detected well before its effect on trajectory becomes noticeable in the raw data.