A simplified ascent trajectory optimization procedure has been developed with application to NASA's proposed Ares I launch vehicle. In the interest of minimizing bending loads and ensuring safe separation of the first-stage solid rocket motor, the vehicle is constrained to follow a gravity-turn trajectory. This reduces the design space to just two free parameters, the pitch rate after a short vertical rise phase to clear the launch pad, and initial launch azimuth. The pitch rate primarily controls the in-plane parameters (altitude, speed, flight path angle) of the trajectory whereas the launch azimuth primarily controls the out-of-plane portion (velocity heading.) Thus, the optimization can be mechanized as two one-dimensional searches that converge quickly and reliably. The method is compared with POST-optimized trajectories to verify its optimality.

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Physics-based modeling for a stage separation recontact fault is presented. Numerical models and analytical estimations are applied to analyze the physics of the failure and reconstruct the following sequence of events: structural dynamics of the nozzle extension during impact, yielding and melting of the damaged nozzle under plume loadings during engine startup, reduction of the actual thrust and side loads in the steady burning regime, response of the thrust vector control system to the fault-induced torque, and rocket trajectory variations due to the fault. The obtained results are discussed in a context of engineering risk assessment and development of an onboard diagnostic and prognostic system for stage separation failure. Analysis using the models developed as part of this research shows that the damage results in three possible outcomes: actuator failure with resulting loss of control, loss of performance resulting in an inability to reach orbit, and effects that are sufficiently minor so that orbit is still attainable. In the case of crewed missions, abort triggers based on navigation and flight control data (as described in this paper) may be used to determine the need to abort immediately or to estimate the likelihood that orbit will be reachable.

Safety of the next-generation space flight vehicles requires development of an in-flight Failure Detection and Prognostic (FD&P) system. Development of such system is challenging task that involves analysis of many hard hitting engineering problems across the board. In this paper we report progress in the development of FD&P for the re-contact fault between upper stage nozzle and the inter-stage caused by the first stage and upper stage separation failure. A high-fidelity models and analytical estimations are applied to analyze the following sequence of events: (i) structural dynamics of the nozzle extension during the impact; (ii) structural stability of the deformed nozzle in the presence of the pressure and temperature loads induced by the hot gas flow during engine start up; and (iii) the fault induced thrust changes in the steady burning regime. The diagnostic is based on the measurements of the impact torque. The prognostic is based on the analysis of the correlation between the actuator signal and fault-induced changes in the nozzle structural stability and thrust.

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