Nonlinear Life-Extending Control of a Rocket Engine

ROCKET engine has a number of critical components that operate close to mechanical design limits. These components often typify behavior of the remaining components and hence are indicators of the effective service life of a reusable rocket engine. Fatigue damage in the turbine blades is one of the most serious causes for engine failure. This Note focuses on the conceptual development of a nonlinear life-extending control system for rocket engines via damage mitigation in both the fuel (H2) and oxidizer (O2) turbine blades. The fundamental concept of life-extending control (LEC) was introduced by Lorenzo and Merrill. 1 Subsequently, a growing body of literature has emerged for feedforward 2,3 and feedback 4 control of rocket engines for life extension. Whereas the LEC technology was developed initially for rocket engines, it has broad applications for other systems such as fossil-fueled power plants 5 and mechanical structures, 6 where both dynamic performance and structural durability are critical issues. ThedesignapproachpresentedinthisNoteisdifferentfrompreviousworkinthesensethatthisapproachallowsadaptationoftheLEC featuretoaugmentaconventionalperformancecontrollerofarocket engine. Unlike the previously reported design approaches, 2,3,5 the proposed technique does not require an optimal feedforward control sequence, which is sensitive to plant modeling uncertainties and variations in the initial conditions. Furthermore, for other control applications such as military aircraft, the life extension feature ofthecontrolsystemcanbeactivatedordeactivatedattheoperator’ s discretion.