New Pogo Analysis Method Using Rational Fitting and Three-Dimensional Tank Modeling

Considering the flexibility of a liquid rocket propellant tank and the importance of the relationship between oscillatory pressure and outflow near the tank outlet, a three-dimensional modeling technique is developed to provide a more accurate tank simulation. This paper also presents a rational function fitting method that could be used to transform transcendental equations of a feed-line transfer function into a homogeneous second-order matrix form. It is shown that this form of feed-line transfer function can be easily coupled together with governing equations of a liquid rocket structural system, which could be further solved for system stability using mature eigenvalue solvers. By comparison with the telemetry data and traditional methods, this pogo stability method proves to be highly accurate and efficient.