N-II/H-Iロケットのフライト・データに基づくポゴ解析

抄録

Three types of longitudinal oscillations Pre-MECO POGO 1, Pre-MECO POGO 2 and MECO POGO have been observed in the launches of N-II/H-I vehicles. A Nyquist plot of a mathematical POGO model is used to examine stability properties of these oscillations. Pre-MECO POGO 1 and MECO POGO are generated in the LOX feed system installed with an accumulator. Flow fluctuation due to the LOX pump vibration is the main exciting factor for the former, while the fluctuation of LOX tank bottom pressure the latter. Pre-MECO POGO 2, excited in the vicinity of open-pipe resonant frequency of fuel suction line, is affected by fuel flow fluctuation. Frequency, longitudinal structural mode shape and generalized mass related with each POGO are determined from flight data. And the POGO model with these parameters are shown to represent the whole POGO features of N-II/H-I along flight time.