Frequency Analysis of Launch Vehicle Oscillation Absorbent Configuration on Performance of LPE

Pogo phenomenon is considered as low-frequency instability at system level in heavy satellite launchers. This instability results from the frequency interactions between structure and propulsion subsystems. To compensate for or prevent the occurrence of this instability in a satellite launcher, an element that reduces the frequency interaction effects of these two systems is used. This element, which is known as ‘accumulator’, absorbs the pogo vibrations in satellites. In this paper, by dynamically modeling the engine elements (tank, supply line, accumulator, pump, and thrust chamber), and by considering the connection of structure to engine at two points of tank and pump, the effects of the accumulator element and parameters on the natural frequency of the propulsion system have been investigated and the considerations related to operating conditions and the placement of this element along the supply line of the propulsion system have been determined. The findings indicate that placing the accumulator near the pump assembly and along the suction path reduces the natural frequency of the propulsion system; which contributes to a greater stability of the satellite launcher. With the increase in the compliance and inertance of accumulator, accumulator’s influence on the natural frequency of the propulsion system becomes more significant