A Study On The Nutation Instability Of Spinning Spacecraft With Solid Rocket Motor

As the increase of motor size and the time of motor operation, the spin stabilized solid rocket propelled space vehicles performed the unpredictable nutation instability. Small wobbling (often referred to as "nutation" or "coning") induced during separation of spacecraft from its spin plat form in the space shuttle bay, was enormously amplified during the later half burning of the rocket motor. The growth ceased abruptly at motor burnout, and final cone angle as large as 17 degree were reached in some flights.Conventional theories of spinning rocket dynamics failed to explain this behavior. Since the telemetry data shows that the severity of the problem depends on spacecraft mass properties and other system parameters. Although after that it used the nutation control fix in the spacecraft which had behaved this instability but the controlling device was weight too much. It cost a large percent of the negative weight of the vehicle. And this approach is indirect conflict with the philosophy of solid rocket space propulsion, which is based on its inherent simplicity and low cost. So it is crucial that the origins of the instability be understood completely in order that serious mission degradation can be avoided in future orbit raising operations.On the basis of the property description of the spacecraft nutation instability which we already have, this instable phenomenon is studied in this thesis. Key works performed in this thesis are:Firstly, under the analysis of the attitude dynamics of the space vehicles, the nutation instability motion of the spacecraft propelled by the rocket motor is achieved, associating with the real telemetry data and a series of the characteristics of the spacecraft in the phenomenon, some possible mechanisms which could cause the nutation instability are analyzed. It preliminarily gets that the observed nutation instability is caused by the variation of the spacecraft itself and the interaction of the complex unsteady internal flow field within the rocket motor with vehicle wobbling motion.Secondly, base on the whole system dynamic equations and with the assumption for the internal flow in the rocket motor, examining the influence of the variable mass on the system attitude dynamics. After a few classical cases were computed, it can be seen that the variation of the attitude is very different with varied type of propellant and varied burning pattern. The mass dissipation of propellant is advantageous to the spinning motion in end burn, which makes the transverse angular velocity tend to stable gradually; but it is opposite in radial burn that the transverse angular velocity grows exponentially, thus causes the unstableness of the flight.Thirdly, analysis of the attitude dynamic equations of the spacecraft system with no assumption, especially considering the jet damping torque and the misalignment torque effects in the equations. Piecewise linear models are adopted for the evolution of the system parameters. Induce the real spacecraft parameters to solve the motion equations and get that the different spacecraft parameter variations have the different influence on the system attitude motion.Fourthly, introduce disturbing torque produced by the unsteady gas flow which has already been obtained by Flandro. And also with the piecewise linear models to solve the system motion equations, it comes out that the disturbing torque produced by the unsteady gas flow is the most significant effect which lead to the nutation instability of the spacecraft.Finally, base on the conclusions we already have, the incompressible unsteady internal gas flow in the motor is simulated. And get the variable regularity of the vortex core flow in the spinning rocket. As the complexity of the burning surface of the propellant increases, the flow of the vortex is more complex. The interaction between the internal gas flows in the form of traveling inertial pressure waves and the rocking motion of the spacecraft induced the unsteady gas flow which is the main reason causes the nutation instability of the spacecraft.The results achieved and the conclusions drawn in this thesis are of great importance and applicable in the nutation instability phenomenon of solid rocket motor spacecraft.