Investigation of mal-launch correction in spin-stabilized rockets

Spin stabilization of ground launched ballistic rockets is used as a means to reduce variation in their flight trajectory. Due to the lack of any closed-loop flight path control, the accuracy of such rockets is strongly influenced by numerous factors including tip-off errors at launch tube exit, wind disturbances, motor misalignment, etc. At the other extreme, some rocket or munitions systems may use an on-board guidance and control system to improve targeting accuracy to within meters or even sub-meters of a desired target position. We discuss a control approach that attempts only to reduce the effects of disturbances in the first few seconds of flight, e.g., launch tube blow-back, rail misalignment, etc. Under reasonable assumptions a simple linear time-varying model can be used that leads to an extended Kalman filter for angular rate estimation based on imprecise angular rate measurements (e.g., low cost MEMS gyroscope devices). In turn, these angular rates can be used in tandem with a simple sliding mode control law that regulates the angular rates to a nonlinear sliding surface. The resulting control commands, applied during the first few seconds of flight, can significantly improve the accuracy (CEP) of a spin-stabilized rocket relative to the accuracy achieved in open-loop flight.