Dispersion Reduction of a Direct Fire Rocket Using Lateral Pulse Jets

Abstract

Impact point dispersion of a direct e re rocket can be drastically reduced with a ring of appropriately sized lateral pulse jets coupled to a trajectory tracking e ight control system. The system is shown to work well against uncertainty in the form of initial off-axis angular velocity perturbations as well as atmospheric winds. For an example case examined, dispersion was reduced by a factor of 100. Dispersion reduction is a strong function of the number of individual pulse jets, the pulse jet impulse, and the trajectory tracking window size. Proper selection of these parameters for a particular rocket and launcher combination is required to achieve optimum dispersion reduction. Forrelatively lowpulsejetimpulse, dispersion steadily decreasesasthenumberofpulsejetsisincreased or as the pulse jet impulse is increased. For a e xed total pulse jet ring impulse, a single pulse is the optimum pulse jet cone guration when the pulse jet ring impulse is small because the effect of a pulse on the trajectory of a rocket decreases as the round e ies downrange. Nomenclature CDD = e n cant roll moment aerodynamic coefe cient CLP = roll damping aerodynamic coefe cient CMQ = pitch damping aerodynamic coefe cient CNA = normal force aerodynamic coefe cient CX0 = zero yaw axial force aerodynamic coefe cient CX2 = yaw axial force aerodynamic coefe cient D = rocket reference diameter ethres = trajectory tracking window size L; M; N = total applied moments about rocket mass center expressed in the aft body reference frame nJ = number of individual lateral pulse jets nRXi ;nRYi , = ith main rocket motor direction cosines in the nRZi body frame p;q;r = components of the angular velocity vector of the projectile in the body reference frame T = P ° time constant TJi = ith lateral pulse jet thrust TRi = ith main rocket motor thrust t ¤ = time of the most recent pulse jet e ring u;v;w = components of the velocity vector of the mass center of the composite body in the body reference frame uA;vA;wA = components of the velocity of the mass center of the projectile with mean wind expressed in the body reference frame VA = magnitude of the velocity vector of the mass center of the projectile experienced with mean wind expressed in the body reference frame VMW;aeMW = magnitude and wind factor of the mean atmospheric wind expressed in the initial reference frame X;Y; Z = total applied force components in the aft body reference frame