Sounding Rocket Dispersion Reduction by Second Stage Pointing Control

Abstract

The mission architecture of SHEFEX II features a two-stage solid propellant sounding rocket vehicle on a suppressed trajectory, which is induced by a cold gas pointing maneuver of the vehicle before second stage ignition. The impact point is subject to a 3-� dispersion of roughly�110 kmin downrange and�90 kmin crossrange, which makes a recovery of the vehicle particularly difficult, as the whole impact area is located off shore and the vehicle needs to be recovered by ship. As the major part to dispersion is contributed during the atmospheric ascent of the vehicle, a control algorithm is developed that considers the actual deviation from the nominal trajectory after atmospheric exit and recommends a vehicle pointing that corrects for this deviation. The analytic control algorithm is found by linear/quadratic approximation of the impact point sensitivity towards the deviations after atmospheric exit and to the pointing angles. The effectiveness of the algorithm is tested by implementing it in a full six-degree-offreedom simulation and applying dispersion factors in a Monte Carlo simulation. The result is a reduction of the impact point dispersion area by about 78%.