LOAD RELIEF FOR LAUNCH VEHICLES USING AN ENGINE BIASING ECHNIQUE 892305

Space launch vehicles incur considerable costs by having launch scrubs due to winds aloft. Two major existing techniques are used to alleviate this problem. The first technique uses prelaunch defined trajectory shaping to minimize expected in flight loads, the second technique uses in-flight autopilot compensation based on lateral acceleration measurements. This paper deals with a simple closed-loop means of doing effective onboard trajectory shaping through variable engine biasing using prelaunch wind data. This technique has no significant impacts on vehicle stability and is readily implemented with very little computational load. Its effectiveness is demonstrated through samples of improved launch probabilities for various Delta vehicle configurations.

ONE OF THE MORE SEVERE CONSTRAINTS ON TODAY'S SPACE LAUNCH VEHICLES is the ability to cope with upper wind conditions. These wind conditions can cause problems with structural loading, controllability, and performance loss. Although structural loading and controllability problems can theoretically be handled with autopilot designs that provide appropriate vehicle response to encountered winds, in reality the vehicle response generally cannot follow wind shear conditions. This, plus the fact that performance loss minimization required trajectory shaping before encountering the wind conditions has led most designs toward trajectory reshaping as a necessary part of coping with this problem. This paper deals with providing the necessary trajectory shaping compatible with onboard mechanization through a closed-loop design.