1877. Weight Control of a Large Space Booster

Paper

Abstract

The Titan III had successfully performed many missions placing satellites in orbit from both coasts. The challenge was to design a longer ”stretched” vehicle by lengthening the fuel and oxidizer tanks on both stages while holding the diameter constant at ten feet. The new Titan IV vehicle would have to withstand larger P-equivalent loads due to the increased weight required by structural beefup to the skin, stringers, and frames. Different sections of the vehicle were assigned different amounts of beef-up based on their relative axial load-carrying capabilities. An initial design vehicle was established. Upon further analysis, it was determined that the increased vehicle and payload fairing lengths imparted a large bending moment on the booster at design Q-Alpha-Total flight conditions. This caused a vehicle redesign, and it was found that stiffness rather than axial load became the design driver in most areas. As the new stiffness requirements were translated into structural detail sizing and analyzed by the mass properties group, the weight problems began to surface Target weights had been established in the proposal phase and revised due to the stiffness criteria, but both values were being exceeded in design. A method to control vehicle weight was urgently needed. The paper discusses how this challenge was met by analyzing critical frames, stringers, and skins with a target weight versus stress margin comparison. Details are presented to show how items became identified for weight reduction and results are quantified. A significant performance gain resulted from this weight reduction program. The excellent teamwork that produced the weight savings has carried over into subsequent phases of vehicle development. Various design groups were united by this effort, and for a while everyone became a ”weights engineer” and worked for a common goal.