1664. Automated Approach to Weight Estimating for Reusable Launch Vehicle Concepts

Paper

Abstract

Variations in mission requirements and vehicle design characteristics for advanced reusable earth-to-orbit-to-earth transportation systems necessitate the development of computerized mass property estimating programs. This paper will describe automated systems developed within the Boeing Military Airplane Company to estimate vehicle and 1aunch system mass properties with perturbation of mission requirements and/or vehicle design characteristics and geometries.
For every pound of inert or payload added to a single stage rocket propelled system, approximately 30 to 35 pounds of additional propulsion, structure, and propellant must be added to accomplish the same mission. This exchange ratio will be reduced for two-stage systems or improved specific impulse systems. However, two-stage systems magnify weight prediction requirements since mission profiles, aero thermal loadings and subsystem requirements vary enormously for each vehicle. Automated weight estimating systems allow rapid and consistent prediction of vehicle(s) weights for perturbations in design criteria.
The next operational launch system will be completely reusable and either single-stage-to-orbit or two stage. Efforts have been directed toward developing mass property predicting computer programs to accommodate both systems. Automated programs were developed which allow rapid and consistent concept evaluation. Schematics of these computer programs will be illustrated. Typical program input and output data will be discussed. Key to development of these automated programs is the requirement to produce defined weight relationships of individual subsystem candidates with realistic design requirements. These trending relationships must include both existing and advanced subsystem concept.
One of the primary drivers in vehicle and launch system weight is vehicle shape and structural concept. Automated sizing programs allow variations in payload weight and volume, propellant tankage concepts, and environmental protection systems in combination with wing and empennage geometry modifications. Rocket system main stage propellants will be limited to liquid oxygen and hydrogen for this paper. Typical trade data developed from these systems will be illustrated.
Sample program weight calculations and comparison to reported weights for the Space Shuttle will also be included.