Aerothermal Databases and Heat-Load Prediction for Re-Usable Launch Vehicle Configurations

Abstract

Orbital launch vehicles with re-useable major components or stages provide the potential to decrease the operational costs and to increase the flexibility of the entire system. DLR is conducting systematic studies of such configurations. The present analyses focus on different vertical take-off two stage systems which include a re-usable first stage. This stage is either configured for vertical landing using retro-propulsion or horizontal landing as a winged configuration. The layout and system analysis of such vehicles includes challenges related to the application of robust, light-weight, inexpensive and serviceable thermal protection systems. The thermal protection design requires accurate predictions of thermal loads for the entire atmospheric flight path. Due to the limitations and cost of ground based testing for large scale vehicles and the difficulty to apply general fluid mechanical scaling laws, these predictions rely intensively on numerical simulations (CFD). These CFD-based load predictions need to be coupled with an analysis of the structural response (heating model). Because of the large disparity of fluid mechanical and structural time scales, an unsteady CFD analysis over the entire trajectory is practically impossible and fast-response surrogate models for the aerothermal loads are required. This paper describes the structure and construction of such a model based on an aerothermal database. The database is composed of a series of steady-state CFD results which cover the entire atmospheric flight trajectory. Interpolation algorithms are used to estimate the local heating rate on each point of the vehicle surface as a function of flight time and local surface temperature. Particular challenges of the CFD analyses such as the plume-interactions during retropropulsion maneuvers or the heat flux scaling depending on the local wall temperature are addressed. Exemplary applications and results of surface temperature predictions are shown.