The future of commercial space activity is inherently dependent on the availability of an economic launch system. In order to be able to embark on the full development of such a system it will be necessary to bring a wide range of technologies to maturity in all the major disciplines. These technologies are largely common to all proposed configurations of Advanced Space Transportation Systems.Estimates of hypersonic aerodynamic parameters are currently uncertain due to the inadequacy of aerodynamic theories and wind tunnel techniques in the presence of molecular dissociation of the air, viscous effects, separation and surface catalysis.This paper will address the areas of aerodynamic heating and force/moments/control powers. The current methodology as applied for HOTOL is described, including comparisons between prediction and wind tunnel measurements. A programme of technology development covering theoretical methods, wind tunnel experiments and free flight models is described.