The High-Speed Flight Demonstration (HSFD) project is the latest in a series of flight experiments in a joint research program into reusable space transportation systems being conducted by the National Aerospace Laboratory of Japan (NAL) and the National Space Development Agency of Japan (NASDA). (NAL and NASDA were merged to form the Japan Aerospace Exploration Agency, JAXA, on October 1, 2003.) The HSFD project was planned in two phases, with the Phase II experiment being a series of drop tests to obtain flight data to clarify the transonic aerodynamic characteristics of the demonstrator. A Phase II test was conducted at the Esrange test site in Sweden in July 2003 in collaboration with Centre National d'Etudes Spatiales of France (CNES), which developed and operated the stratospheric balloon system used for the drop tests. Although the test campaign was interrupted following this test due to an anomaly in the demonstrator’s recovery system, data were obtained during flight at Mach 0.8. By analyzing these data, the longitudinal aerodynamic characteristics of the High Speed Flight Demonstrator were estimated and the results found to be similar to wind tunnel test predictions within the uncertainties pertained to the predictions. The data obtained from the HSFD project will serve as a reference for evaluating wind tunnel test results and Computational Fluid Dynamics predictions, and are expected to provide essential information for development of future reusable space transportation systems.