Features such as lowcost, safety, throttleability, and a wide range of appealing applications (e. g., interplanetary landers, boosters for space launcher, upper stage for Vega launcher) make hybrid rocket engines a very attractive option for aerospace propulsion. However, problems such as low regression rates of the solid fuel and low combustion e©ciency have so far hindered the development of large-scale hybrid rocket engines. Space Propulsion Laboratory (SPLab) at Politecnico di Milano has developed a series of proprietary techniques to evaluate, on a relative grading, the quasi-steady regression rates of solid fuels while visualizing at the same time the §ame structure. Numerical modeling, thermochemical calculations, and mechanical testing complete the range of tools set up to assess the quality of new solid fuels. In this paper, HTPB polymer has been taken as baseline and characterized at laboratory level.