Review on the Regression Rate-Improvement Techniques and Mechanical Performance of Hybrid Rocket Fuels

Human spaceflight, space tourism, and the launch of microsatellites are all expected to grow in the future. In fact, with the recent increase of the satellite market, almost 1000 smallsats per year are foreseen to be launched over the next decade. Hybrid rocket propulsion has received significant attention for military and commercial applications due to its potential safety, throttleable, and restart ability when compared with solid rockets, economicity, simplicity, and compactness features when compared to liquid rockets. However, in order to make this new technology the future of the next generation of rockets, some drawbacks of the heterogeneous combustion in hybrid rockets such as low fuel regression rate and varying oxidizer-to-fuel ratio during the combustion process must be well addressed. The diffusion-limited combustion in hybrid rocket motor is responsible for the low regression and poor combustion efficiency of fuels such as Hydroxyl-terminated polybutadiene (HTPB), Poly methylmethacrylate (PMMA), and other polymeric binder-fuels. The paraffin-based solid fuel represents a potential solution to the slow regression rate of current solid polymeric fuels. However, paraffin-based fuels suffer from poor mechanical properties and rapid volatilization, preventing their full development and applications for a space mission. In this work, a review of various techniques to improve hybrid rocket fuel's ballistic and mechanical performance is presented.