1 American Institute Of Aeronautics and Astronautics ENHANCEMENT OF REGRESSION RATE IN HYBRID ROCKETS Gaurav Marothiya 1 , Rajiv Kumar 2 and Ramakrishna P.A. 3 Indian Institute of Technology Madras, Chennai-600036, India This study has identified a potential HTPB based propellant that gives a very good density specific impulse but yet does not burn like a solid propellant. Due to low solid loading in this propellant, pre-curing of the HTPB and IPDI mixture is a necessity to get uniform density across the length of the grain. Nearly 7 hours of pre-curing gave the best results in terms of uniformity of the propellant composition. The paper also discusses the enhancement of regression rate of this propellant with known burn rate modifiers like iron oxide and copper chromite. Nomenclature d f, r = Final port diameter after r th burning d i, 0 = Initial port diameter m f = Mass of the fuel burnt ρ f = Density of fuel grain L g = Length of fuel grain t b = Burn time ṙ = Regression rate G ox = Oxidizer mass flux, (4ṁ ox /πd p 2 ) n = Oxidizer mass flux index I sp = Specific Impulse ṁ ox = Mass flow rate of oxidizer d p = Average port diameter; ((d i +d f )/2) HTPB = Hydroxyl Terminated Polybutadine DOA = Di octyl adipate IPDI = Isophorone Di-isocynate TDI = Toluene Di-isocynate AP = Ammonium Per-chlorate IO = Iron oxide (Fe 2 O 3 red) CC = Copper Chromite Al = Aluminum RP-1 = Kerosene (Rocket fuel) I. Introduction A hybrid rocket is a combination of solid and liquid rockets, where the fuel and oxidizer are in different phases. Usually, fuel is stored within the combustion chamber, which is in solid phase and oxidizers are stored separately either in liquid or gaseous phase. As fuel and oxidizer are stored separately, it is safer as compared to the solid rockets. Hybrid rockets as compared to the liquid rockets need plumbing system only for oxidizer which reduces the complexity of the system by half. In hybrid rockets the throttling is easier compared to liquid rockets as only oxidizer needs to be controlled. 1 MS Research Scholar, Department of Aerospace, IIT Madras, AIAA Student Member 2 Ph.D. Research Scholar, Department of Aerospace, IIT Madras, AIAA Student Member 3 Associate Professor, Department of Aerospace, IIT Madras, Non Member