a cost - effective , renewable ethanol - based solid fuel compound , and method of making the fuel for hybrid rocket engines . gelling agents , preferably methylcellulose can be used in conjunction with calcium acetate or calcium acetate alone make a stiff plastic out of ethanol to improve its properties for hybrid rocket engine . the increased stiffness of an ethanol - based fuel gel , increases yield stress that allows rapid acceleration of rockets . the low cost bio - fuel based on solidified ethanol rather than expensive petroleum derived substances lowers the cost of volume rocket launches , lowers the cost of access to orbit and provides safer sounding rocket flights into space . the resulting raw gel can further be mixed with a cross linking compound and water to form a stiffer material . alternatively , the resulting raw gel can be frozen by liquid nitrogen .