A newly developed gel rocket fuel can transition from a solid to a liquid on demand, combining the stability of solid propellants with the controllability of liquids.
The fuel consists of kerosene gelled with lecithin, a food-grade emulsifier, and a small amount of calcium chloride, which causes the lecithin to form a three-dimensional network of micelles that traps the hydrocarbon.
This network gives the gel a solid-like behavior at rest, preventing the sloshing that plagues liquid fuels, but it collapses under shear stress, dropping viscosity by more than a factor of one hundred and allowing the fuel to be pumped and sprayed.
The gel can also be liquefied by heating to 59-68 C or by contact with ethanol, providing additional trigger options, and it remains stable for over a year without phase separation.
Although the fuel has not yet been tested in full-scale engines, its ability to switch states on command could enable more flexible and reliable propulsion for future space missions.