Overview of the German Gel Propulsion Technology Program

Abstract

Gelled fluids are homogeneous mixtures of a liquid and a gelling agent. They behave like a solid at rest in the tank but can be liquefied if a sufficiently high shear stress is applied upon injection into the combustion chamber. Gelled propellants are of interest for rocket and ramjet propulsion systems because of their inherent safety and performance benefits compared to pure storable liquids. Due to their non-Newtonian flow behavior, gelled propellants combine the advantages of liquid and solid propellants. Engines with gelled propellants can be throttled and restarted, similar to engines with liquid propellants. On the other hand, engines with gelled propellants have simple handling and storage characteristics and reduced sloshing. Gelled propellants spill not through leaks and have a reduced vapor pressure in comparison to their basic (Newtonian) fluid. In this respect gel propellant engines behave like solid-propellant motors. In the last two decades a growing interest in gelled propellants for rocket and ramjet propulsion applications has been observed worldwide. In Germany, within the German Gel Propulsion Technology Program (GGPT), which was started in 2001, necessary technologies to build a green gel propellant rocket engine are developed and its capabilities demonstrated by static tests and in 2009 two successful demonstration flights. Ongoing activities comprise development of next generation gelled propellants which combine relatively high ballistic performance with insensitivity and low environmental hazards, maturing technologies like thermal management and control as well as deepening the knowledge on the combustion chamber processes i.e. injection, atomization, evaporation and combustion. The paper gives an extensive overview on challenges, activities and findings obtained within the GGPT.