Alain Lacombe

3D Carbon-Carbon composites are revolutionizing upper stage Liquid Rocket Engine performance by allowing introduction of large nozzle extension.

The need to increase the payload capacity of the current launchers drives rocket engine manufacturers to seek higher thrust level, specific impulse and thrust to weight ratio. The use of high temperature C-C composite materials is an efficient way to reach these objectives by allowing use of high expansion ratio nozzle extensions benefiting of the outstanding thermal, mechanical and fatigue resistance of these materials to decrease mass and featuring high temperature margins.

High temperature composite nozzle extensions, a mature and efficient technology to improve upper stage Liquid Rocket Engine performance.

The need to increase the payload capacity of the current launchers drives rocket engine manufacturers to seek higher thrust level, specific impulse and thrust to weight ratio. An efficient way to do this is to use of increased expansion ratio nozzle extensions for upper stage engines, using high temperature composite materials in order to allow higher temperature material capability, and take benefit of the outstanding thermal, mechanical and fatigue resistance of these materials to decrease mass. Up to the mid 90s, the use of Carbon -Carbon (C-C) or Carbon-Silicon carbide (C-SiC) composite nozzles was limited to solid rocket motors, but challenging performance reqirements led to C -C nozzle extension flight qualification on the RL10B-2 engine of the Delta IV upper stage, in the late 90’s, and both materials are planed for use on the next Ariane 5 ECB upper stage generation powered with the liquid Vinci ® engine. Both engines are equipped with very large extendible composite nozzles developed and produced by Snecma Propulsion Solide, SAFRAN Group. This paper describes the technological background of Snecma Propulsion Solide in the design, materials and manufacturing of high temperature composite nozzles inherited from solid rocket motors and extended to liquid rocket engines. It provides an up-to-date status of the demonstrations already performed on different liquid rocket engines and details all of the recent progress on technical and manufacturing performance. The manufacturing process has also been improved and simplified in order to allow the manufacturing of larger scale nozzles at lower cost.

HERAKLES thermal-structural composite materials boost rocket nozzle performance.

The first step consisted in using the Carbon-Carbon at the most sensitive location of the nozzle: the throat area. The low density, around 1.8, the high temperature resistance, more than 3000C combined with high mechanical strength, associated with a very low erosion when facing the Mach 1 combustion gas flows, the very low thermal expansion together with very high thermal conductivity to confer strong heat shock resistance, are making the Carbon-Carbon well suited for throats. Very innovative fiber constructions have been invented in order to improve the mechanical behavior of the material, giving it more isotropic characteristics which increases its erosion resistance. One of them is well known: the 4D preform which is composed of carbon fiber rods put along the directions created by the 4 diagonals of a cube.