Abstract: A solid fuel rocket engine comprises a casing which defines a combustion chamber with a solid propellant charge in the combustion chamber and an insulating layer of a water containing alkali silicate and fibers disposed between the casing and the charge. The layer is a type which will froth at a predetermined temperature which occurs during burn off of the propellant charge so that it increases in its thickness dimension in the area of the hot gases which develop and provides an adequate insulation. A method of producing the layer comprises heating the alkali silicate layer to a temperature in which it becomes plastic and sheathing the propellant charge with the plastic layer. Thereafter the sheath charge is inserted into the combustion chamber casing leaving an annular gap between this layer and combustion chamber casing. Thereafter heat is applied to the vicinity of the chamber to cause the layer to froth and expand to close the annular gap.

Abstract: An insulating layer is effected between a propellant charge in the interior walls of a combustion chamber of a rocket engine by applying an expandable plastic to the inside of the combustion chamber housing between the housing and the outer circumferential wall of the propellant charge then expanding the plastic. Advantageously the combustion chamber is preheated before introducing the charge and the expandable plastic into the combustion chamber. Preferably the ratio of the layer of the thickness of the expandable plastic to the spacing between the propellant charge and the walls of the combustion chamber ranges from 1 to 11/2; 1 to 1 and 1 to 3. The expandable plastic is advantageously a polybutadiene.