Abstract: The invention comprises an expansion nozzle for a rocket engine destined to function successively in atmospheric and space conditions. The nozzle is comprised of a main wall defining a surface of revolution that splays outwardly and further comprises a complementary annular convergent divergent nozzle having an exhaust port and also having its axis coinciding with the principal axis of the main wall. The complementary annular nozzle is located outside the main wall and has a gas distribution torus cooperating with gas flow supply means to produce an annular flow of gas surrounding a main flow of gas exhausted at the down stream extremity of said main wall of the expansion nozzle. The annular flow of gas forms a source of static pressure P.sub.s that is substantially lower than atmospheric pressure P.sub.a. P.sub.s has a value of between 0.3 and 0.8 times P.sub.a.