A propulsion system for a combined aircraft/spacecraft including: a jet engine having a longitudinal axis defined in a direction from a front end at an air intake to a rear end at a jet exhaust: a front end at an air intake to a rear end at the jet exhaust; a rocket engine having a longitudinal axis defined normal to a rear end at a rocket exhaust; a common engine housing having an elongated shape and wherein the jet engine and the rocket engine are configured substantially coaxially and with respective rear ends facing the same direction when the rocket engine is operated.