A gas generator includes a housing sized and configured to be located within a launch tube for a projectile. The housing defines a first propellant chamber; at least a second propellant chamber comprising a ring situated concentrically around the first propellant chamber; an expansion chamber; at least one first aperture between the first propellant chamber and the expansion chamber; and at least one second aperture between the at least a second propellant chamber and the expansion chamber. The gas generator also includes at least one propellant within each of the first propellant chamber and the at least a second propellant chamber of the housing; and a pyrotechnic delay connecting the first propellant chamber and the second propellant chamber. A launch tube assembly includes a tube containing at least one projectile and a gas generator. Related methods of launching a projectile are also disclosed.