Abstract: A propellant cross-feed system of the present invention for use with a two-stage rocket. The rocket (or reusable launch vehicle) includes a booster and an orbiter. The booster includes a booster propellant tank that is connected to a booster engine by a booster feed line. The orbiter includes an orbiter propellant tank that is connected to an orbiter engine by an orbiter feed line. Each propellant tank supplies propellant through its respective feed line to its respective engine. The cross-feed system includes a cross-feed line that connects the booster feed line to the orbiter feed line, thereby allowing propellant flow from the booster tank to the orbiter engine for parallel (simultaneous) engine burn. Cross-feed propellant flow is managed by a low pressure, cross-feed check valve that is responsive to propellant flow rate changes that occur as a result of the motorized operation of a switch-over valve.