Abstract: A method for increasing the payload that can be delivered by a given launch vehicle to a selected target in an interplanetary space mission, without increasing the transfer time to reach the target. In accordance with the disclosed method, a conventional multi-stage launch vehicle is used to accelerate a payload spacecraft to near earth's escape velocity. Then the spacecraft is separated from the upper stage of the launch vehicle and is further accelerated by applying a velocity impulse with an onboard propulsion system into a transfer trajectory that takes the spacecraft to the target planet. Because the upper stage of the launch vehicle is not accelerated into the same transfer trajectory, a larger payload mass can be delivered to the target planet without increasing the transfer time. Alternatively, the transfer time can be reduced without decreasing the payload mass or changing the launch vehicle configuration.