A new method is developed for preliminary design of hybrid rocket motors. A cooperative evolutionary method is used with an indirect approach to perform the coupled optimization of hybrid rocket motor and trajectory for a sounding rocket. Different propellant combinations are considered for a sounding rocket application (microgravity platform). The motor grain is cylindrical with a single circular port: blowdown and self-pressurized feeding systems are used. The eects of throat erosion are discussed, taking into account recent CFD evaluation of throat regression rate in nozzles of hybrid rocket motors. The method shows to be very promising with respect to other procedures and can be applied to complex applications such as launcher upper stages or landers. Due to the peculiarity of the present problem also a purely evolutionary approach is used to perform optimization. Even if the nested evolutionary/indirect method is able to find a better solution, the purely evolutionary method is able to find a near-optimal solution with a CPU time which is one order of magnitude lower