Fuel for the energy supply in space travel must be elevated by other fuel, requiring more fuel for its elevation. The consequence is a limit to the size of space transporting systems and to the duration of travel. This limitation can be removed, if an energy supply can be constructed, which doesnÂÂÂÂt need to combust ponderable matter. A possible appropriate energy source is the zero point energy of the quantum-vacuum (ZPE). The necessary research is the development of an energy converter, which can tap ZPE-energy from the quantum vacuum. An electrostatic rotor presented here, which the author analyzed at the Otto-von-Guericke- University in Magdeburg, demonstrates a verification that ZPE-energy can be converted into classical mechanical energy. Due to the small amount of converted power (150 nanowatts), the experiment is regarded as a fundamental scientific proof, not as an engineering construction of a ZPE-motor. Additionally, computer-simulations of a powerful ZPE-engine are developed in theory, arising the expectation to operate in the range of several hundred watts or some kilowatts ÂÂÂÂ with the future perspective to build a prototype of a useful engine. If energy can be gained from the quantum-vacuum, the recoil of photons can be used for propulsion techniques.