**2. The key autonomous navigation techniques**

Different from the traditional navigation techniques, the autonomous navigation [18] can realize the perception, the computation, and the decision making of the flight trajectory all by the aerospace prober itself. No exterior information is needed. Sometimes the autonomous navigation system can also emit some state information to the ground for the safety monitoring purpose. Many methods can be used to assist the autonomous navigation flight. The popular methods include the inertial navigation [19], the celestial navigation [20], the visual navigation, and the integrated navigation. **Figure 2** shows the sketch map of the popular autonomous navigation methods.
