**2.4 The integrated navigation**

The integrated navigation uses the combination of two or more than two basic navigation methods above to realize the high precision direction guidance and the attitude estimation of carrier. Its key techniques include the computer-based feature extraction, the information fusion, and the time synchronization [42]. The integrated navigation can make up the disadvantage of the sole navigation method, realize the seamless navigation, and achieve the information redundancy designing of the navigation system [43]. Its system reliability and the navigation accuracy can be improved a lot. Currently, the most successful integrated navigation is the inertial plus the Global Positioning System (GPS)-based navigation method, that is, the combination of the inertial navigation and the satellite navigation. Regarding the autonomous navigation technique for the deep space exploration, **Table 5** presents the popular integrated navigation methods. From **Table 5**, any two basic navigation methods can be used for the integrated navigation application. The integrated navigation also has some drawbacks. For example, its complex system design, its big size, and its high power consumption are all the problems for the spacecraft application.
