**3.3 The time service technique**

The navigation system cannot leave the time service. The time service can provide a benchmark for the signal processing applications in the prober. Currently, the commonly used time service device in the satellite is the atomic clock [62]. In general, the atomic clock can include the cesium clock, the hydrogen clock, and the rubidium clock. Regarding the time service system, first, its time service precision should be high. For example, the time precision of some ground atomic clocks can reach 10<sup>−</sup>18 s. Second, the integrated performance of atomic clock [63] should be good. The service life span, the mechanical performance, the temperature sensitivity, and the working stability should be calibrated and tested strictly before it is sent to the space. Third, the time synchronization ability of atomic clock should also be excellent. Although the autonomous navigation will not use any exterior information for its navigation; however, it needs to transmit some important state information to the ground sometimes. As a result, the clock synchronization issue should be another key technique for the atomic clock.

## **3.4 The practical navigation application for Mars exploration**

In a practical application, although the autonomous navigation has many merits; however, because of the high maturity and the good reliability, the nonautonomous navigation technique will be used in the Mars exploration mission as long as it is possible. Regarding the Mars exploration mission, the nonautonomous navigation method can include the satellite navigation [64], the ground radio navigation [65], and the Doppler radar navigation [66]. Here, the ground radio navigation is a typical application of the radio-based navigation. Lots of ground radio equipment or beacons can be used to provide the navigation information for the prober. The


#### **Table 7.**

*The application of the autonomous navigation and the nonautonomous navigation for the Mars exploration mission.*

**23**

**4.2 The future works**

*Autonomous Navigation for Mars Exploration DOI: http://dx.doi.org/10.5772/intechopen.92093*

**4. The challenges and the future works**

**4.1 The challenges**

future.

Doppler radar navigation also belongs to a typical application of the radio-based navigation. The Mars prober can use an active radar system to emit and receive signal to realize that navigation. Because of the extensive applications of these methods, both the ground radio navigation and the Doppler radar navigation are presented separately in this chapter. **Table 7** illustrates the integrated navigation method using both the autonomous navigation and the nonautonomous navigation for the Mars exploration. In fact, the nonautonomous navigation still plays a more important role in the flight mission than the autonomous navigation currently.

Although the explorations of the red planet have been performed for many years and lots of research plans have been proposed, many challenges still exist in the research field of autonomous navigation, including its accuracy, its reliability, and its service life of navigation system. **Table 8** shows some drawbacks of the autonomous navigation techniques. First, the accuracy issue can determine how precise when a navigation method is used for the Mars exploration task. Generally speaking, the accuracy of the integrated navigation is better than that of other sole navigation method. In the practical mission, both the autonomous navigation and the nonautonomous navigation should be used. Currently, the reported navigation accuracy of Mars landing mission is still not high. For example, the landing deviation of the curiosity rover (a Mars prober, which was launched by NASA in November 26, 2011) is about 10 km, while most of other landers could only reach the precisions from 100 to 300 km. The biggest uncertainty comes from the EDL phase. To improve the landing accuracy, the Mars atmosphere model, the orbit dynamics model, and the aerodynamics model should be researched elaborately in

Second, the reliability [67] is another problem. The reliability includes both the element reliability and the system reliability. The element reliability points to the probability of error free working state of each electronic or optic element. Also, the system reliability means the probability of error free working state of the whole navigation system. The redundancy designing degree of an aerospace system is also an evaluation index of the reliability. To improve the reliability, the environment experiments should be performed on ground to select the proper elements and test the robustness of the whole system. In general, the environment experiments include the temperature cycle experiment, the impact and the vibration experiment, the radiation experiment, the aging experiment, and the electromagnetic compatibility experiment. Third, the service life [68] of the Mars prober and its sensors also determine the result of the exploration mission. In many cases, the service life of a satellite can reach from several months to several years. The satellite healthy management is the new developed technique, which can extend the service life of satellite effectively. Its key techniques include the multiple sensors signal collection, the big data analyses, and the intelligent decision making and control.

Since the nature environment between the Earth and the Mars is similar, all the autonomous navigation methods developed in the Earth can be utilized in Mars. The first method should be the new-type inertial navigation techniques. The atom interferometric gyroscope [69], the nuclear magnetic resonance gyroscope [70],

*Autonomous Navigation for Mars Exploration DOI: http://dx.doi.org/10.5772/intechopen.92093*

Doppler radar navigation also belongs to a typical application of the radio-based navigation. The Mars prober can use an active radar system to emit and receive signal to realize that navigation. Because of the extensive applications of these methods, both the ground radio navigation and the Doppler radar navigation are presented separately in this chapter. **Table 7** illustrates the integrated navigation method using both the autonomous navigation and the nonautonomous navigation for the Mars exploration. In fact, the nonautonomous navigation still plays a more important role in the flight mission than the autonomous navigation currently.
