**2.2 The celestial navigation**

*Mars Exploration - A Step Forward*

1 The piezoelectric accelerometer

2 The vibrating string accelerometer

3 The vibrating beam accelerometer

accelerometer

*A kind of classification of the linear accelerometer.*

4 The optical

5 The pendulous accelerometer

**Table 1.**

1 The mechanical rotor gyroscope

2 The electrostatic suspended gyroscope

3 The vibratory gyroscope

5 The fiber optic gyroscope

*A kind of classification of the gyroscope.*

4 The laser gyroscope

**16**

**Table 2.**

It can realize the all-weather and the all-time working modes in any places. Second, it can provide the position, the speed, the course, and the attitude information of carrier accurately. And its data updating ratio is also high. Third, it has the good performances in the anti-interference and the low system noise. Clearly, the inertial navigation also has some shortcomings. For example, according to its navigation principle, its navigation error will be accumulated. Another problem is that the inertial navigation also cannot give out the time information. Recently, the Micro Electro Mechanical Systems (MEMS) technology [26] has met its great development opportunity. The MEMS technology can realize the optoelectronics product

**No. The name The basic principle The application**

**No. The name The basic principle The application**

effect

acceleration

acceleration

The principle of piezoelectric

The relationship between the resonant frequency of string and the corresponding

The relationship between the resonant frequency of beam and the corresponding

The principle of optical interference effect

The relationship between the rotation angle and the corresponding acceleration

The Newton's mechanics laws: the mechanical rotor can maintain its rotation orientation regardless of its base movement

The ball rotor, which works in a vacuum electric field, can maintain its rotation orientation regardless of its shell movement

The Coriolis effect, which is observed from a vibrating

structure

The gas-floated mechanical rotor gyroscope, the liquid- floated mechanical rotor gyroscope, and the ordinary mechanical rotor gyroscope

The quartz crystal or the piezoelectric

The electromagnetic oscillator-based accelerometer with the string

The electromagnetic oscillator-based accelerometer with the beam

The grating accelerometer, the fiberoptic accelerometer, or the polymer

The liquid-floated pendulous accelerometer, the flexure hinged pendulous accelerometer, and the pendulous integrating accelerometer

accelerometer

ceramics accelerometer

The electrostatic suspended gyroscope with a solid rotor, the electrostatic suspended gyroscope with a hollow

The tuning fork gyroscope, the hemispherical resonator gyroscope,

gyroscope, the mechanically dithered ring laser gyroscope, and so on

gyroscope, the resonator fiber optic gyroscope, and the Brillouin fiber

rotor, and so on

optic gyroscope

and so on

The Sagnac effect The four-mode differential laser

The Sagnac effect The interferometric fiber optic

The celestial navigation uses the space object, such as the sun, the moon, or the other stellar [27] as a reference to guide the flight direction and the flight attitude of the prober. Clearly, the star sensor [28] should be employed in this method. As a kind of optical measurement device, besides the visible light camera, the infrared camera, the ultraviolet camera, the X-ray camera, the γ-ray camera, and so on can all be used. Many methods have been designed for the celestial navigation, that is, the angle measurement-based navigation [29], the distance measurement-based navigation [30], and the speed measurement-based navigation [31]. The angle measurement-based navigation uses the angles among the sun, the other planets, the planet satellite, the asteroid, or the comet to carry out the autonomous navigation. The distance measurement-based navigation mainly employs the detection result of the arrival time difference between the X-ray pulsar and the standard pulse of the solar system center to estimate the navigation information and the time offset. In addition, the speed measurement-based navigation utilizes the optical Doppler effect [32] to implement the navigation. **Table 3** presents the popular methods of the celestial navigation.

The celestial navigation at least has three advantages. First, as a kind of optic measurement device, most of the celestial navigation systems are immune to the traditional electromagnetic interference problem [33]. Also, their working reliabilities are comparable high. Second, its navigation accuracy is good. Because the spatial distance between the celestial body and the prober is really large, the navigation precision can be very high if the star sensor performance and the corresponding data processing algorithm are proper. Third, most of the celestial navigation devices can work all-time long as long as the corresponding celestial bodies are visible. The celestial navigation also has some shortcomings. The biggest problem is that some devices cannot be used in the complex light environment. For example, the strong environment light or the cosmic rays will affect the application effect of these optic devices seriously. Another drawback is that some celestial navigation devices cannot give out the sequential output because of the target star occlusion problem. Comparing with the inertial navigation technique, the celestial navigation is still immature, and most techniques do not get the test of the practical flight mission. In future, the new modeling technique of the orbit function [34], the new measurement theory of the star, and the new estimation method of the navigation information can all be researched extensively to improve the application effect of the celestial navigation.
