Study On Application Technique Of CMOS Iimager In Star Tracker

Star tracker is a high precision attitude measurement instrument which takes sky as the working object and star as the frame of reference; it's now the most precise attitude measurement instrument with lowest excursion and is widely used in satellite, Intercontinental Ballistic Missile, and spaceship etc. It's capable of giving attitude parameters independently like inertia gyro but without excursion, so the star tracker is going to replace the inertia gyro in many space applications.Most star trackers being used now are based on CCD image sensor which is the most common imaging device in star tracker. Many more shortcomings of CCD have been discovered in many application projects for a long time, such as bad anti-radiation capability, many power sources needed in CCD data acquisition board, serilizition of the signal charge from the well to output of the CCD, complicated manufacturing technology and in-compatible with general IC manufacture technology which is widely used in modern IC manufacturing. With the development of technology, some parameters like attitude measurement precision, volume, weight and power dissipation of the star tracker are stricter than before and the star tracker based on CCD is complicated in electronic design and hungry for power.CMOS image sensors are also solid state imaging device like CCD, it now become increasingly competitive with respect to their CCD counterparts, while adding advantages such as no blooming, simpler driving requirements, small volume, low power dissipation, wide dynamic range, anti-radiation capability and the potential of on-chip integration of sensor, analogue circuitry, and digital processing functions. It has great potential in star tracker application and now is being investigated in many countries. Some countries are now developing star trackers based on CMOS imager, further more, the experience gained with star tracker can be applied to smart cameras for planetary exploration.The main purpose of this thesis is to study the application possibility and technique of CMOS imager in star tracker and the practical matter that may be encountered in the design and implementation of the star tracker. Some key work has been done around thegoal to build a star tracker based on CMOS imager, just as follows:1. First of all, this thesis give a brief introduction of development background, present situation and developing trend of the CMOS imager based on analyze, comparation and inducemen.2. In the second chapter of this thesis, the main working principle, structure scheme, technical parameters of the CMOS imager are all disscussed in detail based on the foregoing introduction. The key characteristis of the CMOS imager and the CCD are compared and analyzed in detail; key parameters of some typical CMOS imagers are compared briefly. The main status in quo of application of CMOS imager in star tracker in domestic and foreign countries is also intruduced and disscussed at the end of this chapter.3. In the third chapter of this thesis, the main performance parameter of the star tracker and some key techniquesin in the design of star tracker based on CMOS imager are discussed in detail. Some important digital signal processing technique like threshold decision, star object picking up and sub-pixel interpolation subdivision are also discussed.4. In the fourth chapter of this thesis, design method, experimental ways and means, analyze of the experimental data of the experimental star tracker are discussed in detail for the experimental star tracker based on CMOS imager IBIS5 and OV7620. Two key problems: rolling shutter and sub-pixel measurement precision of the CMOS imager are disscussed in detail, analyze of the experimetal data are made at the end of this chapter.5. Conclusion is given at the end of the thesis based on the discussion and analyzation of the principle and experimental results.The result of this thesis indicates that CMOS imager can be successfully applied in aerospace instruments like star trakcer, space digital camera etc, a new star tracker will be built with capability of being small volume, light weight, low power dissipation and anti-radiatio.