Ccd Star Sensor Circuit Design Study

Without accurate measurement of spacecraft attitude,it is impossible to make space system in good condition.The spacecraft attitude can be measured by earth sensors,sun sensors,moon sensors,star sensors,magnetic field meters or gyroscopes. Star sensors are so far the most precise attitude measurement instrument.Their accuracy can be several arc seconds.Star sensors take a photograph of the sky in FOV(Field of View).Starlight illuminates the pixels of optoelectronic sensor.Then optic energy is converted into video analog signal of which amplitude is propotional to the starlight illumination.After being amplified,correlated double sampled,video signal is digitized by an A/D(anolog to digital)convertor and data are stored in SRAM(static random access memory).After processing those data,stars are extracted from background.Coordinate position of stars can be obtained exactly by centroiding algorithm.Stars in FOV are identified by calculating the angle distances between star pairs and by matching to the angle distances between star pairs stored in ROM(Read Only Memory).Then the direction of optical axis of star sensor can be calulated.Thus the attitude of spacecraft on which the star sensor is fixed can be calculated too with their installation relationship.Because position of stars has been located accurately by astronomic method,star sensors have very high accuracy.Star sensors are small as well as accurate.And they have low power dissipation.Star sensors have various operating mode -star trackers,star scanners and star mappers.Star sensors are widely used by advanced countries as spacecraft attitude measurement instrument.In our country,spacecraft attitude is mainly measured by earth sensor,sun sensor and gyroscope.These attitude measurement instruments have poor accuracy.So it is very important to develop star sensors.There are star sensors with CCD(Charge Coupled Device) array image sensor and with CMOS APS(Complementary Metal Oxide Semiconductor Active Pixel Sensor).Because of excellent sensitivity and high SNR(Signal Noise Ratio),CCD star sensors are more precise.And CMOS APS star sensors are smaller and lower power dissipation because CMOS APS has advantage of high integration and dispensing with peripheral driving circuit.The circuit design of High reliable CCD star sensor is the subject of this paper.A star sensor with a high reliable structure is proposed in this paper.This star sensor has dual CCD circuits,dual digital processing systems with cold redundancy and dual power supply units with cold redundancy.It is verified by experiment that this star sensor features high reliability and low power dissipation.The design of electronic circuits of CCD star sensor is discussed in this paper.The main subjects are as follows:1.Development of star sensor.2.Basic frame of electronic circuits of star sensor.It is comprised of optoelectronic sensor,video signal processing circuit,A/D converting circuit and digtal processing system.3.Design of driving circuit of CCD and amplifying circuit of video signal,and discussion the relationship between gain and distortion.4.Application of DSP(Digital Signal Processor) and how to design its peripheral memory system.5.Application of FPGA(Field-Programmable Gate Array).6.Design of asynchronous Serial COM port.7.Design of DC/DC circuit.8.Evaluation in laboratory and the real night sky observation with this star sensor.9.The conclusion of this paper.