The Development Of Scientific CCD Camera For Space Debris Monitoring

As human being take actions more frequently in exploration of space,larger amount of space equipment such as satellites and detectors are sent to space,resulting in abundant wastes and collision debris,collectively referred to as space debris.Debris in the sharp increase of number has huge potential hazard for space exploration for all countries involved.Each great power in aerospace has its own monitoring system and network.China's current monitoring sites are still on the mainland,and the scale of monitoring is still limited.Benefits from its superior geographical location and climate conditions,Antarctic Kunlun Station is an ideal site to establish operational monitoring,statistics collecting,tracking and orbit determination for space debris.At present,it is in the plan to deploy a group of telescopes at the station for monitoring.While for astronomical telescopes,CCD cameras are key components.CCD charge-coupled device has high quantum efficiency,high resolution,and low noise beyond comparison to other image detectors.It has been widely used in astronomical observations shortly after its invention.Due to its unique readout characteristics,it can also realize the function of drift scanning.That means it can track the celestial objects whose imaging of motion trajectory is straight,while needs no movement of camera or lens,greatly improving the efficiency of space observation.In this paper,in order to meet the need of the debris monitoring telescope,two scientific-grade CCD cameras have been developed according to the size of the field of view.The first one has small field of view with KAF-3200 CCD chip,and it is named SDM(Space Debris Monitoring)-K3200 camera.It passed the fundamental tests,and has been used in the star-guiding system of Quantum 1.2 meter telescope.The second camera has larger field of view with KAF-16803 CCD chip,named SDM-K16803 camera.The electronics and the structure of SDM-K16803 are optimized on the basis of the last one,and it is still in the designing and testing period.Since the two camera use the same KAF series of CCD produced by ONSEMI company,there are many similarities between them,so they will be introduced together in this article.Both camera systems are composed of CCD sealed chambers,temperature control systems,and camera control circuitry.This paper makes a specific research on the key technologies of the two camera.First,as a miniaturized CCD camera,this paper fully considers the spatial arrangement in the structural design.It adopts a compact CCD refrigeration sealed chamber,and forms a closed-loop temperature control system with a multi-stage thermoelectric cooling TEC device,a temperature sensor,and control circuits outside the chamber.Secondly,this paper designs an ultra-low noise clock and bias generation circuit for CCD driving,so the impact of the driving source on the CCD output noise could be minimized as far as possible.Finally,a low-noise front-end processing and a high-speed ADC sampling circuit for the CCD output are proposed.Different gains and sampling rates can be selected according to requirements.The electric circuit of the camera is distributed on a front-end board and a main control board.The front-end board mainly contains power supply,CCD driver and readout circuits.The main control board is mainly composed of field programmable gate array(FPGA),universal serial bus(USB)module,and temperature control circuit,shutter drive and so on.The FPGA on the main control board is the control center of all function modules,controlling the CCD driver,shutter,temperature acquisition,etc.It also realizes the drift scanning function for debris monitoring,as well as the functional prototype of image filtering and target recognition.The FPGA interacts with the controlling software on the computer through the USB,receives and executes user commands and provides feedback.The main work of this article is as follows:1.Designed the refrigeration and sealed cavity structure of two scientific-grade CCD cameras.When TEC is working,the CCD can be cooled to 45? below the ambient temperature.2.Designed the clock generation and bias generation circuit,and readout circuit for the KAF series CCD chip.Designed the drive circuit for the shutter and other modules,the temperature control module based on the microcomputer STM32 and the FPGA main control circuit.3.Completed the FPGA-based logic writing and debugging for shutter control,CCD drive and readout,drift scanning and image processing function.Also finished the temperature control algorithm based on SCM32 microcontroller;4.Completed the function and performance test of the SMD-K3200 camera.When the CCD is cooled to-20?,the readout image noise at the readout rate of 1M pixel/s can be as low as 10e-or less,and the dark current can be as low as 0.015e-/.s,which reaches the index requirements.