Mini APS CMOS Star Tracker: Introduction

After more than half a century of development, star sensors have entered the fourth generation: The Mini APS CMOS Star Tracker.

In the 1990s, the Jet Propulsion Laboratory (JPL) in the United States invented the APS CMOS image sensor.

In order to solve the problems of relatively large quality, power consumption, and volume of CCD star sensors, it is necessary to adapt to the development and application of micro/nano small satellites, The development of CMOS technology, especially APS CMOS technology and backlit near-infrared CMOS technology, has made CMOS, as a photosensitive detector, approach the sensitivity level of CCD. Moreover, CMOS has some unique properties that make it more suitable for applications in the aerospace field, especially in the field of star sensors. At present, industry insiders generally believe that APS CMOS photodetectors will replace CCD as the mainstream of the next generation of micro star sensors.

The overall configuration of APS CMOS star tracker：

1) Integrated star sensor configuration: mainly including a hood, lens, and electronic system.

Compact structure, compact size, convenient installation and use; However, the combination of signal processing, computation, and imaging components results in high power consumption and relatively large volume, which also requires relatively high requirements for thermal control.

2) Split type star sensor configuration: Optical Head (OH) and Electronic Unit (EU), which are connected through data transmission lines such as Low Voltage Differential Signal (LVDS).

OH itself has low power consumption and is installed outside the cabin, making it easy to be sensitive to starlight and also beneficial for thermal control; The installation of EU in the cabin will greatly reduce the impact of temperature and space environment on it.

The main technical specifications of the micro ASP CMOS star sensor are:

Overall implementation diagram of a miniature APS CMOS star sensor:

With the emergence and maturity of new sensing and microelectronics technologies, as well as new optical systems, the design and application of new optical systems and the development and application of APS are the two most active hotspots in star sensor technology. Performance and demand complement each other, and with the improvement of performance and the reduction of price, the application field of star sensors is bound to expand day by day.

Comparison of research status at home and abroad

International level

Given the outstanding advantages of APS detectors, APS image sensors have been widely used in star sensors. In order to adapt to the rapid development and demand of aerospace and develop star sensors with smaller size and lower power consumption, most foreign enterprises and research institutes are currently working hard to research star sensors based on APS detector technology and have produced some representative products.

Table 1.3 shows several typical APS star sensors and their technical specifications from abroad. Among them, well-known APS star sensors include the ASTRO APS star sensor developed by Jena Optronik in Germany (as shown in Figure 1.2), the representative model HYDRA  star sensor from SODERN in France, the MAST (Micro APS Based Star Tracker) developed by JPL, and the AA-STR star sensor developed by Galileo Avionica Aerospace Company in Italy, The ASCoS star sensor produced and developed by the European Space Agency and the MST star sensor developed by AreoAstro.

Made in China

Compared with the development level of foreign star sensors, the research on star sensors in China started late in the 1980s, and due to the limitations of its field, the research scope of star sensors is mainly concentrated in major scientific research institutions and universities, including the Institute of Optoelectronics Technology of the Chinese Academy of Sciences [43-45], Beijing Institute of Control Engineering, Beijing University of Aeronautics and Astronautics, Harbin Institute of Technology Tsinghua University, etc. At present, various domestic institutions and universities mainly focus on the field of light and small APS star sensors. As a representative of Tsinghua University, it has completed years of technological accumulation and achieved relatively high research results in fields such as high-precision centroid extraction, fast star point recognition, attitude calculation, and ground calibration. Tsinghua University’s star sensor research achievements have won the second prize of the National Technology Invention Award, and in recent years, Tsinghua University has been heavily involved in the development of commercial aerospace star sensors, leading the domestic forefront in light, small, and low power consumption. at present

The typical APS star sensor product models of the same type in China are shown in Table 1.4:

China has made significant progress in the basic theory and application research of star sensors, and many units and universities have also developed the ability to develop related products. However, regardless of hardware design or software algorithms, China’s star sensors still have a certain gap compared to foreign countries. Therefore, China still needs to make greater progress in the technological research of star tracker.