Astronomical autonomous navigation has become an important field in spacecraft technology and a major trend for future development. As a high-precision attitude measurement instrument, star sensors will inevitably have good development and application prospects. Overall, airborne star sensors, micro star sensors, and very high-precision star sensors will be the main development directions for future star sensors.
At present, airborne navigation in aviation mainly relies on inertial navigation systems and GPS technology. Inertial navigation systems have the advantages of high output accuracy and strong autonomy, but their measurement errors accumulate over time, which is limited in the use of long-endurance aircraft. GPS technology can provide high-precision navigation and positioning around the clock, and correct drift errors in inertial navigation systems. However, GPS signals are unstable and prone to interference, especially in military use, which is greatly limited. Although some aircraft have already used astronomical navigation technology, star sensors are only used to track a fixed star to correct the drift deviation of the inertial navigation system and do not have the ability to independently navigate. Therefore, introducing star sensors as independent attitude measurement instruments into airborne navigation equipment to improve the accuracy and reliability of airborne navigation will be one of the main directions for the development of star sensors in the future.
Due to the low output frequency of airborne star sensors and the high attitude output frequency of inertial navigation systems, traditional integrated navigation algorithms have certain difficulties when using airborne star sensors and inertial navigation systems for system integrated navigation. The use of data fusion combination algorithms to establish attitude calculation models under different attitude output frequency states will be an important method for solving the integrated navigation of airborne star sensors and inertial navigation systems.
Miniaturization and low cost are one of the main directions for the development of future spacecraft. With the rapid development of micro and small satellites, especially Pina satellites, micro and even button type star sensors will inevitably appear in future spacecraft attitude control systems. The first step for micro star sensors is to address how to reduce the size, mass, and power consumption of the star sensor without reducing the attitude output accuracy and frequency. At present, the MAST star sensor developed by JPL in the United States has a mass of 42g and a power consumption of 0.069W. Therefore, in the future research of micro star sensors, optimizing the design of optical systems and attitude calculation methods will be a key research direction. The use of nano optical technology to design micro star sensor optical systems will be a key research direction for breaking through the existing imaging mechanisms of star sensors in the future. Nanooptics breaks through diffraction limit optics and can achieve ideal star point imaging, not only reducing the volume of the optical system, but also obtaining super-resolution star points, improving attitude measurement accuracy. The use of nano optics to design star sensors not only requires research in optical system design, but also has significant differences in attitude calculation methods compared to existing star sensor design methods. This is also the focus of future research on micro star sensors. In addition, the adoption of new high-performance micro image sensors is also a key focus of research on micro star sensors. Image sensors are one of the important factors that constrain the performance of star sensors, and also an important factor affecting the volume and quality of star sensors. New HAS image sensors and IRIS-2 image sensors have also been applied to star sensors. Studying image sensors with higher integration, better performance, and lower power consumption will be an important factor affecting the development of micro star sensors.
At present, the attitude measurement accuracy of star sensors can reach 1 ″. In the context of increasing requirements for attitude control accuracy in spacecraft, improving the attitude measurement accuracy of star sensors is the main research topic in the future.
Studying multi field star sensor technology can improve static measurement accuracy. In order to improve the attitude update frequency of the star sensor, researchers have adopted a large field of view optical system, which can still meet the requirements of star map recognition while reducing the detection of star magnitude by the star sensor. This design method can shorten the search time of the navigation star in the star map recognition process of the star sensor, thereby increasing the frequency of attitude measurement. But at the same time, due to the use of a large field of view structure, not only does the attitude measurement accuracy of a single star point decrease, but also serious distortion occurs during the star image imaging process. Adopting a multi field of view star sensor design method can reduce the field of view without changing the detected magnitude, ensuring the attitude measurement accuracy of the star sensor. This traditional star sensor has an accuracy of 1-10 ″ in the yaw and pitch axis directions, and 8-100 ″ in the roll axis direction. This is because in the optical system of the star sensor, the size of its focal length is much larger than that of the image sensor, resulting in an attitude accuracy error of the star sensor in the optical axis direction that is approximately 6-16 times that of the two directions on the focal plane. In addition to inheriting the initial extraction mode and attitude tracking mode from traditional star sensors, multi field star sensors can also have angular velocity measurement mode and fast attitude update mode. By fusing star maps from multiple fields of view, the attitude error in the optical axis direction can be significantly reduced, resulting in high measurement accuracy for all three axes simultaneously. By controlling the integration time and integration mode of multiple fields of view, the angular velocity of the spacecraft can be measured, thereby replacing the rate gyroscope in the attitude measurement system and reducing the launch cost of the spacecraft. In the fast attitude update mode, differential frequency technology can alternately use star maps obtained from multiple lenses to update spacecraft attitude information, thereby increasing the attitude update frequency of star sensors.
In the research of dynamic measurement accuracy of star sensors, improving the dynamic performance of star sensors is the focus of future research. High precision star sensors require both high dynamic performance and precision in star centroid extraction to ensure sufficient navigation stars in the field of view of the star sensor, as well as sufficient tracking and attitude calculation of navigation stars in adjacent star maps.
The research, development, and application of star sensors have gone through more than half a century. With the emergence of new materials, devices, and technological advancements, accuracy has been improved, power consumption has been reduced, and costs have been reduced. New types of star sensors with increasingly wide application fields will continue to be introduced.
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TY-Space Technology (Beijing) Ltd. is professional focusing on advanced attitude optical sensors, especially Star Trackers for space industry.
