Stars In Field Of View Research Articles

A comparative analysis of star identification algorithms

This paper aims to examine different star identification algorithms in star sensors and compare the previous algorithms with the newly proposed algorithms. The star identification algorithms in this paper include three geometric methods, which require a minimum of five stars in the sensor field of view. These algorithms are compared with the angle, combined triangle, and pyramid algorithms in terms of speed, accuracy, storage capacity, and resistance to false stars using MATLAB software. Except for the angle algorithm, all the other star identification algorithms have high precision and resistance to false stars. In addition, they have a lower speed than those of the algorithms that use fewer stars to form the pattern. Considering the number of stars required for the algorithm, the newly proposed star identification algorithms are suitable for the second generation of star sensors, which have a larger field of view. The simulations are related to the stars brighter than magnitude 4, as well as a star sensor with a square-shaped field of view with a dimension of $13.8^{\circ }\times 13.8^{\circ }$, similar to the ASTRO 15 sensor manufactured by Jena-Optronik GmbH company.

Novel guide star optimal selection algorithm for star sensors based on star clustering

Modern space vehicles face the challenges to obtain more and more accurate attitudes in order to complete the demanding tasks. Onboard star sensors which identify the observed stars in the field of view according to the loaded guide star catalog and output accurate attitude have attracted most interests. Guide stars are usually required to distribute uniformly on the celestial sphere to improve the performance of the star pattern identification. An optimal selection algorithm is proposed to achieve an even distribution of guide stars in this paper. Constellation features are discussed. The mean shift algorithm is analyzed. The idea that distributes stars in the local field of view to constellations is proposed by using the star pair angular separations according to the star positions in the inertial coordinate system. The optimal selection algorithm of guide stars based on star clustering is developed. Its detailed implement procedures are introduced completely. The guide star optimal selection experiment in visible band by using SAO star catalog as the original star data is implemented. It proves that the proposed algorithm has the virtue of simple calculation and easy realization. The obtained guide star distribution is superior to the regression selection algorithm and the magnitude weighted method.

Generation of Guide Star Catalog for Star Trackers

In this paper, a novel guide star catalog generation algorithm is presented, which is a crucial part of an advanced star tracker design since the performance and reliability of star identification and attitude determination depend on the guide star selection. First, we propose an analytical method to estimate the stellar instrument magnitude and characterize the associated errors. Those stars whose instrument magnitudes are higher than the star tracker sensitivity constitute the original catalog. Then, the probability model of each star in the original catalog for attitude determination is established as the function of the field of view (FOV), the brightness accuracy, and the mean number of stars in FOV based on the brightness and uniformity principles, and the stars with larger probability are selected as guide stars. The accuracy of photometry method is validated by estimating the Hipparcos catalog instrument magnitude and comparing them with actual data. The efficiency of guide star selection algorithm is demonstrated by generating guide star catalog for a star tracker with a $16 {^{\circ }}\times 16 {^{\circ }}$ FOV.

Bandwidth maximization for satellite laser communication

Free space optical communication between satellites networked together can make possible high speed communication between different places on Earth. The basic free space optical communication network includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. The pointing systems for laser satellite communication suffer during tracking from vibration due to electronic noise, background radiation from interstellar objects such as Sun, Moon, Earth, and Stars in the tracking field of view, and mechanical impact from satellite internal and external sources. Due to vibrations the receiver receives less power. This effect limits the system bandwidth for given bit error rate (BER). In this research we derive an algorithm to maximize the communication system bandwidth using the transmitter telescope gain as a free variable based on the vibration statistics model and the system parameters. Our model makes it possible to adapt the bandwidth and transmitter gain to change of vibration amplitude. We also present an example of a practical satellite network which includes a direct detection receiver with an optical amplifier. A bandwidth improvement of three orders of magnitude is achieved in this example for certain conditions, as compared with an unoptimized system.