Therefore, both of them were employed by a very limited number of the users.The first practical CCD ISIS was developed by Etoh et al. [6]. Figure 1 shows the ISIS with slanted linear storage CCDs. The collection gates in the figure were the photogates of the original frontside-illuminated (FSI) ISIS. An image signal, a charge packet, generated in a photogate is transferred along a memory CCD, extending linearly in a slightly slanted direction to the pixel grid.Figure 1.Plane structure of ISIS with slanted linear storage CCDs [7,16].During the image capturing operation, the image signals are continuously transferred downward on the linear storage CCD, and drained out of the sensor from the drain attached at the end. Therefore, the image signals are continuously updated and the latest ones are always stored on the storage CCD.
The simple memory structure of the linear CCD maximizes the number of storage elements or minimizes the pixel size for a given number of storage e
With the development of Earth-observing satellites and deep-space exploration satellites, requirements for attitude measurement accuracy are increasing. Thus, error analysis of the accuracy and calibration of the star tracker have become particularly important.At present, research and analysis of the effect factors on the star tracker accuracy are being conducted. References [1] and [2] provides a general overview of the effects of the optical parameters. References [3] and [4] use a geometric method to establish a complicated error model, and obtain variations in accuracy for a certain range of optical parameters, but most of the existing analysis methods discuss the effects of factors separately and qualitatively.
Up to now systemic error analysis and accurate error propagation model are inadequate.Factors such as misalignment, aberration, instrument aging and temperature effects [5] could cause a departure of the star trackers from the ideal pinhole image model, and contribute to the attitude measurement error. Misalignment and aberration are time-independent, or static errors, which need to be calibrated prior to launch, Carfilzomib and can be called ground-based calibration. By contrast, instrument aging and temperature effects are time-varying, or dynamic errors, which must be calibrated in real time, and can be called on-orbit calibration. This paper focuses only on the ground-based calibration method.
The ground-based calibration of star trackers generally includes real night sky observation and laboratory calibration. Real night sky observation can take advantage of the characteristics of the star tracker utilizing the star angular distance. This method is relatively easy to apply, whereas the model parameters interact with one another. Obtaining the global maximum is difficult, and this method is greatly influenced by the environment. Laboratory calibration could use a star simulator as the source.