HIGH-ACCURATE IN-FLIGHT CALIBRATION OF THE OPTICAL-ELECTRONIC SYSTEM OF A SPACECRAFT

In-flight geometric calibration (further — calibration) is interpreted here as a procedure of making more preceise mutual attitude parameters of the onboard imaging camera and star tracker. The problem of calibration is solved with using of observations of geo-referenced landmarks from the orbit. A necessity of in-flight geometric calibration takes place for instance when initial data do not ensure acceptable accuracy of the ground objects geo-referencing by means of space snapshots received with use of optical-electronic complex, or when indefiniteness of camera’s angular attitude relatively to star tracker accumulates in a process of exploiting of the spacecraft on the orbit. The simulation of the calibration algorithms had shown their acceptable accuracy in combination with the contemporary star trackers. The tendency of improvement of onboard devices and gauges and increasing of their accuracy shows advisability of agreement of attainable accuracy of calculations while in-flight geometric calibration with accessible measuring accuracy. It concerns both properly calibration and geo-referencing of space snaps using results of calibration. In particular, it is interesting to consider how accuracy of calibration depends on accuracy of specific measurings and initial data. A main means of investigation is computer simulanion and analysis of its results. Immersing into the domain of calibration with very small measuring errors may essentially change correlation between the factors which influence the calibration accuracy. In particular, raising of the star trackers accuracy reduced a weight of the random errors of such devices in the complex of factors which aggravate results of calibration. In such a case it is necessary to take into account possible influence of omitted nonlinear effects and the other sources of disturbances on the estimations of camera and star tracker mutual attitude parameters. A method of exception of unfavourable nonlinearity errors is developed in this work. The method is based on two effects: high convergence characteristics of estimation algorithm — fuzzy state observer — and succession of iterative calculations. Such an approach diminishes influence of the ignored nonlinear component of the calibration error and improves the convergence of estimates. Methods of data processing are conformed with possibility to access very precise measurings. Computer simulation had showed good accuracy of algorithms of the in-flight geometric calibration and geo referencing in a combination with high-precise characteristics of used technical means.