The article presents the results of analysis of the accuracy of autonomous navigation of a space robot in solving tasks of remote diagnostics of the technical condition of an orbital object in coplanar orbits. The angle between the stellar line and the direction of the orbital object, the distance to the orbital object and the rate of its change are taken as the primary navigation parameters measured onboard of a space robot. The space robot navigation accuracy is assessed on the basis of an analytical method. Assumptions of the normal law of distribution of measurement errors with known characteristics, the motion of the space robot and the orbital object in the central gravitational field of the Earth and the equality of the heights of their reference orbits are introduced. As a result of research covariance matrices of errors of determining the parameters of space robot center-of-mass motion were obtained in analytical form. The analysis of the accuracy of autonomous navigation carried out in the present paper can be used at the stage of feasibility study of the conceptual design of the control and navigation system of a space robot, for example, when solving the problem of choosing the composition of the onboard equipment, determining the accuracy specifications of onboard measuring devices and the amount of measurements carried out within the navigation mode.

A method of preliminary solution of the problem of space robot navigation based on the results of measurements carried out using its onboard optronic equipment is presented. The initial data of the navigation problem are the directional cosines of the space robot orientation vector in the absolute geocentric equatorial coordinate system with reference to time during one revolution. Analytical expressions are obtained for determining unknown parameters of the motion of the space robot center of mass in the form of Keplers elements of the orbit. It is shown that to determine the right ascension of the ascending node, the inclination and the semi-major axis of the orbit of the space robot, information about the orientation of its radius vector at various times is used, and to determine the perigee argument, the moment of passing the perigee and the eccentricity of the orbit, the angular orbital speed of the space robot is used, which is determined by the results of evaluating the speed of change in the orientation of its radius vector over time. The presented results can be used in the development of software for navigation systems that allow autonomous determination of the parameters of the space robots orbit using onboard electro-optical sensors in the absence of a priori information about the parameters of the reference orbit or signals from satellite radio navigation systems.

The article presents the results of an investigation of the accuracy of estimating errors in the determination of the motion parameters of the center of mass of a small spacecraft performing a group flight together with other small spacecraft, among which there is a small spacecraft that acts as the leader of the group. The angles between the directions to the small spacecraft-leader, and navigational stars, one of which is in the plane of the orbit of the small spacecraft, and the direction to the second one coincides with the binormal of this plane are chosen as the primary navigation parameters measured by the onboard facilities of the small spacecraft. When estimating the errors in determining the parameters of the motion of the center of mass of a small spacecraft, assumptions are made about the central gravitational field of the Earth, the normal law of error distribution of on-board navigation measurements with known constant variances. The research was carried out on the basis of the method of analytical estimation of the accuracy of autonomous navigation of space vehicles. As a result of the studies, analytical expressions of covariance matrices are obtained that allow one to estimate the maximum achievable accuracy of the solution of the problem posed, depending on the altitude of the orbit of a group of small space vehicles, the displacement of the slave small spacecraft relative to the small spacecraft-leader by the latitude argument, the variances of measurement errors and the number of measurements during a navigation mode. The presented results can find application when it is necessary to substantiate ways of improving the accuracy of autonomous navigation of small spacecraft performing group flights.

No abstract

The results of comparative estimation of the accuracy of autonomous navigation of small spacecraft in formation flying are presented. To carry out the research, the “zenith” method and the method of navigation by orbital references were chosen. These methods are based on measurements of the angular position of the Earth and an orbital reference point relative to navigational stars. Assumptions concerning the central terrestrial gravitational field and the normality of errors of the on-board navigation measurements with known constant variability were introduced in the studies. The studies were carried out using the theory of analytical estimation of the accuracy of spacecraft autonomous navigation methods. The use of this theory makes it possible to obtain the covariance error matrix of the required vector of navigation parameters and to estimate the potential (maximum achievable) characteristics of the accuracy of the navigation methods used. A dimensionless navigation error coefficient was chosen as an indicator of the accuracy of small spacecraft navigation method. The coefficient is associated with the elements of the main diagonal of the covariance matrix, it characterizes the precision properties of the method, is integrated by nature and does not depend on the volume and accuracy of the results of navigation measurements. The criterion of expediency of applying the method of determining the parameters of motion of the spacecraft center of mass is based on the comparison of navigation error rates. The presented results allow us to make reasonable choice of the method of autonomous navigation and of the composition of the onboard control of small spacecraft in formation flying.