METHOD OF AUTONOMOUS NAVIGATING SPACECRAFT

Abstract

The paper deals some problems related with some issues of spacecraft navigation and attitude control in near-earth coordinate space. It is shown that the first problem is to determine an appropriate orientation of the axes of the coordinated system, that is related to the spacecraft airframe, and to orient them as desired in relation to reference systems that set the position of a spacecraft on orbit and in inertial space. The second problem is to determine the spacecraft cog and its velocity in inertial space. The paper defines the axes of basic reference systems, which are the orbital and second equatorial ones, and determines their directions, as well as those of the instrument systems that are related with star trackers and purpose designed equipment. Main methods of spacecraft independent navigation and attitude control in near-earth space are inertial navigation methods that are based on measuring the components of spacecraft linear velocity by accelerometers and its angular velocity by gyroscopes. In this case current coordinates of a spacecraft and its attitude are calculated by integrating the measured values of relevant velocities. Modern accelerometers and gyroscopes are able to operate efficiently in a wide range of spacecraft velocities, however, there are such unavoidable disadvantages as “zero offset” and “axes wander” that result from the built-up of measurement errors due to continuous integration of the spacecraft linear and angular velocities. As a consequence the parameters of linear and angular motion of a spacecraft have to be adjusted regularly in terms of the spacecraft cog in inertial space and the orientation angles of the axes of the spacecraft coordinate system in relation to the axes of basic reference and instrument coordinate systems. The paper discusses a method of independent determination of the parameters of a spacecraft circular orbit in near-earth space and justifies the use of this method to adjust the readings of an inertial navigation system in the absence of satellite navigation measurements.