In this paper a novel approach is developed for relative navigation and attitude estimation of spacecraft flying in formation. The approach uses information from an optical sensor, which employs relatively simple electronic circuits with modest digital signal processing requirements, to provide multiple line-of-sight vectors from spacecraft to another. The sensor mechanism is well suited for both near-Earth and deep space applications since it is fully independent of any external systems. The line-of-sight measurements are coupled with gyro measurements and dynamical models in an extended Kalman filter to determine relative attitude, position and gyro biases. The quaternion is used to describe the relative kinematics and general relative orbital equations are used to describe the positional dynamics. Simulation results indicate that the combined sensor/estimator approach provides accurate relative position and attitude estimates.

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A space plasma facility has been operated with a back-diffusion-type plasma source installed in a mid-sized vacuum chamber with a diameter of ~1.5 m located in Satellite Technology Research Center (SaTReC), Korea Advanced Institute of Science and Technology (KAIST). To generate plasma with a temperature and density similar to the ionospheric plasma, nickel wires coated with carbonate solution were used as filaments that emit thermal electrons, and the accelerated thermal electrons emitted from the heated wires collide with the neutral gas to form plasma inside the chamber. By using a disk-type Langmuir probe installed inside the vacuum chamber, the generation of plasma similar to the space environment was validated. The characteristics of the plasma according to the grid and plate anode voltages were investigated. The grid voltage of the plasma source is realized as a suitable parameter for manipulating the electron density, while the plate voltage is suitable for adjusting the electron temperature. A simple physical model based on the collision cross-section of electron impact on nitrogen molecule was established to explain the plasma generation mechanism.