STARS - Standalone Three-axis Attitude Reconstruction Sensor

Current attitude determination systems on-board Earth orbiting, Nadir pointing spacecraft rely on Earth crossing sensors which allow the detection of the Earth/atmosphere horizon and, hence, the Earth centre direction. This information enables the computation of two attitude angles, while the angle about the sensor line-of sight remains unknown, unless another source of attitude information is available. In the framework of the project internally funded by the University of Bologna, named STARS - Standalone Three-Axis spacecraft oRientation Sensor, the authors have investigated the feasibility of a novel standalone spacecraft attitude sensor, capable of estimating the full three-axis orientation of an Earth-orbiting satellite. The underlying idea is that by capturing from space a sequence of images of the Earth surface (in the visible bands) and elaborating them in pairs through (1) feature extraction (2) feature matching (3) homography estimation and, finally (4) attitude estimation. In the last two years the two groups participating to this projects, with different expertise in the field of S/W and H/W engineering, respectively, have devoted their effort to the following project steps: Selection of enabling technologies; Attitude determination algorithms; Numerical Simulations; Experimental tests; Preliminary results showed that the algorithm was able to work also with real images (affected by high noise level due to printing characteristics) with reduced performances of about 100 arcseconds (0.02°) on the controlled angle.