No abstract

No abstract

No abstract

We present an autonomous visual landmark recognition and pose estimation algorithm designed for use in navigation of spacecraft around small asteroids. Landmarks are selected as generic points on the asteroid surface that produce strong Harris corners in an image under a wide range in viewing and illumination conditions; no particular type of morphological feature is required. The set of landmarks is triangulated to obtain a tightly fitting mesh representing an optimal low resolution model of the natural asteroid shape, which is used onboard to determine the visibility of each landmark and enables the algorithm to work with highly concave bodies. The shape model is also used to estimate the centre of brightness of the asteroid and eliminate large translation errors prior to the main landmark recognition stage. The algorithm works by refining an initial estimate of the spacecraft position and orientation. Tests with real and synthetic images show good performance under realistic noise conditions. Using simulated images, the median landmark recognition error is 2m, and the error on the spacecraft position in the asteroid body frame is reduced from 45m to 21m at a range of 2km from the surface. With real images the translation error at 8km to the surface increases from 107m to 119m, due mainly to the larger range and lack of sensitivity to translations along the camera boresight. The median number of landmarks detected in the simulated and real images is 59 and 44 respectively. This algorithm was partly developed and tested during industrial studies for the European Space Agency’s Marco Polo-R asteroid sample return mission.

Solar sails are currently being studied and developed as alternate propulsion vehicles that can provide high velocities. Their ability to reflect photons coming from the sun on a large lightweight reflective surface enables many unique space science missions. One such mission is the GeoSail mission, for which the aim is the study of Earth's magnetotail. Recent advances in solar sail technologies, satellite bus miniaturization, and attitude control motivate the present, study of an alternate systems design approach for GeoSail. This paper details a practical systems approach toward the design of a 40 x 40 m sail, focusing on the design and use of niche enabling technologies with applications to the proposed GeoSail mission. The study is based on mission kind system design requirements from ESA's technology reference studies, which focus on the development of strategically important technologies in preparation of future scientific missions: in this case, for the 2015-2025 time frame