Space antennas with a helical geometry are an advantageous choice for many applications, for instance if the transmission of electromagnetic waves with a circular polarization is intended, or if signals from terrestrial objects shall be received with a high angular resolution. In all these cases the desired electromagnetic properties of a helical geometry can be combined with the mechanical advantage that the antenna acts as a compression spring, provided that its core structure has the necessary high spring stiffness but can nevertheless easily be compressed. Such an antenna has been developed by DLR Institutes in Bremen and Braunschweig together with some industrial partners for a small satellite named AISat which shall be able to pursue the position of individual ships in critical sea areas in order to improve the security of seafare trade. The development was very challenging since the antenna must expand from a stowed stack length of only 10 centimeters to a total length of 4 meters. Only a special carbonfiber core under the conductive coating and a system of stabilizing cords led to a satisfying solution. Both the self-deployment and the self-stabilization function of this innovative antenna concept have been successfully tested and verified under zero-gconditions in the course of a parabolic flight campaign. It could be convincingly demonstrated that the helical antenna can really achieve its desired contour in weightlessness within some seconds and maintain the required stability. Beyond the current application for the AISat satellite it is therefore a quite promising concept for future satellites.
We present a technique for the multi-sensor registration of featureless datasets based on the photogrammetric tracking of the acquisition systems in use. This method is developed for the in situ study of cultural heritage objects and is tested by digitizing a small canvas successively with a 3D digitization system and a multispectral camera while simultaneously tracking the acquisition systems with four cameras and using a cubic target frame with a side length of 500 mm. The achieved tracking accuracy is better than 0.03 mm spatially and 0.150 mrad angularly. This allows us to seamlessly register the 3D acquisitions and to project the multispectral acquisitions on the 3D model.
Abstract. We present a novel method to register multispectral acquisitions on a 3D model. The method is based on the external tracking of the acquisition systems using close-range photogrammetric techniques: multiple calibrated cameras simultaneously observe the successive acquisition systems in use. The views from these cameras are used to precisely determine the position of each acquisition system. All datasets can then be projected in the same coordinate system. The registration is thus independent from the quality and content of the data. This method is well suited to the study of cultural heritage or any other application where we do not wish to place targets on the object. We describe the method and the simulation pipeline used to find an adequate setup for two case studies.
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