Modeling and design of a plasma-based transmit-array with beam scanning capabilities

Abstract This work presents the proof of concept of a novel plasma-based transmit-array antenna with beam scanning capabilities. The transmit-array operates above the GHz (precisely at 1.6 GHz) and is capable of steering its main lobe up to thirty degrees. A metallic half-wave dipole is used as the active element of the transmit-array, while twenty-five cylindrical plasma discharges are adopted to steer the beam of the antenna simply by turning them on or off. These passive elements are geometrically displaced in a triangular lattice. A customized two-steps optimization strategy is used to choose the best geometrical parameters of the array and to select the subset of plasma discharges that maximizes the gain of the antenna for each desired scanning angle. Towards this aim, a particle swarm optimization is first used to optimize the geometrical parameters of the array, and then a genetic algorithm is adopted to select the optimal subset of plasma discharges that need to be turned on to scan the beam towards different directions. The designed transmit-array was modeled in CST Microwave Studio, using realistic plasma parameters extrapolated from measurements of a fabricated plasma discharge prototype

A Highly Integrated Navigation Unit for On-Orbit Servicing Missions

VINAG (VISION/INS integrated Navigation Assisted by GNSS) is a highly integrated multisensor navigation unit, particularly conceived for On-Orbit Servicing missions. The system is designed to provide all-in-one, on-board real time autonomous absolute navigation as well as pose determination of an uncooperative known object orbiting in LEO (Low Earth Orbit), GEO (GEosynchronous Orbits) and possibly in HEO (Highly Earth Orbit). The system VINAG is under development by a team of Italian companies and universities, co-financed by the Italian Space Agency. Thanks to a tight optimized integration of its subsystems, VINAG is characterized by a low power and mass total budgets and therefore it is suitable for small and very small satellites. In order to provide both 1) absolute orbit and attitude determination and 2) vision-based pose determination, the unit integrates three metrology systems: a Cameras Subsystem (a monocular camera and a Star sensor), an Inertial Measurement Unit (IMU) and a GNSS (Global Navigation Satellite System) receiver. In this paper, we introduce the complete system architecture, the adopted algorithms and then the adopted hardware design solutions. In addition, we describe preliminary numerical simulation results obtained for different orbits from LEO to GEO carried out for the validation phase of VINAG

Common-clock very long baseline interferometry using a coherent optical fiber link

Among the most powerful techniques for the exploration of the Universe is very long baseline interferometry (VLBI), which is based on the simultaneous observation of radio sources in the sky with arrays of distant ground-based antennas. One of the effects currently limiting its ultimate sensitivity is the phase-instability of the reference clocks adopted at each antenna. This termcan be made negligible delivering the same clock signal to multiple telescope sites using optical fibers. We realized such an infrastructure by disseminating a coherent optical frequency signal to two distant radio telescopes using a 1739-km-long fiber.We performed a 24 h geodetic VLBI campaign in which the same clock reference was used at both telescopes and analyzed it using standard VLBI procedures. The results were consistent with the expectations, confirming that the proposed approach is feasible and configures as a novel tool for studying the role of clocks, troposphere, and systematic effects in the ultimate VLBI resolution

Star Sensor Image On-Board Processing for Orbiting Objects Detection – SPOT

This work presents the status of the study conducted by the School of Aerospace Engineering of Sapienza University of Rome in the framework of the Italian Space Agency project SPOT (Star sensor image on-board Processing for Orbiting objects deTection). The idea is to exploit star sensors to detect moving objects, which appear as streaks in the acquired image. Usually, star sensors discard information of observed moving objects against the fixed stars, losing many data that could be very useful for the Space Situational Awareness. On the contrary, SPOT processes the streaks to detect potential orbiting objects. The main factors that affect the visibility have been considered: the sensor characteristics (sensitivity, field of view, exposure time, and boresight direction), the optical properties of the observed objects, the environment influence, and the relative velocity between target and observer. The SPOT architecture consists of an On-Board Unit, which detects objects, and a Ground Unit, which processes the received On-Board data providing a database of the observations along the orbit

A Highly Integrated Navigation Unit for On-Orbit Servicing Missions

VINAG (VISION/INS integrated Navigation Assisted by GNSS) is a highly integrated multisensor navigation unit, particularly conceived for On-Orbit Servicing missions. The system is designed to provide all-in-one, on-board real time autonomous absolute navigation as well as pose determination of an uncooperative known object orbiting in LEO (Low Earth Orbit), GEO (GEosynchronous Orbits) and possibly in HEO (Highly Earth Orbit). The system VINAG is under development by a team of Italian companies and universities, co-financed by the Italian Space Agency. Thanks to a tight optimized integration of its subsystems, VINAG is characterized by a low power and mass total budgets and therefore it is suitable for small and very small satellites. In order to provide both 1) absolute orbit and attitude determination and 2) vision-based pose determination, the unit integrates three metrology systems: a Cameras Subsystem (a monocular camera and a Star sensor), an Inertial Measurement Unit (IMU) and a GNSS (Global Navigation Satellite System) receiver. In this paper, we introduce the complete system architecture, the adopted algorithms and then the adopted hardware design solutions. In addition, we describe preliminary numerical simulation results obtained for different orbits from LEO to GEO carried out for the validation phase of VINAG