Keywords: Constellation missions, Earth-bounded Missions, Sensor fusion
Abstract: Nowadays, Earth observation satellites are of utmost importance in several fields, as in the case of agriculture and emergency management, and they will be exploited even more frequently in the next decades. Precision farming is a modern concept that involves enhanced management of the available resources through digital techniques to monitor and optimise agricultural production, improving its efficiency while avoiding waste of resources. Moreover, disaster management is a crucial tool for the prevention and well-management of emergencies. The increase in frequency of these events (such as wildfires, droughts, etc.) requires faster and reliable observations to properly respond to crises. Both precision farming and emergency management benefit from the use of satellites, which are very suitable platforms for carrying the sensors needed in these applications. Satellites can be arranged in a constellation, potentially providing several measurements of the same site in a short period of time. However, designing a constellation is a challenge, as there are no general rules. In fact, the overall cost of the constellation depends on several parameters, and the design will consider different drivers through trade-offs. In this work, a model of a hybrid optical-SAR microsatellites constellation has been prototyped. In fact, optical and SAR measurements can be merged through data fusion, leading to more accurate and reliable information by combining their strengths. The orbital model of the constellation has then been employed through a multi-objective genetic algorithm optimisation to find a subset of few possible optimal constellations which are satisfying the mission requirements for a selected emergency use case (wildfires), exploiting a multi-fidelity method to reduce the computational time. In fact, the goal of this work consist in enhancing constellation design methodologies through the development of a modeling and simulation tool and the employment of genetic algorithms to generate optimal constellation solutions. This work has been developed as a collaboration in the frame of master thesis between the Department of Aerospace Science and Technology of Politecnico di Milano and Thales Alenia Space Italia S.P.A..

Keywords: Constellation missions, Innovative sensors, actuators
Abstract: The paper presents the design of an innovative space payload to be embarked on a cubesat and devoted to detection and localization of ground emitters in the UHF bandwidth, but with the capability to operate up to the C band. Most of the current systems for the EM emission detection and localization are based on formation of satellites that operate in collaboration. The novel payload, hereby called GIDE, allows to operate even in a standalone configuration. The estimation of the direction of arrival to localize the emitter is performed using an amplitude comparison monopulse approach, fully implemented in digital. Moreover, a novel element is represented by the fact that the amplitude comparison processing is performed in the frequency domain. Also, the MUSIC algorithm has been implemented. The final paper will present the experimental results achieved with the implemented demonstrator.

Keywords: Innovative technologies for distributed systems, Formation Flying missions
Abstract: Motion planning is a computational problem that seeks to find a sequence of actions that can safely guide a robot/object from a given initial state to a goal state. Traditional guidance algorithms in the field of astrodynamics, like Lambert's solution, compute the transfer orbit for a spacecraft between two given position vectors. But such algorithms do not come with collision-avoidance capabilities. In this work, we seek a computationally efficient motion planning technique that can be implemented for astrodynamics problems subject to kinodynamic (simultaneous kinematic and dynamics) constraints. We leverage the theoretical advances in the field of sampling-based motion planning in robotics and present a sparse astrodynamics-informed kinodynamic motion planning (AIKMP) algorithm. Using multiple collision-avoidance scenarios, we demonstrate that this algorithm takes advantage of stochastic sampling along with a spacecraft's natural motion (whenever possible) to compute a near-optimal, fuel-efficient, and collision-free trajectory for relative spacecraft motion without requiring an initial guess of the solution. We also show that a pruning module adds to the sparse nature of the algorithm and can significantly improve the computation efficiency of such tree-based motion planning algorithms.

Keywords: Sensor fusion, Advanced Image Processing, Vision-based Navigation
Abstract: NOTE: short version. Full text according to IWSCFF guidelines (>700 words) uploaded in pdf.

The paper proposes an effective approach for uncooperative objects proximity operations, focusing on on-board reconstruction of the chaser-target state vector through imaging. That capability to play a crucial role in incoming missions is evident: formation flying missions, on orbit servicing demonstrators (OOS) paving the way to regular in orbit services are hot topics in our decade, which still need a significant technology development burst to become feasible. The close proximity manoeuvring requires a guidance, navigation and control chain solved autonomously on-board to ensure reactivity, effectiveness, robustness during operations. The first ring of that chain is the relative navigation. Leaning on the chaser capabilities only, uncooperative targets are the most challenging: in that direction, imaging with passive sensors is the obvious choice to get measurements. In fact, solutions related to visible (VIS) cameras have been widely studied and practically applied. However, VIS imaging strongly depends on illumination conditions, which constrain operations planning, possibly leading to limited opportunity to properly detect and track the target itself, mostly in OOS. The paper proposes to supplement VIS with thermal infrared (TIR) images, that are clearly insensitive to illumination but suffer from lower resolution and poorer texture. The proposed strategy fuses the two source images before being fed to the Image Processing (IP) algorithm to get a more informative and robust input. To support the implementation and verification campaign of the implemented IP-NAV algorithms, a comprehensive simulation framework is needed which, currently is not available on the market; therefore a specific GSE-SW for TIR/VIS images generation has been implemented. Given the resolution mismatch between VIS and TIR images, the most common fusion methods cannot be directly applied. Results according to two different strategies currently investigated (upscaling TIR images before fusion with VIS images or adopting method insensitive to different image resolution) are discussed and quality metrics adopted to compare the two are presented.

Keywords: Innovative technologies for distributed systems, Innovative sensors, actuators, Perturbations Analysis
Abstract: A new class of reflectivity control devices is presented for extremely high precision satellite formation flight for cubesats and larger satellites. When illuminated, the actuator is capable of enacting solar radiation pressure force that can be electrically controlled both in magnitude and direction. The proposed device is a planar liquid-crystal panel suitable for mounting on satellite bodies and solar panels. This panel contains a large number of pixels that can be individually activated - to promote specular reflection, or deactivated - to promote diffuse reflection. Each pixel is slanted by a unique angle with respect to the panel reference plane, which enables the device to vector its output force by selectively activating the necessary pixels. The performance of this device is analyzed using semi-analytic means and by numerical modeling using ray-tracing techniques. At normal incidence, the device can generate up to 9.1E-7N/m^2 of lateral force for the four-faceted device and 8.6E-7N/m^2 for the three-faceted device. The performance of the device has been assessed in two example mission scenarios: geostationary formation flight for microwave interferometry and solar sail formation flight in the L2 miniaturized halo orbit for infrared interferometry. The analysis has shown that the necessary correction forces may be generated by the device, using SRP alone.

Keywords: Perturbations Analysis, Modelling and Parametrization of Relative Dynamics, Mission Analysis tool for Mission Control
Abstract: A formation of satellites operating in low Earth orbits is subject to perturbations associated to the non-uniform gravitational field of the Earth, whose entities depend on the position, resulting in a different effect on each satellite of the formation. As a result, any bounded configuration designed using the traditional methods, based on the Hill-Clohessy-Wiltshire (HCW) equations, is not immutable, but instead degrades over time, and periodic reconfiguration maneuvers are required. We propose a method to characterize bounded configurations for satellite formations which are stable with respect to the gravitational perturbation associated to the zonal harmonics. The problem is modeled using the Hamiltonian formalism and canonical transformations are introduced to set the Hamiltonian function of the perturbed problem to a form equivalent to that associated to the HCW equations plus some negligible terms. This method allows selecting the desired configuration for bounded formation flying from the well-known analytical solutions of the HCW equations for the unperturbed case and determining the corresponding ones for the perturbed case by applying the inverse of the canonical transformation. The suitability of the problem is verified by means of numerical analysis on satellites formations in sun-synchronous orbits and medium inclination low Earth orbits.

Keywords: Modelling and Parametrization of Relative Dynamics, Mission Analysis tool for Mission Control, Optimal Control
Abstract: Modern space missions demand that vehicles operate in multi-body environments. Further, they will require that spacecraft are able to coordinate with each other to complete complex objectives. We present an impulsive control strategy for driving spacecraft to bounded relative trajectories. The approach is grounded in dynamical systems theory. The invariant manifold structures of frequency matched quasi-periodic orbits are utilized to transport spacecraft to orbits that then naturally maintain a bounded relative trajectory between them.

Keywords: Constellation missions, Earth-bounded Missions
Abstract: In the current new space economy, the demand of remote sensed Earth Observation data is constantly increasing, and the end users needs require the data providers to generate more precise and frequent information to be exploited. The current market is evolving to a constellation-based approach; however, the current market is based on individual industries providing a single type of information thus not exploiting the added value of observation combination. In this paper, various constellations configuration was designed based on the opposite approach thus starting from the end user applications and the corresponding requirements. The focus is the performances of medium-size constellations of small satellites embarking on different satellites classes, different type of EO remote sensors exploiting the capabilities and orbital configuration provided by the high number of small satellites. The input for the performances analysis is based on a detailed analysis of the application requirements retrieving the observations needs identified by the users, grouped by type of services to be covered; for each of them the typical figures of merit as spatial and temporal resolution are quantitatively compared to the requirements. More detailed figures of merit, specific for the constellation configuration design, can be added in the comparison. The main assumptions for the constellation configuration option generation included the satellite classes, the state-of-the-art payload and the identification of the AoI. Based on these assumptions, three satellites segment and six payloads were combined in four configurations based both on SSO and inclined orbits. The results obtained highlights the importance high performing payload, but also demonstrate the benefits of non-conventional EO orbits exploitation. Moreover, the combination of payloads type and performances allows for the exploitation of advanced post-processing as super-resolution, data fusion and machine learning. The findings highlight the disruptive potential of Earth Observation multi-sensor constellations with respect to the current market. This also represents a starting point for developing innovative constellation configuration and advanced post-processing tools.

Keywords: Mission Analysis tool for Mission Control, Distributed systems disposal strategies, Distributed system deployment strategies
Abstract: The 2020s will most certainly become a decade influenced by a wide interest towards the Moon both scientifically and commercially, with many different missions planned to visit the lunar environment. In par- ticular many surface activities are envisioned in the following years, targeted mainly at the South Pole. Such interest in Moon exploration will surely require infrastructures to provide regular Navigation and Communi- cation services. Among all possible constellation configurations, those taking advantages of Elliptical Lunar Frozen Orbits (ELFO)1 show very good coverage capabilities and orbital stability over long periods, making less complex and expensive the fleet Operation and the maintenance.2,3 The paper critically presents the results obtained in trading off different efficient and robust strategies to deploy the constellation, considering different orbital scenarios and different launch conditions. Moreover, the fleet maintenance and disposal costs are preliminary investigated.

Keywords: Constellation missions, Earth-bounded Missions
Abstract: During the last decades, the Space sector has changed its landscape with injection of new actors by shaping new business modelling and accessible to various forms of entrepreneurship. The commercial space business, as public and private investors, look for new sources of economic growth, especially in the form of diversity and creativity and digital transformation is influencing the growing economy with the age of Artificial Intelligence (AI), data analytics, and machine learning (ML). (New Space Economy phenomenon). The EO Small Satellite constellations are driving the market demands towards information closer to the final user needs with solutions influencing the price of data/services through a lower-cost approach and potentially disrupting the market, although this market still is to be demonstrated. Large satellite still remain competitive in very high performance and life time (by reducing replacements cycle time). Aim of paper is to highlight the complementarity between the Earth Observation (EO) Small-SAT constellation and the EO very high performance (VHP) satellite which cooperation can further improve the information requested from the final users for the different application domains such as emergency management, agriculture, environment, security, maritime and others. The SAR Small/micro-SAT constellations class is at the beginning of the market trend and in continuous evolution. The principal actors are very agile, such as the start-up, and they started with a TRL (Technology Readiness Level) low by improving performance step by step with the ambition to populate in the upcoming years constellations to provide high revisit data. The Large System Integrator has entered in this market with new space partnerships or in-house solutions. The paper, based on selected final user test cases, will address possible future constellation architectures, and some technical analyses, to showing win-win scenarios among the EO large satellites space system with the micro-small satellite constellation space system. In this overall scenario the complementary between large and small EO satellites in the Earth Observation constellations is discussed in terms of prospective of system performances and constella