Browsing by Author "D'Anniballe, Antonio"

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    Collision analysis for multiple satellites released from a common dispenser
    (ESA Conference Bureau / ATPI Corporate Events, 2023-06-16) D'Anniballe, Antonio; Felicetti, Leonard; Hobbs, Stephen
    The number of small spacecraft launched to space has increased dramatically in the past few years, and with the emergence of mega-constellations it is projected to increase even more in the coming decades. Small satellites are usually launched together in rideshare launches and released from a common dispenser when reaching nominal orbit. Due to the lack of available measurement and control capabilities, the release phase is vulnerable to collision risk, as small uncertainties in the initial position can quickly grow causing a high probability of collision. In this paper a framework for analysing the safety of a genric dispenser is proposed and applied to the study of a cylindrical dispenser. Through numerical simulations and linear covariance propagation, the evolution of the spacecraft state is retrieved and used for computing a set of performance metrics, such as the total probability of collision and the number of conjunction events. This method is then applied to a parametric analysis of the dispenser, examining how the performance metrics vary with parameters such as the velocity of release or the time between releases. The results thus obtained will be relevant to the safe design of spacecraft dispensers.
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    Cooperative tracking strategies for optical space-to-space surveillance constellations
    (International Astronautical Federation (IAF), 2024-10-18) D'Anniballe, Antonio; Felicetti, Leonard; Hobbs, Stephen
    Most space surveillance and tracking systems are constituted by networks of ground stations of observing radars and optical telescopes. These systems are usually reliable, easily serviceable, and effective under ideal conditions, but suffer from strong bounds on scalability and coverage due to the heavy constraints on their geographic locations, potential cloud coverage and the perturbing effect of the atmosphere. A large constellation of small satellites carrying optical telescopes could complement these limitations, thanks to the lack of such constraints and the possibility of observing target objects at close range. As a result, it would be theoretically possible to track objects more accurately and for longer times, improving the accuracy of collision risk analysis and manoeuvre detection amid other tasks. However, due to the small fields of view of suitable onboard optical sensors, a random static arrangement of their lines of sight would be largely inefficient in reaching good performance levels, as the target would unpredictably enter and exit the observable portion of the sky. To solve this problem, we propose a cooperative intelligent tracking strategy for the constellation. Assuming known initial states for some targets, we use predictions on the future states to dynamically control the attitudes of the constellation satellites to maximise the length of the tracking window while minimising energy expenditures. We evaluate the performance of the strategy using quality figures such as the number of effectively trackable targets and the mean square error of the estimation error during tracking. We repeat the analysis for various constellation geometries and multiple target orbits to investigate the general applicability of such a strategy. In conclusion, we check for robustness by analysing performance drops under the loss of operating nodes. The results thus obtained will inform on the usefulness of space-to-space SST constellations and the general design of strategies for the dynamic scheduling of operations of distributed systems observing multiple targets.
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    Optimal orbital configurations of spaceborne optical sensors constellations for space surveillance
    (International Astronautical Federation (IAF), 2023-10-06) D'Anniballe, Antonio; Felicetti, Leonard; Hobbs, Stephen
    With the increasing number of satellites, there is a progressively higher demand for accurate surveillance and collision risk analysis systems. Most of the space situational awareness domain depends today on ground-based telescopes and radar sensors, which have the disadvantage of being highly constrained in terms of their potential geographic positions. A more versatile approach may instead be the use of a constellation of spacecraft carrying space-based sensors that can cover any desired orbital region allowing for complete coverage of the orbiting population, enabling a more accurate orbit estimation and consequent collision risk analysis. This work investigates the optimal orbital configurations of a LEO constellation of satellites carrying optical sensors when these are used for the orbit estimation and the conjunction assessment of resident space objects. Collision risk assessment is performed through covariance analysis using unscented transform techniques and unscented Kalman filtering and assessed using Monte Carlo analysis. The optimal configuration of the constellation is found using nonlinear optimization techniques, maximizing the performance in terms of estimation accuracy, number of detected conjunction events, and probability of collision over short and long-term periods. Different requirements and drivers will be considered and traded off in the analysis, including specific orbital regions to be covered by the system, different capabilities of the optical instruments, and lead time on the detection and transfer of the eventual warnings to ground stations. The outcome of the study will be the set of optimal orbital configurations of the constellation for an increasing number of constellation satellites and the given population of LEO target satellites. The results thus obtained will inform on how to optimally deploy constellations of satellites carrying optical sensors for surveillance and collision assessment of uncooperative spacecraft and on the effect that the number of constellation satellites has on performance.
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    Quantifying improvements in debris risk analysis using a constellation of spaceborne optical sensors
    (International Astronautical Federation (IAF), 2023-10-06) D'Anniballe, Antonio; Felicetti, Leonard; Hobbs, Stephen
    As the number of resident space objects (RSO) increases, operators face growing pressure for more accurate surveillance and collision risk analysis systems. Most of the space situational awareness domain depends today on ground-based telescopes and radar sensors, which have the disadvantage of being highly constrained in terms of their potential geographic positions. A more versatile approach may instead be using a constellation of spacecraft carrying space-based sensors. Such a distributed network of orbiting sensors can cover any desired orbital region allowing for complete coverage of RSOs, enabling a more accurate state estimation and consequent collision risk analysis. This work investigates quantitatively the benefits that an eventual network of orbiting sensors in LEO would bring to the current capabilities of the space surveillance network, in terms of improvement of the accuracy of predictions and number of detected conjunction assessments among RSOs. Collision risk assessment is performed through covariance analysis using unscented transform techniques and unscented Kalman filtering and assessed using Monte Carlo analysis. The simulation is carried out in three different scenarios: ground-based sensors only, space-based sensors only, and hybrid ground- and space-based sensors. Each of such scenarios is analyzed based on parametric analysis and trade-space explorations obtained by varying the optical features of the sensors, the orbital parameters and the number of satellites. Performance is evaluated in terms of accuracy on the orbit estimation, number of detected conjunction events, and probability of collisions calculated over short- and long-term prediction horizons. The outcome of the work is the performance evaluation in terms of collision risk assessment for each parametric analysis. After the scenarios are compared and discussed, the obtained results are used to inform the space community how to best use a combination of ground- and space-based sensors for enhanced collision risk analysis.