NASA’s ACS3 mission will be the first Earth-bound solar-sail mission to fly so-called calibration steering laws. These steering laws are designed to expose the sailcraft to a variety of dynamical conditions to isolate the effects of different parameters on the dynamics, thereby facilitating the estimation of these parameters. This paper presents the set of candidate calibration steering laws of ACS3, highlighting their operational challenges and impact on the estimation of the sail’s reflectivity and specularity. The results show that, for a conservative GPS position accuracy of 10 m, accurate estimation of the reflectivity and specularity with uncertainties in the order of 10−4 − 10−3 can be achieved by flying any of the proposed calibration laws. However, ACS3’s calibration steering laws were also found to introduce operational challenges that may hinder their implementation for extended periods of time. In particular, the decreased power generation capability of solar arrays was found to be the most severe operational challenge for two out of the five ACS3’s calibration laws analysed. @en

Solar sailing is a propulsion method that takes advantage of solar radiation pressure to generate thrust. Although most of near-future solar-sail missions will fly in low Earth orbit, where planetary radiation pressure can be as large as 20% of solar radiation pressure, studies on the accelerations produced by the Earth’s albedo and blackbody radiation have only been conducted to a very limited first-order extent. This paper therefore provides a novel, detailed analytical model for these perturbing accelerations, valid for perfectly reflecting solar sails. The full derivation of the model is described, and a thorough analysis of the blackbody and albedo radiation pressure accelerations is conducted for different orbital conditions. Then, to determine the model’s accuracy, a comparison with the state of the art (the finite-disk radiation source model and a high-fidelity numerical model) is provided. Ultimately, different analyses to quantify the effect of planetary radiation pressure acceleration on the solar-sail maneuvering capabilities are presented, using NASA’s upcoming ACS3 mission as reference scenario. The results highlight the nonnegligible effect of uncontrolled planetary radiation pressure acceleration, which can reduce the sailcraft’s achievable altitude and inclination gains to 76 and 80%, respectively, of the gains obtained when planetary radiation pressure is not accounted for.@en

Solar sailing is a propellantless propulsion method that exploits solar radiation pressure to generate thrust. In recent years, several solar sails have been launched into Earth-bound orbit to demonstrate this technology’s potential. Because planetary radiation pressure can reach magnitudes comparable to that of solar radiation pressure in proximity of the Earth, it cannot automatically be neglected in near-Earth solar-sail mission design studies. Nevertheless, its effect on the solar-sail dynamics has been investigated only to a very limited, first-order extent, and every study considered an “ideal” – i.e., perfectly reflecting – sail model. Although employing the ideal sail model proves useful for preliminary orbital analyses, its limited fidelity prevents more in-depth research into the near-Earth solar-sail dynamics and trajectory optimization. In light of this, this paper provides a new planetary radiation pressure acceleration model for optical solar sails. This model forms an extension of the “spherical” planetary radiation pressure acceleration model for ideal solar sails devised by Carzana et al. in Reference [1]. In the current paper, the underlying assumptions and full derivation of the newly devised optical model are presented. Subsequently, the accuracy of the optical model is analyzed through a comparison with the ideal model, using NASA’s upcoming ACS3 mission as reference scenario. @en

Solar sailing is a propulsion method which takes advantage of solar radiation pressure (SRP) as main source of thrust. However, around Earth, other sources also affect the solar-sail dynamics, including planetary radiation pressure (PRP) and atmospheric drag. In literature, the accelerations from SRP, PRP, and atmospheric drag are modeled using different theoretical and idealistic models, which make use of simplifying assumptions to describe the near-Earth dynamical environment, the sail’s geometry, and optical properties. Consequently, sailcraft in orbit experience accelerations different from the theoretically predicted ones. In order to quantify these discrepancies between the real and modeled solar-sail dynamics, a first definition and preliminary assessment of a set of calibration steering laws is provided in this paper. These steering laws allow to characterize the solar-sail acceleration at every sail orientation and to identify the contributions due to solar radiation pressure, planetary radiation pressure, and aerodynamic drag. The analyses presented make use of NASA’s upcoming ACS3 mission as baseline scenario and account for different possible orientations of its orbit. The results highlight the benefits and implementation challenges of each steering law and the impact that they have on the orbital elements, with particular focus on the orbital altitude. @en

This paper addresses the significance of uncertainty quantification in solar-sail missions, focusing on the uncertainties associated with the sail’s optical coefficients, structural deformation, and attitude profiles for missions in the Earth environment. Due to the relatively low technological maturity of solar-sailing systems, understanding and quantifying uncertainties is crucial for mission success and reliability. This paper employs the Gauss von Mises method for uncertainty propagation and stochastic integration of Ornstein-Uhlenbeck processes, which proved to be robust methodologies for quantifying and modelling uncertainties. The results show a significant impact of uncertainties in the optical coefficients on mission performance, exemplified by a 3-σ uncertainty of 7.5% on the increase in semi-major axis achieved during orbit raising maneuvers using the coefficient uncertainties of the NEA Scout mission. As another example, the analysis on attitude uncertainty demonstrates a 3% lower mean performance in terms of altitude gain compared to ideal control profiles. The research furthermore underscores the effectiveness of the Gauss von Mises method, offering great computational efficiency compared to Monte Carlo simulations. These findings highlight the necessity of considering uncertainty in solar-sail missions and provide valuable insights for improved mission planning, risk assessment, and decision-making. @en

Solar sailing is a spacecraft propulsion method relying solely on solar radiation pressure to provide thrust and is therefore propellantless by nature. Although it represents a practical and promising propulsion system particularly suited for heliocentric flight regimes, the majority of sailcraft missions flown to date have remained Earth-bound and more Earth-bound missions are scheduled for the near future. However, the fundamental dynamics and trajectory optimization of a solar sail around the Earth have only been investigated to a limited extent, often neglecting the effect of non-negligible perturbations in the dynamics and the optimal control problem. Among these perturbations are the effect of eclipses, non-spherical gravity, and aerodynamic drag. Their magnitude can be comparable to, or even exceed that of solar radiation pressure and their effect on the solar-sail dynamics should be investigated to ensure the sailcraft's transfer capabilities and controllability. This article does so by including these perturbations in the dynamics and by considering aerodynamic drag in the optimal control problem. Using this formulation, it is shown that the optimal control problem is independent of the solar-sail loading parameter and that, by solving it, locally optimal steering laws can be derived to effectively change individual orbital elements. These newly derived steering laws form an extension to the laws found by McInnes for unperturbed solar-sail Earth-bound motion. By accounting for the perturbations in the derivation of the steering laws, it is possible to characterize how the perturbations affect the solar-sail maneuvering capabilities. This is quantified based on the established increase of the targeted orbital element. Furthermore, a range of different starting orbits will be considered to analyze the effects of perturbations in different orbital regimes. As demonstration of the real need for this investigation, NASA's Advanced Composite Solar Sail System (ACS3) mission will be considered as real-case scenario. This mission is scheduled for launch in mid-2022 and may benefit from the steering laws derived in this article to prove the maneuverability of solar sails in Earth orbit.

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Solar sailing is a propellantless propulsion method that takes advantage of solar radiation pressure to generate thrust. The last decades have seen the launch of several solar-sail missions to demonstrate the technology’s potential for space exploration and exploitation. Even more missions are scheduled for launch in the near future, including NASA’s ACS3 and NEA Scout missions and Gama’s Alpha sailcraft. Although most of these sailcraft have flown – or will fly – in LEO, where the planetary radiation pressure is strong (up to approximately 20% of the solar radiation pressure), studies on the perturbing accelerations produced by the Earth’s albedo and blackbody radiation have been conducted only to a very limited first-order extent. This paper therefore provides a novel, detailed analytical model for these perturbing accelerations, valid for double-sided perfectly reflecting solar sails. The underlying assumptions of the model are presented and its full derivation is described. A thorough analysis of the blackbody and albedo radiation pressure accelerations is conducted for a variety of orbital conditions and Sun-Earth-sail configurations. In order to quantify the accuracy of the model, a comparison with the state of the art (the finite-disk radiation source model) is provided. Ultimately, a variety of analyses to quantify the effect of Earth’s albedo and blackbody radiation on the maneuvering capabilities of solar sails are provided, using the orbit of the ACS3 mission as reference scenario. These analyses show that, for an orbit-raising steering law, losses in the altitude gain of 19.6% of the total gain are incurred over a 10-day orbit-raising period. Similarly, losses in the inclination gain of up to 25% of the total gain are observed when implementing an inclination-changing steering law. These results highlight the non-negligible effect of uncontrolled planetary radiation pressure acceleration on the maneuvering capabilities of solar sails in LEO. @en

This work demonstrates the usability of differential dynamic programming (DDP) to obtain optimal Earth-centred solar-sail trajectories. The dynamical model is implemented as a two-body problem, augmented with an ideal solar-sail reflectance model and accounts for eclipses. The numerical performance of the optimisation algorithm is enhanced by integrating the sailcraft state in modified equinoctial elements and performing a Sundman transformation to change the independent variable from time to the true anomaly. The DDP algorithm is proven to be robust for trajectories extending up to 500 revolutions and, compared to known locally optimal steering laws, allows to obtain equally optimal solutions. The latter is demonstrated in this paper through a set of test cases that range from theoretical scenarios to realistic mission applications, including increasing the specific orbital energy of NASA’s upcoming ACS3 mission. Additionally, the algorithm's ability to cope with different optimisation settings, perturbing accelerations and constraints is demonstrated.@en

Solar sailing is a spacecraft propulsion method relying solely on solar radiation pressure to provide thrust and is therefore propellantless by nature. Although it represents a practical and promising propulsion system particularly suited for heliocentric flight regimes, near-term sailcraft missions will remain Earth-bound due to the current technology readiness level. This paper aims to show the suitability of solar sailing for planetocentric applications for future Earth-bound solar-sail missions. In Earth orbit, the sailcraft is subjected to perturbations absent or negligible in heliocentric flight, including the effect of eclipses, non-spherical gravity and aerodynamic drag. The magnitude of these perturbations can be comparable to, or even exceed that of solar radiation pressure and their effect on the solarsail dynamics should be investigated to ensure the sailcraft’s transfer capabilities and controllability. This paper does so by including the gravitational and aerodynamic perturbations in the optimal control problem. From this formulation, steering laws can be derived to optimally change individual orbital elements. These newly derived steering laws form an extension to the laws found by McInnes for unperturbed solar-sail Earth-bound motion. By accounting for the perturbations in the derivation of the steering laws, their effect can be exploited by the sailcraft to achieve orbits otherwise unreachable. The improved maneuverability will be quantified based on the established increase of the targeted orbital element. A range of different starting orbits will be considered to characterize how the perturbations affect the solar-sail maneuvering capabilities in different orbital regimes. As demonstration of the real need for this investigation, NASA’s Advanced Composite Solar Sail System (ACS3) mission will be considered as real-case scenario. This mission is scheduled for launch in mid-2022 and may benefit from the steering laws derived in this paper to proof the maneuverability of solar sails in Earth orbit. @en

Earth observation (EO) data delivered by remote sensing satellites provide a basic service to society, with great benefits to the civilian. The data is nowadays ubiquitously used throughout society for a range of diverse applications, such as environment and resource monitoring, emergency management and civilian security. Over the past 50 years, the EO data chain that has been mastered involves acquisition process of sensor data on-board the satellite, its compression and storage on-board, and its transfer to ground by a variety of communication means, for later processing on ground and the generation of the downstream EO image products. The EO-ALERT project, an H2020 European Union research activity, addresses the challenge of a “high speed data chain” and the need for increased EO data chain throughput. EO-ALERT proposes the definition and development of the next-generation EO data and processing chain, based on a novel flight segment architecture that moves optimised key EO data processing elements from the ground segment to on-board the satellite. The objective is to deliver the EO products to the end user with very low latency for increased throughput. This paper presents the activities performed during the first part of the EO-ALERT project, focussing on the definition of the user requirements for the EO-ALERT EO data processing chain, based on the identified market needs and application scenarios, now and in the future. Several application scenarios for EO data are reviewed and those which need and drive a high speed data processing chain are identified, considering commercial and institutional applications and focusing on those applications with a low latency need. Considering the innovative on-board processing chains implemented in the EO-ALERT project, the end users consider that the corresponding technology advances can enable very competitive and effective applications in the maritime surveillance and the disaster management, especially to cope with extreme weather events. These applications require a high responsiveness to events, reducing the response time to few hours, or even to minutes, after an emergency situation arises. Ship detection application includes, among others, traffic surveillance, protection against illegal fisheries, oil discharge control and sea pollution monitoring. One of the main objectives in maritime surveillance in Europe is to improve the European capability in the field of ship detection in both open and coastal waters for the purposes of security, providing observations on very short notice and near real-time detection. Flexibility and responsiveness for the provision of EO data are very important for maritime surveillance and security services. Two European EO missions have been selected to develop and test the on-board data processing chain for the ship detection scenario: the TerraSAR-X satellite mission embarking an X-band Synthetic Aperture Radar instrument able to image day and night under almost all meteorological conditions; and the Very High Resolution and agile optical satellite, Deimos-2 for detection and classification of small ships. There are many different segments of society that benefit from an early detection and warnings of the extreme weather events. Defence, police and emergency authorities use extreme weather warnings to reduce loss of human life and property by providing people with instructions, building containers for foods, evacuating people from risky areas, just to cite a few. Also, environmental and road authorities need these kinds of warnings to reduce loss of natural resources and human life. Aviation needs information about storm occurrence and exact position in order to plan flight routes to reduce loss of human life, property and fuel. The shipping and fishing trades take advantage of this information to re-plan and take less risky routes. The industry energy sector uses wind speed warnings, associated to convective storms, to reduce windmill breakdown. Two meteorological phenomena are going to be detected in the extreme weather scenario: convective storms and surface winds overseas and oceans. The main objective is the provision of early warnings for these two phenomena from satellite information. Considering the specific needs for the meteorological scenario, the following current sensors have been considered: SEVIRI on board Meteosat Second Generation to be used operationally, the radar on board TerraSAR-X to be used operationally and SLIM6 on board Deimos-1 to be used for research purposes. A high-level mission analysis for the above mentioned assets is presented, encompassing: coverage analysis, ground station contact analysis and data latency. For ship detection, a scenario that combines optical images from Deimos-2 and SAR images from TerraSAR-X is studied, providing information on possible common observation windows. An experimental campaign at the end of the project is intended to validate the technology performances in the experiment scenarios. The objective is to acquire the necessary in-situ data at the same time that SAR and optical remote sensing images are acquired on the region of interest, so as to provide a holistic knowledge of the monitored area and data for validation of the processing chain performances. @en

A laser-enhanced solar sail is a solar sail that is not solely propelled by solar radiation but additionally by a laser beam that illuminates the sail. This way, the propulsive acceleration of the sail results from the combined action of the solar and the laser radiation pressure onto the sail. The potential source of the laser beam is a laser satellite that coverts solar power (in the inner solar system) or nuclear power (in the outer solar system) into laser power. Such a laser satellite (or many of them) can orbit anywhere in the solar system and its optimal orbit (or their optimal orbits) for a given mission is a subject for future research. This contribution provides the model for an ideal laser-enhanced solar sail and investigates how a laser can enhance the thrusting capability of such a sail. The term ”ideal” means that the solar sail is assumed to be perfectly reflecting and that the laser beam is assumed to have a constant areal power density over the whole sail area. Since a laser beam has a limited divergence, it can provide radiation pressure at much larger solar distances and increase the radiation pressure force into the desired direction. Therefore, laser-enhanced solar sails may make missions feasible, that would otherwise have prohibitively long flight times, e.g. rendezvous missions in the outer solar system. This contribution will also analyze exemplary mission scenarios and present optimial trajectories without laying too much emphasis on the design and operations of the laser satellites. If the mission studies conclude that laser-enhanced solar sails would have advantages with respect to ”traditional” solar sails, a detailed study of the laser satellites and the whole system architecture would be the second next step @en

A laser-enhanced solar sail is a solar sail that is not solely propelled by solar radiation but additionally by a laser beam that illuminates the sail. This way, the propulsive acceleration of the sail results from the combined action of the solar and the laser radiation pressure. The potential source of the laser beam is a laser satellite that coverts solar or nuclear power into laser power. Such a laser satellite (or many of them) may orbit anywhere in the Solar System and its optimal orbit (or their orbits) for a given mission is still subject to future optimization. This contribution provides the model for an ideal laser-enhanced solar sail and investigates how a laser can enhance its thrusting capability. The term “ideal” means that the solar sail is assumed to be flat and perfectly reflecting and that the laser beam has constant areal power density over the whole sail area. Since a laser beam has a limited divergence, it can provide radiation pressure also at large solar distances and increase the propulsive force into the desired direction. This way, significant reductions in the flight time may be achieved for a variety of missions. This contribution also provides the analysis of some exemplary laser-enhanced solar sailing mission scenarios and presents optimized trajectories without laying too much emphasis on details of the design and operations of the laser source(s).

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