Applying autonomy to distributed satellite systems: Trends, challenges, and future prospects

While monolithic satellite missions still pose significant advantages in terms of accuracy and operations, novel distributed architectures are promising improved flexibility, responsiveness, and adaptability to structural and functional changes. Large satellite swarms, opportunistic satellite networks or heterogeneous constellations hybridizing small-spacecraft nodes with highperformance satellites are becoming feasible and advantageous alternatives requiring the adoption of new operation paradigms that enhance their autonomy. While autonomy is a notion that is gaining acceptance in monolithic satellite missions, it can also be deemed an integral characteristic in Distributed Satellite Systems (DSS). In this context, this paper focuses on the motivations for system-level autonomy in DSS and justifies its need as an enabler of system qualities. Autonomy is also presented as a necessary feature to bring new distributed Earth observation functions (which require coordination and collaboration mechanisms) and to allow for novel structural functions (e.g., opportunistic coalitions, exchange of resources, or in-orbit data services). Mission Planning and Scheduling (MPS) frameworks are then presented as a key component to implement autonomous operations in satellite missions. An exhaustive knowledge classification explores the design aspects of MPS for DSS, and conceptually groups them into: components and organizational paradigms; problem modeling and representation; optimization techniques and metaheuristics; execution and runtime characteristics and the notions of tasks, resources, and constraints. This paper concludes by proposing future strands of work devoted to study the trade-offs of autonomy in large-scale, highly dynamic and heterogeneous networks through frameworks that consider some of the limitations of small spacecraft technologies.Postprint (author's final draft

Towards the sequential assimilation of SAR-derived water stages into hydraulic models using the Particle Filter : proof of concept

With the onset of new satellite radar constellations (e.g. Sentinel-1) and advances in computational science (e.g. grid computing) enabling the supply and processing of multimission satellite data at a temporal frequency that is compatible with real-time flood forecasting requirements, this study presents a new concept for the sequential assimilation of Synthetic Aperture Radar (SAR)-derived water stages into coupled hydrologic-hydraulic models. The proposed methodology consists of adjusting storages and fluxes simulated by a coupled hydrologic-hydraulic model using a Particle Filterbased data assimilation scheme. Synthetic observations of water levels, representing satellite measurements, are assimilated into the coupled model in order to investigate the performance of the proposed assimilation scheme as a function of both accuracy and frequency of water level observations. The use of the Particle Filter provides flexibility regarding the form of the probability densities of both model simulations and remote sensing observations. We illustrate the potential of the proposed methodology using a twin experiment over a widely studied river reach located in the Grand-Duchy of Luxembourg. The study demonstrates that the Particle Filter algorithm leads to significant uncertainty reduction of water level and discharge at the time step of assimilation. However, updating the storages of the model only improves the model forecast over a very short time horizon. A more effective way of updating thus consists in adjusting both states and inputs. The proposed methodology, which consists in updating the biased forcing of the hydraulic model using information on model errors that is inferred from satellite observations, enables persistent model improvement. The present schedule of satellite radar missions is such that it is likely that there will be continuity for SAR-based operational water management services. This research contributes to evolve reactive flood management into systematic or quasi-systematic SAR-based flood monitoring services

Nanosatellites and Applications to Commercial and Scientific Missions

In the past two decades, a silent revolution has taken place in the space domain, leading to what today is known as “New Space.” We have passed from a selected group of countries, space agencies, and big industries building, launching, and operating satellites and other spacecrafts, of a scenario in which many universities and research institutes can do it. The key of this was the definition of the “CubeSat” standard, back to 1999. In 2013, it all took off on the commercial Earth Observation sector with the first launches from two companies that are now running 100+ CubeSat constellations for optical imaging or weather prediction, with very low revisit times. Today, the same revolution is taking place in the fields of Telecommunications, and Astronomical Scientific missions. In this chapter, the evolution of the space sector is briefly revised until the arrival of the CubeSats. Then, the CubeSat intrinsic limitations are discussed as they are key to understand the development and current situation of the CubeSat sector. NASA and ESA strategies are also presented. The chapter concludes with a summary of the technology roadmap to enable the next generation of CubeSat-based missions, including satellite constellations or federations, formation flying, synthetic apertures

Contribution de la mission SWOT pour le suivi des étendues et niveaux d’eau dans les milieux humides boréaux

Il est estimé que les milieux humides constituent entre 5% à 8% du couvert terrestre. Ceux-ci sont d’une importance particulière puisqu’ils remplissent de nombreuses fonctions essentielles à la santé et prospérité de plusieurs espèces vivantes. Cependant, il est estimé que les milieux humides ont globalement perdu environ 21% de leur superficie depuis le début des années 1700. De nombreux efforts ont depuis été mis en place pour réduire et remédier à cette perte. Une saine gestion des milieux humides utilise donc plusieurs méthodes de surveillance, particulièrement pour les fluctuations des niveaux et étendues d’eau. La télédétection offre un grand éventail d’outils pour la détection des eaux en milieu humide. Les données optiques et radars à synthèse d’ouverture (RSO) permettent la délimitation des étendues d’eau et les missions altimétriques mesurent l’élévation de l’eau de façon relativement précise, mais avec une couverture spatiale limitée. La mission Surface Water and Ocean Topography (SWOT) regroupe ces deux types de mesures sous une seule mission et procurera des données d’élévation spatialisées pour plus de 90% de la Terre. Cette thèse porte sur le potentiel et les enjeux que SWOT pourrait rencontrer pour la détection des plans d’eau dans les milieux humides boréaux. Les objectifs principaux sont, d’abord, d’évaluer de multiples missions satellitaires pour la détection d’un évènement d’inondation extrême en milieu humide boréal afin de dégager le potentiel de SWOT et ensuite d’analyser l’impact de la végétation sur la capacité de SWOT à détecter les plans d’eaux. Brièvement, les simulateurs SWOT large échelle (SWOT-LS) et SWOT haute résolution (SWOT-HR) ont été utilisés pour simuler des données SWOT afin de répondre aux objectifs de recherche. D’abord, l’été 2020 a vu l’un des plus importants évènements d’inondations sur le delta des rivières de la Paix et Athabasca (PAD) depuis l’inondation de 1935. C’est une excellente opportunité d’évaluer la capacité d’une multitude de missions satellitaires ainsi que celle du satellite SWOT pour le suivi d’un tel évènement en milieux humides. Le chapitre 4, présenté sous la forme d’un article scientifique, se concentre donc sur l’utilisation de SWOT-LS pour simuler une série temporelle de données SWOT durant un épisode d’inondation extrême sur le PAD à l’été 2020. La détection de l’évolution des étendues d’eau est aussi évaluée pour les missions Sentinel-1, Sentinel-2, Landsat-8 et RADARSAT Constellation tandis que les niveaux d’eau sont évalués pour les missions Sentinel-3 et Jason-3. Ensuite, le chapitre 5, aussi présenté sous la forme d’un article scientifique, évalue l’impact de la végétation aquatique et émergente sur le signal SWOT à l’aide de SWOT-HR. Des données de coefficent de rétrodiffusion provenant de la mission AirSWOT lors d’un survol au-dessus du PAD en 2017 ont été utilisées comme données d’entrée afin d’avoir une meilleure représentation des valeurs attendues du signal SWOT dans un tel environnement. L’ensemble de ces résultats permet de brosser un portrait du potentiel et des enjeux du satellite SWOT pour la détection des plans d’eaux en milieux humides boréaux

Earth observations from space: Outlook for the geological sciences

Remote sensing from space platforms is discussed as another tool available to geologists. The results of Nimbus observations, the ERTS program, and Skylab EREP are reviewed, and a multidisciplinary approach is recommended for meeting the challenges of remote sensing

Space Studies Board Annual Report 1995

During 1995, the Space Studies Board and its committees and task groups gathered for a total of 40 meetings. Highlights of these meetings are presented. Formal study reports and short reports developed and approved during the meetings and issued during 1995 are represented in this annual report either by their executive summaries (for full-length reports), or by reproduction in full (for short reports). Nine full-length reports were distributed or delivered, including a congressionally mandated report by the Committee on the Future of Space Science and a comprehensive survey of Earth observation programs by the Committee on Earth Studies. Major research guidance reports were completed and published by the Committee on Microgravity Research and by the federated Committee on Solar and Space Physics/Committee on Solar-Terrestrial Research. Several significant assessment reports were also published, including an assessment of small missions by the Committee on Planetary and Lunar Exploration, a scientific evaluation of Gravity Probe B by the Task Group on Gravity Probe B, and an analysis of technologies for a 4-meter active optics telescope by the Task Group on BMDO New Technology Orbital Observatory. In addition, the Committee on Astronomy and Astrophysics Panel on Ground-based Optical and Infrared Astronomy released its report, and the Task Group on Priorities in Space Research issued its second and final report. Five short reports were also prepared and released during 1995. They addressed such diverse topics as reflight of shuttle-borne synthetic aperture radars, the role of NASA centers and center scientists in scientific research, guidelines for establishment of NASA research institutes, and clarification of findings of the microgravity research opportunities report and of the Future of Space Science Committee's management study

Setting Priorities for Space Research: Opportunities and Imperatives

This report represents the first phase of a study by a task group convened by the Space Studies Board to ascertain whether it should attempt to develop a methodology for recommending priorities among the various initiatives in space research (that is, scientific activities concerned with phenomena in space or utilizing observations from space). The report argues that such priority statements by the space research community are both necessary and desirable and would contribute to the formulation and implementation of public policy. The report advocates the establishment of priorities to enhance effective management of the nation's scientific research program in space. It argues that scientific objectives and purposes should determine how and under what circumstances scientific research should be done. The report does not take a position on the controversy between advocates of manned space exploration and those who favor the exclusive use of unmanned space vehicles. Nor does the report address questions about the value or appropriateness of Space Station Freedom or proposals to establish a permanent manned Moon base or to undertake a manned mission to Mars. These issues lie beyond the charge to the task group