Experimental Evaluation of On-Board Contact-Graph Routing Solutions for Future Nano-Satellite Constellations

Hardware processing performance and storage capability for nanosatellites have increased notably in recent years. Unfortunately, this progress is not observed at the same pace in transmission data rate, mostly limited by available power in reduced and constrained platforms. Thus, space-to-ground data transfer becomes the operations bottleneck of most modern space applications. As channel rates are approaching the Shannon limit, alternative solutions to manage the data transmission are on the spot. Among these, networked nano-satellite constellations can cooperatively offload data to neighboring nodes via frequent inter-satellite links (ISL) opportunities in order to augment the overall volume and reduce the end-to-end data delivery delay. Nevertheless, the computation of efficient multi-hop routes needs to consider not only present satellite and ground segments as nodes, but a non-trivial time dynamic evolution of the system dictated by orbital dynamics. Moreover, the process should properly model and rely on considerable amount of available information from node’s configuration and network status obtained from recent telemetry. Also, in most practical cases, the forwarding decision shall happen in orbit, where satellites can timely react to local or in-transit traffic demands. In this context, it is appealing to investigate on the applicability of adequate algorithmic routing approaches running on state-of-the-art nanosatellite on-board computers. In this work, we present the first implementation of Contact Graph Routing (CGR) algorithm developed by the Jet Propulsion Laboratory (JPL, NASA) for a nanosatellite on-board computer. We describe CGR, including a Dijkstra adaptation operating at its core as well as protocol aspects depicted in CCSDS Schedule-Aware Bundle Routing (SABR) recommended standard. Based on JPL’s Interplanetary Overlay Network (ION) software stack, we build a strong baseline to develop the first CGR implementation for a nano-satellites. We make our code available to the public and adapt it to the GomSpace toolchain in order to compile it for the NanoMind A712C on-board flight hardware based on a 32-bit ARM7 RISC CPU processor. Next, we evaluate its performance in terms of CPU execution time (Tick counts) and memory resources for increasingly complex satellite networks. Obtained metrics serve as compelling evidence of the polynomial scalability of the approach, matching the predicted theoretical behavior. Furthermore, we are able to determine that the evaluated hardware and implementation can cope with satellite networks of more than 120 nodes and 1200 contact opportunities

Socio-Economic Analysis of the Results of Implementing a Rights-Based Management System in a Small-Scale Fishery in the Gulf of California: The Gulf Curvina

Annual socio-economic surveys, pared with third-party landing monitoring data, have allowed a multi-year analysis of the economic impacts and perceptions of implementing an individual vessel quota rights-based management system in the gulf corvina (Cynoscion othonopterus) fishery. This fishery is targeted by four communities, including an indigenous one, in the Upper Gulf of California region shared by the states of Sonora and Baja California, and is one of the most highly regulated fisheries in Mexico, including gear and season limits, as well as a total allowable catch (TAC). In 2012, as a measure to better manage the overall TAC, action was begun by federal government, in partnership with state government, fishermen, processors, fishery scientists and NGOs to start a transition to a RBM system. Since then, significant changes have occurred. Here we present the measured economic changes in landing, ex-vessel prices, revenue, costs, profits and market share, and how they impacted fishermen, permit holders and local buyers. Surveys have also permitted detailed analysis of community perceptions of these changes. These results are discussed in light of both fishery-specific management changes, as well as regional conservation challenges which have also impacted to fishery indirectly. This case highlights the potential of the approach followed – participation, science based decisions and partnerships - to improve the livelihood of small-scale fishermen, particularly those occurring in low governance contexts such as Mexico

Preneoplastic lesions of the lung

Lung cancer is the leading cause of cancer deaths worldwide. If we can define and detect preneoplastic lesions, we might have a chance of improving survival. The World Health Organization has defined three preneoplastic lesions of the bronchial epithelium: squamous dysplasia/carcinoma in situ; atypical adenomatous hyperplasia; and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. These lesions are believed to progress to squamous cell carcinoma, adenocarcinoma and carcinoid tumors, respectively. In this review we summarize the data supporting the preneoplastic nature of these lesions, and delve into some of the genetic changes found in atypical adenomatous hyperplasia and squamous dysplasia/carcinoma in situ

MRAC with SMC Applied to Lateral Control of a Fixed-Wing MAV

Abstract: This paper presents a PD control law with adaptive gains with the MIT (Massachusetts Institute Technology) rule with different sliding modes; that is, the MIT rule has been designed with is known in the literature with first order sliding mode, second order sliding mode and high order sliding mode (HOSM) to obtain a better gain scheduling taking advantage the sliding modes techniques-the PD control law with adaptive gains that is designed for the lateral dynamics of a fixed-wing MAV. To apply the methodology of the model reference adaptive control (MRAC), sometimes called model reference adaptive system (MRAS), to the adaptive gains of the PD control, a sliding manifold is proposed considering the output of the lateral dynamics and with the output of the reference model

DtnSim: Bridging the Gap Between Simulation and Implementation of Space-Terrestrial DTNs

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