Interstellar Object Uncertainty Evolution and Effect on Fast Flyby Delivery and Required Delta-V

Interstellar objects (ISOs) are small bodies that can travel through our solar system from other star systems. When present in our solar system, they represent an opportunity to study the properties and origins of these objects, as well as the potential for cross-pollination of material between star systems. With current propulsion technology, rendezvous with these objects is likely infeasible, and thus the maximum science return results from a rapid response flyby and impactor. However, while trajectories to ISOs may be feasible, their potentially high ephemeris uncertainties and high-speed hyperbolic orbits present significant challenges to navigation. In this paper we assess these challenges by modeling the uncertainties of reachable synthetic ISOs as a function of time, as derived by measurements from ground observatories and an approaching spacecraft. From these uncertainties we derive the final delivery accuracy of fast flyby spacecraft to the ISO and required statistical delta-v for navigation. We find that these two challenges can lead to hundreds of meters-per-second or even kilometers-per-second of required statistical delta-v for navigation, reduce delivery accuracy to hundreds of kilometers, and make autonomous navigation a requirement

Interstellar Object Accessibility and Mission Design

Interstellar objects (ISOs) are fascinating and under-explored celestial objects, providing physical laboratories to understand the formation of our solar system and probe the composition and properties of material formed in exoplanetary systems. This paper will discuss the accessibility of and mission design to ISOs with varying characteristics, including a discussion of state covariance estimation over the course of a cruise, handoffs from traditional navigation approaches to novel autonomous navigation for fast flyby regimes, and overall recommendations about preparing for the future in situ exploration of these targets. The lessons learned also apply to the fast flyby of other small bodies including long-period comets and potentially hazardous asteroids, which also require a tactical response with similar characteristicsComment: Accepted at IEEE Aerospace Conferenc

EndoNet: an information resource about regulatory networks of cell-to-cell communication†

EndoNet is an information resource about intercellular regulatory communication. It provides information about hormones, hormone receptors, the sources (i.e. cells, tissues and organs) where the hormones are synthesized and secreted, and where the respective receptors are expressed. The database focuses on the regulatory relations between them. An elementary communication is displayed as a causal link from a cell that secretes a particular hormone to those cells which express the corresponding hormone receptor and respond to the hormone. Whenever expression, synthesis and/or secretion of another hormone are part of this response, it renders the corresponding cell an internal node of the resulting network. This intercellular communication network coordinates the function of different organs. Therefore, the database covers the hierarchy of cellular organization of tissues and organs as it has been modeled in the Cytomer ontology, which has now been directly embedded into EndoNet. The user can query the database; the results can be used to visualize the intercellular information flow. A newly implemented hormone classification enables to browse the database and may be used as alternative entry point. EndoNet is accessible at: http://endonet.bioinf.med.uni-goettingen.de

Energy Management Strategies for a Pneumatic-Hybrid Engine Based on Sliding Window Pattern Recognition Stratégies de gestion de l’énergie pour un moteur hybride pneumatique basées sur la reconnaissance du cycle de conduite

This paper presents energy management strategies for a new hybrid pneumatic engine concept which is specific by its configuration in that it is not the vehicle but only the engine itself which is hybridized. Different energy management strategies are proposed in this paper. The first is called Causal Strategy (CS) and implements a rule-based control technique. The second strategy, called Constant Penalty Coefficient (CPC), is based on the minimization of equivalent consumption, where the use of each energy source is formulated in a comparative unit. The balance between the consumption of different energy sources (chemical or pneumatic) is achieved by the introduction of an equivalence factor. The third strategy is called Variable Penalty Coefficient (VPC). In fact, it is beneficial to consider the equivalence coefficient as variable within the amount of pneumatic energy stored in the air-tank i.e. state of charge, because the choice of propulsion mode should be different if the tank is full or empty. In this case, the penalty coefficient appears as a non linear function of the air-tank state of charge. Another way to adapt the penalty coefficient is to recognize a reference pattern during the driving cycle. The coefficient value can then be changed according to an optimized value found for each of the reference cycles. This strategy is called Driving Pattern Recognition (DPR). It involves a technique of sliding window pattern recognition. The concept is to convert the whole driving cycle into smaller pieces to which the equivalence factor can be appropriately adapted. This strategy is based on the assumption that the current driving situation does not change rapidly and thus the pattern is likely to continue into the near future. The identification window size is a parameter which has to be adjusted to attain the maximum of identification success over the reference cycle. We propose to define reference patterns as statistical models. The pattern recognition method is based on a correlation function. To improve analysis, all the results obtained with different energy management strategies are compared with a Dynamic Programming approach (DP) considered as the optimal solution. Results show that about 40% of fuel saving can be achieved by DP. The VPC and DPR strategies give better results than the CPC strategy, not so far from the results obtained with DP. <br> Cet article présente comparativement des stratégies de gestion de l’énergie pour un nouveau concept de moteur hybride : l’hybride pneumatique. Dans cette configuration spécifique, c’est le moteur lui-même qui est hybridé (et non le véhicule). Plusieurs stratégies de gestion d’énergie sont proposées dans cet article. La première est dite Causale (CS) car basée sur des principes heuristiques de décision. La deuxième est basée sur la minimisation d’un critère d’équivalence et est appelée stratégie à Coefficient de Pénalité Constant (CPC). Dans ce cas, les flux d’énergie (depuis chaque source chimique ou pneumatique) sont décrits dans des unités identiques. Ainsi, pour un même travail à produire, il est possible de faire une « balance » entre la consommation nécessaire selon chacune des deux sources d’énergie, et ceci avec un coefficient de pondération constant. La troisième stratégie utilise un coefficient de pondération variable selon la quantité d’air disponible dans le réservoir (i.e. état de charge) et est appelée stratégie à Coefficient de Pénalité Variable (VPC). Dans ce cas, le coefficient de pénalité est une fonction non-linéaire de la pression dans le réservoir. Un autre raisonnement consiste à considérer qu’il est nécessaire d’adapter également le coefficient à la situation de conduite (embouteillage, urbain, routier, autoroutier...), pour cela il est impératif de reconnaître la situation de conduite. Le coefficient peut alors être adapté, selon la situation reconnue à la valeur optimale prédéterminée pour des situations types. Cette stratégie, à reconnaissance de situation de conduite (DPR), se base sur une fenêtre glissante où la situation de conduite est considérée à changements lents (conservatisme). Une partie du travail a été d’optimiser la taille de la fenêtre d’identification.Les situations de conduite types sont décrites par des modèles statistiques (densité de présence). La reconnaissance du cycle est basée sur une fonction de corrélation. Afin de comparer les résultats obtenus sur différents cycles de conduite (homologués et Artemis) avec les différentes stratégies proposées, les consommations minimales atteignables obtenues par Programmation Dynamique (DP) sont également données. Les résultats montrent que 40% de gain de consommation peuvent être atteints sur certains cycles. Les résultats obtenus avec les stratégies « adaptatives » (VPC et DPR) sont meilleurs que ceux obtenus avec les stratégies « constantes » (CS et CPC). De plus, les résultats obtenus sont proches des résultats optimaux obtenus avec la programmation dynamique

Performance and aging of microtubular YSZ-based solid oxide regenerative fuel cells

Fuel electrode supported microtubular solid oxide fuel cells (SOFC) fabricated at ICMA have been characterised in both solid oxide steam electrolyser (SOEC) and fuel cell modes. The cells consists of a fuel electrode supporting tube of Ni/YSZ with 40% porosity, ∼400 μm thickness, 2.4 mm diameter and 100–150 mm length, a 15 μm thick YSZ electrolyte and a 50 vol% LSM/YSZ composite air electrode of 20 μm thickness and LSM/YSZ (80/20 vol%) up to 2 cm2 area as current collector in the air side. Platinum paste and wires were used as interconnectors in the air chamber and Ni felt in the fuel side. SOFC and SOEC experiments were performed at temperatures between 750 and 950 °C using synthetic air in the oxygen electrode and different partial pressures of steam in the fuel side. Analysis of the polarisation contributions to the j–V curve in FC operation mode was performed using theoretical models, as discussed in the text. The effect of the steam concentration and temperature on the electrolysis and fuel cell experiments is presented and discussed. The cells are reversible in both modes of operation at low fuel conversion rates. According with previous observations, when cells are operated at high steam conversion rates the cell voltage tends to saturate. Irreversible damage was observed by SEM at the YSZ–oxygen electrode interface after operation, probably due to the electrolyte reduction produced at high voltages.We would like to thank UKERC (NERC-TSEC programme grant number: NE/C516169/1), and grants MAT2009-14324-C02-01, GA-LC-009/2009 and CIT-120000-2007-50 financed by the Spanish Government, DGA-Caixa and Feder program of the European Community for funding the project.Peer Reviewe