In-situ approach for thermal energy storage and thermoelectricity generation on the Moon: Modelling and simulation

Human, tele-operated rovers, and surface infrastructures are now being actively considered for lunar polar exploration. Current approaches to energy provision consider, among others, hybrid direct energy/chemical technologies, such as solar photovoltaic arrays, batteries, and regenerative fuel cells. Due to the long period of darkness on the Moon and the challenges this poses to the aforementioned conventional energy generation and storage technologies, there is a need to assess the potential of In-Situ Resources Utilization (ISRU) methods to enable or supplement long duration missions. We present a computational model (MATLAB) of a Thermal Energy Storage (TES) system coupled to drive a heat engine (Thermoelectric Generator) to produce electricity. The TES medium designed is based off processed lunar regolith, an abundant material present on the surface of the Moon. The architecture has been optimized to provide a minimum electrical power of 36 W per unit after 66 h of polar night, but the modular nature of the model allows other ranges of parameter to be simulated. A trade-off between this ISRU-based concept and conventional approaches for energy production and storage was performed and ranked TES and thermoelectricity generation as the least appropriate option. This result is valuable in a period of enthusiasm towards ISRU. It shows that processes exploiting extraterrestrial materials instead of Earth supplies are not systematically attractive. Despite the non-favorable performances for the proposed concept, some perspectives for the TES system are given as well as potential model improvements such as the need to assess the use of a Stirling heat engine

STA, the Space Trajectory Analysis Project

This article describes the objectives of the Space Trajectory Analysis (STA) project. The article also details the birth of STA, and its present configuration. STA is a project to develop an open source astrodynamics software suite involving university science departments and space research institutions. It was initiated by ESA as internal activity in 2005 and now it involves 16 partners. The article explains the partnership into the STA Steering Board. The main purpose of the STA is to allow advanced simulation for the analysis of space trajectories in an open and free environment under the premises of innovation and reliability.Further, the article explains that the STA development is open source and is based on the state of the art astrodynamics routines that are grouped into modules. Finally, the article concludes about the benefits of the STA initiative: the STA project allows a strong link among applied mathematics, space engineering, and informatics disciplines by reinforcing the academic community with requirements and needs coming from real missions

Side-branch growth in two-dimensional dendrits. Part II: Phase-field model

The development of side-branching in solidifying dendrites in a regime of large values of the Peclet number is studied by means of a phase-field model. We have compared our numerical results with experiments of the preceding paper and we obtain good qualitative agreement. The growth rate of each side branch shows a power-law behavior from the early stages of its life. From their birth, branches which finally succeed in the competition process of side-branching development have a greater growth exponent than branches which are stopped. Coarsening of branches is entirely defined by their geometrical position relative to their dominant neighbors. The winner branches escape from the diffusive field of the main dendrite and become independent dendrites

Side-branch growth in two-dimensional dendrits. Part II: Phase-field model

The development of side-branching in solidifying dendrites in a regime of large values of the Peclet number is studied by means of a phase-field model. We have compared our numerical results with experiments of the preceding paper and we obtain good qualitative agreement. The growth rate of each side branch shows a power-law behavior from the early stages of its life. From their birth, branches which finally succeed in the competition process of side-branching development have a greater growth exponent than branches which are stopped. Coarsening of branches is entirely defined by their geometrical position relative to their dominant neighbors. The winner branches escape from the diffusive field of the main dendrite and become independent dendrites

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Side-branch growth in two-dimensional dendrits. Part I: Experiments

The dynamics of growth of dendrites’ side branches is investigated experimentally during the crystallization of solutions of ammonium bromide in a quasi-two-dimensional cell. Two regimes are observed. At small values of the Peclet number a self-affine fractal forms. In this regime it is known that the mean lateral front grows as t 0.5 . Here the length of each individual branch is shown to grow (before being screened off) with a power-law behavior t α n . The value of the exponent α n ( 0.5 ⩽ α n ⩽ 1 ) is determined from the start by the strength of the initial disturbance. Coarsening then takes place, when the branches of small α n are screened off by their neighbors. The corresponding decay of the growth of a weak branch is exponential and defined by its geometrical position relative to its dominant neighbors. These results show that the branch structure results from a deterministic growth of initially random disturbances. At large values of the Peclet number, the faster of the side branches escape and become independent dendrites. The global structure then covers a finite fraction of the two-dimensional space. The crossover between the two regimes and the spacing of these independent branches are characterized

Pattern formation during mesophase growth in a homologous series

Remarkable differences in the shape of the nematic-smectic-B interface in a quasi-two-dimensional geometry have been experimentally observed in three liquid crystals of very similar molecular structure, i.e., neighboring members of a homologous series. In the thermal equilibrium of the two mesophases a faceted rectanglelike shape was observed with considerably different shape anisotropies for the three homologs. Various morphologies such as dendritic, dendriticlike, and faceted shapes of the rapidly growing smectic-B germ were also observed for the three substances. Experimental results were compared with computer simulations based on the phase field model. The pattern forming behavior of a binary mixture of two homologs was also studied