Study of the Performance of Propulsion Units with Nitrogen-Jet Thrusters for Astronaut Extravehicular Activities’ (EVAs)

The future plans of the space agencies all across the globe, mainly focus on the advance of the Extravehicular Activities (EVAs) that are orientated in the repair and maintenance of the space vehicles. This thesis presents a brief history of the space suits (EMU, Orlan-M) utilized in space applications and the propulsion units (Hand-Held Maneuvering Unit, Manned Maneuvering Unit and the Simplified Aid for Extravehicular Activity Rescue-SAFER which is currently being used for performing self-rescue maneuvers, in the case the EVA crew member becomes untethered from the orbiter) that have been used during the space activities. After introducing the space environment and the critical conditions that surround the astronaut during these activities, the fundamentals of the Cold Gas Propulsion Systems on which the function of the SAFER propulsion unit is based, are presented. The aim of this thesis is to perform a performance analysis of the SAFER propulsion unit, with the extraction of the basic space propulsion concepts, i.e. thrust, specific impulse, etc. and the verification of the produced results with the technical characteristics of the unit. The orbital dynamics applying on the astronaut during an EVA are also being studied in this thesis, starting from the scenario where the crew member becomes untethered and floats freely in the vacuum of space and at the same time, examining the case where the SAFER propulsion unit is being activated for the performance of the self-rescue maneuver, and the return of the astronaut to the orbiter

Spatio-temporal variability of benthic macrofauna in a coastal lagoon assessed by ecological interaction networks

An ecological survey of the benthic communities was carried out, at both spatial and temporal scales, in Papapouli Lagoon, the first ecotouristic park in Greece by applying for the first time, ecological network analysis. The application of ecological network analysis provided novel information on the quality of interactions among species, undetected by the most frequently used methods. The sorting of substrate samples enabled the identification and density determination of 40,036 individuals belonging to 31 different taxa, although, strong dominance of only a few species was observed. “Deposit feeders” were the dominant trophic group in all sampling sites and seasons while “suspension feeders” exhibited relatively the lowest abundance. The periodic opening of the sea inlet seems to be of crucial importance. In coastal lagoons, where there is constant communication with the sea, benthic fauna patterns seem to change according to the sea-land gradient. However, in intermittently closed lagoons, such as Papapouli Lagoon, a more homogenous pattern is evident. The obtained networks showed that when communication with the sea is interrupted all the benthic fauna patterns tend to be destabilized and centralized around one species, which in most cases is a “deposit feeder”. When the inlet opens and communication with the sea is restored, the benthic composition seems to be more cohesive, especially in the most distant regions. Knowledge generated by network analysis should provide a valuable tool in order to assess potential environmental changes and assist management decisions

Numerical solution of LOx flow in a liquid rocket engine additively manufactured cooling channel

The present work has been conducted in the framework of the DemoP1 demonstrator for the design of a LOx/LNG aerospike engine carried out by Pangea Aerospace. The main objective of the demonstrator is to highlight the central features of the next generation booster-class engines such as reusability, the utilisation of cryogenic coolants and the benefits arising from the ever-growing field of Additive Manufacturing (AM) for high heat flux aerospace applications with increasing thermal load management demands. In the present study a numerical investigation of the cryogenic liquid oxygen coolant flow in an AM cooling channel of the DemoP1 engine is implemented. The simulations are performed on a three-dimensional curvilinear cooling channel of variable, rectangular cross-section of the aerospike engine. Different variations of the two-equation k − ω turbulence model are employed and assessed for the closure of the fluid flow governing equations and the identification of the efficient formulations for the accurate prediction of the spatial development of the primitive variables. The numerical solutions obtained for the characterisation of heat transfer and pressure drop in the AM cooling channel are compared against experimental data provided from Pangea Aerospace for the full-scale single-injector element hot-fire test campaign of the DemoP1 aerospike engine demonstrator.The present research work was financially supported by the Centre for Propulsion and Thermal Power Engineering and the Cranfield Air and Space Propulsion Institute (CASPI) at Cranfield University, UK in collaboration with Pangea Aerospace, Spain.34th Congress of the International Council of the Aeronautical Science

Life cycle assessment of a high-tech vertical decoupled aquaponic system for sustainable greenhouse production

IntroductionAquaponics provide multiple benefits due to the simultaneous yield of vegetables and fish, however they are characterized by increased greenhouse gas emissions owing to intensive production system. The most appropriate method for quantifying the environmental effects of these systems is Life Cycle Assessment with which the identification of hotspots and the suggestion of improved production plans can be achieved. The purpose of the present study was to evaluate the environmental impact of a pilot high-tech aquaponic system utilized for the simultaneous production of baby lettuce and rocket as well as rainbow trout, in indicators such as Global Warming Potential.Materials and methodsTo achieve this goal, data on inputs and outputs were collected from 12 case studies that were implemented, combining different fertilizer treatments, substrate choices, plant species cultivated and water source provision. Life Cycle Assessment was performed using SimaPro v.9.4.0.2 software.ResultsThe results showcase that the optimal case studies include the cultivation of baby lettuce and rocket in perlite substrate using wastewater from fish and partial use of synthetic fertilizers. Indicatively, Global Warming Potential of these cases was calculated at 21.18 and 40.59 kg CO2-eq/kg of vegetable respectively. The parameter with the greatest impact on most of the environmental indicators was electricity consumption for the operation of the oxygen supply pump for the fish tanks, while greenhouse infrastructure had the greatest impact in Abiotic Depletion and Human Toxicity impact categories. In an alternative production scenario tested where renewable energy sources were used, system impacts were reduced by up to 50% for Global Warming Potential and 86% for Eutrophication impact. The results of this study aspire to constitute a significant milestone in environmental impact assessments of aquaponic production systems and the adoption of more sustainable farming practices

Soil biochemistry and microbial activity in vineyards under conventional and organic management at Northeast Brazil.

The São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that orgThe São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that organic fertilization can improve soil quality, we compared the effects of conventional and organic soil management on microbial activity and mycorrhization of seedless grape crops. We measured glomerospores number, most probable number (MPN) of propagules, richness of arbuscular mycorrhizal fungi (AMF) species, AMF root colonization, EE-BRSP production, carbon microbial biomass (C-MB), microbial respiration, fluorescein diacetate hydrolytic activity (FDA) and metabolic coefficient (qCO2). The organic management led to an increase in all variables with the exception of EE-BRSP and qCO2. Mycorrhizal colonization increased from 4.7% in conventional crops to 15.9% in organic crops. Spore number ranged from 4.1 to 12.4 per 50 g-1 soil in both management systems. The most probable number of AMF propagules increased from 79 cm-3 soil in the conventional system to 110 cm-3 soil in the organic system. Microbial carbon, CO2 emission, and FDA activity were increased by 100 to 200% in the organic crop. Thirteen species of AMF were identified, the majority in the organic cultivation system. Acaulospora excavata, Entrophospora infrequens, Glomus sp.3 and Scutellospora sp. were found only in the organically managed crop. S. gregaria was found only in the conventional crop. Organically managed vineyards increased mycorrhization and general soil microbial activity