Analysis of the plasma transport in numerical simulations of helicon plasma thrusters

The accurate simulation of the plasma transport in helicon sources is a key aspect to improve the design of Helicon Plasma Thrusters (HPTs). Specifically, the 3D-VIRTUS code was proven to provide satisfactory estimations of the propulsive performance of realistic HPTs (difference between measures and numerical estimations of the thrust <30%). Nonetheless, further investigations are needed to deepen the influence that the plasma chemistry model, the formulation of the energy equation, and the definition of the diffusion coefficients have on the results of the simulation. First, a quantitative analysis has been conducted on a simplified configuration of HPT to study each phenomenon separately. Second, the generalized fluid model has been benchmarked against measures of plasma density performed on a helicon source. The radiative decay reactions affect the estimation of the performance (e.g., thrust) up to 40%. The quasi-isotherm formulation of the energy equation affects results (e.g., electron density) up to 30%. Accounting for anomalous transport or defining diffusion coefficients classically does not have a major effect on the simulation (e.g., thrust varies less than 20%). The generalized formulation of the fluid model provides estimations of the plasma density, which are within the uncertainty band of the measures (i.e., differences <20%)

LISA: Mars and the limits of life

We describe the results of the first tests made on LISA, a simulator of planetary environments designed and built in Padua, dedicated to the study of the limit of bacterial life on the planet Mars. Tests on the cryogenic circuit, on the UV illumination and on bacterial coltures at room temperature that shall be used as references are described.Comment: 4 pages, 3 figures. Mem. SAIt, in pres

Three dimensional fluid-kinetic model of a magnetically guided plasma jet

A fluid-kinetic model of the collisionless plasma row in a convergent-divergent magnetic nozzle is presented. The model combines the leading-order Vlasov equation and the fluid continuity and perpendicular momentum equation for magnetized electrons, and the fluid equations for cold ions, which must be solved iteratively to determine the self-consistent plasma response in a three-dimensional magnetic field. The kinetic electron solution identifies three electron populations and provides the plasma density and pressure tensor. The far downstream asymptotic behavior shows the anisotropic cooling of the electron populations. The fluid equations determine the electric potential and the fluid velocities. In the small ion-sound gyroradius case the solution is constructed one magnetic line at a time. In the large ion-sound gyroradius case, ion detachment from magnetic lines makes the problem fully three-dimensional.This work was supported by National R&D Plan (Grant ESP2016-75887) from the Gobierno de España. Jesús Ramos thanks the financial sponsorship of the Chair of Excellence award granted by UC3M and Banco de Santander

REGULUS CubeSat Propulsion System: In-Orbit Operations

A robust, versatile, and cost-effective propulsion system to provide wide mobility to small satellite platforms and nanosatellite deployers. A Plug&Play propulsion system designed to be easily integrated into different satellite platforms and to match customer\u27s requirements, with minimal customization efforts and costs

Active space debris removal by a hybrid propulsion module

During the last 40 years, the mass of the artificial objects in orbit increased quite steadily at the rate of about 145 metric tons annually, leading to a total tally of approximately 7000 metric tons. Now, most of the cross-sectional area and mass (97% in LEO) is concentrated in about 4600 intact objects, i.e. abandoned spacecraft and rocket bodies, plus a further 1000 operational spacecraft. Simulations and parametric analyses have shown that the most efficient and effective way to prevent the outbreak of a long-term exponential growth of the catalogued debris population would be to remove enough cross-sectional area and mass from densely populated orbits. In practice, according to the most recent NASA results, the active yearly removal of approximately 0.1% of the abandoned intact objects would be sufficient to stabilize the catalogued debris in low Earth orbit, together with the worldwide adoption of mitigation measures. The candidate targets for removal would have typical masses between 500 and 1000 kg, in the case of spacecraft, and of more than 1000 kg, in the case of rocket upper stages. Current data suggest that optimal active debris removal missions should be carried out in a few critical altitude-inclination bands. This paper deals with the feasibility study of a mission in which the debris is removed by using a hybrid propulsion module as propulsion unit. Specifically, the engine is transferred from a servicing platform to the debris target by a robotic arm so to perform a controlled disposal. Hybrid rocket technology for de-orbiting applications is considered a valuable option due to high specific impulse, intrinsic safety, thrust throttle ability, low environmental impact and reduced operating costs. Typically, in hybrid rockets a gaseous or liquid oxidizer is injected into the combustion chamber along the axial direction to burn a solid fuel. However, the use of tangential injection on a solid grain Pancake Geometry allows for more compact design of the propulsion unit. Only explorative tests were performed in the past on this rocket configuration, which appears to be suitable as de-orbiting system of new satellites as well as for direct application on large debris in the framework of a mission for debris removal. The paper describes some critical aspects of the mission with particular concern to the target selection, the hybrid propulsion module, the operations as well as the systems needed to rendezvous and dock with the target, and the disposal strateg

Applied live art : co-authorship in socially engaged and site-responsive performance practice

This thesis looks at the ways in which performance can integrate participants and local context into the development of new devised work. This practice-led research is based on a methodology that grew out of three performance case studies completed in diverse international settings with a varied range of participants. The case studies are: Napoli Scorticata completed in 2007 in Naples, Italy; Youth Visions, completed in 2008 in Northeastern Ghana, West Africa; Triangulated City, completed in 2009 in Beirut, Lebanon. Within these diverse contexts the research questions the role of authorship when working in socially engaged practice, focusing on how practitioners can shift the focus from the artist to the body politic. Merging social engagement with a site-responsive approach, the research proposes that the artistic medium is the social system and as such argues that the modes of employment require a focus of appreciation on the generative process, context and product combined. The research is presented in two parts. Part I is an interactive DVD with images of the development process and final presentations as well as a video of each performance work. Part II is a written thesis that explores the modes of engagement, outlines the methods of development and structures a general working methodology that can be referenced by other performance practitioners. The thesis proposes Applied Live Art as a term to describe practices that include a hybrid of time-based media options, which include a social component as their primary focus. The research outcomes conclude with an analysis of place making and its importance when working with both site and society.EThOS - Electronic Theses Online ServiceBritish Council Middle EastBritish Council ItalyRoyal Holloway Drama DepartmentUniversity of London Central Research FundPresident's Emergency Fund for AIDS ReliefTheatre Communications GroupGBUnited Kingdo

Inductive Plasma Thruster (IPT) design for an Atmosphere-Breathing Electric Propulsion System (ABEP)

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft, therefore an efficient propulsion system is required to extend the mission lifetime. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to use as propellant for an electric thruster. This would minimize the requirement of limited propellant availability. The system could be applied to any planet with atmosphere, enabling new mission at these altitude ranges for continuous orbiting. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such components are erosion source of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems (RIT and HET). IRS is developing within the DISCOVERER project an intake and a thruster for an ABEP system. This paper deals with the design and first operation of the inductive plasma thruster (IPT) developed at IRS. The paper describes its design aided by numerical tools such as HELIC and ADAMANT. Such a device is based on RF electrodeless discharge aided by externally applied static magnetic field. The IPT is composed by a movable injector, to variate the discharge channel length, and a movable electromagnet to variate position and intensity of the magnetic field. By changing these parameters along with a novel antenna design for electric propulsion, the aim is to achieve the highest efficiency for the ionization stage by enabling the formation of helicon-based discharge. Finally, the designed IPT is presented and the feature of the birdcage antenna highlighted

Mortality risk in a cohort of subjects reported by authorities for cannabis possession for personal use. Results of a longitudinal study.

OBJECTIVE: to study mortality risk in a cohort of cannabis consumers. DESIGN: longitudinal study on a cohort of 2,511 subjects reported to the Drug Addiction Control Force (DACF) for cannabis possession for personal use between 1990 and 2004 residents in the metropolitan area of Bologna. METHODS: to identify people already treated for drug dependence, the cohort was linked with the clinical archive of the public treatment centers for drug addiction (PTC) in the metropolitan area of Bologna and the results were separated into PTC clients (subjects in treatment at a PTC, all heroin users) and non-PTC clients (subjects not in treatment at a PTC, no knowledge regarding other illicit drugs being used besides cannabis). RESULTS: an excess of mortality was observed for all causes in the cohort compared to the general population, both among PTC clients (SMR 14.61 CI 95% 9.21-23.19) and non-clients (SMR 2.43 CI 95% 1.67-3.55). Among PTC clients the highest and most statistically significant SMRs were for overdose, suicide, and AIDS. Among non PTC clients there was an excess for traffic accidents and overdose. CONCLUSION: the results of the study show an elevated risk of death for consumers of cannabis, a percentage of which probably also consumed other substances, and a very few which presented themselves for treatment at a public drug treatment center