Design Criteria of Remote Sensing Constellations of Small Satellites with Low Power Electric Propulsion and Distributed Payloads

The recent explosion in proposed microsatellite missions is based on the possibility to mass-produce cheap platforms capable to deliver acceptable performance over a limited lifetime. The assumption behind such scheme is that individual microsatellites are expected/allowed to fail in reasonable numbers, the resulting degradation of constellation performance being limited due to the large population of active spacecraft. We argue that cheap platforms do not necessarily need to be seen as disposable assets, so that low cost constellations featuring a low number of microsatellites may nevertheless be capable of remarkable performance. The key technology needed to enable such feat is low power electric propulsion, whereby microsatellites are allowed to acquire and maintain precisely tuned orbital locations, compensate atmospheric drag to fly longer, and de-orbit safely at end of life. A number of such microsatellites may be fitted with an instrument each from a suite of different sensors operating in various spectral bands. The constellation would operate as an actively controlled system, with the individual instruments providing well coordinated raw data that may be processed using data fusion techniques to yield the final product. Starting from the proven performance of a currently available low power Hall thruster, we present general design criteria for constellations based on a 50 kg-class microsatellite bus. The potential benefits of such technology are outlined with respect to applications such as precision farming, urban area monitoring, and dual use land surveillance

Recent Developments in Ionic Liquid Field Emission Electric Propulsion

The study herein reported was aimed at the characterization of the plume of a ionic liquid fed, linear slit FEEP thruster, in terms of composition and velocity of the constituents. Ionic liquid propellants are actively investigated as promising alternatives to alkali metals in field emission thrusters, in order to reduce system cost and ground operation complexity. To this end, a large number of tests was carried out using the EMI-BF4 ionic liquid as a propellant. The thruster was fired in either positive polarity or negative polarities to check the capability to extract anions and cations alone. Then, most of the testing was carried out in alternate polarity mode, in order to avoid electrochemical poisoning of the propellant, due to the unbalanced extraction of charged particles[1]. Such operating mode is believed to be the most promising candidate for flight operation, as it would allow to get rid of an external neutralizer to maintain electrical neutrality of the spacecraft. Ion beam composition was investigated by means of a time-of-flight mass spectrometry technique. The measurements show that the emitted beam is mostly composed of monomers (BF4)-, dimers (C6H11BF4N2) (BF4)- and polymers (C6H11BF4N2)n (BF4)- (with n a function of applied extraction voltage). Under the assumption of a certain beam composition, propellant consumption was indirectly evaluated by means of time integration of the emitted current and independently verified by means of direct observation of the depletion of the propellant reservoir. The estimated resulting specific impulse is around 1400 s. The thruster behaviour resulted quite variable, especially when operated at high voltage levels in continuous polarity mode. Better performance was registered in alternate polarity operation with an alternation period of several tens of a seconds at extracted current of just a few µA

Development and Test of Low Cost Solar Panel Technologies for Small Satellites

This paper presents the activities carried out in collaboration between the University of Pisa and Alta SpA for the development, testing and integration of an efficient, yet inexpensive photovoltaic panel for microsatellite applications. The approach adopted, aimed at reducing cost and developing “low tech” techniques to assembly and qualify solar panels for small satellite applications, uses a printed circuit board designed to optimize the use of external surfaces partially occupied for power generation, where bare cells are installed by means of a double-sided insulating adhesive tape and each cell is covered with cerium doped borosilicate glass, using a controlled volatility silicone. Bonding was performed with a dedicated vacuum bag technique, developed in-house. This method achieves a significant cost reduction with respect to traditional techniques, while retaining high performance and reliable repeatability and avoiding complex technological procedures during the integration. A prototype solar panel was manufactured, tested and integrated on the UniSat-5 small spacecraft by GAUSS Srl in preparation of a flight scheduled for late 2013. Thorough mechanical testing was performed as a part of the integration with UniSat-5. The panels manufactured during the development programme were subject to electrical characterization to evaluate the current-voltage characteristic curve and the efficiency of the array and to thermal vacuum tests according to ECSS standards to estimate the outgassing properties of the protoflight model. For both tests, a low cost experimental setup was developed on purpose. The recorded flight unit total mass loss (TML) is well under the acceptable limits, so that the panel was accepted for space flight. In-orbit validation of the panel is expected with the upcoming flight of UniSat-5. The techniques and procedures developed under this programme allow for quick and inexpensive manufacture of reliable solar arrays, specially suited for micro- and nano-satellites. To improve the thermal and mechanical properties of the solar array, a substrate in carbon fibre composite laminate is under investigation. A thermal analysis is developed to characterize and compare the thermal response of the solar array with different substrate subjected to space heat flux

Slit FEEP Thruster Performance with Ionic Liquid Propellant

By replacing the liquid metal propellant with a ionic liquid, it is possible to develop a new, simplified FEEP system that combines most of the heritage and the advantages of the linear slit geometry with the easy of handling and operation of a more benign propellant. In view of the development of such Ionic Liquid FEEP thruster (IL-FEEP), an internal development activity is underway at Alta, aimed at the design and testing of an innovative linear slit thruster derived from the cesium experience. This paper presents the results of recent experimental campaigns aimed at assessing the performance of linear slit FEEP emitters fed with a ionic liquid propellant. For the first time, beam composition was evaluated using a time-of-flight mass spectrometry technique, allowing for a reliable estimate of the thruster’s specific impulse

Low-Thrust Propulsion Systems for Small Satellites

Small platforms represent valuable options for small scientific and Earth observation missions. One of the main challenges for microspacecrafts with launch mass below approx. 100 kg is the inclusion of a propulsive subsystem. Such addition would significantly enhance the performance of these platforms, broadening the possible applications and/or extending the operational lifetime. For these applications, electric propulsion systems are more suitable than classical chemical systems as they allow a larger payload mass fraction reducing the propellant mass requirement. The aim of this study is to investigate about state of the art of electric propulsion options for small spacecraft. A selection of possible electric propulsion systems for small satellite based on several requirements (power, thrust, specific impulse) is presented. This paper discusses four typical orbital manoeuvres of fundamental relevance for satellites in low Earth orbit: scenario No. 1 considers a 350 km decrease of orbital altitude; scenario No. 2 is about drag compensation for 90 days at very low altitude. Scenario No. 3 is a combined manoeuvre to change both semi major axis (by 150 km) and inclination (by 0.563 deg) at once. The fourth scenario is about orbit circularization. Results are thus normalized to obtain dimensionless parameters to be compared. Our analysis shows that an electric propulsion system offers significant advantages for small satellites in low Earth orbits in case of altitude variation, moderate inclination change, circularization and drag compensation at very low altitude

A Multi-Hop Broadcast Wave Approach for Floating Car Data Collection in Vehicular Networks

Inter-Vehicle Communication (IVC) is bringing connected and cooperative mobility closer to reality. Vehicles today are able to produce huge amounts of information, known in the literature as Floating Car Data (FCD), containing status information gathered from sensing the internal condition of the vehicle and the external environment. Adding networking capabilities to vehicles allows them to share this information among themselves and with the infrastructure. Collecting real-time FCD information from vehicles opens up the possibility of having access to an enormous amount of useful information that can boost the development of innovative services and applications in the domain of Intelligent Transportation System (ITS). In this paper we propose several solutions to efficiently collect real-time FCD information in Dedicated Short-Range Communication (DSRC)-enabled Vehicular Ad Hoc Networks (VANETs). The goal is to improve the efficiency of the FCD collection operation while keeping the impact on the DSRC communication channel as low as possible. We do this by exploiting a slightly modified version of a standardized data dissemination protocol to create a backbone of relaying vehicles that, by following local rules, generate a multi-hop broadcast wave of collected FCD messages. The proposed protocols are evaluated via realistic simulations under different vehicular densities and urban scenarios

Explanation of the Charge Trapping Properties of Silicon Nitride Storage Layers for NVMs-Part II: Atomistic and Electrical Modeling

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The mechanics of congenital heart disease: from a morphological trait to the functional echocardiographic evaluation

Advances in pediatric cardiac surgery have resulted in a recent growing epidemic of children and young adults with congenital heart diseases (CHDs). In these patients, congenital defects themselves, surgical operations and remaining lesions may alter cardiac anatomy and impact the mechanical performance of both ventricles. Cardiac function significantly influences outcomes in CHDs, necessitating regular patient follow-up to detect clinical changes and relevant risk factors. Echocardiography remains the primary imaging method for CHDs, but clinicians must understand patients' unique anatomies as different CHDs exhibit distinct anatomical characteristics affecting cardiac mechanics. Additionally, the use of myocardial deformation imaging and 3D echocardiography has gained popularity for enhanced assessment of cardiac function and anatomy. This paper discusses the role of echocardiography in evaluating cardiac mechanics in most significant CHDs, particularly its ability to accommodate and interpret the inherent anatomical substrate in these conditions

The mechanics of congenital heart disease: from a morphological trait to the functional echocardiographic evaluation

Advances in pediatric cardiac surgery have resulted in a recent growing epidemic of children and young adults with congenital heart diseases (CHDs). In these patients, congenital defects themselves, surgical operations and remaining lesions may alter cardiac anatomy and impact the mechanical performance of both ventricles. Cardiac function significantly influences outcomes in CHDs, necessitating regular patient follow-up to detect clinical changes and relevant risk factors. Echocardiography remains the primary imaging method for CHDs, but clinicians must understand patients' unique anatomies as different CHDs exhibit distinct anatomical characteristics affecting cardiac mechanics. Additionally, the use of myocardial deformation imaging and 3D echocardiography has gained popularity for enhanced assessment of cardiac function and anatomy. This paper discusses the role of echocardiography in evaluating cardiac mechanics in most significant CHDs, particularly its ability to accommodate and interpret the inherent anatomical substrate in these conditions

FEEP New Propellants CCN2 - Final Report

Final report to CCN 2 to ESA Contract 22873/09/F-VS, "FEEP New Propellants" - This document reports the design, the manufacturing and the test campaign of a new emitter unit for the FEEP thruster suitable to operate with ionic liquid as working fluid. The main modifications to the existent emitter, the motivations and the results of this new design are here described. The test setup and the main results are also presented