Communication Networks in CubeSat Constellations: Analysis, Design and Implementation

CubeSat constellations are redefining the way we approach to space missions, from the particular impact on scientific mission possibilities, constellations potential is growing with the increasing accessibility in terms of low development and launch costs and higher performances of the available technologies for CubeSats. In this thesis we focus on communication networks in CubeSat constellations: the project consist of developing a clustering algorithm able to group small satellites in order to create an optimized communication network by considering problems related to mutual access time and communication capabilities we reduce the typical negative effects of clustering algorithms such as ripple effect of re-clustering and optimizing the cluster-head formation number. The network creation is exploited by our proposed hardware system, composed by a phased array with up to 10dB gain, managed by a beamforming algorithm, to increase the total data volume transferable from a CubeSat constellation to the ground station. The total data volume earned vary from 40% to a peak of 99% more, depending on the constellation topology analyzed

Communication and Mutual Physical Position Estimation System for CubeSat

In recent years, constellations of CubeSats organized as a swarm are redefining the classical concept of space missions. The biggest challenge for the realization of an efficient swarm is to provide to the CubeSats the ability to interact and communicate each other. In this paper we present a system able to provide to the CubeSats belonging to a swarm the ability to establish an inter-satellite communication crosslink and to determine the mutual physical positioning. The basic idea is to provide every CubeSat with a system involving a smart-antenna array. By exploiting the array, CubeSats can transmit or receive signals to / from every element of the swarm so as to perform the inter-satellite communication. The smart-antenna is managed by a beamforming control strategy: during the transmission, the beamforming algorithm controls the smart-antenna in order to shape the beam and establish a reliable and directive communication link with other spacecraft and/or with the ground station. Hence, the beam shaping avoid to perform attitude maneuvers to optimize the transmission. Every CubeSat acquires signals transmitted from other elements of the swarm and estimate the Direction-of-Arrival (DOA) and the distance (Range) in order to calculate the mutual physical positioning. By an appropriate distribution of the antennas on the structure of the CubeSat it is possible to obtain a working range of 4π steradians. Every element of the smart-antenna is connected to a signal conditioning chain able to modify the phase and the amplitude of the signal transmitted / received. The beamforming algorithm manages this signal conditioning chain dynamically to maximize the performance of the system. Thanks to his small footprint, the system can be mounted on every CubeSat geometry and it is completely integrated with the bus so as not to occupy space dedicated for the payload as shown in figure [1]. Through the use of a deployable structure fully developed at Politecnico di Torino, we increase the external surface of CubeSats: this surface allows to gain the interspace between elements of the smart-antenna (figure [2]). As a consequence, the directivity and detection performance of the DOA system in terms of directivity and accuracy are improved. Moreover, the deployable structure offers a greater usable surface, so a larger number of solar panels can be used, e.g.: up to 40x30 cm2 for a 1U CubeSat. Hence, the communication distance increase because a power up to 6W is available for the transmit mode. This paper describes the physical implementation of the antenna array system on a 1U CubeSat using the deployable structure developed. In section I we describe how the subsystem has been designed, we analyze how the hardware works and we focus on the main blocks that realize the positioning measurement / network communication. In the section II we describe how the swarm subsystem can be hosted on every CubeSat structure (even 1U) by exploiting a deployable structure able to increase the useful surface of the CubeSat and the antenna baseline. This structure allows to gain the available power supply for the transmission (also for the other on board systems) and improves the precision of the mutual positioning estimator. In section III we describe how the subsystem establishes the communication between the CubeSats and how it measures the direction of arrival (DOA) and the distance (Range) of the received signals in order to establish the mutual physical position of every CubeSat composing the swarm

Renormalization group evaluation of exponents in family name distributions

According to many phenomenological and theoretical studies the distribution of family name frequencies in a population can be asymptotically described by a power law. We show that the Galton-Watson process corresponding to the dynamics of a growing population can be represented in Hilbert space, and its time evolution may be analyzed by renormalization group techniques, thus explaining the origin of the power law and establishing the connection between its exponent and the ratio between the population growth and the name production rates.Comment: 8 pages, no figures, many typos correcte

Utilização de plantas medicinais no entorno do Parque Estadual da Serra Furada, Santa Catarina, Brasil: uma abordagem etnobotânica

The objective of this study was to ethnobotanical approach in the region of the State Park of Serra Furada (PESF) /SC, in a rural community that lives near the park and uses medicinal plants for therapeutic purposes. Home visits were made to the residents surrounding the PESF when we applied aquestionnaire/interviews, in order to obtain more information about the possible use by the respondent, the most widely used medicinal plant for later identification and data collection bibliography. We interviewed five residents, a representative sample compared to   to the small number of dwellings present in the study area (15). There were five reports of using herbal preparations: a decoction with Sambucus australis Cham. & Schltd. and Cymbopogon citratus (DC.) Stapf together, a syrup with Ruta graveolens L.; prepared from a Croton macrobothrys Baill., a decoction with Cuphea carthagenensis (Jacq.) JF Macbr., and an infusion with Plantago major L.. Scientific information was gathered and compared to the information provided by the sampled population. The results of this study will provides data for future studies and ethnopharmacological research of therapeutic activities mentioned by respondents.O objetivo deste estudo foi realizar uma abordagem etnobotânica na região do Parque Estadual da Serra Furada (PESF) /SC, em uma comunidade rural que vive nas proximidades do parque e utiliza plantas medicinais para fins terapêuticos. Foram realizadas visitas domiciliares aos moradores do entorno do PESF, quando se executou uma entrevista com o auxilio de um questionário com perguntas abertas e fechadas, visando obter o maior número de informações possíveis sobre o uso da planta medicinal mais utilizada, para posterior identificação e coleta de informações bibliográficas. Entrevistaram-se cinco moradores, uma amostra representativa se comparada ao pequeno número de unidades familiares que residem na área de estudo (15). Houve o relato de cinco preparações utilizando plantas medicinais: um decocto com Sambucus australis Cham. & Schltd. e Cymbopogon citratus (DC.) Stapf em conjunto; um xarope com Ruta graveolens L.; um preparado com Croton macrobothrys Baill.; um decocto com Cuphea carthagenensis (Jacq.) J.F. Macbr. e uma infusão com Plantago major L.. Foram levantadas informações científicas e comparadas com as informações prestadas pela população amostrada. Os resultados obtidos neste estudo poderão fornecer dados para estudos etnofarmacológicos e investigação das atividades terapêuticas mencionadas pelos entrevistados

Association of kidney disease measures with risk of renal function worsening in patients with type 1 diabetes

Background: Albuminuria has been classically considered a marker of kidney damage progression in diabetic patients and it is routinely assessed to monitor kidney function. However, the role of a mild GFR reduction on the development of stage 653 CKD has been less explored in type 1 diabetes mellitus (T1DM) patients. Aim of the present study was to evaluate the prognostic role of kidney disease measures, namely albuminuria and reduced GFR, on the development of stage 653 CKD in a large cohort of patients affected by T1DM. Methods: A total of 4284 patients affected by T1DM followed-up at 76 diabetes centers participating to the Italian Association of Clinical Diabetologists (Associazione Medici Diabetologi, AMD) initiative constitutes the study population. Urinary albumin excretion (ACR) and estimated GFR (eGFR) were retrieved and analyzed. The incidence of stage 653 CKD (eGFR < 60 mL/min/1.73 m2) or eGFR reduction > 30% from baseline was evaluated. Results: The mean estimated GFR was 98 \ub1 17 mL/min/1.73m2 and the proportion of patients with albuminuria was 15.3% (n = 654) at baseline. About 8% (n = 337) of patients developed one of the two renal endpoints during the 4-year follow-up period. Age, albuminuria (micro or macro) and baseline eGFR < 90 ml/min/m2 were independent risk factors for stage 653 CKD and renal function worsening. When compared to patients with eGFR > 90 ml/min/1.73m2 and normoalbuminuria, those with albuminuria at baseline had a 1.69 greater risk of reaching stage 3 CKD, while patients with mild eGFR reduction (i.e. eGFR between 90 and 60 mL/min/1.73 m2) show a 3.81 greater risk that rose to 8.24 for those patients with albuminuria and mild eGFR reduction at baseline. Conclusions: Albuminuria and eGFR reduction represent independent risk factors for incident stage 653 CKD in T1DM patients. The simultaneous occurrence of reduced eGFR and albuminuria have a synergistic effect on renal function worsening

Studio dell influenza di diversi agenti aeranti ed antischiuma sul'inglobamento d'aria

studio delle caratteristiche chimiche che maggiormente influenzano lo spiralling effec

Heat transfer characteristics of a two-phase, air-water direct contact evaporator

The purpose of the research was to carry out an experimental and theoretical investigation of the heat transfer on a direct contact column for desalination purposes. The effect of air and water mass flow rates and air inlet temperature on the temperature distribution and moisture content of the air outlet stream was measured. The experimental heat transfer coefficient was estimated and, in order to simulate the experimental results, a comparison with available correlations was performe

Clustering Algorithm for CubeSat Constellations

In recent years, constellations of CubeSat are redefining the concept of space missions. Complex missions that in the past could only be accomplished using large and expensive satellites can now be performed by CubeSat constellations that, thanks to their coordinated action, can guarantee a certain efficiency level and fulfil the same required goals, reducing costs, system singularities and risk of catastrophic disasters. However, a CubeSat constellation system presents critical organizational issues in terms of creation and managing of network structures and interaction between elements. Orbital characteristics of CubeSats, mutual mobility, low-level features and obviously the final goal of the constellation are some of the critical factors that affect the efficiency of the system. In our paper, we present a novel algorithm able to consider the specific characteristics and the mobility behaviours of every CubeSats to autonomously create and optimize a network structure for the constellation. This network structure will be exploited to facilitate the data flow inside and outside the constellation and to facilitate the management of the CubeSat constellation. The basic idea is to consider the CubeSat constellation as a Mobile ad-hoc network (MANET): MANETs are systems of autonomous mobile nodes connected between them to form a graph by a wireless ad-hoc network. The formation and management of MANETs is mostly related to the physical structure and mobility behaviour of nodes composing the network; clustering algorithms aim to face several problems related to the network formation and maintenance of the MANETs structure. The main goal of the clustering algorithms is to group nodes in virtual sub-groups based on specific grouping parameters which differ depending on the used algorithm. To develop our algorithm, we selected some concepts and specific features from other clustering algorithms to fit the CubeSat constellations scenario requirements. A complete survey of the main clustering algorithms can be found in [1]. By applying some modifications, we unified the strengths and we introduced new concepts during the design process to minimize the weakness points and to be coherent with our concepts of simplicity, flexibility and energy saving. The key factors identified to form the sub-networks (clusters) inside the CubeSat constellation are: mutual relative speed, relative distances, CubeSat ID and cluster-head serving time. These factors are combined to elect the best local managers of a neighbourhood inside the CubeSat constellation: The Cluster-Heads. During the clusters formation process CubeSats can assume different states: Initial, Cluster-Head, Cluster-Member, Cluster-Member-Gateway, Cluster-Guest, Cluster-Guest-Gateway. The Cluster-Head is responsible for its cluster management, it administrates the communication in input and output to/from its cluster and organizes the data flow and the behaviour of the Cluster-Members. The Cluster-Guests are exploited to make the algorithm more flexible in case of undefined or difficulties in the communication link establishment, moreover they are exploited to reduce undesirable effect such as the ripple effect of the re-clustering [1]. The Gateway capability is the ability of a node to create a direct link with other elements of external clusters, it represents the key factor to unify the constellation and create a stable backbone for the data flow over the whole network. Figure 1 shows an example of CubeSat constellation network after the cluster formation process; every node has assumed one of the state described before. A typical cluster trend is shown in figure 2: role that each satellite assume depends on the communication features and the mobility behaviour of each node. Most of the analysed algorithms require an initial frozen period of motion to establish the roles of node. By introducing the dynamic analysis of the mutual velocity and distance, our algorithm does not need this stationary assumption. This characteristic results fundamental in a CubeSat constellation scenario, where the release in orbit makes impossible to obtain a period where satellites remain stationary. The clusters formation results stable and durable in time because an estimation of the motion evolution is considered when mutual motion parameters are exchanged, clusters dynamically adapt and stay stable also in situation where satellites have high mobility behaviour. Thanks to the combination of the selected parameters our algorithm guarantees very high flexibility and results to be efficient over a wide range of mobility behaviour combinations of nodes. During the cluster maintenance phase, the motion behaviour of satellites can affect the entire cluster structures. The ripple effect of the re-clustering is kept under control and the flooding effect is avoided thanks to the ability of the algorithm to limit the re-election process only to the interested satellites. Moreover, the cluster-guest nodes provide additional help in case of high mobility or significant differences in mobility characteristics of node. These factors help to keep the cluster stable in case of dynamic changes or brief meeting period between clusters, thus implying that the whole clusters network is scalable and expandable and the algorithms makes clusters robust enough to deal with radical network structure changes

Clustering Algorithm for CubeSat Constellations

In recent years, constellations of CubeSat are redefining the concept of space missions. Complex missions that in the past could only be accomplished using large and expensive satellites can now be performed by CubeSat constellations that, thanks to their coordinated action, can guarantee a certain efficiency level and fulfil the same required goals, reducing costs, system singularities and risk of catastrophic disasters. However, a CubeSat constellation system presents critical organizational issues in terms of creation and managing of network structures and interaction between elements. Orbital characteristics of CubeSats, mutual mobility, low-level features and obviously the final goal of the constellation are some of the critical factors that affect the efficiency of the system. In our paper, we present a novel algorithm able to consider the specific characteristics and the mobility behaviours of every CubeSats to autonomously create and optimize a network structure for the constellation. This network structure will be exploited to facilitate the data flow inside and outside the constellation and to facilitate the management of the CubeSat constellation. The basic idea is to consider the CubeSat constellation as a Mobile ad-hoc network (MANET): MANETs are systems of autonomous mobile nodes connected between them to form a graph by a wireless ad-hoc network. The formation and management of MANETs is mostly related to the physical structure and mobility behaviour of nodes composing the network; clustering algorithms aim to face several problems related to the network formation and maintenance of the MANETs structure. The main goal of the clustering algorithms is to group nodes in virtual sub-groups based on specific grouping parameters which differ depending on the used algorithm. To develop our algorithm, we selected some concepts and specific features from other clustering algorithms to fit the CubeSat constellations scenario requirements. A complete survey of the main clustering algorithms can be found in [1]. By applying some modifications, we unified the strengths and we introduced new concepts during the design process to minimize the weakness points and to be coherent with our concepts of simplicity, flexibility and energy saving. The key factors identified to form the sub-networks (clusters) inside the CubeSat constellation are: mutual relative speed, relative distances, CubeSat ID and cluster-head serving time. These factors are combined to elect the best local managers of a neighbourhood inside the CubeSat constellation: The Cluster-Heads. During the clusters formation process CubeSats can assume different states: Initial, Cluster-Head, Cluster-Member, Cluster-Member-Gateway, Cluster-Guest, Cluster-Guest-Gateway. The Cluster-Head is responsible for its cluster management, it administrates the communication in input and output to/from its cluster and organizes the data flow and the behaviour of the Cluster-Members. The Cluster-Guests are exploited to make the algorithm more flexible in case of undefined or difficulties in the communication link establishment, moreover they are exploited to reduce undesirable effect such as the ripple effect of the re-clustering [1]. The Gateway capability is the ability of a node to create a direct link with other elements of external clusters, it represents the key factor to unify the constellation and create a stable backbone for the data flow over the whole network. Figure 1 shows an example of CubeSat constellation network after the cluster formation process; every node has assumed one of the state described before. A typical cluster trend is shown in figure 2: role that each satellite assume depends on the communication features and the mobility behaviour of each node. Most of the analysed algorithms require an initial frozen period of motion to establish the roles of node. By introducing the dynamic analysis of the mutual velocity and distance, our algorithm does not need this stationary assumption. This characteristic results fundamental in a CubeSat constellation scenario, where the release in orbit makes impossible to obtain a period where satellites remain stationary. The clusters formation results stable and durable in time because an estimation of the motion evolution is considered when mutual motion parameters are exchanged, clusters dynamically adapt and stay stable also in situation where satellites have high mobility behaviour. Thanks to the combination of the selected parameters our algorithm guarantees very high flexibility and results to be efficient over a wide range of mobility behaviour combinations of nodes. During the cluster maintenance phase, the motion behaviour of satellites can affect the entire cluster structures. The ripple effect of the re-clustering is kept under control and the flooding effect is avoided thanks to the ability of the algorithm to limit the re-election process only to the interested satellites. Moreover, the cluster-guest nodes provide additional help in case of high mobility or significant differences in mobility characteristics of node. These factors help to keep the cluster stable in case of dynamic changes or brief meeting period between clusters, thus implying that the whole clusters network is scalable and expandable and the algorithms makes clusters robust enough to deal with radical network structure changes

Swarm System for CubeSats

Purpose - In this paper we present an innovative system able to provide to the CubeSats belonging to a swarm the ability to establish an inter-satellite communication crosslink and to determine the mutual physical positioning. Design/methodology/approach - Through a system involving a smart-antenna array managed by a beamforming control strategy every CubeSat of the swarm can measure the Direction-of-arrival (DOA) and the distance (Range) in order to estimate the physical position of the received signal. Moreover, during the transmission phase, the smart-antenna shape the beam in order to establish a reliable and directive communication link with the others spacecraft and/or with the ground station. Furthermore, we introduce the use of a deployable structure fully developed at Politecnico di Torino able to increase the external surface of CubeSats: this surface allows to gain the interspace between elements of the smart-antenna. Findings - As a consequence, the communication crosslink, the directivity and the detection performance of the DOA system in terms of directivity and accuracy are improved. Practical implications - Moreover, the deployable structure offers a greater usable surface, so a larger number of solar panels can be used. This guarantees up to 25W of average power supply for the on-board systems and for transmission on a 1U CubeSat (10x10x10 cm). Originality/value - This paper describes the physical implementation of the antenna array system on a 1U CubeSat using the deployable structure developed. Depending on actuators and ability that every CubeSat disposes, various interaction level between elements can be achieved. Thus making the CubeSat constellation an efficient and valid solution for space missions