Design of the Active Attitude Determination and Control System for the e-st@r cubesat

One of the most limiting factors which affects pico/nano satellites capabilities is the poor accuracy in attitude control. To improve mission performances of this class of satellites, the capability of controlling satellite’s attitude shall be enhanced. The paper presents the design, development and verification of the Active Attitude Determination and Control System (A-ADCS) of the E-ST@R Cubesat developed at Politecnico di Torino. The heart of the system is an ARM9 microcontroller that manages the interfaces with sensors, actuators and the on-board computer and performs the control tasks. The attitude manoeuvres are guaranteed by three magnetic torquers that contribute to control the satellite in all mission phases. The satellite attitude is determined elaborating the data provided by a COTS Inertial Measurement Unit, a Magnetometer and the telemetries of the solar panels, used as coarse Sun sensor. Different algorithms have been studied and then implemented on the microprocessor in order to determine the satellite attitude. Robust and optimal techniques have been used for the controller design, while stability and performances of the system are evaluated to choose the best control solution in every mission phase. A mathematical model of the A-ADCS and the external torques acting on the satellite, its dynamics and kinematics, is developed in order to support the design. After the design is evaluated and frozen, a more detailed simulation model is developed. It contains non-ideal sensors and actuators models and more accurate system disturbances models. New numerical simulations permit to evaluate the behaviour of the controller under more realistic mission conditions. This model is the basic element of the Hardware In The Loop (HITL) simulator that is developed to test the A-ADCS hardware (and also the whole satellite). Testing an A-ADCS on Earth poses some issues, due to the difficulties of reproducing real orbit conditions (i.e. apparent sun position, magnetic field, etc). This is especially true in the case of low cost projects, for which complex testing facilities are usually not available. Thanks to a good HITL simulator it is possible to test the system and its “real in orbit” behaviour to a certain grade of accuracy saving money and time for verification. The paper shows the results of the verification of the ADCS by means of the HITL strategy, which are consistent with the expected values

Lessons learned of a systematic approach for the e-st@r-II CubeSat environmental test campaign

CubeSat-standard satellites have become more and more popular during last years. Education objectives, mainly pursued in the first CubeSat projects, have given way to the design of missions with other-than-education objectives, like Earth observation and technology demonstration. These new objectives require the development of appropriate technology. Moreover, is necessary to ensure a certain level of reliability, because education-driven mission often failed. In 2013 the ESA Education Office launched the Fly Your Satellite! Initiative devoted to provide six university teams with the support of ESA specialists for the verification phase of their CubeSats. Within this framework, the CubeSat Team at Politecnico di Torino developed the e-st@r-II CubeSat. E-st@r-II is a 1U satellite with educational and technology demonstration objectives: to give hands-on experience to university students; to demonstrate the capability of autonomous attitude determination and control, through the design, development and test in orbit of an A-ADCS; and to test in orbit COTS technology and in-house developed hardware and software (as UHF communication subsystem and software for on-board and data handling subsystem). The paper describes the application of a systematic approach to the definition, planning and execution of environmental test campaign of e- st@r-II CubeSat and the gathered lessons learned. The approach is based on procedures designed and assessed for the vibrations and thermal-vacuum cycling tests of a CubeSat accordingly to ECSS rules and with the support of ESA specialists. Concretely, ECSS application, tailored to fit a CubeSat project, allowed to define a test plan oriented to reduce verification duration and cost, which lead to a lean verification execution. Moreover, the interaction with ESA thermal and mechanical experts represented a valuable aid to increase the Team know-how and to improve and optimise the verification plan and its execution. The planning encompasses the analysis of the requirements to be verified that have been gathered in such a way that the tests duration has been reduced. The required tests, like thermal- vacuum cycling and bake-out tests, have been combined in order to speed-up the verification campaign. The tests outputs shown that the satellite is able to withstand launch and space environment. Furthermore, satellite expected functionalities have been tested and verified when the CubeSat is subjected to space environment, in terms of temperature and vacuum conditions. In conclusion, it has been successfully demonstrated that the proposed approach allows executing a lean CubeSat verification campaign against environmental requirements following a systematic approach based on ECSS

A tool for nano-satellite functional verification: comparison between different inthe-loop simulation configurations

This paper describes the simulator technology and the verification campaign for the e-st@r CubeSats family, developed at Politecnico di Torino. The satellites’ behavior has been investigated using a Model and Simulation Based Approach. One of the critical issue in the verification and validation of any space vehicle is the impossibility to fully test some features due to the particular and often un-reproducible environment in which it will operate. Simulations result as one of the best means for testing space system capabilities as it may help to overcome the abovementioned problem. In order to perform different simulation configurations for e-st@r CubeSats, an in-house simulator (named StarSim) has been developed. It is a unique infrastructure, modular and versatile, capable of supporting any desired configuration of the system under test, ranging from full algorithm in the loop simulations (AIL), and gradually inserting satellite hardware, until a complete hardware in the loop (HIL) simulation is performed. When a verification campaign is led on a real object, pure AIL computer based simulations (in which all the equipment and mission conditions are reproduced by virtual models) are not sufficient to test the actual software and hardware to a high degree of confidence since real systems can exhibit random and unpredictable dynamics difficult to be perfectly modeled (i.e. communication delays, uncertainties, and so on). For these reasons, Software In The Loop (SIL), Controller In The Loop (CIL) and HIL simulations were planned. SIL simulations foresee that algorithms are written in the final programming language and executed on ground hardware. In CIL simulations, the software runs on the flight processor while other system’s element are still kept virtual. In HIL simulation, the real hardware (i.e. sensors, actuators, and power sources) are included in the loop. In this paper, after the details of the simulator architecture and its characteristics are described, an exhaustive comparison between AIL and HIL simulations is presented, highlighting main differences and singularities: similar trends of the sensible system’s variables are reached but not identical performances (i.e. absolute and average pointing error and stability, attitude determination accuracy, battery charging and discharging duration) arose analyzing the values. Moreover, it is demonstrated how the technology here presented can effectively support and improve the verification and validation activities for a nano-satellite, by increasing the confidence level on the mission objectives achievement

Autonomous Neuro-Fuzzy Solution for Fault Detection and Attitude Control of a 3U Cubesat

In recent years, thanks to the increase of the know-how on machine-learning techniques and the advance of the computational capabilities of on-board processing, algorithms involving artificial intelligence (i.e. neural networks and fuzzy logics) have began to spread even in the space applications. Nowadays, thanks to these reasons, the implementation of such techniques is becoming realizable even on smaller platforms, such as CubeSats. The paper presents an algorithm for the fault detection and for the fault-tolerant attitude control of a 3U CubeSat, developed in MathWorks Matlab & Simulink environment. This algorithm involves fuzzy logic and multi-layer feed-forward online-trained neural network (percep- tron). It is utilized in a simulation of a CubeSat satellite placed in LEO, considering as available attitude con- trol actuators three magnetic torquers and one reaction wheel. In particular, fuzzy logics are used for the fault detection and isolation, while the neural network is employed for adapting the control to the perturbation introduced by the fault. The simulation is performed considering the attitude of the satellite known without measurement error. In addition, the paper presents the system, simulator and algorithm architecture, with a particular focus on the design of fuzzy logics (connection and implication operators, rules and input/output qualificators) and the neural network architecture (number of layers, neurons per layer), threshold and activation func- tions, offline and online training algorithm and its data management. With respect to the offline training, a model predictive controller has been adopted as supervisor. In con- clusion the paper presents the control torques, state variables and fuzzy output evolution, in the different faulty configurations. Results show that the implementation of the fuzzy logics joined with neural networks provide good ro- bustness, stability and adaptibility of the system, allowing to satisfy specified performance requirements even in the event of a malfunctioning of a system actuator

Bariatric Surgery Reduces Oxidative Stress by Blunting 24-h Acute Glucose Fluctuations in Type 2 Diabetic Obese Patients

OBJECTIVE - We evaluated the efficacy of malabsorptive bariatric surgery on daily blood glucose fluctuations and oxidative stress in type 2 diabetic obese patients. RESEARCH DESIGN AND METHODS - The 48-h continuous subcutaneous glucose monitoring was assessed in type 2 diabetic patients before and 1 month after biliopancreatic diversion (BPD) (n = 36), or after diet-induced equivalent weight loss (n = 20). The mean amplitude of glycemic excursions and oxidative stress (nitrotyrosine) were evaluated during continuous subcutaneous glucose monitoring. During a standardized meal, glucagon-like peptide (GLP)-1, glucagon, and insulin were measured. RESULTS - Fasting and postprandial glucose decreased equally in surgical and diet groups. A marked increase in GLP-1 occurred during the interprandial period in surgical patients toward the diet group (P < 0.01). Glucagon was more suppressed during the interprandial period in surgical patients compared with the diet group (P < 0.01). Mean amplitude of glycemic excursions and nitrotyrosine levels decreased more after BPD than after diet (P < 0.01). CONCLUSIONS - Oxidative stress reduction after biliopancreatic diversion seems to be related to the regulation of glucose fluctuations resulting from intestinal bypass. © 2010 by the American Diabetes Association

Effectiveness and safety of secukinumab in Italian patients with psoriasis: an 84 week, multicenter, retrospective real-world study

Background: Long term data on the real-life use of secukinumab are scant. The aim of this study was to investigate the real-life effectiveness, safety and treatment persistence of secukinumab in patients with moderate-to-severe psoriasis. Research design and methods: This 84-week, multicenter (n = 7) retrospective study analyzed data from patients who initiated and received at least 6 months of secukinumab treatment between June 2016 and June 2018 in the Campania region of Italy. Patient demographic and treatment characteristics, duration of treatment and reasons for discontinuation as well as Psoriasis Area and Severity Index (PASI), Body Surface Area (BSA), and Dermatology Life Quality Index (DLQI) scores were assessed. Results: 324 patients (63% male, mean age 50.2 years) were enrolled and received a mean 11.7 months of secukinumab treatment. Overall, 9.5% discontinued secukinumab, including 5.2% who discontinued due to secondary inefficacy and 1.8% due to adverse events. PASI, BSA and DLQI scores were significantly improved from baseline at every follow-up visit (p < 0.001) and mean PASI decreased from 15.3 ± 6.3 at baseline to 0.5 ± 1.0 at week 84. Secukinumab had comparable effectiveness in biologic naïve and non-naïve patients. Conclusions: This study confirmed the effectiveness and safety of secukinumab in real-world patients with psoriasis

Technologies and methodologies for CubeSat performances improvement

The importance of small satellites, and in particular of nano-satellites (e.g. CubeSats) has increased during last years thanks to major improvements in the field of electrical and mechanical miniaturisation. Another important factor is represented by the interest of national and international space agencies, which has led to the creation of many scientific small satellites programmes, beyond several educational ones. “Small satellites” term shall not be considered referring only to mass, but it describes also a new approach to building, operating, and managing risk for satellite systems; in fact, CubeSat standard (whose reference design was proposed in 1999, and first launch occurred in 2003) is becoming a concrete realisation of a new way of thinking space systems, which is changing the way to access the space. Commercial components, rapid scheduling, risk tolerance and lean testing are just some of features behind the success and spread of CubeSats among universities, space agencies, research and scientific centres, and private companies. Current CubeSat and small satellite missions are mostly developed for Low Earth Orbit (LEO) application, and the number of scientific goals/tasks that they can perform is still limited. CubeSats are nowadays a mature technology to perform Earth observation with low-to-medium performance, and they are a valid educational tool to train young engineers and students in the process of conceiving, implementing and operating a space mission. However, it is possible to say we are entering a new CubeSat Era, in which CubeSats will be called to carry out real missions of the future. Within the new framework, they may represent new test-beds for future bigger missions or allow independent and unprecedented new applications. This research aims at contributing to advance the state of the art in CubeSat missions design and implementation by enhancing some technologies that will support those missions and by defining some innovative approaches for CubeSat development. This main objective has been addressed and pursued from two different points of view: -design perspective, to contribute at improving one specific technology in one technical domain of interest at sub-system level. A subsystem, specifically the Attitude Determination and Control Subsystem (ADCS), has been chosen and the attitude determination process is the function that has been specifically analysed -development perspective, to contribute at improving the development process of a CubeSat mission. This activity has been carried out at system-level, and addresses specifically the Assembly, Integration and Test/Verification (AIT/V) process of a CubeSat for which a new approach has been proposed based on lessons learned from past missions and innovative simulation methodologies and tools. The problem definition for this thesis has been expressed with the following questions: “How and to what extent can the CubeSat platform support future space missions for science purposes, technology demonstration, and service applications?”, and “What features of CubeSat platforms and their missions shall be improved to meet the emerging needs and requirements?”. To answer these questions, the whole CubeSat life-cycle has been considered, analysed and eventually adapted to the rising needs. Both design aspects and development processes have been addressed, which might help improving overall CubeSat quality, extend CubeSat applications range, and finally increase mission success. The major results are represented by improvements attainable at different phases of the CubeSat life-cycle, such as design, development and verification phase, and at different levels (i.e. subsystem level and system level), through the use of In-the-Loop (IL) simulator and leveraging lessons learned and heritage from previous missions. The methodology adopted is the Model Based System Engineering (MBSE), which provides a wonderful support to solve complex problems against reduced budgets, fewer resources (in terms of personnel and money) and shorter schedules. The first part of the work has been aimed at the investigation of the CubeSat standard and its diffusion, in order to identify actions to improve performances in view of next commercial and scientific missions. Furthermore, a detailed analysis of state-of-the-art and on-the-horizon technologies has been carried out, with a major focus on ADCS, COMmunication subSYStem (COMSYS), Electrical Power Subsystem (EPS) and propulsion subsystem. For what concerns the subsystem level, the ADCS has been selected as case study, with a direct application on e-st@r-II CubeSat. Determination algorithms have been investigated, both static and recursive ones, and a specific recursive algorithm have been designed, developed and integrated on-board. The algorithm works in the special condition of under-observability: a single vector observation is available, which is the Earth Magnetic Field (EMF) vector. The algorithm is part of the payload of e-st@r-II CubeSat, which was selected by ESA Education Office to participate to Fly Your Satellite! (FYS!) initiative and whose launch is scheduled on 22nd April 2016 on board Soyuz ST-A VS14 from Centre Spatial Guyanais (CSG) in French Guyana. The on-orbit testing will provide additional data to validate the algorithm. In addition to this activity, the adoption of Artificial Neural Network (ANN) technology on-board CubeSats has been investigated. The field of application of ANNs is again the ADCS: they have been designed to act as state estimator and fault detector. Several types of ANNs have been studied, in order to identify the ones with the best performances. In this application, pattern recognition neural networks and Many ADAptive LInear NEuron (MADALINE) networks have been implemented to detect and identify a fault of a gyro and to estimate angular velocities and attitude of the satellite even when a fault occurs. For what concerns the system level, the goal of performances improvement has been pursued working not only on the design phase, but also improving the other phases, such as development, manufacturing, assembly, integration, verification and operations phases. Key aspects have been identified regarding the verification campaign for CubeSats: reference standards can not be adopted integrally, but there is a need for tailoring, creating a set of lean tests, and the use of IL simulators, in all of their forms (Algorithm-In-the-Loop (AIL), Software-In-the-Loop (SIL), Controller-In-the-Loop (CIL) and Hardware-In-the-Loop (HIL)), is fundamental, especially for verifications that could be very demanding for the flight hardware and/or very expensive. These aspects have been discussed, with reference to e-st@r-II CubeSat functional and environmental test campaigns within the participation at FYS! programme of ESA Education Office. Finally, an additional possible way to increase the rate of success has been found into start thinking as a “manufacturing company” (i.e. in terms of mass production), and to evaluate previous missions, gathering lessons learned, extracting possible failures and drawbacks, and deducing possible improvements for future projects, at all phases of the product life-cycle. As example of this methodology, the improvements achieved on e-st@r-II CubeSat thanks to e-st@r-I CubeSat have been presented, together with the lessons learned of the environmental test campaign of e-st@r-II CubeSat performed at ESA-ESTEC, which will have an impact on next projects of the Team (e.g. 3-STAR CubeSat). In conclusion, it has been proven that the proposed technologies and methodologies methods are effective to increase the CubeSats mission success and their performances, investigating some direct applications. Moreover, in view of future missions of CubeSats, some recommendations have been formulated, and they may be useful both for educational programs and scientific/commercial ones

Technologies and methodologies for CubeSat performances improvement

The importance of small satellites, and in particular of nano-satellites (e.g. CubeSats) has increased during last years thanks to major improvements in the field of electrical and mechanical miniaturisation. Another important factor is represented by the interest of national and international space agencies, which has led to the creation of many scientific small satellites programmes, beyond several educational ones. “Small satellites” term shall not be considered referring only to mass, but it describes also a new approach to building, operating, and managing risk for satellite systems; in fact, CubeSat standard (whose reference design was proposed in 1999, and first launch occurred in 2003) is becoming a concrete realisation of a new way of thinking space systems, which is changing the way to access the space. Commercial components, rapid scheduling, risk tolerance and lean testing are just some of features behind the success and spread of CubeSats among universities, space agencies, research and scientific centres, and private companies. Current CubeSat and small satellite missions are mostly developed for Low Earth Orbit (LEO) application, and the number of scientific goals/tasks that they can perform is still limited. CubeSats are nowadays a mature technology to perform Earth observation with low-to-medium performance, and they are a valid educational tool to train young engineers and students in the process of conceiving, implementing and operating a space mission. However, it is possible to say we are entering a new CubeSat Era, in which CubeSats will be called to carry out real missions of the future. Within the new framework, they may represent new test-beds for future bigger missions or allow independent and unprecedented new applications. This research aims at contributing to advance the state of the art in CubeSat missions design and implementation by enhancing some technologies that will support those missions and by defining some innovative approaches for CubeSat development. This main objective has been addressed and pursued from two different points of view: -design perspective, to contribute at improving one specific technology in one technical domain of interest at sub-system level. A subsystem, specifically the Attitude Determination and Control Subsystem (ADCS), has been chosen and the attitude determination process is the function that has been specifically analysed -development perspective, to contribute at improving the development process of a CubeSat mission. This activity has been carried out at system-level, and addresses specifically the Assembly, Integration and Test/Verification (AIT/V) process of a CubeSat for which a new approach has been proposed based on lessons learned from past missions and innovative simulation methodologies and tools. The problem definition for this thesis has been expressed with the following questions: “How and to what extent can the CubeSat platform support future space missions for science purposes, technology demonstration, and service applications?”, and “What features of CubeSat platforms and their missions shall be improved to meet the emerging needs and requirements?”. To answer these questions, the whole CubeSat life-cycle has been considered, analysed and eventually adapted to the rising needs. Both design aspects and development processes have been addressed, which might help improving overall CubeSat quality, extend CubeSat applications range, and finally increase mission success. The major results are represented by improvements attainable at different phases of the CubeSat life-cycle, such as design, development and verification phase, and at different levels (i.e. subsystem level and system level), through the use of In-the-Loop (IL) simulator and leveraging lessons learned and heritage from previous missions. The methodology adopted is the Model Based System Engineering (MBSE), which provides a wonderful support to solve complex problems against reduced budgets, fewer resources (in terms of personnel and money) and shorter schedules. The first part of the work has been aimed at the investigation of the CubeSat standard and its diffusion, in order to identify actions to improve performances in view of next commercial and scientific missions. Furthermore, a detailed analysis of state-of-the-art and on-the-horizon technologies has been carried out, with a major focus on ADCS, COMmunication subSYStem (COMSYS), Electrical Power Subsystem (EPS) and propulsion subsystem. For what concerns the subsystem level, the ADCS has been selected as case study, with a direct application on e-st@r-II CubeSat. Determination algorithms have been investigated, both static and recursive ones, and a specific recursive algorithm have been designed, developed and integrated on-board. The algorithm works in the special condition of under-observability: a single vector observation is available, which is the Earth Magnetic Field (EMF) vector. The algorithm is part of the payload of e-st@r-II CubeSat, which was selected by ESA Education Office to participate to Fly Your Satellite! (FYS!) initiative and whose launch is scheduled on 22nd April 2016 on board Soyuz ST-A VS14 from Centre Spatial Guyanais (CSG) in French Guyana. The on-orbit testing will provide additional data to validate the algorithm. In addition to this activity, the adoption of Artificial Neural Network (ANN) technology on-board CubeSats has been investigated. The field of application of ANNs is again the ADCS: they have been designed to act as state estimator and fault detector. Several types of ANNs have been studied, in order to identify the ones with the best performances. In this application, pattern recognition neural networks and Many ADAptive LInear NEuron (MADALINE) networks have been implemented to detect and identify a fault of a gyro and to estimate angular velocities and attitude of the satellite even when a fault occurs. For what concerns the system level, the goal of performances improvement has been pursued working not only on the design phase, but also improving the other phases, such as development, manufacturing, assembly, integration, verification and operations phases. Key aspects have been identified regarding the verification campaign for CubeSats: reference standards can not be adopted integrally, but there is a need for tailoring, creating a set of lean tests, and the use of IL simulators, in all of their forms (Algorithm-In-the-Loop (AIL), Software-In-the-Loop (SIL), Controller-In-the-Loop (CIL) and Hardware-In-the-Loop (HIL)), is fundamental, especially for verifications that could be very demanding for the flight hardware and/or very expensive. These aspects have been discussed, with reference to e-st@r-II CubeSat functional and environmental test campaigns within the participation at FYS! programme of ESA Education Office. Finally, an additional possible way to increase the rate of success has been found into start thinking as a “manufacturing company” (i.e. in terms of mass production), and to evaluate previous missions, gathering lessons learned, extracting possible failures and drawbacks, and deducing possible improvements for future projects, at all phases of the product life-cycle. As example of this methodology, the improvements achieved on e-st@r-II CubeSat thanks to e-st@r-I CubeSat have been presented, together with the lessons learned of the environmental test campaign of e-st@r-II CubeSat performed at ESA-ESTEC, which will have an impact on next projects of the Team (e.g. 3-STAR CubeSat). In conclusion, it has been proven that the proposed technologies and methodologies methods are effective to increase the CubeSats mission success and their performances, investigating some direct applications. Moreover, in view of future missions of CubeSats, some recommendations have been formulated, and they may be useful both for educational programs and scientific/commercial ones

A multi attribute collaborative tradespace exploration applied to concurrent design

Nowadays space systems are becoming more complex, dynamic, interconnected and automated. Because of these trends and the increasing involvement of stakeholders, the decision makers are facing with difficult decision. Despite the fact that most of the costs are expended in the latest phases of the space mission life cycle, the majority of them are driven by the choices taken during the earliest design phases, which is also characterized by the lowest level of knowledge about the system. For these reasons several design approaches have been developed and studied. With respect to the classical sequential one, a promising alternative design approach is offered by Concurrent Engineering, in which the design method provides better performances, taking full advantage of modern information technology. In this scenario, the complete design team, composed of the various technical domain specialists, starts working concurrently on the different aspects of the project at the beginning of the design process. A potential technology for improving the design performances can be found in the so called Multi-Attribute Trade-space Exploration (MATE). The purpose of MATE is to capture decision maker references and use them to generate and evaluate a multitude of system architectures, with respect to the stakeholder values but without considering the multidisciplinary nature of complex systems. On the other hand, a well suited method used in a practical multidisciplinary design environment, such as space systems design, can be found in the Collaborative Optimization (CO). The key concept in the CO is to decompose the design problem into two levels of optimizations, the discipline level and the system level, supporting disciplinary autonomy while maintaining interdisciplinary compatibility. This paper describes the system engineering principles, models and tools, followed by an analysis of the benefits involved in the trade-space exploration and the multidisciplinary optimization methods. In addition, a hybrid methodology will be proposed, which merges the Multi Attribute Trade-space Exploration and the Collaborative Optimization within the concurrent design environment. This methodology, integrated into the spacecraft system engineering leads to a faster design process and aims to maximize the utility of the system within the subsystems optimization study. Importance is given to the coupling of design variables between the different disciplines, reaching a concurrent friendly and value driven design in the early design phases