E-st@r-I experience: valuable knowledge for improving the e-st@r-II design

Many universities in the world have now permanent hands-on education programs based on CubeSats. These small and cheap platforms are becoming more and more attractive also for other-than-educational missions, such as for example technology demonstration, science application, and Earth observation. This will require the development of adequate technology to increase CubeSat performance. Furthermore, it is necessary to improve mission reliability, because educationally-driven missions have 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 CubeSat. The project aims at increasing CubeSat mission reliability through several actions: to improve design implementation, to define best practice for conducting the verification process, and to make the CubeSat community aware of the importance of verification. Within this framework, the CubeSat team at Politecnico di Torino developed the e-st@r-II CubeSat as follow-on of the e-st@r-I satellite, launched in 2012 on the VEGA Maiden Flight. E-st@r-I and e-st@r-II are both 1U satellites with educational and technology demonstration objectives: to give hands-on experience to university students and to test an active attitude determination and control system based on inertial and magnetic measurements with magnetic actuation. The paper describes the know-how gained thanks to the e-st@r-I mission and how they have been used to improve the new CubeSat in several areas, from design to operations. The CubeSat design has been improved to reduce the complexity of the assembly procedure and to deal with possible failures on the on-board computer, for example implementing a new communication software in the communications subsystem. New procedures have been designed and assessed for the verification campaign accordingly to ECSS rules and with the support of ESA specialists. Different operative modes have been implemented to deal with some anomalies observed during the operations of the first satellite. The main difference is a new version of the on-board software. In particular, the activation sequence of the satellite has been modified to have a stepwise switch-on of the satellite. In conclusion, the e-st@r-I experience has provided valuable lessons during its development, requirements verification and on-orbit operations. This know-how has become crucial for the development of the e-st@r-II CubeSat

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

The extended law of corresponding states when attractions meet repulsions

Short-range attractive colloids show well-defined phase behaviour in the absence of repulsions, and highly intriguing equilibrium gelation in the presence of long-range repulsions. We present the state diagram of short-range attractive colloids with repulsions that range from fully screened to intermediately ranged, i.e. longer-ranged than the attractions, but shorter ranged than the colloid size. We demonstrate that although the macroscopic phase behaviour does not change perceptibly, there is a dramatic increase of inhomogeneities once the repulsions become longer-ranged than the attractions. The interaction potentials are characterized with small angle neutron scattering, and used to renormalize the state diagram with the minimum in the interaction potential, min[U(r)], and with the reduced second virial coefficient, B2∗. We find that the extended law of corresponding states captures the onset of phase separation for shorter ranged repulsions, but fails for longer ranged repulsions. Instead, for a given model of U(r), the transition from visually homogeneous fluid to phase separation and/or gelation can be rescaled with min[U(r)] over the full range of repulsions. Finally, we suggest a generic state diagram to describe the effect of repulsions on short-range attractive systems

Investigation of the elastic and adhesion properties of adsorbed hydrophobically modified inulin films on latex particles using Atomic Force Microscopy (AFM)

Graft polymer surfactants provide very good colloidal stability because of strong steric repulsions between adsorbed surfactant films. The elastic and adhesion properties of adsorbed hydrophobically modified inulin polymer surfactant (INUTEC NRA) have been directly measured using Atomic Force Microscopy (AFM) measurements. For this purpose, poly(methyl methacrylate/butyl acrylate), P(MMA/BuA), latexes prepared in the presence of the hydrophobically modified inulin (INUTEC NRA) were used. These latexes (diameter 118 nm and polydispersity index of 1.05) showed a very high colloidal stability in water and in the presence of electrolyte (up to 0.2 mol dm−3 KBr). The latexes were deposited on mica, which was silanated to enhance the adhesion of the latex particles to the surface. A silicon nitride tip with approximately 10 nm diameter that also contained an adsorbed layer of surfactant was used in the AFM apparatus. The tip was allowed to approach, contact thereafter the particles with an applied force of 12.5 nN, and finally detach from the film. Both elastic (Young's) modulus of the film and adhesion force were studied. The results showed that the adsorbed surfactant films are highly elastic and their elastic modulus and adhesion force did not change significantly with the presence of Na2SO4 up to 0.05 mol dm−3. The high elastic contribution to the steric interaction ensures strong repulsion between the latex particles both in water and at high electrolyte concentrations. In addition, the lack of dependence of adhesion force on electrolyte concentration ensures uniform deposition of the latex particles on a flat substrate as for example in coating applications. These results show the advantages of using a graft polymer surfactant for enhancing the stability of particle suspensions, as illustrated in previous investigations.The authors gratefully acknowledge financial support from BENEO Bio Based Chemicals, from the Spanish Ministry of Economy and competitiveness (CTQ2008-06892-C03-01 and CTQ2011-23842 projects) and Generalitat de Catalunya for the 659 2009SGR961 Grant. G. Oncins acknowledges the Nanometric Techniques Unit from the Scientific-Technical Services (University of Barcelona). The authors also acknowledge CIBER-BBN, CIBER Intramural Projects and the ICTS NANBIOSIS, which are financed by the Instituto de Salud Carlos III, with assistance from the European Regional Development Fund, and the support from Generalitat de Catalunya (2014SGR1655 and TECCIT15-1-0009).Peer reviewe

CFD analysis of a regular sector of the ITER vacuum vessel. Part I: Flow distribution and pressure drop

The 3D steady-state Computational Fluid Dynamics (CFD) analysis of the ITER vacuum vessel (VV) regular sector #5 is presented, starting from the CATIA models and using a suite of tools from the commercial software ANSYS FLUENT ®. The peculiarity of the problem is linked to the wide range of spatial scales involved in the analysis, from the millimeter-size gaps between in-wall shielding (IWS) plates to the more than 10 m height of the VV itself. After performing several simplifications in the geometrical details, a computational mesh with ∼50 million cells is generated and used to compute the steady-state pressure and flow fields from a Reynolds-Averaged Navier-Stokes model with SST k-ω turbulence closure. The coolant mass flow rate turns out to be distributed 10% through the inboard and the remaining 90% through the outboard. The toroidal and poloidal ribs present in the VV structure constitute significant barriers for the flow, giving rise to large recirculation regions. The pressure drop is mainly localized in the inlet and outlet piping

CFD analysis of a regular sector of the ITER vacuum vessel. Part I: Flow distribution and pressure drop

The 3D steady-state Computational Fluid Dynamics (CFD) analysis of the ITER vacuum vessel (VV) regular sector #5 is presented, starting from the CATIA models and using a suite of tools from the commercial software ANSYS FLUENT ®. The peculiarity of the problem is linked to the wide range of spatial scales involved in the analysis, from the millimeter-size gaps between in-wall shielding (IWS) plates to the more than 10 m height of the VV itself. After performing several simplifications in the geometrical details, a computational mesh with ∼50 million cells is generated and used to compute the steady-state pressure and flow fields from a Reynolds-Averaged Navier-Stokes model with SST k-ω turbulence closure. The coolant mass flow rate turns out to be distributed 10% through the inboard and the remaining 90% through the outboard. The toroidal and poloidal ribs present in the VV structure constitute significant barriers for the flow, giving rise to large recirculation regions. The pressure drop is mainly localized in the inlet and outlet piping

Dynamic Depolarized Light Scattering of Small Round Plasmonic Nanoparticles: When Imperfection is Only Perfect

Although small round gold nanoparticles (Au NPs) possess only a small degree of shape anisotropy, they support localized surface plasmon resonances and exhibit intrinsic optical anisotropy. These inherent features promote depolarized light scattering, whose temporal fluctuations carry information about rotational Brownian dynamics, and thus can be used to describe the size distribution of round Au NPs. We demonstrate that this allows for a much more accurate determination of particle size and polydispersity through depolarized dynamic light scattering when compared to standard particle sizing with light scattering