Integrated Magnetic Management of Stored Angular Momentum in Autonomous Attitude Control Systems

Autonomous spacecraft operations are at the front end of modern research interests, because they enable space missions that would not be viable only with ground control. The possibility to exploit onboard autonomy to deal with platform management and nominal housekeeping is thus beneficial to realize complex space missions, which could then rely on ground support only for the mission-critical phases. One routine operation that most spacecraft must perform is stored angular momentum management to maintain fully usable momentum exchange actuators. The execution of this activity may be scheduled, commanded from the ground, or automatically triggered when certain thresholds are reached. However, autonomous angular momentum management may interfere with other primary spacecraft operations if executed with a dedicated and separate system mode. This paper presents the magnetic management of stored angular momentum, integrated with the main attitude control system. The system design and implementation are intended for autonomous spacecraft, and it can be operated without significant ground support. The paper describes the system architecture and the attitude control laws integrated with the magnetic angular momentum management. Specifically, the capability of the autonomous system to keep the internal angular momentum far from the saturation and far from the zero-crossing levels is highlighted. The performance of an example attitude control system with four reaction wheels and three magnetic torquers is presented and discussed, with the simulation results at model-in-the-loop (MIL) level

SPH Method Applied to Naval-Hydrodynamic Problems

Common problems in naval hydrodynamic and coastal engineering are the studies of general internal and external flows. Classic methods of solution have to face break down when dealing with large deformations and fragmentations of the air-water interface. The Smoothed Particles Hydrodynamic (SPH) is an innovative numerical method of solution based on Lagrangian Meshless representation of the flow field. We have applied it to the study of some internal (sloshing and dam-break problem) and external flows (breaking and post-breaking evolution of bores propagation toward beaches and bow breaking waves generated by fast slender vessels). [DOI: 10.1685 / CSC06053] About DO

Asteroids Coupled Dynamics Analysis by Means of Accurate Mass Distribution and Perturbations Modeling

One of the most important aspects when dealing with a Potentially Hazardous Object (PHO) is the accurate determination of its dynamical state. In particular, the determi-nation of orbital and rotational perturbations is important to propagate accurately the heliocentric orbital path of an asteroid or a comet, and to be more precise in the im-pact risk determination and related uncertainty containment. The paper discusses the analysis and study of the motion of an irregularly-shaped celestial body, with par-ticular attention to its complex three-dimensional rotational dynamics: the rotation state, nutation and precession motions are considered while modelling. All perturba-tions, relevant to the case of study, are included in the dynamical model, from the classical to the more complex, such as the Solar Radiation Pressure (SRP), the third body gravitational effect (presence of the Sun), the YORP effect and the internal dis-sipation of energy. In addition, particular attention has been paid to accurately model the shape of the asteroid: simple spherical models demonstrated to possess low ac-curacy when the asteroid or the comet is not spherically shaped. Irregular shapes represent, indeed, one of the most important aspects to compute the disturbances affecting the dynamics of these objects. The study has been performed by consider-ing different characteristic shapes for typical irregular bodies: from the quasi-spherical, to the dog-bone and the elongated shapes. The perturbations due to ex-ternal sources are modelled numerically. The sources of disturbances are then ranked and different criteria to propagate rotational motion have been derived de-pending on the shape of the observed asteroid. Even if the simulation results have been verified on selected asteroids dynamics, the presented methods and approach apply to the dynamical propagation of any kind of asteroid or comet

Hang up on stereotypes: Domestic violence and an anti‐abuse helpline campaign

We estimate the effectiveness of a government-led anti-domestic-abuse campaign launched in the midst of the covid-19 pandemic on the number of calls to the Italian domestic violence helpline. In the week after the start of the campaign, we document a sharp increase in the number of calls. By exploiting geographical variation in the exposure to the campaign ads aired on public TV networks, we find that greater exposure is associated with an increase in the number of calls after the launch of the campaign. However, the effectiveness of the media campaign is hindered in areas where gender stereotypes are stronger

Particle packing algorithm for SPH schemes

Using some intrinsic features of the Smoothed Particle Hydrodynamics (SPH) schemes, an innovative algorithm for the initialization of the particle distribution has been defined. The proposed particle packing algorithm allows a drastic reduction of the numerical noise due to particle resettlement during the early stages of the flow evolution. Moreover, thanks to its structure, it can be easily derived starting from whatever SPH scheme and applies under the hypotheses that the fluid is weakly-compressible or incompressible as well. A broad range of numerical test cases proved this tool to be fast, robust and reliable also for complex geometrical configurations

Experimental and Numerical Investigation of 2D Sloshing with Slamming

Partially filled tanks can experience sloshing in several practical circumstances. This is a resonance phenomenon where the free-surface can highly deform. The liquid will move back and forth rising along the side walls, possibly impacting against the roof. Impact on a side tank wall may also occur,e. g. in shallow water conditions. Resulting slamming loads are of main concern. A synergic experimental-numerical investigation of the sloshing flows is currently performed. Here the main focus is on the occurrence of slamming events and on the prediction of the related loads. Numerically, our approach is based on the SPH method. This method is able to follow the whole flow evolution in the tank and handle the many relevant and complicated phenomena generally involved. Among those we can list: water run-up and run-down along the side walls, roof impacts, freesurface overturning and breaking onto the underlying water, air cushioning. Often these features characterize the flow for intermediate and shallow water depths which can establish in real tanks and are of interest in the present research activity

An improved SPH method for multi-phase simulations

In this work a new SPH model for simulating interface flows is presented. This new model is an extension of the formulation discussed in Colagrossi and Landrini (2003), and shows strong similarities with one proposed by Hu and Adams (2006) to study multiphase flow. The main difference between these two models is that the present formulation allows for simulating multiphase flows together with the presence of a free surface. The new formulation is validated on test cases for which reference solutions are available in literature. A Rayleigh-Taylor instability is first studied. Then, the rise of an air bubble in a water column is investigated. Finally, the model capabilities are illustrated on the case of a drop of a heavy fluid entering a tank filled with water

Theoretical analysis and numerical verification of the consistency of viscous smoothed-particle-hydrodynamics formulations in simulating free-surface flows

The theoretical formulation of the smoothed particle hydrodynamics (SPH) method deserves great care because of some inconsistencies occurring when considering free-surface inviscid flows. Actually, in SPH formulations one usually assumes that (i) surface integral terms on the boundary of the interpolation kernel support are neglected, (ii) free-surface conditions are implicitly verified. These assumptions are studied in detail in the present work for free-surface Newtonian viscous flow. The consistency of classical viscous weakly compressible SPH formulations is investigated. In particular, the principle of virtual work is used to study the verification of the free-surface boundary conditions in a weak sense. The latter can be related to the global energy dissipation induced by the viscous term formulations and their consistency. Numerical verification of this theoretical analysis is provided on three free-surface test cases including a standing wave, with the three viscous term formulations investigated

Whole exome HBV DNA integration is independent of the intrahepatic HBV reservoir in HBeAg-negative chronic hepatitis B

The involvement of HBV DNA integration in promoting hepatocarcinogenesis and the extent to which the intrahepatic HBV reservoir modulates liver disease progression remains poorly understood. We examined the intrahepatic HBV reservoir, the occurrence of HBV DNA integration and its impact on the hepatocyte transcriptome in hepatitis B 'e' antigen (HBeAg)-negative chronic hepatitis B (CHB)