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The LISA Pathfinder mission was flown to test some key technologies for the in-flight detection of gravitational waves. The mechanism developed to initialise the science phase, releasing the test mass into a geodesic trajectory, produced unexpected test mass states, requiring dedicated in-flight and on-ground test campaigns. Due to the limited information available from the telemetry, the analysis of the results required a combination of experimental and analytical approaches. A dynamic model of the release mechanism, integrated by an impact model, is developed to explain the in-flight test results. The proposed interpretation of the mechanism anomalies may provide useful guidelines for the design and development of the flight units for the forthcoming LISA mission.

Brake wear is known as the primary source of traffic-related non-exhaust particle generation. Its generation rate is influenced by parameters at different levels: subsystem (type of brakes, pads, materials, etc.), system (vehicles’ dynamics, driving style etc.) and suprasystem (road geometries, traffic parameters, etc.). At the subsystem level, we proposed a neural network brake emission modeling, trained and validated through emission data collected from a reduced-scale dynamometer. At the system level, a model of a car dynamics was developed to calculate the wheels’ brake torques and angular velocities. At the suprasystem level, the traffic behavior in a sensitive urban area was characterized experimentally and simulated in a traffic microsimulation software. The vehicle traffic-based records were used to calculate the vehicle dynamic quantities, converted into brake emission through the neural network. To examine the overall traffic impacts on brake emission, the total number of brake wear particles was estimated regarding the route choice in the sensitive area and in the whole transportation network. The findings of this study showed significant impacts of brake wear on air pollution. The ground-truth brake emission estimation in a real area provides fundamental information to the decision-makers to better insight into the rate of non-exhaust emissions generation.

L'obiettivo del saggio è quello di presentare una nuova ipotesi sull'ammontare del popolamento a Bologna tra il 1290 e il 1320, proponendo una cifra attorno ai 90.000 abitanti rispetto ai 50.000 fino a ora presentati dalla storiografia. Attraverso l'analisi di quattro diversi fondi documentari, tre dei quali già utilizzati a scopi demografici (liste di atti alle armi, matricole delle società, estimi, inquisizioni sul frumento), si mostrerà come in passato il numero degli abitanti sia stato sottostimato a causa di una estrapolazione dei dati esclusivamente quantitativa influenzata da alcune precomprensioni storiografiche e come i coefficienti adottati in passato non siano funzionali e utilizzabili o vadano ricalcolati.

LISA Pathfinder is a technology demonstrator space mission, aimed at testing key technologies for detecting gravitational waves in space. The mission is the precursor of LISA, the first space gravitational waves observatory, whose launch is scheduled for 2034. The LISA Pathfinder scientific payload includes two gravitational reference sensors (GRSs), each one containing a test mass (TM), which is the sensing body of the experiment. A mission critical task is to set each TM into a pure geodesic motion, i.e. guaranteeing an extremely low acceleration noise in the sub-Hertz frequency bandwidth. The grabbing positioning and release mechanism (GPRM), responsible for the injection of the TM into a geodesic trajectory, was widely tested on ground, with the limitations imposed by the 1-g environment. The experiments showed that the mechanism, working in its nominal conditions, is capable of releasing the TM into free-fall fulfilling the very strict constraint imposed on the TM residual velocity, in order to allow its capture on behalf of the electrostatic actuation. However, the first in-flight releases produced unexpected residual velocity components, for both the TMs. Moreover, all the residual velocity components were greater than maximum value set by the requirements. The main suspect is that unexpected contacts took place between the TM and the surroundings bodies. As a consequence, ad hoc manual release procedures had to be adopted for the few following injections performed during the nominal mission. These procedures still resulted in non compliant TM states which were captured only after impacts. However, such procedures seem not practicable for LISA, both for the limited repeatability of the system and for the unmanageable time lag of the telemetry/telecommand signals (about 4400 s). For this reason, at the end of the mission, the GPRM was deeply tested in-flight, performing a large number of releases, according to different strategies. The tests were carried out in order to understand the unexpected dynamics and limit its effects on the final injection. Some risk mitigation maneuvers have been tested aimed at minimizing the vibration of the system at the release and improving the alignment between the mechanism and the TM. However, no overall optimal release strategy to be implemented in LISA could be found, because the two GPRMs behaved differently., This work has been made possible by the LISA Pathfinder mission, which is part of the space-science programme of the European Space Agency.The French contribution has been supported by the CNES (Accord Specific de projet CNES 1316634/CNRS 103747), the CNRS, the Observatoire de Paris and the University Paris-Diderot.E. Plagnol and H. Inchauspé would also like to acknowledge the financial support of the UnivEarthS Labex program at Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02).The Albert-Einstein-Institut acknowledges the support of the German Space Agency, DLR. The work is supported by the Federal Ministry for Economic Affairs and Energy based on a resolution of the German Bundestag (FKZ 50OQ0501 and FKZ 50OQ1601).The Italian contribution has been supported by Agenzia Spaziale Italiana and Istituto Nazionale di Fisica Nucleare.The Spanish contribution has been supported by contracts AYA2010-15709 (MICINN), ESP2013-47637-P, and ESP2015-67234-P (MINECO).M. Nofrarias acknowledges support from Fundacion General CSIC (Programa ComFuturo).F. Rivas acknowledges an FPI contract (MINECO). The Swiss contribution acknowledges the support of the Swiss Space Office (SSO) via the PRODEX Programme of ESA. L. Ferraioli is supported by the Swiss National Science Foundation.The UK groups wish to acknowledge support from the United Kingdom Space Agency (UKSA), the University of Glasgow, the University of Birmingham,Imperial College, and the Scottish Universities Physics Alliance (SUPA). J. I. Thorpe and J. Slutsky acknowledge the support of the US National Aeronautics and Space Administration (NASA).

Tourist areas are one of the most populated parts of cities. Air quality in these spaces is critical as they are more susceptible to the particles emitted by vehicles. The concentration of exhaust emissions around these sensitive locations may cause untreatable health issues for visitors, commuters, and citizens. Heavy-duty vehicles (HVs) are one of the most influential factors creating adverse impacts on air quality. This study proposes a state-of-the-art simulation-based approach to study the relationship between an HV’s speed, its fuel consumption, and its contribution to exhaust emissions in sensitive locations. For this purpose, air pollution and fuel consumption in various scenarios were simulated and compared. The proposed method was applied to one of the most popular tourist areas in Trento (Italy), using VISSIM and EnViVer traffic simulation software packages. The results confirmed the impact of vehicle speed on fuel consumption and the amount of emission. The results showed that a 100-km/h increase in the speed of both light vehicles and HV can increase the NOx and volatile organic compound emissions by approximately 20%. Also, CO emissions and fuel consumption increase by approximately 33% when the HV speed increases from 30 to 50km/h. The emission per seat can be decreased by up to 40% and 27% by 20- and 10-km/h reductions in speed, respectively, together with a 100% increase in the HV percentage. Implementing this proposed method could avoid the unintentional negative impacts of air pollution on susceptible visitors.

LISA-Pathfinder is an ESA space mission flown between 2015 and 2017 to demonstrate a technological maturity sufficient for building a gravitational waves telescope in space, such as the Laser Interferometer Space Antenna (LISA). A pair of cubic test masses is hosted inside the LISA-Pathfinder spacecraft and shielded from any force other than the interplanetary gravitational field. The purity of the shielding gives the performance of the mission. There are a number of aspects that had to be confirmed in-flight. One of them is the transition phase from the launch configuration, when the test masses are locked, to the science free-falling configuration. Each test mass is initially released from the mechanical constraints via a dedicated mechanism and then captured by an electrostatic control system. In fact, each test mass is surrounded by a set of electrodes for actuation and sensing purposes. The performance criterion of the release is the final velocity of the test mass relative to the spacecraft, with an upper threshold set to 5 $\mu m/s$. The LISA-Pathfinder first in-flight release velocities highlighted an unexpected dynamics with large linear and angular velocities. The electrostatic control was successful, but only relying on a manual procedure that cannot be considered as baseline for LISA. This paper helps investigating the in-flight non-compliance by dealing with the modeling of the electrostatic environment around each test mass and its contribution to the release and capture dynamics. The electrostatic model is based on the method of moments, a boundary element numerical technique suitable for estimating forces and capacitances between conductors. We also provide a short overview of the method, which can be used for the analysis of other phenomena within LISA and for the design of future gravitational waves telescopes and space projects.

M. Armano et al., The Laser Interferometer Space Antenna Pathfinder (LPF) main observable, labeled Δg, is the differential force per unit mass acting on the two test masses under free fall conditions after the contribution of all non-gravitational forces has been compensated. At low frequencies, the differential force is compensated by an applied electrostatic actuation force, which then must be subtracted from the measured acceleration to obtain Δg. Any inaccuracy in the actuation force contaminates the residual acceleration. This study investigates the accuracy of the electrostatic actuation system and its impact on the LPF main observable. It is shown that the inaccuracy is mainly caused by the rounding errors in the waveform processing and also by the random error caused by the analog to digital converter random noise in the control loop. Both errors are one order of magnitude smaller than the resolution of the commanded voltages. We developed a simulator based on the LPF design to compute the close-to-reality actuation voltages and, consequently, the resulting actuation forces. The simulator is applied during post-processing the LPF data., This work was supported by ETH Research Grant No. ETH-05 16-2, and it has been made possible by the LISA Pathfinder mission, which is part of the space-science program of the European Space Agency. The French contribution has been supported by the CNES (Accord Specific de Projet Grant No. CNES 1316634/CNRS 103747), the CNRS, the Observatoire de Paris, and University Paris-Diderot. E. Plagnol and H. Inchauspé would also like to acknowledge the financial support of the UnivEarthS Labex program at Sorbonne Paris Cité (Grant Nos. ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). The Albert-Einstein-Institut acknowledges the support of the German Space Agency, DLR. The work is supported by the Federal Ministry for Economic Affairs and Energy based on a resolution of the German Bundestag (Grant Nos. FKZ 50OQ0501 and FKZ 50OQ1601). The Italian contribution has been supported by the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare. The Spanish contribution has been supported by Contract Nos. AYA2010-15709 (MICINN), ESP2013-47637-P, ESP2015-67234-P, and ESP2017-90084-P (MINECO). Support from AGAUR (Generalitat de Catalunya) contract 2017-SGR-1469 is also acknowledged. M. Nofrarias acknowledges support from Fundacion General CSIC (Programa ComFuturo). F. Rivas acknowledges an FPI contract from MINECO. The Swiss contribution acknowledges the support of the Swiss Space Office (SSO) via the PRODEX Programme of the ESA. L. Ferraioli is supported by the Swiss National Science Foundation. The UK groups wish to acknowledge support from the United Kingdom Space Agency (UKSA), the University of Glasgow, the University of Birmingham, Imperial College, and the Scottish Universities Physics Alliance (SUPA). J. I. Thorpe and J. Slutsky acknowledge the support of the U.S. National Aeronautics and Space Administration (NASA). N. Korsakova would like to thank the support from the CNES Fellowship. The LISA Pathfinder collaboration would like to acknowledge Professor Pierre Binetruy (deceased 30 March 2017) and Professor José Alberto Lobo (deceased 30 September 2012) for their contribution to the LISA Pathfinder science.

LISA Pathfinder (LPF) has been a space-based mission designed to test new technologies that will be required for a gravitational wave observatory in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime (mHz and below), the measurement band of interest for a space-based observatory. The magnetic field can couple to the magnetic susceptibility and remanent magnetic moment from the test masses and disturb them from their geodesic movement. LISA Pathfinder carried on-board a dedicated magnetic measurement subsystem with noise levels of 10 $ \rm nT \ Hz^{-1/2}$ from 1 Hz down to 1 mHz. In this paper we report on the magnetic measurements throughout LISA Pathfinder operations. We characterise the magnetic environment within the spacecraft, study the time evolution of the magnetic field and its stability down to 20 $\mu$Hz, where we measure values around 200 $ \rm nT \ Hz^{-1/2}$ and identify two different frequency regimes, one related to the interplanetary magnetic field and the other to the magnetic field originating inside the spacecraft. Finally, we characterise the non-stationary component of the fluctuations of the magnetic field below the mHz and relate them to the dynamics of the solar wind., Comment: 16 pages, 17 figures. MNRAS LaTeX style file version 3.0

Non-exhaust emissions, generated by the wear of brake systems, tires, roads, clutches, and road resuspension, are responsible for a large part of airborne pollutants in urban areas. Brake wear accounts for 55% of non-exhaust emissions and significantly contributes to urban health diseases related to air pollution. A major part of the studies reported in the scientific literature are focused on experimental methods to sample and characterize brake wear particles in a reliable, representative, and repeatable way. In this framework, simulation is an important tool, which makes it possible to give interpretations of the experimental results, formulate new testing approaches, and predict the emission produced by brakes. The present comprehensive literature review aims to introduce the state of the art of the research on the different aspects of airborne wear debris resulting from brake systems which can be used as inputs in future simulation models. In this review, previous studies focusing on airborne emissions produced by brake systems are investigated in three main categories: the subsystem level, system level, and environmental level. As well as all the information provided in the literature, the simulation methodologies are also investigated at all levels. It can be concluded from the present review study that various factors, such as the uncertainty and repeatability of the brake wear experiments, distinguish the results of the subsystem and system levels. This gap should be taken into account in the development of future experimental and simulation methods for the investigation of airborne brake wear emissions.

Many space missions share the need to fly a free-falling body inside the spacecraft, as a reference for navigation and/or as a probe for the local gravitational field. When a mechanism is required to cage such an object during the launch phase, the need arises to release it to free-fall once the operational phase must be initiated in orbit. The criticality of this phase increases when the mechanical interfaces between the body and the mechanism are affected by adhesion and the actuation authority of the control system on the free-falling body is limited. Both conditions are realized in the LISA Pathfinder mission, which aims at injecting a gold-coated 2 kg cubic test mass into a nearly perfect geodesic trajectory to demonstrate the readiness of the developed technology for in-space gravity wave detection. The criticality of adhesion is widely recognized in space technology, because it can affect and jeopardize the functionality of mechanisms, when arising between moving parts. In the LISA Pathfinder case, metallic adhesion potentially plays a relevant role, mainly for two reasons. First, thanks to its properties (ductility, high surface energy) the gold coating on the proof mass easily produces cold weldings, especially in vacuum conditions. Second, the detachment of the proof mass from the releasing device occurs abruptly and a relevant influence of the separation velocity is expected on the strength of the welding. This can produce an excessive velocity of the proof mass at the retraction of the releasing device for the following capture and centring phase on behalf of the control system. A testing activity is performed to characterize the dynamic behaviour of the adhesive bonds between the proof mass and the releasing device, which can be used to predict their contribution on the residual velocity of the proof mass after in-flight release. The study of such a dynamic phenomenon sets some challenging requirements on the measurement technique, both on the instrumental and on the signal analysis sides. However, the recent improvements on the testing activities make it possible to refine the contribution of adhesion on the proof mass velocity budget at the release. In this paper we describe the recent experimental results, the developments in the measurement technique, the improvements in the repeatability of the results and the related projection to in-flight release dynamics, in comparison with the previous results.

International audience; Non-recurrent short-term variations of the galactic cosmic-ray (GCR) flux above 70 MeV n−1 were observed between 2016 February 18 and 2017 July 3 on board the European Space Agency LISA Pathfinder (LPF) mission orbiting around the Lagrange point L1 at 1.5 × 106 km from Earth. The energy dependence of three Forbush decreases is studied and reported here. A comparison of these observations with others carried out in space down to the energy of a few tens of MeV n−1 shows that the same GCR flux parameterization applies to events of different intensity during the main phase. FD observations in L1 with LPF and geomagnetic storm occurrence are also presented. Finally, the characteristics of GCR flux non-recurrent variations (peaks and depressions) of duration

We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control force needed to compensate the quasistatic differential force acting on two test masses is applied intermittently as a series of "impulse" forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the actuation force, thus eliminating associated noise and force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger actuation forces also shows that the technique can be used to eliminate actuation noise when this is a dominant factor. © 2019 authors. Published by the American Physical Society.

International audience; We present two novel methods, tested by LISA Pathfinder, to measure the gravitational constant G for the first time in space. Experiment 1 uses electrostatic suspension forces to measure a change in acceleration of a test mass due to a displaced source mass. Experiment 2 measures a change in relative acceleration between two test masses due to a slowly varying fuel tank mass. Experiment 1 gave a value of G=6.71±0.42(×10-11) m3 s-2 kg-1 and experiment 2 gave 6.15±0.35(×10-11) m3 s-2 kg-1, both consistent with each other to 1σ and with the CODATA 2014 recommended value of 6.67408±0.00031(×10-11) m3 s-2 kg-1 to 2σ. We outline several ideas to improve the results for a future experiment, and we suggest that a measurement in space would isolate many terrestrial issues that could be responsible for the inconsistencies between recent measurements.

The zodiacal dust complex, a population of dust and small particles that pervades the Solar System, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. Here we present a new set of data obtained using a novel technique: direct measurements of momentum transfer to a spacecraft from individual particle impacts. This technique is made possible by the extreme precision of the instruments flown on the LISA Pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory that operated near the first Sun-Earth Lagrange point from early 2016 through Summer of 2017. Using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum (related to the particle's mass and velocity), direction of travel, and location of impact on the spacecraft. In this paper, we present the results of a systematic search for impacts during 4348 hours of Pathfinder data. We report a total of 54 candidates with momenta ranging from 0.2$\,\mu\textrm{Ns}$ to 230$\,\mu\textrm{Ns}$. We furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system including those resulting from Jupiter-family comets, Oort-cloud comets, Hailey-type comets, and Asteroids. We find that our measured population is consistent with a population dominated by Jupiter-family comets with some evidence for a smaller contribution from Hailey-type comets. This is in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by LISA Pathfinder., Comment: 22 pages, 14 figures, accepted in ApJ

International audience; The LISA Pathfinder (LPF) mission has demonstrated the ability to limit and measure the fluctuations in acceleration between two free falling test masses down to sub-femto-g levels. One of the key elements to achieve such a level of residual acceleration is the drag free control. In this scheme the spacecraft is used as a shield against any external disturbances by adjusting its relative position to a reference test mass. The actuators used to move the spacecraft are cold gas micropropulsion thrusters. In this paper, we report in-flight characterization of these thrusters in term of noise and artefacts during science operations using all the metrology capabilities of LISA Pathfinder. Using the LISA Pathfinder test masses as an inertial reference frame, an average thruster noise of ∼0.17 μN/Hz is observed and decomposed into a common (coherent) and an uncorrelated component. The very low noise and stability of the onboard metrology system associated with the quietness of the space environment allowed the measurement of the thruster noise down to ∼20 μHz, more than an order of magnitude below any ground measurement. Spectral lines were observed around ∼1.5 mHz and its harmonics and around 55 and 70 mHz. They are associated with the cold gas system itself and possibly to a clock synchronization issue. The thruster noise-floor exhibits an excess of ∼70% compared to characterization that have been made on ground on a single unit and without the feeding system. However this small excess has no impact on the LPF mission performance and is compatible with the noise budget for the upcoming LISA gravitational wave observatory. Over the whole mission, nominal, and extension, the thrusters showed remarkable stability for both the science operations and the different maneuvers necessary to maintain LPF on its orbit around L1. It is therefore concluded that a similar cold gas system would be a viable propulsion system for the future LISA mission.

LISA Pathfinder (LPF) was a technology pioneering mission designed to test key technologies required for gravitational wave detection in space. In the low frequency regime (milli-Hertz and below), where space-based gravitational wave observatories will operate, temperature fluctuations play a crucial role since they can couple into the interferometric measurement and the test masses' free-fall accuracy in many ways. A dedicated temperature measurement subsystem, with noise levels in 10$\,\mu$K$\,$Hz$^{-1/2}$ down to $1\,$mHz was part of the diagnostics unit on board LPF. In this paper we report on the temperature measurements throughout mission operations, characterize the thermal environment, estimate transfer functions between different locations and report temperature stability (and its time evolution) at frequencies as low as 10$\,\mu$Hz, where typically values around $1\,$K$\,$Hz$^{-1/2}$ were measured., Comment: 13 pages, 16 figures. MNRAS LaTeX style file version 3.0

In this paper, we describe a software tool developed for the comprehensive management of any kind of project (research, industrial, etc.) from planning to execution and cost reporting within an org...

In this paper a technique for the characterization of small impulses produced by adhesion force is described. The need to address this topic arose in the frame of the ground testing of a space mechanism dedicated to the precise injection of a body into a geodesic trajectory, both as a reference for the spacecraft navigation and for a scientific measurement. The experimental facility consists of a proof mass suspended by a simple pendulum, and a second actuated body which can be moved and quickly retracted from the adhesive contact. At the retraction, the motion of the proof mass is measured to estimate the impulse (and its time duration) produced by the adhesive bonds arose between the two bodies, up to separation. In the current set-up, systematic effects (elastic energy stored in the system), structural vibration modes and measurement noise affect the displacement signal of the proof mass, dominating the adhesion contribution under study. However, the information on the force impulse and time duration – even if with a low signal to noise ratio – is available in the different response of the vibration modes to the same input. An innovative technique is developed to estimate the adhesion impulse and time duration from the amplitudes of oscillation of the vibration modes of the proof mass in a relevant point of the modal shapes. Since no modification nor installation of additional sensors on the sensing body are required, the method can be applied also to systems with limited access and/or possibility of interaction. The vibration modes of the proof mass are calculated by means of FEA allowing for an accurate modal decomposition of the measured signal, focusing on the bottom end of the relevant bandwidth. The amplitudes of oscillation of each mode, even if affected by systematic effects and strong disturbances, are estimated by means of optimal filtering of the dynamic response. By means of the vibration mode-based mathematical model the adhesion impulse and its time duration are calculated from the estimated oscillation amplitudes.

International audience; LISA Pathfinder (LPF) was a European Space Agency mission with the aim to test key technologies for future space-borne gravitational-wave observatories like LISA. The main scientific goal of LPF was to demonstrate measurements of differential acceleration between free-falling test masses at the sub-femto-g level, and to understand the residual acceleration in terms of a physical model of stray forces, and displacement readout noise. A key step toward reaching the LPF goals was the correct calibration of the dynamics of LPF, which was a three-body system composed by two test-masses enclosed in a single spacecraft, and subject to control laws for system stability. In this work, we report on the calibration procedures adopted to calculate the residual differential stray force per unit mass acting on the two test-masses in their nominal positions. The physical parameters of the adopted dynamical model are presented, together with their role on LPF performance. The analysis and results of these experiments show that the dynamics of the system was accurately modeled and the dynamical parameters were stationary throughout the mission. Finally, the impact and importance of calibrating system dynamics for future space-based gravitational wave observatories is discussed.

In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20 μHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05) fm s−2/√Hz above 2 mHz and (6±1)×10 fm s−2/√Hz at 20 μHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency., Physical Review Letters, 120 (6), ISSN:0031-9007, ISSN:1079-7114

The final publication is available at IOS Press through http://dx.doi.org/10.3847/1538-4357/aaa774 Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder, meant for subsystems diagnostics, was devoted to the measurement of GCR and solar energetic particle integral fluxes above 70 MeV n-1 up to 6500 counts s-1. PD data were gathered with a sampling time of 15 s. Characteristics and energy dependence of GCR flux recurrent depressions and of a Forbush decrease dated 2016 August 2 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections is also discussed.

Nell’aprile del 1296 il marchese Azzo VIII d’Este, signore di Reggio, Modena e Ferrara insieme con i ghibellini di Romagna, attaccò Bologna: l’offensiva fu rapida e violenta e diede inizio a una guerra che durò quasi un decennio. Quegli anni furono particolarmente turbolenti per la città felsinea: i costi del conflitto furono difficilmente sostenibili e, soprattutto, a Bologna era presente una fazione fedele all’estense, la pars marchesana, i cui membri tentarono a più riprese di rovesciare il governo di popolo per consegnare la città ad Azzo d’Este, per mezzo di congiure e tumulti. Come si vedrà, il regime bolognese dovette derogare in più occasioni alla sua legislazione, sia per affrontare la guerra sia per fronteggiare l’emergenza interna e i problemi di ordine pubblico a essa legati, arrivando addirittura a modificare il suo ordinamento giuridico. Durante l’emergenza i consigli cittadini persero gradualmente alcune delle loro più importanti prerogative, soprattutto per quel che riguardava la loro attività legislativa e decisionale, mentre furono conferiti in misura sempre maggiore ampi poteri ai rettori forestieri, agli anziani consoli e soprattutto a speciali balìe di sapientes. In April 1296 the marquis Azzo VIII d'Este, lord of Reggio, Modena and Ferrara with the ghibellines of Romagna, attacked Bologna: the offensive was violent and was the beginning of a war that lasted almost a decade. Those years were particularly turbulent for the city of Bologna: the costs of the conflict were difficult to sustain and, above all, in Bologna there was a faction loyal to the Este, called pars marchesana, whose members repeatedly tried to overthrow the government of popolo to deliver the city to Azzo d'Este, by means of conspiracies and riots. As will be seen, the bolognese regime had to derogate from its legislation on several occasions, both to face the war and to face the internal emergency and the problems of public order related to it, even going so far as to change its legal system. During the emergency, city councils gradually lost some of their most important prerogatives while more and more powers were conferred on foreign rectors to the elderly consuls and especially to special balie of sapientes.

The design of a passive control solution based on tuned mass dampers (TMD\'s) requires the estimation of the actual masses involved in the undesired vibration. This task may result not so straightforward as expected when the vibration resides in subsets of different structural components. This occurs, for instance, when the goal is to damp out vibrations on stays. The theoretical aspects are first discussed and a design process is formulated. For sake of exemplification, a multiple TMD\'s configurations is eventually conceived for an existing timber footbridge located in the municipality of Trasaghis (North-Eastern Italy). The bridge span is 83 m and the deck width is 3.82 m.

Adhesive interactions between surfaces have many engineering implications, since they may be exploited to promote joining between bodies but may also jeopardize the functionality of mechanical systems, when they affects surfaces subjected to relative motion. In some applications the interest arises to develop a model which makes it possible to predict the force required to separate two adhered bodies, given the properties of the materials and of the surfaces. Recent advances in the experimental study of metallic adhesion between engineering metallic surfaces lead to a more detailed investigation, where two main improvements are sought. First, the behaviour of the adhesive bonds is studied in dynamic conditions, i.e. when the separation between the adhered surfaces cannot be considered quasi-static. Second, not only the pull-off force but the complete behaviour of the adhesive bonds as a function of the separation between the surfaces is studied. Both aspects are involved in a dedicated experiment, in which adhesion force rules the transfer of momentum between two bodies if one of them is actuated to perform a dynamic separation. The test facility has been recently developed in order to provide a more representative experiment of the case of study, and a more complex measurement system is available to describe the dynamics of the adhesive bonds. The drawback of the evolution of the experiment is the presence of larger systematic effects and a more difficult estimation of adhesion from the experimental data. Therefore, in order to study and separate the behaviour of adhesion from disturbance effects, a specific grey-box estimation procedure has been set up. Thanks to the improved measurement system, the result of this method is the adhesion force as a function of elongation of the bonds, estimated with a better accuracy than that achieved before. The mathematical model, the regression procedure and the results are here presented and discussed.

Modern launch-lock and release mechanisms are mechatronics systems that are often responsible for critical tasks in space applications. In the European Space Agency mission LISA-Pathfinder, a piezoelectrical mechanism performs the dynamic release of an object (in very demanding conditions). A 1.96-kg cubic test mass has to be held during launch and then released into free fall with a velocity below 5 μm/s. Two identical and opposed mechanisms, moved by piezostack actuators, are designed for a nominally symmetrical release in order to minimize this residual velocity. However, deviations from this symmetric release can produce a momentum transfer to the mass that can result in an excessive velocity. Two main critical effects are highlighted. First, metallic adhesion at the contact interface between the mechanisms and the test mass has a limited repeatability and behaves differently on the two nominally identical sides, producing a net force on the test mass. Second, a net force also arises if the retractions of the two opposing mechanisms are not symmetrical during the interaction with the test mass. Models of the electromechanical dynamics of the mechanisms and their physical interaction with the test mass have been formulated, validated with experimental data, and used to run a large set of Monte Carlo simulations. The effect of uncertainty in the piezoelectrical, mechanical, and electrical parameters is included, allowing us to obtain a statistical distribution of the release velocity and to predict the in-flight performance of the mechanism. This paper is also intended as a reference for future scientific and commercial drag-free missions.

© . This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Test mass charging caused by cosmic rays will be a significant source of acceleration noise for space-based gravitational wave detectors like LISA. Operating between December 2015 and July 2017, the technology demonstration mission LISA Pathfinder included a bespoke monitor to help characterise the relationship between test mass charging and the local radiation environment. The radiation monitor made in situ measurements of the cosmic ray flux while also providing information about its energy spectrum. We describe the monitor and present measurements which show a gradual 40% increase in count rate coinciding with the declining phase of the solar cycle. Modulations of up to 10% were also observed with periods of 13 and 26 days that are associated with co-rotating interaction regions and heliospheric current sheet crossings. These variations in the flux above the monitor detection threshold (¿˜¿70¿MeV) are shown to be coherent with measurements made by the IREM monitor on-board the Earth orbiting INTEGRAL spacecraft. Finally we use the measured deposited energy spectra, in combination with a GEANT4 model, to estimate the galactic cosmic ray differential energy spectrum over the course of the mission.

This paper describes a methodology to analyze, in the frequency domain, the steady-state control performances of the LISA Pathfinder mission. In particular, it provides a technical framework to give a comprehensive understanding of the spectra of all the degrees of freedom by breaking them down into their various physical origins, hence bringing out the major contributions of the control residuals. A reconstruction of the measured in-loop output, extracted from a model of the closed-loop system, is shown as an instance to illustrate the potential of such a model breakdown of the data.

LISA Pathfinder, the European Space Agency's technology demonstrator mission for future spaceborne gravitational wave observatories, was launched on 3 December 2015, from the European space port of Kourou, French Guiana. After a short duration transfer to the final science orbit, the mission has been gathering science data since. This data has allowed the science community to validate the critical technologies and measurement principle for low frequency gravitational wave detection and thereby confirming the readiness to start the next generation gravitational wave observatories, such as LISA. This paper will briefly describe the mission, followed by a description of the science operations highlighting the performance achieved. Details of the various experiments performed during the nominal science operations phase can be found in accompanying papers in this volume.

We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0 fm/s^2/sqrt(Hz) across the 0.1-100 mHz frequency band that is crucial to an observatory such as LISA. Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge build up due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument., Comment: 9 Pages, 3 figures

Seismically induced structural damage, as well as any damage caused by a natural catastrophic event, covers a wide area. This suggests to supervise the event consequences by vision tools. This paper reports the evolution from the results obtained by the project RADATT (RApid Damage Assessment Telematics Tool) funded by the European Commission within FP4.The aim was to supply a rapid and reliable damage detector/estimator for an area where a catastrophic event had occurred. Here, a general open-source methodology for the detection and the estimation of the damage caused by natural catastrophes is developed. The suitable available hazard and vulnerability data and satellite pictures covering the area of interest represent the required bits of information for updated telematics tools able to manage it. As a result the global damage is detected by the simple use of open source software. Acase-study to a highly dense agglomerate of buildings is discussed in order to provide the main details of the proposed methodology.

There are a number of experimental apparati aimed at the measurement of small forces, whose performance is strictly related to the availability of an isolated inertial frame. This means that one component of the apparatus has to be set in free-fall condition along selected degrees of freedom. Such a free-fall condition can be achieved thanks to dedicated mechanisms acting as inertial isolation systems. The present work discusses the optimal design, realization, and testing of an inertial isolation system implemented as a 3-D Roberts linkage. The first part of the work describes the design phase: the optimal calculation of the linkage design parameters is performed through the application of a Nelder–Mead optimization scheme. In order to apply the optimization scheme, the calculation of the linkage kinematics is firstly performed through a variational approach, then the sampled surface describing the linkage trajectory is approximated by a set of Zernike polynomials, which allows to effectively define and calculate the target function for the optimization itself. The second part of the work describes the detailed design and realization of a linkage prototype, and its chararacterization by means of a coordinate measuring machine. The characterization of the device is carried out by exploiting a coordinate measuring machine, which is unusually employed for both driving the linkage moveable part along its two DoF trajectory, and for measuring the resulting error about the nominal trajectory.

The problem of cleaning structural monitoring data from thermal effects has been studied since the pioneering developments in this area. The first attempts approached the problem in a statistical way, in terms of time history correlations. The availability of powerful numerical tools able to solve the thermo-mechanical stress-strain analysis suggests pursuing a dynamic modeling approach. However, defining boundary conditions and assigning the initial conditions can be problematic. Some aspects of such an analysis are discussed in this paper and a proposed procedure is exemplified with reference to an existing railway bridge.

For a specific pedestrian timber link case study, the authors had the chance to collect measurements of the structural response for a period of a few days but with the chance to repeat the monitoring in different seasonal weather conditions. This paper provides a synthesis of the data collected up to now. A parallel numerical model was implemented accounting for different potential constitutive law of the timber components and different hypotheses on the supports behavior.

In the LISA Pathfinder mission, the grabbing positioning and release mechanism will perform a critical phase, which is the injection of a test mass into a perfect free-fall condition (also called geodesic trajectory). A possible failure is the test mass remaining adhered to the mechanism or released with an excessive velocity, which would hinder the subsequent capacitive control to the desired geodesic status. In space engineering it is recognized that mechanisms constitute critical subsystems, because they may have single point failures which can seriously affect the mission. In order to limit the risk, a good practice is to test the mechanism critical phases in an environment which simulates the conditions that will be experienced in operation. In the LISA Pathfinder ground testing plan a combined experimental-analytical strategy has been conceived to test this critical phase. The momentum transfer from an actuator to an adhered test mass upon quick separation is measured by means of a dedicated experiment, characterizing the behavior of adhesion under dynamic failure. In parallel, a mathematical model of the release mechanism electro-mechanical dynamics is experimentally validated. The mathematical model of the test mass in-flight injection into geodesic is built, combining the adhesion model with the identified model of the release mechanism. The compliance of the resulting injection with the requirements is presented and discussed.

In this paper, we describe the current status of the LISA Pathfinder mission, a precursor mission aimed at demonstrating key technologies for future space-based gravitational wave detectors, like LISA. Since much of the flight hardware has already been constructed and tested, we will show that performance measurements and analysis of these flight components lead to an expected performance of the LISA Pathfinder which is a significant improvement over the mission requirements, and which actually reaches the LISA requirements over the entire LISA Pathfinder measurement band. © 2012 IOP Publishing Ltd.

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(exp -2)/square root of Hz, or (0.54 +/- 0.01) x 10(exp -15) g/square root of Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm square root of Hz, about 2 orders of magnitude better than requirements. At f less than or equal to 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(exp -2)/square root of Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

The performances of an optimal two-input filter technique for measuring impulses, caused by contact forces, in the nanoN·s range have been investigated. The instrument is based on a sensing element (proof mass) suspended by a simple pendulum. The impulse is exerted to the proof mass and is measured by applying the optimal filter to the measured signal of the resulting swing motion of the pendulum. Since the contact forces cause the mass to rest out of the pendulum equilibrium before the application of an unknown impulse, the resulting swing motion is also affected by such an undesired and unknown input. As a consequence, the pendulum initial position must be included as an additional input of the optimal filter. Main objectives of this article are to: (a) present the mathematical formulation of the two-input optimal filter, (b) apply this formulation to a harmonic oscillator initially set out of the equilibrium position and subjected to an impulse, (c) analyze the performances of the filtering technique in terms of an achievable measurement accuracy taking into account the effect of noise, sampling frequency, width of the sampling window and an unknown instant of an impulse application.

Metallic micro-wires (diameter ≈10 μm) are widely used to suspend reference bodies and isolate them from micro-seismic vibration because of their low bending and torsional stiffness. They make it possible to realize torsion/swing low-resonant frequency oscillators, spectrally separable from the higher frequency physics of interest. In this study, metallic micro-wires are used to provide both seismic isolation through flexural compliance and high-speed actuation thanks to axial stiffness. An experimental apparatus is realized to characterize the dynamic response of a 25 μm diameter tungsten wire used to actuate a suspended mass (10-2 kg) subjected to accelerations up to 0.2 m/s2. A theoretical non-linear model taking into account flexural and axial behaviour of the wire is developed and validated experimentally. Such a model makes it possible to predict the actual motion of the object, which significantly differs from that of the actuator.