Exploiting Lunar Navigation Constellation for GNC Enhancement in Landing Missions

To support the increasing number of planned lunar missions, a collaborative international initiative is underway to conceptualise and establish a lunar satellite constellation for communication and navigation. In this context, the goal of the current paper is to analyse what the obtainable performance is for a lunar lander that executes state estimation employing one-way ranging signals from such a Lunar Navigation Service (LNS). In particular, a small-sized optimised navigation constellation is considered as the main source of measurements, which, coupled with an accelerometer and an altimeter, is used to estimate the lander absolute trajectory during the main braking phase. The guidance is extracted on board by interpolation of a ground-optimised trajectory, followed by a reference-tracking regulator. Two alternative control tuning cases are presented, one targeting high performance, the other targeting low propellant mass. Nominal performance and associated sensitivity analyses assessed the feasibility of supporting such a critical phase with a reduced LNS constellation, reaching final control errors below 500 (Formula presented.), with the better performing one going down to 56 (Formula presented.). Among the two proposed alternatives, the one targeting low fuel expenditure has proven, however, to also be more robust against time and state uncertainty, providing much larger success rates

Adorno e l'idea di un'ultima filosofia

La tesi costituisce un tentativo di interpretazione generale del pensiero teoretico adorniano, secondo il metodo - teorizzato dallo stesso Adorno - della critica immanente. Il movimento concettuale della dialettica negativa è ricostruito nei suoi nessi di fondo, e giudicato in base ai suoi propri presupposti, a partire dall'interpretazione adorniana della storia della filosofia contemporanea. In quest'ultima, la dialettica hegeliana viene riconosciuta come lo spartiacque teorico decisivo, e la convergenza di dialettica e materialismo, mediata in Adorno dal concetto di "non identità", consente di determinare la critica marxiana come superamento interno di Hegel. L'impianto categoriale della dialettica negativa è inteso appunto a fondare gnoseologicamente la svolta materialistica, il che avviene per il tramite della metapsicologia freudiana, in particolare la teoria della genesi dell'Io e i concetti di sublimazione e rimozione. La teoria materialistica della conoscenza così elaborata da Adorno, nel dar conto dell'esperienza oggettiva oltre le antinomie idealistiche, deduce al tempo stesso dall'immanenza conoscitiva la necessità della trasformazione reale del mondo, postulato essenziale della "filosofia della prassi". Dal punto di vista storico-teorico, perciò, Adorno rappresenta la mediazione più radicale fra l'eredità irrisolta della filosofia classica tedesca e il pensiero post-idealistico dell'alterità o del non concettuale. L'elemento specificamente dialettico in Adorno, in antitesi al pregiudizio diffuso del suo irrazionalismo, esprime la possibilità che sia realizzato interamente l'impulso della ragione, quale l'idealismo tedesco lo ha determinato - riproponendo sul piano dell'autoriflessione del pensiero il problema della prova ontologica dell'esistenza di Dio - attraverso il concetto kantiano dell'incondizionato e quello hegeliano dell'assoluto. Tale realizzazione richiede però il superamento della pura posizione del pensiero. Il limite di Adorno è individuato perciò su questo stesso livello, il rapporto fra teoria e prassi. La tesi dell'impossibilità per la teoria di anticipare la prassi è confutata a partire dal concetto adorniano dell'oggettività sociale come astrazione reale invariante, e l'abolizione della necessità del lavoro è determinata come il fine universale a priori di ogni emancipazione pratica. In conclusione è suggerita a titolo ipotetico, contro Adorno, la possibilità che la dialettica materialistica trovi la sua espressione più adeguata in un sistema di filosofia negativa, opposto e complementare alla conoscenza storica

Experimental investigation of a helicopter rotor with Gurney flaps

The present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach

An Experimental Validation of Phase-Based Motion Magnification for Structures with Developing Cracks and Time-Varying Configurations

In this study, Computer Vision and Phase-Based Motion Magnification (PBMM) are validated for continuous Structural Health Monitoring (SHM) purposes. The aim is to identify the exact instant of occurrence for damage or abrupt structural changes from video-extracted, very low amplitude (barely visible) vibrations. The study presents three experimental datasets: a box beam with multiple saw cuts of different lengths and angles, a beam with a full rectangular cross section and a mass added at the tip, and the spar of a prototype High-Aspect-Ratio wing. Both mode-shape- and frequency-based approaches are considered, showing the potential to identify the severity and position of the damage as well A high-definition, high-speed camera and a low-cost commercial alternative have been successfully utilised for these video acquisitions. Finally, the technique is also preliminarily tested for outdoor applications with smartphone cameras

Implicit Extended Kalman Filter for Optical Terrain Relative Navigation Using Delayed Measurements

The exploration of celestial bodies such as the Moon, Mars, or even smaller ones such as comets and asteroids, is the next frontier of space exploration. One of the most interesting and attractive purposes from the scientific point of view in this field, is the capability for a spacecraft to land on such bodies. Monocular cameras are widely adopted to perform this task due to their low cost and system complexity. Nevertheless, image-based algorithms for motion estimation range across different scales of complexities and computational loads. In this paper, a method to perform relative (or local) terrain navigation using frame-to-frame features correspondences and altimeter measurements is presented. The proposed image-based approach relies on the implementation of the implicit extended Kalman filter, which works using nonlinear dynamic models and corrections from measurements that are implicit functions of the state variables. In particular, here, the epipolar constraint, which is a geometric relationship between the feature point position vectors and the camera translation vector, is employed as the implicit measurement fused with altimeter updates. In realistic applications, the image processing routines require a certain amount of time to be executed. For this reason, the presented navigation system entails a fast cycle using altimeter measurements and a slow cycle with image-based updates. Moreover, the intrinsic delay of the feature matching execution is taken into account using a modified extrapolation method

Wind-tunnel tests of a heavy-class helicopter optimised for drag reduction

Wind-tunnel tests of a heavy-class helicopter model were carried out to evaluate the effectiveness of several components optimised for drag reduction by computational fluid dynamics analysis. The optimised components included different hub-cap configurations, a fairing for blade attachments and the sponsons. Moreover, the effects of vortex generators positioned on the back ramp were investigated. The optimisation effect was evaluated by comparison of the drag measurements carried out for both the original and the optimised helicopter configurations. The comprehensive experimental campaign involved the use of different measurement techniques. Indeed, pressure measurements and stereo particle image velocimetry surveys were performed to achieve a physical insight about the results of load measurements. The test activity confirms the achievement of an overall reduction of about 6% of the original model drag at cruise attitude