Aerotecnica Missili & Spazio最新文献

This research is focused on the analysis, design, and numerical testing of a feedback guidance algorithm for autonomous (unmanned) close-range maneuvering of a chaser spacecraft, in the context of orbital rendezvous with a target vehicle. The relative dynamics of the two vehicles, placed in nearby low Earth orbits, is modeled using the nonlinear Battin–Giorgi equations of relative motion, with the inclusion of all the relevant perturbations, i.e. several harmonics of the geopotential, atmospheric drag, solar radiation pressure, and third body gravitational pull due to Moon and Sun. Unlike several former contributions in the scientific literature, this research considers the orbit perturbing actions on both vehicles, proving that this is crucial for a successful maneuver. Feedback linearization provides the theoretical foundation for the definition and development of a guidance algorithm that is capable of driving the chaser vehicle toward the target spacecraft. Moreover, discrete-variable thrust is considered, and an effective modulation scheme is proposed that includes adaptation of the control gains. Monte Carlo simulations demonstrate that the guidance technique at hand is effective and accurate in driving the chaser spacecraft toward the target vehicle, in the presence of orbit perturbations and unpredictable displacements from the nominal initial conditions.

This study employs the circular restricted three-body problem (CR3BP) as the dynamical framework, for the purpose of investigating low-thrust orbit dynamics in the Earth–Moon system. First, the effect of low thrust on some dynamical structures that exist in the CR3BP is analyzed. Low-thrust capture and escape dynamics in the proximity of the Moon is investigated for preliminary mission analysis. Then, low-thrust periodic orbits—with potential practical application—are detected. To do this, the theorem of mirror trajectories, proven 6 decades ago, is extended to low-thrust trajectories. This represents the theoretical premise for the definition and use of a numerical search methodology based on modified Poincaré maps. This approach leads to identifying several low-thrust periodic orbits in the Earth–Moon system that are infeasible if only unpowered paths are considered. Two possible applications of low-thrust periodic orbits are described: (a) cycling transfer trajectories that connect Earth and Moon continuously, and (b) non-Keplerian periodic paths about the Moon, with potential use as operational orbits for satellite constellations.

Carbon fibers reinforced carbon composites (C/C) are special advanced ceramic materials exhibiting outstanding thermal and mechanical properties as low density, high specific modulus, strength and fracture strain retained also at very elevated temperatures, very high thermal conductivity, low thermal expansion coefficients and consequently excellent thermal shock resistance. They are used in several industrial fields, especially in the aerospace and military sectors, e.g., aircraft disc brakes, sharp re-entry nose tips, thermal protection systems of aerospace vehicles and above all nozzle throat inserts and divergent inner walls of solid rocket boosters. The C/C composites’ thermo-mechanical properties are strongly interrelated with the architecture and orientations of carbon fiber preforms. The present paper, based upon previous activities carried out by the authors in C/C design and manufacturing, introduces a novel technical approach, consisting in an innovative combination of pre-rigidized carbon rods preform with pressure gradient chemical vapour infiltration process, aimed to the fabrication of throat insert components for space propulsion, liquid and solid, rocket engines. In details, the whole manufacturing process is examined, starting from the production of carbon rods of predetermined shape and size through a pultrusion line, to the geometrical design of the main 4D architectures, showing different orientations and packing efficiency up to the investigation of the PGCVI process including experimental testing with 2D preforms and the scanning microscope analysis of the C/C samples densified in this way.

The low regression rate of Hybrid Rocket Engines (HREs) is one prominent characteristic that is addressed in most abstracts concerning hybrid propulsion. Over the years, researchers developed and investigated numerous ways to tackle the low regression rate problem of HREs. This article is a collection and assessment of these diverse methods and designs. It allows for a quick overview of the different mechanisms that are being employed and can serve both as information and inspiration. The enhancement ideas are grouped together as (a) adjustments to the solid fuel chemical properties, (b) advanced injection methods and concepts and (c) improving the combustion chamber design. These different techniques are discussed and their individual impact on the regression rate is assessed both qualitatively and quantitatively. All methods that are presented come with a different set of advantages and disadvantages, making the regression rate enhancement a trade-off problem. In our view, the most promising designs and methods are those that only call for minor adjustments to the HRE design, as they can be also added to already existing engines. Above all, it is to be said that regression rate enhancing techniques that change the unique features of HREs (namely safety, simplicity and low cost) are to be employed with caution. Only if the achievable regression rate increase is justifying the implications for the HRE in the envisioned use-case, these concepts represent promising alternatives to the status quo.

As advanced nozzles may offer alternative solutions to conventional nozzles for the future class of reusable launch vehicles, a critical aspect is to tailor these novel technologies to current recovery strategies, more specifically to vertical landing sustained by retro-propulsion. Researchers at Technische Universität Dresden have developed a dedicated test-bench for the vacuum wind tunnel facility, where Advanced Nozzle Concepts (ANCs), such as aerospike and dual-bell nozzles, are tested in cold-gas configuration while invested by subsonic counter-flows. The main objective of the test campaign is to evaluate the performance and altitude–compensation characteristics of such ANCs by simulating a vertical landing manoeuvre through the variation of ambient pressure experienced during the landing burn. A detailed description of design and development of the test-bench, together with preliminary results from the commissioning activities, are here offered to the reader. The force measurements, together with pressure and temperature data, contribute to evaluate thrust levels and coefficients, as well as the monitoring of the interaction between the nozzle cold-flow and the opposing free-stream. A background-oriented schlieren system allows to visualise the external flow-field. In conclusion, an outline of the upcoming test campaign and a description of the expected results is offered.

In a time in which a significant number of launch vehicles are being developed, boosted by numerous new space actors demanding cheaper access to space, the need to ensure the reliability of launch vehicles and the performance of a successful Post-Mission Disposal (PMD) is undeniable. The first step to ensure the reliability of new launch vehicles is to analyse previous launch failures, learning from past mistakes. In this paper, the launch failures that occurred over the past 16 years are analysed. These failures are classified as a function of the subsystems involved in the failure, as well as the phase of the mission in which the failure occurred. As a result, the most critical subsystems are identified for every mission phase. Subsequently, the most critical subsystem is further investigated, and its most critical components are identified. Furthermore, aiming to improve the present PMD practices, an understanding of the current status is necessary. This paper provides an overview of the evolution in terms of mean orbital lifetime of the rocket bodies launched since the year 2000. Moreover, the number of manoeuvres performed and the orbital lifetime saved by these manoeuvres is analysed between 2016 and 2020, further classifying the statistics by launcher family and country.

Hall effect thruster (HET) is nowadays one of the most used and attractive electric propulsion (EP) technologies for satellite applications because of its relatively high specific impulse, efficiency, high thrust-to-power ratio, simplicity and possibility to down-scale. The increasing demand for a higher lifetime pushes research efforts toward the optimization of these devices. The erosion of the accelerating channel is the main limiting lifetime phenomena. Computational modelling is commonly used to study it. The behaviour of plasma heavy particles, namely neutrals and ions, has been analysed by means of axisymmetric particle-in-cell (PIC) code, developed to be coupled with a module solving fluid equations for electrons (i.e. hybrid approach for plasma). The PIC module has been developed to work with non-Cartesian mesh to consider the variation of wall profile due to erosion. The discharge within the accelerating channel of the SPT-100 thruster was selected as a cornerstone test because of the great availability of numerical and experimental data. The study shows that the code is able to describe accurately densities and velocities of ions and neutrals, reproducing with consistency the physics within the accelerating channel and near-plume of HETs with eroded and non-eroded walls. profile.

Passengers’ safety in unconventional situations, such as those of an emergency landing, has become more and more important due to the increase of air traffic. To improve passengers’ safety, certification authorities have imposed specific crashworthiness requirements in airworthiness regulations as defined in Title 14 of Federal Regulations Code—Part 25 for transport aircraft. Over the years, a series of drop tests were carried out to evaluate the structural performance of the airframe and seats and their effects on the occupants. However, the development of a single test is not only time-consuming but also very expensive. In this context, computer modelling and simulation have become increasingly popular for efficient and quick investigations on aircraft’s dynamic behaviour. This study aims to develop a numerical procedure to assess passengers’ safety during a crash landing and optimize the occupant lumbar load for which the impacts of different seat cushion foams are analysed. The experimental data have been collected as part of the research project, which involved the Department of Industrial Engineering Federico II on a drop test of a full-scale fuselage section equipped with two Anthropomorphic Test Devices (ATDs). The finite element model of the test article is generated through the pre/post-processor LS-PREPOST® and is solved using the non-linear explicit dynamic finite element code LS-DYNA®. The parametric study confirms the importance of choosing the appropriate foam material of the aeronautical seat cushion, as it has been observed that DAX 55 foams resulted in a lumbar load peak reduced by 20.6% with reference to the conventional polyurethane foam.