Aerotecnica Missili & Spazio最新文献

The aerodynamic performance of a wing mounting a simple unconventional box winglet are analyzed in detail by CFD simulations. The decomposition of the computed drag in its irreversible (viscous) and reversible (lift-induced) components by a far field drag breakdown method allows for the determination of the span efficiency, not a trivial task in the case of viscous flow. The aerodynamic performance are compared with the ones obtained in case of a simple standard winglet and without any tip appendices.

With regard to the space field, the number of the sensors has grown for a middle-sized spacecraft from more than 500 at the beginning of the twenty-first century [1] to several thousands for nowadays applications. Meanwhile, Reusable Launch Vehicles (RLVs) moved their steps from demonstrators to commercial working systems. As a result, Health Monitoring (HM) is conquered its own space in the field and sensors are the primary elements required for implementing a monitoring unit. The innovative concept of reusable rockets requires, from the point of view of HM implementation, not only the evaluation of the vehicle health status but also the prediction of the reusability of the individual subsystems w.r.t. the next launch cycle. Therefore, the goal of this work is divided in two parts. The former is to identify the most critical points for the development of reusable rockets, focusing on theoretical working conditions and analysis or failures. The latter is to discuss the sensing units useful for addressing the defined points, describing the possible innovative approaches for sensing the system conditions. Among them, piezoelectric units, fiber optics, imaging units, and conductive layers can be identified for enhancing the comprehension of the system working conditions.

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.