Aerotecnica Missili & Spazio最新文献

In this work, the effects of different drag laws regarding the ice crystal impingement on the fuselage of a regional aircraft are investigated. Different probes are considered on the surface of interest and simulated like simple segments normal to the fuselage. Along each of these instrumentations, the collection efficiency has been calculated by using a RANS structured solver named UZEN and an Eulerian impingement code IMP3D, both developed internally at CIRA. The solvers are parallelized and well-assessed. The computational grid has been generated with ICEM CFD. Results show the strong influence of the shape considered for the ice crystal particles and how different laws can guide different water concentrations on the probe surface.

In the next years, the space debris population is expected to progressively grow due to in-space collisions and break-up events; in addition, anti-satellite tests can further affect the debris environment by generating large clouds of fragments. The simulation of these events allows identifying the main parameters affecting fragmentation and obtaining statistically accurate populations of generated debris, both above and below detection thresholds for ground-based observatories. Such information can be employed to improve current fragmentation models and to reproduce historical events to better understand their influence on the non-detectable space debris population. In addition, numerical simulation can also be used as input to identify the most critical objects to be removed to reduce the risk of irreversible orbit pollution. In this paper, the simulation of historical in-orbit fragmentation events is discussed and the generated debris populations are presented. The presented case-studies include the COSMOS-IRIDIUM collision, the COSMOS 1408 anti-satellite test, the 2022-151B CZ-6A in-orbit break-up, and a potential collision of ENVISAT with a spent rocket stage; for these events, results are presented in terms of cumulative fragments distributions and debris orbital distributions.

The Space Rider program falls within the framework of ESA activities for the design of affordable and sustainable reusable aerospace vehicles. Among the greatest challenges for this mission is the design of the Guidance, Navigation and Control (GNC) subsystem for the re-entry phase. The final stage of the latter consists of an autonomous flight under parafoil that must guarantee a smooth and precise landing. To ensure compliance with the requirements in terms of landing accuracy and ground speed constraints at touchdown, the GNC subsystem must be able to counterbalance the effect of the wind during the flight and guarantee an upwind landing. A key role in this regard is played by what is commonly referred to as the Terminal Guidance phase i.e., the final part of the descent under parafoil where the vehicle performs the final approach to the designated landing point. The study presented in this work has been developed at the AOCS/GNC department of SENER Aeroespacial and the objective is to design a complete solution for managing the Terminal Guidance phase of a Space Rider-type case. This includes a guidance algorithm based on a direct method to generate an optimal solution for the trajectory, a path-tracking procedure, and a guidance logic that allows for a correct implementation within the whole GNC software. The optimal terminal guidance algorithm has then been implemented within the six-degrees-of-freedom simulator developed by SENER Aeroespacial demonstrating an excellent functioning for the proposed problem.

Collision avoidance is a topic of growing importance for any satellite orbiting Earth. Especially those satellites without thrusting capabilities face the problem of not being able to perform impulsive collision avoidance manoeuvres. For satellites in low Earth orbits, though, perturbing accelerations due to aerodynamic drag may be used to influence their trajectories, thus offering a possibility to avoid collisions without consuming propellant. Here, this manoeuvring option is investigated for the satellite Flying Laptop of the University of Stuttgart, which orbits the Earth at approximately ({600},{textrm{km}}). In a first step, the satellite is aerodynamically analysed making use of the tool ADBSat. By employing an analytic equation from the literature, in-track separation distances can then be derived following a variation of the ballistic coefficient through a change in attitude. A further examination of the achievable separation distances proves the feasibility of aerodynamic collision avoidance manoeuvres for the Flying Laptop for moderate and high solar and geomagnetic activity. The predicted separation distances are further compared to flight data, where the principle effect of the manoeuvre on the satellite trajectory becomes visible. The results suggest an applicability of collision avoidance manoeuvres for all satellites in comparable and especially in lower orbits than the Flying Laptop, which are able to vary their ballistic coefficient.

The prediction of pressure fluctuations generated over the external surface of aerospace launchers during the atmospheric flight remains a challenging task due to the complexity of the geometry and the effects of compressibility at high supersonic Mach numbers. An experimental database is here analysed to the scope of providing a procedure to model and predict the relevant statistics of the wall pressure fluctuations generated by a supersonic flow overflowing the VEGA-C Launcher Vehicle. Data have been obtained in an extensive Wind Tunnel test campaign carried out in the trisonic wind tunnel of the National Institute for Aerospace Research (INCAS) in Bucharest. Wall-mounted pressure transducers allowed for the computation of the pressure Auto- and Cross-spectra over the fourth (the payload region) and third stages of the launcher model. Coherence functions are modelled through exponential-like analytical functions following the approaches usually adopted in canonical boundary layer flows, whereas the auto-spectra models are based on polynomial fits. The approach adopted for the achievement of proper non-dimensional quantities as well as the procedure implemented for the full-scale extrapolation is presented and discussed.

This paper presents extended sufficiency results for the local minimality of an extremal of the Bolza problem. These results provide an essential improvement in the state of the art because they are applicable for bang–bang control without requiring the strict Legendre and controllability conditions. Extended sufficient conditions subsume the classic Jacobi conjugate point sufficiency conditions. Necessary conditions of the second order allow to exclude the minimality when sufficiency is not verified. All these results are applicable to space trajectory optimization both in low thrust and in impulsive transfer.

In this manuscript, the authors deeply investigate and test a modern technique that allows the analysis of a structure starting from a photo to identify and locate damage present on it, rapidly and non-destructively without any physical interaction with the analyzed structure. The technique suitability is tested on four statically deformed beams, on which notches represent the defects. The core of the proposed method is the correlation between the curvature that each beam presents under load conditions and its flexural stiffness. The proposed methodology consists in taking a photo of the inflected beam; subsequently, the acquired photo is manipulated with specifically designed image processing tools, and the second derivative of the beam axis is estimated using two distinct numerical differentiator filters (Lanczos filter and Gaussian wavelets) along with suitable processing to reduce border distortions. The tests conducted demonstrate that it is possible, with an opportune static deflection amplitude, to accurately detect the position of the notch with the proposed procedure; a sensitivity analysis is also conducted by testing the procedure with different beam thicknesses, notch positions, and amplitude of the static deflection. Although the authors realize that the technique can generally require sensibly large displacements, the results seem promising.

Re-entry capsules, designed with blunt-body shapes to endure hypersonic air velocities and heat, encounter instability in the low subsonic regime during the final descent phase. Ensuring a controlled descent with the appropriate attitude for deploying deceleration systems becomes paramount. To address this challenge, we employ a cost-effective approach to investigate the dynamic stability of a typical re-entry capsule in free fall. This study involves formulating the aerodynamic model of the system and hypothesizing associated coefficients. A meticulously designed and instrumented prototype is dynamically scaled and subjected to low altitude drop tests to recreate the desired scenario. Subsequently, the data collected during these tests is processed, and stability derivatives are estimated using system identification techniques. Our research contributes to a deeper understanding of the dynamic stability of re-entry capsules during free fall, shedding light on their behavior and providing insights essential for improving their performance and safety during descent.