The initiation of rotational motion of a lying object caused by wind gusts

In this paper, the initiation of motion of an object lying on a horizontal floor due to the aerodynamic force produced by a time-dependent wind is considered. It is assumed in this paper that when the aerodynamic force is large enough, the body starts to rotate around the most rearward supporting contact point, or pivoting point. This motion is analyzed by studying the dynamics of the rotation of the body around a pivoting point fixed to the floor, and placed in a gravity field under time-dependent aerodynamic loads produced by a non-steady incoming flow. This rotation initiation phase, which is relevant in the case of a time-varying gusty flow, is an intermediate phase between the two stages generally considered, namely, the initial static equilibrium without motion, and the final flight. In this intermediate phase, which is studied here, the rotational dynamics of the body should be taken into account and the gust characteristics as well, in order to determine whether once initiated the motion it leads to either a frustrated motion or to a successful one. A non-linear mathematical model has been developed, and a linear approximation is deduced, which allows us to obtain the condition for a successful flight. This condition shows two limits, valid for either long or short duration gusts, respectively. Some experiments have been performed in a gust wind tunnel, and results show a satisfactory agreement. To take into account the intrinsic random character of the phenomena in practical situations, expressions for the probability of exceeding the condition for successful flight under short duration gusts are obtained, assuming common probability density functions for the random parameters involved

Feasibility study of a Solar Electric Propulsion mission to Mars

Traditionally, space missions to outer planets have relied on large amounts of chemical propellant or flybys to achieve their objectives. This large mass consumption may be significantly reduced using electric propulsion (EP), since it allows for larger specific impulses. However, this improvement is counteracted by the lower thrust per power levels achievable with EP engines compared to chemical thrusters. Here we discuss how to find a balance for a purely solar EP (SEP) uncrewed mission to Mars. We present system engineering and mission analyses focused on the orbital mechanics. The result is the conceptual design of a realistic mission to Mars, in which any target orbit around Mars can be reached using solely present SEP technology. In particular, for a 2000 kg spacecraft propelled with a Hall effect thruster (HET), the interplanetary transfer can be performed in 363 days with less than 400 kg of fuel consumption, provided that the vehicle leaves the Earth orbit with a suitable specific energy that is attainable using current launchers. Subsequently, 300 kg of propellant are sufficient to allow for the planetary capture, plane change, and circularisation manoeuvres, finally inserting the spacecraft into a polar orbit of height between 300 km and 1000 km above the surface of Mars.Agencia Estatal de Investigación | Ref. PID2020-118613GB-I00Xunta de Galicia | Ref. ED431B 2021/22Ministerio de Universidades | Ref. CAS21/00502Universidade de Vigo/CISU

Conceptual design of Electrodynamic Multi Tether system for self-propelled Jovian capture

Space missions in the environments of the outer planets require a large amount of propellant or assistant flybys. Moreover, the quadratic decrease of the radiation intensity with the distance from the sun makes solar panels less convenient as power source. Electrodynamic tether (EDT) technology is receiving increasing attention since it allows for obtaining both power and propulsion profiting from the high magnetic field and plasma density in the proximity of the giant planets. In particular, it has been shown that a self-propelled vehicle with a single EDT could be captured by Jupiter, were it not for the relativistic effects in the electron collection and the overheating of the tether due to the interaction with the environment. Here, we show that a multi EDT (MEDT) propulsion system can be used to circumvent these limitations. The suitable number, shape, and length of the tethers, depending on the size of the vehicle, are selected by structural and thermal analysis. A possible MEDT-propelled mission to Jupiter is described, including the design of the interplanetary trajectory, the orbital insertion, and the subsequent orbits around the planet. The results obtained demonstrate that such a bare MEDT system is a feasible option to provide propulsion and power in outer planets environments

Gust wind tunnel study on ballast pick-up by high-speed trains

This paper describes the experimental setup, procedure, and results obtained, concerning the dynamics of a body lying on a floor, attached to a hinge, and exposed to an unsteady flow, which is a model of the initiation of rotational motion of ballast stones due to the wind generated by the passing of a high-speed train. The idea is to obtain experimental data to support the theoretical model developed in Sanz-Andres and Navarro-Medina (J Wind Eng Ind Aerodyn 98, 772–783, (2010), aimed at analyzing the initial phase of the ballast train-induced-wind erosion (BATIWE) phenomenon. The experimental setup is based on an open circuit, closed test section, low-speed wind tunnel, with a new sinusoidal gust generator mechanism concept, designed and built at the IDR/UPM. The tunnel’s main characteristic is the ability to generate a flow with a uniform velocity profile and sinusoidal time fluctuation of the speed. Experimental results and theoretical model predictions are in good agreement

An experimental and theoretical study of unsteady flow (gust) effects on structures

The gust wind tunnel at IDR, Universidad Politécnica de Madrid (UPM), has been enhanced and the impact of the modification has been characterized. Several flow quality configurations have been tested. The problems in measuring gusty winds with Pitot tubes have been considered. Experimental results have been obtained and compared with theoretically calculated results (based on potential flow theory). A theoretical correction term has been proposed for unsteady flow measurements obtained with Pitot tubes. The effect of unsteady flow on structures and laying bodies on the ground has been also considered. A theoretical model has been proposed for a semi-circular cylinder and experimental tests have been performed to study the unsteady flow effects, which can help in clarifying the phenomenon

An experimental and theoretical study of unsteady flow (gust) effects on structures

The gust wind tunnel at IDR, Universidad Politécnica de Madrid (UPM), has been enhanced and the impact of the modification has been characterized. Several flow quality configurations have been tested. The problems in measuring gusty winds with Pitot tubes have been considered. Experimental results have been obtained and compared with theoretically calculated results (based on potential flow theory). A theoretical correction term has been proposed for unsteady flow measurements obtained with Pitot tubes. The effect of unsteady flow on structures and laying bodies on the ground has been also considered. A theoretical model has been proposed for a semi-circular cylinder and experimental tests have been performed to study the unsteady flow effects, which can help in clarifying the phenomenon

Experimental set-up of a thermal vacuum chamber for thermal model in-house correlation and characterization of the HYPSO hyperspectral imager

Space environment with changing temperatures and vacuum can affect the performance of optics instruments onboard satellites. Thermal models and tests are typically done to understand the optics performance within large space projects, but less often in nanosatellites projects. It is even more rarer for an optics payload inside a CubeSat platform, made by a third provider, to do functional tests on their optics during space environment test campaign. In this research, an in-house made vacuum chamber with the possibility to warm up (TVAC) the devices under tests, and wall-through transparency for optics experiments is set-up. In parallel, a thermal model of the HYPerspectral Small satellite for ocean Observation (HYPSO) Hyperspectral Imager (HSI) is developed. The HSI, which is a transmissive grating hyperspectral instrument ranged in the visible to near infrared wavelength, has been tested in TVAC. As thermal control is based on heating the device under test, a new method for fitting the thermal models inside vacuum chambers with only heating capability is proposed. Finally, the TVAC set-up and the thermal model fitting method have been demonstrated to be appropriate to validate the HSI thermal model, and to characterize the optics performance of HSI in vacuum and in the range of temperatures found inside the in-orbit HYPSO-1 CubeSat.Research Council of Norway | Ref. 223254Research Council of Norway | Ref. 270959Norwegian Space Agency and the European Space Agency | Ref. 4000132515Ministerio de Universidades | Ref. CAS21/00502Universidade de Vigo/CISU

Comparative study of the effect of several trains on the ballast rotation

The ballast pick-up (or ballast train-induced-wind erosion (BTE)) phenomenon is a limiting factor for the maximum allowed operational train speed. The determination of the conditions for the initiation of the motion of the ballast stones due to the wind gust created by high-speed trains is critical to predict the start of ballast pick-up because, once the motion is initiated, a saltation-like chain reaction can take place. The aim of this paper is to present a model to evaluate the effect of a random aerodynamic impulse on stone motion initiation, and an experimental study performed to check the capability of the proposed model to classify trains by their effect on the ballast due to the flow generated by the trains. A measurement study has been performed at kp 69 + 500 on the Madrid – Barcelona High Speed Line. The obtained results show the feasibility of the proposed method, and contribute to a technique for BTE characterization, which can be relevant for the development of train interoperability standard

Vibrations loads in the process of designing scientific spacecraft payloads

Scientific missions constitute fundamental cornerstones of space agencies such as ESA and NASA. Modern astronomy could not be understood without the data provided by these missions. Scientists need to design very carefully onboard instruments. Payloads have to survive the crucial launch moment and later perform well in the really harsh space environ-ment. It is very important that the instrument conceptual idea can be engineered to sustain all those load

Structural thermal optical performance (STOP) analysis and experimental verification of an hyperspectral imager for the HYPSO CubeSat

The evaluation of space optical instruments under thermo-elastic loads is a complex and multidisciplinary process that requires integrating thermal, structural, and optical disciplines. This thorough analysis often requires substantial resources, leading small satellite projects to exclude it from their schedules. However, even though the instrument discussed in this paper is compact, its complex design and stringent dimensional stability requirements demand a comprehensive evaluation of its performance under thermal loads. The hyperspectral camera, which comprises 18 lenses, a grating, a slit, and a detector, is especially vulnerable to thermo-elastic distortions, as the deformation of even a single lens could significantly impact its performance. In this paper, we present the experimental validation of the STOP analysis applied to the HYPerspectral Small satellite for ocean Observation (HYPSO) Hypespectral Imager (HSI) model. Both the HSI Structural Thermal Optical Performance (STOP) numerical model and the HSI engineering model were subjected to identical thermal conditions in the simulations and in a Thermal and Vacuum Chamber (TVAC), and subsequently the optical results derived from simulations and the test campaign compared. To characterize the thermal field, an infrared camera and thermocouples were used. Moreover, to assess the thermal performance of the HSI, we measured the Full Width at Half Maximum (FWHM) of the main peaks in the intensity-wavelength spectra when the hyperspectral camera targeted a known spectral lamp. After individually calibrating the STOP models so that the FWHM and index of the intensity peaks are in close alignment with the experimentally measured FWHM and index, the lenses most sensitive for displacements were characterizedMinisterio de Universidades | Ref. CAS21/00502Research Council of NorwayNorwegian Space AgencyEuropean Space AgencyUniversidade de Vigo/CISU