1,721,000 research outputs found
On the restricted 3-body problem for the Saturn-enceladus system. Mission geometry and orbit design for plume sampling missions
Full text linkEnceladus has been identified as one of the most interesting targets for future space missions after plume ejecta were discovered in the Tiger Stripes region. Many concepts, aiming to search for habitable zones beyond Earth, require passing through this plume to collect samples of the ejecta. This orbit design is not a trivial task due to the vicinity of Enceladus to Saturn, which causes non-negligible third body perturbations and strongly deflects the orbit of a spacecraft around Enceladus. In this paper we address this problem by extensively studying the Circular Restricted Three Body Problem and linearly stable Halo orbits passing close over Enceladus’ South Pole. Some resonance solutions are then evaluated considering the elliptical problem and, finally, a preliminary validation is given by integrating the spacecraft in a model based on latest planetary/satellite ephemerides
The BepiColombo solar conjunction experiments revisited
No full textBepiColombo ESA/JAXA mission is currently in its 7 year cruise phase towards Mercury. The Mercury orbiter radioscience experiment (MORE), one of the 16 experiments of the mission, will start its scientific investigation during the superior solar conjunction (SSC) in March 2021 with a test of general relativity (GR). Other solar conjunctions will follow during the cruise phase, providing several opportunities to improve the results of the first experiment. MORE radio tracking system allows to establish precise ranging and Doppler measurements almost at all solar elongation angles (up to 7-8 solar radii), thus providing an accurate measurement of the relativistic time delay and frequency shift experienced by a radio signal during an SSC. The final objective of the experiment is to place new limits to the accuracy of the GR as a theory of gravity in the weak-field limit. As in all gravity experiments, non-gravitational accelerations acting on the spacecraft are a major concern. Because of the proximity to the Sun, the spacecraft will undergo severe solar radiation pressure acceleration, and the effect of the random fluctuations of the solar irradiance may become a significant source of spacecraft buffeting. In this paper we address the problem of a realistic estimate of the outcome of the SSC experiments of BepiColombo, by including in the dynamical model the effects of random variations in the solar irradiance. We propose a numerical method to mitigate the impact of the variable solar radiation pressure on the outcome of the experiment. Our simulations show that, with different assumptions on the solar activity and observation coverage, the accuracy attainable in the estimation of γ lays in the range [6-13] ×10−6
JUICE's 3GM gravity experiment around ganymede - Comparison between nominal and extended mission
No full textThe JUpiter Icy Moons Explorer (JUICE) is a European Space Agency (ESA) mission dedicated to investigating Jupiter's icy satellites and Jovian environment. The mission will be launched in 2022 from Kourou, French Guyana, on an Ariane 5 and it will arrive in the Jovian system in 2029. The mission will perform a series of flybys of the icy moons Europa, Callisto and Ganymede before being inserted into a 9-month orbit around Ganymede. The Ganymede orbital phase is divided into a 5-month elliptical orbit (GEO) and a 4-month circular orbit at an altitude of approximately 500 km (GCO-500). JUICE is endowed with a suite of instruments that will investigate the moon's icy crust, interior structure, magnetic field, and exosphere. The 3GM (Geodesy and Geophysics of Jupiter and the Galilean Moons) experiment on board the spacecraft will exploit accurate Doppler and range measurements to determine the moons' orbits, gravity fields, tides and therefore infer features of their internal structures. In this paper, we compare the expected results of the nominal GCO-500 phase with a possible extended mission to a 200 km circular orbit (GCO-200). The simulations of the nominal mission (GCO-500) reveals that 3GM can provide a gravity map of the moon's up to degree and order 40. The Love number k2, modelling the tidal response, is determined with an accuracy of 10-4 (1-s), which will allow us to set a constraint on the internal structure of the moon. The obliquity, f, and the libration at orbital period, ?, can be retrieved with a level of uncertainty of 1 and 2 μrad, respectively. In this paper, we compare the expected results of the nominal GCO-500 phase with a possible extended mission to a 200 km circular orbit (GCO-200). At a lower altitude, the gravity field can be recovered up to degree and order 80, thus, revealing more details about the superficial structures with a resolution of 207 km at the equator. The potential effect of spacecraft drag due to Ganymede's tenuous exosphere, which ranges between 10-17 - 10-16 kg/m3, in the GCO-500 phase is very faint making not possible for 3GM to estimate it. During the extended mission, the drag becomes 2 orders of magnitude higher, thus, 3GM will be able to provide an estimation of the exospheric density
Articolo 26, Sviluppo progressivo
No full textCommento all'Articolo 26, Sviluppo progressivo, della Convenzione americana dei diritti umani. Il terzo Capitolo della Convenzione, nonostante l’ambizioso titolo «Diritti economici, sociali e culturali», è composto dalla sola disposizione dell’art. 26 in materia di “sviluppo progressivo”. Letteralmente la fattispecie contiene molti principi e garanzie, rivolti agli Stati parte e finalizzati a favorire, per mezzo degli ordinamenti nazionali, lo sviluppo e la piena realizzazione dei diritti economici, sociali, scientifici e culturali. A prima vista un fine assai ambizioso ed eterogeneo, ma che a ben vedere accoglie una nozione in linea con la tradizione europea di sviluppo, legata al benessere e al miglioramento complessivo della vita dei singoli. L'articolo analizza tale disposizione alla luce delle decisioni della Commissione e della Corte, proponendo anche una comparazione con l'esperienza europea
Combined surface and cross-hole electric tomography for reservoir monitoring
No full textIn this paper, we introduce an integrated electric/electromagnetic methodology for mapping the dynamic resistivity variations during hydrocarbon production, injection and well intervention. Our approach combines surface and cross-hole measurements and allows obtaining time-lapse models of 3D resistivity distribution between the wells and the surface. The discussion is focused on 3D and 4D inversion of cross-hole DC (Direct Current) measurements, combined with surface-to-borehole DC data. Modelling and inversion of both synthetic and laboratory data confirm that joint cross-hole and surface DC tomography allows mapping reservoir fluid variations even in case of metallic components of the well completion
Frequency-dependent Ganymede's tidal Love number k2 detection by JUICE's 3GM experiment and implications for the subsurface ocean thickness
No full textGanymede will be the first icy satellite in the Solar System orbited by a spacecraft, ESA's JUpiter ICy moons Explorer (JUICE). JUICE launch is scheduled for April 2023 and the arrival at Ganymede is foreseen in 2035. Thanks to the advanced Ka-band radio tracking system, the Geodesy and Geophysics of Jupiter and Galilean Moons (3GM) experiment aboard the mission will provide range and range-rate measurements that will be used to infer the static (up to degree 35-45) and time-varying gravity field and the internal structure of the moon. Ganymede is subject to tidal deformation, which periodically modifies its gravity field. The larger contribution to the time-varying gravity is due to the tidal interaction with Jupiter, modulated by the eccentricity and the inclination of the moon's orbit. In addition, Ganymede also experiences a lower amplitude time-varying tidal interaction with Io, Europa and Callisto. To a good approximation, the corresponding gravitational signals are periodic and they contain several harmonics of the fundamental synodic frequencies. The elastic response of Ganymede is expected to be frequency-dependent as well. In this work we describe a procedure to estimate the Ganymede's tidal Love number k2 at different frequencies in the orbit determination process of the 3GM experiment, supported by numerical simulations. Finally, we show that 3GM measurements can be used to characterize the interior structure of Ganymede, providing a tight constraint on the subsurface ocean thickness. The ocean density can be also constrained, but with a lower precision
Bepicolombo gravity and rotation experiment in a pseudo drag-free system
No full textThe Mercury Orbiter Radioscience Experiment (MORE) on-board the BepiColombo mission was designed to provide an accurate estimation of the gravity field and the rotational state of Mercury. The Mercury Planetary Orbiter (MPO) is equipped with on-board instrumentation that allows highly stable, multi-frequency radio links in X and Ka band in order to achieve range rate and range coherent two-way measurements accurate to 0.003 mm/s (at 1000 s integration time) and 20 cm, respectively. Precise trajectory reconstruction allows us to estimate accurately the spherical harmonic coefficients of the Hermean gravity field, at least up to degree 35, the tide and the rotational parameters (right ascension and declination of the pole and physical librations in longitude). The determination these parameters provides crucial information on the interior structure of the planet. A full numerical simulation of the radioscience orbit determination process has been carried out taking into account the data provided by the on-board Italian Spring Accelerometer (ISA). This allows us to realize a software version of a drag-free system. In this paper, we report on the results of these numerical simulations aiming at a realistic assessment of the attainable accuracy in the determination of the gravity field and the rotation of Mercury with the implementation of a pseudo drag-free orbit determination process
Fully-coupled spherical modular pendulum model to simulate spacecraft propellant slosh
No full textA spacecraft undergoing general translational and rotational motion can be affected by the sloshing of propellant. A spherical pendulum model is used for simulating this phenomenon because it can better represent the sloshing behavior for rotational dynamics in micro-gravity. This paper develops the fully coupled equations of motion of such a system and presents the solution in a form suitable for the back-substitution method. This modular formulation permits the use of as many pendulums as necessary to approximate the actual sloshing behavior. The general formulation makes minimal assumptions for the rigid portion of the spacecraft and is developed in a frame independent manner making the model applicable to wide range of spacecraft configurations. The model is implemented and verified using energy and momentum conservation in the Basilisk astrodynamics software package. The results of a simulation example of a GPS satellite are shown as an application of the model
Improvements in BepiColombo and JUICE radio science experiments with a multi-station tracking configuration for the reduction of Doppler noise
Full text linkRadio science experiments for planetary geodesy mostly rely on measurements of the Doppler shift of microwave signals sent to a spacecraft by an Earth station, and retransmitted back coherently in phase to the same antenna (two-way link). The retransmitted signal can also be received by a different station in a listen-only configuration (three-way link). In state-of-the-art tracking systems, such as the ones will be used on the future ESA's missions JUICE and BepiColombo, the Doppler error budget is dominated by local noise sources arising at the ground-station, in particular tropospheric scintillation and unmodeled motions of the antenna's structure. In this work, a novel technique aimed at reducing these disturbances is analyzed, with particular emphasis on its benefits to BepiColombo's and JUICE's radio science experiments. The method, referred to as Time-Delay Mechanical-noise Cancellation (TDMC), relies on simultaneous two-way and three-way spacecraft tracking, the latter employing a stiffer listen-only antenna with better mechanical stability and located in a favorable dry region more immune to tropospheric noise. In fact, a proper linear combination of time-shifted observables from the two-way and three-way links can replace local noises of the two-way ground-station with those coming from the listen-only antenna, translating into increased accuracy of the final measurements, while preserving the original Doppler content. We show the results of covariance analyses performed with a multi-arc weighted least square estimator for the entire BepiColombo's Hermean phase and JUICE's flybys of Callisto. We compare the two solutions obtained with and without the application of the TDMC technique. For BepiColombo and JUICE radio science experiments, the two-way links are baselined from the 35-m DSA-3 (Malargüe, Argentina) and the 34-m DSS 25 (Goldstone, California). For the three-way link, we select the 12-m Large Latin American Millimeter Array (LLAMA) antenna for three reasons: 1) its mechanical rigidity with respect to large beam-waveguide antennas, 2) its unique position in the extremely dry Puna de Atacama desert, that assures low tropospheric noise, and 3) its limited longitudinal separation from the two other ground-stations, granting sufficient common visibility time to perform the requested combination of the observables. Besides its noise-reduction effect, enabling unprecedented levels of accuracy on Doppler measurements, TDMC provides also a back-up for unique events: a crucial satellite flyby or a specific passage over a site of particular geophysical interest. Indeed, measurements become virtually independent of unfavorable meteorological conditions at the transmitting station
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