1,720,976 research outputs found
Experimental Investigation of Shock Wave/Boundary Layer Interactions over an Artificially Heated Model in Hypersonic Flow
No full textExperimental tests have been carried out to analyze the effect of wall-to-total temperature ratio on the characteristics of a fully laminar shock-wave/boundary-layer interaction in a Mach 6 high enthalpy flow. Test cases were run in a new high-enthalpy arc-heated wind tunnel developed at Centrospazio in the framework of the ESA/FESTIP program. In order to heat-up the model surface a high temperature radiator movable on a remotely controlled displacement system was employed. As the investigation was focused on local dynamic and thermal loads, the model was instrumented with pressure transducers and thin film gauges. The experimental results were compared with numerical simulations carried out at CIRA on the same test cases. Pressure measurements showed a fair agreement with numerics, even if the accuracy of the measurements did not allow to discriminate the differences within the different wall temperature cases numerically calculated. Heat flux data are consistently higher than what calculated by CIRA: further investigation is presently under way to identify the reason of this difference, however the main reason is believed to be related to relaxation phenomena of the frozen flow on the model surface. Additional investigation aimed at evaluating the importance of this effect are presently underway
A New Hypersonic High Enthalpy Wind Tunnel
No full textA hypersonic high enthalpy, arc heated, blow-down wind tunnel has been recently developed at Centrospazio in order to perform experiments in the low to medium Reynolds number range (10^4 - 10^6). The tunnel is capable of delivering Mach 6 flows up to 2-5 MJ/kg in specific total enthalpy on an effective test section 60 mm in diameter. It operates in pulsed quasi-steady mode, with running times ranging from 10 to 30 ms. The uniformity of the potential core of the flowfield has been experimentally assessed in different operational points of the facility, demonstrating good steadyness and repeatability of the test conditions. Activities are presently ongoing aimed at defining the wind tunnel overall capabilities by investigating in detail its characteristics as well as at expanding its operational envelope
Autonomous station keeping for LEO missions with a hybrid continuous/impulsive electric propulsion system
No full textThree-dimensional plume simulation of multi-channel thruster configuration
No full textA three-dimensional hybrid particle-in-cell model of the plume emitted by a four-channel Hall-effect thruster configuration for a preliminary design study has been developed. Results show the presence of a potential well in the central region close to the exit plane of the configuration. Together with the typical characteristics of the single channel ion energy spectrum, a double peak structure in the low energy range is present in the four-channel configuration. It is due to the geometrical effects (four-channel source) and to the anisotropic nature of ion-atom scattering
Autonomous station keeping for LEO missions with a hybrid continuous/impulsive electric propulsion system
No full textModeling and dielectric characterization of EMI/EMC ground test for the evaluation of the electric propulsion thruster emissions
No full textA new EMI test facility for electric propulsion (EP) thrusters has been developed at Aerospazio Tecnologie. The facility consists of a cylindrical dielectric vacuum tank placed in a semi-Anechoic room, connected through a gate valve to a Large Vacuum Test Facility. The electromagnetic characterisation of the facility, along with subsequent measures of the radiated emissions of a Hall effect thruster, is presented
Arcjet Propulsion System Study for NSSK
No full textThe study of a low power arcjet propulsion system and its application to north-south .station keeping of geostationary telecommunication satellites was carried out at Centrospazio in the framework of the arcjet propulsion system development program conducted by BPD Difesa e Spazio under the Italian Space Agency sponsorship. In order to carry out this study, models were developed for all of the main components of the spacecraft. These included: arcjet thruster, propellant storage and feeding systems, power conditioning, solar arrays and batteries. The relevant characteristic parameters and variables, as well as their mutual-relationships, were defined in order to characterize each of the above components in terms of its performance, mass, electrical consumption and heat flux. The modules describing the different spacecraft systems were integrated in a code capable to simulate the system performance in a given mission and to optimize its design parameters on the basis of a properly chosen criterion
Spacecraft localization via angle measurements for autonomous navigation in deep space missions
No full textThis paper addresses the problem of spacecraft localization based on angular measurements, for deep space missions. The dynamic model of the spacecraft accounts for several perturbing effects, such as Earth and Moon gravitational field asymmetry and errors associated with the Moon ephemerides. The measurement process is based on elevation and azimuth of Moon and Earth with respect to the spacecraft reference system. Distance measurements are not employed. Position and velocity of the spacecraft are estimated by using both the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF). The performance of the filters are evaluated on an example of Earth-to-Moon transfer mission. Copyright © 2007 IFAC
Comparison of EKF and UKF for spacecraft localization via angle measurements
No full textThe performance of two nonlinear estimators is compared for the localization of a spacecraft. It is assumed that range measurements are not available (as in deep space missions), and the localization problem is tackled on the basis of angles-only measurements. A dynamic model of the spacecraft accounting for several perturbing effects, such as Earth and Moon gravitational field asymmetry and errors associated with the Moon ephemerides, is employed. The measurement process is based on elevation and azimuth of Moon and Earth with respect to the spacecraft reference system. Position and velocity of the spacecraft are estimated using both the extended Kalman filter (EKF) and the unscented Kalman filter (UKF). The behavior of the filters is compared on two sample missions: Earth-to-Moon transfer and geostationary orbit raising
- …
