EXPERIMENTAL VALIDATION OF A DEPLOYMENT MECHANISM FOR TAPE-TETHERED SATELLITES

The number of space debris orbiting our Earth has been continuously increasing since the beginning of the space era. The space community is converging on responsible conducts and self-regulations to address this serious problem that is degrading the near-Earth environment. In this context, green deorbiting technologies and strategies alternative to the traditional chemical propulsion are under investigation, including Electrodynamic Tethers (EDTs) because they are a promising option. To increase EDT technology maturity level, some critical points shall be addressed and experimentally evaluated, including the deployment of tape tethers, to demonstrate their reliability. This paper presents results of an experimental validation of the Deployment Mechanism (DM) proposed for the H2020 FET OPEN Project E.T.PACK \u2013 Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit. We developed a mockup that hosts the DM and other elements that are on board the tip mass of a tethered system, using off-the-shelf components. The DM is tested for the first part of the tether deployment maneuver employing the SPARTANS facility of the University of Padova. This facility includes a Testing Table where the mock-up can move with almost no friction and a Motion Capture system that provides an accurate estimation of the mock-up motion during this first part of the tether deployment maneuver

Analysis of the HASI accelerometers data measured during the impact phase of the Huygens probe on the surface of Titan by means of a simulation with a finite-element model

In the analysis of Huygens mission data some unexpected features were present in the ACC data sets, so a dedicated study was needed to investigate the presence of dynamic interferences during an acquisition and correct the impact signature. The developed method is based on dynamic analysis of the impact through a three-dimensional finite-element dynamic model of the Huygens probe and the results lead to a corrected interpretation of accelerometer readings and provided an improved description of key aspects of the planetary landing. Although some aspects of probe\u2019s state after impact need some further analysis, as for final resting attitude which is to date not completely agreed on, this study disclosed that the probe experienced a vertical decelerating action which is compatible with two possible scenarios: the first one implies the penetration in a soft substrate material followed by a lateral bounce out of the generated hole and the second one suggests the displacement of pebbles from the surface into the soil. Numerical elaboration of impact data calculated a 12 cm penetration into the surface, which may have been experienced either by the lower dome of the probe or from pebbles that were situated under the dome when contacting the planet. In either case after a few seconds of motion the Huygens probe finally rested above Titan\u2019s surface with a negligible penetration. Since HASI piezo-accelerometer design was driven by the need of high full-scale values to monitor critical events during entry and descent phase, it was not possible to reconstruct horizontal motion after main deceleration phase without consistent uncertainties due to the poor overall accuracy in a low-acceleration range

Aerothermodynamic Simulations of the Huygens Probe During the Hasi Balloon Flight Campaign

An explicit algebraic Reynolds stress model has been developed in order to investigate the turbulent flow around the Huygens probe during its descent phase in earth atmosphere. The developing of the turbulence model has been focused on the achievement of good numerical predictions of the aerodynamic forces, the spin velocity profile, and the convective heat flux trough the probe. The variable turbulent viscosity coefficient has been obtained using a simplified algebraic equation of the second order invariant of the Reynolds stress anisotropy tensor that accounts for the variations of the production to dissipation ratio. The numerical simulations has been performed with a finite element commercial code in which the turbulence model subroutines have been implemented. The results of the numerical simulations have shown that the predictions given by the present model are in good agreement with the data supplied by the experimental campaign of the 2003 HASI balloon flight

Design and validation of a carbon-fiber collapsible hinge for space applications: A deployable boom

This work presents an analysis and validation of a foldable boom actuated by tape-spring foldable elastic hinges for space applications. The analytical equations of tape-springs are described, extending the classical equations for isotropic materials to orthotropic carbon-fiber composite materials. The analytical equations which describe the buckling of the hinge have been implemented in a multibody simulation software where the hinge was modeled as a nonlinear elastic bushing and the boom as a rigid body. In the experimental phase, the boom was fabricated using a thin layer carbon-fiber composite tube, and the residual vibrations after deployment were experimentally tested with a triaxial accelerometer. A direct comparison of the simulation with the physical prototype pointed out the dangerous effect of higher order vibrations which are difficult to capture in simulation. We observed that while the vibrational spectra of simulations and experiments were compatible at low frequencies during deployment, a marked difference was observed at frequencies beyond 30 Hz. While difficult to model, higher order frequencies should be carefully accounted for in the design of self-deployable space structures. Indeed, if tape-springs are used as a self-locking mechanism, the higher vibrational modes could have enough energy to unlock the structure during operation

The planetary Fourier Spectrometer for MarsExpress

This paper summarizes some of the activities performed to qualify the interferometric unit of the PFS instrument to the MarsExpress requirements. The Planetary Fourier Spectrometer, PFS, is a Fourier Spectrometer, originally conceived for the orbiter of the Russian Mars\u201996 mission. After the failure of the Mars\u201996 launch the European Space Agency has approved a mission to Mars that includes, in its orbiting platform, the most scientifically interesting payloads of the Mars\u201996, among them the PFS. PFS has been conceived (and built) by an international team of scientific institutions. The mechanical and thermal designs of the interferometric module are under responsibility of CISAS-Universit\ue0 di Padova, with contributions from Politecnico di Milano. PFS-MarsExpress PI is Prof. Vittorio Formisano of Rome\u2019s IFSI-CNR, CNR is also responsible for the design and manufacturing of the electronic units for data handling and interferometer management and control. The power converter unit and the pointing device are under responsibility of a polish team of SBRC, Warsaw. Interferometer optical issues are care of the Dipartimento di Fisica-Universit\ue0 di Lecce with contributions from DLR. At last scientific and technical participation are provided by many national teams from Russia (IKI-Moscow), Germany (DLR-Berlin), France and US. The first ESA mission to Mars has been named MarsExpress because of the unusually short development time; in fact it had the official start in 1999 with the signing of the contract with the Spacecraft Prime contractor and the launch is foreseen for 2003. The rational for such tight schedule is that the mission uses as far as possible already developed instruments and technologies, that is in particularly evident for the payloads derived from Mars\u201996. The idea of the mission as a simply re-flight in case of the PFS however has soon proved to be strongly misleading because, the mechanical (and thermal) environment foreseen for the new mission is strongly different from that of the Russian one. The initially specified mechanical environment at launch was especially severe with vibration amplitudes ranging from 5 to 10 times those foreseen in the Mars\u201996. Although the qualification to the new mission environment is not concluded yet, the instrument has already past the mechanical tests at qualification levels with a tolerable degradation of the optical alignment, allowing proceeding with the building of the flight model