Overview of the coordinated ground-based observations of Titan during the Huygens mission

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Satumian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental imnortance for the interpretatinn of results from the Huygens mission

Etude expérimentale et modélisation d'un réflecteur à plasma dans l'hélium pour des applications radar

Un @dispositif utilisant le plasma pour réfléchir les micro-ondes a été mis en oeuvre pour des applications aux antennes radar dans la bande X (8-12 GHz). Pour cela, une impulsion de haute tension de 5 à 10 kV est appliquée aux bornes d'une décharge d'hélium pendant environ 100 us. Le plasma dense est engendré en moins de 4 us à basses pressions (0.2-0.5T) par faisceau d'électrons issu de la cathode creuse linéaire. Le plasma est confiné sous forme plane au moyen d'un champ magnétique homogène...VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

Nonequilibrium radiative heat flux modeling for the Huygens entry probe

An electronic collisional-radiative model is proposed to predict the nonequilibrium populations and the radiation of the excited electronic states CN(A, B) and N-2( A, B, C) during the entry of the Huygens probe into the atmosphere of Titan. The model is loosely coupled with flow solvers using a Lagrangian method. First, the model was tested against measurements obtained with the shock-tube of NASA Ames Research Center. Then, the model was applied to the simulation of Huygen's entry. Our simulations predict that the population of the CN( B) state is lower than the Boltzmann population by a factor 40 at trajectory time t = 165 s and by a factor 2 at t = 187 s and that the population of the CN( A) state remains close to the Boltzmann population for both trajectory points. The radiative heat fluxes, driven by the CN( A, B) states, are lower than predictions based on the Boltzmann populations by a factor 15 at t = 165 s and a factor 2 at t = 187 s

Convective and radiative heat flux prediction of Huygens's Entry on Titan

The present paper focuses on the convective and radiative heat flux predictions required for the post-delta Flight Acceptance Review consolidation of the Huygens entry profile and, in particular, the desired flight path angle at entry interface. This consolidation effort has concluded on the appropriateness of the probe's thermal protection system design under the nominal and dispersed entry conditions considered and has supported the positive decision for Huygens's release from its carrier, Cassini, in December 2004. The related predictions are based on the atmospheric model of Yelle as implemented during the Huygens recovery effort (2002–2004) by the companies Alcatel and European Aeronautic Defence and Space, Les Mureaux and subsequent variations thereof. The atmospheric model (with emphasis on chemical composition, gravity wave, and wind profiles) has been updated before probe release during the Titan flybys in October 2004 and the final preentry predictions reported here have been performed with the atmospheric model resulting from the observations recorded during the second Titan flyby and the preflight trajectory baselined during the delta Flight Acceptance Review in February 2004. The results obtained clearly support the appropriateness of the thermal protection system design and the decision for probe release

Radiative heating predictions for Huygens entry

Radiative heat flux predictions for the Huygens probe entry into Titan's atmosphere are presented in this paper. Radiative heating was computed with the radiation code SPECAIR, assuming a Boltzmann distribution of the excited electronic levels at a characteristic temperature taken as the vibrational temperature of the gas. CN violet is found to be the most intense emitter, followed by CN red, C-2 Swan, and at early trajectory points by the first and second positive systems of N-2. Solutions of the 1-D radiative transport equation along stagnation streamlines show that self-absorption by the plasma layer reduces the total emission by up to about 20%. The fine structure of the CN violet spectra (spin-splitting) was taken into account to accurately determine self-absorption by CN violet. The potential importance of argon radiation was estimated and shown to be negligible. The resulting fluxes were found to be sustainable by the Huygens's Thermal Protection System. The feasibility of the mission was deemed possible under the updated entry parameters and atmospheric composition

Balanced/unbalanced planar magnetron plasma behaviour. Microscopic analysis by PIC-MCC modelling of the ion flux on thermal probes

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