Abstract
The problem relating to the formation of solid particles enabled by hypersonic re-entry in methane-containing atmospheres (such as that of Titan) has been tackled in the framework of a combined experimental–numerical approach implemented via a three-level analysis hierarchy. First experimental tests have been conducted using a wind tunnel driven by an industrial arc-heated facility operating with nitrogen as working gas (the SPES, i.e., the Small Planetary Entry Simulator). The formation of solid phases as a result of the complex chemical reactions established in such conditions has been detected and quantitatively measured with high accuracy. In a second stage of the study, insights into the related formation process have been obtained by using multispecies models relying on the NASA CEA code and the Direct Simulation Monte Carlo (DSMC) method. Through this approach the range of flow enthalpies in which carbonaceous deposits can be formed has been identified, obtaining good agreement with the experimental findings. Finally, the deposited substance has been analyzed by means of a set of complementary diagnostic techniques, i.e., SEM, spectroscopy (Raman, FTIR, UV–visible absorption and fluorescence), GC–MS and TGA. It has been found that carbon produced by the interaction of the simulated Titan atmosphere with a solid probe at very high temperatures can be separated into two chemically different fractions, which also include “tholins”.
Highlights
Titan, the main satellite of Saturn, is the only satellite in the solar system with a dense atmosphere
The present study is articulated as follows: Section 2 contains a description of the hardware and related experimental techniques; at the beginning of Section 3.1, we provide relevant information on the experimentally determined presence of carbon on the surface of the probes used for the tests; the formation of this substance is investigated in the framework of sophisticated multispecies numerical models considering the effective conditions established inside the SPES (Section 3.1.3); in Section 3.1.4, the deposited substance is analyzed by means of a variegated set of complementary experimental techniques
The DCM-soluble particulate was analyzed by gas chromatography–mass spectrometry (GC–MS) and UV–visible spectroscopy
Summary
The main satellite of Saturn, is the only satellite in the solar system with a dense atmosphere (surface pressure of 1.5 bar). Conditions for the formation of such particles are studied by means of numerical simulation This hitherto not yet thoroughly explored phenomenon is of great interest due to its important implications with regard to the aforementioned protection systems (high-speed solid particles may represent a significant threat for any spacecraft or probe). Hah mah - (mH 2OCΔT )mc (ii) Enthalpy of the gas leaving the mixer entering the nozzle: Hmc. Hmc − (J/kg), P is nethe electrical power (W), m is the mass m g,twater temperature jump and the subscripts flow rate (kg/s), C is the water specific heat, ΔT(K) is the have the following meaning: ah—arc-heater, g—gas, mc—mixing chamber, ne—nozzle exit, t—total where the symbol H indicates the total enthalpy (J/kg), P is the electrical power (W), m is the mass condition (beginning of expansion), H2O—water, ts—test section.
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