Measurement of the radiation intensity beyond the front of strong shock waves for a methane-nitrogen gas mixture

Abstract

593Study of processes occurring beyond a strong shock front is an urgent problem inherent in the devel opment of projects aimed at space flights to objects of the solar system that possess an atmosphere. In order to save fuel, we have to use aerodynamic damping in the atmosphere. Thus, the right choice and adequate calculation of the thermal screen for a descending spacecraft become basic problems. When entrance into the upper layers of the atmosphere takes place, the shock wave arises ahead of the spacecraft. Under the conditions of high velocities and low gas densities, the radiation flux beyond the shock front can substantially contribute to the summary energy flux onto the ther mal screen surface [1].In the framework of the problem on optimizing the mass, shape, and material of the thermal screen, it is also important to calculate the radiation flux and to choose the least stressed input trajectory of a space craft in the atmosphere, which makes it possible to realize the necessary maneuver. Measurements of the absolute radiation intensity in mixtures identical (with respect to their compositions) to the atmosphere pen etrated by a spacecraft are of great importance for both fundamental and applied studies. Presently, there exists only a limited number of experimental investi gations in which the intensity of the radiation flux beyond a strong shock front has been measured in absolute units [2][3][4].The results reported below significantly comple ment the bulk of experimental data available in the lit erature. These results also allow us to verify kinetic schemes and chemical reactions that proceed under the conditions of noticeable nonequilibrium existing beyond the strong shock front.In order to perform experiments aimed at measure ments of the gas radiation intensity beyond the shock front, we used a shock tube composed of three parts. These were the high pressure chamber (HPC), the low pressure chamber (LPC), and the expansion vol ume. The chambers were separated by a 50 µm brass membrane, whereas the LPC was separated from the expansion volume by the output aluminum dia phragm. The internal LPC diameter and length were 77 mm and 5.5 m, respectively. Preliminarily, the LPC was pumped down to pressures of 5 × 10 -3 Torr and then was filled with the gas mixture under study up to the pressure required.The HPC was filled with a stoichiometric hydro gen-oxygen mixture up to a pressure of 3 atm. Then, with the use of helium and argon, summary pressure was elevated up to 10 atm. Once the mixture was inflamed, the brass membrane between the HPC and the LPC was broken, and the shock wave was formed in the gas under study. By variation of the helium to argon ratio in the HPC, we attained various shock wave velocities in the LPC. In the course of a given experimental series, the shock wave velocity equaled 8.3 km s -1 (for an initial pressure of 0.2 Torr in the LPC).Two piezoelectric pressure sensors were installed in the last two LPC sections to determine the shock wave velocity. There were also two quartz windows...

Radiative Heat Transfer Measurements in Low-Density Titan Atmospheres

“…For the 13 Pa condition, the methane Velocity (km/s) Note Trajectory pressures corrected for laboratory temperature IUSTI (TCM2) [13,14] NASA (EAST) [11] UQ (X2 NRST) [12] UQ (X2 NRST-Al) MIPT [15][16][17] Huygens (nom) [18] Aerocapture (min) [5] Fig. 1 Shock tube conditions investigated for Titan mixtures [11][12][13][14][15][16][17]. The nominal Huygens entry trajectory (nom) [18] and an aerocapture trajectory [5] concentration was reduced at most from 2 to 1.85%.…”

“…Other experiments for Titan atmospheric entry conditions were completed at the Moscow Institute of Physics and Technology (MIPT) in a shock tube facility [15][16][17] at pressures of 0.2, 0.3, and 1 torr (26.7, 40.0, and 133.3 Pa) for shock velocities between 3 and 9 km∕s. Spatially resolved, spectral measurements of the shocked gas were taken, with a resolution of 11 nm over the spectral range 250-700 nm.…”