Spectroscopic study of the gas-cap radiation intensity for simulated martian atmospheric probes

Abstract

Measurements of radiation from the shock-heated stagnation zone of blunt models have been made in a high-temperature plasma tunnel using a gas mixture of 46 per cent carbon dioxide, 23 per cent nitrogen, and 31 per cent argon. The tests were designed to simulate the conditions expected for a probe launched into the Mars atmosphere to make spectral measurements. The velocity simulated ranged from 5 to 7 km/sec; and the density was maintained at low values of the order 10−8 g/cm3, consistent with ambient conditions prior to peak gas radiation during a Mars entry. Measurements of gas-cap radiation were made with non-ablating copper and ablating surface materials. The results of the tests showed that the plasma tunnel radiation measurements for non-ablating surfaces agree qualitatively with current theoretical predictions for equilibrium flow. Expected nonequilibrium radiation was not observed due to predissociation and freezing of the chemical species upstream in the plasma tunnel nozzle. Considerable enhancement of the gas-cap radiation can occur when ablative materials are employed for thermal protection during entry. Scaling laws are presented which estimate the effect of ablation vapor radiation.