Mass spectroscopic investigation of dissociation and ionization in a simulated re-entry plasma

With a new type of a miniaturized fourfold monopole mass spectrometer the hypersonic flow around suitable model targets is investigated and gaseous reactions studied. Flow parameters are chosen such as to simulate the re-entry conditions of a spacecraft returning into the Earth's atmosphere. The dissociation of N₂ and O₂ is measured in the flow around a half sphere as well as in the stagnation point. Under the given condition the degree of ionization of N₂ never reached the sensitivity limit of 5 per cent. O₂, however, was always dissociated to a measurable degree at the stagnation point, while in the flow noticeable dissociation occurred only with small gas density. Theoretical computations are in good agreement with the observed data. Three kinds of ions were found in the stagnation point, NO⁺ abundance as predicted by theory is confirmed for high but not for low pressure.