Speaker
Description
The interaction of the spacecraft material with the atmospheric gases during re-entry is getting attention because of the ever-increasing frequency of spacecraft activity in Earth’s atmosphere. Atmospheric drag and aerodynamic heating are the reason for intense friction of the spacecraft front surface and the atmosphere, inducing ultra-high temperatures and pressures because of the ultrasonic entry speeds (7–8 km/s from LEO) and occurring at about 100 km above surface. Spacecraft demise due to ablation of material is induced by the high temperatures and plasma is also formed. When plasma cools it emits in the UV/Vis/NIR spectral range. Depending on the applied thermal protection systems, ablation of different materials is under a controlled sublimation process, however space debris are mostly of metals.
The same process is observed for the atmospheric entry of meteors (shooting stars), but meteors exceed entry speeds of 20 km/s. There is adequate amount of research that reports shooting star events. Spectroscopic data from the bright teils of meteors constitute chemical signatures of their chemistry in interaction with the atmosphere. Meteor studies are more difficult compared to spacecraft because meteors often have an unknown chemical composition, while variable degree of mineral erosion occurs. For this work, we are taking advantage the of accumulated knowledge from meteor spectra and from multiple experiments we have performed on natural materials (i.e., chondrite and Lunar meteorites, pure mineral phases). We simulate entry conditions using laser ablation with high-power pulsed lasers, with most frequently used a Q-switched nano-pulsed Nd:YAG laser at 1064 nm. Here we report on the sizes and textures of debris, their chemical changes, and the chemical effects on the atmosphere. Mineral debris are melts or fragments often with non-stoichiometric compositions, they can form peculiar alloy compositions, and their surfaces are reactive due to the formation of free tangling chemical bonds as well as the formation of metal superoxides. These, in reaction with air humidity form reactive oxygen species (ROS) and perchlorates, and free radicals such as hydroxyls radicals (•OH). Metal superoxides react exothermically, producing hydrogen peroxide and oxygen gas in a highly explosive reaction in higher concentrations, increasing the heat. We report on all these phenomena, and on the highly toxic and reactive oxygen species (ROS) that can concentrate in clouds and then drop as highly toxic and reactive rain.
