Speaker
Description
An end-of-life scenario for the demise of a LEO satellite might start with deceleration from drag in the LEO environment, followed by heating, ablation, and breakup as the satellite descends into the dense atmosphere. Some key physical and chemical processes would be gas-surface energy transfer, ablation reactions on high-temperature surfaces, and pyrolysis of polymeric materials. Molecular beam methods can provide useful understanding of these processes. Molecular beam-surface scattering of O atoms and N2 molecules on representative satellite materials may be used to measure energy transfers and scattering angles, which are foundational to drag simulations. Molecular beam-surface scattering may also be used to investigate the oxidation reactions that lead to ablation on high-temperature surfaces. In another method, a pulsed hypersonic molecular beam with a high peak flux may be used to create a repeatable shock layer above a heated test article at 2-3 pulses/s, and recession measurements can be made. Such an experiment simulates the rarefied shock layer that forms above a re-entering satellite, allowing ablation phenomena to be studied as a function of material temp. A third method uses mass spectrometry to obtain the molar and mass yields of gaseous products as a function of temperature as a polymer or polymer-composite material is heated rapidly. With such data, finite-rate reaction pathways can be identified by observing the differences in temperature-dependent product yields at different heating rates. Summaries of all three experimental methods will be presented, with examples of gas-surface scattering dynamics of O atoms on representative satellite surfaces, fundamental studies of gas-surface reactions of O atoms on hot carbon surfaces, materials ablation phenomena of carbon subjected to repeated shock layers containing O atoms, and thermal decomposition of phenolic resin.
