Spacecraft Heat Shield study in the DIII-D tokamak*

A study of carbon ablation at high heat flux relevant to hypervelocity spacecraft entries was performed in the DIII-D tokamak. Exploration missions to the Solar System's gaseous giants and hyperbolic re-entries into the Earth's atmosphere require spacecraft heat shields that can withstand high velocity (>10 km/s) and extreme heat flux (>10 MW/m2). Conditions in DIII-D L-mode edge plasma can reproduce the flow velocity and high heat flux experienced during the Galileo probe's entry into the atmosphere of Jupiter. Three types of samples were used for the experiments: stationary graphite rods protruding from the floor of the vessel, 1-mm-diameter porous carbon spheres, and 700-micron-diameter glassy carbon spheres injected from the floor into the scrape-off layer and edge plasma. In the graphite rod experiments, the mass loss rates as a function of heat fluxes determined from an extensive array of spectroscopic measurements are found to agree with semi-empirical ablation models obtained from previous spacecraft flight data. Experimental results for the pellet trajectories and mass loss rates of the porous and glassy carbon pellets are confirmed using the UEDGE-DUSTT simulations. These pellet experiments are also compared against simulations of carbon-based meteorite atmospheric entries for different velocities, initial masses, and angles of entry.