Materials used in space vehicles components are subjected to thermally aggressive environments when exposed to atmospheric reentry. In order to protect the payload and the vehicle itself, ablative composites are employed as TPS (Thermal Protection System). The development of TPS materials generally go through phases of obtaining, atmospheric reentry tests and comparison with a mathematical model. The state of the art presents some reentry tests in a subsonic or supersonic arc-jet facility, and a complex type of mathematical model, which normally requires large computational cost. This work presents a reliable method for estimate the performance of ablative composites, combining empirical and experimental data. Tests of composite materials used in thermal protection systems through exposure to a plasma jet are performed, where the heat fluxes emulate those present in atmospheric reentry of space vehicles components. The carbon/phenolic material samples have been performed in the hypersonic plasma tunnel of Plasma and Process Laboratory, available in Aeronautics Institute of Technology (ITA), by a plasma torch with a 50 kW DC power source. The plasma tunnel parameters were optimized to reproduce the conditions close to the critical re-entry point of the space vehicles payloads developed by the Aeronautics and Space Institute (IAE). The specimens in study were developed and manufactured in Brazil. Mass loss and specific mass loss rates of the samples and the back surface temperatures, as a function of the exposure time to the thermal flow, were determined. A computational simulation based in a two-front ablation model was performed, in order to compare the tests and the simulation results. The results allowed to estimate the ablative behavior of the tested material and to validate the theoretical model used in the computational simulation for its use in geometries close to the thermal protection systems used in the Brazilian space and suborbital vehicles.

Ablatives composite materials are vastly employed in rocket nozzle components and as thermal protection shields in aerospace industry. In this work, an experimental study on the influence of atmospheric pressure on the ablation of carbon-phenolic composites is performed. The composite is produced by wrapping process and used in the manufacture of thermal re-entry protections. Samples were tested in the following thermal fluxes: 0.626; 0.903; 1,376 and 1,725 MW/m 2 in the 30, 50, 70 and 90 sec exposure times in a plasma tunnel simulating the pressure of 400 Pa and compared to the results obtained in the same thermal fluxes and exposure times at atmospheric pressure. Results were also compared with a computational simulation and a simple and reliable model is proposed to express the influence of environment pressure, presenting good agreement and physical coherence. The specific mass loss rate at rarefied pressure was lower than obtained at dense atmospheric pressure but this difference decreases with the increase of the exposure time due to the process of densification of the carbonized layer. The low concentration of oxygen existing in the rarefied air pressure contributes to slow pyrolysis reaction during the ablation process

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