Air resistance is helpful in slowing down the rate at which re-entry capsules of space missions are pulled back to the Earth by gravity. But the friction generated by the capsules hurtling earthwards results in extremely high temperatures. As they re-enters the Earth's atmosphere at supersonic speed, heat is released by the surrounding gas moving against the vehicles' surface. To keep them from burning up, like meteorites when they fall to earth, re-entry capsules fly backwards to slow themselves down and enter the atmosphere at the correct angle. Furthermore, they need to be the correct shape and be covered in the appropriate material. The heat shield needed to survive re-entry has helped drive the development of several new technologies. The aim of the EU-funded 'Radiation-shapes thermal protection investigations for high-speed Earth re-entry' (RASTAS SPEAR) project was the maturation of some key technologies. The initiative was also successful in providing strong technological bases for the preparation of future sample return missions. In addition, project results feed into the design of ESA's MarcoPolo-R Mission to a primitive near-Earth asteroid. To provide a better understanding of phenomena that play a role in the supersonic entry, the RASTAS SPEAR project reviewed the capabilities and limitations of testing facilities. The shock wave formed ahead of the re-entry vehicles and the flow of gas around them can be reproduced in supersonic plasma wind tunnels. The review addressed operation principles of the existing facilities with the testing methodologies applied, as well as all equipment used for collecting measurements. Based on the results of these comparisons, the RASTAS SPEAR partners designed new equipment and methodologies to simulated pressure changes encountered during re-entry. Theoretical models based on computational fluid dynamics were developed for the analysis of impact to the thermal protection system (TPS) of the capsules. The RASTAS SPEAR researchers also combined and tested new crushable materials that can absorb the impact forces and adhesives for joining blocks of a TPS with improved performance. A demonstrator representative of the thermal shield of sample-return mission was designed for testing in plasma wind tunnels. The tests were carried out at Italy's Scirocco plasma wind tunnel in Capua, near Naples, one of the few sites worldwide where such testing is possible. The demonstrator proved that it indeed functions as planned and mathematical modelling is accurate, opening new exciting opportunities for space exploration missions.
Re-entry capsule, planetary exploration, space mission, atmosphere, plasma wind tunnel, thermal shield, computational fluid dynamics