Lately, I have been examining the entire history of hypersonics research and technology, with a particular focus on the re-entry problem and ablation for small vehicles, such as those from ballistic missiles. While reviewing the writings of Wernher von Braun, I was amused to find that he joked about using frozen balsa wood as a potential material for re-entry vehicles. The re-entry challenge was initially posed to the scientific community by Theodore von Kármán of CalTech GALCIT and JPL as one of the most formidable problems to solve.
Early aerodynamic designs, borrowed from supersonic studies, often featured pointed shapes; however, these were soon discounted by experimental results at NASA and associated analysis. Test rocket programs, which explored ballistic trajectories at varying speeds and altitudes, revealed that aerodynamic ‘heating ‘heat barrier’ was the primary problem – unlike in supersonics, where the sound barrier was the main concern.
Ultimately, materials such as glass substrates and nylon were the first to be successfully used as ablative materials. This is quite different from today’s approaches, which involve advanced materials, composites, and sophisticated analyses for active cooling or modern ablative materials.