Hot Structure Approaches

Another option for thermal protection during entry was the use of exotic, high-temperature materials for the external surface that could re­radiate the heat back into space. This concept was proposed for the X-20 Dyna-Soar program, and the vehicle was well under construc­tion at the time of cancellation.[755] In parallel with the X-20 program, the Air Force Flight Dynamics Laboratory developed a small radia – tive-cooled hot structure vehicle (essentially the first 4 feet of the X-20 Dyna Soar’s nose), called the McDonnell Aerothermodynamic/elastic Structural Systems Environmental Tests (ASSET). The ASSET design used the same materials and thermal protection concepts as the X-20 and first flew in September 1963, 3 months before cancellation of the Dyna-Soar. The fourth ASSET vehicle successfully completed a Mach 18.4 entry from 202,000 feet in 1965. Postflight examination indicated

it survived the entry well, although the operational problems and man­ufacturing methods for these exotic materials were expensive and time­consuming. Since that time, joint NASA-Air Force-Navy-industry devel­opmental programs such as the X-30 National Aero-Space Plane (NASP) effort of the late 1980s to early 1990s have advanced materials and fabri­cation technologies that, in due course, may be applied to future hyper­sonic systems.[756]