Reentry Col John E. Keesee MIT Dept of Aeronautics and Astronautics November 25, 2003 Background ? An ICBM with a range of 6500 miles has a stagnation temperature of 12,000 oF, 2000 oF hotter than the surface of the sun ? Calculations showed that the optimum design for structural strength, resistance to heating, and free flight stability was a long, needle nosed reentry body – But it would vaporize during reentry Background ? Harry Julian Allen proposed an alternate solution, using pencil and paper – Contradicted 50 years of research – Suggested a blunt body would better put more of the heat the air and less into the body – Strong bow shockwave Background ? Still needed unusual materials to survive the extreme heating conditions – Heat sinks ? Copper, tungsten, molybdenum, beryllium ? Shuttle – Ablators ? Teflon, nylon, fiberglass ? Mercury, Gemini, Apollo, ICBMs Thermal Barrier 2 2 1 2 2 c c V m Q QmVKE = == Material Energy to Vaporize BTU/lb Melting Temperature oR Tungsten 1870 6500 Titanium 3865 3700 Beryllium oxide 13,400 2900 Graphite 28,700 6800 Stagnation Temperature po pop CVT VTCTC 2/ 2/ 2 2 ∞ ∞∞ = += V (fps) To oR 10,000 8,325 20,000 33,300 26,000 56,277 How Much Heat Actually Enters the Body Reentry Body Shapes ? http://kittyhawk.public.hq.nasa.gov/essay/ Evolution_of_Technoogy/reentry/Tech19.h tm