The scientific tourist #83 — heatsink nosecone

This week’s image comes to you from the U. S. Air Force Space and Missile Museum at Cape Canaveral Air Force Station, Florida. It’s an early “heatsink” style test re-entry vehicle, designed to be carried on the nose of an Atlas ICBM:

In the 1950’s, the U.S. military (and its industrial partners) faced a daunting task in the design of a capsule that could successfully re-enter the Earth’s atmosphere after a trip halfway across the globe. In a typical ICBM flight, the atmosphere ahead of the warhead would be heated to temperatures in excess of 12,000 deg. F — some 2,000 degrees hotter than the surface of the Sun. A number of different approaches to dealing with this heating were tested:

  • Heat sink — a thick plate of metal with good thermal conductivity (like copper) would be used to absorb the heat of re-entry, while insulation behind the heat sink protected the warhead and its electronics
  • Transpiration cooling — water would be injected at the front of the vehicle, absorbing heat as it flashed into steam
  • Ablative cooling — a shield made of a resinous material would char from re-entry heating, resulting in effects similar to transpiration (from gasses generated during the charring process), as well as cooling resulting from the absorption of heat by the charring shield
  • Hot structure — tiles made from metal with a high melting point covered the surface of the vehicle; insulation behind the tiles then kept the vehicle structure down to a relatively cool 200 F

Heat sink technology was simple, if very heavy — so it provided thermal protection for the first ICBM warheads that the U.S. fielded. But testing soon proved the superiority of ablative cooling of re-entry vehicles, rapidly becoming the predominant technology for protecting both warheads and (later) manned spacecraft from the heat of atmospheric re-entry.

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