AAWSAP DIRD, Space Access: Where We’ve Been and Where We Could Go, March 2010

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Al Draper assembled the ASSET (Aerothermodynamic Structural and System
Environmental Test) experimental flight-test program to evaluate current U.S. Air Force
and NASA materials for hypersonic entry vehicles. The intent was to launch a test
vehicle from an Air Force Thor IRBM in the 18,000 to 20,000 feet/second range and
recover the vehicle. The ASSET glider was approximately the forward portion of the X­
20 Dynasoar vehicle and is shown in Figure 25 after recovery. Except for the carbon
leading edges, the materials generally performed as required. As a result, a small team
of McDonnell Douglas Astronautics Company engineers and model builders began
working on an alternative approach for the leading edges. This team's efforts resulted
in the heat pipe leading edge shown in Figure 26, a series of formed stainless steel
tubes brazed together to form a leading edge based on NASA space shuttle
requirements. The tubes contained a stainless steel mesh wick and were filled with
metallic sodium.
figure 25. FOL ASSET flight-Tested From Orbital
Figure 26. Heat Pipe Shuttle Leading Edge
Speeds To Evaluate 1960s' Materials. Carbon
Designed and Built by McDonnell Douglas
leading edges proved the least durable.
Astronautics. Tested extensively at McDonnell
Douglas Corporation, St. Louis, and NASA Langley, it
never failed .
The leading edge was tested in NASA Langley's 8-foot High-Temperature Structures
Tunnel, the NASA Langley Radiation Thermal Test Facility and the McDonnell Douglas
Graphite Thermal-Altitude Test Facility (graphite radiation heaters within a vacuum
altitude chamber). All of these tests showed the installed leading edge to be durable,
robust, and lightweight (equaled the installed NASA carbon-carbon leading edges).
Starts from cold tubes showed the sodium melts and began the heat pump process
without any difficulties. Because this leading edge was made by the engineers and
mechanics as a one of a kind, the tubes developed thermal shorts and other problems
over the span of the testing, all of which were rectified before the test continued.
Although brittle and difficult to manufacture, this leading edge met the
thermodynamacists' solution of a simple radiation structure, not a heat pump. 13
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