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Ames Research Center has been developing new ultrahigh temperature ceramics
(UHTC) for potential use in the sharp leading edges of future space vehicles.
These materials have been developed and tested in ground-based arc-jet
facilities, and a flight test program called SHARP (slender hypervelocity
research aerothermodynamic research probes) has been initiated. The first flight
demonstration, SHARP-B1, incorporated a 0.141-inch-radius UHTC nose-tip on a
U.S. Air Force reentry vehicle in collaboration with Sandia National Laboratory;
it was successfully flown in May 1997. The second flight test, SHARP-B2,
incorporates four instrumented UHTC strakes mounted on the side of the entry
vehicle; it is scheduled to fly in June 2000. The goal of these flight tests is
to assess the performance of the materials under realistic entry conditions.
Computational fluid dynamics (CFD) simulations of the flight environment have
been performed to aid in the design of the test hardware and instrumentation,
and simulations of critical qualifying ground tests in the arc-heated wind
tunnels have been performed to aid in test interpretation and instrument
checkout, and to show traceability of the ground-test environment to flight.
Figure 1 shows computed heat-transfer profiles on the surface of the flight
vehicle and the test article in the arc-heated wind tunnel. Although simulation
of the complex-flow physics in the arc-heated wind tunnel is difficult, the goal
of the simulations is to understand the flow environment well enough that the
similarities and differences in the flight conditions can be assessed. Initial
comparisons between the CFD and arc-jet data are generally within 40% for heat
transfer and 5% for pressure, giving some confidence in the predictive method.
The CFD predictions will be compared with flight results once they are
available.
Point of Contact: M. Loomis
(650) 604-6578
mloomis@mail.arc.nasa.gov
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Fig. 1. Heat-transfer profiles for flight vehicle and test article. Flight: Modified MK-12 RV launched on Minuteman III.
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