Sunday, March 15, 2009

Navy NP-3D Orion will fly below Discovery during re-entry

This flight experiment is designed to demonstrate that a protuberance
on a BRI-18 tile is safe to fly. BRI-18 is a tile originally
developed as a potential heat shield upgrade on the orbiters and is
being considered for use on the Orion crew exploration vehicles. Due
to Orion's geometry, the tiles would experience re-entry heating
temperatures up to 3,400 degrees Fahrenheit, about 500 degrees higher
than the 2,900 degrees experienced by shuttles.

Tested successfully in arc jet facilities, this phase of the
experiment will gather information on the effect of high Mach number
boundary layer transition caused by a protuberance on the space
shuttle during the re-entry trajectory. Boundary layer transition is
a disruption of the smooth, laminar flow of supersonic air across the
shuttle's belly and occurs normally when the shuttle's velocity has
dropped to around eight to 10 times the speed of sound, starting
toward the back of the heat shield and moving forward. Known as
"tripping the boundary layer," this phenomenon can create eddies of
turbulence that, in turn, result in higher downstream heating.

For the experiment, a heat shield tile with a "speed bump" on it was
installed under Discovery's left wing to intentionally disturb the
airflow in a controlled manner and make the airflow turbulent. The
bump is four inches long and 0.3 inch wide. Ten thermocouples will be
installed on the tile with the protuberance and on tiles downstream
to capture test data. The experiment will receive additional support
from a U.S. Navy aircraft that will check the orbiter's exterior
temperatures. A Navy NP-3D Orion will fly below Discovery during
re-entry and use a long-range infrared camera to remotely monitor
heating to the shuttle's lower surface. The imagery captured and
recorded will complement the information collected by the on board
instruments. Both will be used to verify and improve design efforts
for future spacecraft.

Keith Stein
DC Space News Examiner

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