Comments on Various Consequences: Second HTV-2 Flight Test

Hypersonic flight isn't just based on these se...

2012-02-01T00:32:34.504-05:00

Hypersonic flight isn't just based on these set of specific theories. It correlates as well to existing and tested space flight technologies.

"Filling the gaps in our understanding of hyp...

2011-08-19T07:59:46.495-04:00

"Filling the gaps in our understanding of hypersonic flight in this demanding regime requires that we be willing to fly." --Regina Duncan, DARPA

“According to a preliminary review of the data collected prior to the anomaly encountered by the HTV-2 during its second test flight,” said DARPA Director Regina Dugan, “HTV-2 demonstrated stable aerodynamically controlled Mach 20 hypersonic flight for approximately three minutes. It appears that the engineering changes put into place following the vehicle’s first flight test in April 2010 were effective. We do not yet know the cause of the anomaly for Flight 2.”

A detailed analysis conducted by an independent Engineering Review Board following the first flight test, prompted engineers to adjust the vehicle’s center of gravity, decrease the angle of attack flown and use the onboard reaction control systems to augment vehicle flaps during the vehicle’s second flight test. Those changes appear to have been effective. “An initial assessment indicates,” said Schulz, “that the Flight 2 anomaly is unrelated to the Flight 1 anomaly.”
DARPA PR

Day on "control coupling" (my emphasis):...

2011-08-14T17:37:35.606-04:00

Day on "control coupling" (my emphasis): Because this phenomenon had not previously been encountered, no identifying label, such as inertial coupling or dutch roll, existed. The phenomenon was simply referred to as the control parameter. Eighteen years later, Rockwell engineers using wind-tunnel data rediscovered that this instability would occur during the Space Shuttle entry and solved the problem by use of reaction rockets and a sophisticated computer control system; neither of which was available during the X-2 program.

The fixes used by the Rockwell engineers sound quite similar to the fixes DARPA implemented after the first HTV-2 flight test (I imagine they were already using a "sophisticated computer control", my emphasis): For its second test flight, engineers adjusted the vehicle’s center of gravity, decreased the angle of attack flown, and will use the onboard reaction control system to augment the vehicle flaps to maintain stability during flight operations.
Hypersonic Aircraft Ready for Launch