We don’t know what caused the problems but given the maneuvers to be investigated “coupling” could have been a concern given the vehicle “tailless” configuration. All speculation of course. Makes for some good reading from a historical perspective.
Regards
Robert
http://www.nasa.gov/centers/dryden/pdf/88484main_H-2106.pdf
So why go tailless? Shuttle and X-37 have them. Would a tail be an obstacle in reaching the L/D goals at the expense of more difficult control? Or is the tail more important for a vehicle that wants to go subsonic at some point? Just curious and wanting to learn more.
At hypersonic speeds appendages are high heat areas especially if the vehicle spends a lot of its time in the denser atmosphere. They may also be considering the stealth ability in a tailless configuration in a military application.
I'd wondered if the tailless-ness might be stealth-related -- makes sense. Of course, losing control and falling out of the sky isn't exactly stealthy ... nor, for that matter, is a daylight-visible plasma trail. Have to wonder what their options are at this point.
Huh?, the super heated ion trail it leaves in it's wake will negate any stealth technology it employs.
Stealth will vary at different parts of the flight regime. My comment was only at low mach velocities or exo-atmospheric. I guess unless we know the mission profile, all is spec. Maybe we can invite the chief designer in for a Q&A… Think he’ll take us up?
Think he’ll take us up?
Considering it is now Zero for Two, I think I'll pass on the ride
Think he’ll take us up?
Considering it is now Zero for Two, I think I'll pass on the ride
Heh.
True, but remember they were both built before the first flight, so they couldn’t make many changes after the initial failure.
The accident investigation report is now out.
A technology demonstration and data-gathering platform, the HTV-2’s second test flight was conducted to validate current models and increase technical understanding of the hypersonic regime. The flight successfully demonstrated stable aerodynamically-controlled flight at speeds up to Mach 20 (twenty times the speed of sound) for nearly three minutes. Approximately nine minutes into the test flight, the vehicle experienced a series of shocks culminating in an anomaly, which prompted the autonomous flight safety system to use the vehicle’s aerodynamic systems to make a controlled descent and splashdown into the ocean.
“The initial shockwave disturbances experienced during second flight, from which the vehicle was able to recover and continue controlled flight, exceeded by more than 100 times what the vehicle was designed to withstand,” said DARPA Acting Director, Kaigham J. Gabriel. “That’s a major validation that we’re advancing our understanding of aerodynamic control for hypersonic flight.”
The ERB concluded that the “most probable cause of the HTV-2 Flight 2 premature flight termination was unexpected aeroshell degradation, creating multiple upsets of increasing severity that ultimately activated the Flight Safety System.”
Based on state-of-the-art models, ground testing of high-temperature materials and understanding of thermal effects in other more well-known flight regimes, a gradual wearing away of the vehicle’s skin as it reached stress tolerance limits was expected. However, larger than anticipated portions of the vehicle’s skin peeled from the aerostructure. The resulting gaps created strong, impulsive shock waves around the vehicle as it travelled nearly 13,000 miles per hour, causing the vehicle to roll abruptly. Based on knowledge gained from the first flight in 2010 and incorporated into the second flight, the vehicle’s aerodynamic stability allowed it to right itself successfully after several shockwave-induced rolls. Eventually, however, the severity of the continued disturbances finally exceeded the vehicle’s ability to recover.
http://www.darpa.mil/NewsEvents/Releases/2012/04/20.aspx
