posted 08-12-2011 04:02 AM               

DARPA Hypersonic Vehicle Advances Technical Knowledge

HTV-2 collects unique data during several phases of second flight

Today, DARPA attempted to fly the fastest aircraft ever built. The Agency's Falcon Hypersonic Technology Vehicle 2 (HTV-2) is designed to fly anywhere in the world in less than 60 minutes. This capability requires an aircraft that can fly at 13,000 mph, while experiencing temperatures in excess of 3500F.

The second test flight began with launch at 0745 Pacific Time. The Minotaur IV vehicle successfully inserted the aircraft into the desired trajectory. Separation of the vehicle was confirmed by rocket cam and the aircraft transitioned to Mach 20 aerodynamic flight.

This transition represents a critical knowledge and control point in maneuvering atmospheric hypersonic flight. More than nine minutes of data was collected before an anomaly caused loss of signal.

Initial indications are that the aircraft impacted the Pacific Ocean along the planned flight path.

"Here's what we know," said Air Force Maj. Chris Schulz, DARPA HTV-2 program manager and PhD in aerospace engineering. "We know how to boost the aircraft to near space. We know how to insert the aircraft into atmospheric hypersonic flight. We do not yet know how to achieve the desired control during the aerodynamic phase of flight."

"It's vexing; I'm confident there is a solution. We have to find it."

"Prior to flight, the technical team completed the most sophisticated simulations and extensive wind tunnel tests possible. But these ground tests have not yielded the necessary knowledge. Filling the gaps in our understanding of hypersonic flight in this demanding regime requires that we be willing to fly," said DARPA Director Regina Dugan. "In the April 2010 test, we obtained four times the amount of data previously available at these speeds. Today more than 20 air, land, sea and space data collection systems were operational. We'll learn. We'll try again. That's what it takes."

According to Schulz, three technical challenges exist within this HTV-2 flight regime. They are categorized as aerodynamic; aerothermal; and guidance, navigation and control. And each phase of flight introduces unique obstacles within these areas.

"To address these obstacles, DARPA has assembled a team of experts that will analyze the flight data collected during today's test flight, expanding our technical understanding of this incredibly harsh flight regime," explained Schulz. "As today's flight indicates, high-Mach flight in the atmosphere is virtually uncharted territory. "

In the coming weeks, the assembled independent Engineering Review Board will review and analyze the data collected. This data will inform policy, acquisition and operational decisions for future Conventional Prompt Global Strike programs — the goal of which, ultimately, is to have the capability to reach anywhere in the world in less than one hour.

posted 08-19-2011 12:20 PM               

DARPA Hypersonic Vehicle Splash Down Confirmed

Flight 1 engineering changes believed effective

On Thursday, 11 August, the HTV-2 experienced a flight anomaly post perigee and into the vehicle's climb. The anomaly prompted the vehicle's autonomous flight safety system to use the craft's aerodynamic systems to make a controlled descent and splash down into the ocean. Controlled descent is a term typically associated with a human-in-the-loop directing or guiding the unscheduled landing of an aircraft. For DARPA's Hypersonic Technology Vehicle 2 (HTV-2) controlled descent takes on new meaning thanks to the vehicle's safety system.

"We've confirmed that the HTV-2 made impact with the Pacific Ocean along its flight trajectory as planned in the event of an anomaly," explained Air Force Maj. Chris Schulz, DARPA HTV-2 program manager and PhD in aerospace engineering. "This flight safety system is a significant engineering advance in that the system prompts a vehicle to monitor the parameters under which it is operating and exercise safety protocols completely autonomously should those parameters be breached."

"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."

During the reentry phase of the flight plan, the craft is traveling at Mach 20, under extreme conditions as it attempts to enter the glide phase of flight. In the coming weeks an independent ERB will investigate the most probable causes of the new anomaly encountered during the second test flight of HTV-2.

posted 08-19-2011 05:10 PM               

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Originally posted by garymilgrom:
How does this jibe with the space shuttle's record of over 130 flights through the atmosphere starting at Mach 25? Is that experience not relevant?

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What is different here is shuttle is essentially a giant air brake designed to slow down once it enters the atmosphere and it constantly slows down all the time as it goes deep and deeper. While it can encounter some pretty high mach numbers coming back, its structure isn't really designed for sustained flight at high mach speeds in atmosphere as the TPS would burn up if it sustains more of a heat load than it can dissipate over a certain period of time.