What Part of an Aircraft Going Mach 20 Can You See? The Back End.

On Thursday, Aug. 11, DARPA demonstrated stable aerodynamically controlled Mach 20 flight for nearly three minutes in its attempt to fly the fastest aircraft ever flown. This feat was the result of many scientific and technological advances.

Preliminary analysis suggests a clean separation of the HTV-2 from the Minotaur IV launch vehicle. Furthermore, an initial review of the data collected during the flight test reinforces that the Minotaur IV launch vehicle again successfully delivered the HTV-2 to its preprogrammed release point, at the appropriate velocity and orientation. This is not an easy task. According to Air Force Maj. Chris Schulz, HTV-2 program manager and PhD in aerospace engineering, “What the Minotaur IV did was make a three-point shot from the California coastline into a basket between California and Hawaii.”

Most launch vehicles spend very little time — and perform minimal maneuvers — inside the atmosphere. To deliver the HTV-2 to the required mission start point, the Minotaur IV spent its entire flight inside the atmosphere while safely and reliably performing a series of aggressive banks and turns.

Throughout the flight, more than 20 air, land, sea and space data collection systems were operational. Scientists believe that very high-quality data collected from the combined test range assets will aid our further understanding of this unique flight environment.

Data collection assets also provided visuals of flight from the ground. “We were fortunate to also obtain handheld camera footage of the HTV-2 flight. It gives us a visceral feel for what it means to fly at Mach 20,” says DARPA Director Regina Dugan. A video released last week shows how rapidly a vehicle can travel from horizon to horizon at Mach 20. The video was captured from a handheld camera operated by a crewmember aboard the Pacific Tracker — the first sea-born telemetry collection asset able to visually monitor the HTV-2’s initial entry into the atmosphere.

A second video provides an animated visual comparison between the speeds of the HTV-2 at Mach 20, the F18 at Mach 1.5 and the C-5 at Mach .6.

As a test flight, with the goal to validate current assumptions and increase technical understanding of the hypersonic regime, successful collection of data by the largest collection of test assets ever assembled to monitor a test flight was critical. “Data collection was so important during HTV-2 flight tests that 25 to 30 percent of the total test flight cost was spent on collection assets,” explained Schulz.

It’s from the initial analysis of data collected by those assets that another preliminary data point emerges. “We’ve been working for more than 50 years to identify how to predict when the transition from laminar to turbulent flow will occur. This allows us to assess when a vehicle is about to experience its highest drag and heat load. Initial assessment of the data indicates that our pre-flight models successfully predicted transition to within ten seconds of actual transition point,” explained Dugan. “If this information proves true upon further analysis, we’ll have a better understanding of overall system capability and flight dynamics — how far it can fly with more accuracy.”


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