X-43A hypersonic research aircraft
March 27, 2014

Hypersonic Record Set A Decade Ago By NASA X-43A Scramjet

Source Material Provided by NASA

NASA's X-43A shattered existing speed records for aircraft with air-breathing engines on March 27, 2004, when the scram-jet powered plane reached Mach 6.83 - 4,900 miles per hour - during a brief flight over the Pacific Ocean. This new speed record was more than twice as fast as the SR-71 Blackbird, which could cruise at Mach 3.32—2,193 mph. The X-43A's speed even bested the rocket-powered X-15A-2, which had set a record of Mach 6.7 - 4,520 mph - in October 1967.

Even more importantly, this event marks the first time a scramjet engine was used to accelerate a vehicle in flight. A scramjet engine is a ramjet configuration that allows supersonic airflow through the combustion chamber.

The X-43A was autonomously operated, meaning it was a subscale craft with no onboard crew. After the craft exhausted its small amount of hydrogen fuel, it performed a series of maneuvers that allowed scientists to collect hypersonic aerodynamic data that was telemetered back to a control room at what was then NASA's Dryden Flight Research Center. Finally, the X-43A fell into a planned impact zone inside the Pacific Missile Test Range. The data was studied by scientists from both Dryden and NASA's Langley Research Center, who then compared it with predictive models in the following months.

The record-breaking flight was part of an ambitious program to advance research in high-speed air-breathing propulsion technologies from laboratory experiments to flight test. The program, Hyper-X, was a multi-year effort designed to conduct flight research in the hypersonic speed regime—specifically, above Mach 5, or more than 3,600 mph.

At NASA Dryden, recently renamed in honor of former astronaut and research flight pilot Neil A. Armstrong, Brad Neal served as lead operations engineer for the program. He is now the chief engineer at NASA Armstrong, and looks back on the Hyper-X program with pride.

“It was the first demonstration of an integrated scramjet in atmospheric flight,” he recalled. “Nothing like that had ever been attempted before.”

An earlier flight had been scheduled for June 2001, but was cut short due to a malfunction of the booster rocket used to propel the craft to scramjet ignition speeds. A third, and final test of the X-23A occurred on November 16, 2004. This flight achieved a new record of Mach 9.68—6.600 mph.

Joel Sitz managed flight-testing of the X-43A from July 1998 to December 2004. He is currently the Deputy Associate Director for Programs at NASA Armstrong.

"The successful Hyper-X flights were the aeronautical equivalent of landing on the moon,” he said. “We had to overcome tremendous technical and operational challenges.”

According to Sitz, the Hyper-X accomplishments opened up the hypersonic frontier.

“Scramjets have now been proven to work and turbine technology is maturing with materials designed to withstand temperatures at Mach 4, the transition region for converting to ramjet or scramjet propulsion through Mach 10 and beyond,” Sitz noted. "A turbine-based, combined-cycle propulsion system could be used to power an aerospace vehicle capable of taking off and landing on a conventional runway, potentially lowering launch costs while increasing mission flexibility. Developing and testing such a system would be a significant scientific and engineering challenge."

“We need to integrate all these propulsion cycles and see what can be discovered,” he concluded.