On March 27, 2004, NASA’s X-43A shattered existing speed records for aircraft with air-breathing engines when the scramjet-powered vehicle reached a speed of Mach 6.83 (4,900 mph) during a brief flight over the Pacific Ocean. The record speed was more than twice as fast as the SR-71 Blackbird, which could cruise at Mach 3.32 (2,193 mph), and bested even the rocket-powered X-15A-2, which reached Mach 6.7 (4,520 mph) in October 1967.
Perhaps most significant, this was the first time a scramjet engine – a ramjet configuration that allows supersonic airflow through the combustion chamber – was used to accelerate a vehicle in flight.
Having exhausted its small amount of hydrogen fuel, the autonomously operated X-43A, a subscale craft with no onboard crew, performed a series of maneuvers that collected 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 plummeted into a planned impact zone within the Pacific Missile Test Range. Researchers from both Dryden and NASA’s Langley Research Center, Hampton, Va., eagerly studied this data and compared it with predictive models in the ensuring months.
The flight was part of an ambitious program to advance research in high-speed air-breathing propulsion technologies from laboratory experiments to flight test. The multi-year effort, called Hyper-X, was aimed at conducting flight research in the hypersonic speed regime – above Mach 5, or more than 3,600 mph.
Brad Neal served as lead operations engineer for the program at NASA Dryden, recently renamed in honor of former astronaut and flight research pilot Neil A. Armstrong. Now chief engineer at NASA Armstrong, Neal looks back at the Hyper-X achievements 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 in June 2001 was cut short due to a malfunction of the booster rocket used to propel the craft to scramjet ignition speeds. Following the successful second flight, a third and final test of the X-43A on November 16, 2004, achieved a new record speed of Mach 9.68 (6,600 mph).
Joel Sitz, currently Deputy Associate Director for Programs at NASA Armstrong, managed flight-testing of the X-43A from July 1998 to December 2004.
“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.”
Sitz believes the Hyper-X accomplishments have 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.