X-43 Hyper-X Program

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NASA is using the Hyper-X vehicles to test propulsion technologies that could be applied to future reusable space launchers and hypersonic aircraft.
While vehicles with conventional rocket engines carry oxygen on board, the air-breathing Hyper-X vehicles ingest and compress oxygen from the atmosphere using the vehicle airframe.
This type of propulsion system could potentially increase payload capacity on future vehicles since no onboard supply of oxidizer would be required.

Since 1990, the three-stage Pegasus rocket has conducted 30 launches and placed over 70 satellites into orbit from six separate sites worldwide. For the Hyper-X Launch Vehicle, the Pegasus rocket's second and third stages have been eliminated, as has the fairing, which is normally used to protect satellite payloads. The Hyper-X research vehicle and its adapter will ride atop the front of a specially configured Pegasus first stage solid rocket motor. A newly developed thermal protection system will protect the Pegasus composite structures against severe heating loads associated with lower-altitude hypersonic operations. Other modifications to Pegasus include upgraded first stage guidance and an avionics repackaging that permits ballasting of the booster for flight conditions between Mach 7 and 10.

The Hyper-X launch vehicle and scramjet research vehicle "stack" will be air-launched from NASA's B-52B carrier aircraft, the same one used on the original Pegasus missions in the early 1990's, as well as on the X-15 and numerous other experimental aircraft programs in the past.
The booster will accelerate the stack to a predetermined altitude and Mach number, after which the X-43A will separate from the booster and fly under its own power at seven times the speed of sound.

Currently, the world's fastest air-breathing aircraft, the SR-71 Blackbird, cruises slightly above Mach 3, or approximately 2,100 miles per hour.
Hyper-X is planned to fly faster than any air-breathing vehicle before, opening the frontier for aircraft with speeds measured in miles per second.

Mishap

On the 2th of June, 2001, the X-43A and its modified Pegasus booster rocket were launched at about 1:43 p.m. from NASA's B-52 launch aircraft flying at about 24,000 feet altitude over the Pacific Ocean several hundred miles west of the California coast.
About eight seconds after ignition of the rocket, however, a malfunction occurred that caused the Hyper-X stack-the booster and X-43A-to go out of control.
The test director ordered that the flight be terminated, and a signal was sent to the vehicle triggering an explosive charge which destroyed both the booster and the X-43A.
The debris fell harmlessly into the Pacific Ocean within the pre-cleared test range impact area. There were no injuries and no damage to the launch or chase aircraft or to property on the ground.

An interim incident investigation team headed by former astronaut Vance Brand, currently deputy director of Aerospace Projects at NASA's Dryden Flight Research Center, has begun preserving data from the flight.
A final investigation board was appointed by NASA June 4, 2024 to determine the cause of the incident.

NASA Langley carried out various wind-tunnel tests on the X-43A design in an effort to refine the vehicle's design. Dryden is working very closely with Langley in this refinement process, as well as working out the flight test issues, such as flight profile, vehicle instrumentation, and Pegasus/booster/Hyper-X adaptation and integration.

On July 23 2003 NASA released it's official mishap investigation report, which can be downloaded HERE.

The NASA mishap investigation board, charged to review the loss of the X-43A Hyper-X program research vehicle during its June 2, 2024 launch, concluded no single factor or potential contributing factor caused the mishap. The flight failed because the vehicle's control system design was deficient in several analytical modeling areas, which overestimated the system's margins.

Seventy-five minutes after takeoff, at an altitude of approximately 24,000 ft., the Pegasus was released.
Its solid rocket motor ignited 5.2 seconds later sending the launch vehicle and research vehicle payload on its test flight. Eight seconds later, the vehicle began its planned pitch up maneuver, which was expected to take it to an altitude of approximately 95,000 ft.

Shortly thereafter, the Pegasus launch vehicle began to experience a control anomaly characterized by a roll oscillation.
At 13.5 seconds after release and at an altitude of approximately 22,000 ft., structural overload of the starboard elevon occurred.
The severe loss of control caused the X-43A to deviate significantly from its planned trajectory, and as a result, it was destroyed by range safety 48.6 seconds after release.

The mishap board found the major contributors to the mishap were modeling inaccuracies in the fin actuation system, modeling inaccuracies in the aerodynamics, and insufficient variations of modeling parameters.
The flight mishap could only be reproduced when all of the modeling inaccuracies with uncertainty variations were incorporated in the analysis.

Note:
Images and information from news articles, FAS.org and NASA.gov

UPDATE (02/03/2024):

Article about the second Hyper-X captive carry test (01/26/2004).
A captive carry flight was conducted to allow X-43 engineers and technicians to test the X-43's systems at speeds and altitudes it will encounter on launch day. Analysis of data recorded during this dress rehearsal will enable the X-43 team to make the decision to launch the X-43 as early as February 21, 2004.

The flight of vehicle two is programmed for Mach 7 - seven times the speed of sound.
Now, the booster will carry less propellant and will be released from 40,000 feet instead of 20,000 feet as was done in the first flight. Due to risky nature of the flight, the experimental aircraft will fly in the Naval Air Warfare Center Weapons Division Sea Range over the Pacific Ocean off the coast of southern California, where after powered flight, it will glide to a safe impact and sink. NASA's Langley Research Center, Hampton, Va., and Dryden Flight Research Center, Edwards, Calif., conduct the Hyper-X program jointly.

The booster will accelerate the experimental vehicle to Mach 7 at approximately 95,000 feet altitude. At booster burnout, the X-43 will separate and fly under its own power on a preprogrammed path.

The third vehicle of the series is planned to reach Mach 10. Using an air-breathing scramjet engine instead of conventional rocket power, the X-43A could be the forerunner in providing faster, more reliable and less expensive access to space.

UPDATE (03/27/2004):

X-43A Soars on Scramjet Power Source: NASA Press Release

NASA's second X-43A hypersonic research aircraft flew successfully today, the first time an air-breathing scramjet powered aircraft has flown freely.

The unpiloted vehicle's supersonic combustion ramjet, or scramjet, ignited as planned and operated for the duration of its hydrogen fuel supply. The X-43A reached its test speed of Mach 7, or seven times the speed of sound.

The flight originated from NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif. Taking off at 12:40 p.m. PST, NASA's B-52B launch aircraft carried the X-43A, which was mounted on a modified Pegasus booster rocket. The booster was launched from the B-52B just before 2 p.m. PST. The rocket boosted the X-43A up to its test altitude of about 95,000 ft. over the Pacific Ocean, where the X-43A separated from the booster and flew freely for several minutes. During the free flight, the scramjet engine operated for about 10 seconds.

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UPDATE (11/15/2004):

NASA's X-43A Scramjet Breaks Speed Record Source: NASA Press Release

NASA's X-43A research vehicle screamed into the record books today, demonstrating an air-breathing engine can fly at nearly 10 times the speed of sound. Preliminary data from the scramjet-powered research vehicle show its revolutionary engine worked successfully at approximately Mach 10, nearly 7000 mph, as it flew at an altitude of approximately 110,000 feet.

The flight took place in restricted airspace over the Pacific Ocean northwest of Los Angeles. The flight was the last and fastest of three unpiloted tests in NASA's Hyper-X Program. The program's purpose was to explore an alternative to rocket power for space access vehicles.

"This flight is a key milestone and a major step toward the future possibilities for producing boosters for sending large and critical payloads into space in a reliable, safe, inexpensive manner," said NASA Administrator Sean O'Keefe. "These developments will also help us advance the Vision for Space Exploration, while helping to advance commercial aviation technology," Administrator O'Keefe said.

NASA's Photo Collection: NASA Dryden X-43 photo collection