NASA made aviation history with the first and

second successful flights of a scramjet-powered airplane at hypersonic speeds—speeds

greater than Mach 5 or five times the speed of

sound. Compared to a rocket-powered vehicle

like the Space Shuttle, scramjet (supersonic

combustion ramjet) powered vehicles promise

more airplane-like operations for increased

affordability, flexibility and safety for ultra highspeed flights within the atmosphere and into

Earth orbit. Because they do not have to carry

bulky oxygen tanks, as rockets must, vehicles

powered by air-breathing scramjets can be

smaller and lighter. 

Researchers have worked for decades to

demonstrate scramjet technologies, first in

wind tunnels and computer simulations, and

now in an airplane in flight. Ultimate applications include future hypersonic missiles, hypersonic airplanes, the first stage of two-stage-toorbit reusable launch vehicles and singlestage-to-orbit reusable launch vehicles.

High-Risk, High-Payoff Program

The eight-year, approximately $230 million

NASA Hyper-X program was a high-risk, highpayoff research program. It undertook challenges never before attempted. No vehicle

powered by an air-breathing engine had ever

flown at hypersonic speeds before the successful March 2004 flight. In addition, the rocket boost and subsequent separation from the

rocket to get to the scramjet test condition had

complex elements that had to work properly for

mission success. Careful analyses and design

were applied to reduce risks to acceptable levels; even so, some level of residual risk was

inherent to the program.

NASAFacts

National Aeronautics and Space Administration

NASA Hyper-X Program

Demonstrates Scramjet

Technologies

X-43A Flight Makes Aviation History

A modified Pegasus booster rocket ignites moments after release from the B-52B, beginning

the acceleration of the X-43A over the Pacific Ocean in March of 2004. The X-43A vehicle is

mounted on the nose of the rocket.

www.nasa.gov
Hyper-X research began with conceptual

design and wind tunnel work in 1996. Three

unpiloted X-43A research aircraft were built.

Each of the 12-foot-long, 5-foot-wide lifting

body vehicles was designed to fly once and

not be recovered. They are identical in appearance, but engineered with slight differences

that simulate variable engine geometry, generally a function of Mach number. The first and

second vehicles were designed to fly at Mach 7

and the third at Mach 10. At these speeds, the

shape of the vehicle forebody served the same

purpose as pistons in a car, compressing the

air as fuel is injected for combustion. Gaseous

hydrogen fueled the X-43A.

The Record-Breaking Flights

After the first flight attempt in June of 2001 failed

when the booster rocket went out of control, the

second and third attempts resulted in highly successful, record-breaking flights. Mach 6.8 was

reached in March of 2004, and Mach 9.6 was

reached in the final flight in November of 2004. 

At nearly 5,000 mph, the March flight easily broke

the previous world speed record for a jet-powered (air breathing) vehicle. The X-43A research

vehicle was boosted to 95,000 feet for a brief preprogrammed engine burn at nearly Mach 7, or

seven times the speed of sound. During its third

and final flight—at nearly Mach 10—the X-43A

research vehicle flew at approximately 7,000 mph

at 110,000 feet altitude, setting the current world

speed record for an air-breathing vehicle. 

The Mach 10 research vehicle featured additional thermal protection, since expected heating was roughly twice that experienced by the

Mach 7 vehicle. Carbon-carbon composite

material, for instance, was added to the leading

edges of the vehicle’s vertical fins to handle the

higher temperatures. 

Both flights began with the stack being carried

by a B-52B aircraft from NASA’s Dryden Flight

Research Center to a predetermined point over

the Pacific Ocean, 50 miles west of the Southern

California coast. Release altitude from the B-52B

was 40,000 feet for both successful flights. At

100,000

Altitude,

ft

Air launch

Ascent

Distance

Experiment

 completion

Energy maneuvers to

 reduce speed/energy

Descent

Hyper-X free flight

Scramjet engine

 start

Hyper-X booster

 separation

Booster burn-out

(Over water) 40,000

Each of the Hyper-X research vehicles will achieve test speed and altitude with the help of the NASA

Dryden B-52B aircraft and an expendable booster rocket, as shown in this simplified flight trajectory.

Hyper-X vehicle configuration.
that point, each stack was dropped and the

booster lifted each research vehicle to its unique

test altitude and speed. 

Other than differences of altitude, speed and distance covered, the Mach 10 flight profile followed

that of the Mach 7 flight: The Mach 10 research

vehicle separated from the booster and flew

under its own power and preprogrammed control. Shortly after separation from the booster

rocket, its scramjet engine operated for about

ten seconds obtaining large amounts of unique

flight data for an airframe-integrated scramjet. The

engine thrust was very close to its design value

in each flight—sufficient to accelerate the vehicle

during the Mach 7 flight and to allow the vehicle to

cruise at constant velocity in the Mach 10 flight. 

In each case, when the scramjet engine test was

complete, the vehicle went into a high-speed

maneuvering glide and collected nearly ten minutes of hypersonic aerodynamic data while flying

to a mission completion point, hundreds of miles

due west (450 miles at Mach 7, 850 miles at

Mach 10) in the Naval Air Warfare Center

Weapons Division Sea Range off the southern

coast of California. Each vehicle splashed into

the ocean, as planned, and was not recovered.

Guinness World Records has recognized both

the Mach 6.8 and Mach 9.6 accomplishments

and has listed the flights on their web site and in

the 2006 edition of their book of records. Prior to

the 2004 X-43A flights, the previous record was

held by a ramjet-powered missile that achieved

slightly over Mach 5. The highest speed

attained by a rocket-powered airplane, the X-15

aircraft, was Mach 6.7. The fastest air-breathing,

crewed vehicle, the SR-71 achieved slightly over

Mach 3. The X-43A more than doubled the top

speed of the jet-powered SR-71.

2001 Flight and Investigation

The first flight attempt of the X-43A was in June

of 2001. Unfortunately, the booster failed and

had to be destroyed early in flight. As a result,

the research vehicle was not tested because it

never reached test conditions. Although no single contributing factor was found, the root cause

of the problem was identified as the booster’s

flight control system. The booster failed due to

inaccurate design models that overestimated

the capability of the flight control system to

operate within predicted flight conditions.

Numerous actions were taken in response to

the findings. Wind tunnel tests were conducted

to provide data to reduce atmospheric loads

on the booster’s control surfaces, more powerful booster fin actuators were added to overWind tunnel tests were a necessary step before the first flight attempt, as in this Mach 7 test of a full-scale

model with spare flight engine in Langley’s 8-Foot High Temperature Tunnel.

The Hyper-X program has significantly expanded the boundaries

of air-breathing flight by being the first to fly a “scramjet” powered

aircraft at hypersonic speeds.
come aerodynamic loads, and propellant was

machined out of the Pegasus booster to enable

launch at its normal launch altitude of 40,000

feet instead of 23,000 feet—as on the first

flight—in order to reduce aerodynamic loads.

How Scramjets Work

A ramjet operates by combustion of fuel in a

stream of air compressed by the forward speed

of the aircraft itself, as opposed to a normal jet

engine, in which the compressor section (the

fan blades) compresses the air. The air flow

through a ramjet engine is subsonic, or less

than the speed of sound. Ramjet-propelled

vehicles operate from about Mach 3 to Mach 6. 

A scramjet (supersonic-combustion ramjet) is a

ramjet engine in which the airflow through the

engine remains supersonic, or greater than the

speed of sound. Scramjet powered vehicles

are envisioned to operate at speeds up to at

least Mach 15. Ground tests of scramjet combustors have shown this potential, but no flight

tests have surpassed the Mach 9.6 X-43A

flight. See illustration below.

Langley & Dryden-A Joint Effort

The Hyper-X Program, managed by the

Aeronautics Research Mission Directorate in

Washington, was conducted jointly by the Langley

Research Center, Hampton, Va., and the Dryden

Flight Research Center, Edwards, Calif. Langley

was lead center, responsible for hypersonic technology development. Dryden was responsible for

flight research, hardware integration and testing.

NASA’s Aeronautics Research Mission Directorate

develops tools and technologies that can help

transform how the air transportation system operates, how new aircraft are designed and manufactured, and how our Nation’s air transportation

system can reach unparalleled levels of safety.

ATK GASL (formerly MicroCraft, Inc.), Tullahoma,

Tenn. and Ronkonkoma, N.Y., built the three X-43A

research aircraft and engines. Boeing Phantom

Works, Huntington Beach, Calif., designed the

thermal protection and onboard systems. The

booster was a modified Pegasus rocket built by

Orbital Sciences Corp., Chandler, Ariz.

Fuel injection stages

Inlet Isolator Combustor Nozzle

Airflow

Propulsion-airframe integrated scramjet

Forebody

compression Aftbody

expansion

Vehicle

bow-shock

Shock boundary

layer interactions

This simplified graphic illustrates how air and fuel mix at supersonic speeds inside a scramjet

engine to propel the vehicle to many times the speed of sound. Supersonic speeds are greater

than the speed of sound.

National Aeronautics and Space Administration

Langley Research Center Dryden Flight Research Center

Hampton, Virginia 23681 Edwards, CA 93523

www.nasa.gov

FS-2006-01-118-LaRC