The X-43 was an unmanned experimental hypersonic aircraft with multiple
planned scale variations meant to test various aspects of hypersonic flight. It
was part of the X-plane series and specifically of NASA's Hyper-X program.
It set several airspeed records for jet-propelled aircraft. The X-43 is the
fastest aircraft on record at approximately 7,000 miles per hour.
A winged booster rocket with the X-43 placed on top, called a "stack", was
drop launched from a larger carrier plane. After the booster rocket brought
the stack to the target speed and altitude, it was discarded, and the X-43
flew free using its own engine, a scramjet.
The first plane in the series, the X-43A, was a single-use vehicle. Three
of them were built. The first was destroyed after malfunctioning in
flight; the other two have successfully flown, with the scramjet operating for
approximately 10 seconds, followed by a 10-minute glide and intentional crash
into the ocean. Purpose
The X-43 was part of NASA's Hyper-X program, involving the American space
agency and contractors such as Boeing, Micro Craft Inc, Orbital Sciences
Corporation and General Applied Science Laboratory. Micro Craft Inc. built the
X-43A and GASL built its engine. The Hyper-X Phase I was a NASA
Aeronautics and Space Technology Enterprise program being conducted
jointly by the Langley Research Center, Hampton, Virginia, and the Dryden Flight
Research Center, Edwards, California. Langley was the lead center and is
responsible for hypersonic technology development. Dryden was responsible for
flight research. Phase I was a seven-year, approximately
$230 million, program to flight-validate scramjet propulsion, hypersonic
aerodynamics and design methods. Subsequent phases were not continued as
the X-43 series of aircraft was replaced by the X-51.
Design The X-43A aircraft was a small unpiloted
test vehicle measuring just over 3.7 m in length. The vehicle was a lifting
body design, where the body of the aircraft provides a significant amount
of lift for flight, rather than relying on wings. The aircraft weighed roughly
3,000 pounds. The X-43A was designed to be fully controllable in high-speed
flight, even when gliding without propulsion. However, the aircraft was
not designed to land and be recovered. Test vehicles crashed into the Pacific
Ocean when the test was over. Traveling at Mach speeds produces a lot
of heat due to the compression shock waves involved in supersonic drag. At
high Mach speeds, heat can become so intense that metal portions of the
airframe melt. The X-43A compensated for this by cycling water behind the engine
cowl and sidewall leading edges, cooling those surfaces. In tests, the water
circulation was activated at about Mach 3. In the future, fuel may be cycled
through such areas instead, much like what is currently done in many
liquid-fuel rocket nozzles and high speed aircraft such as the SR-71.
= Engine= The craft was created to develop and
test a supersonic-combustion ramjet, or "scramjet" engine, an engine variation
where external combustion takes place within air that is flowing at supersonic
speeds. The X-43A's developers designed the aircraft's airframe to be part of
the propulsion system: the forebody is a part of the intake airflow, while the
aft section functions as an exhaust nozzle.
The engine of the X-43A was primarily fueled with hydrogen. In the successful
test, about two pounds of the fuel was used. Unlike rockets, scramjet-powered
vehicles do not carry oxygen on board for fueling the engine. Removing the
need to carry oxygen significantly reduces the vehicle's size and weight.
In the future, such lighter vehicles could take heavier payloads into space
or carry payloads of the same weight much more efficiently.
Scramjets only operate at speeds in the range of Mach 4.5 or higher, so rockets
or other jet engines are required to initially boost scramjet-powered
aircraft to this base velocity. In the case of the X-43A, the aircraft was
accelerated to high speed with a Pegasus rocket launched from a converted Boeing
B-52 Stratofortress bomber. The combined X-43A and Pegasus vehicle was referred
to as the "stack" by the program's team members.
The engines in the X-43A test vehicles were specifically designed for a certain
speed range, only able to compress and ignite the fuel-air mixture when the
incoming airflow is moving as expected. The first two X-43A aircraft were
intended for flight at approximately Mach 7, while the third was designed to
operate at speeds greater than Mach 9.8 at altitudes of 30,000 m or more.
Testing NASA's first X-43A test on June 2, 2001
failed because the Pegasus booster lost control about 13 seconds after it was
released from the B-52 carrier. The rocket experienced a control oscillation
as it went transonic, eventually leading to the failure of the rocket's starboard
elevon. This caused the rocket to deviate significantly from the planned
course, so the stack was destroyed by the activation of onboard explosive
charges by the Range Safety Officer as a safety precaution. An investigation into
the incident stated that imprecise information about the capabilities of
the rocket as well as its flight environment contributed to the accident.
Several inaccuracies in data modeling for this test led to an inadequate
control system for the particular Pegasus rocket used, though no single
factor could ultimately be blamed for the failure.
In the second test in March 2004, the Pegasus fired successfully and released
the test vehicle at an altitude of about 29,000 metres. After separation, the
engine's air intake was opened, the engine ignited, and the aircraft then
accelerated away from the rocket reaching Mach 6.83 or 7,401 km/h. Fuel
was flowing to the engine for 11 seconds, a time in which the aircraft
traveled more than 24 km. Following Pegasus booster separation, the vehicle
experienced a small drop in speed but the scramjet engine afterward
accelerated the vehicle in climbing flight. After burnout, controllers were
still able to maneuver the vehicle and manipulate the flight controls for
several minutes as the aircraft was slowed by air resistance as it fell into
the ocean. With this flight the X-43A became the fastest free flying
air-breathing aircraft in the world. NASA flew a third version of the X-43A
on November 16, 2004. The modified Pegasus rocket which was launched from a
B-52 mother ship at an altitude of 13,157 meters. The X-43A set a new speed
record of 10,617 km/h or Mach 9.65 or Mach 9.68 at about 33,528 metres
altitude , and further testing the ability of the vehicle to withstand the
heat loads involved. Future of the scramjet: Variants and
replacement After the X-43 tests in 2004, NASA
Dryden engineers said that they expected all of their efforts to culminate in the
production of a two-stage-to-orbit crewed vehicle in about 20 years. The
scientists expressed much doubt that there would be a Single Stage to Orbit
crewed vehicle like the National Aerospace Plane in the foreseeable
future, also known as the "Orient Express", that would take off from an
ordinary airport runway. Other X-43 vehicles were planned, but as
of June 2013 have been suspended or cancelled. They were expected to have
the same basic body design as the X-43A, though the aircraft were expected to be
moderately to significantly larger in size.
= X-43B= The X-43B, was expected to be a
full-size vehicle, incorporating a turbine-based combined cycle engine or a
rocket-based combined cycle ISTAR engine. Jet turbines or rockets would
initially propel the vehicle to supersonic speed. A ramjet might take
over starting at Mach 2.5, with the engine converting to a scramjet
configuration at approximately Mach 5. = X-43C=
The X-43C would have been somewhat larger than the X-43A and was expected
to test the viability of hydrocarbon fuel, possibly with the HyTech engine.
While most scramjet designs have used hydrogen for fuel, HyTech runs with
conventional kerosene-type hydrocarbon fuels, which are more practical for
support of operational vehicles. The building of a full-scale engine was
planned which would use its own fuel for cooling. The engine cooling system would
have acted as a chemical reactor by breaking long-chain hydrocarbons into
short-chain hydrocarbons for a rapid burn.
The X-43C was indefinitely suspended in March 2004. The linked story reports the
project's indefinite suspension and the appearance of Rear Admiral Craig E.
Steidle before a House Space and Aeronautics subcommittee hearing on
March 18, 2004. In mid-2005, the X-43C appeared to be funded through the end of
the year. = X-43D=
The X-43D would have been almost identical to the X-43A, but expanded the
speed envelope to approximately Mach 15. As of September 2007, only a feasibility
study had been conducted by Donald B. Johnson of Boeing and Jeffrey S.
Robinson of NASA's Langley Research Center. According to the introduction of
the study, "The purpose of the X-43D is to gather high Mach flight environment
and engine operability information which is difficult, if not impossible, to
gather on the ground." = Replacements=
In January 2006 the USAF announced the Force Application and Launch from
Continental United States or FALCON scramjet reusable missile.
In March 2006, it was announced that the Air Force Research Laboratory supersonic
combustion ramjet "WaveRider" flight test vehicle had been designated as
X-51A. The USAF Boeing X-51 was first flown on May 26, 2010, dropped from a
B-52. So far, this signals the replacement and end of the X-43 series.
See also Hypersoar
HyShot Rockwell X-30
Project Rheinberry Aircraft of comparable role,
configuration and era Boeing X-51
Hypersonic Technology Demonstrator Vehicle
References = Notes=
= Bibliography= External links
NASA page for the X-43 project International components of the X-43a
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