Editing NASA X-43 (section)

===Engine===
[[Image:Wind tunnel x-43.jpg|thumb|right|Full-scale model of the X-43 plane in [[Langley Research Center|Langley's]] {{convert|8|ft|m|0|adj=on}}, high-temperature [[wind tunnel]]]]
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.<ref>Swinerd, Graham. ''How Spacecraft Fly: Spaceflight Without Formulae.'' New York: Springer, 2010. {{ISBN|978-1-44192-629-6}}. p. 113.</ref> The X-43A's developers designed the aircraft's airframe to be part of the [[Air propulsion|propulsion]] system: the forebody is a part of the intake airflow, while the aft section functions as an exhaust nozzle.<ref name="AircraftInFormation">Martin, Guy. [http://www.aircraftinformation.info/art_x43.htm#vehicles “Hypersonic Pioneer: The X-43A.”]  ''AircraftInFormation.info.'' Retrieved: August 16, 2012.</ref>

The engine of the X-43A was primarily fueled with [[hydrogen fuel]]. In the successful test, about {{cvt|2|lb|kg|0|spell=on|disp=flip}} of the fuel was used. For initial ignition, a mixture of hydrogen with 20% of [[monosilane]], a [[pyrophoric]] gas, was used.<ref>{{Cite journal |last=Hidding |first=Bernhard |last2=Pfitzner |first2=Michael |last3=Simone |first3=Domenico |last4=Bruno |first4=Claudio |date=July 2008 |title=Review of the potential of silanes as rocket/scramjet fuels |journal=Acta Astronautica |volume=63 |issue=1 |pages=379–388 |doi=10.1016/j.actaastro.2007.12.056 |issn=0094-5765}}</ref> 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 [[Payload (air and space craft)|payload]]s into [[outer space|space]] or carry payloads of the same weight much more efficiently.

Scramjets only operate at speeds in the range of Mach&nbsp;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.<ref name="AircraftInFormation"/>

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&nbsp;7, while the third was designed to operate at speeds greater than {{cvt|9.8|Mach|altitude_ft=98000}} at altitudes of {{cvt|30000|m|ft}} or more.