NASA X-43

{{Short description|Unmanned US experimental hypersonic aircraft, 1991-2000}} {{Infobox aircraft |name = X-43 |image = File:X-43A.jpg |caption = [[Pegasus rocket]] booster accelerating NASA's X-43A (dark object mounted on nose) shortly after ignition during test flight (March 2, 2004) |alt =  |type = Experimental hypersonic UAV |national_origin = United States |manufacturer = |design_group = [[NASA]] |designer =  |builder = {{ubli|Micro Craft (airframe) | [[General Applied Science Laboratory|GASL]] (engine)}} |first_flight =  |introduction =  |retired =  |status =  |primary_user = [[NASA]] |more_users =  |produced =  |number_built = 3 |developed_from =  |variants =  |developed_into =  }}

The '''NASA X-43''' was an [[experimental aircraft|experimental]] [[Unmanned aerial vehicle|unmanned]] [[hypersonic]] [[aircraft]] with multiple planned [[scale (spatial)|scale]] variations meant to test various aspects of [[hypersonic flight]]. It was part of the [[X-plane (aircraft)|X-plane]] series and specifically of [[NASA]]'s '''Hyper-X''' program developed in the late 1990s.<ref>{{cite web | url=https://www.aftc.af.mil/News/On-This-Day-in-Test-History/Article-Display-Test-History/Article/2554297/april-28-2001-the-first-captive-carry-flight-nasas-x-43a-hypersonic-research-ve/ | title=April 28, 2001: The First Captive-Carry Flight NASA's X-43A Hypersonic Research Vehicle | date=28 April 2021 }}</ref> It set several [[flight airspeed record|airspeed records]] for [[jet aircraft]]. The X-43 is the fastest jet-powered aircraft on record at approximately [[Mach number|Mach]] 9.6.<ref name=Thompson>Thompson, Elvia, Keith Henry and Leslie Williams. [http://www.nasa.gov/home/hqnews/2005/jun/HQ_05_156_X43A_Guinness.html "Faster Than a Speeding Bullet: Guinness Recognizes NASA Scramjet."] {{Webarchive|url=https://web.archive.org/web/20210730032800/http://www.nasa.gov/home/hqnews/2005/jun/HQ_05_156_X43A_Guinness.html |date=2021-07-30 }} ''[[NASA]].'' Retrieved: August 1, 2011.</ref>

A winged [[booster rocket]] with the X-43 placed on top, called a "stack", was [[drop launch]]ed from a [[Boeing B-52 Stratofortress]]. After the booster rocket (a modified first stage of the [[Pegasus (rocket)|Pegasus 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, of which three were built. The first X-43A was destroyed after malfunctioning in flight in 2001. Each of the other two flew successfully in 2004, setting speed records, with the scramjets operating for approximately 10 seconds followed by 10-minute glides and intentional crashes into the ocean. Plans for more planes in the X-43 series have been suspended or cancelled, and replaced by the [[United States Air Force|USAF]]-managed [[Boeing X-51 Waverider|X-51]] program.

==Development== The X-43 was a 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]] (GASL). Micro Craft Inc. built the X-43A and GASL built its engine.

One of the primary goals of NASA's [[Aeronautics Enterprise]] was the development and demonstration of technologies for air-breathing hypersonic flight. Following the cancellation of the [[National Aerospace Plane]] (NASP) program in November 1994, the United States lacked a cohesive hypersonic technology development program. As one of the "better, faster, cheaper" programs developed by NASA in the late 1990s, the Hyper-X used technology and research from the NASP program which advanced it toward the demonstration of hypersonic air breathing propulsion,<ref>{{cite book |last=Peebles |first=Curtis |author-link=Curtis Peebles |title=Eleven Seconds into the Unknown: A History of the Hyper-X Program |location= Virginia |publisher= AIAA |year= 2010 |isbn= 978-1-60086-776-7}}</ref>

The Hyper-X Phase I was a NASA Aeronautics and Space Technology Enterprise program conducted jointly by the [[Langley Research Center]], [[Hampton, Virginia]], and the [[Dryden Flight Research Center]], [[Edwards, California]]. Langley was the lead center and responsible for hypersonic technology development. Dryden was responsible for flight research.

Phase I was a seven-year, approximately $230,000,000 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 in 2006 by the [[Boeing X-51|X-51]].

==Design== [[Image:X43a2 nasa scramjet.jpg|thumb|Artist's concept of X-43A with [[scramjet]] attached to the underside]] [[Image:B-52 carries X-43A.jpg|thumb|NASA's B-52B launch aircraft takes off carrying the X-43A hypersonic research vehicle (March 27, 2004)]]

The X-43A aircraft was a small unpiloted test vehicle measuring just over {{cvt|3.7|m|ft}} in [[length]].<ref>Harsha, Phillip T., Lowell C. Keel, Anthony Castrogiovanni and Robert T. Sherrill. [https://arc.aiaa.org/doi/abs/10.2514/6.2005-3334 “X-43A Vehicle Design and Manufacture.”] ''AIAA 2005-3334.'' Retrieved: August 1, 2011.</ref> The vehicle was a [[lifting body]] design, where the body of the aircraft provides a significant amount of [[lift (force)|lift]] for flight, rather than relying on [[wing]]s. The aircraft weighed roughly {{cvt|3000|lb|kg|disp=flip}}. The X-43A was designed to be fully controllable in high-speed flight, even when [[gliding]] without [[Air propulsion|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 significant heat due to the [[Wave drag|compression]] [[shock waves]] involved in supersonic [[aerodynamic drag]]. At high Mach speeds, heat can become so intense that metal portions of the airframe could 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.

===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 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 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.

==Operational testing== [[Image:X-43A (Hyper - X) Mach 7 computational fluid dynamic (CFD).jpg|thumb|[[Computational fluid dynamics]] (CFD) image of the X-43A at Mach 7]] [[Image:B-52B with X43.jpg|thumb|right|The X-43A being dropped from under the wing of a [[Boeing B-52 Stratofortress|NB-52B Stratofortress]]]]

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, and it was destroyed 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.<ref name=Bentley2008>Bentley, Matthew A. ''Spaceplanes: From Airport to Spaceport'' (Astronomers' Universe). New York: Springer, 2008. {{ISBN|978-0-38776-509-9}}, p. 110–111.</ref>

In the second test in March 2004, the Pegasus fired successfully and released the test vehicle at an altitude of about {{convert|29000|m|ft}}. After separation, the engine's air intake was opened, the engine ignited, and the aircraft then accelerated away from the rocket reaching {{cvt|6.83|Mach|altitude_ft=29000}}. Fuel was flowing to the engine for 11 seconds, a time in which the aircraft traveled more than {{cvt|24|km|mi}}. Following Pegasus booster separation, the vehicle experienced a small drop in speed but the scramjet engine afterward accelerated the vehicle in climbing flight.<ref name=Bentley2008/> After burnout, controllers were still able to maneuver the vehicle and manipulate the flight controls for several minutes; the aircraft, slowed by air resistance, fell into the ocean. With this flight the X-43A became the fastest free-flying [[Airbreathing jet engine|air-breathing]] aircraft in the world.

NASA flew a third version of the X-43A on November 16, 2004. The Pegasus rocket booster separated from its B-52 carrier at 40,000 feet and its solid rocket took the combination to Mach 10 at 110,000 feet.<ref name=Heppenheimer2007/> The X-43A split away at Mach 9.8 and the engine was started at Mach 9.65 for 10–12 seconds with thrust approximately equal to drag, and then glided to the Pacific Ocean after 14 minutes.<ref name=Heppenheimer2007/> Dynamic pressure during the flight was {{cvt|1,050|psf|bar}}.<ref name=Heppenheimer2007>{{cite web |author= Thomas A. Heppenheimer |url= http://www.dept.aoe.vt.edu/~mason/Mason_f/NASASP2007-4232Hypersonics.pdf |archive-url= https://web.archive.org/web/20110720112614if_/http://www.dept.aoe.vt.edu/~mason/Mason_f/NASASP2007-4232Hypersonics.pdf |url-status= dead |archive-date= 2011-07-20 |title= Facing the Heat Barrier: A History of Hypersonics |page= 277 |publisher= NASA History Division |date= September 2007}}</ref> It reached Mach 9.68,<ref name=PAW>{{cite web |url= http://www.pwrengineering.com/dataresources/AIAA-2005-3256-Paper-R-Kazmar-25071.pdf |archive-url= https://web.archive.org/web/20071021082342if_/http://www.pwrengineering.com/dataresources/AIAA-2005-3256-Paper-R-Kazmar-25071.pdf |url-status= dead |archive-date= 2007-10-21 |title= Airbreathing Hypersonic Propulsion at Pratt & Whitney – Overview |author= Richard R. Kazmar |publisher= American Institute of Aeronautics and Astronautics |year= 2005 }}</ref><ref name=X43>{{cite conference |url= http://www.aiaa.org/Participate/Uploads/AIAA_DL_McClinton.pdf |title= X-43: Scramjet Power Breaks the Hypersonic Barrier |author= Charles McClinton |publisher= NASA Langley Research Center |conference= 44th AIAA Aerospace Sciences Meeting and Exhibit |date= 9 Jan 2006|archive-url= https://web.archive.org/web/20110724231440/http://www.aiaa.org/Participate/Uploads/AIAA_DL_McClinton.pdf |archive-date= 2011-07-24 }}</ref> {{cvt|6,755|mph|sigfig=4}} at 109,440 ft (33,357 m),<ref>{{cite web |url= https://www.guinnessworldrecords.com/world-records/fastest-aircraft-air-breathing-engine |title= Fastest aircraft, air-breathing engine: X-43 |date= 16 Nov 2004 |work= Guinness World Records}}</ref> and further tested the ability of the vehicle to withstand the heat loads involved.<ref name=NASA040>{{cite web |url= http://www.nasa.gov/centers/dryden/news/FactSheets/FS-040-DFRC.html |title= NASA "Hyper-X" Program Demonstrates Scramjet Technologies |publisher= NASA |date= Aug 7, 2017}}</ref>

===Replacements=== In January 2006 the USAF announced the [[DARPA Falcon Project|Force Application and Launch from Continental United States]] or FALCON scramjet reusable missile.<ref>[http://space.com/businesstechnology/060126_darpa_falcon.html "Falcon."] ''space.com.'' Retrieved: August 1, 2011.</ref> In March 2006, it was announced that the Air Force Research Laboratory (AFRL) 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.

==Variants== 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]] (NASP) in the foreseeable future.

Other X-43 vehicles were planned, but {{as of|2013|06|lc=on}} they have been suspended or canceled. 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 a full-size vehicle, incorporating a turbine-based combined cycle (TBCC) engine or a [[rocket-based combined cycle]] (RBCC) [[Integrated Systems Test of an Air-Breathing Rocket|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 [[Scramjet Programs#HyTECH|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.<ref>Morris, Jefferson. [http://www.aviationnow.com/avnow/news/channel_aerospacedaily_story.jsp?id=news/eng03194.xml "X-43C, RS-84 Engine Among Casualties Of NASA Review."] {{Webarchive|url=https://web.archive.org/web/20041118102737/http://www.aviationnow.com/avnow/news/channel_aerospacedaily_story.jsp?id=news/eng03194.xml |date=2004-11-18 }} ''[[Aviation Week]],'' March 19, 2004. Retrieved: January 9, 2010.</ref> 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.<ref>[http://www.boeing.com/news/frontiers/archive/2005/august/ts_sf01.html "Good news travels fast."] ''Boeing Frontiers'', August 2005. Quote: "Thanks to a funding request of $25 million for NASA sponsored by U.S. Rep. Jim Talent (R-Mo.), work on the X-43C program will continue through 2005."</ref>

===X-43D=== The X-43D would have been almost identical to the X-43A, but expanded the speed envelope to 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."<ref>[http://pdf.aiaa.org/preview/CDReadyMISPHST05_1136/PV2005_3416.pdf "X-43D Conceptual Design and Feasibility Study."] {{webarchive|url=https://web.archive.org/web/20080229074624/http://pdf.aiaa.org/preview/CDReadyMISPHST05_1136/PV2005_3416.pdf |date=2008-02-29 }} AIAA. Retrieved: August 1, 2011.</ref>

==See also== {{aircontent |see also= * {{annotated link|DARPA Falcon Project}} * {{annotated link|HyShot}} * {{annotated link|Rockwell X-30}} * {{annotated link|Project Isinglass|Project Rheinberry}} * {{annotated link|Space Launch Initiative}} |related= |similar aircraft= * {{annotated link|Boeing X-51}} * {{annotated link|Hypersonic Technology Demonstrator Vehicle}} |lists= * [[List of X-planes]] }}

==References== {{Reflist}}

===Notes=== {{Reflist|group=note}}

==External links== {{Commons}} * [https://www.youtube.com/watch?v=fpPQ6NN7u20 X-43 Launch NASA Animation] * [http://www.nasa.gov/missions/research/x43-main.html NASA page for the X-43 project] {{Webarchive|url=https://web.archive.org/web/20160213162216/http://www.nasa.gov/missions/research/x43-main.html |date=2016-02-13 }} *[https://www.dfrc.nasa.gov/Gallery/Photo/X-43A/index.html Dryden Flight Research Center X-43 Photo Collection] * [http://www.mathworks.com/cmsimages/x43a_components_wl_8593.jpg International components of the X-43a] {{Webarchive|url=https://web.archive.org/web/20121014092700/http://www.mathworks.com/cmsimages/x43a_components_wl_8593.jpg |date=2012-10-14 }} * [https://www.youtube.com/watch?v=PDE6rANOkgE Launch from B-52], [https://www.youtube.com/watch?v=168p5BK9V08 infrared]  * https://web.archive.org/web/20150316013940/http://videoclip.pk/watch_video.php?v=H1M8DKHXN2HO

{{DEFAULTSORT:Nasa X-43}} [[Category:2001 in spaceflight]] [[Category:Micro Craft aircraft|X-43]] [[Category:2000s United States experimental aircraft]] [[Category:Proposed reusable launch systems]] [[Category:NASA aircraft]] [[Category:Hypersonic aircraft]] [[Category:Scramjet-powered aircraft]] [[Category:Aircraft related to spaceflight]]