View source for LE-7

{{Short description|Japanese hydrolox staged combustion rocket engine}}
{{infobox rocket engine
|image=LE-7 rocket engine.jpg
|image_size=250
|caption=LE-7, Nagoya City Science Museum, 2006
|name=LE-7
|country_of_origin=[[Japan]]
|designer=[[JAXA]]
|manufacturer=[[Mitsubishi Heavy Industries]]
|date=
|purpose=[[Booster (rocketry)|Booster]]
|predecessor=
|status=Succeeded by LE-7A upgrade
|cycle=[[Staged combustion cycle (rocket)|Staged combustion]]
|type=liquid
|fuel=[[LH2|LH{{sub|2}}]]
|oxidiser=[[LOX]]
|capacity=
|combustion_chamber=1
|mixture_ratio=5.9:1
|nozzle_ratio=52:1
|thrust(SL)= {{convert|843.5|kN|lbf|abbr=on}}
|thrust(Vac)={{convert|1078|kN|lbf|abbr=on}}
|specific_impulse_vacuum={{convert|446|isp}}
|specific_impulse_sea_level={{convert|349|isp}}
|chamber_pressure={{convert|12.7|MPa|psi|abbr=on}}
|thrust_to_weight=64.13
|diameter=
|length=3.4 m
|dry_weight={{convert|1714|kg|lb|abbr=on}}
|used_in=[[H-II]] first stage
}}
[[File:Mitsubishi LE-7A.JPG|thumb|250px|LE-7A, (Mitsubishi Heavy Industries show-room, [[Shinagawa]], Japan)]]
The '''LE-7''' and its succeeding upgrade model the LE-7A are [[Staged combustion cycle (rocket)|staged combustion cycle]] [[LH2|LH{{sub|2}}]]/[[LOX]] [[liquid rocket|liquid rocket engines]] produced in [[Japan]] for the [[H-II]] series of launch vehicles. Design and production work was all done domestically in Japan, the first major ([[multistage rocket|main/first-stage]]) liquid rocket engine with that claim, in a collaborative effort from the National Space Development Agency (NASDA), Aerospace Engineering Laboratory (NAL), [[Mitsubishi Heavy Industries]], and [[IHI Corporation|Ishikawajima-Harima]]. NASDA and NAL have since been integrated into [[JAXA]]. However, a large part of the work was contracted to Mitsubishi, with Ishikawajima-Harima providing [[turbomachinery]], and the engine is often referred to as the '''Mitsubishi LE-7(A)'''.
The original LE-7 was an [[expendable launch system|expendable]], high efficiency, medium-sized motor with sufficient thrust for use on the H-II.
==H-II Flight 8, only operational LE-7 failure==
The fuel [[turbopump]] had an issue using the originally designed inducer (a propeller-like [[axial flow pump|axial pump]] used to raise the inlet pressure of the [[propellant]] ahead of the main [[turbopumps]] to prevent [[cavitation]]) where the inducer would itself begin to cavitate and cause an imbalance resulting in excessive [[vibration]]. A comprehensive post-flight analysis of the unsuccessful 8th H-II launch, including a deep ocean retrieval of the wreckage, determined that [[fatigue (material)|fatigue]] due to this vibration was the cause of premature engine failure.
==LE-7A==
The LE-7A is an upgraded model from the LE-7 rocket engine. Basic design is unchanged from the original model. The 7A had additional engineering effort placed on cost cutting, reliability, and performance developments. The renovation was undertaken to mate it with the likewise improved [[H-IIA]] launch vehicle, with the common goal being a more reliable, more powerful and flexible, and more cost effective launch system.
===Changes / improvements===
Specific emphasis was placed on reducing or the amount of required [[welding]] by allowing for more [[machined]] or [[casting|cast]] components, and to simplify as many of the remaining welds as possible. This resulted in a substantial rework of the pipe routing (which makes the outward appearance of the two models considerably different). To combat the fuel inducer complications described above, the fuel inducer was redesigned for the 7A. The oxidizer inducer was also redesigned, but this was primarily due to poor performance at low inlet pressures as opposed to reliability concerns. The fuel turbopump itself was also the subject of various durability enhancements. Additionally the combustion chamber/injector assembly underwent a number of small changes, like decreasing the number of injector elements, to reduce machining complexity (and thus cost) and improve reliability. While these changes overall resulted in a drop in maximum specific impulse to {{convert|440|isp}} (basically making the engine less fuel efficient), the trade off for lower cost and enhanced reliability was considered acceptable.
===New nozzle design (side-loading problem)===
For the new engine model, a [[nozzle]] extension was designed that could be added to the base of the new standard “short” nozzle when extra performance was required. But when the engine was fitted with the nozzle extension, the 7A encountered a new problem with unprecedented side-loads and irregular heating on the nozzle strong enough to damage the [[gimbal]] [[actuators]] and  [[Regenerative cooling (rocket)|regenerative cooling]] tubes during startup. Meticulous [[computational fluid dynamics|computational fluid dynamics (CFD)]] work was able to sufficiently replicate and trace the dangerous transient loading and a new one-piece “long” nozzle with full regenerative cooling (as opposed to the original short nozzle with a separate film-cooled extension) was designed to mitigate the problem. Before this new nozzle was ready, some H-IIA's were launched using only the short nozzle. The 7A no longer uses a separate nozzle extension in any configuration.<ref>{{cite journal|url=https://doi.org/10.2514/6.2003-4763 |title=LE-7A Engine Separation Phenomenon Differences of the Two Nozzle Configurations|author1=Yasuhide Watanabe|author2= Norio Sakazume |author3=Masanori Tsuboi|journal=39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit|date=July 2003|doi=10.2514/6.2003-4763 |isbn=978-1-62410-098-7 |access-date=13 May 2023}}</ref>
===Use on H-IIB===
The new [[H-IIB]] launch vehicles uses two LE-7A engines in its first stage.<ref>{{cite web |url=https://www.jaxa.jp/countdown/h2bf1/overview/h2b_e.html|title=Overview of the H-IIB Launch Vehicle|publisher=JAXA|access-date=13 May 2023}}</ref>
===LE-7A specifications===
* Operational cycle: staged combustion
* Fuel: hydrogen
* Oxidizer: liquid oxygen
* Mixture ratio (oxidizer to fuel): 5.90
* Short nozzle:
** Rated thrust (sea level): {{convert|843|kN|lbf|abbr=on}}
** Rated thrust (vacuum): {{convert|1074|kN|lbf|abbr=on}}
** Specific impulse (sea level):
** Specific impulse (vacuum): {{convert|429|isp}}
* Long nozzle:
** Rated thrust (sea level): {{convert|870|kN|lbf|abbr=on}}
** Rated thrust (vacuum): {{convert|1098|kN|lbf|abbr=on}}
** Specific impulse (sea level): {{convert|338|isp}}
** Specific impulse (vacuum): {{convert|440|isp}}
* Dry mass: {{convert|1800|kg|lb|abbr=on}}
* Length:
** short nozzle: 3.2 m
** long nozzle: 3.7 m
* Throttle capability: 72–100%
* Thrust-to-weight: 65.9
* Nozzle area ratio: 51.9:1
* Combustion chamber pressure: {{convert|12.0|MPa|psi|abbr=on}}
* Liquid hydrogen turbopump: 41,900 rpm
* Liquid oxygen turbopump: 18,300 rpm
==See also==
* [[LE-5]]
* [[LE-9]]
* [[H-II]], [[H-IIA]], & [[H-IIB]]
* [[Comparison of orbital rocket engines]]
* [[liquid-propellant rocket|Liquid-fuel rocket]]
* [[Staged combustion cycle (rocket)|Staged combustion cycle]]
* [[JAXA]]
==References==
{{reflist}}
==External links==
{{commons category|LE-7}}
* [https://web.archive.org/web/20020626171141/http://www.astronautix.com/engines/le7.htm Encyclopedia Astronautica info page on the LE-7]
* [https://web.archive.org/web/20021018023043/http://www.astronautix.com/engines/le7a.htm Encyclopedia Astronautica info page on the LE-7A]
* [[:ja:LE-7|Japanese Wikipedia LE-7 page (in Japanese)]]
* [[:ja:LE-7A|Japanese Wikipedia LE-7A page (in Japanese)]]
* [https://sma.nasa.gov/LaunchVehicle/assets/h-iia-rocket-engine-development2.pdf H-IIA Rocket Engine Development]
* [http://www.jaxa.jp/projects/rockets/h2a/f8/img/h-2af8.pdf Overview of the H-IIA Launch Vehicle] Includes H-IIA-F6 failure analysis
{{Rocket engines}}
[[Category:Rocket engines of Japan]]
[[Category:Rocket engines using hydrogen propellant]]
[[Category:Rocket engines using the staged combustion cycle]]