LE-7

The LE-7 and it’s succeeding upgrade model the LE-7A are staged combustion cycle LH2/LOX 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 (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 Ishikawajima-Harima. NASDA and NAL have since been integrated into JAXA. However, a large part of the work was done by Mitsubishi, with Ishikawajima-Harima providing the turbopumps, and the engine is often referred to as the Mitsubishi LE-7(A).

The original LE-7 was designed to be a high efficiency medium sized motor with sufficient thrust for use on the H-II, and classified as expendable since the engine was non-recoverable after launch.

LE-7 Specifications

* Operational Cycle: staged combustion
* Fuel: liquid hydrogen
* Oxidizer: liquid oxygen
* Mixture Ratio (oxidizer to fuel): 5.90
* Rated Thrust:
** vacuum = 1078 kN (242,300 lbs)
** sea level = 843.5 kN (189,600 lbs)
* Specific Impulse (Isp)
** vacuum = 446 seconds
** sea level = 349 seconds
* Dry Mass: 1714 kg (3778 lbs)
* Length: 3.4 m
* Throttle Capability: n/a (not throttleable)
* Thrust-to-weight: 64.13
* Nozzle Area Ratio: 52:1
* Combustion Chamber Pressure: 12.7 MPa (1842 PSI)
* Liquid Hydrogen Turbopump: 42,200 rpm
* Liquid Oxygen Turbopump: 18,100 rpm

H-II Flight 8, only operational LE-7 failure

The fuel turbopump had an issue using the originally designed inducer (a propeller-like axial pump used to raise the inlet pressure of the propellant ahead of the main turbomachinery 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 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 rocket, 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 and allow for more machined or cast components, and to simplify as many of the remaining welds as possible. This resulted in a substantial rework of the pipe routing. 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 more due to poor suction performance at low inlet pressures as opposed to stability 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 440 seconds (basically meaning the engine was less 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 regenerative cooling tubes and gimbal actuators during startup and shutdown. Meticulous 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. [ [http://pdf.aiaa.org/preview/CDReadyMJPC2003_775/PV2003_4763.pdf AIAA technical paper abstract on LE-7A Nozzle Configurations] ]

LE-7A Specifications

* Operational Cycle: staged combustion
* Fuel: hydrogen
* Oxidizer: liquid oxygen
* Mixture Ratio (oxidizer to fuel): 5.90
* Rated Thrust (vacuum):
** short nozzle = 1074 kN (241,000 lbs)
** long nozzle - 1098 kN (247,000 lbs)
* Rated Thrust (sea level):
** short nozzle = ?
** long nozzle = 870 kN (195,600 lbs)
* Specific Impulse (vacuum):
** short nozzle = 429 seconds
** long nozzle = 440 seconds
* Specific Impulse (sea level):
** short nozzle = ? seconds
** long nozzle = 338 seconds
* Dry Mass: 1800kg (3900 lbs)
* 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: 12.0 MPa (1740 PSI)
* Liquid Hydrogen Turbopump: 41,900 rpm
* Liquid Oxygen Turbopump: 18,300 rpm

ee also

* LE-5
* H-II & H-IIA
* liquid rocket engine
* staged combustion cycle
* JAXA

References

Note: you may find conflicting technical information in these sources depending on the date of publish and source of the information. This article was written with the intent of collecting the most recent and accurate specifications, though no guarantees are given.
* [http://www.astronautix.com/engines/le7.htm Encyclopedia Astronautica info page on the LE-7]
* [http://www.astronautix.com/engines/le7a.htm Encyclopedia Astronautica info page on the LE-7A]
* [http://ja.wikipedia.org/wiki/LE-7 Japanese Wikipedia LE-7 page (in Japanese)]
* [http://ja.wikipedia.org/wiki/LE-7A Japanese Wikipedia LE-7A page (in Japanese)]
* [http://www.mhi.co.jp/tech/pdf/e392/e392051.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]

External links