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The LE-5
liquid rocket A liquid-propellant rocket or liquid rocket utilizes a rocket engine that uses liquid propellants. Liquids are desirable because they have a reasonably high density and high specific impulse (''I''sp). This allows the volume of the propellant ta ...
engine and its derivative models were developed in Japan to meet the need for an
upper stage A multistage rocket or step rocket is a launch vehicle that uses two or more rocket ''stages'', each of which contains its own engines and propellant. A ''tandem'' or ''serial'' stage is mounted on top of another stage; a ''parallel'' stage is ...
propulsion system for the H-I and H-II series of launch vehicles. It is a
bipropellant The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical (a monopropellant) or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into ...
design, using LH and
LOX Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an appli ...
. Primary design and production work was carried out by
Mitsubishi Heavy Industries is a Japanese multinational engineering, electrical equipment and electronics corporation headquartered in Tokyo, Japan. MHI is one of the core companies of the Mitsubishi Group and its automobile division is the predecessor of Mitsubishi Mo ...
. In terms of liquid rockets, it is a fairly small engine, both in size and thrust output, being in the 89 kN (20,000 lbf) and the more recent models the 130 kN (30,000 lbf) thrust class. The motor is capable of multiple restarts, due to a
spark ignition A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, ty ...
system as opposed to the single use
pyrotechnic Pyrotechnics is the science and craft of creating such things as fireworks, safety matches, oxygen candles, explosive bolts and other fasteners, parts of automotive airbags, as well as gas-pressure blasting in mining, quarrying, and demolition. ...
or
hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. The ...
igniters commonly used on some contemporary engines. Though rated for up to 16 starts and 40+ minutes of firing time, on the H-II the engine is considered expendable, being used for one flight and jettisoned. It is sometimes started only once for a nine-minute burn, but in missions to GTO the engine is often fired a second time to inject the payload into the higher orbit after a temporary
low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
has been established. The original LE-5 was built as a second stage engine for the H-I launch vehicle. It used a fairly conventional gas generator cycle.


LE-5A

The LE-5A was a heavily redesigned version of the LE-5 intended for use on the new H-II launch vehicle's second stage. The major difference is that the operation of the engine was switched from the gas generator to expander bleed cycle. The LE-5A was the world's first expander bleed cycle engine to be put into operational service.
Cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
liquid hydrogen fuel for the cycle is drawn through tubes and passages in both the engine's nozzle and combustion chamber where the hydrogen heats up incredibly while simultaneously cooling those components. The heating of the initially cold fuel causes it to become significantly pressurized and it is utilized to drive the turbine for the propellant pumps.


LE-5B

The LE-5B (in Japanese) was a further modified version of the LE-5A. The changes focused on lowering the per-unit cost of the engine while continuing to increase reliability. The modifications veered towards simplification and cheaper production where possible at the cost of actually lowering the specific impulse to 447 seconds, the lowest of all three models. However, it produced the highest thrust of the three and was significantly cheaper. The primary change from the 5A model was that the 5B's expander bleed system circulated fuel around only the combustion chamber as opposed to both the chamber and the nozzle in the 5A. Alterations to the combustion chamber cooling passages and constituent materials were made with special emphasis on effective heat transfer to allow this method to be successful.


LE-5B-2

After flight F5 of
H-IIA H-IIA (H-2A) is an active expendable launch system operated by Mitsubishi Heavy Industries (MHI) for the Japan Aerospace Exploration Agency. These liquid fuel rockets have been used to launch satellites into geostationary orbit; lunar or ...
on March 28, 2003 resulted in severe (although not damaging) vibration of the upper stage during LE-5B firing, work was initiated on an upgraded version of the LE-5B. The upgraded engine, named LE-5B-2, was first flown on a
H-IIB H-IIB (H2B) was an expendable space launch system jointly developed by the Japanese government's space agency JAXA and Mitsubishi Heavy Industries. It was used to launch the H-II Transfer Vehicle (HTV, or ''Kōnotori'') cargo spacecraft for ...
on September 10, 2009. The main fixes were adding flow-laminarizing plates in the expander manifold, a new mixer of gaseous and liquid hydrogen in the hydrogen feed line, and a new injector plate with 306 smaller coaxial injectors (versus 180 in LE-5B). Se
LE-5B-2 development summary (Japanese)
The upgrade reduced the vibrations produced by the upper stage by half.


LE-5B-3

For the new H3 launch vehicle, the veteran design of the LE-5B was once again revisited. To meet the requirements of the H3 and to ensure a stable supply of parts over H3's lifetime, performance was to be improved and costs were to be lowered, all while keeping development risk as low as possible. Obsolete parts that were becoming hard to acquire such as the electronics in the engine controller were to be replaced with modern components that could be reliably sourced for years to come, and the manufacturing method for the combustion chamber was to be likewise updated for similar reasons. The liquid hydrogen turbopump and turbine nozzle were to be updated for H3's longer mission duration times, and the performance of the liquid oxygen turbopump and fuel mixer was to be improved. The first example of the updated design was test fired in March, 2017. The engine's certification for flights on the H3 rocket are currently ongoing.


Specifications

:*, tank head pressure only


See also

* H-I Japanese carrier rocket * H-II Japanese carrier rocket * H-IIA Japanese carrier rocket * H-IIB Japanese carrier rocket *
LE-7 The LE-7 and its succeeding upgrade model the LE-7A are staged combustion cycle LH/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 m ...
*
LE-9 The LE-9 is a liquid cryogenic rocket engine burning liquid hydrogen and liquid oxygen in an expander bleed cycle. Two or three will be used to power the core stage of the H3 launch vehicle. The newly developed LE-9 engine is the most import ...

Development of the LE-X Engine, MHI Technical Review Vol. 48 No. 4


References


External links

{{Rocket engines Rocket engines of Japan Rocket engines using hydrogen propellant Rocket engines using the gas-generator cycle