The LE-5 liquid rocket

Liquid rocket

A liquid-propellant rocket or a liquid rocket is a rocket engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight pumps to pump the propellant from...

 engine and its derivative models were developed in Japan to meet the need for an upper stage

Multistage rocket

A multistage rocket is a rocket that usestwo or more 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 attached alongside another stage. The result is effectively two or more rockets stacked on top of or...

 propulsion system for the H-I

H-I

The H-I or H-1 was a Japanese liquid-fuelled carrier rocket, consisting of a licence-produced American first stage and set of booster rockets, and all-Japanese upper stages. It was launched nine times between 1986 and 1992...

 and H-II

H-II

The H-II rocket was a Japanese satellite launch system, which flew seven times between 1994 and 1999, with five successes. It was developed by NASDA in order to give Japan a capability to launch larger satellites in the 1990s. It was the first two-stage liquid-fuelled rocket Japan made using only...

 series of launch vehicles. It is a bipropellant design, using LH2 and LOX

Lox

Lox is salmon fillet that has been cured. In its most popular form, it is thinly sliced—less than in thickness—and, typically, served on a bagel, often with cream cheese, onion, tomato, cucumber and capers...

. Primary design and production work was carried out by Mitsubishi Heavy Industries

Mitsubishi Heavy Industries

, or MHI, is a Japanese company. It is one of the core companies of Mitsubishi Group.-History:In 1870 Yataro Iwasaki, the founder of Mitsubishi took a lease of Government-owned Nagasaki Shipyard. He named it Nagasaki Shipyard & Machinery Works, and started the shipbuilding business on a full scale...

. In terms of liquid rockets, it is a fairly small engine, both in size and thrust output, being in the 20000 lbf (88,964.4 N) and the more recent models the 30000 lbf (133.4 kN) thrust class. The motor is capable of multiple restarts, due to a spark ignition system as opposed to the single use pyrotechnic or hypergolic 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

Geostationary transfer orbit

A geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....

 the engine is often fired a second time to inject the payload into the higher orbit after a temporary low Earth orbit

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 has been established.

LE-5

The original LE-5 was built as a third stage engine for the H-I launch vehicle. It used a fairly conventional gas generator cycle

Gas-generator cycle (rocket)

The gas generator cycle is a power cycle of a bipropellant rocket engine. Some of the propellant is burned in a gas-generator and the resulting hot gas is used to power the engine's pumps. The gas is then exhausted...

.

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 first expander bleed cycle engine to be put into operational service. Cryogenic 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 was a farther 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 the 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.

Specifications

LE-5 Model Specifications

LE-5 Model	(units)	LE-5	LE-5A	LE-5B
Operational Cycle	-	Gas Generator	Expander Bleed (Nozzle/Chamber)	Expander Bleed (Chamber)
Rated Thrust	kN (lbs)	102.9 (23,100)	121.5 (27,300)	137.2 (30,800)
Mixture Ratio	Oxidizer to Fuel	5.5	5	5
Expansion Ratio	-	140	130	110
Specific Impulse Specific impulse Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,... (Isp)	Seconds	450	452	447
Chamber Pressure	MPa (PSI)	3.65 (529)	3.98 (577)	3.58 (519)
LH2 Rotational Speed	rpm	50,000	51,000	52,000
LOX Rotational Speed	rpm	16,000	17,000	18,000
Length	m (ft)	2.68 (8.84)	2.69 (8.88)	2.79 (9.21)
Weight	kg (lbs)	255 (562)	248 (547)	285 (628)