The RL10 is a liquid-fuel cryogenic rocket engine built in the

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Aerojet Rocketdyne Aerojet Rocketdyne is a subsidiary of American Arms industry, defense company L3Harris that manufactures rocket, Hypersonic flight, hypersonic, and electric propulsive systems for space, defense, civil and commercial applications. Aerojet traces ...

that burns

cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...

liquid hydrogen Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule, molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point (thermodynamics), critical point of 33 Kelvins, ...

and

liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...

propellants. Modern versions produce up to of

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

per engine in vacuum. RL10 versions were produced for the

Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

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 Rocket engine, engines and Rocket propellant, propellant. A ''tandem'' or ''serial'' stage is mounted on top of anoth ...

of the

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas (rocket family), Atlas launch vehicle family. It was developed by Lockheed Martin and has been operated by United Launch Alliance (ULA) since 2006. Primarily used to ...

and the DCSS of the Delta IV. More versions are in development or in use for the Exploration Upper Stage of the

Space Launch System The Space Launch System (SLS) is an American Super heavy-lift launch vehicle, super heavy-lift Expendable launch system, expendable launch vehicle used by NASA. As the primary launch vehicle of the Artemis program, Artemis Moon landing progra ...

and the Centaur V of the Vulcan rocket. The

expander cycle Expander may refer to: *Dynamic range compression operated in reverse *Part of the process of signal compression *Part of the process of companding *A component used to connect Serial Attached SCSI#SAS expanders, SCSI computer data storage, device ...

that the engine uses drives the turbopump with waste heat absorbed by the engine combustion chamber, throat, and nozzle. This, combined with the hydrogen fuel, leads to very high

specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...

s (''I''_sp) in the range of in a vacuum. Mass ranges from depending on the version of the engine.

History

The RL10 was the first liquid hydrogen rocket engine to be built in the United States, with development of the engine by

Marshall Space Flight Center Marshall Space Flight Center (officially the George C. Marshall Space Flight Center; MSFC), located in Redstone Arsenal, Alabama (Huntsville, Alabama, Huntsville postal address), is the Federal government of the United States, U.S. government's ...

and

Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation (formerly Raytheon Technologies). Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially ...

beginning in the 1950s. The RL10 was originally developed as a throttleable engine for the USAF Lunex lunar lander. The RL10 was first tested on the ground in 1959, at

's Florida Research and Development Center in

West Palm Beach, Florida West Palm Beach is a city in and the county seat of Palm Beach County, Florida, United States. It is located immediately to the west of the adjacent Palm Beach, Florida, Palm Beach, which is situated on a barrier island across the Lake Worth Lag ...

. The first successful flight took place on November 27, 1963. For that launch, two RL10A-3 engines powered the

upper stage of an

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launch vehicle. The launch was used to conduct a heavily instrumented performance and structural integrity test of the vehicle. Multiple versions of this engine have been flown. The S-IV of the Saturn I used a cluster of six RL10A-3S, a version which was modified for installation on the Saturn and the

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

program included Centaur D-1T upper stages powered by two RL10A-3-3 Engines. Four modified RL10A-5 engines were used in the McDonnell Douglas DC-X. A flaw in the brazing of an RL10B-2 combustion chamber was identified as the cause of failure for the 4 May 1999 Delta III launch carrying the Orion-3

communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a Transponder (satellite communications), transponder; it creates a communication channel between a source transmitter and a Rad ...

. The

DIRECT Direct may refer to: Mathematics * Directed set, in order theory * Direct limit of (pre), sheaves * Direct sum of modules, a construction in abstract algebra which combines several vector spaces Computing * Direct access (disambiguation), ...

version 3.0 proposal to replace Ares I and Ares V with a family of rockets sharing a common core stage recommended the RL10 for the second stage of the J-246 and J-247 launch vehicles. Up to seven RL10 engines would have been used in the proposed Jupiter Upper Stage, serving an equivalent role to the

Exploration Upper Stage.

Common Extensible Cryogenic Engine

In the early 2000s, NASA contracted with

Pratt & Whitney Rocketdyne Pratt & Whitney Rocketdyne (PWR) was an American company that designed and produced rocket engines that use liquid rocket propellants, liquid propellants. It was a division of Pratt & Whitney, a fully owned subsidiary of United Technologies Corpo ...

to develop the Common Extensible Cryogenic Engine (CECE) demonstrator. CECE was intended to lead to RL10 engines capable of deep throttling. In 2007, its operability (with some "chugging") was demonstrated at 11:1 throttle ratios. In 2009, NASA reported successfully throttling from 104 percent thrust to eight percent thrust, a record for an expander cycle engine of this type. Chugging was eliminated by injector and propellant feed system modifications that control the pressure, temperature and flow of propellants. In 2010, the throttling range was expanded further to a 17.6:1 ratio, throttling from 104% to 5.9% power.

Early 2010s possible successor

In 2012 NASA joined with the US Air Force (USAF) to study next-generation upper stage propulsion, formalizing the agencies' joint interests in a new upper stage engine to replace the Aerojet Rocketdyne RL10. From the study, NASA hoped to find a less expensive RL10-class engine for the upper stage of the

(SLS). USAF hoped to replace the Rocketdyne RL10 engines used on the upper stages of the Lockheed Martin Atlas V and the Boeing Delta IV Evolved Expendable Launch Vehicles (EELV) that were the primary methods of putting US government satellites into space. A related requirements study was conducted at the same time under the Affordable Upper Stage Engine Program (AUSEP).

Improvements

The RL10 has evolved over the years. The RL10B-2 that was used on the DCSS had improved performance, an extendable carbon-carbon nozzle, electro-mechanical

gimbal A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of ...

ing for reduced weight and increased reliability, and a

of . As of 2016,

was working toward incorporating additive manufacturing into the RL10 construction process. The company conducted full-scale, hot-fire tests on an engine that had a printed main injector in March 2016. Another project by Aerojet Rocketdyne was an engine with a printed thrust chamber assembly in April 2017.

Applications

Current

* Centaur III: The single engine centaur (SEC) version uses the RL10C-1, while the dual engine centaur (DEC) version retains the smaller RL10A-4-2. An Atlas V mission (SBIRS-5) marked the first use of the RL10C-1-1 version. The mission was successful but observed unexpected vibration, and further use of the RL10C-1-1 model is on hold until the problem is better understood. The engine was used again successfully on SBIRS-6. * Centaur V stage: On May 11, 2018, United Launch Alliance (ULA) announced that the RL10 upper stage engine had been selected for its Vulcan Centaur rocket following a competitive procurement process. Early versions of the Centaur V will use the RL10C-1-1, but later versions will transition to the RL10C-X. Vulcan flew its successful maiden flight on January 8, 2024. * Interim Cryogenic Propulsion Stage: The Interim Cryogenic Propulsion Stage or ICPS is used for the SLS and is similar to the DCSS, except that the engine is an RL10B-2 and it is adapted to fit on top of the 8.4 meter diameter core stage with four

RS-25 The RS-25, also known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is used on the Space Launch System. Designed and manufactured in the United States by Rocketd ...

Space Shuttle Main Engines.

In development

* Exploration Upper Stage: The Exploration Upper Stage will use four RL10C-3 engines.

Cancelled

* OmegA Upper Stage: In April 2018,

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announced that two RL10C-5-1 engines would be used on

OmegA Omega (, ; uppercase Ω, lowercase ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and last letter in the Greek alphabet. In the Greek numerals, Greek numeric system/isopsephy (gematria), it has a value ...

in the upper stage.

Blue Origin Blue Origin Enterprises, L.P. is an American space technology company headquartered in Kent, Washington. The company operates the suborbital New Shepard rocket and the heavy-lift New Glenn rocket. In addition to producing engines for its own ...

's BE-3U and

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Safran's Vinci were also considered before Aerojet Rocketdyne's engine was selected. OmegA development was halted after it failed to win a National Security Space Launch contract. * Advanced Cryogenic Evolved Stage: , an enhanced version of the RL10 was proposed to power the Advanced Cryogenic Evolved Stage (ACES), a long-duration, low-boiloff extension of existing ULA

and Delta Cryogenic Second Stage (DCSS) technology for the Vulcan launch vehicle. Long-duration ACES technology is intended to support

geosynchronous A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...

, cislunar, and interplanetary missions. Another possible application is as in-space propellant depots in LEO or at that could be used as way-stations for other rockets to stop and refuel on the way to beyond-LEO or interplanetary missions. Cleanup of

space debris Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in spaceprincipally in Earth orbitwhich no longer serve a useful function. These include dere ...

was also proposed.

Table of versions

Partial specifications

All versions

* Contractor: Pratt & Whitney * Propellants: liquid oxygen, liquid hydrogen * Design:

* Ignition: electric spark.

RL10A

* Thrust (altitude): 15,000 lb-f (66.7 kN) *

Specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...

: * Engine weight, dry: 298 lb (135 kg) * Height: 68in (1.73m) * Diameter: 39in (0.99m) * Nozzle expansion ratio: 40 to 1 * Propellant flow: 35 lb/s (16 kg/s) * Vehicle application: Saturn I, S-IV 2nd stage, 6 engines * Vehicle application:

upper stage, 2 engines

RL10B-2

Second stage of a Delta IV Medium rocket

* Thrust (altitude): 24,750 lbf (110.1 kN) *

: * Engine weight, dry: 664 lb (301.2 kg) * Height: 163.5in (4.14m) * Diameter: 84.5in (2.21m) * Expansion ratio: 280 to 1 * Mixture ratio: 5.88 to 1 oxygen:hydrogen mass ratio * Propellant flow: fuel, 7.72 lb/s (3.5 kg/s); oxidizer 45.42 lb/s (20.6 kg/s) * Vehicle application: Delta III, Delta IV second stage (1 engine)

Gallery

File:Rl-10engine.jpg, RL10A-1 File:RL-10 with cutaway.JPG, RL10A-3S File:500px photo (140471371).jpeg, RL10A-4 File:RL-10onstand.jpg, RL10A-4-2 File:RL-10B-2 engine during nozzle extension testing.jpg, RL10B-2

Engines on display

* An RL10A-1 is on display at the New England Air Museum,

Windsor Locks, Connecticut Windsor Locks is a New England town, town in Hartford County, Connecticut, United States. The town is part of the Capitol Planning Region, Connecticut, Capitol Planning Region. As of the 2020 United States Census, 2020 census, its population was ...

* An RL10 is on display at the Museum of Science and Industry,

Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

* An RL10A-1 is on display at the Cernan Earth and Space Center, River Grove,

* An RL10 is on display at the U.S. Space & Rocket Center,

Huntsville, Alabama Huntsville is the List of municipalities in Alabama, most populous city in the U.S. state of Alabama. The population of the city is estimated to be 241,114 in 2024, making it the List of United States cities by population, 100th-most populous ...

* An RL10 is on display at

Southern University Southern University and A&M College (Southern University, Southern, SUBR or SU) is a Public university, public historically black colleges and universities, historically black land-grant university in Baton Rouge, Louisiana, United States. It i ...

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* Two RL10 engines are on display at US Space Walk of Fame,

Titusville, Florida Titusville is a city in and the county seat of Brevard County, Florida, United States. As of the 2020 United States census, 2020 census, the population of the city was 48,789, up from 43,761 at the 2010 census. Titusville is located along the ...

* An RL10 is on display at the Cox Science Center and Aquarium,

. * An RL10 is on display in the Aerospace Engineering Department, Davis Hall at

Auburn University Auburn University (AU or Auburn) is a Public university, public Land-grant university, land-grant research university in Auburn, Alabama, United States. With more than 26,800 undergraduate students, over 6,100 post-graduate students, and a tota ...

. * An RL10A-4 is on display at the

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, UK. * An RL10 is on display at the Museum of Life and Science in Durham, NC * An RL10 is on display at the

San Diego Air & Space Museum The San Diego Air & Space Museum (SDASM) is an aviation and space exploration museum in San Diego, California. It is located in Balboa Park (San Diego), Balboa Park and is housed in the former Ford Building (San Diego), Ford Building, which is li ...

San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

, CA. * An RL10B-2 is on display outside the Discovery Cube Orange County in Santa Ana, CA.

References

Bibliography

External links

RL10B-2 at AstronautixSpaceflight Now articleSpaceflight Now article
{{Thor and Delta rockets North American Aviation Rocket engines of the United States Rocket engines using hydrogen propellant Rocket engines using the expander cycle Rocketdyne engines Space Launch System