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

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

Aerojet Rocketdyne Aerojet Rocketdyne is an American manufacturer of rocket, hypersonic, and electric propulsive systems for space, defense, civil and commercial applications. Headquartered in Sacramento, California, the company is owned by Aerojet Rocketdyne Hold ...

that burns

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 Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully l ...

and

liquid oxygen 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 app ...

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. Three RL10 versions are in production for the

Centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as bein ...

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 ...

of the

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Mart ...

and the DCSS of the

Delta IV Delta IV is a group of five expendable launch systems in the Delta rocket family introduced in the early 2000s. Originally designed by Boeing's Defense, Space and Security division for the Evolved Expendable Launch Vehicle (EELV) program, th ...

. Three more versions are in development for the

Exploration Upper Stage The Exploration Upper Stage (EUS) is being developed as a large second stage for Block 1B and Block 2 of the Space Launch System (SLS), succeeding Block 1's Interim Cryogenic Propulsion Stage. It will be powered by four RL10C-3 engines burnin ...

of the

Space Launch System The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle developed by NASA. As of 2022, SLS has the highest payload capacity of any rocket in operational service, as well as the greatest liftoff thrust of any ...

and the Centaur V of the Vulcan rocket. The

expander cycle The expander cycle is a power cycle of a bipropellant rocket engine. In this cycle, the fuel is used to cool the engine's combustion chamber, picking up heat and changing phase. The now heated and gaseous fuel then powers the turbine that drives ...

that the engine uses drives the

turbopump A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpo ...

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 (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...

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 The George C. Marshall Space Flight Center (MSFC), located in Redstone Arsenal, Alabama (Huntsville postal address), is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's firs ...

and

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

beginning in the 1950s. The RL10 was originally developed as a throttleable engine for the USAF Lunex lunar lander, finally putting this capability to use twenty years later in the

DC-X The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an uncrewed prototype of a reusable single-stage-to-orbit launch vehicle built by McDonnell Douglas in conjunction with the United States Department of Defense's Strategic D ...

VTOL vehicle. 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, which is situated on a barrier island across the Lake Worth Lagoon. The populati ...

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

upper stage of an

Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...

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 The Saturn I was a rocket designed as the United States' first medium lift launch vehicle for up to low Earth orbit payloads.Terminology has changed since the 1960s; back then, 20,000 pounds was considered "heavy lift". The rocket's first st ...

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 The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an uncrewed prototype of a reusable single-stage-to-orbit launch vehicle built by McDonnell Douglas in conjunction with the United States Department of Defense's Strategic D ...

. A flaw in the

brazing Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal. Brazing differs from ...

of an RL10B-2 combustion chamber was identified as the cause of failure for the 4 May 1999

Delta III Delta III was an expendable launch vehicle made by Boeing. The vehicle was developed from the highly-successful Delta II to help meet the launch demand of larger satellites. The first Delta III launch was on August 26, 1998. Of its three flight ...

launch carrying the Orion-3

communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth ...

. 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 Ares I was the crew launch vehicle that was being developed by NASA as part of the Constellation program. The name "Ares" refers to the Greek deity Ares, who is identified with the Roman god Mars. Ares I was originally known as the "Crew Launc ...

and

Ares V The Ares V (formerly known as the Cargo Launch Vehicle or CaLV) was the planned cargo launch component of the cancelled NASA Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also pl ...

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

Common Extensible Cryogenic Engine

In the early 2000s, NASA contracted with Pratt & Whitney Rocketdyne 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 Vehicle National Security Space Launch (NSSL) — formerly Evolved Expendable Launch Vehicle (EELV) from 1994 to 2019 — is a program of the United States Space Force (USSF) intended to assure access to space for United States Department of Defense and o ...

s (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 gimbaling for reduced weight and increased reliability, and a

of . As of 2016, Aerojet Rocketdyne was working toward incorporating

additive manufacturing 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...

into the RL10 construction process. The company conducted full-scale, hot-fire tests on an engine with a printed main injector in March 2016, and on an engine with a printed

thrust chamber 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 sy ...

assembly in April 2017.

Current applications for the RL10

Centaur (rocket stage) The Centaur is a family of rocket propelled upper stages produced by U.S. launch service provider United Launch Alliance, with one main active version and one version under development. The diameter Common Centaur/Centaur III flies as the u ...

: 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. *

Delta Cryogenic Second Stage The Delta Cryogenic Second Stage (DCSS) is a family of cryogenic rocket stages used on the Delta III and Delta IV rockets, and on the Space Launch System Block 1. The stage consists of a cylindrical liquid hydrogen (LH2) tank structurally separate ...

: The current DCSS has an RL10C-2-1 with an extensible nozzle. * 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 Aerojet Rocketdyne 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 currently used on the Space Launch System (SLS). Designed and manufactu ...

Space Shuttle Main Engines.

Engines in development

* Exploration Upper Stage (EUS): EUS will initially use four RL10C-3 engines. When RL10C-X becomes available, the C-3 engines will be swapped out for C-X. *OmegA Upper Stage: In April 2018,

Northrop Grumman Innovation Systems Northrop Grumman Innovation Systems (NGIS) was a sector (business segment) of Northrop Grumman from 2018 through 2019. It was formed from Orbital ATK Inc. a company which resulted from the merger of Orbital Sciences Corporation and parts of Alli ...

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

OmegA Omega (; capital: Ω, lowercase: ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and final letter in the Greek alphabet. In the Greek numeric system/ isopsephy ( gematria), it has a value of 800. The ...

in the upper stage.

Blue Origin Blue Origin, LLC is an American private spaceflight, privately funded aerospace manufacturer and sub-orbital spaceflight services company headquartered in Kent, Washington. Founded in 2000 by Jeff Bezos, the founder and executive chairman of Am ...

BE-3U The BE-3 (''Blue Engine 3'') is a LH2/LOX rocket engine developed by Blue Origin. The engine began development in the early 2010s, and completed acceptance testing in early 2015. The engine is being used on the New Shepard suborbital spaceflig ...

and

Airbus Airbus SE (; ; ; ) is a European multinational aerospace corporation. Airbus designs, manufactures and sells civil and military aerospace products worldwide and manufactures aircraft throughout the world. The company has three divisions: '' ...

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. * Centaur V: On May 11, 2018,

United Launch Alliance United Launch Alliance (ULA), legally United Launch Alliance, LLC, is an American spacecraft launch service provider that manufactures and operates a number of rocket vehicles that are capable of launching spacecraft into orbits around Earth, a ...

(ULA) announced that the RL10 upper stage engine had been selected for ULA's next-generation

Vulcan Centaur Vulcan Centaur is a two-stage-to-orbit, heavy-lift launch vehicle that is under development by the United Launch Alliance (ULA) since 2014 with an initial flight expected in early 2023. It is principally designed to meet launch demands for th ...

rocket following a competitive procurement process. Centaur V will normally use the RL10C-1-1, but on Vulcan Centaur Heavy the RL10C-X will be used.

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

(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 depot An orbital propellant depot is a cache of propellant that is placed in orbit around Earth or another body to allow spacecraft or the transfer stage of the spacecraft to be fueled in space. It is one of the types of space resource depots that ...

s 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, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacec ...

was also proposed.

Table of versions

Partial specifications

All versions

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

RL10A

* Thrust (altitude): 15,000 lbf (66.7 kN) *

Specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...

: * 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:

, 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 IV second stage (1 engine)

Engines on display

* An RL10A-1 is on display at the

New England Air Museum The New England Air Museum (NEAM) is an American aerospace museum located adjacent to Bradley International Airport in Windsor Locks, Connecticut. The museum consists of three display hangars with additional storage and restoration hangars. Its co ...

Windsor Locks, Connecticut Windsor Locks is a town in Hartford County, Connecticut, United States. As of the 2020 census, its population was 12,613. It is the site of Bradley International Airport, which serves the Greater Hartford-Springfield region and occupies approxi ...

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

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...

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

Huntsville, Alabama Huntsville is a city in Madison County, Limestone County, and Morgan County, Alabama, United States. It is the county seat of Madison County. Located in the Appalachian region of northern Alabama, Huntsville is the most populous city in ...

* An RL10 is on display at

Southern University Southern University and A&M College (Southern University, Southern, SUBR or SU) is a public historically black land-grant university in Baton Rouge, Louisiana. It is the largest historically black college or university (HBCU) in Louisiana, a ...

Baton Rouge, Louisiana Baton Rouge ( ; ) is a city in and the List of capitals in the United States, capital of the U.S. state of Louisiana. Located the eastern bank of the Mississippi River, it is the county seat, parish seat of East Baton Rouge Parish, Louisiana, E ...

* Two RL10 engines are on display at

US Space Walk of Fame The American Space Museum is a museum in Titusville, Florida. It includes the US Space Walk of Fame, an outdoor plaza on the Indian River that honors both the astronauts and the NASA and contractor personnel who made American manned space explora ...

Titusville, Florida Titusville is a city in eastern Florida and the county seat of Brevard County, Florida, United States. The city's population was 43,761 as of the 2010 United States Census. Titusville is located along the Indian River, west of Merritt Island and ...

* 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 land-grant research university in Auburn, Alabama. With more than 24,600 undergraduate students and a total enrollment of more than 30,000 with 1,330 faculty members, Auburn is the second largest ...

. * An RL10A-4 is on display at the Science Museum in London, 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 San Diego Air & Space Museum (SDASM, formerly the San Diego Aerospace Museum) is an aviation and space exploration museum in San Diego, California, United States. The museum is located in Balboa Park and is housed in the former Ford Building, ...

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States ...

, CA.

References

Bibliography

External links

RL10B-2 at AstronautixSpaceflight Now articleSpaceflight Now article
{{Thor and Delta rockets Rocket engines using hydrogen propellant North American Aviation Rocket engines using the expander cycle