This article needs to be updated. The reason given is: Info on improvement projects is dated..June 2020)(
An RL10A-4 engine in London's Science Museum
|Country of origin||United States of America|
|First flight||1962 (RL10A-1)|
|Application||Upper stage engine|
Space Shuttle (canceled)
Space Launch System (future)
|Propellant||Liquid oxygen / liquid hydrogen|
|Nozzle ratio||84:1 or 280:1|
|Thrust (vac.)||110.1 kN (24,800 lbf)|
|Isp (vac.)||465.5 seconds (4.565 km/s)|
|Burn time||700 seconds|
|Length||4.15 m (13.6 ft) w/ nozzle extended|
|Diameter||2.15 m (7 ft 1 in)|
|Dry weight||301 kg (664 lb)|
|Notes||Performance values and dimensions are for RL10B-2.|
The RL10 is a liquid-fuel cryogenic rocket engine built in the United States by Aerojet Rocketdyne that burns cryogenic liquid hydrogen and liquid oxygen propellants. Modern versions produce up to 110 kN (24,729 lbf) of thrust per engine in vacuum. Three RL10 versions are in production for the Centaur upper stage of the Atlas V and the DCSS of the Delta IV. Three more versions are in development for the Exploration Upper Stage of the Space Launch System, the upper stage of the OmegA rocket, and the Centaur V of the Vulcan rocket.
The expander cycle 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 impulses (Isp) in the range of 373 to 470 s (3.66–4.61 km/s) in a vacuum. Mass ranges from 131 to 317 kg (289–699 lb) depending on the version of the engine.
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 and Pratt & Whitney 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 VTOL vehicle.
The RL10 was first tested on the ground in 1959, at Pratt & Whitney's Florida Research and Development Center in West Palm Beach, Florida. The first successful flight took place on November 27, 1963. For that launch, two RL10A-3 engines powered the Centaur upper stage of an Atlas launch vehicle. The launch was used to conduct a heavily instrumented performance and structural integrity test of the vehicle.
The DIRECT 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 Space Launch System Exploration Upper Stage.
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.
"We know the list price on an RL10. If you look at cost over time, a very large portion of the unit cost of the EELVs is attributable to the propulsion systems, and the RL10 is a very old engine, and there's a lot of craftwork associated with its manufacture. ... That's what this study will figure out, is it worthwhile to build an RL10 replacement?"— Dale Thomas, Associated Director Technical, Marshall Space Flight Center
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 are 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).
The RL10 has evolved over the years. The RL10B-2 that was used on the DCSS had improved performance, an extendable nozzle, electro-mechanical gimbaling for reduced weight and increased reliability, and a specific impulse of 464 seconds (4.55 km/s).
As of 2016, Aerojet Rocketdyne was working toward incorporating additive manufacturing 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 assembly in April 2017.
Current applications for the RL10
- Atlas V Centaur (rocket stage): The single engine centaur (SEC) version uses the RL10C-1, while the dual engine centaur (DEC) version retains the smaller RL10A-4-2.
- Delta Cryogenic Second Stage: The current DCSS has an RL10C-2-1 with an extensible nozzle.
Engines in development
Three RL10C-X engine versions are undergoing the qualification process, and will include major engine components using 3D printing, which is expected to reduce lead times and cost.
- SLS Exploration Upper Stage: In April 2016, four RL10 engines were selected to fly on the Exploration Upper Stage (EUS) of the Block 1B Space Launch System. In October 2016, NASA announced that the EUS will use the new RL10C-3 version, the biggest and most powerful of the RL10C-X engines.
- OmegA Upper Stage: In April 2018, Northrop Grumman Innovation Systems announced that two RL10C-5-1 engines would be used on OmegA in the upper stage. Blue Origin's BE-3U and Airbus 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.
- Vulcan Centaur Upper Stage: On 11 May 2018, United Launch Alliance (ULA) announced that the RL10C-X upper stage engine had been selected for ULA's next-generation Vulcan Centaur rocket following a competitive procurement process. Centaur V will use the RL10C-1-1.
Advanced Cryogenic Evolved Stage
As of 2009[update], 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 Centaur and Delta Cryogenic Second Stage (DCSS) technology for the Vulcan launch vehicle. Long-duration ACES technology is intended to support geosynchronous, cislunar, and interplanetary missions. Another possible applications is as in-space propellant depots in LEO or at L2 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 was also proposed.
Table of versions
|Version||Status||First flight||Dry mass||Thrust||Isp (ve), vac.||Length||Diameter||T:W||O:F||Expansion ratio||Chamber pressure||Burn time||Associated stage||Notes|
|RL10A-1||Retired||1962||131 kg (289 lb)||67 kN (15,000 lbf)||425 s (4.17 km/s)||1.73 m (5 ft 8 in)||1.53 m (5 ft 0 in)||52:1||40:1||430 s||Centaur A||Prototype|
|RL10A-3||Retired||1963||131 kg (289 lb)||65.6 kN (14,700 lbf)||444 s (4.35 km/s)||2.49 m (8 ft 2 in)||1.53 m (5 ft 0 in)||51:1||5:1||57:1||32.75 bar (3,275 kPa)||470 s||Centaur B/C/D/E
|RL10A-4||Retired||1992||168 kg (370 lb)||92.5 kN (20,800 lbf)||449 s (4.40 km/s)||2.29 m (7 ft 6 in)||1.17 m (3 ft 10 in)||56:1||5.5:1||84:1||392 s||Centaur IIA|||
|RL10A-5||Retired||1993||143 kg (315 lb)||64.7 kN (14,500 lbf)||373 s (3.66 km/s)||1.07 m (3 ft 6 in)||1.02 m (3 ft 4 in)||46:1||6:1||4:1||127 s||DC-X|||
|RL10B-2||Active||1998||277 kg (611 lb)||110.1 kN (24,800 lbf)||465.5 s (4.565 km/s)||4.15 m (13.6 ft)||2.15 m (7 ft 1 in)||40:1||5.88:1||280:1||44.12 bar (4,412 kPa)||5-m: 1,125 s
4-m: 700 s
|Delta Cryogenic Second Stage,
Interim Cyrogenic Propulsion Stage
|RL10A-4-1||Retired||2000||167 kg (368 lb)||99.1 kN (22,300 lbf)||451 s (4.42 km/s)||1.53 m (5 ft 0 in)||61:1||84:1||740 s||Centaur IIIA|||
|RL10A-4-2||Active||2002||168 kg (370 lb)||99.1 kN (22,300 lbf)||451 s (4.42 km/s)||1.17 m (3 ft 10 in)||61:1||84:1||740 s||Centaur IIIB
|RL10B-X||Cancelled||317 kg (699 lb)||93.4 kN (21,000 lbf)||470 s (4.6 km/s)||1.53 m (5 ft 0 in)||30:1||250:1||408 s||Centaur B-X|||
|CECE||Demonstrator project||160 kg (350 lb)||67 kN (15,000 lbf), throttle to 5–10%||>445 s (4.36 km/s)||1.53 m (5 ft 0 in)|||
|RL10C-1||Active||2014||190 kg (420 lb)||101.8 kN (22,890 lbf)||449.7 s (4.410 km/s)||2.12 m (6 ft 11 in)||1.45 m (4 ft 9 in)||57:1||5.88:1||130:1||Centaur SEC|
|RL10C-1-1||In development||188 kg
|453.8 s||2.46 m
(8 ft 0.7 in)
(4 ft 9 in)
|465.5 s||4.15 m
(13 ft 8 in)
(7 ft 1 in)
|37:1||5.88:1||280:1||Delta Cryogenic Second Stage|||
|RL10C-3||In development||230 kg
|460.1 s||3.15 m
(10 ft 4.3 in)
(6 ft 1 in)
|5.7:1||Exploration Upper Stage|||
|453.8 s||2.46 m
(8 ft 0.7 in)
(4 ft 9 in)
- Contractor: Pratt & Whitney
- Propellants: liquid oxygen, liquid hydrogen
- Design: expander cycle
- Thrust (altitude): 15,000 lbf (66.7 kN)
- Specific impulse: 433 seconds (4.25 km/s)
- Engine weight, dry: 298 lb (135 kg)
- Height: 68 in (1.73 m)
- Diameter: 39 in (0.99 m)
- 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: Centaur upper stage, 2 engines
- Thrust (altitude): 24,750 lbf (110.1 kN)
- Design: Expander cycle
- Specific impulse: 465.5 seconds (4.565 km/s)
- Engine weight, dry: 664 lb (301.2 kg)
- Height: 163.5 in (4.14 m)
- Diameter: 84.5 in (2.21 m)
- Expansion ratio: 280 to 1
- Mixture ratio: 5.88 to 1 oxygen:hydrogen mass ratio
- Propellants: liquid oxygen, liquid hydrogen
- 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)
Engines on display
- An RL10A-1 is on display at the New England Air Museum, Windsor Locks, Connecticut
- An RL10 is on display at the Museum of Science and Industry, Chicago, Illinois
- An RL10 is on display at the U.S. Space & Rocket Center, Huntsville, Alabama
- An RL10 is on display at Southern University, Baton Rouge, Louisiana
- Two RL10 engines are on display at US Space Walk of Fame, Titusville, Florida
- An RL10 is on display in the Aerospace Engineering Department, Davis Hall at Auburn University.
- 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 in San Diego, CA.
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- Connors, p 319
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ACES design conceptualization has been underway at ULA for many years. It leverages design features of both the Centaur and Delta Cryogenic Second Stage (DCSS) upper stages and intends to supplement and perhaps replace these stages in the future. ...
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