Liquid fuel cryogenic rocket engine, typically used on rocket upper stages
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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.[3][4]
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 and Pratt & Whitney beginning in the 1950s. The RL10 was originally developed as a throttleable engine for the USAF Lunex lunar lander.[5]
The RL10 was first tested on the ground in 1959, at Pratt & Whitney's Florida Research and Development Center in West Palm Beach, Florida.[6][7] The first successful flight took place on November 27, 1963.[8][9] 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.[10]
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[11] and the Titan program included Centaur D-1T upper stages powered by two RL10A-3-3 Engines.[11][12]
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.[14]
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.[15] Up to seven RL10 engines would have been used in the proposed Jupiter Upper Stage, serving an equivalent role to the Space Launch SystemExploration Upper Stage.
Common Extensible Cryogenic Engine
The CECE at partial throttle
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.[16] In 2007, its operability (with some "chugging") was demonstrated at 11:1 throttle ratios.[17] 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.[18] In 2010, the throttling range was expanded further to a 17.6:1 ratio, throttling from 104% to 5.9% power.[19]
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[20]
From the study, NASA hoped to find a less expensive RL10-class engine for the upper stage of the Space Launch System (SLS).[20][21]
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.[20] A related requirements study was conducted at the same time under the Affordable Upper Stage Engine Program (AUSEP).[21]
Improvements
The RL10 has evolved over the years. The RL10B-2 that was used on the DCSS had improved performance, an extendablecarbon-carbon nozzle, electro-mechanical gimbaling for reduced weight and increased reliability, and a specific impulse of 465.5 seconds (4.565 km/s).[22][23]
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 that had a printed main injector in March 2016.[24] Another project by Aerojet Rocketdyne was an engine with a printed thrust chamber assembly in April 2017.[25]
Current applications for the RL10
Atlas VCentaur (rocket stage): The single engine centaur (SEC) version uses the RL10C-1,[2] while the dual engine centaur (DEC) version retains the smaller RL10A-4-2.[26] 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.[27] The engine was used again successfully on SBIRS-6.
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 Space Shuttle Main Engines.
Vulcan Centaur's Centaur V stage: On May 11, 2018, United Launch Alliance (ULA) announced that the RL10 upper stage engine had been selected for ULA's next-generation Vulcan Centaur rocket following a competitive procurement process.[28] Centaur V will normally use the RL10C-1-1,[2] but on Vulcan Centaur Heavy the RL10C-X will be used.[29] Vulcan flew its successful maiden flight on January 8, 2024.[30]
Engines in development
Exploration Upper Stage (EUS): EUS will initially use four RL10C-3 engines. The RL10C-X will replace these engines when it becomes available.[31]
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.[32]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.[33]
^ abWade, Mark (November 17, 2011). "RL-10B-2". Encyclopedia Astronautica. Archived from the original on February 4, 2012. Retrieved February 27, 2012.
^ abWade, Mark (November 17, 2011). "RL-10A-1". Encyclopedia Astronautica. Archived from the original on November 15, 2011. Retrieved February 27, 2012.
^Zegler, Frank; Bernard Kutter (September 2, 2010). "Evolving to a Depot-Based Space Transportation Architecture"(PDF). AIAA SPACE 2010 Conference & Exposition. AIAA. Archived from the original(PDF) on October 20, 2011. Retrieved January 25, 2011. 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. ...
^Wade, Mark (November 17, 2011). "RL-10A-4-1". Encyclopedia Astronautica. Archived from the original on November 17, 2011. Retrieved February 27, 2012.
^Wade, Mark (November 17, 2011). "RL-10A-4-2". Encyclopedia Astronautica. Archived from the original on January 30, 2012. Retrieved February 27, 2012.
^ ab"RL10 Engine". Aerojet Rocketdyne. Archived from the original on April 30, 2017. Retrieved March 13, 2016.
^Wade, Mark (November 17, 2011). "RL-10B-X". Encyclopedia Astronautica. Archived from the original on November 15, 2011. Retrieved February 27, 2012.
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