RL10

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.[2]

RL10
An RL10A-4 engine in London's Science Museum
Country of originUnited States of America
First flight1962 (RL10A-1)
ManufacturerAerojet Rocketdyne
ApplicationUpper stage engine
Associated L/VAtlas
Saturn I
Titan IIIE
Titan IV
Delta III
Delta IV
DC-X
Space Shuttle (canceled)
Space Launch System (future)
OmegA (canceled)
Vulcan (future)
StatusIn production
Liquid-fuel engine
PropellantLiquid oxygen / liquid hydrogen
Mixture ratio5.88:1
CycleExpander cycle
Configuration
Nozzle ratio84:1 or 280:1
Performance
Thrust (vac.)110.1 kN (24,800 lbf)
Isp (vac.)465.5 seconds (4.565 km/s)
Burn time700 seconds
Dimensions
Length4.15 m (13.6 ft) w/ nozzle extended
Diameter2.15 m (7 ft 1 in)
Dry weight301 kg (664 lb)
Used in
Centaur
DCSS
S-IV
References
References[1]
NotesPerformance values and dimensions are for RL10B-2.

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, finally putting this capability to use twenty years later in the DC-X VTOL vehicle.[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 the engine have been flown. The S-IV of the Saturn I used a cluster of six RL10A-3's, and the Titan program included RL10-based Centaur upper stages as well.

Four modified RL10A-5 engines were used in the McDonnell Douglas DC-X.[11]

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.[12]

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.[13] 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
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.[14] In 2007, its operability (with some "chugging") was demonstrated at 11:1 throttle ratios.[15] 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.[16] In 2010, the throttling range was expanded further to a 17.6:1 ratio, throttling from 104% to 5.9% power.[17]

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[18]

From the study, NASA hoped to find a less expensive RL10-class engine for the upper stage of the Space Launch System (SLS).[18][19]

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.[18] A related requirements study was conducted at the same time under the Affordable Upper Stage Engine Program (AUSEP).[19]

Improvements

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,[20] and on an engine with a printed thrust chamber assembly in April 2017.[21]

Current applications for the RL10

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.[2]

  • 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.[25] In October 2016, NASA announced that the EUS will use the new RL10C-3 version,[26] the biggest and most powerful of the RL10C-X engines.[2]
  • 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.[27] 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.[28]
  • 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.[29] Centaur V will use the RL10C-1-1.[2]

Advanced Cryogenic Evolved Stage
Main article: Advanced Cryogenic Evolved Stage

As of 2009, 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.[30] 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.[31]

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
[22][32][33]
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
S-IV		 [34]
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 [35]
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 [36]
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		 [1][37]
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 [38]
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
Centaur SEC
Centaur DEC		 [39][40]
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 [41]
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) [42][43]
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
[44][45][46][40]
RL10C-1-1 In development 188 kg

(415 lb)

 106 kN

(23,825 lbf)

 453.8 s 2.46 m

(8 ft 0.7 in)

 1.57 m

(4 ft 9 in)

 5.5:1 Centaur V [2]
RL10C-2-1 Active 301 kg

(664 lbs)

 109.9 kN

(24,750 lbf)

 465.5 s 4.15 m

(13 ft 8 in)

 2.15 m

(7 ft 1 in)

 37:1 5.88:1 280:1 Delta Cryogenic Second Stage [47]
RL10C-3 In development 230 kg

(508 lb)

 108 kN

(24,340 lbf)

 460.1 s 3.15 m

(10 ft 4.3 in)

 1.85 m

(6 ft 1 in)

 5.7:1 Exploration Upper Stage [2]
RL10C-5-1 Cancelled 188 kg

(415 lb)

 106 kN

(23,825 lbf)

 453.8 s 2.46 m

(8 ft 0.7 in)

 1.57 m

(4 ft 9 in)

 5.5:1 OmegA [2][28]

Partial specifications
RL10A information and overview
RL10 engine undergoing testing at NASA

All versions
  • Contractor: Pratt & Whitney
  • Propellants: liquid oxygen, liquid hydrogen
  • Design: expander cycle

RL10A
  • Thrust (altitude): 15,000 lbf (66.7 kN)[32]
  • 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

RL10B-2
Second stage of a Delta IV Medium rocket featuring an RL10B-2 engine

Engines on display

See also

References
  1. Wade, Mark (November 17, 2011). "RL-10B-2". Encyclopedia Astronautica. Archived from the original on February 4, 2012. Retrieved February 27, 2012.
  2. "Aerojet Rocketdyne RL10 Propulsion System" (PDF). Aerojet Rocketdyne. March 2019.
  3. "RL-10C". www.astronautix.com. Retrieved April 6, 2020.
  4. "RL-10A-1". www.astronautix.com. Retrieved April 6, 2020.
  5. Wade, Mark. "Encyclopedia Astronautica—Lunex Project page". Encyclopedia Astronautica. Archived from the original on August 31, 2006.
  6. Connors, p 319
  7. "Centaur". Gunter's Space Pages.
  8. Sutton, George (2005). History of liquid propellant rocket engines. American Institute of Aeronautics and Astronautics. ISBN 1-56347-649-5.
  9. "Renowned Rocket Engine Celebrates 40 Years of Flight". Pratt & Whitney. November 24, 2003. Archived from the original on June 14, 2011.
  10. "Atlas Centaur 2". National Space Science Data Center. NASA.
  11. Wade, Mark. "DCX". Encyclopedia Astronautica. Archived from the original on December 28, 2012. Retrieved January 4, 2013.
  12. "Delta 269 (Delta III) Investigation Report" (PDF). Boeing. August 16, 2000. MDC 99H0047A. Archived from the original (PDF) on June 16, 2001.
  13. "Jupiter Launch Vehicle – Technical Performance Summaries". Archived from the original on June 8, 2009. Retrieved July 18, 2009.
  14. "Common Extensible Cryogenic Engine (CECE)". United Technologies Corporation. Archived from the original on March 4, 2012.
  15. "Throttling Back to the Moon". NASA. July 16, 2007. Archived from the original on April 2, 2010.
  16. "NASA Tests Engine Technology for Landing Astronauts on the Moon". NASA. January 14, 2009.
  17. Giuliano, Victor (July 25, 2010). "CECE: Expanding the Envelope of Deep Throttling Technology in Liquid Oxygen/Liquid Hydrogen Rocket Engines for NASA Exploration Missions" (PDF). NASA Technical Reports Server.
  18. Roseberg, Zach (April 12, 2012). "NASA, US Air Force to study joint rocket engine". Flight Global. Retrieved June 1, 2012.
  19. Newton, Kimberly (April 12, 2012). "NASA Partners With U.S. Air Force to Study Common Rocket Propulsion Challenges". NASA.
  20. "Aerojet Rocketdyne Successfully Tests Complex 3-D Printed Injector in World's Most Reliable Upper Stage Rocket Engine" (Press release). Aerojet Rocketdyne. March 7, 2016. Retrieved April 20, 2017.
  21. "Aerojet Rocketdyne Achieves 3-D Printing Milestone with Successful Testing of Full-Scale RL10 Copper Thrust Chamber Assembly" (Press release). Aerojet Rocketdyne. April 3, 2017. Retrieved April 11, 2017.
  22. Wade, Mark (November 17, 2011). "RL-10A-1". Encyclopedia Astronautica. Archived from the original on November 15, 2011. Retrieved February 27, 2012.
  23. "ULA Vulcan Launch Vehicle (as announced/built) - General Discussion Thread 3". forum.nasaspaceflight.com. Retrieved June 6, 2020.
  24. "Delta IV Data Sheet". www.spacelaunchreport.com. Retrieved June 6, 2020.
  25. Bergin, Chris (April 7, 2016). "MSFC propose Aerojet Rocketdyne supply EUS engines". NASASpaceFlight.com. Retrieved April 8, 2016.
  26. "Proven Engine Packs Big, In-Space Punch for NASA's SLS Rocket". NASA. October 21, 2016. Retrieved November 22, 2017.
  27. "RL-10 Selected for OmegA Rocket". Aerojet Rocketdyne. April 16, 2018. Retrieved May 14, 2018.
  28. "Northrop Grumman to terminate OmegA rocket program". SpaceNews. September 9, 2020. Retrieved November 23, 2020.
  29. "United Launch Alliance Selects Aerojet Rocketdyne's RL10 Engine". ULA. May 11, 2018. Retrieved May 13, 2018.
  30. Kutter, Bernard F.; Zegler, Frank; Barr, Jon; Bulk, Tim; Pitchford, Brian (2009). "Robust Lunar Exploration Using an Efficient Lunar Lander Derived from Existing Upper Stages" (PDF). AIAA.
  31. 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. ...
  32. Bilstein, Roger E. (1996). "Unconventional Cryogenics: RL-10 and J-2". Stages to Saturn; A Technological History of the Apollo/Saturn Launch Vehicles. Washington, D.C.: NASA History Office. Retrieved December 2, 2011.
  33. "Atlas Centaur". Gunter's Space Page. Retrieved February 29, 2012.
  34. Wade, Mark (November 17, 2011). "RL-10A-3". Encyclopedia Astronautica. Archived from the original on December 6, 2011. Retrieved February 27, 2012.
  35. Wade, Mark (November 17, 2011). "RL-10A-4". Encyclopedia Astronautica. Archived from the original on November 15, 2011. Retrieved February 27, 2012.
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  39. Wade, Mark (November 17, 2011). "RL-10A-4-2". Encyclopedia Astronautica. Archived from the original on January 30, 2012. Retrieved February 27, 2012.
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  45. "Atlas-V with RL10C powered Centaur". forum.nasaspaceflight.com. Retrieved April 8, 2018.
  46. "Evolution of Pratt & Whitney's cryogenic rocket engine RL-10". Archived from the original on March 3, 2016. Retrieved February 20, 2016.
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  48. "RL10B-2" (PDF). Pratt & Whitney Rocketdyne. 2009. Archived from the original (PDF) on March 26, 2012. Retrieved January 29, 2012.
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  53. "American Space Museum & Space Walk of Fame". www.facebook.com. Retrieved April 8, 2018.

Bibliography
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