one engine ran at full thrust for 1,680 s (28 minutes)
In short
The RL10 is a rocket engine for upper stages, burning liquid hydrogen with liquid oxygen. It first ran in 1959 and began at 15,000 pounds-force of thrust. Current versions are rated at nearly 25,000. Pratt & Whitney designed it, as the company's first rocket engine, and Aerojet Rocketdyne makes it today in West Palm Beach, Florida.
The original design's thrust chamber is a bundle of thin stainless steel tubes brazed together, and its pumps are aluminium. Hydrogen runs through the tubes, picks up heat from the chamber walls, and then drives the turbine that pumps the propellants. This is the expander cycle.
Application
RL10 is the upper-stage engine on ULA’s Centaur stage, used on Atlas V and Vulcan. It burns liquid hydrogen and liquid oxygen and is built for restartable in-space burns, so its materials must handle both cryogenic propellant and hot exhaust.
Photos
How it is built
Thrust chamber
The tapered tubes are Type 347 stainless steel, with walls only 0.012 inch thick, rolled by the LeFiell Company. They are silver-brazed together in a gas furnace for 20 hours, with manifolds at each end, to make one light chamber. Hydrogen flowing inside protects the tubes from combustion at nearly 6,000 degrees Fahrenheit.
Thrust chamber tubes (RL10 as described in P&W-era history)
Tube braze joints
Thrust chamber tube bundle (180 up tubes and 180 down tubes)
Chamber inlet and discharge manifolds with stiffening bands
RL10C-1 thrust chamber tubes
Injector
The injector face is Rigimesh, stacks of Type 347 stainless steel mesh hot-rolled into a porous sintered plate. It carries 216 injector elements in concentric circles, each a central stream of liquid oxygen wrapped in a ring of gaseous hydrogen. A spark igniter set into the face starts combustion.
Injector face plate (Rigimesh)
Injector elements (x216)
Spark igniter
Pumps and turbine
The fuel pump's impellers and body are aluminium, and its shaft and bearings are stainless steel. Both turbine stages, both disks and the hub are machined from one aluminium alloy forging. A gear train of 6260 alloy gears drives the oxygen pump, which has a stainless steel impeller in an aluminium housing.
Fuel pump inducer, impellers and body
Fuel pump drive shaft and bearings
Turbine blades, disks and hub
Drive gears
Oxidizer pump impeller and inducer
Nozzle extensions
Some versions add a nozzle extension to improve performance. The RL10A-4 had an extendible, radiation-cooled nozzle of columbium, a name for niobium alloy, and the RL10A-4-2 has a fixed 51-centimetre columbium extension. The RL10B-2 uses carbon-carbon from Safran Ceramics, and no other American liquid engine has flown with one.
Aerojet Rocketdyne has tested an RL10 thrust chamber of copper alloy made by 3D printing. It has only two main copper parts in place of the brazed tube bundle, a part count more than 90 percent lower. A full-scale 3D-printed injector was hot-fired with it.
The fuel pump, turbine blades and disks, and the oxygen pump housings, in unnamed alloys.
Columbium (niobium) alloy
The radiation-cooled nozzle extensions of the RL10A-4 and RL10A-4-2.
Carbon-carbon
The nozzle extension of the RL10B-2, made by Safran Ceramics from a needled preform.
Copper alloy
The 3D-printed test chamber. It is a development part, not a flight engine.
The materials by familyHow many of the parts that name a material use each one
Stainless steel5
Other5
Aluminium4
Gold and silver2
Polymers and foams1
Copper1
How it connects to other things
The RL10 was created for Convair's Centaur stage. Today one or two power the Centaur on Atlas V, two power Vulcan's Centaur V, and one powers the upper stage of NASA's Space Launch System. Earlier users include the Delta III and IV second stages, Titan Centaurs and, in a cluster of six, the Saturn I's S-IV stage. At least three of its technologies passed into the J-2.
ICPS upper-stage engine: it sent Orion to the Moon with the translunar injection burn on Artemis I and raised Orion's orbit on Artemis II, where Orion's own main engine did translunar injection; launcher engine, not carried by the capsule
Aluminium. Here: Fuel pump inducer, impellers and body; Turbine blades, disks and hub and more. There: Booster LO2 and RP tanks; Propellant feedlines and more.
stainless steel. Here: RL10C-1 thrust chamber tubes; Fuel pump drive shaft and bearings and more. There: Centaur propellant tanks.
Aluminium. Here: Fuel pump inducer, impellers and body; Turbine blades, disks and hub and more. There: Structure, three major assemblies; Through-hole spacers, aluminium, 15.24 mm x 6.0 mm OD (x16) and more.
stainless steel. Here: RL10C-1 thrust chamber tubes; Fuel pump drive shaft and bearings and more. There: Chassis screws (ten per structure, M3x5mm flathead); Threaded rods, M3 stainless (x4) and more.
Aluminium. Here: Fuel pump inducer, impellers and body; Turbine blades, disks and hub and more. There: Cabin front-face, RCS cluster trusses, decks and bulkheads; Micrometeoroid shield and more.
The detailed accounts of its materials describe the original Pratt & Whitney engine, so current versions may differ. The alloys of today's valves, bearings, igniters and injectors are not published, and the RL10C-1's chamber tubes are called only stainless steel.
The detailed data
What is written above is built from these numbers and quotes. Each row links to the page it was taken from. Get all of it as JSON, or ask our MCP server.
Features
Hydrogen heated in the chamber tubes drives the turbine, which pumps the propellants
Only US liquid engine to fly a carbon-carbon nozzle extension (RL10B-2)
Thrust chamber is built from thin tubes joined into one lightweight part
Specifications
What
Value
First run
1959
Propellants
Liquid hydrogen and liquid oxygen
Cycle
Expander cycle
Thrust and Isp (current)
Nearly 25,000 lbf, Isp nearing 467 s
RL10A-4 vacuum thrust
20,800 lbf (upgraded from 16,500 lbf)
RL10A-4 expansion ratio
84:1 with extendible nozzle
Turbine power
About 644 hp
Original thrust and specific impulse
15,000 lbf, Isp about 444 s (RL10A-1 era)
First flight-rated production model
RL10A-1, preliminary flight rating testing completed November 1961
First experimental engine test
July 1959
RL10A-4-2 thrust and Isp
99.2 kN (22,300 lbf), 450.5 s
RL10B-2 thrust (ICPS)
24,750 lbf (110 kN)
RL10C-1-1A thrust (Vulcan Centaur V)
23,825 lbf (106 kN) each
Exploration Upper Stage thrust
about 97,000 lbf from four RL10C-3 engines
Dual-engine Centaur missions
Centaur evolution proven over more than 260 missions, over 150 with a dual-engine Centaur
Engine temperature and pressure
combustion temperature nearly 6,000 F
Longest single run
one engine ran at full thrust for 1,680 s (28 minutes)
RL10C-1 first flight
December 2014 (Atlas V)
Materials in detail
Each material named in the sources: where it is used here, which other products use it, and its key numbers when its material page exists.
Chamber tubes, injector plate, pump and gear materials are described in a detailed EngineHistory.org account of the P&W-era engine; nozzle extension materials come from NASA and P&W papers. Components, suppliers and links were added from public sources. A material is left blank where no source states it.
Current-production alloy grades for RL10C versions not confirmed. No standards (AMS/ASTM numbers) are given in the sources. Valve, bearing and igniter materials not covered. More detail: Internals of current RL10C-1, RL10C-1-1A and RL10C-3 hardware (valve, bearing, igniter, injector alloys) are not published in the pages read; the EngineHistory description is of the P&W-era RL10A. The B14643 page is a third-party compilation of two primary papers (Santiago, Pratt & Whitney 1996; Rudman and Austad, Lockheed Martin 2002), used for the variant-to-vehicle table, whose rows are flattened text. Engine counts per stage for Delta IV, Atlas III and Titan rows come from that table. Surveyor, Viking and Voyager launches on Centaur are named only in lists, without a source tying each to a specific RL10 variant. The EUS status should be re-checked (see the SLS entry). More detail: Internals of current RL10C-1, RL10C-1-1A and RL10C-3 hardware (valve, bearing, igniter, injector alloys) are not published in the pages read; the EngineHistory description is of the P&W-era RL10A. The B14643 page is a third-party compilation of two primary papers (Santiago, Pratt & Whitney 1996; Rudman and Austad, Lockheed Martin 2002), used for the variant-to-vehicle table, whose rows are flattened text. Engine counts per stage for Delta IV, Atlas III and Titan rows come from that table. Surveyor, Viking and Voyager launches on Centaur are named only in lists, without a source tying each to a specific RL10 variant. The EUS status should be re-checked (see the SLS entry).
