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 of thrust per engine in vacuum. Three RL10 versions are still 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, 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 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 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.
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.
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.
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 demonstrator. CECE was intended to lead to RL10 engines capable of deep throttling. In 2007, its operability 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 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 Space Launch System.
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 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.

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.
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

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.
, an enhanced version of the RL10 was proposed to power the Advanced Cryogenic Evolved Stage, a long-duration, low-boiloff extension of existing ULA Centaur and Delta Cryogenic Second Stage 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 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

Partial specifications

All versions