RL10 Engine

More than half a century of powering space exploration and national security

For more than fifty years, Aerojet Rocketdyne’s RL10 has been the nation’s premier upper-stage rocket engine. Evolved from a technological breakthrough in harnessing high-energy liquid hydrogen as an aerospace propulsion fuel, the RL10 has amassed one of the most remarkable lists of accomplishments in the history of space propulsion.

The RL10 has played a vital role in placing numerous military, government and commercial satellites into Earth’s orbit, and has helped send spacecraft to explore every planet in our solar system, including Voyager 1, the first spacecraft to reach interstellar space, and New Horizons, the fastest spacecraft to ever leave Earth orbit.

Today, three engines derived from the very core of the legendary RL10, the RL10A-4-2, RL10B-2 and RL10C-1 carry on the RL10’s legacy as the launch industry’s “workhorse” by powering the upper stages of United Launch Alliance’s Atlas V and Delta IV launch vehicles.

The RL10C-1 represents the first step toward a common core engine for the Atlas and Delta launch vehicles. This new engine model combines the best attributes of the RL10A-4-2 engine model, developed for use on the Centaur upper stage of the Atlas V launch vehicle, and the RL10B-2, which is currently used on the second stage of the Delta IV launch vehicle.

RL10 engines also are slated to help power NASA’s Space Launch System (SLS) rocket that is in development to lift astronauts to deep-space destinations aboard Orion spacecraft. A single RL10 will power the Interim Cryogenic Propulsion Stage during the first uncrewed test flight of SLS and Orion, known as Exploration Mission-1, targeted for launch in 2018. Four RL10 engines will be on the more powerful Exploration Upper Stage for SLS that will support the first crewed flight of SLS and Orion, known as Exploration Mission-2 that is targeted for launch in 2021.

Program Milestones

  • 1959 First RL10 test
  • 1963 First successful Atlas Centaur flight (two RL10 engines powered upper stage)
  • 1964 Saturn S-4 Launch (six RL10 engines powered upper stage)
  • 1993 First DC-X “Delta Clipper” flight (four RL10A-5 engines powered vehicle)
  • 1999 First successful Delta III flight (one RL10B-2 engine powered upper stage)
  • 2002 First Atlas V flight (two RL10A-4-2 engines powered Centaur upper stage)
  • 2003 500th production RL10 delivered
  • 2009 400th RL10 engine flight
  • 2010 Demonstrated deep-throttling from 104 percent of rated power down to 5.9 percent (an unprecedented thrust range of 17.6:1)
  • 2013 RL10 marks 50 years of service
  • 2014 First flight of RL10C-1






Thrust: 22,300 lbf 24,750 lbf 22,890 lbf
Weight: 370 lbs 664 lbs 420 lbs
Fuel: Liquid hydrogen Liquid hydrogen Liquid hydrogen
Oxidizer: Liquid oxygen Liquid oxygen Liquid oxygen
Mixture Ratio: 5.5:1 5.88:1 5.5:1
Specific Impulse: 451.0 sec 465.5 sec 449.7 sec
Length: 90” 86.5” (stowed) 86”
  163.5” (deployed)
Nozzle Diameter: 46” 84.5” 57”

Data Sheet

Latest News

Aerojet Rocketdyne recently completed successful hot-fire testing of a full-scale, additively manufactured thrust chamber assembly for the RL10 rocket engine at its West Palm Beach, Florida facility.