![](https://spaceflightnow.com/wp-content/uploads/2023/11/20190329-RL10s_small.jpg)
A rocket engine with a protracted pedigree marked a giant milestone on Monday. It’s 60 years because the hydrogen-fueled RL10 engine debuted onboard a Centaur upper stage launched from Cape Canaveral on Nov. 27, 1963.
With that first launch, the RL10 engine, currently manufactured by Aerojet Rocketdyne, became the primary engine powered by a mix of liquid hydrogen and liquid oxygen to be fired in space. The milestone got here at a pivotal time for america, because it was just five days after the assassination of former President John F. Kennedy.
Since that time 60 years ago, 522 RL10 engines have flown in space, with the lion’s share of those flights aboard United Launch Alliance’s (ULA) Delta and Atlas rockets. These engines power the Delta Cryogenic Second Stage and Centaur upper stage respectively.
“Centaur and the RL10 have made it possible for us to launch spacecraft at greater size and weight over any of the opposite upper stage designs in use,” said Gary Wentz, ULA vp of presidency and business programs, during a media event celebrating the milestone. “It has delivered unbelievable missions to the Sun, our Moon, asteroids, every planet within the [solar] system.”
The engine was developed by Pratt & Whitney within the late Fifties through the oversight of NASA’s Lewis Research Center, which was renamed the NASA John H. Glenn Research Center at Lewis Field in 1999. Centaur was originally developed by General Dynamics.
![](https://spaceflightnow.com/wp-content/uploads/2023/11/1960-Centaur-testing-small.jpg)
The mixture helped prove the viability of liquid oxygen and liquid hydrogen as a propellant combination for future launch vehicles. The RL10s themselves would go on for use aboard the Saturn 1, Atlas, Titan and Delta rockets.
The engine also enjoyed use onboard the experimental suborbital vehicle, the DC-X, which was utilized by NASA and the Department of Defense to show a vertical rocket landing.
“It’s very exciting to be at 60 years and it’s a testament to the incredible teamwork that’s gone on between Aerojet Rocketdyne and ULA over all these years, a testament to all of the individuals who worked on this product all these years and an incredible design that was originally specified by the lat Fifties,” said Jim Maus, Aerojet Rocketdyne vp of program execution and integration.
Maus said despite the successes they’ve seen over tons of of engine flights, they proceed to lean on ULA’s motto of specializing in launching separately.
“After we go to launch day, we’re very focused on that day’s launch,” Maus said. “And so, whenever you come to a giant milestone, you form of stand back and recognize, you already know, take a look at all that we’ve done. So, it’s great to be a part of the team that does that and we’re really thrilled to be at 60 years.”
![](https://spaceflightnow.com/wp-content/uploads/2023/11/19631127_Atlas-Centaur-2_launch_small.jpg)
Evolving the RL10
Currently, there are two variants of the RL10 in use: the RL10C-1-1 on ULA’s Atlas rockets and the RL10B-2, which is used on the ULA Delta 4 Heavy and NASA Space Launch System (SLS) rockets.
The latter variant has a limited life though since there is barely yet another Delta 4 Heavy rocket, which is scheduled to launch in 2024 on a mission for the National Reconnaissance Office (NRO). A single RL10B-2 can be used on the SLS’s Interim Cryogenic Propulsion Stage (ICPS) for the primary three Artemis missions to the Moon.
Later versions of the SLS will use the Exploration Upper Stage, which is being engineered by Boeing. That shall be powered by 4 RL10C-3 engines, which together will provide greater than 97,000 kilos (431kN) thrust. For comparison, the one RL10B-2 on the Artemis 1 ICPS produced about 24,750 kilos (110kN) of thrust.
To this point, Maus said there have been eight major upgrades of the RL10 engine. The subsequent major iteration of the engine, the RL10C-X, which remains to be in development, will power future version of ULA’s forthcoming Vulcan rocket.
The largest change seen with this version of the engine comes through its use of additive manufacturing techniques, more commonly often called 3D printing.
“We’re already flying the RL10 with an additive manufactured injector, but now we’re doing an additive manufactured thrust chamber and we’re going through that certification right away,” Maus said. “That engine shall be delivering the best performance of what we now have available in protection today and can extend the lifetime of the RL10 into the long run.”
![](https://spaceflightnow.com/wp-content/uploads/2023/11/20231127_Jim_Maus_RL10_anniversary.jpg)
Maus added that the brand new production techniques will even bring cost savings, but declined to enter specifics on the drivers of the price reduction.
“It’s been a major improvement in cost on the chamber of the engine. We’re also putting a big carbon silicone nozzle on it, that’s pushing up the ISP to present us good performance,” Maus said. “After which, the turbo machinery and what I’ll call the powerhead and the backbone of the engine is similar to what we’ve been flying on the balance of the inventory. So, that it’s going to proceed to delver the very high reliability on day one, launch one.”
The precise date of launch one still stays TBD, but Maus said they’re aiming to debut the RL10C-X in 2025 on a ULA Vulcan rocket. That said, Maus noted that they’ve orders for the present RL10C-1-1 engines through 2026.
Each NASA and ULA are driving what Maus described as a backlog of greater than 150 engines, that are a mix of the legacy versions in addition to the X-C variants with the additive manufactured features. He said NASA remains to be making a determination on whether or not they need to purchase more of the legacy engines or begin to purchase engines using the additive manufacturing technology for future Artemis missions.
In a typical yr, Maus said Aerojet Rocketdyne produces between 16 and 18 engines, but with the incorporation of more additive manufacturing into their production line, they’re ramping as much as 40 engines annually.
“We quickly recognized that by 3D printing the combustion chamber, we could really make a giant change to the price of the engine and the reliance readily available fabricators,” Maus said. “So, moving away from the chrome steel fabrication to the 3D printed copper, we’re capable of now construct geometries we couldn’t have built otherwise with additive manufacturing. After which, we’re capable of produce the engine now with the high volumes and the high rates that ULA needs.”
Classic engine, latest rocket
In lower than a month, ULA plans to debut its Vulcan rocket. The mission, dubbed Vulcan Cert-1, will use a pair of RL10C-1-1A engines to power the Centaur 5 upper stage and send Astrobotic’s Peregrine lunar lander on its strategy to the Moon.
After shipping an upgraded Centaur 5 from its factory in Decatur, Alabama, ULA integrated upper stage onto the Vulcan booster on Nov. 19. The mission is ready to fly no sooner than Dec. 24, 2023.
![](https://spaceflightnow.com/wp-content/uploads/2023/11/20231120_Vulcan_Centaur_stacking.jpg)
ULA is preparing for a wet dress rehearsal in the primary half of December during which the fully integrated Vulcan rocket shall be rolled out to the launch pad and fueled because it if were launching. Maus said Aerojet Rocketdyne engineers shall be on headsets during that fueling test to observe the Centaur and the way the engine is cooled and conditioned as it can be on launch day.
“We’ve engineers taking a look at all the info coming off the engine during wet dress rehearsal and we are able to just about understand in real time that every thing goes right,” Maus said. “But then after all, there’s an information review that’ll come after that to be certain that every thing performed as required.”
Ron Fortson, the director and general manager of launch operations for ULA, said they are going to then roll the rocket out to the launch pad the day before liftoff and get on console to start the countdown about 12 hours ahead of time.
Fortson said integrating the RL10C-1-1A with the Vulcan vehicle went easily.
“Every thing went well in our production facility after which here, it already comes fully assembled and we just mate it with our rocket and we’re able to go,” Fortson said. “So, it’s been an ideal activity.”
Fortson said he and the team at ULA have been working closely with Aerojet Rocketdyne as they work towards the debut of the RL10C-X engine in a few years.
![](https://spaceflightnow.com/wp-content/uploads/2023/11/Vulcan_Centaur_graphic.jpg)
“We’re working very closely with them on their design and their testing. Once that’s all accomplished, we’ll be looking forward to truly just integrating it onto our Vulcan rocket,” Fortson said. “After which after all, we’ll be taking a look at all of our missions which can be coming forward when it comes to what those requirements are and ensuring we are able to satisfy those requirements with this latest engine.”
He said there likely won’t be a selected flight profile that can required for the debut of the RL10C-X on Vulcan, adding that “This engine’s going to be able to doing anything we’d like it to do.”
“I believe whatever requirements we now have for it, we’re confident that this engine will have the opportunity to satisfy it,” Fortson said.
“We’ve a philosophy of test such as you fly, which suggests the engine will only see in flight that which it has experienced on the bottom throughout the limits of what we are able to test or analyze,” Maus said. “So, we’ve been through all of that testing over the past several years to know how the engine operates within the Vulcan scheme.”
Maus said as they give the impression of being forward to flying the RL10 on latest rockets and in latest iterations, they give the impression of being forward to a different key milestone: flying humans via the Industrial Crew and the Artemis programs.
“We’ve been bringing astronauts all the way down to West Palm Beach, to our facility to discuss with our team concerning the reality of what we deliver and it’s very motivating for us to see our passengers standing in front of the room, telling us about how much they’re relying upon us,” Maus said. “But the truth is, we design and construct a highly reliable product and it has demonstrated its reliability.”