Spolier alert: it's a superalloy Aerojet Rocketdyne is qualifying for high-performance rocket engines, including the AR1 vying with Blue Origin's BE-4 to power Vulcan

Aerojet Rocketdyne’s success in developing AR1, an engine designed to replace Russian-made RD-180 engines on United Launch Alliance rockets, hinges in part on its use of Mondaloy, a nickel-based superalloy invented in the 1990s by metallurgists Monica Jacinto, then working at Rocketdyne, and Dallis Hardwick from the Rockwell Science Center.

Prior to the 1990s, U.S. engine makers shied away from developing oxygen-rich staged combustion cycle engines because high-pressure gaseous oxygen would burn components. When engineers identified materials that didn’t burn in this environment, the materials were so weak that they needed to be reinforced, which made the engines heavy.

Jacinto started to concentrate on that problem soon after she graduated from Columbia University with a bachelor’s degree in metallurgical engineering and joined Rocketdyne in 1988. By the mid-1990s, Jacinto and Hardwick had honed in on a composition that would work, a nickel-based superalloy that could withstand gaseous oxygen without excessive weight.

For the last 20 years, Jacinto has helped to shepherd Mondaloy, which is now a family of superalloys, through multiple Air Force and NASA contracts as well as the company’s internal research program. Aerojet Rocketdyne now relies on Mondaloy for key components of the kerosene-fueled AR1 engine, which it plans to deliver to the Air Force for qualification in 2019, and the Hydrocarbon Boost Technology Demonstrator, a U.S. Air Force effort to develop a reusable 250,000-pound-thrust-class engine.

SpaceNews spoke with Jacinto about Mondaloy’s past and future.

What is unique about Mondaloy?

It has the kind of oxygen compatibility and strength we need to build rocket engine components. Prior to Mondaloy, off-the-shelf alloys that were oxygen-compatible were quite weak, which meant it was going to be hard to build structural components out of them. The things you put in the alloy to make it stronger are the things that take away some of this oxygen compatibility. The real challenge was to find that sweet spot where the alloy was strong enough and oxygen compatible enough for a rocket engine component.

When did the government begin funding that work?

In 1999, we entered the first cost-sharing program with the Air Force Research Laboratory. In the early 2000s, NASA was also very interested in having a big oxygen-rich booster engine. Because Mondaloy is a family of alloys, I worked with the Air Force to scale up production, look at different processing methods and get the material ready for insertion into a rocket engine.

All of that positioned us very nicely to have the alloy at a maturity level that it could be used for the AR1 and the Hydrocarbon Boost and a few other programs.

How is Mondaloy used in AR-1 and the Hydrocarbon Boost Technology Demonstrator?

They both have about 12 different components that are made out of Mondaloy.

In AR1, it’s used in most of the components that will be exposed to hot gaseous oxygen, such as the preburner, turbine rotor, turbine housing, ducts, lines and hot gas manifold.

Why is Mondaloy important to AR1?

It helps us meet our affordability goals. We have this alloy that we developed in-house that has the needed characteristics: it’s compatible with the high-pressure, high-temperature oxygen and has high strength. It allows us to avoid the use of coatings, which saves weight and expense while improving safety and reliability.

Can Mondaloy be additively manufactured?

Yes. There are additively manufactured parts of Mondaloy on the AR1. We can manufacture it with conventional wrought methods and powder metallurgy, which includes additive manufacturing.

Where does Mondaloy go from here?

We started in the mid-90s with lab-scale work on an alloy composition that we knew would work. Since then, we have scaled it up to look at two different chemistries: Mondaloy 100 and Mondaloy 200.

If we just want to scale up for one component and one processing method, that would have taken a much shorter time. But we are looking at dozens of components all having different requirements and all made slightly differently. There are similarities across the board, but it is never exact. They might operate at different temperatures and pressures. All these factors keep broadening that matrix that we are studying. But it’s very exciting. It seems like all of that diligent work upfront, taking one step at a time, has paid off.

We have a team of bright, enthusiastic engineers who are all working this. It is heart-warming for me to see the teamwork involved and some of the great technical expertise that’s coming out of it.

What has been the most challenging part of this work?

Programs come and go. Keeping it funded continuously since the mid-90s, I’d consider one of our team’s biggest feats.

By slowly, methodically gaining maturity to the point where a program like AR1 blossoms into all these different components and all these different processing methods is very rewarding and makes all the effort worth it.