One key feature of the tiny engine was almost a throwaway. The regeneratively cooled Rutherford was built using additive manufacturing (AM), essentially 3-D-printed in Inconel and titanium. As the traditional government customers for space vehicles see their budgets flatten or shrink, industry is taking a deep dive into AM to keep its products competitive in an increasingly commercial marketplace.
That includes companies that have traditionally counted governments as their only customers as well as more-entrepreneurial startups like Rocket Lab and(SpaceX).
Rocketdyne (AJR) is using the technology to speed development of the AR-1 engine it is proposing as a replacement for the Russian RD-180 on the Atlas V. has been studying large-scale AM for the warplane for about a decade, and is moving the technology into spacecraft with a new $6 million AM center near Denver.
Of that sum, more than $4 million went to buy a “Direct Manufacturing” system from Sciaky Inc., the Chicago-based aerospace supplier that turned its expertise in electron-beam welding into large-scale AM tools. Using the Sciaky system to build spacecraft-propellant tanks from titanium wire, as well as laser-sintering techniques that turn metal powders into brackets and other parts, Lockheed Martin Space Systems Co. hopes to cut the time to manufacture a satellite from as long as 48 months to 18, according to Dennis Little, vice president for production.
“If you’re going to build a titanium tank for a satellite that we currently build, you have to buy a billet of forged titanium, and the latent time is 14 to 18 months to get it from the supplier, and then you have to machine it down to its final geometry,” Little says. “This machine, the Sciaky, lays it up bead by bead, and then you machine it to the final thickness, and you have two spheres and probably a barrel section for the final tank geometry. So you get a tank for a small satellite, machined in three pieces, and within a week’s time.”
Lockheed Martin engineers worked with Sciaky to design the satellite-tank AM tool, which uses an electron beam in vacuum to melt the titanium wire and lay it up onto the spinning article (photo). It already has produced 35-in. tanks, and is moving on to 40-in. and ultimately 48-in. tanks. The hardware will go into the company’s A2100 satellite-bus “technology refresh” already underway, and perhaps the planned Jupiter space tug in contention for’s next International Space Station cargo resupply service contract (CRS-2).
To date, tanks produced in the independent research and development effort have scored “in the high 90s” in tests to failure, compared to tanks machined from forged billets, which Little terms “pretty darned good, and probably good enough.” Any shortfall can be covered by adding thickness to the tank walls, he says.
SpaceX uses laser-sintering AM to make impellers and other parts for the Merlin engines that drive its Falcon 9 launch vehicle, which is now in the process of being certificated for human spaceflight under aCommercial Crew Transportation Capability contract. Aerojet Rocketdyne (AJR) is using the same technique, applying some “engineering rigor” to ensure the resulting engine parts have performance comparable to parts produced with the traditional subtractive machining.
“In general, we’re using it across the board on traditional products to bring the cost down for those types of geometries that lend themselves to it, and then we’re also exploring what type of new products you can build, because it is a very different way of building and thinking about things,” says Julie Van Kleeck, the company’s vice president of advanced space and launch systems.
Given the high speeds and pressures and low temperatures that rocket engine parts must withstand, materials properties of parts produced with AM are particularly important. An engineer may be able to design a part for additive production that would be impossible to create with traditional machining, but it still must meet fatigue and hydrogen-embrittlement specifications before it can fly.
The results are starting to pay off, according to Linda Cova, executive director of hydrocarbon engine programs at AJR. Some of the AM-generated parts have enough fidelity to their designs that they can be hot fired without additional finishing, she says.
“We’ve learned a lot about the properties that you can actually get, and what influences the properties,” Cova says. “Is it the size of the powder? There are so many different elements that go into it, so we spend a lot of time understanding that, so we know when we’re done we have a part that’s reliable, repeatable and clearly [has] the benefit of shorter schedule.”