When we last left Tom Williams and his team of young engineers, they were busy bringing monster 1960s-era rocket engines back to life. That work continues to pay dividends, but Williams and the propulsion systems team at NASA's Marshall Space Flight Center in Huntsville, Alabama, have a wide variety of projects in the works at the moment. Their latest? 3D printing rocket components from scratch and firing them.

The test shown above, which occurred on August 22, involved an entire 3D printed injector plate—the largest 3D printed component NASA has ever tested. It delivered enough fuel and oxygen to produce 20,000 lbs of thrust (about 89 kilonewtons), a bit more than you can get from an F-15's Pratt and Whitney F100 turbofan running at full military power.

Of course, NASA's 3D printing doesn't have much in common with the kind of home 3D printing I've spent the past few weeks experiencing. While I've been faffing about with thermoplastics and fused deposition modeling, NASA has been busy forming metal powders into solids with a technique called direct metal laser sintering (referred to as DMLS or just MLS). For last week's test, NASA had a contractor build a duplicate of a conventionally machined injector—a structure that introduces fuel and oxidizer into a rocket's combustion chamber.

The traditional 28-element injector consists of a housing and a plate to divide the propulsion flow paths from the oxidizer flow paths and 28 separately machined injector components. Each injector is in turn made up of several elements joined together, including an oxidizer feed path, a fuel feed path, and a connector to fix the injector in place. The 3D printed version, though, is all a single monolithic piece from end to end. There are some minor differences in design, but the 3D printed version was designed to work with the same propulsion flow paths and the same chamber pressure.

Fidelity is an issue with 3D printed parts, even using advanced techniques like MLS. Greg Barnett, the lead propulsion engineer on the project, explained that DMLS introduces small surface variations into the mix. "The surface is a little rougher," he explained; however, those variations are within a consistent range and can be compensated for in the design. In other words, each DMLS-produced component doesn't have to be individually tested for variation—the "fix" to overcome the imperfections can be designed into the component.

The test results on the 3D printed components have been extremely positive; Barnett and Williams told Ars that the 3D printed injector is equivalent in performance to the traditional machined one. The next step is to move on to an injector with more elements, which will mean testing with more power.

3D printing—or "additive manufacturing," as it's called when you get industrial like this—is seen by NASA as a vital way to keep rocket component development costs down. In a lot of ways, the ability to rapidly prototype via DMLS harkens back to the Apollo-era development method of fast physical iteration. Rather than spending a tremendous amount of time performing deep, computer-based analyses of rocket components, NASA can rough in a design and then print and test a component within hours or days.

The deep analysis and simulation tools are still available and still used, but the months- or years-long physical manufacturing time is drastically reduced. This gives engineers the flexibility to design and build in the most optimal fashion. They can use complex software analysis where necessary, but they don't have to rely solely on computer modeling.

In the days of Apollo, NASA operated with effectively unlimited funding, which it used to create a nation-wide army of contractors with tremendous manufacturing capabilities. Design-by-iteration was feasible because there was so much design going on. These days, the picture is entirely different. "It's almost a cultural issue," explained Williams, "where a part can cost so much, you get into what I call 'analysis paralysis.'" Without additive manufacturing, prototype rocket parts that can withstand actual hot-firing can cost so much and take so long to produce that when you finally get a physical component to test, you're already hoping the tests show that it's perfect—otherwise it would take too long to redesign. With additive manufacturing, that paralysis goes away, and engineers can iterate as needed on actual physical components.

Williams sees NASA's work in this space as part of the service that a responsible government agency should be providing. The lessons learned will be available for use by any US-based company that wishes to take advantage of them, which puts NASA into the role of a technology incubator and advanced research and development shop.

"In 2008, about eighty percent of our workforce was focused on supporting Shuttle and keeping the shuttle flying safely and on getting Ares designed," he explained. Now, in the post-Shuttle and post-Constellation world, "we're about forty percent focused on SLS. So sixty percent of our workforce is working on research and technology development: things that can help push the industry to new levels that they wouldn't otherwise be able to achieve."

"And it's cool stuff," he finished. "The guys really enjoy it. It's motivating and it's making a difference. It's really exciting." The idea of NASA being freed to play a government-funded R&D role in rocket technology is a fascinating one and makes it similar to the approach taken by many of the national labs run by the Department of Energy. In this case, the knowledge and techniques that result will be available to private space flight companies like SpaceX, freeing them in turn to focus on delivering economic returns.

In the near term, NASA will continue pushing to develop additive manufacturing for rocket components. One of the first major applications will almost certainly be for the proposed SLS heavy lift rocket. SLS' core stage will be powered by the legacy RS-25 Space Shuttle Main Engines, of which NASA has a small existing stockpile. If SLS is able to fly regularly, that inventory of engines will quickly be exhausted and replacements will need to be built. The RS-25 itself is an extremely efficient, extremely complex machine, and utilizing additive manufacturing could potentially decrease its build costs by orders of magnitude.