New Tool For Space Exploration: Onboard 3-D Printer
Challenges abound, but off-planet manufacturing can expedite exploration
Nestled in a cargo bag scheduled to fly on the next SpaceX Dragon cargo carrier in September is a piece of equipment its builders hope will begin to change the way humans—and their robots—explore and exploit space.
The device, essentially a 3-D polymer printer rated for spaceflight, will be installed in a glove box on the International Space Station (ISS) where the crew will evaluate how well it works in microgravity. Whatever the results, it will be the first space-based factory ever, and could herald a drastic shift in how terrestrial engineers plan deep-space missions.
“If we didn’t have to launch everything from the surface of the Earth, maybe we would be further along than we are in space,” says Jason Dunn, who co-founded the Silicon Valley-based startup Made In Space Inc. They designed and built the 3-D Printing in Zero-G Technology Demonstration with a small-business-innovation-research grant from NASA (AW&ST June 23, p. 29).
The U.S. space agency is interested in using additive manufacturing (AM) to replace broken parts and build needed tools on deep-space human missions. On a trip to Mars, with no source of resupply, AM would be an enabling technology, allowing crews to recycle hardware over and over by essentially printing what they need and throwing it back in the hopper as feedstock when they are done with it.
But that day is a long way off, according to a new National Research Council (NRC) study of the state of space-based AM. While the technology is advancing by leaps and bounds on the ground, there is a lot of difficult engineering to do before the technology becomes truly “disruptive,” to use the adjective Dunn favors.
“There has been a substantial degree of exaggeration, even hype, about its capabilities in the short term,” says the NRC Committee on Space-Based Additive Manufacturing in its report 3-D Printing in Space. “The public often believes that these technologies are further along than they actually are. The realities of what can be accomplished today, using this technology on the ground, demonstrate the substantial gaps between the vision for additive manufacturing in space and the limitations of the technology, and the progress that has to be made to develop it for space use.”
Commissioned by NASA and the U.S. Air Force, the NRC report includes an entire chapter on problems that must be surmounted before space-based AM becomes more than a test-bed project. Major issues include the three-dimensional parts resolution that can be achieved with additive manufacturing processes, as opposed to the reductive machining traditionally used in the aerospace industry, and the time it takes to build it. The closer an AM part is to the computer-stored design that guides its printing head, the longer it takes to build—on the ground or in space. Also of concern is the effect of microgravity on the materials, processes that industry is just learning to control with AM on the ground.
While the vacuum of space may actually enable some AM techniques, such as the electron-beam technology Sciaky Inc. of Chicago is using to build large aircraft parts in vacuum chambers on the ground (AW&ST Feb. 4, 2013, p. 18), microgravity is another story.
“In the absence of gravity, surface tension forces become important determiners of system behavior, and processes that rely on the control of fluid or flow conditions will need further research,” the NRC report states.
However, the microgravity environment in space also may make it possible to build complex and extremely lightweight parts that could not be made on the ground.
“The absence of gravity might permit a printer to work on the ‘bottom’ and the ‘top’ of an object at the same time,” the NRC experts suggest. “Imagine a printer for use in space that has multiple print heads and works on all six sides of an object resting in the space between the heads. Air jets or electrostatic attraction might be used to keep the growing object in place, or even to move it to the orientation most suitable for printing.”
There are limits to how far AM can go. Engineering students at Montana State University hope to launch a printed cubesat this fall that was built up from Windform XT 2.0, a polyamide-based carbon-filled material, in a demonstration of using AM to make spacecraft structures. But building a full satellite is more difficult.
Even on the ground, the technology is just beginning to find ways to merge different kinds of spacecraft components, such as structure and electronics, in a single AM build. And even if it can be done, “a single manufacturing defect or anomaly in one function results in the overall failure of the combined system,” according to the NRC.
“[A]n acceptance testing failure of an embedded wire would result in scrapping the entire part, not just replacing a wire, even though strength and stiffness of the structure may be unaffected,” the report says.
For more complex electronics, the most advanced AM techniques fall far short of the photolithography used to produce the integrated circuits that are in spacecraft flight computers, the NRC panel found, and improving on that particular state of the AM art in the drive to print full spacecraft “will be a significant development challenge.”
“Although lesser capabilities may be acceptable for some applications (and can be traded off for other benefits, such as cost), they will likely not be acceptable for critical or high-value applications,” the NRC experts say. “This may prove to be one of the most intimidating technology areas. The ultimate solution may be to use additive manufacturing to produce what is reasonable and place or integrate components produced by other means.”
For now, the Made In Space testbed is scheduled to print 21 different parts on the ISS using extrusion-based AM. Those will include test coupons, space station tools and sample parts. The company plans to develop a commercial manufacturing center for the station tentatively set for launch in 2015.
“Made In Space now has first-hand experience of the full ‘A-to-Z’ process for designing, building and testing hardware for spaceflight,” says Niki Werkheiser, NASA 3-D Print project manager.
Beyond that, the company’s young engineers have big ideas for space manufacturing over the long term, including using AM techniques to build habitats out of lunar and Martian regolith—a concept also under study at the European Space Agency—and perhaps finding a way to recycle space debris.
“We’re talking about mining asteroids for their resources,” says Dunn. “We’ve got aerospace-grade metal in orbit. Let’s go get that.”
Ultimately, as Dunn says, the objective of building things in space—with AM, recycled materials or in-situ resources—is to reduce the load that launch vehicles must carry. John Mankins, a longtime advocate of using massive satellites to collect solar energy in space and beaming it to the ground to power the electric power grid, has based his latest space solar power (SSP) concept on the use of robotics to manufacture the collection satellites in orbit from components manufactured on the ground (AW&ST June 9, p. 42).
Former NASA Administrator Michael Griffin, long a skeptic of SSP because of the launch requirements, says he could change his mind if resources mined in space were used to build the spacecraft there. And current NASA exploration managers plan to test in situ resource utilization (ISRU) with an experiment on the agency’s next Mars rover that would pull oxygen from the planet’s carbon dioxide-rich atmosphere. That automated propellant factory would provide future explorers with a local supply of rocket-fuel oxidizer for the long trip home, saving launch costs at the beginning of the journey (AW&ST May 15, p. 18).
“Once we know the answers, they can dramatically affect the architecture and affect the mission scenarios we put together in the future,” says NASA spaceflight chief William Gerstenmaier, of the ISRU work planned for Mars.