As part of the study, the committee interviewed government, industry, and academic subject-matter experts on the topic of additive manufacturing. This chapter captures opportunities for space-based additive manufacturing currently envisioned by various groups. The committee offers no opinion on these ideas and neither endorses nor validates the proposed concepts and approaches.
There has lately been great public and industry interest in additive manufacturing because of some progress in laboratory experiments, and some ingenious demonstrations. It is discussed in the general press and popular science magazines and is attracting private investment by manufacturing firms interested in cost savings, as well as by many new small and startup businesses interested in additive manufacturing’s compelling possibilities. Academia and government laboratories are also planning experiments. But the technology is still in its infancy and could greatly benefit from well thought out technology roadmaps, standards of quality and performance, common terminology, and other professional engineering standards.
With this as background, this chapter serves as a panorama of possibilities that NASA and the Air Force are considering, but not an endorsement of their likelihood or feasibility.
The most immediate application of additive manufacturing in space relates to creation of replacement parts and components. Data show that a significant percentage of hardware failures on the International Space Station (ISS) involve plastics and composites that may be suitable for repair using additive manufacturing techniques (Figures 2.1 and 2.2 and Box 2.1). This is an area where additive manufacturing could play a significant role. Instead of carrying additional, redundant components to the ISS, parts can be manufactured as needed.
NASA has several efforts under way to bring this vision to fruition.
- A contract with Made In Space, Inc., to verify extrusion-based additive manufacturing in microgravity. The contract’s objectives are to print 21 parts (e.g., ASTM standard test coupons, ISS tools, and other parts) that will later be studied on the ground. To date, engineering test units of the printer have been delivered to NASA and have passed environmental tests, and the flight unit is in production. Although this is an experimental platform, the company plans to develop an operational version for operation on the ISS starting in 2015.
- An optical scanner to verify the integrity of parts.
- Research on trade/systems study for metals-based additive manufacturing.
In addition to U.S. efforts, the European Space Agency and member states have similar plans. In 2017, the Italian Space Agency plans to take an fused-deposition-modeling printer on the ISS.
In addition to fabricating components, additive manufacturing may present new opportunities for recycling (Figure 2.3). Current NASA efforts include a 2014 Phase I Small Business Independent Research (SBIR) call entitled “Recycling/Reclamation of 3-D Printer Plastic for Reuse.” NASA is currently considering eventually transitioning from SBIR to ISS Technology Demonstration in conjunction with planned additive manufacturing activities.
Recycling and reusing materials on the ISS might have a significant impact on space station operations. Currently, astronauts pack trash into robotic spacecraft such as the Russian Progress and the Orbital Sciences’ Cygnus for disposal. The spacecraft are detached from the station and burn up in the atmosphere. But before that happens, astronauts spend a considerable amount of time moving the trash, simply to get it out of the way. Using recycled materials in additive manufacturing might ease this logistics and operations problem. Both the component creation and recycling scenarios offer the ability to launch feedstock in bulk instead of delicate hardware. However, separating products and materials is a large portion of any recycling effort. On a vehicle like the ISS, this may be a time-consuming manual task. Clearly this will require careful evaluation to determine if it is the most efficient solution.
FIGURE 2.1 The percentage of failed parts and components on the International Space Station (ISS) that are candidates for repair or fabrication divided into categories. Some of these could in the near term conceivably be replaced with additively manufactured parts made on the ISS. SOURCE: Courtesy of Made In Space, Inc.
FIGURE 2.2 Parts that can be additively manufactured. SOURCE: Courtesy of NASA.
In contrast to the possibility of creating replacement components onboard human spacecraft, the prospects for producing replacement components for robotic spacecraft in orbit are far less clear. For robotic spacecraft, up to 50 percent of the failures are attributable to power subsystem failures.1 In 1992, a survey was published of 2,500 spacecraft failures that took place between 1962 and 1988. About 50 percent were identified and traceable to issues encountered in operations, the space environment, or with design problems. About 30 percent of the failures were random, likely due to manufacturing and workmanship. In nearly 19 percent of the failure cases, causes could not be determined, perhaps indicating that system telemetry was inadequate.2 Given the complexity and types of failures, it is difficult to envision how in-space additive manufacturing would be able to successfully contribute to the manufacture of replacement parts for robotic spacecraft.
1 “Commercial Communications Satellite Bus Reliability Analysis,” Frost & Sullivan, August 2004; D.M. Harland and R.D. Lorenz, Space System Failures, Springer-Praxis Publishing, Chichester, U.K., 2005.
2 H. Hecht, Reliability during space mission concept exploration, in Space Mission Analysis and Design (W.J. Larson and J.R. Wertz, eds.), Microcosm, Torrance, Calif., 1992.
Emergency Repairs in Space
FIGURE 2.1.1 The adapter assembled by the Apollo 13 astronauts from equipment inside their spacecraft including pieces of folders, plastic bags, and duct tape. Such a device could be produced by an additive manufacturing machine today. SOURCE: Courtesy of NASA.
In 1970, the Apollo 13 Command Module suffered a catastrophic failure on its way to the Moon. The crew encountered many risks to their survival during the mission. They were forced to use the Apollo Lunar Module as a “lifeboat” to keep them alive during the return trip. But the lithium hydroxide canisters for the Command Module were different from the ones for the Lunar Module and did not fit in the same receptacle. With the assistance of engineers on the ground, the astronauts developed a makeshift adapter to connect the two. In 2013, an engineer from the firm Made In Space, Inc., spent 1 hour designing an adapter for the lithium hydroxide canister and was able to print it and demonstrate its operation by the end of the day (Figure 2.1.1). This experience demonstrates the flexibility and adaptability of this technology to address unforeseen situations.
Additive manufacturing is not simply a way to produce the same parts in a different way. Much more importantly, it enables users to design parts for ultimate use rather than for their machining qualities. In other words, additively manufacturing hardware in space could enable production of ultra-low-mass systems and parts for use, thereby easing stowing and launch requirements. Currently, large components and systems such as antennas, booms,
FIGURE 2.3 Parts that can be recycled for new additive manufacturing. SOURCE: Courtesy of NASA.
and panels are designed for launch. Their delicate structures, sizes and shapes are limited by the requirement to stow them within available launch fairings. This severely limits functionality with respect to scaling. Accommodating these structures involves trade-offs between launch vehicle lift capability and shroud size. This problem is often solved by using a larger-diameter shroud that imposes a mass penalty.
While deployable structures have enabled construction of large systems, their packing efficiency is not sufficient to enable the kind of kilometer-size scaling required for many applications such as long-baseline interferometry and sparse aperture sensing.3
With the use of additive manufacturing and supporting technologies in space, on-orbit construction and “erectables” technologies can enable deployment of systems that need not conform to weight and volumetric constraints posed by launch fairings and shrouds.4 Structures envisioned include ultra-thin mirrors, gossamer structures like ribbons, large antennas and arrays, reflectors, and trusses, among others. Such structures can be envisioned to better enable exploration (e.g., provide better sources of power for long-duration exploration activities).
The vision for building such structures involves launching raw materials in a compact, durable state together with software for fabricating, assembling, and integrating components to an already on-orbit additive manufacturing machine that will manufacture the new operational space system. NASA is currently funding Tethers Unlimited, which proposes to take compact materials that are easy to launch, such as spools of thread, to form large truss-based structures such as kilometer-long solar arrays and antennas in space. The company claims that by constructing these structures on-orbit, they can be made with much lower tensile strength requirements; nor do the structures need to survive the harsh vibrations of launch and deployment. The firm has identified several applications, including a star shade to block light from stars so that a space-based telescope can image exoplanets around those stars. This would involve the deployment of a large “SpiderFab,” a spider-like robot that can “extrude” long beams and join together large structures (Figure 2.4).
Additive manufacturing in space could potentially enable production of not just components, but also entire subsystems and systems. An example the committee was briefed on included production, assembly, and launch of sensor-loaded CubeSats from the ISS or other platforms in orbit.
3 Adapted from Robert Hoyt’s NASA NIAC Phase 1 report, available at http://www.nasa.gov/directorates/spacetech/niac/2012_phase_I_fellows_hoyt_spiderfab.html#.UvZAofldWtY.
4 Such structures have been built today without additive manufacturing. For example, the ISS was built on-orbit by assembling multiple components launched separately. Unfortunately, the cost of multiple launches and the labor required for such assembly is high enough that the ISS is not an ideal model for deployment of large space-based structures. ISS assembly required, for example, 89 Russian and 37 shuttle launches, 168 spacewalks spanning 1,061 hours, transport of 924,739 lbs of material, and 2.3 million lines of computer code.
FIGURE 2.4 SpiderFab, a combination of a machine that creates structural elements and a multi-dextrous robot that can manipulate those elements. SOURCE: Courtesy of Tethers Unlimited.
Additively manufactured in-space satellites deployed not only singly, but also as “swarms” have also been envisioned. The proposed Automated Manufacturing Facility on-board the ISS or a standalone CubeSat platform could build swarms of satellites. The swarm could have a range of capabilities, and possibly even act as a fully functional satellite system.
Additive manufacturing research and development is under way in several Air Force Research Laboratory (AFRL) directorates as well other parts of the Department of Defense. The Defense Advanced Research Projects Agency (DARPA) is also exploring additive manufacturing in space. For example, the DARPA Phoenix program is developing and demonstrating technologies to harvest and reuse valuable components from retired, nonworking satellites in geosynchronous orbit and to demonstrate the ability to create new space systems at greatly reduced cost (Figure 2.5). The program envisions developing a new class of small “satlets” that could be sent to the geosynchronous orbit region as a “ride along” on a commercial satellite launch. The “satlets” would then attach to the antenna of a non-functional cooperating satellite robotically, essentially creating a new space system.
The concept of a fabrication laboratory or “fab lab” was developed at the Center for Bits and Atoms at the Media Laboratory at the Massachusetts Institute of Technology to explore how the content of information relates to its physical representation. A typical fab lab is equipped with an array of flexible computer-controlled tools, often including additive or 3D printers, with the aim to make “almost anything,” in the words of its creators. The concept
FIGURE 2.5 Artist illustration of the Defense Advanced Research Projects Agency’s (DARPA’s) Phoenix program. In this illustration a robotic spacecraft is attaching new components to an antenna harvested from a decommissioned spacecraft. SOURCE: Courtesy of DARPA, see http://www.milsatmagazine.com/story.php?number=562432496.
of a fab lab in space is similar: users—human or robotic—would be able to access tools in space to manufacture what is needed without bringing it from Earth. An additive manufacturing capability would be the heart of such a fab lab. There are several free-flying spacecraft that are either currently available or will probably become available within the next decade that could serve as free-flying fab labs for additive manufacturing in space.
Additive manufacturing technology can be applied to subsystems as well as entire spacecraft and can be useful even when what it produces does not meet the conventional definition of a spacecraft. An example of a two-dimensional sensor being developed at the NASA Jet Propulsion Laboratory, funded by the NASA Innovative Advanced Concepts (NIAC) program, is shown in Figure 2.6. This is not a “spacecraft” by common definitions. It is essentially a transparent sheet of plastic with printed electronics that has been proposed to collect environmental data in space or in a planet’s atmosphere. It demonstrates that technology can change conventional understanding of what is possible.
Some people have suggested that additive manufacturing in space could—autonomously or with human
FIGURE 2.6 A two-dimensional printed spacecraft being developed at the Jet Propulsion Laboratory. SOURCE: Courtesy of PARC, a Xerox company; http://gigaom.com/2013/08/20/nasa-wants-to-print-a-spacecraft-but-first-its-printing-the-electronics/.
support—create not just components but an entire spacecraft in space. The spacecraft could be built as a single unit with a single machine or assembled by humans or even autonomously. How long it would take to realize this vision depends not only on technical advancements made but also on how a spacecraft is defined. A single-function spacecraft (one that, for example, only measures solar radiation during a space weather event and then degrades) is feasible on a shorter timeline than a multiple-function spacecraft that is radiation and nuclear hardened, intended to last multiple years, made of multiple materials, and which serves many functions. The latter is likely many decades away.
Availability of construction material (e.g., metals, water) in space (e.g., on asteroids or on surfaces of planetary bodies) enables the possibility of additively building settlements and other facilities without having to take expensive and bulky prefabricated materials out of Earth’s gravitational field. Lunar regolith, for example, could be used to construct pressurized habitats for human shelter as well as other infrastructure (e.g., landing pads,
FIGURE 2.7 A robot on the Moon using “contour crafting” to build up a structure, layer by layer. SOURCE: Courtesy of Behrokh Khoshnevis, University of Southern California.
roads, blast walls, shade walls, and hangars for protection against thermal radiation and micrometeorites) on the Moon (Figure 2.7).
Another NIAC grant to a team at the University of Southern California is exploring the concept of using a technique called contour crafting to build infrastructure (landing pads) on the Moon using simulated lunar regolith. This technique extrudes a material such as concrete layer by layer to build up structures such as walls. The European Space Agency is funding similar research with a technology called D-Shapes to design a Moon-based habitat (Figure 2.8).
Additive manufacturing might provide the means to transform space system architectures. Space system configurations that are now dominated by requirements to survive ground manufacturing, assembly, test, transport, and launch could be reexamined as this new capability becomes available. Relaxation of volume limitations of a launch vehicle shroud, which currently place restrictions on the physical size of a spacecraft, could enable structures beyond what is presently attainable. Structural designers of spacecraft could have an entirely new set of implementation approaches for spacecraft configuration that might not need to account for loads and accelerations in the launch vehicle ascent process.
A launch vehicle transporting material for additive manufacturing in bulk could deliver a payload to space with volumetric densities up to 100 times that currently attainable. Launching materials in bulk would enable more economical ballistic departures.
A space-based manufacturing center tailored to the production of spacecraft on orbit will need to be conceived that will enable designers of tomorrow’s spacecraft to create a digital concept that the space-based manufacturing center would transform into a functioning machine, using the bulk material, tailored to the zero-gravity environ-
FIGURE 2.8 Additively built lunar settlement. SOURCE: Courtesy of the European Space Agency and Foster + Partners.
ment. Full software simulations in the hands of a new generation of scientists and engineers could enable digital simulation of novel configurations for systems to be constructed in space.
The process of developing spacecraft in support of space missions—a process that currently extends up to a decade in length for large spacecraft—might be transformed through the use of (as yet) undeveloped design and construction tools tailored to the additive manufacturing process. Additive manufacturing holds the promise of relaxing current constraints on physical shape and size—opening up the opportunities for physical scales (both large and small) that may be approached by designers in entirely new ways.
The following chapters will explain that the possibilities of additive manufacturing in the near-term are modest—creating replacement components, recycling parts into feedstock, etc. However, in the long run, if near-term efforts are carefully designed and executed, the knowledge base to functionally reconceptualize space architectures could be developed. The application of additive manufacturing to the space environment could lead to a change in ideas and concepts of what satellites look like, how they are designed, and what functionality they have.
The rest of this report examines the possibilities discussed above in light of current technology capabilities and trajectories and proposes a roadmap of how to get from where additive manufacturing in space is today to where it could be in the next 20-40 years.