Space: The Final Frontier [for materials innovation]? It's a far-out idea but the notion of manufacturing materials in a microgravity environment is quite intriguing. Without all that pesky force we call gravity holding us back, we can explore lots of unusual phenomena perhaps impossible to replicate on the surface of our blue gravity-producing planet.
From mammalian cells to compound semiconductors, material exposed to microgravity can undergo profound changes. In a microgravity environment, many of the physical constraints materials are subjected to here on earth are significantly reduced or removed. There is no hydrostatic pressure, reduced hydrodynamic shear, and no sedimentation in microgravity enabling, for example, high-quality protein crystal growth impossible to obtain in 1g. Furthermore, mass transfer is limited to the rate of diffusion and materials can achieve their lowest energy states in microgravity. Potentially, metal alloys impossible to make on earth could be made in space and the crystallinity of many semiconductors could be enhanced.
There are a variety of ways to obtain microgravity. Perhaps the simplest is the drop tower (or drop shaft if below ground). In free fall, microgravity is achieved for a few seconds. From there, we must go skyward. Planes that fly in parabolic arcs can achieve microgravity in about 25 second intervals. NASA's "vomit comet" is perhaps the best-known example. For minutes of continuous microgravity, sub-orbital or sounding rockets can do the trick. If you really want sustained microgravity however, you should probably venture in to orbit with a satellite, space shuttle, or aboard the space station.
As strange as it sounds, materials grown in microgravity can help us better understand our own bodies right here on the ground. In microgravity, protein crystals can be grown larger at higher purities that is impossible to replicate here on earth. High quality protein crystals makes it possible to better determine the underlying structure and function of various important proteins helping us develop better ways to combat diseases. Early stage research on organ growth in microgravity looks quite encouraging as well with the promise of improved efficacy and reduced transplant rejection rates for organs grown in zero-g.
While terrestrial additive manufacturing is gaining momentum (discussed here: Additive Manufacturing: Printing a Better and Cleaner World), 3D printing in space could be a game-changing proposition as well. Building parts on demand can reduce launch mass and size constraints, two of the major cost factors for getting things in to space. Down the line, harvesting resources from asteroids and printing with materials already in space opens many new doors. Made in Space is a startup based out of NASA Research Park attempting to develop a 3D printer for space and onboard the ISS. Let's just hope their printer prototypes extrude more plastic on NASA's "vomit comet" than their technicians' extrude… Well, it's called the vomit comet for a reason, right?
Pangaea recently invested in A2M. A2M is a promising early stage venture developing microgravity-enhanced materials. The first commercial focus is on compound semiconductors like silicon carbide (SiC). Silicon carbide is a wide bandgap semiconductor that has been touted for its high thermal conductivity, electric field breakdown voltage, and maximum current density making it a very promising candidate to replace silicon in certain power electronics applications. However SiC wafers today are prone to yield-killing defects reducing performance and impacting cost. A2M is pioneering a commercially viable way of producing wafers with significantly reduced defect densities and exceptional performance.
As access to microgravity becomes more widespread in academic and commercial research, I expect to see many more materials science breakthroughs. Leveraging the dropping costs of obtaining near weightlessness, the sky truly is the limit!