Methods Reduce Cost, Enhance Quality of Nanotubes
- Sunday, 01 November 2009
Originating Technology/NASA Contribution
For all the challenges posed by the microgravity conditions of space, weight is actually one of the more significant problems NASA faces in the development of the next generation of U.S. space vehicles. For the Agency’s Constellation Program, engineers at NASA centers are designing and testing new vessels as safe, practical, and cost-effective means of space travel following the eventual retirement of the space shuttle. Program components like the Orion Crew Exploration Vehicle, intended to carry astronauts to the International Space Station and the Moon, must be designed to specific weight requirements to manage fuel consumption and match launch rocket capabilities; Orion’s gross liftoff weight target is about 63,789 pounds. Future space vehicles will require even greater attention to lightweight construction to help conserve fuel for long-range missions to Mars and beyond.
In order to reduce spacecraft weight without sacrificing structural integrity, NASA is pursuing the development of materials that promise to revolutionize not only spacecraft construction, but also a host of potential applications on Earth. Single-walled carbon nanotubes are one material of particular interest. These tubular, single-layer carbon molecules—100,000 of them braided together would be no thicker than a human hair—display a range of remarkable characteristics. Possessing greater tensile strength than steel at a fraction of the weight, the nanotubes are efficient heat conductors with metallic or semiconductor electrical properties depending on their diameter and chirality (the pattern of each nanotube’s hexagonal lattice structure). All of these properties make the nanotubes an appealing material for spacecraft construction, with the potential for nanotube composites to reduce spacecraft weight by 50 percent or more. The nanotubes may also feature in a number of other space exploration applications, including life support, energy storage, and sensor technologies.
NASA’s various efforts with carbon nanotubes have made it a global leader in this field. Among the many examples are Johnson Space Center’s Carbon Nanotube Project, which focuses on bulk nanotube production, purification, and application, and Goddard Space Flight Center’s improved arc discharge method of nanotube production, developed under the direction of Jeannette Benavides (featured in Spinoff 2007 and 2008). While the Agency continues its own research, it partners with private companies to advance this unique technology for use on Earth as well as among the stars.
One of the significant challenges involved with taking advantage of single-walled nanotube technology lies in how the nanotubes are made. Typical manufacturing methods are expensive, are not amenable to large scale production, and can be inefficient, resulting in samples containing as low as 10–15 percent nanotubes. Costly and time-consuming separation procedures are needed to sort out nanotubes of the desired diameter, length, and chirality. In addition, nanotube samples can be tainted with residual catalyst impurities and common byproducts like amorphous carbon and graphite nanofibers. Thus, affordable, largely pure nanotube supplies with tailored properties for research and commercial efforts have been lacking.