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Conference attendees and Clarke
Conference attendees watch Arthur C. Clarke discuss the space elevator from Sri Lanka. (credit: J. Foust)

The space elevator: going up? (part 2)

In the last several years the concept of the space elevator has migrated from science fiction to at least science possible. A new approach to the concept, coupled with recent technological developments, has made the elevator at least look feasible. The technology needed to develop an elevator is still years away, at the very least, but the promise the space elevator holds at reducing the costs of putting payloads into orbit has encouraged people to further refine the concept and work on the needed technologies.

About 75 people, ranging from scientists and engineers to people best described as space elevator enthusiasts, gathered in Santa Fe, New Mexico on September 12th through the 15th for the Second International Conference on the Space Elevator. (The first was held last year in Seattle.) The conference brought together people from a wide range of disciplines to discuss the current state of research into the various components of a space elevator, as well as hash out the softer economic, political, and social issues that must be addressed for the space elevator to become a reality. No breakthroughs were made—at least publicly—at the conference, but the groundwork was laid for future work on the elevator concept.

Nanotube progress and other technologies

The development that pushed the space elevator from the pages of science fiction into a topic worthy of two conferences is the carbon nanotube. Discovered in 1991, the elongated carbon structure is potentially 100 times as strong as steel, but far lighter. A ribbon made of carbon nanotubes, or of a composite fiber that incorporates nanotubes, would be strong enough to support its own weight as well as the weight of vehicles climbing up the ribbon from the ground to geosynchronous orbit. Without nanotubes, a space elevator would likely not be possible with any other known materials. “The cable is the riskiest part,” said Bryan Laubscher of Los Alamos National Laboratory, one of the co-organizers of the conference.

One of the first sessions of the conference dealt with current research into carbon nanotubes. Rodney Andrews of the University of Kentucky discussed the work his research group has done creating composite fibers containing nanotubes. His group recently created five kilometers of fiber containing two percent nanotubes, and he believes that that can easily make far longer lengths of cable. “The length is not the challenge,” he said. “It’s getting the strength.”

“The length is not the challenge,” Kentucky’s Andrews said of making nanotube composite fibers. “It’s getting the strength.”

To that end he and his colleagues have been working on developing multiwalled nanotubes, which as the name suggests are carbon nanotubes that contain multiple layers of carbon. They are currently able to produce 1.2 kilograms of such nanotubes a day, with a purity of at least 95 percent. Such nanotubes should have a tensile strength of at least 150 gigapascals (compared to steel’s 0.4 gigapascals), based on recent tests at the University of California Berkeley, and could be as high as 300 gigapascals. Andrews said that strength should be sufficient to make composite fibers with a strength of at least 100 gigapascals, the requirement for a space elevator.

A different approach is being undertaken by Yuntian Ted Zhu of Los Alamos. Rather than work with relatively short carbon nanotubes, a few microns long, he is trying to develop continuous lengths of nanotubes that could be woven into fabrics and threats. The continuous nanotubes, he believes, could get around some of the problems of using shorter nanotubes in composites, where the interface between the nanotube and the composite material can cause stress concentrations or become a point of weakness.

Attendees agreed, though, that nanotubes presented the only solution to the material requirements for a space elevator. “This is the long pole because it is new technology,” said Brad Edwards, director of research at the Institute for Scientific Research (ISR) and the leading developer of the new space elevator concept.

Nanotubes “are not completely inert in mammalian tissue,” said Ron Morgan of Los Alamos. “Don’t be the guinea pig.”

One issue the conference addressed that had not previously been widely contemplated is the environmental and health risks that nanotubes pose. Ron Morgan of Los Alamos noted that nanotubes could pose a health risk through skin irritation, ingestion, or inhalation. “The human body has never been subjected to materials like this,” he noted, saying the material most like nanotubes was asbestos, a known carcinogen. Animal tests of nanotubes are just beginning, he noted, and early results do show some adverse affects. “These are not completely inert in mammalian tissue,” he said. He urged researchers to treat the materials with caution, using fume hoods and other equipment to keep them from inhaling the material. “Don’t be the guinea pig.”

Other sessions of the conference tackled other technical issues, ranging from beaming power from the ground to vehicles on the elevator to the dynamics of the elevator cable itself. In a session about the “climbers” that would travel up the elevator, Laubscher noted that there has been very little technical work done to date on the technical design of these vehicles. “There are many aspects of the space elevator that no one has thought about,” he said.

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