Living up to the Hype: Superconductors
NASA research is unlocking the amazing potential of high-temperature superconductors.
5, 2003: Few technologies ever enjoy the sort of rock-star
celebrity that superconductors received in the late 1980s.
Above: The MLX01 experimental "maglev" train, currently being tested by Japan's Railway Technical Research Institute, uses "old fashioned" low-temperature superconductors that require liquid helium for a coolant. High-temperature superconductors can use liquid nitrogen instead, which is cheaper, more abundant, and easier to handle. Image courtesy RTRI.
†††† What ever happened to the "high-temp" hype? "It was the hottest potato of its time, but it fizzled out," says Louis Castellani, president of Metal Oxide Technologies. The problem was learning to make wire out of it. These superconductors are made of ceramics - the same kind of material in coffee mugs. Ceramics are hard and brittle. Finding an industrial way to make long, flexible wires out of them was difficult. Indeed, the first attempts were disappointing. "First generation" HTS wire was relatively expensive: 5 to 10 times the cost of copper wire. The amount of current it could carry often fell far short of its potential: only 2 or 3 times that of copper, vs a potential of more than 100 times.
Left: "Second generation" HTS wire can carry the same amount of current as copper wire hundreds of times as thick.
†††† But now, thanks to years of research involving experiments flown on the space shuttle, this is about to change. The NASA-funded Texas Center for Superconductivity and Advanced Materials at the University of Houston is teaming with MetOx to produce the "smash hit" that scientists have been seeking since the '80s: a "second generation" HTS wire that realizes the full 100-fold improvement in current capacity over copper yet costs about the same as copper to produce. Once-famous superconductors may be about to step back into the limelight.
The audience awaits: The special "talent" of superconductors is that they have zero resistance to electric current. Absolutely none. In theory, a loop of HTS wire could carry a circling current forever without even needing a power source to keep it going. In normal conductors, such as copper wire, the atoms of the wire impede the free flow of electrons, sapping the current's energy and squandering it as heat. Today, about 6 to 7% of the electricity generated in the United States gets lost along the way to consumers , partly due to the resistance of transmission lines, according to U.S. Energy Information Agency documents. Replacing these lines with superconducting wire would boost utilities' efficiencies, and would go a long way toward curbing the nation's greenhouse gas emissions.
†††† The fledgling "maglev" train industry would also
welcome the availability of higher-quality, cheaper HTS wire. Economic
realities stalled the initial adoption of maglev transit systems, but maglev
development is still strong in Japan, China, Germany, and the United States.
NASA is looking at how superconductors could be used for space. For example,
the gyros that keep satellites oriented could use frictionless bearings made
from superconducting magnets, improving the satellites' precision. Also, the
electric motors aboard spacecraft could be a mere 1/4 to 1/6 the size of
non-superconducting motors, saving precious volume and weight in the
†††† Should we ever establish a base on the moon, superconductors would be a natural choice for ultra-efficient power generation and transmission, since ambient temperatures plummet to 100 K (-173 C, -280 F) during the long lunar night--just the right temperature for HTS to operate. And during the months-long journey to Mars, a "table top" MRI machine made possible by HTS wire would be a powerful diagnosis tool to help ensure the health of the crew. Worldwide, the current market for HTS wire is estimated to be US$30 billion, according to Castellani, and it is expected to grow rapidly.
A backstage pass: The University of Houston has licensed this new wire-making technology to MetOx, a company founded in 1997. MetOx plans to begin full-scale production of this high-quality HTS wire in 2003, Castellani says. The primary scientist for the NASA group at TcSAM, Dr. Alex Ignatiev, can't reveal exactly how they make their HTS wire. The technologies springing from these NASA/industry research partnerships must be patented to achieve NASA's goal of using space to benefit American businesses, Ignatiev says.
Basically, the wire is made by growing a thin film of the superconductor only a few microns thick (1,000ís of a millimeter) onto a flexible foundation. This well-known production method was improved upon in part through "Wake Shield" experiments flown on the space shuttle to learn about growing thin films in the hard vacuum of space. "We learned how to grow higher-quality oxide thin films from the shuttle experiments, and used that in the lab to improve the quality of our superconducting films," Ignatiev says.
In the years to come, that quality will translate into improvements in dozens of industries from power generation to medical care. Keep an eye on this one: the glamorous career of superconductors has only just begun.
The Science Directorate at NASA's Marshall Space Flight Center sponsors the Science@NASA web sites, whose mission is to help the public understand how exciting NASA research is and to help NASA scientists fulfill their outreach responsibilities.
Why do we call them high-temperature superconductors? The first superconductors discovered in 1911 were simple metals like mercury and lead. They were ordinary conductors at room temperature, but they became superconductors when the temperature dropped to only a few degrees (3 K) above absolute zero. These superconductors were too cold for many practical applications. Ever since researchers have been trying to figure out how to make substances superconduct at room temperature (~273 K). High temperature superconductors operate at 100 K to 150 K. That's very cold compared to the air around you, but much warmer than the original superconductors of 1911. Hence we call them high-temperature superconductors. [more]
Space Product Development -- (NASA/SPD) The goal of NASA's Space Product Development (SPD) program is to help American businesses explore the potential--and reap the rewards--of doing business in space. Doing this helps bring the benefits of space down to Earth where it can, and does, enrich the everyday lives of the American public. "Industry investment in space is high," says Mark Nall, manager of NASA's SPD program at Marshall Space Flight Center. "We assist companies developing experiments and help them explore how space research can contribute to the growth of their businesses."
Texas Center for Superconductivity and Advanced Materials -- TcSAM is one of 15 "Research Partnership Centers" around the country that are run by NASA's Space Product Development program at the Marshall Space Flight Center.
Superconductor applications: Uses for superconductors (Superconductors.org); How Maglev Trains Work (HowStuffWorks.com); Maglev news and other links (University of Washington); New superconducting camera for astronomers (EDTN Network); Superconductors to sustain Internet growth (Superconductors.org); E-bomb (Superconductors.org);
Wake Shield Facility used to create an ultra-vacuum in space to conduct research on thin films like those used in HTS wire