Super Spaceships

"Even if all the technical obstacles were solved today, exploring our solar system still needs to be affordable to be practical," says Dr. Neville Marzwell, manager of Revolutionary Aerospace Technology for NASA's Next Decadal Planning Team.

Lowering the cost of space flight primarily means reducing weight. Each pound trimmed is a pound that won't need propulsion to escape from Earth's gravity. Lighter spaceships can have smaller, more efficient engines and less fuel. This, in turn, saves more weight, thus creating a beneficial spiral of weight savings and cost reduction.

The challenge is to trim weight while increasing safety, reliability, and functionality. Just leaving parts out won't do.

Scientists are exploring a range of new technologies that could help spacecraft slim down. For example, gossamer materials - which are ultra-thin films - might be used for antennas or photovoltaic panels in place of the bulkier components used today, or even for vast solar sails that provide propulsion while massing only 4 to 6 grams per square meter.

Composite materials, like those used in carbon-fiber tennis rackets and golf clubs, have already done much to help bring weight down in aerospace designs without compromising strength. But a new form of carbon called a "carbon nanotube" holds the promise of a dramatic improvement over composites: The best composites have 3 or 4 times the strength of steel by weight - for nanotubes, it's 600 times!

more The tensile strength of carbon nanotubes greatly exceeds that of other high-strength materials. Note that each increment on the vertical axis is a power of 10.

"This phenomenal strength comes from the molecular structure of nanotubes," explains Dennis Bushnell, a chief scientist at Langley Research Centre (LaRC), NASA's Centre of Excellence for Structures and Materials. They look a bit like chicken-wire rolled into a cylinder with carbon atoms sitting at each of the hexagons' corners. Typically nanotubes are about 1.2 to 1.4 nanometers across (a nanometer is one-billionth of a meter), which is only about 10 times the radius of the carbon atoms themselves.

Nanotubes were only discovered in 1991, but already the intense interest in the scientific community has advanced our ability to create and use nanotubes tremendously. Only 2 to 3 years ago, the longest nanotubes that had been made were about 1000 nanometers long (1 micron). Today, scientists are able to grow tubes as long as 200 million nanometers (20 cm). Bushnell notes that there are at least 56 labs around the world working to mass produce these tiny tubes.

"Great strides are being made, so making bulk materials using nanotubes will probably happen," Bushnell says. "What we don't know is how much of this 600 times the strength of steel by weight will be manifest in a bulk material. Still, nanotubes are our best bet."