Man May Go to Mars in a Textile Spacecraft
New composite materials of woven or braided carbon fibers are lighter and stronger than the aluminum usually used in rockets
IN a decade or so, the National Aeronautics and Space Administration (NASA) proposes to put man on Mars. And to get there, researchers here at North Carolina State University are working on a spacecraft made of textiles.
These composite textiles, specially woven or braided carbon fibers encased in graphite or epoxy, will be lighter and stronger than the aluminum typically used in today's spacecraft.
``Composite materials will save one-third the weight of metals,'' says Fred DeJarnette, director of the university's Mars Mission Research Center. And ``we think it can be built cheaper.''
If you play tennis or golf, you're probably familiar with high-tech composites used in rackets and golf-club shafts. Such composites use fibers laid or woven in two dimensions. Here, researchers have found ways to weave and braid these fibers into three-dimensional shapes.
``My dream is that you can go to a hardware store and pick up a composite T-section [beam],'' says Mansour Mohamed, professor of textile engineering at North Carolina State University and the inventor of a patented three-dimensional weaving machine.
``NASA is interested in what we call textile technology,'' says James Starnes, head of the aircraft structures branch of NASA Langley Research Center in Hampton, Va. One application, for example, would be in the frames of airplanes and spacecraft. Although NASA's space shuttle uses many composites, its frame is still aluminum. That makes it relatively heavy, and NASA is eager to reduce weight. It takes 11 pounds of fuel to launch every pound of payload into space, Dr. Starnes says.
In August, McDonnell Douglas Space Systems Company test-launched a scaled-down version of its DC-X. The full-scale rocket is expected to be light enough to reach orbit without the extra boosters that fall away in stages in today's launches.
The 3-D technique may be useful in specific areas of stress, such as joints, which make up a large proportion of a spacecraft's weight. ``It gives us another alternative in design applications,'' Starnes says of 3-D textiles. ``It really broadens my vision of the things that I might be able to do.''
Three dimensions provide strength in all three directions. Two-dimensional composites tend to splinter when hit by a force perpendicular to the weave. For example, when scientists at the University of Stuttgart shot bullets through the thickness of a two-dimensional composite, they splintered and pierced the material at 86 joules (a measure of energy equal to moving one newton one meter). But bullets did not penetrate Dr. Mohamed's three-dimensional weave, even at 110 joules.
Three-dimensional braiding, another technique being refined by several scientists, including the university's Aly El-Shiekh, has properties that make it more useful in certain applications. Braiding is stronger if a part is being twisted. Weaving is stronger if it's being pulled apart.
Researchers at Drexel University, the University of Delaware, and Albany International Research Company - as well as scientists in Europe and Japan - are also working on 3-D textiles. It's not clear whether these new techniques will be enough to finally push composites into the mainstream.
The biggest obstacle is cost. Composites are lighter and just as strong as metals, but they're too expensive to mass-produce.
Where ``performance is the main criterion, it doesn't matter how much it costs; $200 a pound is OK,'' Mohamed says. But ``in the automotive industry, anything that's over $2 a pound won't even be looked at.''
In some areas, particularly aeronautics, the advantages outweigh the initial costs.
Eric Klang, professor of mechanical and aerospace engineering at North Carolina State University, is working on two industry-related composite projects. One is a bridge that would last longer than conventional bridges and not expand and contract. He is also working with General Motors and Chrysler to build composite-based manual transmission and transfer cases.
``If there's an energy crisis, it's going to be a popular material,'' he says, but increasing demand is not a given. ``It's going to take something to trigger it.''
One push for the material may come from the government. In September, the Clinton administration announced a partnership with the Big Three US auto makers to create a new generation of fuel-efficient cars. The goal is to have by 2003 a car that's no more expensive to own and operate than today's models but achieves above 80 miles to the gallon. The administration plans to redirect current federal research activities to better help the auto makers. Some of that research involves high-tech composites, which are crucial to reducing weight.
Weight-reduction is almost as important to auto makers as it is to aircraft manufacturers. If engineers were able to make every component in today's automobile one ounce lighter, they would save 125 pounds per car and extend the fuel efficiency by 1/4 mile per gallon, says John Jelinek, a spokesman for Ford Motor Company's car-product development.
``Essentially the car that emerges in the future is going to be a combination of steel, aluminum, plastics, composites, glasses,'' Mr. Jelinek says.