Feature Presentation

No, they aren't the hottest newcomers on the women's tour since the Williams sisters. Anita and Arabella were a pair of spiders that flew on NASA's Skylab, the first U.S. space station. In 1973, these "animalnauts" were part of a student experiment to study if spiders spin webs differently in "microgravity" (very low gravity, 10^-6 of Earth's).

Arabella

"The spiders did not spin their web patterns differently, but the threads themselves were different", Dr. David Noever told us. "And there is a definite application to tennis racquet string technology as well as to other recreational sports."

Dr. Noever is a research scientist at the NASA Marshall Space Flight Center. NASA Marshall is home to the one of the largest space sciences laboratories in the world. He has worked at Marshall since 1987. Prior to that David graduated from Princeton in 1984, was named a Rhodes scholar and attended Oxford University where he earned a doctorate in theoretical physics.

Skykab, America's First Space Station

One of David's responsibilities is to evaluate the information from space-borne experiments. "ED-52 Web Formation" was actually a student experiment aboard the 59-day Skylab 3 mission. "We hoped to use the results to reduce vibration on future space platforms. For example, on the Soviet space station Mir (Russian word for "Peace") whenever someone used the exercise equipment the entire station shook. On the ground Mir weighs 120 tons, but in space these structures vibrate a great deal. The idea was to reduce these vibrations by building a large space station networked together."

To understand how this applies to tennis racquets, let's look at how a spider spins webs on Earth. Spider webs are used to catch insects. The spider is a master stringer; the density of the pattern, the tension and loads are all balanced. The webs have to absorb the impact of their prey. A fluid material called "silk" is secreted out of the abdomen of the spider to build the web. Spider silk is incredibly strong. David told us, "A bridge cable made out of spider silk would be much stronger than a cable made out of steel. The silk is really a plastic or what is known as a polymer."

Polymers and other materials like ceramics and metals are classified by properties such as: stretching (tensile strength); bending (flexural strength); and elasticity (the materials ability to return to its original shape after a force, stress or strain is applied). Certain plastics called "elastomers" act like rubber. They rapidly spring back to their original shape, like an elastic band. Some polymers and elastomers are used to isolate (separate or set apart) and dampen (absorb) vibrations and the shock of impact. It's why we have shock absorbers on our cars. "That's the secret of the silk's strength - it can be stretched a great deal without breaking.", David told us. It is twice as elastic as nylon!

"But on Earth, the silk has a very uniform thickness. It's amazing, especially when you consider that the spider is not a machine. In space, the strands did not have this constant diameter. The same thread was thick in one place and thin in another. We realized that this "start and stop" nature of the web was also a way to control the elasticity at every point."

Arabella's and Her Web Aboard Skylab

The diameter or cross-section area of the string governs the properties we mentioned. For example, a thinner string is more elastic and stretches longer but is not as strong as a slightly thicker string. The opposite is true for a thicker string. And as Howard Brody points out in his book, "Tennis Science for Tennis Players", "It is the elasticity of the strings that makes your racket play well.". David, who plays tennis, recognized the benefits for racquet strings.

You know how it feels when you don't hit the ball at the sweet spot, or center of percussion, of your racquet. You feel that uncomfortable vibration that travels down your hand and forearm. But by varying the thickness and tapering the strings the sweet spot can be shifted to different positions on the racquet. One of the most important advantages of this technology will be the reduction in vibration. This may prevent injuries such as tennis elbow and aid players with chronic arm problems.

Where else can this technology be used? The Department of Defense has actually looked at using spider web silk for bullet-proof vests. Researchers at Cornell believe that the material can be used for parachutes and seat belts. In recreation, David told us, "The material can be used for fishing line." (Pacific Islanders use web silk to make fishing lines and nets, because of its strength.) "We've even been contacted by a yo-yo company. Right now yo-yo string is made out of all cotton material." You can see the similarities, the technology can be used wherever there is a need for a long lasting, strong, elastic fiber.

So does this mean that you'll be playing tennis with a spider's web versus gut or a synthetic? Not really. Researchers are looking at ways to reproduce the silk without the army of spiders needed to create this much material.

Astronaut Owen Garriot with Camera in Front of the Web Formation Experiment.

Coincidentally, NASA refers to space-age technology used in "down to Earth" applications as "spin-offs". NASA has an entire commercial technology division devoted to transferring their technology to the private sector. But it still takes someone like Dr. David Noever to understand a technology and visualize how it can be used in other ways. As the inventor, NASA allowed David to commercialize his "Rocket Racquet". David's currently working with the same group of designers that first developed the oversized racquet. We hope to follow up with David and report on how his project is progressing!