September 18 – Of Discs And Spacemen

Today’s Factismal: The Frisbee™ was patented in 1958.

If you’ve ever played Ultimate Fribee™ or Fribee™ Golf, then you owe a debt of gratitude to Walter Morrison. In 1938, he and his wife discovered that people wanted to do more on a beach than just lie in the sun; they wanted to throw things at each other. So Morrison sold cake pans to beach-goers for a quarter each. His business was growing steadily until it was interrupted by World War II and Morrison went into the US Army Air Corp as a pilot. But he spent his spare time developing an improved flying disc that he would call the “Pluto Platter”. He continued to tinker with the design until 1958, when he was awarded a US Patent and sold the rights to Wham-O, who marketed it under the now-familiar name of Frisbee™. Since then, Morrison was been paid nearly $2,000,000 in royalties for his twenty-five cent toy.

Rocks fall along a parabola because they don't generate lift. Flying discs soar because they do create lift.

Rocks fall along a parabola because they don’t generate lift. Flying discs soar because they do create lift.

But what makes this flying disc worth two million dollars? The answer lies in physics. It you throw something, then it falls thanks to gravity. But if the thing you throw is just the right shape (like a paper airplane or a disc, for example), then it will also generate lift which means that it won’t fall as quickly. Instead of making the classic parabola of a rock tossed into the air, it glides along a gentler curve.

Spinning is important, but which axis you spin around is even more so.

Spinning is important, but which axis you spin around is even more so.

But that isn’t the only bit of physics that makes a disc soar. Indeed, there is another, more important phenomenon at play, and it helped save the US Space program. When an object spins, it generates gyroscopic forces. If these forces are applied along the longest axis, then they make the object tumble. But if they are applied along the shortest axis, then the object spin-stabilizes and it will not tumble. This is why the Frisbee™ can make such long flights; the spinning keeps the disc from tumbling and so keeps the lift pointed the right way. This turned out to be just as important for spacecraft as it was for toys.

Explorer-1's shape doomed it to tumble

Explorer-1’s shape doomed it to tumble (Image courtesy NASA)

The first satellite launched into orbit by the United states was Explorer 1. It was shaped like a five-foot tall pencil and weighed 31 lbs. It was intended to measure radioactivity levels in outer space, to see if it was possible for anything to survive. But soon after the satellite went into orbit, it started to tumble erratically. NASA scientists soon realized that the problem was that the satellite had been designed to spin along the long and unstable axis instead of the short and stable one. This discovery would literally shape satellite design for the next fifty years. From then on, satellites would either be spherical with symmetrically-arranged antennas (like the Vanguard series) or short, squat cylinders with just a few antennas (like the Pioneer series).

The Pioneer spacecraft were designed not to tumble

The Pioneer spacecraft were designed not to tumble (Image courtesy NASA)

Satellite work continues today. If you’d like to get involved, consider the ArduSat program:
https://www.ardusat.org/

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