On Earth, a properly thrown boomerang will return to the person who threw it. Is the same true aboard the International Space Station?
Boomerangs feel more like magic than science when they return after a good throw. A boomerang works by aerodynamics, but does it still work in zero gravity? Astronaut Takao Doi threw a boomerang on the International Space Station to test it out.
The throws work perfectly, reliably returning the boomerang to Doi time after time. While the International Space Station is in near-zero gravity, the air that keeps our astronauts alive and breathing also allows the boomerang to perform its aerodynamic trick.
The arms of a boomerang are asymmetrical. One side is slightly curved, forcing air to travel farther compared to the flat side. This curves the air flow, turning the moving fluid and producing lift. The uneven aerodynamic forces induce a spin in the boomerang. Torque from the spin produces a slight wobble, causing the boomerang to precess around the axis of rotation like a toy top. The precession pulls on the flight path, curving the boomerang into a circular route that returns it to the thrower.
And all this works without even the smallest helping hand from gravity.
But what about in true space? If a boomerang was thrown outside the International Space Station in a zero-gravity vacuum, would it's trick still work? No. Without any air, the aerodynamics of a boomerang would do nothing at all. No curving, no returning to the thrower, no even slowing down while tumbling through the vast expanses of (mostly) empty space.
Earth space is crowded, and 95% of it is junk. Image credit: NASA
However, a force besides aerodynamics may come into play. With an absolutely perfect throw at the right angle, the boomerang could theoretically reach sufficient velocity to be in perpetual free-fall around the Earth. In that circumstance, gravity would be the driving force and the boomerang's fancy shape would be utterly irrelevant as it took the long way around to return to the sender. The boomerang would join the swarm of space debris, paint chips and micrometeroites orbiting the planet. If, by ill luck, it collided into something, the tiny oddly-shaped meteorite could pack a powerful enough punch to ding a satellite or chip a window.
An idea brought up in the discussions is that a vacuum-friendly boomerang could potentially be designed to respond to the gentle push of solar radiation. Considering that the Kepler space telescope is currently compensating for a broken gyroscope by balancing against solar radiation, the idea of a boomerang could also be influenced is plausible. Thoughts on how to design such a creation?
Video via Jennifer Ouellette of Cocktail Party Physics. Want more games in zero-g? Check out these Star Wars inspired robotic spheres! Or just ogle a beautiful photograph from space. Top image modified from a Chandra photo of the Pacman Nebula (NGC 281).
An earlier version of this article stated that the asymmetrical surfaces produced a difference in velocity. Here's why it was rephrased, and this is the same science of how a boomerang functions explained a different way.