What Do Satellites Have in Common with Falling Cats? Attitude Control

Have you ever wondered how the Hubble Space Telescope and other satellites can be pointed in any direction at the will of scientists on the ground? Given the energy constraints for satellites designed to stay in space for years, the technical challenges are immense.

In this video from the “Smarter Every Day” YouTube series we learn a little about two clever methods scientists use to control the attitude, or orientation, of satellites with very little energy. The first method exploits the power of the Earth’s magnetic field by using electric current to selectively activate electromagnets and nudge the satellite in a desired direction, rather like the needle of a compass. The second and, in some ways, more fascinating method takes its inspiration from the amazingly agile cat. It has long been known that cats can fall from any initial orientation and almost always land on their feet. They can reorient themselves 180 degrees without violating the conservation of angular momentum. They do it by adjusting their shape and thus rearranging the mass, and changing the moment of inertia, within their bodies. Scientists employ a similar tactic using moving parts within satellites.

The host of the “Smarter Every Day” videos goes only by the name of “Destin,” and is reportedly a missile engineer at the U.S. Army’s Redstone Arsenal, near Huntsville Alabama. Some viewers will, like us, find the tone and sensibility of this video juvenile and annoying, with its overuse of the words “cool” and “awesome” and with the gratuitous cat-dropping scenes (note to future YouTube auteurs: consider using stock footage) but the science itself is, without a doubt, fascinating.

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