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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