Stories from Physics for 11-14 14-16
Some satellites are deliberately spun about an axis perpendicular to their orbital plane in order to prevent their position drifting. As in a gyroscope, this provides some inertia against perturbations and angular velocities of between 30 and 100 rpm are typical. In an alternative application, a technique known as yo-yo de-spin has been used to slow the rotation of a satellite. Two masses attached to lengths of cord released from opposite sides of the craft, like the extended arms of a pirouetting skater, are used to cause the rotational velocity of the satellite to decrease. Yo-yo de-spin was used on early, unmanned space flights in the 1950s and on recent missions, including the 1999 Mars Polar Lander and the 2003 Mars Exploration Rover.