A Geometric Perspective on Gimbal Lock in the Apollo program
The phenomenon of gimbal lock rose in prominence during the time of NASA's Apollo program. Inside the inertial measurement unit of the Apollo spacecraft was a stable (inertial) platform about which the spacecraft rotated. The hinged platform was suspended in two gimbals to give it three degrees of freedom. Its role was to give an accurate measure of the spacecraft's orientation. At a particular orientation of the spacecraft, the gimbals became coplanar and control torques became ineffective at stabilizing the platform.