In Apollo 13 they talk a lot about being close to "gimbal lock", when two planes in a gyroscope align, then they cannot be separated. > **Gimbal lock** is the loss of one degree of freedom in a three-dimensional, three-gimbal mechanism that occurs when the axes of two of the three gimbals are driven into a parallel configuration, "locking" the system into rotation in a degenerate two-dimensional space. https://en.wikipedia.org/wiki/Gimbal_lock