Читать книгу Global Navigation Satellite Systems, Inertial Navigation, and Integration - Mohinder S. Grewal - Страница 78

A limiting design factor in momentum wheel gyroscope (MWG) performance has been bearing torque, which has been addressed by going from sleeve bearings to jewel bearings, to ball bearings, to air bearings, and to electrostatic bearings. Even though electrostatic suspension is inherently unstable, it can achieve very low bearing torques. Perhaps the most accurate momentum wheel gyroscopes to date were the superconducting electrostatic gyroscopes used in a theoretical physics experiment named “Gravity Probe B” [4], a NASA‐funded program to resolve two fine points of Einstein's theory. It was able to achieve drift rate accuracies in the order of deg/h, but only in a zero‐g environment, and at enormous cost. Unfortunately, scaling down the size of momentum wheel gyroscopes tends to scale up the ratio of surface area to angular momentum, which scales up angular drift rates due to bearing torques.