A Pocket of Near-Perfection
The gyroscopes in GP-B are the most perfect spheres ever made by humans. (The experiment actually carries four gyroscopes for redundancy.) These ping pong-sized balls of fused quartz and silicon are 1.5 inches across and never vary from a perfect sphere by more than 40 atomic layers…
…Finally, it’s necessary to measure the gyroscopes’ spin without nudging the gyroscopes in the slightest.
Once again, superconductivity comes to the rescue. A superconducting sphere, when spun, will produce a weak magnetic field that is precisely aligned with the axis of rotation. The gyroscopes are therefore coated with a metallic layer of niobium of near-perfect uniformity. At the cryogenic temperature in the core of GP-B, niobium becomes a superconductor and it produces a magnetic field when the spheres are spun. By monitoring the magnetic field, engineers can monitor the spin of the gyroscopes—no touching required!
