Perfect Gyroscope

by David Bradley

Imagine putting a perfect gyroscope in earth orbit and pointing it at a guide star and observing the predictions of effects of the theory of General Relativity. There will be two, explained Professor Francis Everitt of Stanford University, USA. The first will be a precession, a rolling of the gyroscope's axis, in the plane of the orbit (a geodetic effect), the second will be the "frame dragging" effect caused by the earth's gravitational field dragging space-time as it rotates on its axis.

The NASA-Stanford Gravity Probe B (GP-B) was launched from Vandenberg Air Force Base on 20 April 2004 and carried four such gyroscopes in to orbit to test these two effects. Everitt described the six new precision measurement technologies onboard.

First, the GB-P carries an electrically suspended gyroscope with an on-orbit drift performance seven orders of magnitude better than even the best Earth-based gyroscopes, a hair's breadth viewed at 100 miles. Second, the system has a gyro readout based on the London moment in a spinning superconductor, with a very high resolution. The third instrument, almost as important as the gyroscope itself, is a cryogenic star tracking telescope, that zooms in on a guide star which acts as a "stationary" reference point. Fourth is a container, a Dewar flask, carrying 2500 litres of superfluid helium, which Everitt explains is expected to stay liquid for sixteen months in space. The fifth technology are pointing and drag-free control technologies with proportional thrusters, and finally precision quartz manufacturing technologies within which the gyroscope sits.

Everitt went on to discuss the technological obstacles that faced the team in developing the GP-B. For instance, they successfully addressed a serious conundrum in how to spin up a gyroscope without the applied torque causing it to deviate too much from the ideal. GP-B is orbit around the earth at this moment, measuring probing the predictions of Einstein's theory in the centenary year of its publication. GP-B may find flaws in the theory that could help reconcile the incompatibilities between Einstein's work which predicts the behaviour of the very large, planets, stars and galaxies and the quantum world of the very small electrons, protons and neutrons. The probe will not only investigate the validity of Einstein's theory but will provide an accurate value for the fundamental unit, gamma.

Read on... Tempus Fugit