NASA Gravity Probe B Mission Update 7 July 2006 | SpaceRef - Space News as it Happens

NASA Gravity Probe B Mission Update 7 July 2006 | SpaceRef - Space News as it Happens

"As of July 7, we are continuing to progress through Phase II of the data analysis process, which began at the beginning of March and is scheduled to run through late August 2006. During Phase II, our focus is on understanding and compensating for certain long-term systematic effects in the data that span weeks or months. The primary products of this phase will be monthly spin axis precession estimates for each gyro, as well as refined daily spin axis orientation estimates. In this phase, the focus remains on individual, rather than correlated gyro performance.

During June, the team made significant progress modelling the polhode motion of the gyroscopes. This polhode motion - a natural, periodic exchange of rotational energy among the inertial axes of a spinning body - does not affect the ability of the gyroscopes to measure relativistic precessions, but does introduce some subtle systematic errors that need to be removed to obtain the most accurate measurements. Using SQUID measurements of the trapped magnetic flux on the rotor, a very precise measurement of the polhode period history was identified. This information, together with the history of the spin speed of the gyroscope has allowed the team to build accurate physical models of the polhode motion and how it has evolved for each gyroscope over the mission. These models will form the base from which the effects of this class of systematic errors can be largely eliminated."