[FPSPACE] From the Gravity Probe B Update -- October 22, 2004

LARRY KLAES ljk4 at msn.com
Sun Oct 24 17:07:35 EDT 2004


Gravity Probe B Update -- October 22, 2004We have received inquiries about a recent letter to Nature by Ignazio Ciufolini and Erricos Pavlis claiming to have verified the Lense-Thirring frame-dragging effect of general relativity through laser ranging data observations of the LAGEOS I & II spacecraft. In their measurement, the frame-dragging effect needs to be separated by an extremely elaborate modeling process from Newtonian effects more than 10,000,000 times larger than the effect to be measured. The letter does not provide enough detail of the methods of verification and validation to allow a critical evaluation.  We and other members of the relativity community look forward to a more complete account.  If verified, their result will be of considerable interest. 


The GP-B science instrument and spacecraft were specifically designed to create a pristine environment to perform direct measurements of both the frame-dragging and geodetic effects of  general relativity with all Newtonian disturbances several orders of magnitude smaller than the effects to be measured. Theoretically, only one  gyroscope  is needed to make GP-B's measurements, but we use four gyroscopes to give highly accurate independent checks of the two effects.  As a further validation, throughout the whole GP-B mission we conduct a continuing series of verification/calibration  tests. In particular,  during our final month-long instrument re-calibration following data collection, we will perform a series of tests in which certain classes of potential disturbances are deliberately increased in order to uncover any previously unknown effects. Tests  of this kind, where possible disturbances are enhanced in order to calibrate and remove them, are a vital part of good experimental physics practice. 


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