The team was led by Dr. Ignazio Ciufolini of the University of Lecce, Italy, and Dr. Erricos C. Pavlis of the Joint Center for Earth System Technology, a research collaboration between NASA’s Goddard Space Flight Center, Greenbelt, Md., and the University of Maryland Baltimore County.
Ciufolini’s team, using the LAGEOS satellites, previously observed the Lense-Thirring effect. It has recently been observed around distant celestial objects with intense gravitational fields, such as black holes and neutron stars. The new research around Earth is the first direct, precise measurement of this phenomenon at the five to 10 percent level. The team analyzed an 11-year period of laser ranging data from the LAGEOS satellites from 1993 to 2003, using a method devised by Ciufolini a decade ago.
The measurements required the use of an extremely accurate model of the Earth’s gravitational field, called EIGEN-GRACE02S, which became available only recently, based on an analysis of GRACE data. The model was developed at the GeoForschungs Zentrum Potsdam, Germany, by a group who are co-principal investigators of the GRACE mission along with the Center for Space Research of the University of Texas at Austin.
LAGEOS II, launched in 1992, and its predecessor, LAGEOS I, launched in 1976, are passive satellites dedicated exclusively to laser ranging. The process entails sending laser pulses to the satellite from ranging stations on Earth and then recording the round-trip travel time. Given the known value for the speed of light, this measurement enables scientists to precisely determine the distances between laser ranging stations on Earth and the satellite.
NASA and Stanford University, Palo Alto, Calif. developed Gravity Probe B. It will precisely check tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting 400-miles directly over the poles. The experiment will test two theories relating to Einstein’s Theory of General Relativity, including the Lense-Thirring Effect. These effects, though small for Earth, have far-reaching implications for the nature of matter and the structure of the universe.
The following paragraphs were in the most recent email updae put out by the Gravity Probe B folks:
We 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.