Recent Results from SLR Experiments in Fundamental Physics

Satellite laser ranging provided for decades the most precise measurement of positions and velocities of earthbound tracking stations, as well as the most precise orbits of earth-orbiting artificial satellites. While the latter applies to any satellite carrying the appropriate reflectors, the use of these orbits for precise geodetic products requires the use of specially designed target satellites in high altitude orbits, such as the two LAGEOS satellites. To achieve such high quality, the motion of these satellites must be described with equally accurate models, such as those made available recently, thanks to missions like CHAMP and GRACE. This led to the synergistic application of such precise products to devise tests of fundamental physics theories. Nearly twenty years after conceiving and proposing an initial concept for a General Relativity (GR) prediction test, our recent experiment resulted in a positive and convincing measurement of the Lense-Thirring effect, also known as the gravitomagnetic effect of the rotating Earth. Using state-of-the-art Earth gravitational field models based on data from the CHAMP and GRACE missions, we obtained an accurate measurement of the Lense–Thirring effect predicted by GR, analyzing eleven years of LAGEOS and LAGEOS 2 Satellite Laser Ranging (SLR) data. The new result, in agreement with the earlier one based on Earth models JGM-3 and EGM96, is far more accurate and more robust. The present analysis uses only the nodal rates of the two satellites, making NO use of the perigee rate, thus eliminating the dependence on this unreliable element. Using the EIGEN-GRACE02S model, we obtained our optimal result: µ = 0.99 (vs. 1.0 in GR), with a total error between ±0.05 and ±0.1, i.e., between 5% and 10 % of the GR prediction. Results based on processing with NASA and GFZ s/w will be presented, along with preliminary tests with very recent improved GRACE models. Further improvement of the gravitational models in the near future will lead to even more accurate tests. We discuss the LAGEOS results and some of the crucial areas to be considered in designing the future LARES mission dedicated to this test.