Comparison of LARES 1 and LARES 2 Missions - One Year After the Launch

With the successful launch of LARES 2, the constellation of laser ranged satellites to be used for the accurate measurement of frame-dragging of the theory of general relativity has improved significantly. The lift-off was from the European spaceport in French Guyana by the inaugural flight of VEGA C the 13th of July 2022. This launch occurred 10 years after the other maiden flight of VEGA that was carrying as main payload LARES satellite. Both launch vehicles are developed, financed and managed by ESA, Avio and ASI, with Arianespace commercialising them. The two orbits are quite special because are neither sun-synchronous nor equatorial. Particularly the LARES 2 orbit needed to be quite high compared to the classical LEO orbits. In the paper it will be explained in detail the reason for this particular orbit. Differently from LARES satellite this time the orbit did not have large tolerances in the orbit parameters. The injection accuracy for LARES was very high, though as mentioned not required, but with LARES 2 the accuracy was spectacular because it matched the orbit 10 times better than required. This will allow to improve the accuracy of the frame-dragging (also known as Lense-Thirring effect) measurement by one order of magnitude with respect to what obtained with LARES satellite thus allowing to reach an accuracy of at least a few parts in a thousand. Frame-dragging is measured by observing the node of the satellite orbit that is shifted by the dragging of spacetime induced by the Earth rotation. In fact in general relativity spacetime is deformed not only by mass but also by energy, so that also currents of mass, such as the Earth rotation, will affect gravity. The laser ranging technique will provide the most accurate ranging measurement achievable today and is thus capable to provide the necessary data for the goal of the LARES missions. However the main problem of the measurement is due to the classical gravitational and non-gravitational perturbations whose effects on the node are huge with respect to frame-dragging. To achieve this tremendous task of extracting frame-dragging to the node shift, a combination of the data of the two LARES satellites and the two LAGEOS satellites is required. Furthermore very accurate knowledge of the gravitational field of Earth is necessary, so that during the data analysis the gravitational field from GRACE and GRACE Follow On missions are used. In this work some engineering aspects of the two missions are compared along with the results obtained with the LARES mission and the expected ones from LARES 2.