Comparison of Optical Quality of Some Passive Laser Ranged Satellites

The LAser RElativity Satellite (LASER) was launched in 2012 by ASI for studying general relativity. A new mission, LARES 2, will be launched in 2019/2020 on a higher orbit and using a different design of the optical payload. LARES is a target for Satellite Laser Ranging; the passive satellite carries 92 cube corner reflectors that allow to measure with high accuracy the position of the centre of mass of the satellite with respect to the ground stations. Aside from the principal scientific goal, the measurement of the relativistic frame-dragging effect, data from LARES (and in future, from LARES 2) are used also in other research related to the study of gravity, to space geodesy, and to Earth science. The accuracy of the laser ranging depends both on the characteristics of the ground station that is tracking the satellite, on the environmental conditions of the atmosphere during the pass of the satellite, and on the design of the target. Each laser ranging station provides the data collected for a particular satellite in a specific format, called Normal Points (NP) that are released daily. By comparing the quantity of NPs produced by a satellite, and the quality of those datasets, with the NPs produced by other satellites having a similar design (passive, spherical targets), it is possible to assess the quality of the optical design of that satellite. For its main scientific mission, the data of LARES are combined with the data of LAGEOS and LAGEOS 2 satellites, orbiting on much higher orbits and considered two benchmarks for laser ranging. The data of geodetic satellites such as LARES, LAGEOS, Stella and Starlette satellite are used by the scientific community for measurements of space geodesy, for the study of the effect of global climate changes on the rotation of the Earth, and for other research related to Earth science. The availability of high-quality targets for laser ranging will improve the accuracy of the results of the research in all the above scientific fields. In this paper the quality of the satellite laser ranging data from LARES is compared with the data of the LAGEOS satellites, with the data of the Stella/Starlette satellites (on lower orbits) and with the data of AJISAI (orbiting at a similar altitude). This information will provide important information for the design of the new LARES 2 satellite.