COST EFFECTIVE CENTER OF MASS DETERMINATION OF LARES SATELLITE

LAser RElativity Satellite (LARES) is a satellite designed for measuring gravitomagnetism predicted by Einstein general relativity. One of the requirements imposed on LARES satellite is to have the distance between the center of mass and the geometric center of the satellite lower than 0.2 mm. The material used for LARES satellite is a tungsten alloy. The producer provided two spheres manufactured with liquid sintering, a process that bring the Cu and Ni present in the alloy in liquid phase. The two spheres are among the biggest tungsten alloy items ever manufactured and the producer could not guarantee the uniformity of the alloy. Also the center of mass could not be predicted with a sub-millimeter level of accuracy. Balancing of satellites is usually made by adding masses at pre-configured positions. In case the distance between the center of mass and the geometric center is bigger than 1 mm, adding masses on the LARES satellite would be very difficult and will increase the surface-to-mass ratio, a very important parameter connected to the scientific objective of the mission. For this reason a procedure for a rough measurement of the satellite center of mass has been devised. Purpose of the paper is to show how to use a lathe machine and a homemade system with load cells, to measure the position of the center of mass with an accuracy of about 0.5 mm.