QUALIFICATION TESTS ON THE OPTICAL RETRO-REFLECTORS OF LARES SATELLITE

摘要

LARES Satellite has been successfully launched on February 13th 2012 with the first flight of the new EuropeanLauncher VEGA. The passive, laser ranged satellite carries 92 cube corner reflectors (CCR). Due to its high densityLARES represents the known orbiting object with the highest mean density in the solar system. This property makesit an almost perfect proof particle in the gravitational field of Earth. LARES is now operational and it is tracked bythe International Laser Ranging Service stations. It will be used to test General Relativity and in particular the factthat the rotating Earth drags spacetime. The satellite design is quite innovative in the use of tungsten alloy as astructural material; indeed, the satellite body has been machined from a single piece of high density sintered alloy.The sintered alloy is characterized by a porous surface that shall be carefully cleaned before the integration of theoptical components, in order to avoid contamination of the back faces of the CCR from the metal. Two cleaningprocedures have been identified, to be performed on LARES. One procedure consisted in chemical cleaning withdifferent solvents and cleaning agents; the second procedure consisted in a chemical cleaning followed by degassingin a high vacuum oven. The cleanness procedures have been tested on breadboards reproducing the satellitematerials. The breadboards were tungsten alloy cylinders, carrying a cube corner reflector. The test was performedon two different breadbords each one for one of the two cleaning procedure. To simulate the operative spaceconditions the Thermal Vacuum Facility of Sapienza University of Rome has been used. The breadboards weremaintained in simulated space environment to allow degassing of possible contaminants from the metal and possibledetachment of contaminants from the metal to the back faces of the CCR. Visual inspection and Far Field DiffractionPatter tests have been performed to verify the possible presence and effect of contaminants on the of the CCR backfaces. In the paper some detail on the LARES mission and on the scientific objectives will be described along withall the details on this qualification process.