LARES: a satellite for studying General RelativityLARES, acronym for LAser RElativity Satellite, is a passive, laser ranged satellite. The main goal of LARES mission is the measurement of the relativistic frame-dragging effect. Principal Investigator of the mission is Prof. Ignazio Ciufolini (Università del Salento - Italy).
LARES, a completely passive satellite, has been designed to minimize the effects of non-gravitational perturbations on its orbit. In order to maximize the mass/surface ratio (minimizing the effects of atmosferic drag and solar wind pressure), the spacecraft is a sphere made of high density tungsten alloy (THA-18N), covered with 92 cube corner reflectors (CCR) for precise laser-ranging of the satellite from ground stations. The satellite body has been manufactured from a single piece of tungsten alloy to facilitate the heath exchange inside the spacecraft material, helping to reach a homogeneous temperature on the whole toungsten sphere, so avoiding important perturbation effects due to the so-called "thermal thrust". All the metal components of the satellite (body, CCR mounting rings and screws) are made of the same alloy. Being made of such an high density material LARES weights about 387 kg, even if its diameter is only about 36 cm. The choice of this unusual material introduced some technological challenges that had to be solved for manufacturing the spacecraft. Also, the shape of LARES and the scientific requirements (there shall not be components protruding from the spherical surface) needed a dedicated separation system to hold the satellite during the launch and to release it once on the final orbit.
The data analysis of the first years on orbit demonstrate the success of the design: the un-modeled residual acceleration on the trajectory of LARES are about 0.4 pm/s2, and the satellite is behaving like a "drag-free test particle" in the gravitational field of the Earth.
LARES is the densest known object orbiting in the Solar System!
LARES Satellite integrated on the separation system.
Laser-rangingLARES payload are 92 cube corner reflectors (CCR). A CCR reflects an incoming laser beam back toward the source regardless to the orientation of the reflector (unlike a mirror, which reflects the beam back toward the source only if perpendicular to the mirror surface).
Laser-ranging technique allows to measure the position of LARES with an extremely high precision. A worldwide network of ground stations is operated by the International Laser Ranging Service (ILRS). Each ground station sends high frequency laser pulses toward satellites carrying CCRs. By timing the time-of-flight of the laser pulses it is possible to measure the distance between the satellite and the ground station with the precision of about 1 cm over thousand kilometers.
A retroreflector of LARES
LARES launchLARES is a mission of the Italian Space Agency (ASI). The satellite was launched by the European Space Agency (ESA) with the maiden flight of the new European small launcher VEGA, from the European spaceport in Kourou, French Guiana, on 13 February 2012. The launch was successful and VEGA placed LARES on a circular orbit with an altitude of 1450 km and an inclination of 69.5°
The numbers of LARES