Stella was a French geodetic satellite, carrying 60 laser reflectors mounted on a dense sphere of uranium alloy, which is tracked to measure small perturbations in Earth's gravitational field. Reflected laser beams enable measurements, accurate to about 1 centimeter, of the geoid, oceanic and terrestrial tides, and tectonic movements. Stella's twin, Starlette, launched in 1975, is also still in use. See also France in space.