Stella was a 48 kg French satellite that was launched along with
SPOT 3. It was a dense sphere of uranium alloy with 60 laser
reflectors on the surface. Reflected laser beams enabled
accurate geodetic ... measurements for the determination, with an
accuracy of 1 cm, of the geoid, of oceanic and terrestrial
tides, and of tectonic movements. It joined its still
operational twin, Starlette, that was launched in 1975.
[Summary provided by NASA0