Testing General Relativity and gravitational physics using the LARES
  satellite
  The discovery of the accelerating expansion of the Universe, thought to be
driven by a mysterious form of `dark energy' constituting most of the Universe,
has further revived the interest in testing Einstein's theory of General
Relativity. At the very foundation of Einstein's theory is the geodesic motion
of a small, structureless test-particle. Depending on the physical context, a
star, planet or satellite can behave very nearly like a test-particle, so
geodesic motion is used to calculate the advance of the perihelion of a
planet's orbit, the dynamics of a binary pulsar system and of an Earth orbiting
satellite. Verifying geodesic motion is then a test of paramount importance to
General Relativity and other theories of fundamental physics. On the basis of
the first few months of observations of the recently launched satellite LARES,
its orbit shows the best agreement of any satellite with the test-particle
motion predicted by General Relativity. That is, after modelling its known
non-gravitational perturbations, the LARES orbit shows the smallest deviations
from geodesic motion of any artificial satellite. LARES-type satellites can
thus be used for accurate measurements and for tests of gravitational and
fundamental physics. Already with only a few months of observation, LARES
provides smaller scatter in the determination of several low-degree
geopotential coefficients (Earth gravitational deviations from sphericity) than
available from observations of any other satellite or combination of
satellites.
