  A consistent Hamiltonian formulation of the teleparallel equivalent of
general relativity (TEGR) requires the theory to be invariant under the global
SO(3) symmetry group, which acts on orthonormal triads in three-dimensional
spacelike hypersurfaces. In the TEGR it is possible to make definite statements
about the energy of the gravitational field. In this geometrical framework two
sets of triads related by a local SO(3) transformation yield different
descriptions of the gravitational energy. Here we consider the problem of
assigning a unique set of triads to the metric tensor restricted to the
three-dimensional hypersurface. The analysis is carried out in the context of
Bondi's radiating metric. A simple and original expression for Bondi's news
function is obtained, which allows us to carry out numerical calculations and
verify that a triad with a specific asymptotic behaviour yields the minimum
gravitational energy for a fixed space volume containing the radiating source.
This result supports the conjecture that the requirement of a minimum
gravitational energy for a given space volume singles out uniquely the correct
set of orthonormal triads.
