  We formulate Lorentz-covariant classical perturbation theory to deal with
relativistic bremsstrahlung under gravitational scattering. Our approach is a
version of the fast motion approximation scheme, the main novelty being the use
of the momentum space representation. Using it we calculate in a closed form
the spectrum of scalar, electromagnetic and gravitational radiation. Our
results for the total emitted energy agree with those by Thorne and Kovacs. We
also explain why the method of equivalent gravitons fails to produce the
correct result for the spectral-angular distribution of emitted radiation under
gravitational scattering, contrary to the case of Weizs\"acker-Williams
approximation in quantum electrodynamics.
