  In high-precision atomic gravimeters, a rest mass is needed to provide a
gravity reference, which is typically the retro-reflecting mirror of the Raman
laser beams that addresses the two hyperfine ground states of the specific
free-falling atomic test mass. We constructed a compact active feedback control
system for the retro-reflecting mirror that provides vibration isolation in the
vertical axis as well as two rotation stabilization in the horizontal plane.
The active feedback control provides vertical vibration reduction of up to a
factor of 300 in the frequency range of 0.03 to 10 Hz and tilt stabilization of
approximately $\pm$ 1 $\mu$rad in the noisy lab environment. This system has
enabled high-precision gravity measurements on a portable gravimeter with
sensitivity reaching $6.4\times 10^{-8}$ g/$\sqrt{\text{Hz}}$ and resolution of
$2.8\times 10^{-9}$ g after an integration time of 4000 s.
