Interferometric Measurement of Acceleration at Relativistic Speeds
  We show that an interferometer moving at a relativistic speed relative to a point source of light offers a sensitive probe of acceleration. Such an accelerometer contains no moving parts, and is thus more robust than conventional "mass-on-a-spring" accelerometers. In an interstellar mission to Alpha-Centauri, such an accelerometer could be used to measure the masses of planets around other stars as well as the mass distribution of the Milky Way Galaxy. 
Pierre Christian and Abraham Loeb
astro-ph.IM