In May 2013, I responded with the present paper to ESAs call for White Papers for the definition of Large missions. This was half a year before the launch of ESAs large astrometry mission Gaia. The present proposal for a Gaia successor mission is sim
ilar to Gaia, because two Gaia-like missions at an interval of about twenty years would provide a foundation for studies of dynamics in all branches of astronomy from the solar system and stellar systems to compact galaxies, quasars and dark matter by astrometric data which cannot be surpassed in the next 50 years.
