The European Space Agency’s Hipparcos satellite measured accurate positions of some 100,000 stars. Doing so from space represented a fundamentally new discipline in space science. ESA adopted the Gaia mission, a vastly more advanced star-mapping satellite, in 2000. Gaia was launched in 2013 and continues to operate flawlessly, measuring the positions of more than two billion stars with extreme accuracy. In this recording of a live online talk, Dr Michael Perryman reviews the 2,000 year history of this branch of astronomy (astrometry), explains why and how these measurements are made from space, and why the measurement of star positions is of such profound scientific importance. During a 30-year career with the European Space Agency, Dr Perryman was the scientific leader of the Hipparcos mission from 1981 to 1997, also serving as project manager during its operational phase, 1989 to 1993. He was the co-originator of the Gaia satellite mission, and ESA’s project scientist from its earliest concepts in 1995 until the Critical Design Review in 2008.