Beschreibung:
<jats:p>A ground-based project for a small telescope about 20 cm aperture is proposed. It would be able to obtain 500 million astrometric observations per year of all stars between V=7 and 18 mag, based on the Hipparcos-Tycho reference net of one million stars. In addition, V and I magnitudes for all stars from V=7 to 17 mag would be obtained. — A new space mission is proposed, capable of obtaining 10 microarcsecond (μas) precision for parallaxes and proper motions of stars of <jats:italic>V</jats:italic> = 11 mag, and a precision of 0.5 millimagnitude (mmag) for intermediate-band photometry. The mission is here called Roemer Plus (or Roemer+) and the design is derived from Hipparcos and Roemer, but a larger telescope aperture and high-precision metrology is applied. At magnitude <jats:italic>V</jats:italic> = 20 a precision of 1.0 milliarcsecond (mas) would be achieved.</jats:p>