A Gaia successor with NIR Sensors

The expected accurate astrometric data from Gaia offer the opportunity and the obligation to exploitation by a second all-sky mission. Therefore a proposal was submitted to ESA in May 2013 for a Gaia-like mission in about twenty years. Two new designs are here considered with NIR sensors in addition to the visual CCDs as in Gaia. This has been suggested by several colleagues in order to get better astrometry in obscured regions. A first design with CMOS sensors was quickly abandoned for technical reasons. The second design with specially developed CCDs for NIR looked more promising. But a deeper study showed that the longer wavelength in the near infrared at two microns deteriorates astrometry so much that only heavily obscured stars of extremely red types as M5III would obtain a better accuracy. Thus, an option with NIR sensors does not seem promissing.