Published online by Cambridge University Press: 15 February 2011
Since January 1st, 2010, the IAU (International Astronomical Union) fundamental celestialreference frame has been the 2nd International Celestial Reference Frame (ICRF2), which iscomposed of Very Long Baseline Interferometry (VLBI) positions for more than 3000extragalactic radio sources. This frame is constantly improving through joint efforts ofthe VLBI community. By surveying the whole sky up to magnitude 20, the European spaceastrometric mission Gaia will soon create its own celestial reference frame directly inthe optical domain and with many more sources. By 2015–2020, the two frames will thuscohabit and it will be important to align these to the highest accuracy for consistencybetween optical and radio positions. In this paper, we present the various observationalapproaches that are undertaken to improve the VLBI frame in the future. These includeextension to weaker sources for densification, extension to higher radio frequencies totake advantage of the more compact morphology of the sources at these frequencies, andfurther observations in the southern hemisphere for homogeneous sky coverage. We alsoelaborate on how such future radio frames should contribute to highly-precise alignmentbetween the VLBI and Gaia frames within the next decade.