Solar Orbiter is proposed as a space mission dedicated to study the solar surface, the corona and the solar wind by means of remote sensing and in‐situ measurements, respectively. At 0.21 AU, closest approach to the Sun, the full 3‐D particle velocity distribution should be sampled as fast as a few tens of msec in order to study the growth phase of the instabilities. This implies some restrictions on the maximum phase space resolution given the limited allowed bit‐rate for data transmission. In this paper we evaluate consequences of this limitation for solar wind distributions with different parameters. © 2003 American Institute of Physics