On the Phase-Space Resolution for the Solar Wind Plasma Experiment on Board ESA-Solar Orbiter

Solar Orbiter is 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. It will help us to understand in more detail the underlying nature of fundamental plasma kinetic processes acting in the Sun's atmosphere and in the extended corona as it will explore the inner regions of the Solar System with a perihelion of 0.21 AU. In particular, it will help us to understand the role of microinstabilities generated by non-Maxwellian features of the particle velocity distribution function. The best way to study these microinstabilities would be sampling the particle distribution function during their growth phase. In other words, we should be able to sample the whole 3-D velocity distribution function with a time resolution of the order of a few tens of msec, which is the time taken by the s/c to go across a scale length of the order of the typical Larmor gyroradius at 0.21 AU. This implies some restrictions on the maximum phase space resolution given a limited bit-rate for data transmission. In this paper we evaluate consequences of this limitation for solar wind distributions characterized by different values of the relative parameters.