Smart dust option for geomagnetic tail exploration

In-situ measurements are necessary for a long-term analysis of the spatial structure of the geomagnetic tail. This type of mission requires the use of a propellantless propulsion system, such as a classical solar sail, to continuously rotate the design orbit apse line such that it remains parallel to the Sun-Earth direction. To reduce the mission costs, this paper suggests the employment of Sun-pointing smart dusts, which are here investigated in terms of propulsive acceleration level necessary to guarantee a mission’s feasibility. A Sun-pointing smart dust can be thought of as a millimeter-scale solar sail, whose geometric configuration allows it to passively maintain an alignment with the Sun-spacecraft line. The smart dust external surface is coated with an electrochromic reflective film in such a way that it may change, within some limits, its propulsive acceleration magnitude. A suitable control law is necessary for the smart dust to enable an artificial precession of its Earth-centred orbit, similar to what happens in the GeoSail mission. This paper analyzes the required control law using an optimal approach. In particular, the proposed mathematical model provides a set of approximate equations that allow a simple and effective tradeoff analysis between the propulsive requirements, in terms of the smart dust acceleration, and the characteristics of the design orbit.