ESA GNC Conference Papers Repository

Formation flying missions are now at the forefront of new flight qualified space technologies, an example being the precise propulsion systems like that flown on the PRISMA mission. One such mission concept designed by Surrey Space Centre is to perform on-orbit visual inspection of a solar sail which aims to demonstrate and validate a new imaging system and a micro chemical propulsion system (microCPS) currently under development by a consortium led by Astrium GmbH. Applications of this new utility can be utilized towards redundant satellite systems, cluster-based sensor networks, rendezvous and docking operations, and visual inspection missions. A model of the solar sail is developed from the classical catenary, whose shape is typically defined by gravitational forces. This method however can be applied to estimate the ‘billowing’ in the solar sail and the resultant net thrust from combined solar radiation pressure and atmospheric drag forces. Furthermore, by investigating the light reflection patterns returned from the solar sail as a function of the sail surface, the accurate estimation of the solar sail shape can be achieved. As sunlight is reflected from the sail, it is important to understand how the Sun angle affects potential observation points in an orbit. Results for various Sun angles in an inertially-fixed solar sail case-study are presented to find that there are 2 key opportunities for imaging: i) looking at the micro-structure, i.e. shape and attitude, and ii) the macro-structure, i.e. the grazing Sun incidence angles for the sail surface. At these points, the sail shape, attitude, and surface structure can be learnt. A recent example of such a mission is the Japanese Space Agency (JAXA) Ikaros solar sail mission and, together with a deployed satellite, DCAM2, obtained imagery to confirm full deployment of the solar sail. In this imagery, it can be clearly seen when DCAM2 enters the focal point of the sail and the camera is completely saturated with light and little information, other than sail shape, can be made out. Using our simulations and models, a billow of 31.3 cm was estimated for this mission. This paper proposes the solar sail inspection mission parameters, introduces the new light reflection model and methodology for solar sails, and the formation flying experiment of potential observation points in a 2-1 safety ellipse around the solar sail target using the microCPS.