TETHERED NANO-SATELLITES TO OBSERVE THE SOLAR CROWN

摘要

Last year the Group of Space Solar Physics at the Osservatorio Astronomico di Torino, OATo, and the AeroSpace Systems Engineering Team, ASSET, at Politecnico di Torino begun a cooperation for an ASI (Italian Space Agency) Call of Proposal on Studies of Solar System Exploration. The request that the OATo made to ASSET was the development of the capability of taking picture of both the solar crown and the solar sphere by means of simple and low cost cameras. If this was proved to be feasible, the utilization of complex optical devices could be avoided and an innovative means to perform a challenging task could be implemented. ASSET immediately realized that the simpler the payload the more complex the whole system carrying the payload would have been. However, we tackled the problem and we developed the concept of a system constituted by two low cost tethered nano-satellites, the "Detector" and the "Observer". The Observer carries one camera on-board to take pictures of the solar crown, whereas the Detector is provided with an optical device (a disk) to obscure the solar sphere and with a camera to take pictures of the solar sphere. Considering the requirement of tens of meters of distance between the camera to observe and the disk to detect, we realized that the side-length of the nano-satellites could be of about twenty centimetres. Taking into account the pointing accuracy requirement, the alignment between the two nano-satellites and the sun could be met by means of an attitude determination and control subsystem (ADCS), constituted by magnetometer, solar sensors and magnetic torques, and by means of and orbit control subsystem (OCS), constituted by positioning sensors and reaction control cold gas jets as actuators. In particular, while the ADCS is used to control the attitude of the satellites, whose cameras have to be directed towards the sun, the OCS is used to control the alignment of both satellites to the sun. The paper addresses first the requirements and then it proceeds with the development of the feasibility study of the system, thus defining both the system itself and its main subsystems. The capabilities of the system are then demonstrated through the extensive use of functional simulation of different scenarios. To conclude it is worth underlying that, notwithstanding the problems arisen both in managing the physical phenomenon and in mathematically modelling the whole system, the first results obtained are encouraging.