Mission Design for the CubeSat OUFTI-1

CHAPTER7ATTITUDE CONTROL SYSTEMThe Attitude Control System (ACS) stabilizes the spacecraft and orients it indesired directions despite to the external disturbing forces acting on it. Actually,it’s part of a more complex system: the Attitude Determination andControl System (ADCS) but, in the case of OUFTI-1, speaking about attitudedetermination is inappropriate as it won’t be on board.An ADCS needs in fact sensors and actuator with the consequent mass andpower needed: this is often incompatible with a CubeSat.The incompatibility with OUFTI-1 doesn’t come much from the mass requirementas we expect to fulfill it but from the power. As explained in chapter 10,the power produced in orbit is low because of the limited solar arrays surfaceand just enough to guarantee a good communication when the satellite is atthe apogee. Furthermore, we intend to provide OUFTI-1 with omni-directionalantennas: in this context, it does not need a priori to point in a specific directionand may gently tumble about all three axes. Therefore we opt for twopossible solutions: not having any kind of ACS or have a totally passive ACSwith the goal of slowing down its rotation rate due to disturbing torques and ofguaranteeing an acceptable equilibrium position.63