I. Introduction
This paper considers the development of an attitude control system, with application to two of the QB50 satellites designed to conduct a survey of the upper atmosphere at low-Earth orbit altitudes (see Fig. 1) [1], [2]. The primary enabler for this survey mission is a constellation of 40 2U cubesats, each equipped with an ion-and-neutral mass spectrometer (INMS) sensor mounted to one of the 1U faces. To function correctly, this sensor must be kept pointed to within a 20° half-angle cone of the velocity vector. The key challenge in maintaining this attitude is that it corresponds to the cubesat being near a gravity-gradient unstable equilibrium. The purpose of this paper is to demonstrate controllability of the linearized time-varying dynamic system and to design a controller for the attitude of a 2U cubesat using first magnetic torque rod actuators alone and in combination with a hardware modification that involves an additional set of four air drag panels. The passive air drag panels are introduced to enhance, in combination with a magnetic rod actuator controller, the satellite’s stability and disturbance rejection characteristics.
Front face of one of the 2U cubesats, featuring the INMS sensor array. This face must be kept pointed within a 20° half-angle cone of the satellite’s orbital velocity vector for the array to function correctly. Two of the air drag panels are visible in their undeployed configurations.