Search

Many satellites are required to be pointed at a target with high accuracy, a task which can in some scenarios be either better or only performed using thrusters. Control algorithms are well studied for solving this problem around a single axis using on/off thrusters, but not for cases where significant inter-axis coupling is present in the moment of inertia or thruster torque matrices, as is often the case when using commercial-off-the-shelf components in nanosatellites. This work proposes a linear programming-based method for applying single-axis phase plane control techniques in a multi-axis environment, while minimizing fuel usage and obeying constraints on minimum impulse bit and pointing accuracy. A multi-axis extension of a feedback pulse-width pulse-frequency modulation scheme is also developed. Simulations are performed where these methods are compared to existing multi-axis control techniques in the presence of realistic disturbances and non-ideal thruster behaviour. [ABSTRACT FROM AUTHOR]

The paper describes the development and simulation results of a full ADCS subsystem for the deOrbitSail drag sail mission. The deOrbitSail satellite was developed as part of an European FP7 collaboration research project. The satellite was launched and commissioning started on 10th July 2015. Various new actuators and sensors designed for this mission will be presented. The deOrbitSail satellite is a 3U CubeSat to deploy a 4 by 4 m drag sail from an initial 650 km circular polar low earth orbit. With an active attitude control system it will be shown that by maximising the drag force, the expected de-orbiting period from the initial altitude will be less than 50 days. A future application of this technology will be the use of small drag sails as low-cost devices to de-orbit LEO satellites, when they have reached their end of life, without having to use expensive propulsion systems. Simulation and Hardware-in-Loop experiments proved the feasibility of the proposed attitude control system. A magnetic-only control approach using a Y-Thomson spin, is used to detumble the 3U Cubesat with stowed sail and subsequently to 3-axis stabilise the satellite to be ready for the final deployment phase. Minituarised torquer rods, a nano-sized momentum wheel, attitude sensor hardware (magnetometer, sun, earth) developed for this phase will be presented. The final phase will be to deploy and 3-axis stabilise the drag sail normal to the satellite’s velocity vector, using a combined Y-momentum wheel and magnetic controller. The design and performance improvements when using a 2-axis translation stage to adjust the sail centre-of-pressure to satellite centre-of-mass offset, will also be discussed, although for launch risk reasons this stage was not included in the final flight configuration. To accurately determine the drag sail’s attitude during the sunlit part of the orbit, an accurate wide field of view dual sensor to measure both the sun and nadir vector direction was developed for this mission. The calibration results for this new Cubesat sensor ( CubeSense ), will also be presented. [ABSTRACT FROM AUTHOR]