ESA GNC Conference Papers Repository
A Miniaturised Attitude Control and Determination System for the QB50 and SME-SAT Missions
This paper focuses on the development of a miniaturised Attitude Control and Determination System (ADCS) used for two different FP7 CubeSat missions: QB50 and SME-SAT. The QB50 mission aims to assist in atmospheric research by utilising a series of 40 double CubeSats carrying identical sensors in a space network. The vehicles will be launched into a low circular 350 km orbit where aerodynamic disturbance torques on the satellite are significant; sufficient attitude control is thus required to point the scientific instrumentation in a specific direction. SME-SAT is a mission aiming to space qualify a range of state of the art terrestrial sensors requiring a triple CubeSat which uses a nano-CMG pyramid configuration for attitude control. The nano-CMGs provide an unprecedented level of agility compared to existing CubeSats. The CubeSat ADCS module presented in this paper has the ability to stabilise the satellite attitude and allows for the pitch angle to be controlled to a specific offset. It does this using a combination of three magnetorquers and a momentum wheel. From a sensor perspective, the system incorporates a magnetometer, coarse sun sensing using photodiodes, a higher accuracy optical sun and nadir sensor, and a MEMS rate sensor in addition to a GPS receiver for fine orbital position measurements. The ADCS module is designed and integrated as a collaborative effort between the Space Vehicle Control group at the Surrey Space Centre and the Electronic Systems Laboratory (ESL) at Stellenbosch University. The miniaturized system fits in a volume of 10 x 10 x 5.5 cm and weighs less than 350 grams. Simulations are presented which verify the operation and performance for various satellite configurations. For an aerodynamically stable satellite, the attitude can be controlled to 0.5 degrees accuracy (RMS) above a 300 km altitude. Under a 200 km altitude with severe aerodynamic disturbances, a pointing accuracy of 2.5 degrees is achieved.