ESA GNC Conference Papers Repository

It is becoming an increasingly common challenge for modern spacecraft with strict pointing requirements to maintain its performance during mission phases where mechanism steering occurs. When these mechanisms are operated, the spacecraft attitude and rates are affected by the exchange of momentum between the spacecraft and the operated mechanism. This effect can be a significant source of disturbance for fine spacecraft attitude control and therefore it must be well studied and characterised. This paper presents a simplified approach developed by Airbus Defence & Space Ltd. to analysing and characterising the disturbance induced by the mechanism operation based on simplified, but still representative, multi-body dynamics equations. First, the generalised dynamics equations for a rigid body are presented. Then, a simplification of these equations is performed based on retaining first order effect terms. Eventually, simplified expressions in order to characterise disturbance torque and angular momentum exchange that can be used for fine pointing budgets are derived. At a second stage, the derived simplified formulae are assessed against a fully-representative multibody dynamic simulator. Finally, an application example for Solar Orbiter (an ESA M-class mission) is also presented. In conclusion, the approach presented in this paper allows one to accurately and efficiently address the mechanism disturbance effects without the need for time-consuming and involved temporal simulation during design and tuning phases.