ESA GNC Conference Papers Repository

Many pointing mechanisms are used on spacecraft for different purposes: Solar Array Drive Mechanism (SADM), Antenna Pointing Mechanisms (APM), scanning mirror, filter wheel, etc. These mechanisms generally drive flexible appendages (solar arrays, antenna, mirrors, etc.) that can be excited during the actuation, leading to important disturbances applied onto the spacecraft. These disturbances can be detrimental to the payload line of sight stability and can degrade the overall mission performances. This situation can be solved by stopping noisy mechanisms while the payload is activated, but it can reduce mission availability and reactivity and impose important constraints on mission planning. That’s why it is interesting to develop low noise pointing mechanisms that can be used continuously during the mission without interfering with payload performances. Together with the French Space Agency (CNES), Airbus Defence & Space explored different architectures that can reduce the disturbance level generated by pointing mechanisms. Two target missions have been selected which are representative of the next generation missions in terms of accuracy and stability requirements. A complete simulation framework was developed to take into account spacecraft structure and flexible appendages as well as drive mechanism architecture and internal disturbances. Special care was taken to finely model friction behaviour inside the mechanism since early simulations proved that it could have a huge impact on final performances. This framework was used to study several improvements of current state of the art pointing mechanisms. These improvements were at different levels of complexity and maturity. First level was a simple optimization of the angular profile commanded to the mechanism (smoothing, spreading, shaping, etc.). Interesting improvement can be reached, especially if a modification of the control electronics can be envisaged, allowing microstepping commands for instance. Then more complex improvements have been analysed, like motor configuration or transmission architecture optimization, leading to an important noise level reduction. Finally reference architectures have been selected for each reference mission that fulfil stability and pointing requirements.