Hoog-precieze richtnauwkeurigheid van mini-satellieten – Tweetraps controletechnieken voor optische instrumenten

Small satellites, often referred to as smallsats, embody a rapidly growing class of spacecraft. This class of satellites, particularly CubeSats, has capitalised on advancements in technology miniaturisation and component standardisation, making them a popular and cost-effective solution for space access over the past decades. Today, international space agencies recognise their potential for demonstrating new technologies or exploring the atmospheres of remote planets. Additionally, space companies see opportunities to deploy large constellations of small satellites to provide global coverage for communication and Earth observation purposes. To fulfil their objectives and accomplish their missions, nearly all of these satellites are equipped with an attitude determination and control subsystem. This subsystem determines and controls the orientation, or attitude, of the spacecraft. It is used, for example, to direct an antenna towards a ground station or aim a camera at a specific target for observation. Existing small spacecraft subsystems typically achieve pointing precision within the range of arcminutes, primarily constrained by their volume, mass, and power limitations. However, as spacecraft pointing accuracy improves, the quality of optical payloads is enhanced, enabling new applications. One approach to further enhancing pointing precision, achieving accuracy within the range of arcseconds, is to implement a line-of-sight control system in addition to the attitude determination and control subsystem, thereby forming a dual-stage pointing control approach. This dissertation focuses on three key aspects of the dual-stage pointing control strategy for small spacecraft missions equipped with optical payload instruments. Reaction wheels generate micro-vibrations onboard a spacecraft, which can degrade the optical quality of payload instruments. A micro-vibration experiment is conducted on a representative smallsat reaction wheel designed at KU Leuven. From the experimental data, the unbalances, bearing harmonics, and non-linear dynamics are characterised. This characterisation led to the development of a realistic reaction wheel micro-vibration simulation model and provided insights to optimise the next-generation reaction wheel design. Dual-stage pointing control requires a fast and accurate sensor. Particularly for astronomy missions, fine-guidance sensors can provide highly accurate pointing knowledge when embedded in the payload optical instrument. This pointing accuracy is primarily determined by the ability to calculate the centroid of stars within the detector's focal plane. A methodology is developed to estimate the fine-guidance sensor centroiding accuracy, with the novelty lying in accounting for the spectral content of the star flux. This methodology is applied to the CubeSpec mission to estimate the fine-guidance sensor centroiding accuracy and optimise the optical design and detector settings. Finally, a comprehensive pointing error model is developed for a smallsat mission employing a dual-stage pointing control strategy. This linear time-invariant simulation model incorporates the most significant pointing error sources and dynamics to compute the overall pointing error budget. The pointing error model is used to evaluate the dual-stage pointing control approach for the CubeSpec mission and to conduct parameter sensitivity analyses.