A Mechanisms Perspective on Microvibration –  Good Practices and Lessons Learned  Geert Smet* and Sandro Patti* Abstract  In September 2017, the ESA Mechanisms Section organized the first Advanced Mechanisms Design  Course. The course focused on how to anticipate and avoid the most common problems encountered in  several different fields of space mechanisms design. One of the topics addressed was ‘A Mechanisms  Perspective on Microvibration’. This tutorial paper draws from the content of this well-received training,  focusing on practical tips and good practices, complemented by lessons learned from operational  missions and their on-orbit performance.  Introduction  The purpose of this paper is to make mechanisms engineers aware of the microvibration problem and  offer practical knowledge and tools on how to deal with it. This paper will cover:  •What microvibration is •What causes microvibration in mechanisms •How microvibration is typically handled at the system level •What a microvibration requirement for a mechanism looks like •Which verification methodologies are appropriate in which circumstances •How verification approaches can be used most effectively and which pitfalls to avoid •Which approach can be used to minimize microvibration This paper does not cover recovery actions to be undertaken in case a microvibration problem manifests  on orbit. If possible, changing operational parameters of the mechanisms generating the noise is  recommended. In certain cases, post-processing the data from the payload may be used to offset the  effects of microvibration.  Microvibration and Mechanisms  What is microvibration?  Microvibration can be defined as a structure-borne vibration generated from equipment in the spacecraft  that causes motion of the payload or other sensitive equipment that could cause degradation in  performance. It is important to note that several terms are typically used interchangeably to discuss one  phenomenon: microvibration, micro-vibration, microdisturbances, jitter or even simply noise.  Microvibration disturbances are usually in the range of micro-g’s (μg) typically occurring at frequencies  from as low as 0.1 Hz up to 1000 Hz. Mechanisms such as Reaction Wheels (RW), Control Moment  Gyros, Antenna Pointing Mechanisms (APM), Cryocoolers, Solar Array Drive Mechanisms (SADM),  scanners, and optical mechanisms are typically the main sources of mechanical noise on a spacecraft.   Microvibration is a significant technical challenge for the current generation of space missions due to the  stringent stability requirements of the payloads. The current state of the art is ~0.1 μrad Line of Sight  stability. This equates to motions in the order of only a few nanometres in payloads. A further order of  magnitude improvement is required for future missions. Microvibration is a system-level problem and  involves several disciplines, such as systems, mechanisms, mechanical systems & analysis, optical,  attitude & orbital control systems, and spacecraft ops. This further complicates the mechanisms  designer’s task.  *European Space Agency, Noordwijk, The Netherlands Proceedings of the 44th Aerospace Mechanisms Symposium, NASA Glenn Research Center, May 16-18, 2018 NASA/CP—2018-219887 191