Comparing the frequency range of the requirement to the test facility specifications shows that both  facilities would be required to cover the entire range. Even then, the 6dMVMS can measure as low as  0.03 Hz, whereas the requirement goes lower than 0.001 Hz.   The sensitivity and measurement range of both facilities are also relevant. It seems the sensitivity and  range of the RCF is only compatible with the requirement up to 150 Hz. At higher frequencies the  requirement is below the sensitivity of the facility. The 6dMVMS can actually measure forces lower than  the minimum force specified of 1 mN. However, it can only measure up to 1 N. For an instrument this  large, rotating at <1 Hz, the exported force is unlikely to be as low as 1 N at the main rotating frequency.  The instrument requires gravity offloading to operate under a 1g environment, although it can also be  operated for short periods of time without gravity offloading. However, a measurement in both of these  configurations impacts the data in a different way. The offloading MGSE itself includes bearings as it  needs to allow for the rotation. These can generate additional noise. Furthermore, the MGSE changes the  inertia and the modal behavior of the instrument. On the other hand, operating without offloading  significantly changes the preload of the bearings in the scan mechanism. This may in turn have a  significant impact on the microvibration performance. Both potential test configurations have clear  drawbacks.  Lastly, the scanner is not axisymmetric and has a large cut-out on one side. As a consequence, there are  significant additional unbalance forces due to windage losses when operating in air. In order to make  meaningful measurements, the test would need to take place in vacuum.   It is clear for this particular case that the specified requirement along with the specified verification  method is very challenging to achieve. As mechanism designer, discussing these issues early during the  development with the customer is strongly advised in order to avoid unnecessarily ambitious design  constraints and to come up with a feasible verification approach.   Which Approach can be Used to Minimize Microvibration?  There are several potential approaches on how to minimize the microvibration generated by mechanisms.  This includes potential design improvement methodologies, minimizing the impact of assembly,  integration and test (AIT) on the microvibration performance as well as solutions external to the  mechanism in case design optimization and other measures prove to be insufficient.  A mechanism designer can attempt to optimize a mechanism for low noise performance during the design  phase. The following tactics can be used:  •Reduction of the amplitude of the noise generated by carefully selecting components, materials, surface finishes and lubricants. It is recommended to try out different options at breadboard stage for especially demanding applications. •Screening of components and subassemblies during the manufacturing stage. As shown in the example in Figure 1, identical mechanisms can still differ significantly. Performance of key components or subassemblies can be screened prior to integration in the mechanism to minimize the spread of the noise performance and reduce it as much as possible. This approach is generally taken in case larger numbers of identical mechanisms need to be made, as setting up the screening process requires quite some effort. •Improve the modal design. The main structural modes of the mechanism are likely to be excited by internally generated noise and therefore amplify the exported microvibration. This can be seen very clearly in Figure 2. Designing the mechanism structural modes in frequency ranges where higher microvibration is allowed by the specification will reduce the impact of these modes getting excited. The requirement in Figure 5 shows a clear frequency range allowing higher amplitudes of exported microvibration. If compatible with the structural requirements of the mechanism or instrument, this would be an obvious target area in terms of modal design. NASA/CP—2018-219887 202