Microvibrations induced by a cantilevered wheel assembly with a soft-suspension system

Microvibration management onboard spacecraft with high stability requirements has drawn increasing interest from engineers and scientists; and this article discusses a Reaction Wheel design which allows a significant reduction of mid to high frequency microvibrations, and that has been practically implemented in Industry. Disturbances typically induced by mechanical systems onboard a spacecraft (especially rotating devices such as reaction wheel assemblies andmomentum wheel assemblies) can severely degradethe performance of sensitive instruments. Traditionally, wheel-induced high-frequency (over 200 Hz) vibrations,generated by a combination of phenomena from bearing noise to dynamic amplifications due to internal resonances,are especially difficult to control. In this paper, the dynamic behavior of a newly designed wheel assembly, with acantilevered flywheel configuration supported by a soft-suspension system, is investigated. The wheel assembly’smathematical model is developed and later verified with vibration tests. Wheel-assembly-induced lateral and axial Q4 microvibrations are accurately measured using a seismic-mass microvibration measurement system, which represents an alternative to typical microvibration measurement setups. Finally, the performance of this wheel assembly in terms of microvibration emissions is compared with a traditional design (with a rigid suspension) through comparison of frequency spectra, and it is shown that this design produces significantly lower vibrations at high frequenc

Hydrolysis of bis((trimethylsilyl)methyl)tin dihalides. Crystallographic and spectroscopic study of the hydrolysis pathway

The synthesis and characterization by multinuclear NMR spectroscopy of the diorganotin dihalides (Me3SiCH2)2SnX2 (1, X = Cl; 2, X = Br), the diorganotin dichloride water adduct (Me3SiCH2)2SnCl2&middot;H2O (1a), the dimeric tetraorganodistannoxanes [(Me3SiCH2)2(X)SnOSn(Y)(CH2SiMe3)2]2 (3, X = Y = Cl; 4, X = Br, Y = OH; 5, X = Br, Y = F; 6, X = Y = OH; 8, X = Cl, Y = OH), and the molecular diorganotin oxide cyclo-[(Me3SiCH2)2SnO]3 (7) are reported. The structures in the solid state of compounds 1a, 3, 6, and 7 were determined by single-crystal X-ray analysis. In toluene solution, the hydroxy-substituted tetraorganodistannoxane 6 is in equilibrium with the diorganotin oxide 7 and water. The eight-membered diorganotin oxide cyclo-[(Me3SiCH2)2SnO]4 (7a) is proposed to be involved in this equilibrium. On the basis of the results of this and previous works, a general hydrolysis pathway is developed for diorganotin dichlorides containing reasonably bulky substituents.<br /