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Zhang Z.,University of Southampton | Zhang Z.,Astronautics Research Group | Aglietti G.S.,University of Southampton | Aglietti G.S.,Astronautics Research Group | Zhou W.,National University of Defense Technology
AIAA Journal | Year: 2011

Microvibration management onboard spacecraft with high stability requirements has drawn increasing interest from engineers and scientists, and this paper discusses a reaction wheel design that 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 and momentum wheel assemblies) can severely degrade the performance of sensitive instruments. Traditionally, wheel-induced high-frequency (over 100-200 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 a cantilevered flywheel configuration supported by a soft-suspension system, is investigated. The wheel assembly's mathematical model is developed and later verified with vibration tests. Wheel-assembly-induced lateral and axial 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 frequency. Copyright © 2010 by Zhe Zhang. Source


Sairajan K.K.,University of Southampton | Sairajan K.K.,Astronautics Research Group | Aglietti G.S.,University of Southampton | Aglietti G.S.,Astronautics Research Group
Journal of Spacecraft and Rockets | Year: 2014

The modal assurance criterion and normalized cross-orthogonality check are widely used to assess the correlation between the experimentally determined dynamic characteristics and the finite element model predictions. In this paper, the effectiveness of these criteria on the base excitation responses of three spacecraft models is carried out. The dynamic characteristics obtained from a nominal finite element model are considered as experimental or true characteristics, and those obtained from a model produced by introducing errors in the nominal model are considered as analytically predicted characteristics. It is observed that these criteria are not suitable, particularly when the model is used to predict forced response characteristics such as the force transmitted to the base, peak acceleration response, and dynamic displacement in the spacecraft. Thus, a qualitative indicator named as base-force assurance criterion is defined by comparing the experimentally determined dynamic force at the base and the finite element predicted force such that the criterion can state the possible error in the peak acceleration and the dynamic displacement under the base excitation. The method is applied to assess the performance of three spacecraft structures, and the results show that new criterion can better correlate with the acceleration and the dynamic displacement error than the conventional criteria. Copyright © 2013 by K. K. Sairajan and G. S. Aglietti. Source


Coletti M.,University of Southampton | Coletti M.,Astronautics Research Group | Gabriel S.B.,University of Southampton | Gabriel S.B.,Astronautics Research Group
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit | Year: 2010

At the end of 2008 a European Union sponsored project called HiPER (High Power Electric propulsion: a Roadmap for the future) started in Europe with the aim of defining the roadmap for the future of electric propulsion. Within this project several different propulsive systems are under study and among these the dual stage ion engine. In this paper a full design of the ion optics of a dual stage ion engine will be presented and numerically analyzed to assess its performances and lifetime. Its performances will be compared with areference conventional 2 gridded ion engine. The dual stage ion engine has been found to be able to provide higher Isp, higher thrust density and lower beamlet divergence with respect to the reference GIE. Copyright © 2010 by Michele Coletti. Source


Coletti M.,University of Southampton | Coletti M.,Astronautics Research Group | Gabriel S.B.,University of Southampton | Gabriel S.B.,Astronautics Research Group
47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 2011 | Year: 2011

In the frame of the HiPER project a parametric study has been performed over the ion optics of a dual stage ion engine. The goal of the study is to identify the effect of the ion optics design parameters over performances and lifetime. The parametric study will focus on both low, medium and high Isp operation. In this paper the past results will be quickly presented for then focusing on the medium to high Isp operation. The influence of the grids aperture radii, accel stage gap and grid thickness over the jet divergence, beamlet current capability and minimum centerline potential will be presented and the lifetime of a DS3G thruster at different Isp levels investigated and compared to the one of a conventional GIE. The dual stage ion optics has been found to provide no lifetime improvement at 5,000s and worse lifetime that a GIE at 6,000s. The DS3G lifetime has been found to increase with Isp from 6,000s onwards providing improvements in comparison to a GIE for Isp of 7,000 and higher. The reason for this lifetime trend has been found to be the improved CEX focusing at high Isp. Some of the causes of this phenomenon have been investigated and in particular the electric field in the second stage has been found to be one of the main driver of the improved CEX focusing. © 2011 by Michele Coletti. Source

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