Equipment vibration budget for the TMT

MacMartin, Douglas G.; Thompson, Hugh A.

doi:10.1117/12.2057179

Cited by 3 publications

(2 citation statements)

References 4 publications

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“…The MAViC isolates at a natural frequency below 0.7Hz, combining this with a rigidly mounted six axis accelerometer capable of DC measurements, allows very accurate measurements to be made. Measurements were compared against the instrument requirement for the VLT 2 , GMT, and TMT 3 . Based on those, the amount of required isolation can be derived and used as a guideline for designing cryocooler mounts.…”

Section: Methodsmentioning

confidence: 99%

Vibration measurement and mount design for cryocoolers on GMT and large telescopes

Adams¹,

Vaccarella²,

Schofield³

et al. 2020

Advances in Optical Astronomical Instrumentation 2019

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Cryocoolers have long been demonstrated to be a dominant source of vibration that have caused significant problems with AO systems on large telescopes. Existing large telescopes have already imposed strict vibration requirements on instruments in response to existing problems, and have often struggled to achieve them. As the field moves into the next generation telescopes with GMT, TMT and eELT, vibration requirements continue to get ever tighter. Instrument teams must respond to these more demanding requirements by careful selection of cryocoolers and thoughtful design of cryocooler mounts that are matched closely with the specific requirements of the telescope. As we will demonstrate in this paper there is not a one-size-fits-all solution for every instrument and every telescope.In this paper we demonstrate a general method of deriving the required performance for an anti-vibration mounts for cryocoolers. First we characterize a linear Stirling-type cryocooler as a source of vibration, and determine what compliant mounts would be required to make them acceptable for use on the VLT, GMT and TMT. Measurements are taken of vibration from a Cryotel GT linear Stirling cooler (with active vibration cancellation enabled). By comparing the measured vibration against the requirements of each telescope, we are able to determine the required transfer function and therefore the required spring rate for compliant mounts. The results indicate that while some simple rubber mounts may be sufficient for use with the VLT and TMT, but a compliant mount with natural frequency below 14 Hz must be used for GMT.

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Section: Methodsmentioning

confidence: 99%

Vibration measurement and mount design for cryocoolers on GMT and large telescopes

Adams¹,

Vaccarella²,

Schofield³

et al. 2020

Advances in Optical Astronomical Instrumentation 2019

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show abstract

“…11 These disturbances apply equal and opposite torques to the telescope structure and the relevant optic. While the former can result in excitation of telescope resonances and motion of other optical surfaces, the resulting image jitter and M1 response are negligible compared with the direct response of the driven surface, which can be roughly estimated from the mirror inertial response.…”

Section: Sensitivity Analysismentioning

confidence: 99%

Vibration budget for observatory equipment

MacMartin

Thompson

2015

J. Astron. Telesc. Instrum. Syst

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Abstract. Vibration from equipment mounted on the telescope and in summit support buildings has been a source of performance degradation at existing astronomical observatories, particularly for adaptive optics performance. Rather than relying only on best practices to minimize vibration, we present here a vibration budget that specifies allowable force levels from each source of vibration in the observatory (e.g., pumps, chillers, cryocoolers, etc.). This design tool helps ensure that the total optical performance degradation due to vibration is less than the corresponding error budget allocation and is also useful in design trade-offs, specifying isolation requirements for equipment, and tightening or widening individual equipment vibration specifications as necessary. The vibration budget relies on model-based analysis of the optical consequences that result from forces applied at different locations and frequencies, including both image jitter and primary mirror segment motion. We develop this tool here for the Thirty Meter Telescope but hope that this approach will be broadly useful to other observatories, not only in the design phase, but for verification and operations as well.

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Measuring transmission and forces from observatory equipment vibration

et al. 2014

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We describe measurements of both the vibration forces imparted by various types of observatory equipment. and the transmission of these forces through the soil, foundations and telescope pier. These are key uncertainties both in understanding how to mitigate vibration at existing observatories and for developing a vibration budget in the design of future observatories uch as the Thirty Meter Telescope. Typical vibration surveys have measured only the resulting motion (acceleration); however. this depends on both the source and the system being excited (for example, isolating equipment results in less force being t ransmitted, but greater motion of the equipment itself). Instead, here we (a) apply a known force input to the pier from a shaker and measure the response at different locations, and (b) use isolator properties combined with measured acceleration to infer the forces applied by various equipment directly. The soil foundation and pier transmission can then be combined with a finite element model based vibration transmission analysis to estimate the optical consequences. Estimates of plausible source levels supports the development of a vibration budget for TMT that allocates allowable forces to the sources of vibration: this is described in a companion paper.

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Equipment vibration budget for the TMT

Cited by 3 publications

References 4 publications

Vibration measurement and mount design for cryocoolers on GMT and large telescopes

Vibration measurement and mount design for cryocoolers on GMT and large telescopes

Vibration budget for observatory equipment

Measuring transmission and forces from observatory equipment vibration

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