Edge sensor design for the TMT

Mast, Terry S.; Chanan, G. A.; Nelson, Jerry; Minor, R.H.; Jared, R. C.

doi:10.1117/12.672028

Cited by 16 publications

(11 citation statements)

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“…The TMT capacitive sensor prototype 5,6,7 , shown on the left side of Figure 2 and in Figure 3, has a face-on design allowing segment exchange without moving sensor parts.…”

Section: Capacitive Edge Sensorsmentioning

confidence: 99%

“…1,2,3,4 These movements are based on error signals generated from edge sensors that are exquisitely sensitive to the relative height and tilt of neighboring segments. 5,6,7 While the segments are actively controlled in optical surface height, lateral motion is only passively constrained, by the backing structure. Thus there will be some small change in the gaps between segments, and some "shear" (segment-tosegment relative motion along an edge), as changing telescope orientation and temperature make small distortions in the steel backing structure.…”

Section: Introductionmentioning

confidence: 99%

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Advances in edge sensors for the Thirty Meter Telescope primary mirror

et al. 2008

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The out-of-plane degrees of freedom (piston, tip, and tilt) of each of the 492 segments in the Thirty Meter Telescope primary mirror will be actively controlled using three actuators per segment and two edge sensors along each intersegment gap. We address two important topics for this system: edge sensor design, and the correction of fabrication and installation errors.The primary mirror segments are passively constrained in the three lateral degrees of freedom. We evaluate the segment lateral motions due to the changing gravity vector and temperature, using site temperature and wind data, thermal modeling, and finite-element analysis.Sensor fabrication and installation errors combined with these lateral motions will induce errors in the sensor readings. We evaluate these errors for a capacitive sensor design as a function of dihedral angle sensitivity. We also describe operational scenarios for using the Alignment and Phasing System to correct the sensor readings for errors associated with fabrication and installation.

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“…The TMT capacitive sensor prototype 5,6,7 , shown on the left side of Figure 2 and in Figure 3, has a face-on design allowing segment exchange without moving sensor parts.…”

Section: Capacitive Edge Sensorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Advances in edge sensors for the Thirty Meter Telescope primary mirror

et al. 2008

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“…Similarly, the boundary conditions for M2CA and M3CA are shown in Figure 4(b). The boundary condition equations satisfying M2CA and M3CA are determined in the same manner as M1SA with three exceptions: (1) only radiation between the mirror and cell is considered and not to the atmosphere, (2) convection is added to the mirror edges, and (3) heat flux is applied to the cell back instead of the mirror back.…”

Section: Introductionmentioning

confidence: 99%

Thermal performance prediction of the TMT optics

et al. 2008

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Thermal analysis for the Thirty Meter Telescope (TMT) optics (the primary mirror segment, the secondary mirror, and the tertiary mirror) was performed using finite element analysis in ANSYS and I-DEAS. In the thermal analysis, each of the optical assemblies (mirror, mirror supports, cell) was modeled for various thermal conditions including air convections, conductions, heat flux loadings, and radiations. The thermal time constant of each mirror was estimated and the temperature distributions of the mirror assemblies were calculated under the various thermal loading conditions. The thermo-elastic analysis was made to obtain the thermal deformation based on the resulting temperature distributions. The optical performance of the TMT optics was evaluated from the thermally induced mirror deformations. The goal of this thermal analysis is to establish thermal models by the FEA programs to simulate for an adequate thermal environment. These thermal models can be utilized for estimating the thermal responses of the TMT optics. In order to demonstrate the thermal responses, various sample time-dependent thermal loadings were modeled to synthesize the operational environment. Thermal responses of the optics were discussed and the optical consequences were evaluated.

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“…Two sensors are also needed on each edge to measure the relative motion between segments, as on ground-based segmented-mirror telescopes [17], where differential height between segments can be measured with a resolution of a few nanometers using either differential capacitive [18] or differential inductive sensors [19]. Unless a manufacturing approach is used that ensures sensor installation errors of nanometers, an initial phasing approach using star light would be needed after the mirror was assembled in order to determine the correct set point for each sensor; these techniques are well established on the ground, but some modifications to the approach would be required to handle many thousands of segments [6].…”

Section: Modelmentioning

confidence: 99%

Control of a Hypersegmented Space Telescope

MacMynowski

2012

Journal of Guidance, Control, and Dynamics

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The primary mirror diameter of affordable space telescopes is limited by mass and manufacturing cost. Currently planned optical/near-infrared space telescopes use a segmented primary mirror with relatively few segments and make limited use of real-time position control. However, control can be used as an enabler for a fundamentally different, very highly segmented architecture, leading to a significant reduction in areal density, and hence a significant increase in the realistically achievable diameter of a space telescope. Weight can be reduced by minimizing the structure that supports mirror segments and instead relying on control for overall stiffness. Furthermore, smaller segments can be thinner (hence, lighter) while still providing sufficient internal rigidity. However, with these architectural changes, the control problem involves not only thousands of actuators and sensors but also many lightly damped modes within the control bandwidth. The objective here is to demonstrate that this control problem is solvable by applying a local control approach. This is illustrated for a 30-m-diam primary mirror composed of 12,000 0.3-m-diam segments.

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Edge sensor design for the TMT

Cited by 16 publications

References 0 publications

Advances in edge sensors for the Thirty Meter Telescope primary mirror

Advances in edge sensors for the Thirty Meter Telescope primary mirror

Thermal performance prediction of the TMT optics

Control of a Hypersegmented Space Telescope

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