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The mechanical and thermal design and analysis of the VISTA

infrared camera

R. L. Edeson, B. M. Shaughnessy, M. S. Whalley, K. Burke, J. Lucas

Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot,

Oxfordshire, OX11 0QX, United Kingdom

ABSTRACT

The infrared camera for the Visible and Infrared Survey Telescope for Astronomy (VISTA) sets many technicalchallenges for mechanical and thermal design. The flexion between optical subsystems must be minimised to maintainalignment in various camera orientations and meet performance requirements. Thermally induced stresses, atmospheric

pressure and earthquake loads place high demands on structural components, some of which must also thermally isolatethe cold (~70 K) detectors and optics. The success of the design hinges on the optimisation of heat flow to minimisethermal loads on the detectors whilst holding external temperatures very close to ambient to reduce misting andconvective disturbances in the field of view.

This paper describes the mechanical and thermal components of the design and discusses the analyses in detail.

Keywords: VISTA, infrared camera, mechanical, thermal, modelling, cryogenic, vacuum.

1 INTRODUCTIONThe VISTA infrared (IR) camera is a wide-field infrared imager which is an integral part of the VISTA telescope1,2,3.Observations will begin in 2006 at the European Southern Observatory site at Cerro Paranal in Chile. The camera willbe built, aligned and tested at the Rutherford Appleton Laboratory (RAL) in the UK. It is currently entering itsmanufacturing phase.

The mechanical and thermal design of the camera was performed largely at RAL, with input from project collaborators

at the UK Astronomy Technology Centre and University of Durham. The various structural, thermal and opticalrequirements on the design necessitated an iterative approach between design and analysis models. Consequently,

analysis models were created at an early stage in the design program, and continually updated as the overall designmatured.

2

DESIGN OVERVIEW

2.1 Camera descriptionThe VISTA IR camera will be approximately three metres long and weigh around three tonnes (see Fig. 1). The outercryostat vacuum vessel will be assembled from several fabricated aluminium alloy sections, and essentially comprises atube with a large bulge in one side to accommodate a filter wheel. A fused silica window seals the end of this cameratube. A series of electronics boxes are mounted around the base of the camera for detector control and signal processing.

A flange around the midsection constitutes the mechanical interface with the Cassegrain rotator on the telescope. Threetwo-stage cryo-coolers are used to maintain the camera at the required operating temperature (see Sec. 3).


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Fig. 1. Section view of the VISTA IR camera.

Positioned in the bore of the camera is a tubular assembly housing a series of ellipsoidal baffles. The base of this baffletube is mounted on an optical bench, a large aluminium alloy structure which is also the support for the lens assembly, aliquid nitrogen heat exchanger (for cooldown of the camera to operating temperature), and the structure supporting the

focal plane. Directly below the lens barrel is a pair of wavefront sensors. Filters, housed in a rotating filter wheelassembly, are positioned between the wavefront sensors and the focal plane. At the focal plane is an array of 16

detectors, each mounted to a molybdenum base, which are then in turn bolted onto a molybdenum detector plate (see

Window

Baffles

Cooler

Wavefront Sensor (WFS)Electronics boxFocal Plane Assembly (FPA)

Liquidnitrogen heat

exchanger

Filter wheel

Glass FibreReinforced

Plastic (GFRP)

trusses

Optical

bench

Interface flange

Lens barrel


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Fig. 2). This detector plate is supported from an aluminium superstructure by three titanium flexures, and locatedlaterally by a spherically-ended molybdenum pin in a cylindrical hole. Thermal straps connect each detector to athermally controlled plate. Beneath this focal plane assembly (FPA) is a cold electronics box, connected to those

outside the cryostat vessel via vacuum feedthroughs in the vessel base.

Fig. 2. Section view of the detector mounting plate.

2.2 The mechanical design modelThe mechanical design of the camera was performed mostly using the 3D CAD software Pro Engineer

4. A main

assembly model of the entire camera was created, made up of various sub-assemblies and parts which could be worked

on by different designers at the same time. This approach successfully gave ownership of different parts of the model todifferent people, and enabled different areas to develop concurrently5.

Project engineers and work package managers had visibility of the overall model at any point in time. This way they

could monitor progress, allowing potential problems to be identified early, as well as extracting information such asdimensions and mass properties for hand calculations and analysis models. The overall CAD assembly model was also a

valuable tool during technical meetings. Over time, the design has been iterated with other subsystems, such as thermal,structural, and optical.

The collaborative nature of the project means that there have been several instances where geometry had to be imported

from other CAD systems. In these cases, STEP format files were used as the intermediary. Although this approach wassuccessful in bringing together complex assemblies of different formats, the imported geometry could not be modified

and the files sometimes contained more detail than required in the overall model.

Molybdenum

location pin

FPA supportframe

(aluminium)

Titanium flexure

Molybdenum plateDetectors


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2.3 Design at different temperaturesOne issue with the cold parts of the assembly (the baffles, FPA, filter wheel and attached parts which operate at well-below ambient temperature) was whether to design them hot or cold; for some of the larger components, there aresignificant dimensional changes from room temperature to operating temperature. For instance aluminium (as used in

the FPA) would shrink approximately 4 mm per metre during the cooldown.

It was decided at an early stage to generate the initial CAD geometry using operating temperature dimensions. This isbecause the optical configuration had been defined at operating temperature, and it is the optical design that determinescertain key dimensions for the layout of the camera. Only when the details of temperatures and materials have beendetermined is it possible to determine the geometry at other temperatures. Interface control documents with other

subsystems were also defined cold.

The thermal analysis (see Sec. 3) showed that much of the cold aluminium structure could be assumed isothermal, andtherefore a constant scaling factor could be applied to obtain room temperature dimensions for manufacturing drawings.The baffle tube assembly, however, has a temperature gradient along its length. On cooling this results in a change ingeometry rather than a uniform scaling of dimensions. This necessitated a more detailed examination of cooldowneffects along its length. The same assembly shrinks about 6 mm in the axial direction on cooldown. Quite apart fromany possible issues with material stress or movements of sensitive optical assemblies, this required an examination of

clearances between close-fitting parts to ensure that assembly would still be possible at room temperature, and

conversely, that no unwanted interferences or gaps would occur during cooldown.

A related issue is with loss of preload on bolted joints due to the different coefficients of thermal expansion (CTE) ofbolt and joint materials during cooldown. In particular this could have a detrimental effect on baffle temperatureperformance, which relies on good thermal conduction across bolted interfaces. Therefore provision was made during

the design for the addition of low-CTE spacers or spring washers to counteract the differential contraction and thereforemaintain preload.

2.4 Design for assembly, installation and maintenanceThe mechanical design of the camera was carried out with assembly sequences in mind. There are parts of the camerathat are very complex and will be difficult to handle due to their size and weight. The cryostat vessel is designed around

a central midsection with good internal access when the main cryostat tube and lower section are removed.Assembly will be conducted with the camera in a horizontal position, and with the midsection supported by dedicatedhandling equipment at its Cassegrain rotator interface. CAD models were used to aid design for access and installation,and mechanism models run to ensure that the full range of movement of the camera (pitch and roll) was possible.

3 THERMAL DESIGN3.1 Thermal requirementsThe temperature requirements for camera internal components are defined from requirements on radiative flux reachingthe focal plane (see table 1).

The camera must operate, without misting of the window, in ambient temperatures of 0 to 15 C and relative humidityup to 70%. Further functional temperature ranges have been defined, for which the humidity for operation withoutwindow misting must be determined. There are also requirements on maximum allowable temperature difference

between the cryostat and the ambient air, in order to minimise the effect of convective disturbances in the field of view.The operational requirements for external surfaces are given in Table 2.


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Item Temperature, K

Baffles as seen by detectors < 190

Correction lens mounting < 170

Optics < 190

Region between detectors and lower lens < 150

Filters < 150

Infrared detectors 77 5 (a,b)(a) passive equilibrium temperature must be < 70 K to demonstrate activecontrol can be achieved.

(b) gradients within any one detector must not exceed 0.5 K, and gradientsbetween any two detectors must not exceed 0.5 K.

Table 1. Summary of internal temperature requirements.

Temperature requirement, C

0 C Ambient 15 C AmbientItem

Maximum Minimum Maximum Minimum

Window 1.5 -4.6 16.5 10.0

Cryostat aboveCassegrain rotatorinterface

1.5 -3.0 16.5 12.0

Cryostat belowCassegrain rotator

interface

1.5 -5.0 16.5 10.0

Table 2. Operational temperature requirements for camera external surfaces.

3.2 Summary of thermal designThe design principle is to thermally isolate the camera internals from the warm cryostat vacuum vessel. In general,

internal components viewing the warmer cryostat have a low emissivity finish to minimise radiative heat transfer,whereas surfaces viewing the detectors are black-painted to minimise stray-light. The external surfaces, however, must

be well-coupled to the ambient environment to minimise temperature differences. The key drivers for the thermal designare the strict temperature requirements defined in Sec. 3.1.

The cryostat is cooled by three two-stage Leybold 5/100T cryo-coolers. Analysis has shown that requirements are verynearly achieved with only two coolers, therefore the third cooler provides a considerable margin against uncertainties in

heat-lift. The first stage of each cooler is coupled to the optical bench by high-purity copper links. Considerable designeffort was required to develop a link design that allows for contractions during cooldown and is also relativelystraightforward to assemble. The second stage of each cooler is coupled to the detector thermal plate (see below) bycopper straps.

The external surface temperature of the cryostat is maintained by software controlled heaters (~40 W maximum). It is

decoupled from the cold internal components by virtue of a low-emissivity internal finish and polished stainless steelradiation shields, which form a second skin within the cryostat. The edge of the window is fitted with a kapton film

heater (~90 W maximum) to provide additional heat to prevent misting.

Attached to the optical bench is a liquid nitrogen heat exchanger, used for initial cooldown of the camera from ambienttemperature, and thermal links to the cryo-coolers. A heater is also fitted for warm-up of the cryostat. To minimise the

parasitic heat loads the optical bench is mounted to the cryostat using a series of low-conductance glass fibre reinforcedplastic (GFRP) trusses which restrict the heat flow from the structure to about 1 W.

Baffle components are manufactured from aluminium and all interfaces are required to be firmly bolted to ensure thattemperature requirements are achieved. The baffles absorb stray-light in the near infrared, however, as they are cold,


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they must have a low emissivity in the thermal infrared to decouple them from the window. Therefore the window-facing surfaces are covered with a selective absorber. The opposite faces are black-painted to absorb stray light.

The detectors, and molybdenum plate to which they are mounted, are conductively isolated from the rest of the internalsby the three titanium flexures. Thermal straps connect each detector to a separate, high-conductivity, thermal plate thatis cooled via straps to the second stage of the cryo-coolers and controlled via a 10 W heater.

3.3 ModelsDetailed thermal mathematical models of the camera have been constructed using the European Space Agency standardsoftware ESATAN and ESARAD

6. ESATAN uses a thermal network representation. Nodes are defined and can be

allocated a thermal capacitance to enable transient calculations. The thermal network is established by specifyingconductive, radiative and convective couplings between nodes. The user may incorporate further routines to describe,for example, the operation of the cryo-coolers, or fluctuations in power dissipation. The radiative couplings werecalculated using ESARAD, a geometric modelling package.

3.4 PredictionsThe steady-state predictions for the nominal operating conditions are summarised in Table 3. Fig.3 shows the ESARADgeometric model with temperatures overlaid for the 0 C ambient case. All temperature requirements are met withsubstantial margin, demonstrating that the camera thermal performance is compliant with the technical specifications. Asensitivity study was undertaken to assess the impact of key parameters on temperature predictions of items without

active temperature control. With the exception of the baffle assembly, the uncertainty was predicted to be within 10C. The maximum uncertainty in the baffle temperatures was -12 C / +22 C and is due to the large number of boltedinterfaces. The uncertainty is lower for baffles closer to the interface with the optical bench.

Fig. 3. Predicted temperature profile within the cryostat in the 0 C ambient case (temperatures in C).


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Temperature Prediction

0 C Ambient 15 C Ambient

Maximum Minimum Maximum Minimum

Internal Items, K

Baffles 147 108 169 123

Lens assembly 94 80 108 90

Filters 81 77 91 85Detectors(a) 48.6 48.5 43.5 43.4

External items, C

Window outer surface 1 -3 16 11

Cryostat above Cassegrain rotator interface 0 -1 15 14

Cryostat below Cassegrain rotator interface 0 -1 15 14(a) To demonstrate that the detector can be cooled below 70 K, the detector plate heater is inactive. A further simulation has shownthat the detectors may be driven to about 90 K by applying the 10 W heater, demonstrating that detectors can be controlled within

requirements.

Table 3. Raw temperature predictions for the nominal operating cases.

4 STRUCTURAL ANALYSIS4.1 Load casesThe structural requirements for the IR camera required verification by analysis for a number of different loading states.The results of interest included flexion of the focal plane under different conditions, stresses and strains in structuralcomponents, and interface loads for the sizing of bolts. A summary of the considered effects and resulting load cases isgiven in Table 4. The load cases are divided into four categories: operating, short term accidental loading (STAL),

survival loading and flexion.

Operational Loading

Short Term

Accidental

Loading

Survival

Loading FlexionStructural Considered

Effects1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Atmospheric and internal

pressures loadsX X X X X X X X X X X

Gravity at 0, 45, 90

degrees altitude angleX X X X X X X X

Operating thermal X X X X X X X X X X

Cool-down / warm-up

non-equilibrium thermalX

Cryogenic failure thermal X

Earthquake OBE X X

Earthquake MLE X

Slewing decelerations X

Survival wind speed X

Handling X X

Transport X

Gravity at 20, 45, 88degrees altitude angle

X X

Table 4. Summary of applicable load cases for each of the 17 load cases, the considered effects are marked with an X.


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Atmospheric pressure loading was taken at sea level as 101,325 Pa. This pressure load will be seen during testingactivities at RAL, however in operation, atmospheric loading will be about 75% of this value. Gravitationalacceleration was taken as 9.81 ms-2.

An Operating Basis Earthquake (OBE) is defined as an earthquake of moderate size but with a high probability ofoccurrence during the lifetime of the observatory. A maximum likely earthquake (MLE) is an earthquake with a large

magnitude but a lower probability of occurrence. Some data on the levels was available in the form of ground-responseacceleration spectra for the region.

Slewing decelerations are rotational decelerations which come about during braking of the telescope. Handling andtransport loads involved loads around special lifting features in the camera, and potential drop-loads during transport.

4.2 Structural requirementsMargins of safety on failure for static loads must be above zero for compliance and were calculated as:

(maximum allowable load)MOS =

(actual applied load safety factor)-1 (1)

Safety factors were required on ultimate tensile strength (UTS), yield and fatigue strengths as given in Table 5. For

slipping at bolted friction-grip interfaces, the yield safety factors were used.

UTS Yield Fatigue

Operational Loading 4 1.5 2

Short Term Accidental Loading 4 1.5 N/A

Survival 2.5 1.2 N/ATable 5. Safety factors.

4.3 Model philosophyThe cold mass and cryostat vessel were de-coupled for ease of analysis. Both structures are similar in terms of themodelling complexity required, and structurally the only link between the two is the series of eight thermally insulatingGFRP trusses. For the cryostat model, the cold mass was treated as a point mass and from the cold mass point of view,

the cryostat was a rigid body.

4.4 Model generationThe Finite Element Analysis (FEA) package used was ANSYS 6.17. An import/export feature between ANSYS and ProEngineer was used.

Both models were necessarily complex, involving a combination of solid, shell, beam and point mass elements. Thegeneration of geometry from scratch in ANSYS would be too time consuming, and would give rise to possible non-conformances with the CAD model. Conversely, the Pro Engineer model was far too complex to easily de-feature, andwould have necessitated much re-assembly work to ensure that the removal of unwanted features (i.e., tapped holes andsmall fillet radii) did not alter the overall assembly geometry.

Instead, a hybrid approach was used for generating the initial ANSYS geometry. Complex 3D solid parts were de-

featured in Pro Engineer and directly imported to ANSYS for assembly and meshing. For thin-walled structures, anapproach was taken to build simplified volume models in CAD using primitive geometric entities. The exteriors of theseCAD solids were modified slightly so they would lie in the mid-plane of the resulting shell elements (see Fig. 4).

In areas where shell elements (with six degrees-of-freedom per node) were attached to solid elements (with only three

degrees-of-freedom) per node, a thin mesh of shells was generated over the solid elements to transmit the rotationaldegrees-of-freedom and avoid hinge-type effects. A similar strategy was used with beam elements.


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Material properties were input over a range of temperatures from room temperature to absolute zero. For most relevantproperties, such as Youngs Modulus and Poissons Ratio, there was little change over this range. Thermal contraction,however, varies appreciably for many of the materials used, so had to be defined as a series of data points in the model.

Fig. 4. Generation of FEA shell geometry from CAD model, with FEA results leading to further design iteration.

4.5 LoadingBoundary conditions for the outer cryostat were defined simply by constraining a circle of nodes around the Cassegrain

rotator interface flange corresponding to mounting bolt positions. These constraints were moved to the lifting pointinterface locations for analysis of handling loads.

For earthquake loads, it was decided that a quasi-static acceleration would suffice if it could be demonstrated that therewas little or no dynamic response of the structure below a certain frequency (thereby avoiding any coupling with

Solid model generated in CAD,with exterior surfaces at mid-

planes of true geometry

Final meshed FEA

model

Original CAD model


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telescope and building resonances). Gravity was applied combined with these, giving a resultant acceleration vector.There were a large number of permutations when combining different gravity vectors required for analysis (due tochanging telescope orientation) with an effectively arbitrary choice of direction for assumed quasi-static earthquake

accelerations. To simplify this, four harsher load cases were identified which enveloped the possible loads. This wasdone by finding the maximum possible resultant acceleration magnitude, and applying it in three mutually orthogonaldirections simultaneously. This approach yields substantially conservative results.

Temperature loads were taken from the thermal analysis model. Average temperatures for the various sub-assemblieswere applied at several nodes around the centre of the sub-assembly in the FEA model. For the baffle tube, maximum

and minimum temperatures were used at the top and bottom of the baffle tube respectively. Then an analysis was run inANSYS which generated interpolated temperatures at every other node in the model. The output from this run can beused as a load input for further analyses.

Other loads analysed were air pressure and wind loading on the exterior of the cryostat vessel, handling loads (where thecamera is supported at certain handling points), transport loads, and rotational decelerations.

4.6 SolutionTo simplify the running of a large number of analyses, and to help file management and archiving, ANSYS loadstepswere used. A loadstep is a particular loading case for the FEA model defined in a separate file. A number of loadsteps

can be solved sequentially in a single run, with all results being written to a single file.

4.7 ResultsIn general, stresses in the outer cryostat vessel were dominated by atmospheric pressure while stresses in the cold masswere dominated by thermo-elastic effects (see Table 6).

Baffles

Baffletube

Trusses

OBstructure

WFSPlate

FPAframe

and

subframe

Detector

plateandPin

Flexures

Thermal

plate

FWHub

Electronics

box

Cryostat

Vessel

Structure

Material: Al Al GFRP Al Al Al Mo Ti Cu Al Al Al

Loading:

Atmospheric - - - - - - - - - - - 58.8

Gravity 0.3 0.6 19.2 38.3 0.8 3.1 7.4 12.7 1.8 0.4 0.6 9.5

0.7 1.3 15.5 12.5 0.8 2.4 13.8 11.7 1.5 0.3 0.5 10.3

0.7 1.4 7.4 17.4 1.1 3.1 19.7 8.8 0.6 0.3 0.4 10.5

0.8 1.3 13 14.9 0.7 3.6 15.9 14.2 1.3 0.4 0.7 9.9

0.8 1.4 7.2 20.5 0.6 4.9 22.6 8.7 0.7 0.2 0.9 10.7

Operating

thermal 1.6 2.1 74.4 49.5 11.9 62.1 71.4 548 6.8 3.5 25.4 16

Combined 1.6 2.4 70.6 50.6 11.9 62 71.6 543 6.8 3.5 25.3 58.7

1.6 2.4 74.6 50.8 12 62 71.1 546 6.7 3.4 25.3 58.6

1.6 2.4 80.3 50.3 12.1 62.1 70.8 551 6.7 3.4 25.3 60.4

1.6 2.8 74.1 50.2 11.9 62.1 55.4 548 6.3 3.4 25.1 58.9

1.6 2.6 80.2 49.4 12 62.1 48.6 553 6.1 3.7 25.3 59.2

Handling - - - - - - - - - - - 56.3

MOS on UTS 42.0 23.6 -0.1 0.4 4.7 0.1 0.8 -0.6 11.7 17.6 1.7 0.1

MOS on yield 51.1 28.8 1.5 0.6 5.9 0.3 2.9 0.0 18.1 21.5 2.3 0.4

Table 6. Von Mises stress results in MPa in different parts of the model under operational loading, along with margins of safety onUltimate Tensile Strength (UTS) and yield strength.


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For operational loading results, there were initially negative margins of safety at the GFRP trusses and the titaniumflexures. These are both areas where the accommodation of large deflections is necessary, without compromisingstiffness. A low but positive MOS can therefore be seen as a sign that the design is near-optimal in meeting these

conflicting requirements. In the case of the titanium flexures, it was shown that halving their thickness would halvestress levels on cooldown to an acceptable level, without impacting on tilts or translations at the FPA appreciably.Similarly, it was possible to reduce the stiffness of the GFRP trusses in the radial direction (the direction of large

deflection) and maintain compliance with natural frequency and deflection requirements.

For the STAL and survival load cases, margins of safety were positive except for several of the earthquake scenarios. In

these particular cases, the earthquake acceleration state was decomposed and more realistic loads were applied. Theresulting stress levels were acceptable (see Sec. 4.5).

Results for translations and rotations at the focal plane were fed into the optical image quality analysis. Other results ofinterest were reaction loads at mounting positions, which were used in sizing mounting bolts.

Modal and buckling analyses both gave results compliant with requirements.

4.8 SubmodelsThere were a number of areas which required special analysis; one such area was the cryostat window. Being a brittle

material, failure would be through crack propagation in areas of tension in the material. A seating arrangement wasdesigned whereby silicone rubber pads prevent glass-to-metal contact occurring once the sealing O-ring had beencompressed. This problem was examined using a 2-dimensional axi-symmetric model with contact elements allowingsliding with frictional forces between glass and seal (see Fig. 6).

Fig. 6. Contact analysis of O-ring seal at window, showing silicone rubber pads preventing glass-to-metal contact.

O-ring

Aluminium seat

Window

Silicone

rubberpad

Pressure


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5 CONCLUSIONThe VISTA IR camera is a complex design which has required an iterative approach between CAD, structural FEA andthermal analyses. The design process has benefited greatly from the specialised software packages available, as well asexpert users. A number of technical challenges have been overcome through close cooperation between the relevantdisciplines.

The bulk of the mechanical design work on the camera has been performed at RAL using powerful CAD tools.Throughout the design phase, careful attention has been given to assembly and integration issues, as well as themechanical effects of the low operating temperatures. The thermal design has matured with the mechanical design, andrequirements on thermal flux at the focal plane have been met. Finite element analysis has also been an aspect of thedesign process. Requirements of structural integrity under many environmental conditions have been verified throughanalysis, and movements of optical components have been assessed.

Having been verified successfully by analysis, the design has recently passed a final design review, and the project hasnow entered its manufacturing phase.

ACKNOWLEDGEMENTS

The VISTA IR team gratefully acknowledges help and advice received from University of Durham and the UKAstronomy Technology Centre.

VISTA is funded by a grant from the UK Joint Infrastructure Fund, supported by the Office of Science and Technologyand the Higher Education Funding Council for England, to Queen Mary University of London on behalf of the 18

University members of the VISTA Consortium of: Queen Mary University of London; Queen's University of Belfast;University of Birmingham; University of Cambridge; Cardiff University; University of Central Lancashire; Universityof Durham; University of Edinburgh; University of Hertfordshire; Keele University; Leicester University; LiverpoolJohn Moores University; University of Nottingham; University of Oxford; University of St Andrews; University of

Southampton; University of Sussex; and University College London.

REFERENCES

[1] Emerson, J. P. et al., The Visible and Infra Red Survey Telescope for Astronomy: Overview, Proc SPIE Int.

Soc. Opt. Eng 4836, p.35-42 (2002).[2] McPherson, A. et al., The VISTA Project: a Review of its Progress and Lessons Learned Developing the

Current Programme, Proc SPIE Int. Soc. Opt. Eng. 5489-46 (2004).[3] Dalton, G. et al., The VISTA IR Camera, Proc SPIE Int. Soc. Opt. Eng. 5492-34 (2004).[4] Parametric Technology Corporation, Pro Engineer, http://www.ptc.com/[5] Caldwell, M. et al., Aspects of Concurrent Design During the VISTA IR Camera Detailed Design Phase,

Proc SPIE Int. Soc. Opt. Eng. 5497-06 (2004).[6] Alstom Power Technology Centre, Software Products - Overview, http://www.techcentreuk.power.alstom.com/[7] ANSYS, Inc., ANSYS FEA software, http://www.ansys.com/

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