SKA TDP & CART 15m OFFSET(DVA-1) ANTENNA DESIGN 13

SKA WP2 Meeting at Oxford UKOctober 27, 2010

Matt Fleming Gordon Lacy

Contributions fromJack WelchLynn BakerBill Imbriale

German Cortes

Design Collaboration

The current antenna design effort combines the knowledge and skills of the Canadian NRC CART staff and US TDP staff to create a innovative new SKA antenna design.

CART stands for Composite Applications for Radio Telescopes. A team based at DRAO Penticton generated a first 10m prototype in 2007 and conducted critical testing. An improved 10m was produced in spring of 2008. Experiments showed good performance. Innovation continues with further materials development.

The US TDP studied optic configurations and selected a shaped offset design. This reflector arrangement will be used on a specialized mount with features based on 6m ATA design experience.

SKA WP2 Meeting, Oxford, 2010-10-27 Lacy & Fleming slide 2 of 36

Antenna Design Drivers

1 Low cost per unit area of aperture. ( good sky coverage ) ( installed )( low cost materials, low mass design, low fabrication labor ) ( favors symmetric )

2 Very low operational cost for a 30 year life( very few maintenance visits required )

3 Frequency range of 0.3 to 10 GHz with WBSPF( 4.0m Gregorian secondary ) ( favors offset )

4 Excellent Ae / Tsys.( accurate surfaces, controlled spillover, low diffraction ) ( favors offset )

5 Exceptional dynamic range.( very rigid surfaces, very good pointing, )

Specifications have been generated.

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Antenna Features

Light weight single shell rim supported primary, metal or composite.

Secondary & feed support via rim.

Pedestal with turning head mount with tightly nested El axis.

Very low maintenance sealed drives, with easy replacement.

Container sized independent deliverables.

Low on site labor requirements.

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Current Antenna Design

6500 kg rotateson elevation axis

15m pri, 4m sec

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Today’s PresentationCovers the Following

Composite primary reflector design.Reflector support system design.Reflector tooling fabrication & costs.Feed & indexer concept details.PAF positioner concept details.Mount and movements design.Az & El drive design.Pedestal design.Motions control & position feedback.Electronics enclosures & cooling.Foundation concepts.

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Composite secondary

support shell

Composite Primary Reflector with faceted rim

Composite tubular feedlegs

‘Forward’ feedleg sweeps almost to dish center (the result of optimization studies).

Minor differences to feed support configuration due only to further development by Matt in this area

CART Configuration of CART-TDP

15m Gregorian Offset

CART Composite Primary and Secondary Reflector and Tubular Metal Back Frame Model

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Principle Design Elements:•Composite molded one piece primary reflector:

•High thermal stability, very low CTE

•High part-to-part repeatability

•No assembly labour

•Very durable, zero corrosion

•Very high strength

•Low cost

•Feed leg design refined using Topological optimization

•Backing structure Matt Fleming design optimized with Shape and Size optimization routine

•Laminate thicknesses and feedleg sizes also optimized using Shape and Size optimization

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Topological Optimization of feedlegs Topological Optimization of shell back structure with “Holes”

Design and Optimization Work

Shape and size optimization run on latest design

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What has it taken to get here?•Several Topological and Shape and Size optimizations have been done (5 separate studies)

•A wind tunnel test series was commissioned last year. These data are now being used to investigate stresses and deflections in the current model under wind loads.

•Extensive FEA analysis has been performed at DRAO

•Many different computer models have been developed of alternate dish configurations. The current model represents a culmination of all of these earlier ideas.

•Extensive Materials and Process testing has been performed over the last 5 years, and this work is ongoing.

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•Some earlier composite dish designs

Earlier Composite Dish Designs

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Latest Results

•Deflection analysis shows a very stiff structure.

•Preliminary results compare the deformed surface with the un-deformed design surface and not the best fit surface which is the traditional method.

•A table of preliminary RMS half pathlength errors (between design surface and deflected surface) are listed.

•Buckling analysis in 162kph frontal winds shows that the dish can survive this load.

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15m CART-TDP Gravity Only

•Gravity only at 90 degrees elevation

•Gravity only at 15 degrees elevation

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15m CART-TDP 25kph Wind

•Gravity +25kph wind at 90 degrees elevation

•Gravity +25kph wind at 15 degrees elevation

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Wind Speed/kmh Azimuth/degrees Elevation/degrees RMS Pathlength error/mm

0 0 15 0.76

0 0 55 0.84

0 0 90 0.86

25 0 15 1.27

25 0 30 1.2

25 0 55 1.04

25 0 90 1.13

45 0 15 2.18

45 0 55 1.23

45 0 90 1.56

15m CART-TDP Primary Reflector RMS Error (to design surface only, not best fit)

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The two small peaks near the rim at the lower right indicate a potential buckling failure mode for 162kph full frontal or backside wind at 15 degrees elevation. But since the eigenvalue is 2.89, which is well over 1, this indicates no failure at the input load.

15m CART-TDP 162kph Wind, Elev. 15, Buckling Modes

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Next Steps•A spring-back analysis has been started. This comprises physical coupon testing and computer modelling and will allow us to predict any mold-to-part variation.

•A 4.5m offset (test part) will be fabricated this year.

•The spring-back prediction methodology will be tested first on this part, then used to predict spring-back on the 15m.

•Detailed design of joints and other areas of stress concentration will be carried out in the preliminary design stage.

•A best fit analysis to the deflected surface has been started.

•Further optimizations are planned.

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Feeds Location & Support

Secondary ( blue )

SPF Indexer ( gray ) PAF & positioner ( purple )

Secondary support spars ( yellow )

Feed center frame ( green )

Primary Center Frame ( red )

Primary support spars ( blue )

Feed support spars ( orange )

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Current Feed Indexerhas 3 Stations

Cooled ATA Feed-5with focus device

Quad-ridge Uncooled

High gaincorrugated horn type

For more details see the TDP memo: Indexer for SP Feeds Proposal

300 kg, feeds at 483 mm radius1.340 m focus to mount flange

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Current PAF Assumptions

ASKAP PAF PAF positioner

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PAF Positioner Movement

PAF mass 200kg, positioner 350kg, movement requires 7,708 Nm

It is very likely PAF & positioner mass will be reduce, however we assumed the following:

For more details see the TDP memo: PAF at Prime Positioner

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Beam Path Images

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Support Frameworkfor Feeds & Secondary

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Feed Center Frame

For more details see the TDP memo: Concept for Secondary & Feed Support

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Masses for Elevation Structures

Secondary reflector 85 Kg FRP composite

Secondary support 143 Kg Alum tube 80 dia x 4 mm tubes

PAF & positioner 350 Kg Steel

SPFs & indexer 380 Kg Steel & alum

Feed platform 400 Kg Steel ? x 6 mm tubes

Platform support spars 200 Kg FRP Composite

Total forward of primary: 1558 Kg Not optimized

Primary reflector 2,360 Kg FRP composite

Primary support spars 686 Kg Steel

Primary center frame 1,836 Kg Steel

Primary diaphragm connector 60 Kg FRP composite

Total full reflector assy: 6,500 Kg Estimate

Consider that all of these values are still evolving.

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Determining Wind Loads

Wind load data sources•NRC has wind tunnel data a for similar dish.•Modified symmetric JPL data. +/- 15%•CFD on when model is closer to final version.•Eventual full wind tunnel tests will be needed.

Best survival positionis still under review.

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Mount & Primary SupportCenter Frame

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Deliverable Antenna Elements

Primary not shownIt is an on sitefabrication

Pedestal Turning head

Secondary

Primary center frame

Electronics enclosures

Secondary and feed support

Feed and indexer

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Pedestal Fabrication

Consider use of ring forgings

Machined Flange

Alternate foundation concepts are still under consideration

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Turret Head Assembly

Deliverable AssemblyIncludes az drives, bearings, encoders, electronics

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Primary Center Frame

Pentagonal frame shown

Machining of this portion may be necessary and a little expensive

Tubes all have parallel end cuts

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Turning Head & Az drives

Deliverable Assy

Double row ang contact,Or crossed roller, or 4 pt,With oil bath

Lubrication 60 months

Machinedfabrication

Az drivemodules

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Azimuth Drives

Dual idler supported pinion

Multiple modular drives

Access to drives

Full oil bath lubrication for 60 month period

RFI control

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El Bearings & El driveGravity loading helpful.Low clearance importantBearing choices tuff.

El drive is a sealed custom ball screw actuator

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Encoders & Pointing

Attachment to reflector surface away from loaded areas

Both encoders can be interior to the turret head allowing environmental protection and easy cabling.

Limit switch gearing

Az tube could extend to ground for higher accuracy, but …….

Addition of tilt meter and accelerometer devices will enhance performance

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Questions

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