SKA TDP & CART 15m (DVA-1) ANTENNA DESIGN 11

SKA TDP & CART 15m(DVA-1) ANTENNA DESIGN 11

US SKA Consortium Meeting at Arlington VA

June 3-4, 2010

Matt Fleming

Contributions from

Jack WelchRoger SchultzGordon LacyLynn Baker

German

Antenna Design Drivers

1 Must achieve survival. ( 100 mph wind )

2 Low cost per unit area of aperture. ( good sky coverage ) ( installed )

( low cost materials, low mass design, low fabrication labor ) ( favors symmetric )

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

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

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

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

pt source sensitivity

survey survey speed

Performance vs Cost

Tradeoffs

These will shape specifications.

US SKA Consortium, Arlington, 2010-06-04 Matt Fleming slide 2 of 28

Design Driver 2, Cost

Raw material costs. ( fairly constant world wide )( a good design is light weight )

Labor cost. ( varies by type and location based on economic and social conditions )

For some designs material is often traded for labor

Technology. ( application of intellect to use of material, labor & energy )

Number of units needed. ( investment in tooling )

Transportation. ( where made, where assembled, where installed )

Basic fabrication cost drivers

Remote fabrication of smaller elements allows use of global labor competition.

Understanding these items for every design allows engineering shortcutsWe cannot do detailed design on every possible design approach


What is New

We have an aperture diameter specified at 15m.

We will maintain the offset high configuration for now.

We have a new approach for the primary reflector. (CART)

We have better relative cost info from 12m for tradeoff decisions.

We have a better understanding system operations cost. (SPDO)

We have a well defined shaped optics design.

We have new specifications.


Specifications 1 of 2


Specifications 2 of 2


•Single piece reflectors often have low labor cost relative to alternate designs.•Reflector edge support by itself preserves accuracy extremely well.•The reflector surface can act as the structural front side of a deeper system.•Rim edge and center support works better if the center has axial flexibility.•The concept can work for symmetric or offset designs.

Primary as a monocoque elementSingle shell or stressed skin

Jump to single shellOn Az-El mount


•A frame & spar system gives good edge & center support with an open center.•Wind & gravity moment loads are reduce with Az & El near the shell center.•The support system allows a compact turret head to be nested close to shell.•A compact turret head can contain almost all the precision machining needs.•A relatively simple pipe pedestal can support the turret head. ( wind & thermal )

ATA 6.1m Implementation


The TDP 15m Implementation

Spars 13 membersCenter frame 16 members

Secondary & feed support 22 members

2,4004,9507,35010,05010,25014,450

Total Secondary AssyTotal Primary AssyTotal on El BearingTotal on Az bearingTotal Turret FlangeTotal Antenna

Preliminary Weight Est ( Kg )

Materials & sections can be adjusted


•Hydroforming has low production cost and is a fast process.•Hydroforming a 12m symmetric is considered quite possible at 3mm thickness.•Hydorforming a 15m x 18m offset is definitely more difficult to predict.•Manufacturing repeatability is better with thickness, worse with flatness.•Plastic deformation FEA is needed to predict 15m repeatiblility. ( Ohio State )•Tooling will be very expensive. ( 12m was considered to be 2M$ ) (DVA-1)

Hydroforming Big Reflectors


Information from Composite Investigations

DRAO = Dominion Radio ObservatoryCART = Composite Application Radio Telescope

Prototype 10m complete.Symmetric with Core, Beams & Hub.SKA Memo 116 costing information

Starting to investigate Offset monocoque V3

Canada DRAO CART Project and South Africa MeerKAT Project have generated cost and performance information for composite on site reflector fabrication.


HM & FRP shells are similarBoth hydroformed metal and fiber reinforced plastic create good monocoque structures

FRP can replace HM reflectors and can provide edge support

Rim beam & spars favored over shell support


Additional Views


Beam Path

Close approximation of TDP shaped optics design

Feeds


Structural Simplicity

Triangular deep trusses goodCured beams and curved shells bad

Tubular structures are very efficient at handling bending and torsion

More about PAF position later


Secondary & Feed Support

Light weight structure180 Kg

Heavier structure


TDP & CART Team Collaboration

Gordon Lacy is beginning to run FEA optimizations on reflectors & supports

Matt Fleming beginning to analyze and detail 15m mount and drive systems


Deliverable Antenna Elements

Primary not shownIt is an on sitefabrication

Pedestal Turret head

Secondary

Primary center frame

Electronics enclosures

Secondary and feed support

Feed and indexer


Pedestal Fabrication

Consider use of ring forgings

Machined Flange

Alternate foundation concepts are still under consideration


Turret Head Assembly

Deliverable AssemblyIncludes az drives, bearings, encoders, electronics


Primary Center Frame

Pentagonal frame shown

Machining of this portion may be necessary and a little expensive

Tubes all have parallel end cuts


Turret Head & Az drives

Deliverable Assy

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

Lubrication 60 months

Machinedfabrication

Az drivemodules


Azimuth Drives

Dual idler supported pinion

Multiple modular drives

Access to drives

Full oil bath lubrication for 60 month period

RFI control


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

Currently envision a custom actuator


Encoders & Pointing

Attachment to reflector surface away from loaded areas

Long light weight tube might be problematic

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

Unatainium box on back of dish is the best option


Feeds & Indexer & PAF

Space for PAF implies two leg support frame

Pivot & structural support

ATA in glassPAF shown1m x 1m x 1m

PAF at secondary focus

still under consideration

Lindgren in can


Feed Indexer Concepts

Consider cable wraps, precision, access, dirt.

sector type. turret type.

linear slide.

Quick release fast exchange for feeds.

Position repeat to 1.0mm.


Questions


12mComputed RMS

0.008 inches0.20 mm


12mComputed RMS

0.013 inches0.33 mm


12mComputed RMS

0.001 inches0.03 mm


Documents

SKA TDP & CART 15m (DVA-1) ANTENNA DESIGN 11