CURRENT SKA TDP ANTENNA DESIGN 10

CURRENT SKA TDP ANTENNA DESIGN 10

DVA1 Meeting at NSF Arlington VA

April 15-16, 2010

Matt Fleming

Contributions from

Jack WelchRoger SchultzGordon Lacy

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( 3.5m 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 lead to specifications: ???

DVA1, NSF, Arlington, 2010-04-16 Matt Fleming slide 2 of 43

Basic fabrication cost drivers

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 )

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

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 )


Note on Transportation


Physical size of antenna elements will influence transport cost.Remote fabrication of smaller elements allows use of global labor competition.Remote fabrication usually means greater on site assembly labor.Onsite fabrication of large elements can allow lower on site assembly labor.

Non modal transport is also possible, but likely more expensive.

Types of Reflectors & Support

This is an arbitrary identification systemjust for discussion

This slide just a reminder about initial choices


•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 Implementation


•A 6.1m diameter symmetric shell can be made with only a 3mm thickness.•The surface accuracy can be quite high.•A study showed 3mm alum 3003 will have good repeatability in production .•Another study showed 3mm alum 3003 can be extended to a 12m symmetric.

JPL, DSN, Prototype


Identify 3 Optical Designs of Interest

B1

E2

D1E1

Data points for SKA cost modelInform Tradeoff symmetric vs offset


Select 3 Designs for Costing

FEA Design & Costing for HMR to meet survival requirements

HMR = Hydroformed Metal Reflector


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.


TDP Antenna Cost ( summary estimates )

8% 15%0% 0% 11%

Adding 15% 113,000 122,000 130,000 137,000 152,000

25%

( survival design shown )( add 15% for performance design )


TDP Antenna Cost (summary estimate )

a little more detail

Masses are low


Optics 42 used for costing

2 Gregorian feeds with rotary indexer & possibly a PAF

Shown with Feed Up but optics can be the same with Feed Down

Costing Allows Selection

PAF = Phased Array Feed

Preffered mechanical configuration Acceptable optical configuration

Note feed support locations


Computed RMS0.008 inches

0.20 mm



0.33 mm



0.03 mm


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


Specifications 1 of 2


Specifications 2 of 2


Beginning to work on details

Rain snow ice

Survival wind

Security and vandalism

Ease of maintenance


Additional Views


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


Pedestal Mount & Frame


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


Transport Check

Looks good for global sourcing


Turret Head Assembly

Deliverable AssemblyIncludes az drives, bearings, encoders, electronics


Transport Check

Note 3.1 m secondary shown

Looks like a little larger is possible.


Primary Center Frame

Pentagonal frame shown

Machining of this portion may be necessary and a little expensive

Tubes all have parallel end cuts


Transport CheckNot so good

Design for assembly or ship prepared kit to near site fabricator for final weld and paint then transport to site.


Secondary Support Frame

FRP fabrication may be ideal for rear section from the primary lower rim to the feed support plane.

If made from metal, we will consider some on site assembly.

More information is needed about feed support requirements.


Transport CheckNot goodDensity very poorReconsider this

Design for assembly or ship prepared kit to near site fabricator for final weld and paint then transport to site.

Electronics enclosure shown


Turret Head & Az drives

Deliverable Assy

Double row ang contactOr crossed rollerWith 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 may enhance performance

Unatainium box on back of dish is the best option


Cable Wraps & Enclosures

Cooling is important to consider early in the design

Current Az wrap 540° and envisioned with only 5 elements Power 1, Power 2, Ground, Control fibers, Signal fibers

Security, access, swapping

Current El wrap 75°envisioned with many elementsPower 1, Power 2, Ground, Control fibers, Signal fibers


Feeds and Indexer 1

Space for PAF implies two leg support frame

Pivot & structural support

Lindgren in canATA in glass

Track ?

PAF shown1m x 1m x 1m

Maybe sector not turntable

PAF at secondary focus

still under consideration

Min angle on wraps


Feeds and Indexer 2

Some comments:

It will be expensive.It will introduce additional deflection.It will introduce additional pointing considerations.It will require more cables and cable wrap loading.

Is it really possible to imagine future feed upgrades?

I look at the ATA WBSPF with 1.0 to 10.0 GHz, weighing 40 Kg and wonder If we gave 0.3 to 1.0 GHz to another solution then the dish is much simpler.


Mount Discussions


Issues to rememberand questions remaining

For the DVA-1Diameter Primary ( 12 15m )( done )Diameter Secondary ? ( 4m ) go to ( 3.5 )Optics design – shaping – illumination angle ?High shrouding concept.Analysis high shroud ?High Low decision ?Diffraction from secondary support braces and other items ?Tolerances on component positions ?Determine spec for high performance

US SKA Consortium, Madison, 2008-11-17 Matt Fleming slide 42 of 35

Questions


CURRENT SKA TDP ANTENNA DESIGN 10

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