Radio Astronomy Antennas by the Thousands Roger Schultz - - PowerPoint PPT Presentation

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Radio Astronomy Antennas by the Thousands Roger Schultz - - PowerPoint PPT Presentation

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Radio Astronomy Antennas by the Thousands Roger Schultz 650-964-5899 schultz_assoc@pipeline.com July 21, 2004 SKA2004, Pentiction B.C. p1 of 23 Cost Effective Radio Telescope Development Existing cost expectations, established by ATA

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SLIDE 1

July 21, 2004 SKA2004, Pentiction B.C. p1 of 23

Radio Astronomy Antennas by the Thousands

Roger Schultz

650-964-5899

schultz_assoc@pipeline.com

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SLIDE 2

July 21, 2004 SKA2004, Pentiction B.C. p2 of 23

Cost Effective Radio Telescope Development

  • Existing cost expectations, established by ATA et. al. -

1,000$US/meter2

  • Achieve this by extending the existing evolution of steerable

microwave antennas.

  • Careful, thorough and realistic selection from myriad innovations.
  • High quantity required allows development of mass production
  • Utilize effective analytical techniques and prototyping
  • Utilize new and more efficient industrial processes
  • Goal: Lowest cost concepts to meet SKA performance
  • Conceptual examples follow that relate to current USSKA strawman

antenna development

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SLIDE 3

July 21, 2004 SKA2004, Pentiction B.C. p3 of 23

Reflector surface evolution -the old complex way

  • 15.5 meter S band

antenna

  • Small man handleable

panels, ~80 pie panels

  • Panel size drives very

complex backstructure to support each panel corner

  • Structural frame work

point (node) required at each panel corner

  • This complexity is

unnecessarily costly

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SLIDE 4

July 21, 2004 SKA2004, Pentiction B.C. p4 of 23

Pie panel / reflector backstructure interaction

  • Dark members hold panel surface

shape

  • White members near panels form

front members of reflector back frame structure

  • Panels are dead weight which

make no contribution to reflector back structure strength or rigidity

  • Connection, panel to frame, is a

flexure perpendicular to reflective surface designed to relieve differential thermal expansion of steel back structure and aluminum panel

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SLIDE 5

July 21, 2004 SKA2004, Pentiction B.C. p5 of 23

Shop reflector surface sweep

  • 14 meter S/K band

reflector surface adjusted in shop.

  • Structure is dowel

pinned, disassembled, shipped, reassembled at site (next slide)

  • Early attempt to cut

costs

  • Poor surface accuracy

results at site

  • Too many pinned

interfaces, surface had to be reset in field

  • COSTLY

Photo shows outer end of sweep boom. Center pivot is out

  • f picture to right. Dial indicators on templates below

boom structure show reflector surface error as boom

  • rotates. Dial indicators zeroed to template profile.
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SLIDE 6

July 21, 2004 SKA2004, Pentiction B.C. p6 of 23

Field Assembly and Alignment

14 meter S&K band antenna assembled and aligned on ground

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SLIDE 7

July 21, 2004 SKA2004, Pentiction B.C. p7 of 23

Panel assembly up on antenna mount

  • Again, panel small enough to be

handled by workmen in light winds

  • Again, structural work point

(node) required at each panel corner

  • Reflector surface adjusted by

extending or retracting clip at each panel corner

  • Adjustment performed by

workmen climbing through back structure.

  • COSTLY
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SLIDE 8

July 21, 2004 SKA2004, Pentiction B.C. p8 of 23

Pie panel reflector alignment in air

  • Rough adjustment by radial tape from theodolite

mount and elevation angle (lower picture)

  • Targets placed on reflective surface at a fixed

radius by chordal linkages resting on rough set surface (left picture)

  • Panel clip height fine adjusted to theodolite

angle

  • Technique produced

about 1 mm RMS accuracy for 4-6 GHz

  • New instruments now

producing much better accuracy but process still takes too much time and too much money

  • COSTLY

Upper: chordal linkages guide drilling of target mounting holes. Right: Schultz instructs height adjustment to setting angle. 30 meter domsat antenna, circa 1970’s

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SLIDE 9

July 21, 2004 SKA2004, Pentiction B.C. p9 of 23

Early Pie Panel Tooling

  • Flat sheet metal shaped only by

tooling bows at panel bracing

  • Bonding (adhesive) fills gap

between flat hat or Z section flanges

  • Rivets used
  • COSTLY

F ig u r e 1 reflective sheet is h e ld d

  • w

n

  • n

F i gure 1 riv

e t

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SLIDE 10

July 21, 2004 SKA2004, Pentiction B.C. p10 of 23

Higher accuracy “full face” pie panel tooling

  • Whole sweep boom (upper

picture)

  • Female CNC cut template

sweeps out surface of “full face” pie panel fabrication fixture (lower picture)

  • Full face tool controls panel

surface more accurately than bows shown in previous slide

  • COSTLY
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SLIDE 11

July 21, 2004 SKA2004, Pentiction B.C. p11 of 23

Current panel production

  • “Bonded” pie panel

– Panel back structure “bonded” i.e. glued to reflective aluminum sheet while on shaped tooling – reflective sheet not curved until pulled to tooling – savings from deletion of drilling many holes and installing rivets – Widespread successful use confirms concept – .01 mm RMS surface accuracy

  • Stretch formed Panels

– Aluminum sheet stretched over shaped tool to generate reflective surface – Stretch formed ribs bonded to reflective surface

  • BOTH COSTLY
  • MUST EVOLVE TO LESS

COSTLY CONCEPTS

Bonded photos courtesy Antedo, Inc. Photo courtesy Patriot Antenna Systems

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SLIDE 12

July 21, 2004 SKA2004, Pentiction B.C. p12 of 23

First Hydroformed Allen Telescope Array dish

  • Dave DeBoer, SETI, examines 1st ATA 6 meter dish
  • John Anderson, Anderson Mfg, behind Dave
  • Process now making 0.2 mm RMS surface accuracy on 6 meter
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SLIDE 13

July 21, 2004 SKA2004, Pentiction B.C. p13 of 23

6 meter ATA antenna at Hat Creek

  • ATA 6 meter offset

Gregorian

  • Extremely low weight /

LOW COST antennas, $1,500/sq. meter

  • “Throated” reflector,

gimbal mechanism within reflector structure

  • Elevation axis close to

dish center

  • Less wind torque allows

use of less costly mount to achieve pointing

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SLIDE 14

July 21, 2004 SKA2004, Pentiction B.C. p14 of 23

Challenge : 12 meter surface accuracy

  • 12 meter hydroforming

development

– Springback and thinning in the hydroforming process are repeatable and can be modeled with nonlinear FEA. Figures show calculated spring back for 12 meter dish

  • figures courtesy Dimitri Antos, JPL

– Springback and thinning calculations are used to adjust mold to produce desired dish shape – process proprietary, Anderson Mfg. – Ohio State U will continue spring back & thinning simulations – all previous size increases at Anderson (and there have been many) have been successful!

0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 1 2 3 4 5 6 Radial Distance (m) Springback (m)

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SLIDE 15

July 21, 2004 SKA2004, Pentiction B.C. p15 of 23

Splitting hydroformed dish

  • 12 meter too large to

truck with permit to remote sites

  • Splitting of dish with

precision splice

  • 2 concepts being

studied

– C flanges (proprietary) – strip over zigzag cut (proprietary)

C flange Zigzag cut

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SLIDE 16

July 21, 2004 SKA2004, Pentiction B.C. p16 of 23

USSKA 12-16 meter Strawman antenna

  • 12 m reflector splits into 2-pieces

– red members define split plane; center hub and red members are split and flanged for shipping (see next slide) – reflective 12 meter shell IS VERY STIFF and forms the front half of the “backstructure”

  • shell replaces all front radials and hoops and

eliminates most diagonals

  • decreases number of radial trusses

– sub reflector, tripod legs and 2 meter skirt are removed for shipping – “Throated” for low cost / performance

  • Mass produced components

– large dish shells, castings, stampings – CNC machinings – mature industrial components (turntable bearings, gear boxes, etc.)

  • Minimized site assembly and alignment
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SLIDE 17

July 21, 2004 SKA2004, Pentiction B.C. p17 of 23

Split 12 meter reflector down the road

  • 6 meter wide

load with permit

  • Passes under

– 4.6 meter (15 ft) high underpass with standard trailer – 4.0 meter (13 ft) using “low boy” trailer

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SLIDE 18

July 21, 2004 SKA2004, Pentiction B.C. p18 of 23

12-16 meter Convertible optics

  • 16 meter prime focus operation

down to 100 MHz

  • 12 meter Gregorian 1.2 to 34

GHz plus flipped feed, wide field, 0.1 to1.5 GHz operations

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SLIDE 19

July 21, 2004 SKA2004, Pentiction B.C. p19 of 23

“Throated” vs. Conventional antennas

  • Shell reflector with throat 30% to 50% lighter than for typical pie

panel reflector

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SLIDE 20

July 21, 2004 SKA2004, Pentiction B.C. p20 of 23

Performance/ cost comparisons

  • Axis wind and gravity drive torque

– Conventional antenna azimuth peak wind torque 50% higher than for “Throated” antenna

  • Thrust term moment arm much shorter

– Conventional antenna elevation peak torque 100% higher than for “Throated” antenna

  • Conventional antenna has the elevation axis unbalance all to one side at a long moment

arm

  • “Throated” antenna has an evenly “split” unbalance to both sides
  • Thrust term moment arm much shorter
  • Wind “gust gain” lower in proportion to steady wind comparisons

above

– Lowest Resonant Frequency (LRF) requirements go down in proportion to about the square root of the decrease in wind gust gain – Reduces LRF requirement to meet absolute pointing requirement

  • Antenna costs significantly reduced by reductions of reflector weight,

drive torque and LRF requirements.

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SLIDE 21

July 21, 2004 SKA2004, Pentiction B.C. p21 of 23

12-16 meter Reflector surface accuracy

  • Preliminary results

– 12-16 meter USSKA strawman reflector, May 04’ – mounted on pedestal – EL=0 – deflection, no gravity load to gravity load – no wind – no fitting pictured – best fit 0.0023”=.058mm RMS (best fit

calculations compliments of Bill Imbrialli, JPL)

  • These results point to

concept validity

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SLIDE 22

July 21, 2004 SKA2004, Pentiction B.C. p22 of 23

Lowest Resonant Frequency analysis (LRF)

  • Wind gusts deflect antenna

pointing

  • servo system reacts to

restore pointing

  • RMS pointing error

controlled by higher servo band pass response

  • band pass of servo system

must be lower than the lowest resonant frequency

  • f the antenna to prevent

violent instability

12-16 M reflector only, LRF 5.7Hz for tripod leg sideways bending. tripod leg may need to be thickened

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SLIDE 23

July 21, 2004 SKA2004, Pentiction B.C. p23 of 23

Conclusion

  • Developments, including those shown here, can be expected to

produce 100, to 200 M$ savings over conventional antenna concepts.

– Shell reflector, reflective surface included in structure (hydroforming or stretchforming) –

  • ptimized antenna geometry (throated reflector structures)

– automated castings of complex geometries – more, from next few years of development

  • bearing optimization
  • axis drive optimization
  • instrumentation
  • more
  • Ongoing Task: Develop lowest cost concepts to meet SKA antenna

performance