Developing a low cost dish for Meer KAT

Developing a low cost dish for Meer. KAT Willem Esterhuyse Subsystem manager: Antenna Structures willem@ska. ac. za 083 447 1615

Overview • Introduction • Partners • Main Specs • Philosophy • Schedule • Progress • Analyses (CFD/FEA) • Detail Design • Manufacturing/Construction • Acceptance/Verification • Life after XDM (Cost optimization and KAT 7 – composite dish) • Conclusion

Introduction (1) KAT Project Phases XDM Antenna structures open tender. Equatorial mount still considered – many suppliers not interested. KAT 7 Meer. KAT Antennas open tender Antennas open – proposal deadline 31 tender? ? March. Costs sensitive at this stage • This presentation from mechanical design perspective • Antenna performance/Feeds – EMSS (LJ du Toit/ Isak Theron)

Introduction (2) - XDM 15 meter PF antenna on ALT-AZ mount with feed rotator • One-piece composite reflector that is structural • Simple back-up structure • No Panels to align • Weight saving • Concrete pedestal • Pedestal only 30% of foundation (bedrock) volume • Aim – Antenna for KAT that is relevant to SKA. • Technical/Cost • Development Subcontracted (time constraints) • IST Dynamics (PTY) LTD • Single line of responsibility (time, risk) • MMS subcontracted for dish

Partners - IST Prototype development subcontracted to IST Dynamics. Shared IP. • IST Dynamics • Prime contractor – IST exists for more than 25 years • High tech electro-mechanical systems + software • Military is biggest client • ISO 9001 and ISO 14001 • www. ist. co. za, follow link to dynamics

Partners - MMS • Subcontracted by IST • Dish construction and design • Exceptional experience in Composite design and manufacture • Existing for more than 20 years • For more detail, see www. mmstechno. co. za

Main Specifications and Design Goal XDM Spec Design Goal KAT 7/Meer. KAT Provisional 0. 04 0. 02 25 arcsec RMS 4 1. 5 2 (target 1)mm Frequency Range (MHz) 700 - 1700 Up to 8 GHz Wind (Operational) km/h 20 36 36 Wind (Marginal Operation) km/h 36 45 45 Wind (Drive to Stow) km/h 36 55 55 Wind (Survival) km/h 160 160 1 2 2 Elevation speed (deg/s) 0. 5 1 1 Diameter 15 15 12 F/D 0. 5 0. 38 3 3+ 3+ 200 Single pixel Pointing Accuracy (deg) Surface Accuracy (mm rms) Azimuth Rotation speed (deg/s) Lowest Natural Frequency (Hz) Feed Mass (kg) Mount Type All-Az with Rotator, but equatorial considered. Alt-Az

Philosophy • Highest risk (technical and cost) – Reflector • Preferably one-piece reflector (no alignment of panels) • This requires manufacturing on site • Tooling costs very high for steel, much lower for composites • Composites attractive for smaller quantities (limited budget) • Composites offer other advantages as well • Lighter for same stiffness/strenght • On site manufacturing easy (minimal equipment required) • Better thermal performance • Going to offset antennas not significant impact on reflector • Preferably very simple backup structure (if any) – structural reflector • Pedestal – concrete (30% of foundation concrete) • Revisited in cost optimization study

Schedule (KAT Antenna Structures) XDM • Contract Signed • PDR • CDR • FATS • Installation Completed • ATP Completed • Documentation Completed 24 April 06 20 June 06 28 Aug 06 12 Feb 07 16 May 07 17 July 07 (DONE) (DONE) KAT 7 & Meer. KAT • 12 m Design/Cost optimization • KAT 7 Tender • KAT 7 Contract award • KAT 7 Array Completed • Meer. KAT Contract award • Meer. KAT Array Completed Sept 07 – Dec 07 Jan 07 April 07 Nov 09 Jan 2010 Nov 2012 (DONE) (Progress)

ANALYSES - CFD • Detailed CFD (Computational Fluid Dynamics) analyses to determine pressures on dish as result of wind loading (for use in FEA analyses) • Results compared to published results – good correlation • Results compared with limited experimental data – good correlation

Analyses – FEA – Modes Mode 1: Mode 2: 4. 2 Hz 4. 4 Hz side to side dish “flaps” Mode 3: 4. 7 Hz nodding

Analyses – FEA - displacements LC Dish RMS error to focus [mm] 1 Actual focus point movement relative to best fit parabola focus point Ux [mm] Focus Uy [mm] In-plane Uz [mm] In-plane 0. 437 -4. 39 0 -4. 33 2 0. 147 +3. 43 0 +0. 16 3 0. 165 -0. 3 -0. 16 0 4 0. 229 +3. 54 +0. 17 +0. 05 5 0. 334 +6. 62 0 +1. 55 6 0. 416 -4. 73 0 -1. 94 7 0. 464 +15. 94 0 0 8 0. 685 +19. 72 0 +1. 54 9 0. 616 -8. 30 0 +3. 11 10 0. 983 +5. 18 0 +2. 07 11 0. 447 -5. 68 0 -6. 09

Detail Design/Manufacture - Dish • Very simple backup structure • Dish is structural (approx. 5 Tons) • Symmetric, to eliminate curing distortions • Manufacturing (see pictures later): • Machine patterns (composite pattern material) • Make composite moulds of the patterns • Combine composite moulds to create dish mould • Innovative and cheap honeycomb structure (off the shelf honeycomb cores very expensive). • Vacuum Infusion process used for molding entire dish as a unit

Detail Design/Manufacture - Dish Typical dish lay-up Layer no Material Thickness [mm] 1 Paint 0. 05 – 0. 1 2 Reflective aluminium layer 0. 1 – 0. 2 3 Gelcoat layer/FSP layer 4 E-glass vinylester 5 Quasi honeycomb structure 6 E-glass vinylester 7 Flowcoat layer/FSP layer 0. 5 6 150 6 0. 5

Detail Design – Drives/Controls • Azimuth axis • 1 spring - loaded drive • 2 deg/s, 460 degree travel • Elevation axis • 1 spring - loaded drive • 1 deg/s, 0 to 95 degree elevation range • Elevation axis is BALANCED • Light dish (composites) makes this possible with minimal use of counter weights • Feed rotator axis • 380 degree travel

Verification/Acceptance • Completed • Achieved all design goals • Dish tested at 1. 42 and 12 GHz • Dish accuracy around 1. 7 mm RMS • (Confirmed with Theodolite and Photogrammetry measurements) • Improve? – pattern from Al, mold. • Al Flame sprayed surface works well • Pointing – 25 arcsec RMS (optically) • Improve? – probably 2 drives • Thermal performance – thermocouples molded into dish front and rear to verify analyses assumptions.

Life after XDM - Dishes • Optimization and redesign (12 m dish) effort completed. • Feb 08 – tender out for KAT 7 • Apr 08 – KAT 7 tender award • Open tender, ie composite dish one of options • Dec 09 - KAT 7 completion • KAT 7 prototype for Meer. KAT • Aggressive timescales

Gravity

Wind from front

Temperature, -5ºC from 20ºC

Gravity + Wind from side + Temperature, +40ºC, dish front +60ºC, from 20ºC

Gravity

Wind from side

Gravity + Temperature, +40ºC, dish front +60ºC, from 20ºC

Mode 1: 4. 58 Hz Frequencies

Mode 1: 4. 51 Hz Frequencies

Conclusion • XDM • Well engineered dish – not optimized for low frequencies • Believe we have made good progress in developing a fairly innovative dish in a short period of time from zero experience • Major specifications were met • Dish can be manufactured on site with little infrastructure requirement • Cost optimization on 12 m dish completed by IST • Tender for KAT 7 currently open (closes 31 March) • Cost sensitive at this stage • Composite dish competes on cost • Meer. KAT choice of dish not decided yet. • Final word – SKA Cost targets (risks, approach, site work)