Developing a low cost dish for MeerKAT Willem Esterhuyse Subsystem manager: Antenna Structures...
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Transcript of Developing a low cost dish for MeerKAT Willem Esterhuyse Subsystem manager: Antenna Structures...
Developing a low cost dish for MeerKATWillem Esterhuyse
Subsystem manager: Antenna Structures
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 KAT7 –
composite dish)
• Conclusion
Introduction (1)
KAT Project PhasesXDM KAT7 MeerKAT
Antenna structures open tender. Equatorial mount still considered – many suppliers not interested.
Antennas open tender – proposal deadline 31 March.
Costs sensitive at this stage
Antennas open tender??
• This presentation from mechanical design
perspective
• Antenna performance/Feeds – EMSS (LJ du Toit/ Isak
Theron)
Introduction (2) - XDM15 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
• 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
Prototype development subcontracted to IST Dynamics.
Shared IP.
Partners - MMS
• 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
KAT7/MeerKATProvisionalSpec Design Goal
Pointing Accuracy (deg) 0.04 0.02 25 arcsec RMS
Surface Accuracy (mm rms) 4 1.5 2 (target 1)mm
Frequency Range (MHz) 700 - 1700 Up to 8 GHz 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 160 160 160
Azimuth Rotation speed (deg/s) 1 2 2
Elevation speed (deg/s) 0.5 1 1
Diameter 15 15 12
F/D 0.5 0.5 0.38
Lowest Natural Frequency (Hz) 3 3+ 3+
Feed Mass (kg) 200 200 Single pixel
Mount TypeAll-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 24 April 06 (DONE)
• PDR 20 June 06 (DONE)
• CDR 28 Aug 06 (DONE)
• FATS 12 Feb 07 (DONE)
• Installation Completed 16 May 07 (DONE)
• ATP Completed 17 July 07 (DONE)
• Documentation Completed 17 July 07 (DONE)
KAT7 & MeerKAT
• 12m Design/Cost optimization Sept 07 – Dec07 (DONE)
• KAT7 Tender Jan 07 (Progress)
• KAT7 Contract award April 07
• KAT7 Array Completed Nov 09
• MeerKAT Contract award Jan 2010
• MeerKAT Array Completed Nov 2012
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:
4.2 Hz
side to side
Mode 2:
4.4 Hz
dish “flaps”
Mode
3:
4.7 Hz
noddin
g
Analyses – FEA - displacements
LC
Dish RMS error
to focus[mm]
Actual focus point movement relative to best fit parabola focus point
Ux [mm]Focus
Uy [mm]In-plane
Uz [mm]In-plane
1 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
Layer no MaterialThickness
[mm]
1 Paint 0.05 – 0.1
2 Reflective aluminium layer 0.1 – 0.2
3 Gelcoat layer/FSP layer 0.5
4 E-glass vinylester 6
5 Quasi honeycomb structure 150
6 E-glass vinylester 6
7 Flowcoat layer/FSP layer 0.5
Typical dish lay-up
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 1.7mm 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 (12m dish) effort
completed.
• Feb 08 – tender out for KAT7
• Apr 08 – KAT7 tender award
• Open tender, ie composite dish one of
options
• Dec 09 - KAT7 completion
• KAT7 prototype for MeerKAT
• 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
Frequencies
Mode 1:
4.58 Hz
Frequencies
Mode 1:
4.51 Hz
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 12m dish completed by IST
• Tender for KAT7 currently open (closes 31 March)
• Cost sensitive at this stage
• Composite dish competes on cost
• MeerKAT choice of dish not decided yet.
• Final word – SKA Cost targets (risks, approach, site work)