ska dish system overviewska-sdp.org/sites/default/files/attachments/ska-tel-dsh-0000017_rev4... ·...

Name Designation Affiliation Signature & Date

Authored and Release by:

T. Kusel DSH

Systems Engineer

SARAO

SKA DISH SYSTEM OVERVIEW

Document number ........................................................................ SKA-TEL-DSH-0000017 Revision ........................................................................................................................... 4 Author ................................................................................................................... T. Kusel Date ................................................................................................................. 2018-09-07 Document Classification ........................................................................... UNRESTRICTED Status ................................................................................................................... Released

Document No.: Revision: Date:

SKA-TEL-DSH-0000017 4 2018-09-07

UNRESTRICTED Author: T. KUSEL

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DOCUMENT HISTORY Revision Date Of Issue Engineering Change

Number

Comments

A 2014-11-20 - First draft release for internal review

B 2014-12-05 - Update based on changes to [6]

1 2015-05-26 - First formal release updated with changes as per PDR

COAR.

2 2015-12-17 ECP-DSH-001 Updated according to ECP-DSH-001

3 2017-05-30 ECP-DSH-160002

ECP-160022

Ambient Band1 feed

Band5 split

4 2018-09-07 CN-0055 Update document for DSH Pre-CDR release

DOCUMENT SOFTWARE Package Version Filename

Word processor MsWord Word 2007 SKA-TEL-DSH-0000017_Rev4_DSHSystemOverview

ORGANISATION DETAILS Name SKA Organisation

Registered Address Jodrell Bank Observatory

Lower Withington

Macclesfield

Cheshire

SK11 9DL

United Kingdom

Registered in England & Wales

Company Number: 07881918

Fax. +44 (0)161 306 9600

Website www.skatelescope.org


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TABLE OF CONTENTS

1 PURPOSE AND SCOPE ..................................................................................... 6

2 REFERENCES ................................................................................................ 7

2.1 Applicable documents............................................................................................................. 7 2.2 Reference documents ............................................................................................................. 7

3 INTRODUCTION ............................................................................................. 9

3.1 Context .................................................................................................................................... 9 3.2 Key science drivers and design features ................................................................................. 9

4 REQUIREMENTS .......................................................................................... 10

5 OVERVIEW ................................................................................................ 11

6 PERFORMANCE ........................................................................................... 14

7 PRODUCT BREAKDOWN STRUCTURE (PBS) ....................................................... 15

8 MAJOR COMPONENTS ................................................................................. 17

8.1 Dish Structure ....................................................................................................................... 17 8.2 Single Pixel Feed (SPF) feed packages ................................................................................... 17 8.3 Receivers (Digitisers) ............................................................................................................. 18 8.4 Local Monitoring & Control (LMC) ........................................................................................ 19

9 STATES & MODES ....................................................................................... 20

10 FUNCTIONS............................................................................................. 21

10.1 Intercept Dish Signal ............................................................................................................. 22 10.2 Receive MID Dish Signal ........................................................................................................ 23 10.3 Control and Monitor Dish ..................................................................................................... 24 10.4 Manage Dish Safety .............................................................................................................. 24 10.5 Manage Dish Power .............................................................................................................. 25

11 INTERFACES ............................................................................................ 26

11.1 Dish External Interfaces ........................................................................................................ 26 11.2 Dish Internal Interfaces ......................................................................................................... 27

12 POWER CONSUMPTION ............................................................................. 29

13 RFI AND EMC ........................................................................................ 30

13.1 RFI requirements ................................................................................................................... 30 13.2 RFI design philosophy ........................................................................................................... 30 13.3 Earthing and lightning protection. ........................................................................................ 31

14 ENVIRONMENT ........................................................................................ 33

14.1 Deployed Environment ......................................................................................................... 33 14.2 Transportation Environment ................................................................................................ 34 14.3 Storage Environment ............................................................................................................ 34

15 RELIABILITY, AVAILABILITY AND MAINTAINABILITY ............................................ 35


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15.1 Availability ............................................................................................................................. 35 15.2 Maintenance workload ......................................................................................................... 35

16 SUPPORT CONCEPT ................................................................................... 35

16.1 Maintenance Locations: SKA_MID ........................................................................................ 35 16.2 Maintenance activities .......................................................................................................... 36 16.3 Support Equipment ............................................................................................................... 36

16.3.1 Support Facilities ........................................................................................................... 37 16.3.2 Packaging, Handling, Storage & Transportation ........................................................... 37 16.3.3 Other Support Concept elements ................................................................................. 37

LIST OF FIGURES

Figure 1: DSH design information managed in the MBSE tool. ............................................................ 10 Figure 2: SKA_MID Dish overview ......................................................................................................... 11 Figure 3: Overview of DSH Signal Path ................................................................................................. 12 Figure 4: Dish control and monitoring topology ................................................................................... 13 Figure 5: Dish Element Modes .............................................................................................................. 20 Figure 6: Dish functional model: top tier functions .............................................................................. 21 Figure 7: Dish Intercept Signal Functions .............................................................................................. 22 Figure 8: Dish signal path functions ...................................................................................................... 23 Figure 9: Dish control and monitoring functions .................................................................................. 24 Figure 10: Dish power management functions ..................................................................................... 25 Figure 11: SKA_MID Dish External Interfaces ....................................................................................... 26 Figure 12: MeerKAT earthing and lightning protection ........................................................................ 32 Figure 13. Breakdown of Environmental Conditions ............................................................................ 33 Figure 14: Transporter and elevated work platform for indexer item maintenance ........................... 37

LIST OF TABLES Table 1: Required SKA_MID Dish sensitivity ......................................................................................... 14 Table 2: Partial Dish Product Breakdown Structure ............................................................................. 15 Table 3: SKA_MID frequency bands and digitisation parameters ........................................................ 19 Table 4: ICDs defining the Dish external interfaces .............................................................................. 26 Table 5: Dish Internal Interfaces ........................................................................................................... 27 Table 6: Dish electrical power budget .................................................................................................. 29 Table 7. Functionality and Performance mapping under the different Environmental Conditions in

the Deployed State ..................................................................................................................... 34


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LIST OF ABBREVIATIONS

ATE Automated Test Equipment

Az Azimuth

BF Beam Former

CSP Central Signal Processor

DLM Depot Level Maintenance

DS Dish Structure

DSH Dish Element

ECP Engineering Change Proposal

El Elevation

EM Electromagnetic

EMC Electromagnetic Compatibility

EMI Electromagnetic Interference

ETSI European Telecommunication Standards Institute

GM Gifford McMahon

ILM Intermediate Level Maintenance

LMC Local Monitoring and Control

LNA Low Noise Amplifier

LRU Line Replaceable Unit

O/E Optical / Electrical

OLM Organisational Level Maintenance

PBS Product Breakdown Structure

PSU Power Supply Unit

RF Radio Frequency

RFI Radio Frequency Interference

RFoF Radio Frequency over Fibre

SaDT Signal and Data Transport

SKA Square Kilometre Array

SKAO SKA Office

SLM Service Level Maintenance

SPF Single Pixel Feed

SPFRx SPF Receiver

SW Software

TM Telescope Manager

TRL Technology Readiness Level

UPS Uninterrupted Power Supply


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1 Purpose and Scope

This document provides an introduction to the SKA1 Dish Element System. The purpose is to summarise the Dish Design, with references to the documents that contain more details. It gives a high level overview of the various design aspects, including:

a) Key performance requirements and expected performance. b) Product Breakdown Structure. c) Brief description of major components. d) Overview of all internal and external interfaces. e) States and modes. f) Functional and data flow architecture. g) RFI and EMC design. h) Operating, transportation and storage environments. i) Power management and power budget. j) Reliability requirements. k) Maintenance tasks and support concept.

The detailed information of the design is provided in the reference documents.


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2 References

2.1 Applicable documents

The following documents are applicable. In the case of conflict between this document and the applicable documents, the applicable documents shall have precedence:

[1] M. Caiazzo, “SKA Phase 1 System Requirements Specification”, SKA-TEL-SKO-0000008, Rev 11.

[2] T. Kusel, A. Peens-Hough, H. Niehaus, “Dish Element Requirements Specification”, SKA-TEL-DSH-0000005, Rev5.

2.2 Reference documents

The following documents are referenced in this document.

[3] T. Kusel, “SKA1 Dishes Consortium System Engineering Management Plan”, SKA-TEL.DSH.SE-NRF-MP-001, Rev 1.

[4] P. Dewdney, “SKA1 System Baseline Design”, SKA-TEL-SKO-DD-001. [5] A. Peens-Hough, “Performance Requirements Analysis”, SKA-TEL.DSH.SE-NRF-R-002. [6] A. Peens-Hough, “Summary of the expected performance of the preferred dish optics for

SKA”, SKA-TEL.DSH.SE-NRF-R-003. [7] I. Theron, “Dish Optics Selection Report”, SKA-TEL-DSH-0000018. [8] L. Stenvers, “Dish Structure Detail Design Document”, 316-000000-022. [9] I. Theron, “SKA Dish Single Pixel Feed System Design Report”, SKA-TEL-DSH-0000020. [10] K. Caputa, “SKA Dish Single Pixel Feed Receiver Design Report”, SKA-TEL-DSH-0000021. [11] C. Trigilio, “SKA Dish Local Monitoring & Control Design Report”, SKA-TEL-DSH-0000023. [12] T. Kusel, “SKA_MID Interfaces Identification Document”, SKA-TEL.DSH.SE-NRF-DD-001. [13] R. Lord, “SKA Dish RFI requirements analysis”, SKA-TEL-DSH-0000008. [14] T. Kusel, D. Liebenberg, “SKA Dish Reliability and Logistical Requirements Analysis”, SKA-

TEL-DSH-0000009. [15] D. Liebenberg, “SKA Dish Operational and Support Concept”, SKA-TEL-DSH-0000004. [16] G. Smit, “SKA Dish Power Management”, SKA-TEL-DSH-0000041. [17] H. Niehaus, “Environmental Conditions for the SKA1 MID Site in South Africa”, 301-000000-

009. [18] A. Peens-Hough, “MeerKAT L-Band Receptor Preliminary Test Results”, M1100-0000-045. [19] T. Kusel, “SKA Dish States & Modes”, 301-000000-010. [20] A. Cremonini, A. Peens-Hough, “L1 Requirements Improvement for Pointing and Motion

Behaviour of SKA1 MID Array Telescope”, SKA-TEL-SKO-0000648. [21] T. Kusel, “SKA- Dish to Infrastructure Inteface Control Document”, SKA-TEL-SKO-0000115. [22] B. Carlson, K. Caputa, T. Kusel, “SKA1-MID Inteface Control Document Dish to CSP”, SKA-

TEL-SKO-0000124. [23] R. Gabrielczyk, G. Smit, “SKA1 Dish to SADT Inteface Control Document”, 300-000000-026. [24] M di Carlo, A Marassi, S Riggi, G Smit, PS Swart, “SKA1-MID Inteface Control Document TM

to DSH”, SKA-TEL-SKO-0000150. [25] D. Gammon, “Inteface Control Document MeerKAT to SKA1_MID Dish”, SKA-TEL-AIV-

2310005. [26] G. Smit, “DSH Lightning Protection System Requirements”, SKA-TEL-DSH-0000078. [27] D. Liebenberg, “RAM & LSA Report for the SKA-Mid Dish”, 301-000000-031. [28] T. Kusel, “Dish Element Requirements Traceability Matrix”, 301-000000-006. [29] T. Kusel, “Dish Element Compliance Matrix”, SKA-TEL-DSH-0000069.


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[30] H. Niehaus, A. Peens-Hough, T. Kusel, G. Smit, “Dish Structure Requirements Specification”, SKA-TEL-DSH-0000011.

[31] A. Peens-Hough, T. Kusel, G vd Merwe, G. Smit, “Single Pixel Feeds Requirements Specification”, SKA-TEL-DSH-0000012.

[32] A. Peens-Hough, T. Kusel, G vd Merwe, G. Smit, “SPF Receiver Requirements Specification”, SKA-TEL-DSH-0000013.

[33] T. Kusel, G. Smit, “Dish Local Monitoring and Control Requirements Specification”, SKA-TEL-DSH-0000016.


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3 Introduction

3.1 Context

The SKA Observatory requirements are defined in [1] and the baseline design of the SKA Observatory is defined in [4]. The SKA Observatory consists of two telescopes (SKA_LOW and SKA_MID) and a central head office. The SKA_MID Dish is one of the elements (subsystems) of the SKA_MID Telescope. The requirements of the SKA_MID Dish are defined in [1] and the overview of its design is presented in this document.

3.2 Key science drivers and design features

According to [4], the primary science cases for determining the performance of the SKA_MID system are:

a) Local and high red-shift HI-line observations to study the evolution of galaxies. b) All-sky pulsar surveys. c) Follow-up observations of detected pulsars at high resolution. d) Long pulsar timing campaigns.

From these science drivers, the key design features of the SKA_MID array and dishes are:

a) Array configuration: The array consists of 133 SKA dishes plus the 64 MeerKAT dishes. The array is arranged in a dense core with quasi-random distribution, and spiral arms going out to create the long baselines that go up to ~156km.

b) Sensitivity: The dish has a 15m projected diameter offset Gregorian reflector geometry. The single-pixel feeds, reflector structure and feed optics are optimised for sensitivity as a primary design driver, with low system noise temperature and a shaped optics to achieve high efficiency. For Bands 2, 3, 4 and 5 the LNAs are cryogenically cooled using a helium system to provide low system noise.

c) Beam shape and sidelobes: The offset Gregorian reflector geometry was selected because it provides a clear optical path (free of struts), which results in good circular symmetry in the sidelobes. The circular symmetry is required for high dynamic range imaging. However, there is no constraint/specification on the magnitude of the sidelobes. The similarity (between dishes) of primary beam shape is also tightly constrained for the purpose of high dynamic range imaging.

d) Frequency range: Five bands cover the frequency range as follows: a. Band 1: 0.35 – 1.05 GHz b. Band 2: 0.95 – 1.76 GHz c. Band 3: 1.65 – 3.05 GHz d. Band 4: 2.80 – 5.18 GHz e. Band 5a: 4.6 – 8.5GHz f. Band 5b: 8.3GHz - 15.4 GHz

The Dish is designed to accommodate all five bands, but only Bands 1, 2 and 5 will be populated for the first phase of construction. The feed packages are mounted on a fan indexer, and only one band will be available for observation at any given time. For all bands, the signal is directly sampled without heterodyne down-conversion. For Bands 1-5a, the entire instantaneous bandwidth is transmitted to the central signal processor. For Band 5b, two individually tuneable sub-bands of 2.5GHz bandwidth each are selected after digitisation and digitally down-converted before transmission. Switching between bands is required for calibration and the receivers are required to maintain coherency when switching to another band and back.


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e) Polarisation: instrumental polarisation must be stable and accurately characterised across the field of observation for imaging, and at the beam centre for pulsar timing.

4 Requirements

Dish requirements were derived from the SKA System Requirements [1] (Level 1 requirements) and the SKA System Baseline Design [4]. All non-compliances of the Dish design in respect of the SKA System Requirements are documented in a Compliance Matrix [29]. A comprehensive set of requirements was derived for the Dish, which is documented in [2] (Level 2 requirements). Detailed requirements have been derived for each major subsystem of the Dish (Level 3 requirements). All Level 1, 2 and 3 requirements are stored and managed in a Model Based Systems Engineering (MBSE) tool. This tool is used to manage traceability between the different levels of requirements and facilitates the management of changes to requirements. Requirement Specification documents are printed directly from the tool. An overview of the information that is managed in the tool is shown in Figure 1. The traceability between Level 1, 2 and 3 requirements is documented in a requirements traceability matrix document [28]. The traceabiliy of requirements to DSH verification plans is also managed in the MBSE tool as shown in Figure 1. The link between requirements and the system architecture (functional architecture and interfaces) is also established in the MBSE tool as shown in Figure 1. An overview of the functional architecture is provided in Section 10.

SKA-MID (L1)

Requirements

DSH (L2)

Requirements

DSH

Functions

DSH Verification

Requirements

DSH Verification

Events

DSH Test

Configurations

DSH Sub-subsystem (L3)

Requirements

employ

DSH Test

Procedures

verified by fulfilled at

fulfilled by

employ

employ

DSH Sub-system (L3)

Components

DSH

Internal Interfaces

performed

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Req

traceability

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Verification model

Architectural model

Subsystem

Functions

performed

by

refined by

Non-functional

requirements specify

Figure 1: DSH design information managed in the MBSE tool.


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5 Overview

The design concept for the SKA_MID dish configuration is shown in Figure 2.

Indexer with:

- Single Pixel Feeds:

- Band 1 feed package



- Vacuum system

- Samplers (Digitisers)

RFI shielded compartment with:

- Dish motion controller

- SPF feed controller

- Local Monitor & Control (LMC)

- Receiver (packetiser)

- SaDT equipment

- Helium compressor

Figure 2: SKA_MID Dish overview

Dish Optics: The offset Gregorian optics configuration was chosen to provide low spill-over noise and circular symmetric antenna pattern. The circular symmetry in the beam and sidelobe patterns is important to ensure high dynamic range imaging. Extensive electromagnetic studies were conducted as part of the Conceptual Design Review to explore the parameter space of the dish optics, including variable F/D, sub-reflector size, feed-high/feed-low, sub-reflector extensions (shroud), and the effect of shaping. This culminated in a final decision on the Dish Optics as documented in [7]. The optical design also makes provision for fitting a PAF in future without significantly compromising the performance. Dish Structure Options: Two main concepts were considered for implementation of the Dish main reflector: single-piece composite and panelised metal with supporting space-frame. A rigorous trade-off analysis between these concepts resulted in a decision on the metal panel design, mainly due to risk factors and technology maturity. The chosen design simplifies:

a) High volume production: all parts can be manufactured in factory and the part count for the back-up structure components was minimised.

b) Transportation between factory and site: the dish can be transported in four standard 12m shipping containers. This simplifies storage and shipping of parts over sea and land.

c) On-site installation: the chosen design can be assembled at the location of the dish in the field, only requiring a flat compacted soil platform, with minimum assembly tools and jigs.

Signal Path: There are three Feed Packages: Band 1 (ambient), Band 2 (cryogenically cooled) and Band 3/4/5a/5b (cryogenically cooled). All these feed packages provide the dish illuminating feed horn, low noise amplification, calibration noise sources and local control and monitoring. In all cases, the output of the feed packages is an RF over cable. The RF cables are routed for a short distance on the indexer to two Receiver units (Band 1/2/3 and Band 4/5a/5b units) that are located on the indexer, which contain the digitisers. The digitised data is transmitted over fibre from the indexer to


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a Packetiser in the Pedestal. The Packetiser formats the data into Ethernet packets and transmits the signal over a high speed Ethernet link (maximum distance 180km) to the Central Signal Processor (CSP) which is located at the central array site facility. The frequency and time reference signals are provided from the central Synchronisation and Timing (SAT) system up to the Receiver Master Clock unit in the Pedestal. The Receiver Master Clock unit is responsible to distribute these signals to the sampler units on the indexer.

Long-haul

data

transmission

equipment

Band 345 Feed

assembly

CryostatB3 feed horn

B4 feed horn

B5a feed horn

Band 2 Feed assembly

OM

Ts

LN

As

B5b feed horn

Band 4/5b

digitiser

Band 5a

digitiser

Band 1/2

digitiser

Band 3

digitiser

B2 feed horn Cryostat

OM

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As

Band 1 Feed assembly

B1 feed horn

LN

As

Rx Band 123

Sampler Unit

Rx Band 45

Sampler Unit

Prim

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Feed indexer (focus position)

Az &

El ca

ble

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ps

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Figure 3: Overview of DSH Signal Path


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Control and monitoring: Control and monitoring is managed centrally in the Dish by the Local Monitoring and Control (LMC) computer. The LMC unit communicates control and monitoring data with the SKA-MID Telescope Manager (TM) and distributes all control and monitoring communications to the different Dish subsystems. The Receiver’s Digital Processor Unit serves as a central communication hub for all Receiver components. The SPF controller located in the pedestal serves as the central communication hub for all SPF components, including the helium compressor, vacuum station and a feed package controller in each SPF feed package. An overview of the control and monitoring topology for the Dish System is shown in Figure 4. The TANGO protocol is used by the central Telescope Manager for all elements of the telescope. This protocol is also used for the communication between LMC and the Receiver controller and SPF controller, but other protocols are used elsewhere, as shown in Figure 4.

Feed indexer

(focus position)

TurnheadPedestal

Band 1 Feed

assembly

Band 123

Sampler Unit

Band 45

Sampler Unit

Feed package

controller

Band 2 Feed

assembly

Feed package

controller

Band 345

Feed

assembly

Feed package

controller

Vacuum

pump

Helium

Compressor

SPF

controller

DSH

LMC

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Figure 4: Dish control and monitoring topology


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6 Performance

The derivation of the Dish performance requirements is documented in [5]. A brief summary is given below:

a) Sensitivity: The SKA_MID Dish is expected to meet or exceed the specified sensitivity in Bands 1-5, shown in Table 1. For all the bands, the expected performance has been confirmed with detailed analysis. In some cases the analysis is supported by measurements on precursors (MeerKAT) or prototypes. The confidence in the predicted sensitivity values for SKA_MID is high.

b) Aperture Efficiency: The Dish is expected to meet the specified aperture efficiency requirements.

c) Sidelobe levels: There are no specifications on sidelobe levels, and the agreed design philosophy was to optimise for sensitivity, and then to evaluate the expected sidelobe levels. The shaped optics that is applied to increase sensitivity also increases the near-in sidelobes. The expected sidelobe levels for shaped and unshaped optics are given in [6].

d) Polarisation: A cross-polarisation of better than -15dB is specified across the half-power beam width for all bands. This specification will be exceeded substantially in most frequencies and this is regarded as a low risk.

e) Spectral Dynamic Range: Spectral dynamic range is specified as a deviation of the bandpass response to a linear fit over a very narrow fractional bandwidth. This specification is considered to be a low risk.

f) Performance relating to Imaging Dynamic Range: A number of requirements relating to imaging dynamic range have been allocated to the Dish, but no analysis results are currently available to indicate the expected level of conformance to these requirements.

g) Pointing: Pointing performance is one of the key cost driving requirements. The pointing requirements under various environmental conditions is defined in [20].

Table 1: Required SKA_MID Dish sensitivity

Band

[m2/K]

per Dish

Specified

1

350 MHz 2.1

650 MHz 4.2

1050 MHz 4.2

2 0.95 – 1.76 GHz 7.0*

3 1.65 – 3.05 GHz 7.0*

4 2.80 – 5.18 GHz 6.4*

5a 4.6 – 8.5 GHz 8.7*

5b 8.3 – 15.4 GHz 6.3*

* Average across frequency range and over elevation range from zenith to 30° above horizon.


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7 Product Breakdown Structure (PBS)

The PBS is used as a framework to manage the development, production and maintenance of the system. A partial breakdown of the product is shown in Table 2 below. The complete PBS is managed in the SKA configuration management system. The PBS is the structure that is used to delineate responsibilities, allocate requirements, identify points of interface and define procedures for integration and verification. Further, all engineering, production and operational data is structured according to the PBS. Table 2: Partial Dish Product Breakdown Structure

level Item Number Item Name

0 [301-000000] Dish MID

1 [316-000000] Dish Structure MID

2 [316-010000] Pedestal

2 [316-020000] Turnhead

2 [316-030000] Elevation Assembly

3 [316-030001] Main Reflector

3 [316-030002] Subreflector

3 [316-030003] Backing Structure

2 [316-040000] Indexer

2 [316-050000] Plant Installations

2 [316-060000] Dish Control System

2 [316-070000] Dish Structure Support Equipment

3 [316-070002] Dish Structure Maintenance Equipment

3 [316-070004] Dish Structure Test Equipment

3 [316-070006] Dish Structure Test Equipment

1 [317-000000] Single-Pixel Feeds (SPF) MID

2 [317-010000] SPF Band 1 Feed Package

3 [317-011000] SPF Band 1 Horn Assembly

3 [317-012000] SPF Band 1 Control Assembly


3 [317-021000] SPF Band 2 Horn Assembly

3 [317-022000] SPF Band 2 Cryostat and Control Assembly

3 [317-023000] SPF Band 2 Mount Assembly

3 [317-024000] SPF Band 2 Sun Shield Assembly


3 [317-031000] Cryostat Subsystem

3 [317-032000] Vacuum Subsystem

3 [317-033000] Cryogenic/thermal Subsystem

3 [317-034000] RF Subsystem

3 [317-035000] RF Noise Source Subsystem

3 [317-036000] Feed Package Controller

3 [317-037000] Feed Package Weathershield

2 [317-050000] SPF Helium System

3 [317-055000] Feed Hoses

3 [317-053001] Helium Supply Manifold


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3 [317-051000] Interconnect Lines

3 [317-054000] Helium Compressor Assembly

3 [317-052000] Helium Bottle Assembly

2 [317-060000] SPF Vacuum

3 [317-061000] Vacuum Pump Assembly

3 [317-062000] Vacuum Hoses

3 [317-063000] Vacuum Manifold

2 [317-070000] SPF Support Equipment

2 [317-040000] SPF Controller

3 [317-042000] Single Pixel Feed Controller Software

3 [317-041000] Single Pixel Feed Controller Hardware Assembly

1 [318-000000] SPF Receivers (SPFRx) MID

2 [318-010000] Receiver Pedestal Unit

2 [318-060000] Indexer RF Sampler B123

2 [318-070000] Indexer RF Sampler B45

2 [318-080000] SPF Receiver Support Equipment

1 [319-000000] Dish Infrastructure MID

2 [319-010000] Dish Optical Fibre Network MID

1 [320-000000] Dish Local Monitor and Control (LMC) MID

2 [320-010000] LMC Hardware

2 [320-020000] LMC Software

3 [320-020003] LMC Software Dish Manager

3 [320-020017] LMC Software Alarm Handler

3 [320-020018] LMC Software Logger

3 [320-020028] Archive

3 [320-020001] DS Manager

3 [320-020005] LMC Software SMC

3 [320-020031] Power Manager

2 [320-030000] LMC Software Utilities


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8 Major Components

This section gives a high level overview of each of the major subsystems of the Dish. For more detail, please refer to the referenced individual design reports for each subsystem.

8.1 Dish Structure

The Requirements of the Dish Structure are defined in [30]. The Dish structure design is described in [8] and includes the following components:

a) An offset Gregorian reflector system with a feed-down configuration. The main dish is made from aluminium panels with a space frame backup structure. The sub-reflector is constructed using metalized composite panels.

b) A fan-type feed indexer at the focal position allows for changing between the frequency bands by moving the appropriate feed into position.

c) In the pedestal, the Dish Structure provides a RFI shielded compartment for housing electronics. The shielded compartment houses (a) a Drive Cabinet for the motion control equipment and (b) a RFI shielded cabinet for housing the receiver electronics, SPF controller, LMC controller, data network equipment and synchronisation and timing equipment.

d) Power distribution to the Dish Structure and all equipment on the indexer and in the Pedestal.

e) Lightning protection and earthing. f) Cooling: the current design does not include active cooling, but supplies forced ventilation

for equipment in the RFI shielded compartment.

8.2 Single Pixel Feed (SPF) feed packages

The Requirements of the SPF feed packages, Helium and Vacuum systems are defined in [31]. The SPF subsystem design is documented in [9] and is summarized below:

a) The Band 1 feed package covers the 0.35 – 1.05 GHz frequency range. The feed package includes a Quad Ridge Flared Horn design to cover the 3:1 frequency range. Band 1 has an ambient-temperature receiver, with the LNA integrated on the feed horn. The SPF feed package also includes a second amplification stage and a calibration noise source.

b) The Band 2 feed package covers the 0.95 – 1.76 GHz frequency range using a corrugated conical horn feed. A cryostat with GM coolers cools the first stage LNA to ~20K. The cryostat assembly also includes a second stage amplifier and a noise diode for calibration.

c) Bands 3, 4, 5a and 5b (1.65 – 3.05, 2.80 – 5.18, 4.6 – 8.6, 8.3 – 15.4 GHz respectively) share one cryostat. For Bands 3 and 4 only the OMTs are cooled, while for Band 5a and 5b the feed horn and receiver front-end are cooled. Provision is also made for future upgradeability to Band 5c.

d) Helium System: The two cryostats share a common helium supply system with a single helium compressor located at the antenna yoke, with helium supply lines routed to the indexer. The compressor has capacity to cool both cryostats simultaneously.

e) Vacuum System: A roughing vacuum pump is located on the indexer with vacuum lines to the two cryostats and is only turned on if either one of the cryostat vacuums needs to be re-generated. A turbo bump is located on the Band 345 feed to provide the higher level of vacuum needed for the large cryostat.


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f) SPF controller: A single controller located in the pedestal controls and monitors all three feed packages, helium system and vacuum system, and interfaces with the Dish LMC for external control and monitoring.

8.3 Receivers (Digitisers)

The Requirements of the Receivers are defined in [32]. The Receivers design is documented in [10] and summarized below:

a) RF over cable transport: The RF over coax cable between the SPF feed packages and the digitiser units (both on the indexer) are defined as being part of the Receivers, for the purpose of performance budgeting. The layout of components on the indexer and the routing of the RF coax cables was done to minimise the cable length for Band 5.

b) Band 1, 2 and 3 digitiser unit mounted on the indexer. An analogue front-end includes limiters, band-pass filtering and variable gain block, followed by the digitizers. Band 1 and 2 share one pair of digitizers, sampling at 4 GS/s – both in the first Nyquist range. Band 3 is sampled at 3.2 GS/s in the second Nyquist range. The digitised data is transferred by digital optical links to the data packetiser, which is located in the Pedestal. The digitizer unit also contains the clock synthesizer to generate the 4GHz and 3.2GHz clocks for the samplers, which are derived from a 4GHz reference received from the pedestal. The digitizer samples a 1PPS signal to provide a time recovery function for the central signal processor.

c) Band 4, 5a and 5b digitiser unit mounted on the indexer. An analogue front-end includes limiters, band-pass filtering and variable gain block, followed by the digitizers. Band 4 and 5b share one digitiser sampling at 16 GS/s: Band 4 in the first Nyquist range and Band 5b in the second Nyquist range. Band 5a is sampled at 9 GS/s in the second Nyquist range. The digitised data is transferred by digital optical links to the data packetiser, which is located in the Pedestal. The digitizer unit also contains the clock synthesizer to generate the 9GHz and 16GHz clocks for the samplers, which are derived from a 4GHz reference received from the pedestal. The digitizer samples a 1PPS signal to provide a time recovery function for the central signal processor.

d) Digital Processor unit located in the Pedestal. This unit receives the digitised signals via the digital optical links for all the bands from the digitiser units. An FPGA processor receives the digitised signals, packetizes the data into the required format and transmits the data to the SKA-MID Central Signal Processor (CSP) which is located in the central site processing facility. For Bands 1-4, the full RF bandwidth is transmitted. For Bands 5a and 5b, two 2.5GHz sub-bands are extracted and transmitted to the CSP. The extracted bands can overlap in frequency. The centre frequency of these two sub-bands is adjustable by the central Telescope Manager. The transmission to CSP is in the form of a 100Gbps Ethernet link which can transmit the data directly to the CSP on fibre cable lengths up to 10 km (i.e. sufficient for most dishes in the core area of the array). For dishes located further than 10km from the processing facility, the packetiser transmits the data to a long distance router which is also located in the Pedestal. The Digital Processor unit also serves as the central point of contact for the control and monitoring of the Receiver System. The control and monitoring data is transferred via a 1Gbps Ethernet link to the Dish Local Monitoring and Control unit, which is located in the Pedestal.

e) Master Clock Timer unit located in the Pedestal. This unit receives a 1PPS time reference and 4GHz frequency reference from the SKA-MID central Synchronisation and Timing (SAT) system that is located in the central processing facility. The Receiver system is able to tolerate a small frequency offset on the 4GHz reference frequency, which can be uniquely set for each dish, to allow for a sampling frequency offset scheme that may be applied by


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the SAT if/when needed. The Master Clock Timer unit distributes the 1PPS and 4GHz reference signals to the sampler units on the indexer. The unit also measures the round-trip delay between itself and the sampler units on the indexer to allow for accurate delay measurements for the reference signals from the central facility up to the point of the sampler.

f) Pedestal Power Supply unit converts the AC mains power from the Pedestal power supply to 12V DC power and supplies this power to the Digital Processor and Master Clock Timer via a shared backplane. These three units share a 6U rack chassis in an enclosure that is mounted in the RFI shielded compartment in the Pedestal.

The following table summarizes the frequency ranges, bandwidths, sampling rates and bit depths for all the frequency bands. Table 3: SKA_MID frequency bands and digitisation parameters

RF frequency range (GHz)

RF Bandwidth

(GHz)

Sampled Bandwidth

(GHz)

ADC sampling rate

(GSps)

Transport bit depth

Band 1 0.35 – 1.05 0.70 0.70 4 12

Band 2 0.95 – 1.76 0.81 0.81 4 12

Band 3 1.65 – 3.05 1.40 1.40 3.2 12

Band 4 2.80 – 5.18 2.38 2.38 16 8

Band 5a 4.60 – 8.50 3.9 2 x 2.5 9 4

Band 5b 8.30 – 15.30 7.0 2 x 2.5 16 4

8.4 Local Monitoring & Control (LMC)

The Requirements of the Dish LMC are defined in [33]. The LMC design is described in [11]. The hardware is a rack mountable commercial-off-the-shelf ruggedized computer. The function of the LMC is to serve as a single point of entry for all control and monitoring messages to and from the central SKA_MID Telescope Manager (TM). It configures all the static configurations of the subsystems to implement the states and modes of the system and sets up the frequency bands and other settings required to configure an observation scan. It also relays the real-time pointing control received from TM and translates it into the format required by the Dish Structure controller. The pointing model is configured and applied in the Dish Structure controller. For the monitoring, LMC aggregates and filters monitoring data as set up from the external (central) controller. The LMC allows for a drill-down capability for maintainers to access detailed diagnostic information of sub-elements on request. The LMC also has a data recovery “black box” using a circular buffer of detailed monitoring information that can be downloaded remotely in case such information is needed for diagnostics after a system failure.


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9 States & Modes

The Dish Element States and Modes are defined in detail in [19], which defines: a) Dish Element Modes and States.

i. Modes. ii. Capability States.

iii. Pointing States. iv. Power States.

b) Dish Element Requirements relating to states and modes. c) Sub-Element Modes and States. d) Derived Sub-Element requirements relating to states and modes. e) Mapping between Dish Element level states and sub-Element states/modes.

The Dish Element Modes are shown below:

Off

Startup

Standby

LP

Maint

Stow

Shutdown

Standby

FP

Config

Operate

L

L

FL

U

F

FL

F

F

From any mode:

- Power failure

DS: Point

SPF: Operate (Full perf OR Degraded perf)

SPFRx: Data capture

DS: Point, Stow or Standby (Index to Band x)


SPFRx: Configure Band x

DS: Standby_FP


SPFRx: Data Capture (or Standby_FP in exceptions)

DS: à Stow

SPF: Maint

SPFRx: Maint

DS: à Stow

SPF: Standby LP or Operate in FP

SPFRx: Standby LP/FP or Data Capture

DS: Standby LP

SPF: Standby LP

SPFRx: Standby LP

DS: Startup à Standby LP

SPF: Startup à Standby LP

SPFRx: Startup à Standby LP

DS: off

SPF: off

SPFRx: off

DS: Stow à Standby LP

SPF: Standby LP

SPFRx: Standby LP

Maint

Conf Bandx

ß O

pe

rate

Sta

nd

by

_F

P

à

From any mode:

- Forced power off (manual)

Stow

ßStandby_FP

Standby_FP

à

Legend:

F – Full power

L – Low power

U – UPS power

From any mode, if STOW command is

issued From any LP or

FP mode

ß S

tan

db

y_

LP

Sta

nd

by

_F

P à

ß Standby_LP

Standby

_LP à

Figure 5: Dish Element Modes


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10 Functions

The system functions and major data flows have been modelled in the CORE™ Model-based Systems Engineering tool as part of the requirements analysis and architectural design (see Section 4). This functional model forms an integral part of the definition and allocation of functional and performance requirements for the Dish Element and its sub-Elements. It also helps with the definition of internal data exchange interfaces. Each of the major sub-functions is briefly described in the following sections. The model is a combination of logical function flow and data flow. The functional model is hierarchical and allows for the de-composition of system functions until functions can be uniquely allocated to sub-elements. The data model is also hierarchical and allows for the aggregation of data on higher levels to simplify the representation of data flow at the higher system levels. Functions can be allocated to items in the PBS, and data items can be allocated to interfaces. Also, performance and functional requirements can be allocated to functions. Figure 6 shows the top tier functions and data flow. Each function in this diagram has an associated functional diagram that breaks down these high level functions and allocates them to sub-Elements.

Figure 6: Dish functional model: top tier functions

Support

Monitoring & Control

AND

F.D.1

Intercept DSHSignal

Dish Element

F.D.2

Receive DSH_MIDSignal

Dish Element

F.D.4

Control & MonitorDSH

Dish Element

AND

F.D.5

Manage DSHsafety

Dish Element

F.D.6

Manage DSHPower

Dish Element

AND

AND

IncidentEM signal

LMC_DS Feedselect

InterceptedEM signal

SaDT_DSH TimeReference

SaDT_DSH FrequencyReferences

SaDT_DSH1PPS

SPFRx_CSP Signaldata

TM_LMC ControlData

TM_LMC Configure Dish

LMC_TM C&M Data

LMC_TM Meta-data

TM_LMC power control


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10.1 Intercept Dish Signal

Intercepting the signal encompasses the electromagnetic and mechanical aspects of the dish, and includes:

a) The reflection and focusing of the electromagnetic signal and all RF performance relating to the reflector phase efficiency of the Dish Structure, and the associated tolerances on alignment and positioning of the reflectors, in relation to the focal point of the feed.

b) Positioning of the feeds and the associated tolerances. In the case of a PAF feed, this also includes mechanical de-rotation of the feed to compensate for parallactic angle rotation (this function is designed for, but not fitted).

c) Illumination of the reflectors by the feed and the associated performance requirements. d) Mechanical pointing of the reflector system, measuring of encoder values and other local

pointing sensors (e.g. tilt sensor), if applicable. e) Maintaining the physical location of the antenna phase centre and orientation of the dish

structure.

Figure 7: Dish Intercept Signal Functions

MID

Survey

AND

1.1

DS Reflect & focussignal

Dish Structure

OR

1.3

DS Position PAF

Dish Structure

F.PAF.1

Illuminate Opticswith PAF

PAFs

1.2

DS Position SPF

Dish Structure

1

Illuminate Opticswith SPF

SPF

OR

1.4

DS Maintain pointing

Dish Structure

F.D.1.1

Maintain Position

Dish Element

AND

IncidentEM signal

LMC_DS SelectPAF Feed

InterceptedEM signal

LMC_DS selectSPF Feed


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10.2 Receive MID Dish Signal

This includes all the signal path functions required to convert the incoming electromagnetic signal to digital data for transmission from the Dish to the Central Signal Processor, as shown in Figure 8:

a) Feed Package functions of converting the electromagnetic signal to RF and amplification. b) RF over fibre conversion, RFoF transport, RF conditioning and digitisation. c) Data packaging and transmission. d) Generating time and frequency reference signals. e) Generation and control of a gain calibration signal using a switched noise source that is

located in the feed package.

Figure 8: Dish signal path functions

AND

F.D.2.1

Capture SPFSignals

Dish Element

F.D.2.2

Digitise SPFSignals

Dish Element

F.D.2.3

Transmit SPFdata to CSP

Dish Element

F.D.2.4

Synchronise SPFdata

Dish Element

F.D.2.5

Calibrate SPFdata

Dish Element

AND

Intercepted EMsignal

SPF RFsignals

LMC_SPFRxConfigure sub-bands

SPFRx Digitisedvoltage data

SPFRx MonitoredGains & Phases

SPFRx Dataflags

RxTimestamp

SPFRx_CSPSignal data

SaDT_DSH FrequencyReferences

SaDT_DSH 1PPS


LMC_SPFRx Inhibitcalibration


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10.3 Control and Monitor Dish

This function describes all the sub-functions that are needed to interface between internal components and the external, centralised control and monitoring system. These functions are mainly implemented by the LMC sub-element and are shown in Figure 9.

Figure 9: Dish control and monitoring functions

10.4 Manage Dish Safety

Managing dish safety includes the functions in the LMC and the Dish Structure to ensure that the Dish is safe to approach for maintenance and to ensure that it is locally fail-safe under all expected environmental conditions. This includes the provision to stow the dish automatically if communication is lost to the central controller or in the case of a loss of supplied power (for which a small UPS is provided).

AND

F.D.4.1

Manage DSHCapability

Dish Element

F.D.4.2

Manage DSH_TMinterface

Dish Element

F.D.4.3

Control DSH

Dish Element

F.D.4.4

Configure DSH

Dish Element

F.D.4.5

Monitor DSH

Dish Element

F.D.4.6

Provide DSHmeta-data

Dish Element

F.D.4.7

Provide DSHremote support

Dish Element

AND

TM_LMC ConfigureCapability LMC_TM Capability

Reporting

TM_LMC Interfaceconfiguration

LMC_TM DSH interfaceself-descriptionTM_LMC pointing

commands


TM_LMC BeamWeights

TM_LMC Pointingmodel

TM_LMC PAFde-rotation position

TM_LMC DSH States,Modes & Parameters

LMC_TM MID Dish Monitoring Data

LMC_TM Meta-data

TM_LMC Engineeringinterface commands


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10.5 Manage Dish Power

The power is distributed to all sub-elements by the Dish Structure. Due to the large number of dishes in the SKA_MID system, some power management functions are required to help facilitate centralised power control. This includes the ability to power up in a defined low-power state, and to enable the central controller to place the dish in different power consumption levels, depending on the availability of site power and the required Dish functionality. Monitoring of power consumption and monitoring the quality of supplied power is also provided.

Figure 10: Dish power management functions

Control

Monitor

AND

3.1

DS Distribute power

Dish Structure

2.8

DS Monitor power

Dish Structure

AND

LMC Control Dishpower consumption

Dish LMC

2.7

DS Control power

Dish Structure

AND

3.2

DS Provide UPS powersupply

Dish Structure

AND

DS_LMC PowerMonitoring

TM_LMC powercontrol

LMC_DS Powercontrol MID

LMC_DS Powercontrol SURVEY

DS__ Power cycle


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11 Interfaces

This paragraph gives an overview of all Dish external and internal interfaces.

11.1 Dish External Interfaces

The Dish External interfaces are identified in the context diagram below (Dish Element components shown in Green).

Figure 11: SKA_MID Dish External Interfaces

The interfaces are defined in ICDs as listed in Table 4 below: Table 4: ICDs defining the Dish external interfaces

ICD document Document number Interfaces defined in the ICD

[21] DSH to INFRA SKA-TEL-SKO-0000115 I.S1M.INFRA_DSH.001 I.S1M.INFRA_DSH.002 I.S1M.INFRA_DSH.003

[22] DSH to CSP SKA-TEL-SKO-0000125 I.S1M.DSH_CSP.001

[23] DSH to SaDT 300-000000-026 I.S1M.SaDT_DSH.001 I.S1M.SaDT_DSH.002 I.S1M.SaDT_DSH.003 I.S1M.SaDT_DSH.004 I.S1M.SaDT_DSH.005 I.S1M.SaDT_DSH.006 I.S1M.SaDT_DSH.007 I.S1M.SaDT_DSH.008 I.S1M.SaDT_DSH.009 SAT.STFR.UTC-DSH.SPFRx SAT.STFR.FRQ-DSH.SPFRx

[24] DSH to TM SKA-TEL-SKO-0000150 I.S1M.TM_DSH.001

INFRA-SA

DISH

SATSADT

MeerKAT

I.S1M.DSH_CSP.001

I.S1M.SaDT_DSH.007

I.S

1M

.IN

FRA

_D

SH

.001

XXX SAT.STFR.FRQ-DSH.SPFRx

I.S1M.AIV_DSH.009

I.S1M.SaDT_DSH.004

I.S1M.TM_DSH.001

I.S1M.SaDT_DSH.001

I.S

1M

.SaD

T_D

SH

.003

I.S

1M

.IN

FRA

_D

SH

.003

I.S1M.SaDT_DSH.008

I.S

1M

.IN

FRA

_D

SH

.002

I.S

1M

.SaD

T_D

SH

.009

I.S1M.SaDT_DSH.005

Contains Interfaces between MeerKAT Interfacing Items andDISH SPFRx

SAT.STFR.UTC-DSH.SPFRx

Contains Interfaces between MeerKAT Receptors and DISH SPFRx

I.S1M.SaDT_DSH.006

I.S1M.SaDT_DSH.002

316-000000

Dish Structure

Component

317-000000

Single Pixel Feeds(SPF)

Component

318-000000

SPF Receivers(SPFRx)

Component

319-000000

Dish Infrastructure

Component

320-000000

Dish Local Monitorand Control (LMC)

Component

402-000003

INFRA Array PowerDistribution

Component

M1100-0000

MeerKAT Receptors(Dishes)

Component

311-000000

CSP Correlator andBeamformer (CBF)

Component

308-000000

MeerKAT InterfacingItems

Component

M1140-0000

MeerKAT ReceptorFibre Network (RFN)

Component

342-000000

SaDT Non-Science DataNetwork (NSDN)

Component

341-022000

SAT STFR.FRQ

Component

341-030000

SAT.STFR.UTC

Component

340-000000

SaDT Trenching andReticulation Network

Component

406-000003

INFRA Dish Foundation

Component

345-000000

SaDT Digital Data BackHaul (DDBH)

Component

341-000000

SAT_MID

Component

303-000000

TM_MID Products

Component


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[25] DSH to MeerKAT I.S1M.AIV_DSH.001 I.S1M.AIV_DSH.002 I.S1M.AIV_DSH.004 I.S1M.AIV_DSH.005 I.S1M.AIV_DSH.006 I.S1M.AIV_DSH.007 I.S1M.AIV_DSH.008 I.S1M.AIV_DSH.009 I.S1M.AIV_DSH.0010

11.2 Dish Internal Interfaces

The internal interfaces of the SKA_MID dish configuration are identified in [12]. The document identifies the boundaries between sub-elements for the following types of interfaces:

a) Signal path interfaces.

b) Control and monitoring interfaces.

c) Timing and frequency distribution interfaces.

d) Power supply interfaces.

e) Mechanical.

A summary of the identified interfaces is given below in Table 5, with reference to the ICD in which they are defined. Table 5: Dish Internal Interfaces Internal Interfaces ICDs

Category Interface # Description Lead ICD document #

Func Data I.M.DS_LMC.01 Data Exchange interface between the Dish LMC and DS controller.

LMC SKA-TEL-DSH-0000053

Func Data I.M.LMC_Rx.01 Data Exchange interface between the Dish LMC and Receiver controller.


Func Data I.M.LMC_SPF.01 Data Exchange interface between the Dish LMC and SPF controller.


Phys Mech I.M.DS_LMC.03 Mechanical interface of LMC in pedestal LMC SKA-TEL-DSH-0000056

Phys Power I.M.DS_LMC.02 Power supply to LMC

Phys Mech I.M.DS_Rx.02 Mechanical interface of the Recever Pedestal Unit

Rx SKA-TEL-DSH-0000057

Phys Mech I.M.DS_Rx.03 Mechanical interface of RX Indexer RF Sampler B123

Phys Mech I.M.DS_Rx.05 Mechanical interface of RX Indexer RF Sampler B45

Phys Power I.M.DS_RX.04 Power supply to RX Indexer RF Sampler B123

Phys Power I.M.DS_RX.06 Power supply to RX Indexer RF Sampler B45

Phys Mech I.M.DS_RX.07 Mechanical interface of the signal and clock fibre cables

Phys Power I.M.DS_RX.01 Power supply to the Receiver Pedestal Unit

Phys Mech I.M.DS_SPF.07 Mechanical interface of SPF Band 1 feed package on indexer

SPF SKA-TEL-DSH-0000058

Phys Power I.M.DS_SPF.01 Power supply to SPF Band 1

Phys Mech I.M.DS_SPF.08 Mechanical interface of SPF Band 2 feed package on indexer


Phys Power I.M.DS_SPF.02 Power supply to SPF Band 2


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Internal Interfaces ICDs

Category Interface # Description Lead ICD document #

Phys Mech I.M.DS_SPF.09 Mechanical interface of SPF Band 3/4/5 feed package on indexer


Phys Power I.M.DS_SPF.03 Power supply to SPF Band 3/4/5 feed package

Phys Mech I.M.DS_SPF.10 Mechanical interface of Vacuum Services (pump, lines, manifold)


Phys Power I.M.DS_SPF.04 Power supply to SPF Vacuum station

Phys Mech I.M.DS_SPF.11 Mechanical interface of Helium Services (compressor, bottle, pipes, manifold)


Phys Power I.M.DS_SPF.05 Power supply to SPF Helium compressor

Phys Mech I.M.DS_SPF.13 Mechanical interface of SPF Controller (controller, optical fibre)


Phys Power I.M.DS_SPF.06 Power supply to SPF Controller

Phys RF I.M.RX_SPF.01 RF output signal SPF Band 1 SPF SKA-TEL-DSH-0000065

Phys RF I.M.RX_SPF.02 RF output signal SPF Band 2



Phys RF I.M.RX_SPF.08 RF output signal SPF Band 5a

Phys RF I.M.RX_SPF.09 RF output signal SPF Band 5b

Func TFR I.M.RX_SPF.04 Noise diode control signal to SPF Band 1

Func TFR I.M.RX_SPF.05 Noise diode control signal to SPF Band 2

Func TFR I.M.RX_SPF.06 Noise diode control signal to SPF Band 3/4/5

Phys Fibre I.M.DI_SPF.01 Vacuum Pump Station Fibre connector DI SKA-TEL-DSH-0000066

Phys Fibre I.M.DI_SPF.02 SPF Band1 Feed Package Fibre connector



Phys Fibre I.M.DI_SPF.05 SPF Controller Fibre connectors

Phys Fibre I.M.DI_SPF.06 Helium Compressor Fibre connector

Phys Fibre I.M.DI_Rx.01 SPFRx Indexer RF Sampler B123 Fibre connector DI SKA-TEL-DSH-0000067

Phys Fibre I.M.DI_Rx.02 SPFRx Indexer RF Sampler B45 Fibre connector

Phys Fibre I.M.DI_Rx.06 SPFRx Pedestal Unit Fibre connectors

Phys Mech I.M.DS_DI.01 Mechanical interface of indexer fibre routing panel

DI SKA-TEL-DSH-0000068

Phys Mech I.M.DS_DI.02 Mechanical interface of Shielded Cabinet fibre routing panel

Phys Mech I.M.DS_DI.03 Mechanical interface of Fibre cables to Dish Structure

Phys Mech I.M.DS_DI.04 DS Controller Fibre Connector


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12 Power Consumption

The Dishes are one of the largest consumers of electrical power on the SKA-MID site, which is a major driver of operational costs. The Dish Power Management design is defined in [16], which defines:

a) Power distribution design in the Dish. b) Dish power management and control. c) Power consumption and pedestal heat load. d) Dish power supply quality characteristics. e) Electrical safety requirements for Dish.

A summary of the power consumption budget is given in the table below: Table 6: Dish electrical power budget

Heat Load

(pedestal)

Peak

Inst

anta

neo

us (

<0.5

sec)

[V

A]

Peak

Inst

anta

neo

us

(<5

sec)

[V

A]

Max

Sho

rt T

erm

Ave

(5 s

ec -

10m

in) [

W]

Long

Ter

m A

ve

(>30

min

) [W

]

Uni

t Em

erge

ncy

Pow

er

[W]

Cen

tral

Em

erge

ncy

Pow

er

[W]

Ave

rage

- S

cien

ce (W

)

1 Dish Structure: Processing, Sensors, Interlocks 0.9 500 500 500 500 500 0

2 Dish Structure: Servo Amplifiers 0.95 18920 4730 5500 1850 5500 0 861

3 Dish Structure: Cooling 0.8 3750 938 750 500 0 220 -

5 Local Monitor and Control 0.9 333 333 300 300 300 300 300

6 SPF Band 1 0.75 540 133 100 100 0 100 -

7 SPF Band 2 0.75 270 67 50 50 0 50 -

8 SPF Band 3, 4, 5 0.75 800 200 150 150 0 150 -

9 SPF Helium System 0.82 23500 6098 5000 5000 0 5000 -

10 SPF Vacuum System 0.35 6900 1286 450 0 0 0 -

11 SPF Controller 0.5 400 100 50 50 0 50 50

12 SPFRx Band 1/2/3 digitizer, FPGA, RF module 0.9 96 96 86 86 0 86 86

13 SPFRx Band 4/5 digitizer, FPGA, RF module 0.9 36 36 32 32 0 32 32

14 SPFRx AC/DC + fans 0.9 72 72 65 65 0 65 65

15 SPFRx RFoF drivers 0.9 50 50 45 45 0 45 45

16 SPFRx Packetizer 0.9 67 67 60 60 0 60 60

UNIT MARGIN N/A 0 0 500 0 0 0

Total: 33322 14704 13138 9288 6300 6158 1499

Name / DescriptionNo.

Power

Factor

Power Consumption


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13 RFI and EMC

13.1 RFI requirements

RFI requirements are an important design and cost driver. Radiated and self-induced RFI requirements are derived in [13]. They include:

a) Radiated RFI requirements: specifying the level that a component is allowed to radiate so as not to inject signals into the SPF feed that may cause interference in the astronomy signal. The allowed radiation level is specified as a function of the proximity of the component to the SPF feed antenna. These are very challenging for the Dish due to the low levels of the astronomy signals.

b) Self-induced RFI levels: RF interference level that a component may introduce into the signal path internally to the component, either through radiated or conducted means. These levels are derived from the radiated requirements, and referenced to the input of the LNA.

c) Electromagnetic Compatibility standards and related requirements. d) Receiver linearity: to ensure that no compression of the signal of interest is caused by

common RFI sources in the environment (e.g. satellites). e) Receiver survivability: to ensure that no damage to the signal path components occurs as a

result of high powered RFI sources that may occur on site (e.g. aircraft distance measurement equipment).

13.2 RFI design philosophy

Meeting the RFI requirements is one of the major design challenges. The following design principles are applied:

a) Minimise exposure of the analog RF signal path to avoid self-induced RFI. The only vulnerable parts are inside the SPF feed assembly and inside the Sampler units. The RF Coaxial cables are well shielded. In the feed assembly, this risk is minimised by using only low speed digital electronics and driving these electronics with filtered digital signals. This strategy has been successfully demonstrated on MeerKAT. The bigger challenge is in the sampler units, where high speed digital electronics are co-located with the analog RF signal path. However, it has been demonstrated in the MeerKAT project that the required levels of internal isolation are possible through careful choice of components, routing and isolation design, and workmanship.

b) Where possible, locate COTS digital electronics in a well shielded RF cabinet in the Pedestal. There are two shielded cabinets in the pedestal: one contains the Dish Structure motion controller and drive electronics and the second contains all the other control electronics, data network equipment and time/frequency reference equipment. Both of these cabinets are located within the Pedestal Shielded Compartment, which provides a second layer of shielding.

c) Identify all digital electronics outside the shielded compartment early and find and select components that have low radiation levels. An example of this is the azimuth and elevation encoders.

d) Where possible, use low speed communication to all components external to the shielded compartment. This was implemented for all SPF communications.

e) Use only optical fibre for digital communications. f) Routing of wiring throughout the system should hug metal surfaces to minimise pick-up

loops. g) Earthing and bonding of all conductive components.


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13.3 Earthing and lightning protection.

The Earthing and lightning protection requirements and overall design are defined in [26]. Earthing is designed to meet safety regulations and to ensure equipment safety under various conditions. Lightning poses a threat to equipment on the Dish Element, because it is deployed in a moderate lightning occurrence environment (~2 lightning strikes per square kilometre per year). The following earthing and lightning protection design principles will be applied during the detailed design phase:

a) Low resistance-to-earth points provided on the foundation interface, symmetrically placed around the pedestal.

b) Lightning rods on the main and sub-reflectors. c) Low resistance conductive paths (copper, not steel) from the lightning rods to the

foundation earthing points, routed symmetrically around the pedestal. d) Low resistance (copper) earth straps accompanying conductive cables to equipment on the

Indexer. Conductive cables on the elevation assembly to be routed inside closed cable trays. e) Analysis and definition of lightning zones on the dish structure to define the level of surge

protection required for equipment located in each zone. f) Earthing and neutral connections on the electrical distribution system to comply with

electrical safety regulations. Figure 12 shows an overview of the earthing and lightning protection design for the Dish.


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Figure 12: MeerKAT earthing and lightning protection


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14 Environment

The environmental conditions for the DSH element are defined in [17], and are summarised in this section. Environmental conditions are defined for the three different States of the Dish Element namely Deployed, Transportation and Storage as shown in Figure 13.

Figure 13. Breakdown of Environmental Conditions

The classification and specification of the environmental conditions is based on the European Telecommunications Standards Institute (ETSI). The standard is tailored in cases where the conditions drive availability or cost. All tailoring is justified with site climate data.

14.1 Deployed Environment

The deployed environment falls clearly into the ETSI category of an “Extremely Warm Dry” climate.

The Deployed state is decomposed into two sub-states namely the “Operating Conditions” and the “Non-Operating Conditions”. Different levels of functionality and performance are required under the different conditions in the Deployed State as stated in Table 7.

a) The “Operating Conditions” includes the three types of conditions namely Precision, Standard and Degraded Conditions where specific performance and functionality is specified. It also includes the Extreme Operating Conditions, during which observations will typically not be performed, but still requires some functionality (e.g. stowing and monitoring). The Operating Conditions proposed in [17] are chosen to satisfy the operational availability requirements and are based on measured environmental conditions at the SKA_MID site.

b) The “Non-Operating Conditions” defines all the conditions under which the equipment is not required to be operational, but is required to survive without sustaining residual damage.

Environmental

conditions

Deployed

Transportation

Storage

Operating Conditions

Non-Operating Conditions


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Table 7. Functionality and Performance mapping under the different Environmental Conditions in the Deployed State

14.2 Transportation Environment

The Transportation conditions are envisaged to include the transportation of items from various factories and maintenance facilities worldwide, to the storage facilities and Dish locations in the SKA host countries. It excludes any transportation requirements of integrated or semi-integrated assemblies between site integration facilities and the Dish foundations where specially designed transport equipment may be used.

The proposed requirements are based on the ETSI EN 300 019-1-2 Class 2.2 “Careful transportation” with some tailoring. This allows for transportation in all types of trucks and trailers in areas with well developed roads. It also includes transport by sea and train with specially designed shock reducing buffers. It also includes transport by air, but only in pressurised aircraft holds. It provides for handling of all equipment by crane and forklift, or by hand for items lighter than 20kg.

The requirements are applicable to the equipment, preserved as required inside its intended transport/storage packaging. For packaged line replaceable units, it is assumed that items are transported in an enclosed container that provides weather protection.

14.3 Storage Environment

In [17], it is stated that the storage facilities are situated somewhere within the host countries in close vicinity of the SKA1_MID and SKA1_Survey sites. Therefore the expected climatic conditions include that of the sites and the closest airport and harbour regions. For the SKA1 these conditions typical vary between Warm Dry, Mild Warm Dry and Extremely Warm Dry climates including coastal areas. For SKA2 there are a limited number of remote sites close to tropical conditions. For these limited number of locations it is assumed that the storage facilities provide additional protection as well as special packaging and preservation will be sufficient. This also applies to interim storage facilities in other parts of the world.


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The approach to tailoring the storage conditions was to avoid letting the storage conditions drive the cost of the equipment. Different requirements are stated for equipment stored inside weather-protected storage facilities and outside directly exposed to the environment. It is assumed that storage facilities are warehouse type buildings that provide weather protection and access control. No climatic control is assumed, only natural ventilation. The buildings are assumed not to be air tight leaving the opportunity for dust and insects to enter. Large structural components are assumed to be stored outside, directly exposed to the elements.

The requirements are based on the ETSI 300 019-1-1 standard with some tailoring. The requirements are applicable to the equipment, preserved as required, inside its intended storage packaging.

15 Reliability, Availability and Maintainability

The detailed reliability requirements analysis and allocation of requirements to the Dish and its subsystems are defined in [14]. A summary is given below. RAM requirements are driven by the following operational needs:

a) System availability: to maximise the time available to perform science observations. b) Maintenance cost: Considering the large number of Dishes, the total maintenance workload

per Dish should be minimised.

15.1 Availability

It is shown in [14], that even with a modest MTBF (600 hours) for individual antennas, a high availability (99.2%) can be achieved for an array (of 64 dishes), provided that the support system can keep up with servicing all the failures. System availability is thus not a significant driver for individual Dish reliability.

15.2 Maintenance workload

It was shown in [14] that the main driver for individual dish reliability is maintenance workload (i.e. operational cost). The driving requirement is a specification of Direct Maintenance Man-hours per year of less than 24hrs. The analysis of the Dish conformance with this requirement is presented in the FMECA analysis in [27].

16 Support Concept

The operations and support concept is defined in [15]. A summary is given below: The maintenance philosophy is to limit the on-site repair to simple tasks, and to make complex repair items line replaceable units (LRUs) that can be replaced. Faulty LRUs are shipped off-site for repair.

16.1 Maintenance Locations: SKA_MID

The following levels of support are defined: a) Organisational Level Maintenance (OLM): is executed on site at the Dishes. This will include

the replacement of faulty LRUs, on-equipment repairs and on-equipment preventive maintenance.


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b) Intermediate Level Maintenance (ILM): The ILM is located at the Klerefontein support facility ±80km from the core site and ±12km from Carnarvon.

c) Depot Level Maintenance (DLM): It is not yet clear whether this level of maintenance will exist. If so, the Depot level support will be located at the operations support centre in Cape Town.

d) Supplier Level Maintenance (SLM): Supplier level support is at the facilities of those suppliers who are contracted to perform repair of faulty LRUs.

16.2 Maintenance activities

From the Dish FMECA analysis [27], the major maintenance activities are summarised below: a) SPFs: Maintenance workload for the SPFs will be high and will include:

i. Cryostat: The maintenance workload for the SPFs will be dominated by the servicing of the Cryogenic cooler, which typically needs corrective maintenance every 1.3 years. For an array of 133 + 64 dishes, each with 2 cryostats, this means on average 1.4 Cryogenic coolers need to be serviced per working day (assuming 220 working days). The mode of repair is remove-and-replace of the SPF package on site, and the SPF package is repaired either at ILM, DLM or SLM. The same mode of repair is used for failure of components inside the cryostat.

ii. Helium Service: The maintenance of the helium service will include corrective actions on the helium lines, preventive maintenance on the helium compressor (adsorber replacement), and corrective maintenance on the helium compressor. The compressor and helium line segments are LRUs.

iii. Vacuum Service: The maintenance of the vacuum service will include preventive and corrective maintenance on the vacuum pump and corrective maintenance on the vacuum lines.

b) Dish Structures: Maintenance workload for the DS is moderately high and will include: i. A 6-monthly cycle of OLM preventive maintenance, including lubrication, cleaning

and visual inspections. For SKA_MID with an array of 133 + 64 dishes, this implies that on average, 1.8 antennas need to be serviced every working day (assuming 220 working days). Lubrication mechanisms have been simplified as far as possible.

ii. Corrective maintenance of DS is a combination of on-equipment repair and remove-and-replacement of faulty LRUs.

c) Receivers: Maintenance of the receiver components is expected to be low. However, the design does include high-performance electronics components (Digitisers & FPGAs), which may have higher failure rates than equivalent low speed digital electronics. The maintenance mode will be by remove-and-replacement of faulty LRUs that are repaired at DLM or SLM.

d) LMC: Maintenance of LMC components is expected to be low because a ruggedized commercial computer is used, which will be replaced if it fails.

e) Optical Fibre network: the maintenance load of the optical fibre network is expected to be low, and will mostly entail on-equipment corrective action (cleaning, repair and splicing).

16.3 Support Equipment

Specialised support equipment required for maintaining the dishes includes: a) Transporter and elevated work platform with lifting and handling equipment for

replacement and repair of Feed Packages and other equipment located on the indexer (see Figure 14).

b) Cherry pickers for preventive maintenance of Dish Structure. c) Helium leak detection equipment. d) General electrical and mechanical repair equipment.


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e) Specialised RF and digital equipment including Automated Test Equipment (ATE). f) Optical fibre maintenance equipment.

Figure 14: Transporter and elevated work platform for indexer item maintenance

16.3.1 Support Facilities

Support facilities required for the maintenance of the Dish Element includes: a) Mechanical workshop at ILM level. b) Electronic workshop at ILM. c) Specialised electronic workshops at DLM or SLM for the repair and testing of Receiver and

controller components. d) Storage facilities for spare parts at OLM, ILM and SLM levels. e) Cryostat repair facility for repairing the cryogenic cooler, cryostat components, and

integrated SPF package, including all test equipment, probably at ILM level. f) Helium line and helium compressor repair facilities, probably at ILM level. g) Vacuum line and vacuum pump repair facilities, probably at DLM or SLM level.

16.3.2 Packaging, Handling, Storage & Transportation

Transport: Many LRUs are transported using an extensive road network, including transport over gravel roads. Packaging of LRUs should ensure sufficient protection for these journeys; this may include the use of purpose built transport containers. Qualification of all transported LRUs shall include vibration and shock testing that is representative of the expected transportation and handling conditions.

16.3.3 Other Support Concept elements

The following additional support elements are described in [15]: a) Support Training. b) Support Publications. c) Supply Support. d) Support Data. e) Product Supplier Support.

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