Dish

Dish_blue

The Dish Consortium has witnessed the remarkable efforts and huge progress of all sub element teams. The SKA First Prototype Dish Inauguration Ceremony was successfully held in Shijiazhuang China on 6th Feb 2018. It was a very inspiring event not only for the Dish Structure team but also for the Dish Consortium. Various kinds of sub element prototypes and qualification models have become alive in the past few months. The SPF Band 2 CDR was successfully held in December 2017 and SPF Receiver B123 DDR was closed in February 2018. All the teams are on their full speed towards to the CDRs. The Dish Schedule is being continuously updated at the monthly schedule meeting and the schedule slippage is being monitored and reported to the SKAO continuously. The critical path of the schedule has slipped significantly since baselined in October 2017. A new ECP should be issued soon to update the relevant DSH milestones. The cost updates remain relatively stable. The Dish Structure and some elements kept the cost unchanged and some other elements slightly increased the cost. The increase in Band 1 has been discussed. Also the signing for the extension of Dish Consortium Agreement is on process.

Dish Consortium with SKA-P, 6th Feb 2018

System Engineering

The Systems Engineering team is coordinating all the technical activities on the Dish Consortium and is conducting bi-weekly SE meetings to track progress and to put actions into place to mitigate technical risks. The SE team is driving a rigorous process of qualification for subsystems, including a test readiness review (TRR) before the start of formal qualification testing and a CDR after qualification testing.

The SE team have coordinated the following DSH reviews since November 2017:

  • SPF Band 2, Vacuum and SPF controller CDR (Dec 2017).
  • LMC TRR (Dec 2017).
  • SPF Band 1 TRR (Jan 2018).
  • Receiver B123 DDR closure (Feb 2018).
  • Indexer TRR (Dec 2017).

Preparations are underway to support the testing of the Band 1 feed on a MeerKAT dish. The MeerKAT Receptor Test System will be used to conduct these tests.

Dish Structure

Immense activities continued in the Dish Structure group for the manufacturing of two Prototypes SKA-P and SKA-MPI. More than 128 precision Aluminum Main Reflector Panels have been developed during the timeframe and each of it with a surface accuracy of better than 100 µm RMS. JLRAT has gathered over the last fifty years a special know how to produce such accurate Panels in a large quantity.

Figure 1 JLRAT’s SKA Main Reflector Panel

The progress on the 5m large CFRP Subreflector, also developed by the Chinese experts from JLRAT, resulted into two completely finished assembly for both dishes. Fully assembled in the CFRP Truss Frame Structure, each subreflector consists of six pieces, showed a better surface accuracy than specified.

The Pedestal and the Turnhead Structure including all mechanical components have been assembled and aligned in the Factory. The team was being stressed to meet the progressive schedule for the first dish inauguration event. A milestone was the Big Lift of the M1 Reflector to its Pedestal on the eve of 2018.

Figure 2 Big Lift of the Main Reflector to the Pedestal

The pressure was also very high on the European side of the Dish Structure Team.

In Germany at MT Mechatronics the entire Servo System including all Drive Components were manufactured, Factory tested and air shipped before the New Year to China. SKA is pushing boundaries everywhere and to be able to move the 18 x 15 m Reflector with an accuracy of 1/1000 of a degree, one of the largest direct Drive Elevation Spindle drives were designed and manufactured.

Figure 3 Left side MeerKAT Prototype and Right side SKA El Drive Spindle

At SAM in Italy the first Indexer underwent successful, a series of Factory Tests before it joined the SKA-P Structure in China. The Test readiness Review (TRR), a further important milestone for the Feed Indexer System was held before the Tests were conducted in the Factory near Naples.

Figure 4 Feed Indexer Factory Test at SAM

In South Africa, ITC finished also their contribution for the SKA-P. The 19” EMI Shielded Cabinet passed successfully the stringent EMI Requirements of the SKA Observatory and went also on its journey to meet the Structure for the first time.

Two Years of intensive work on the design reached its climax in late January. Different Components, made by different identities in different countries went smoothly together for the first time at SKA-P in Shijiazhuang, China.

Hard work on the Prototype continued until the very last moment before the official Inauguration Ceremony of the first SKA-P Telescope was celebrated with VIP’S from all over the World. This Event was extremely well prepared by the colleagues from JLRAT/CETC54 and the Dish Structure Team was very proud to show and present a key element of the SKA Observatory for the first time.

Figure 5 Official Group Picture of the Inauguration of first SKA Telescope

Figure 6 Impression of inauguration ceremony in Shijiazhuang, China

Figure 7 SKA-P on the inauguration ceremony, CETC54, Shijiazhuang

The Recreation after many over hours of work for the Dish Structure Group was not too long. The second prototype SKA-MPI for the Max Planck Society passed also successfully its first Factory Tests in February. The structure and the other components will be shipped soon to South Africa. While testing continues on the first Prototype SKA-P in China, the assembly of the second one SKA-MPI will start in the next few weeks. The Pressure continues this Year for a fabulous joint working team at Dish Structure.

LMC

In this period, LMC made important steps towards the CDR. The TRR for the software component was successfully done in December 2017. All the procedures for the test of the software have been implemented and tests will be performed in the next months. The software almost ready, it needs only some implementation in particular for the communication with the Dish Structure. This will be accomplished as soon as the final version of the interface DS-LMC will be released. For the hardware component, the TRR will be done at the end of March.

Full integration with Dish sub-elements simulators is planned in June. The CDR for the LMC is planned in the second half of July 2018.

Single Pixel Feed

During the December 2017 to March 2018 period, the single pixel feed (SPF) teams continued with the pre-production developments. The Band 2 team is currently closing the open items on their CDR held in December 2017 and getting ready to install the feed with services on the SKA-MPI in the third quarter of 2018. The Band 1 team is in the process of qualifying the qualification model and the Band 345 team, starting later than everybody else, is preparing to close off their delta preliminary review (PDR) and are continuing with the feed package design in preparation for a detailed review (DDR) planned for middle 2018.

Band 2

The highlight during this period has been the CDR event for SPF band 2 and services, in Stellenbosch South Africa 6-7Dec2017, quoted as “The panel considers the CDR a success and it can be closed once the issues identified by the panel are resolved”. The final panel report was received in Feb 2018 and the band 2 Feed was deemed ready for industrialization. There are some EMC/EMI and Tango issues to be solved for the vacuum service and the SPF controller respectively but the improvements are impressive. The team is working to close the CDR in order to issue a qualification baseline (QBL) and to prepare the feed and services for installation on the MPI dish on site in the latter half of this year.

An initial site test has been done on the EMSS Antennas site test jig. Measurement data is currently being processed. The band 2 qualification model is the first feed of the dish element that has been tested at the site.

Figure 8 SPF band 2 and services CDR – the team and reviewers

Figure 9 SPF band 2 qualification model

Figure 10 SPF band 2 team performing the first site tests

Band 1

Another big SPF milestone was achieved when the test readiness review (TRR) was performed for the band 1 qualification model (QM). There were some observations which are being closed before the formal qualification testing can commence. However, the hardware for the RFI qualification (band 1 back-to-back model) in South Africa is ready for shipment. The QM for the on-dish-testing for the MeerKAT dish is also being made ready for shipment to site. Some environmental testing is planned on the QM in Sweden CW14 before on-site testing on MeerKAT. A back-short model has also been prepared for temperature testing in Sweden. Initial functional qualification testing on the band1 QM has resulted in as predicted results.

Figure 11 SPF band 1 qualification model

Figure 12 SPF band 1 back-to-back model for RFI testing and back-short model for temperature testing. The back end is the same as that of the actual feed, allowing installing and testing the feed package controller.

Figure 13 SPF band 1 Y-factor test results. Note that this includes a contribution from the ground picked up by the feedback-lobe which will not be present on the dish.

Band 345

The SPF Band 345 team has been focusing on the cryostat design towards the DDR in July 2018. The cold plumbing system has now being manufactured to verify that the cryogenic system can maintain the cold temperature (20 K) under the heat load of all the feeds. The first prototype Band 5a and 5b feed horns and ortho-mode transducers have been designed and manufactured by JLRAT in China. They have arrived at Oxford for further tests and incorporation. Design work has also been continuing on the FPC electronics.

The one outstanding item from the PDR was the provision of a new turbo vacuum pump. The testing result was good and the pump is waiting for the final RFI testing at the SARAO test chamber.

Figure 14 Configuration of the five-arm cold plumbing in the large test cryostat

Figure 15 First-light configuration with just the Band 5a and 5b feeds installed.

SPF Receiver

The SPFRx Band 123 delta DDR closeout documents were submitted and signed off over the course of January and February. The SPFRx Qualification Model construction started in January and continues with a target of Test Readiness at the end of May. The work towards Band 4-5 DDR has commenced at LAB facilities at Bordeaux University in France notwithstanding the delays of delta PDR telecon which remains unscheduled on March 26.

Here are some highlights of progress made in January to March.

SPFRx ODL_ADC frequency response

Early in the development of the ADC12J4000, the team realize that a steep rolloff of ADC conversion gain must be corrected to ensure a flatness of frequency response. To address this, two versions of model, wideband balun method and attenuator solution, have been built and tested. It is shown that the rolloff can only be compensated by external to the ADC RF conditioning.

Figure 16 NRC ODL_ADC board – RF and clock inputs at left, optical output fiber ribbons on right

Figure 17 The NRC ODL_ADC board (integrated 6dB attenuators) sensitivity spectrum, tested in January 2019. using single tone generator at a constant power and varied in frequency in 50 MHz steps.

Integrated Band Switch Gain Block development

A custom SPFRx B123 integrated Band Switch – Gain Block with gain variability by 46 dB has been under development. Due to the nonconformance of proposal by early prototype supplier and the need for compensating the ADC rolloff, the team decide to undertake the further development in NRC. The circuit has been fabricated on a 4-layer FR4 substrate and populated with all RF, biasing and control components. Early test results are very encouraging. Individual control of each of two attenuators (type PE43712) is fully operational.

Figure 18 fully assembled 4-way RF switch + variable gain block board

Figure 19 Integrated RF switch gain block connected up to VNA and control computer

Figure 20 VNA measured gain of SPFRx integrated RF switch gain block.

RXPU construction

All printed circuits for wiring up the RXPU have been fabricated and populated with components. The backplane printed circuit has been mounted in the RXPU enclosure and hooked up to the AC power input module. The RXPU.DGP1 and power supply module are fully operational, waiting for the final air circulation and RFI sealing. The RXPU.MCT Master Clock Timer has been partially integrated and connected up electrically.

Figure 21 RXPU wired up and populated with DGP1 MCT and PS modules.

Design of Hardware Clock Cycle Counter for coherence maintenance

A crucial issue was identified in the SPFRx delta DDR that the clock and 1pps distribution hardware does not provide for maintaining time coherence through all band changes. To close this the team proposed to implement an additional circuit – Hardware Clock Cycle Counter that would run uninterrupted by band changes and provide timing standard on which to base the coherent sampling. The frequency divider, counter logics and Fast AND gate has been selected based on cost effective components. The conceptual design of phase coherence has been implemented. And PCB layout artwork is to be finished soon.

Figure 22 Hardware Clock Cycle Counter 1pps+ generator conceptual diagram


Report provided by the DISH consortium