The Assembly, Integration and Verification (AIV) work package represents one of nine key elements that will make up the SKA1 Telescope. Whereas the other eight elements are tasked with designing key components of the SKA1 Telescope, the AIV element is tasked to perform all necessary planning to integrate these key components into a telescope system that meets the engineering (Level-1) requirements.
The SKA1 Telescope will consist of SKA1-mid, which will be located in South Africa, and SKA1-low, which will be located in Australia. SKA1-mid will consist out of approximately 133 SKA1-mid Dishes, plus a further 64 MeerKAT Precursor Dishes. The AIV work package therefore also includes the planning for integrating the MeerKAT Precursor into the SKA1-mid Telescope. SKA1-low will consist out of 512 SKA1 LOW Stations, which will include a total of approximately 125,000 individual low-frequency antennas.
The member organisations of the AIV Consortium are SKA SA, CSIRO and ASTRON, with SKA SA leading the consortium. All three member organisations have significant experience in building radio telescopes, and therefore have a vast amount of integration and verification know-how that is benefitting the AIV work package.
SKA 2017 Engineering Meeting
The entire AIV Consortium attended the Engineering Meeting in Rotterdam, The Netherlands, in June 2017. As always, these face-to-face meetings prove to be hugely beneficial, and good progress has been made in all areas.
The workshop regarding the Integration Test Facility (ITF) was well attended by all Design Consortia, who also gave presentations about how they intend to use the ITF, what products they intend to ship to the ITF, and what test activities they intend to perform in the ITF. Although the planning of ITF activities still requires work, it was encouraging to see that the concept of performing early testing and integration in a laboratory environment is fully supported by all Design Consortia.
Various meetings were held to further discuss the issue of MeerKAT integration into SKA1-mid. This included discussions with interfacing consortia, such as SaDT, to advance the status of existing ICD documents, and discussions with systems engineers at the SKA Office to include the modelling of MeerKAT integration into the existing SKA1-mid model that is maintained in CORE.
The AIV Consortium also hosted a workshop regarding “L1 Verification Requirements”, which are high-level descriptions of how to verify the Level-1 Telescope Requirements. Design Consortia were encouraged to give presentations regarding their Element-level verification planning. The ensuing discussions contributed significantly towards establishing a common understanding with regard to verification planning across the entire project.
Figure 1: AIV Team at the Engineering Meeting in Rotterdam, June 2017. Adam MacLeod, Richard Lord, Peter Hekman, Donald Gammon, Michael Hayes, Nico Ebbendorf, Marchel Gerbers (LFAA Consortium, honorary AIV member of the week).
Integration & Verification Plans
The development of I&V Plans for both SKA1-mid and SKA1-low is high on the agenda of the AIV Consortium. The I&V Plan provide a structured framework, in which all integration and verification activities will be carried out in a coordinated manner.
As shown in the Figure 2, the key inputs to the I&V Plan are obtained from the Verification Requirements and the Roll-Out Plan. Both of these document sets have been reviewed extensively, paving the way for delivering the I&V Plan as part of the documentation pack for the System Pre-CDR towards the end of 2017.
The I&V Plan identifies:
- Integration Events
- Verification Events
Where each event is characterised by:
- Start date
This information is captured in Microsoft Project, where Gantt charts and high-level views of the I&V schedule can be produced, as shown in Figure 3.
Design Qualification versus Product Verification
The difference between design qualification and product verification is often a matter of definition.
Qualification is associated with design and is therefore important during the design phase, i.e. the Pre-Construction Phase. Product verification or product acceptance is associated with manufactured products and is therefore important during the Construction Phase. Both design qualification and product acceptance are often regarded as verification activities.
All Design Consortia are expected to deliver qualification results at their respective Element CDR, which provide confidence to the SKA Office that their design will meet their L2 Requirements, which can be traced to the L1 Requirements. The qualification results are obtained either by analysis (i.e. paper work) or by test (i.e. a prototype has been built). If the design qualification is incomplete at Element CDR, it is expected that the affected Design Consortia also deliver a Qualification Plan, which describes how and when the design qualification will be completed (e.g. at the System ITF).
Once a product has been manufactured (this includes software/firmware products), it needs to be verified against its requirements (e.g. L2 Requirements). One distinguishing feature between design qualification and product verification is therefore that qualification testing is usually performed on a prototype, whereas verification testing is usually performed on the final product.
Design qualification and product verification are performed at all levels of the system:
- Level-2 Design Qualification should be completed at Element CDR, although it is likely that some of it will be completed at the System ITF.
- Level-1 Design Qualification, i.e. system-level design qualification, will be partially performed with the system installed in the System ITF and partially with Array Assembly 1.
- Level-2 Product Verification is expected to be performed at the contractor’s factory as part of factory acceptance. Such products may be shipped to the System ITF or to site, where final acceptance testing will be performed by the product contractor after installation, as part of the hand-over process.
- Level-1 Verification of the Telescope system is performed in a staged manner with the four Array Assemblies on site. A significant amount of verification testing can also be performed with the system installed in the System ITF.
In addition to the qualification results, all Design Consortia are expected to deliver a Verification Plan at their respective Element CDR. This Verification Plan should contain the following:
- A high-level description of how each of the product’s L2 Requirements will be verified. These descriptions are not as detailed as a test procedure.
- At what level of system integration the verification will be performed. Verification testing could happen at the contractor’s factory using simulators or emulators, or it could happen at the System ITF, where the product can be interfaced with other products.
Experience with other radio telescopes has consistently shown that the roll-out activities and AIV work scope is often under-estimated, even at component level, and often causes delays in deployment, due to re-engineering and retrofitting of components. This may significantly increase the total cost of the system.
Many issues that are discovered during “downstream” integration and verification are the result of “upstream” neglect. Early in the project, during the design stage, science requirements need to be accurately translated to Element-level requirements, and interfaces between products need to be accurately defined.
Another major challenge is that the software/firmware dominated Elements (CSP, SDP and TM) need to deliver systems with basic functionality very soon after tenders have been awarded.