1. 2 nd convergence workshop: introduction R. T. Schilizzi Penticton 22 July 2004

2. SKA Development Plan 2000-7technology prototyping and demonstrators 2004-5 site testing 2006 selection of site, major external review of design 2007prepare funding proposal for 5% area demonstrator 2008 selection of technical design (may be a combination) 2009start construction of 5% demonstrator on selected site 2010 submit funding proposal for full array 2012 start full construction 2015initial operations 2020complete construction

3. the selection process for SKA design concept we plan to select the technical design in 2008 following concept prototyping and demonstration we recognise that the SKA is affordable only through a global collaboration, so we need find ways to keep all SKA players on-board even if their national concept is not selected -Selection criteria -captures significant fraction of the science in the Key Science Projects -demonstrated engineering feasibility and compatibility with site choice -maintainable at a reasonable cost -upgradable -within the nominal cost envelope of 1B Euro/$

4. the selection process for SKA design concept ISSC-defined options for the selection process in order of desirability from an international point of view (anno 2003) 1)mutual convergence to a single cooperative design concept that is inclusive and engages the global community 2)down-selection amongst cooperative designs including combinations of two or more concepts (hybrids), and 3)down-selection amongst individual concept team proposals

5. Selection process a year on….. Option 1 looks unlikely in view of the timelines for proving the individual concepts via demonstrators We can already see that no single design concept can meet all the key science requirements, so.… How viable is option 2, the hybrid idea? Are there combinations of designs that capture all the key science goals, and yet remain within the nominal 1B€/$ budget….. Or, do we rescope the project either as a hybrid or as an individual concept with less than the full key science complement

6. What did we accomplish in the 1 st convergence workshop? (see memo 48) AAT + SD CYL + SD LAR (LL + SD) (LL + CYL) SD+fpa now added We narrowed the hybrid options down to 5 possibilities: We discussed SKA pathfinders and noted a number of niche- science/national large scale demonstrators under consideration. Concern was noted w.r.t. resources for the full SKA. We discussed the broad issue of the continued engagement of the community over the long period between now and 2020

7. Information requested on hybrids 1)frequency range of each hybrid component 2)sketch of component collecting areas within stations and central arrays 3)updated costing info 4)A eff /T sys for each hybrid component at band edges 5)Type of antenna elements and dimensions 6)# FOV 7)for each hybrid component: # stations, # antennas/station, A phys /station, Aeff/station, station dimensions, shadowing limits 8)Array configuration, total bandwidth transmitted, station or antenna FOV at spot freq 9)Feeds, focal plane arrays, RF beamforming, bits/sample 10)Sharing of station and central infrastructure

8. End of introduction

9. Issues for Discussion Hybrids, even with decrease of A eff, are still 1.5-2 B€/$ (including contingency and management) projects Can we afford a hybrid at all - what are the perils of multiple technologies from the construction and operation viewpoint? Are there any new hybrid solutions requiring attention?

10. Issues for Discussion Should we give higher priority to the science goals in one part of the nominal frequency range and select one of the design concepts in that frequency range? Or do we concentrate on short baselines first Or reduce the FOV spec? Or should we go for 2 B€/$? -up-front for a full-scale hybrid or -over a 20-year period and phase the construction of the SKA such that, say, the low frequency component (0.1 < ν <1.5 GHz) is built first, followed later by the high frequency component (1.2 < ν < 25 GHz) Keep cost, risk, benefit clearly in focus Evolutionary process?

11. Global demonstrator Should any large-area international demonstrator be a hybrid? Can the global astronomy community afford more than one large-area demonstrator? If AAT is to be the final technology at low freq (and it is still too expensive for a large area demonstrator in 2009), could SD+fpa be an intermediate solution for the demonstrator?

12. Strategies for the SKA SKA memo 45 0.1< ν <25 GHz, A eff /T sys ~20000, 20m< baseline<~3000km Cost <~1 B€/$? Select hybrid in 2008 6 individual concepts3 hybrids Construct international 5% demonstrator Construct full SKA yes Develop process to optimise scientific return: rescope Increase nominal budget no phased Implementation of priorities 2 sites? hybrid Prioritise key science select on ν, baseline, FOV hybrid Select individual concept in 2008 Construct international 5% demonstrator Construct SKA Select  5% demonstrator  construct SKA

13. Issues for Discussion Has the existing descriptive process reached a useful conclusion? How should the design convergence process proceed? Wait for the system definition document from the EWG. Use cost/performance tool for hybrids as well Further develop Jaap Bregman’s generic approach designate a reference design concept. Is the AAT+SD the front-running hybrid on the long term for the SKA? Prioritise science requirements, can we accept less than the full complement?