The Australia SKA Pathfinder (ASKAP) is a new telescope under development as a world-class high-dynamic-range wide-field-of-view survey instrument. It will utilize focal plane phased array feeds on the 36 12-m antennas that will compose the array. The large amounts of data present a huge computing challenge, and ASKAP will store data products in an archive after near real-time pipeline processing. This powerful instrument will be deployed at a new radio-quiet observatory, the Murchison Radio-astronomy Observatory in the midwest region of Western Australia, to enable sensitive surveys of the entire sky to address some of the big questions in contemporary physics. As a pathfinder for the SKA, ASKAP will demonstrate field of view enhancement and computing/processing technology as well as the operation of a large-scale radio array in a remote and radio-quiet region of Australia.

In image reconstruction by the method of convex projections an image vector is successively projected on to subsets defined by various items of prior information and by the measured data. Some of these operators are quite complex and can exhibit numerical instability caused by partial redundancy of the information. We illustrate this, and the application of inverse theory to the method of convex projections, by deriving an operator for projecting on to the subset defined by the measured data and analysing its stability. We show that, with pixel basis functions, nearest-neighbour interpolation with averaging leads to a simple but exact implementation of the stabilized operator. We use this to derive an approximation for some other basis functions.