The Square Kilometre Array (SKA) project will build the largest radio telescope in the world with telescope facilities deployed in Australia and South Africa covering a frequency range from 50 MHz to 15 GHz (initial phase). The approval for the start of construction from its governing Council occurred in June 2021. This paper reviews the key science drivers and the outline observatory organization, design summary and site locations. We note the current progress and status of the SKA construction and projected schedule, noting the challenges within the current global climate.

The Square Kilometre Array (SKA) is a next-generation radio astronomy facility that will revolutionize our understanding of the Universe and the laws of fundamental physics. To achieve the intended objectives, it needs a stable reference frequency and accurate timing signals at each digitizer. These references are used for digitizing astronomical signals received from the receptors. The stability and accuracy of these references are highly important for coherently sampling the astronomical data. They are distributed using long-distance fibers that are susceptible to environmental perturbations, which makes meeting the requirements a challenge. The system overcomes these perturbations by actively stabilizing the noise during fiber transmission to achieve the required reference signal stability and sub-nanosecond level of timing accuracy. We collect together summary descriptions of the sub-systems designed for distributing the reference frequency and timing signals for each telescope, to provide an overview of the whole timing and frequency system for the SKA.

The Square Kilometre Array Observatory (SKAO) will construct two radio telescopes: SKA-Low in Australia and SKA-Mid in South Africa. When completed, the Square Kilometer Array (SKA) will be the largest radio telescope on Earth, with unprecedented sensitivity and scientific capability. The first phase of SKA-Mid (called SKA1-Mid) includes an array of 197 dish antennas incorporating the recently completed MeerKAT dishes to cover the frequency range of 350 MHz to 15.4 GHz. The 19 Tb / s digitized data stream is transported from the dishes in the remote Karoo to Cape Town where data are correlated and processed through high-performance computing systems. The demanding scientific performance requires extremely accurate timing and synchronization of the data measured by the distributed dishes. The combination of large-scale deployment, significant real-time processing, geographic distribution, and limited budget poses significant challenges for the physical, control, and processing architectures. We present the architectural highlights of the SKA1-Mid Telescope baseline design, for which its Critical Design Review was completed in 2019 and construction was started in July 2021.

For many scientific projects, data management is an increasingly complicated challenge. The number of data-intensive instruments generating unprecedented volumes of data is growing and their accompanying workflows are becoming more complex. Their storage and computing resources are heterogeneous and are distributed at numerous geographical locations belonging to different administrative domains and organisations. These locations do not necessarily coincide with the places where data is produced nor where data is stored, analysed by researchers, or archived for safe long-term storage. To fulfil these needs, the data management system Rucio has been developed to allow the high-energy physics experiment ATLAS at LHC to manage its large volumes of data in an efficient and scalable way. But ATLAS is not alone, and several diverse scientific projects have started evaluating, adopting, and adapting the Rucio system for their own needs. As the Rucio community has grown, many improvements have been introduced, customisations have been added, and many bugs have been fixed. Additionally, new dataflows have been investigated and operational experiences have been documented. In this article we collect and compare the common successes, pitfalls, and oddities that arose in the evaluation efforts of multiple diverse experiments, and compare them with the ATLAS experience. This includes the high-energy physics experiments Belle II and CMS, the neutrino experiment DUNE, the scattering radar experiment EISCAT3D, the gravitational wave observatories LIGO and VIRGO, the SKA radio telescope, and the dark matter search experiment XENON.

Deep galaxy surveys have revealed that the global star formation rate (SFR) density in the Universe peaks at 1 < z < 2 and sharply declines towards z = 0. But a clear picture of the underlying processes, in particular the evolution of cold atomic (~100 K) and molecular gas phases, that drive such a strong evolution is yet to emerge. MALS is designed to use MeerKAT's L- and UHF-band receivers to carry out the most sensitive (N(HI)>10$^{19}$ cm$^{-2}$) dust-unbiased search of intervening HI 21-cm and OH 18-cm absorption lines at 0 < z < 2. This will provide reliable measurements of the evolution of cold atomic and molecular gas cross-sections of galaxies, and unravel the processes driving the steep evolution in the SFR density. The large sample of HI and OH absorbers obtained from the survey will (i) lead to tightest constraints on the fundamental constants of physics, and (ii) be ideally suited to probe the evolution of magnetic fields in disks of galaxies via Zeeman Splitting or Rotation Measure synthesis. The survey will also provide an unbiased census of HI and OH absorbers, i.e. cold gas associated with powerful AGNs (>10$^{24}$ W Hz$^{-1}$) at 0 < z < 2, and will simultaneously deliver a blind HI and OH emission line survey, and radio continuum survey. Here, we describe the MALS survey design, observing plan and the science issues to be addressed under various science themes.

We present H i imaging of the galaxy group IC 1459 carried out with six antennas of the Australian Square Kilometre Array Pathfinder equipped with phased-array feeds. We detect and resolve H i in 11 galaxies down to a column density of ∼1020 cm−2 inside a ∼6 deg2 field and with a resolution of ∼1 arcmin on the sky and ∼8 km s−1 in velocity. We present H i images, velocity fields and integrated spectra of all detections, and highlight the discovery of three H i clouds – two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an H i mass of ∼109 M⊙ and accounts for ∼15 per cent of the H i associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data, we find evidence of additional extended, low-column-density H i emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intragroup gas within the IC 1459 group. Altogether, the H i found outside galaxies in this group amounts to several times 109 M⊙, at least 10 per cent of the H i contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.

At the altitude of 3,370 m on the Peruvian Andes, a 32m antenna owned by the telecommunications company Telefonica del Peru will be transformed to a Radio Telescope, it would be transferred to the Geophysical Institute of Peru (IGP). The parabolic antenna was constructed in 1984 by Nippon Electric Co. (NEC) and worked as an INTELSAT station until 2000. A team of the National Observatory of Japan (NAOJ) evaluated the antenna in 2003 and reported its availability to be used as a Radio Telescope. In collaboration of the NAOJ a 6.7 GHz receiver is under construction and will be installed within this year. Initially the telescope as a single dish will monitor and survey Methanol Maser of YSO, higher frequencies equipment and VLBI instruments will be considered. The antenna will be managed by the IGP and used by universities in Peru, becoming a VLBI station will be a grate contribution to astronomy and geodetic community.