VGOS observing strategy for 2026

The VLBI Global Observing System (VGOS) entered operational service in 2020 with a small, northern-hemisphere-dominated network and a modest observing cadence constrained primarily by correlator capacity, data transport, and storage limitations. Since then, the network has continued to expand steadily. By 2025, the VGOS network comprised approximately 16 stations, including key southern-hemisphere sites, resulting in improved global geometry. However, the growing network required changes in observing strategy to avoid exceeding current processing and data transport resources. In this work, we present the VGOS observing plan for 2026, developed by the IVS Observing Program Committee (IVS-OPC) in close consultation with the community and IVS Operations Centers.

The 2026 plan anticipates growth of the VGOS network to over 20 stations and introduces a total of 56 24-hour VGOS sessions, marking the first year in which VGOS exceeds a weekly observing cadence. Simulations reveal that we can expect the results of routine VGOS sessions to surpass those of the legacy S/X observations, in terms of station positions and EOPs. The core VGOS-OPS program will include 38 global sessions, typically scheduled on Wednesdays with a uniform 00:00 UT start time and capped at 200 TB per session to balance scientific return and resource constraints. To support faster product delivery, a new rapid-turnaround series, VGOS-R3, will be implemented, mimicking legacy S/X rapid sessions and targeting data transfer within five days for a subset of stations with proven high-performance data links. Additional specialized sessions include four quarterly VGOS-CRF sessions to support celestial reference frame maintenance and eight VGOS-R&D sessions designed for conceptual and technology development.

Overall, the 2026 observing plan represents a critical transition toward routine, high-cadence VGOS operations, laying the groundwork for faster turnaround, improved geodetic and astrometric products, and future continuous observing.