Scientific rationale
Modern scientific challenges increasingly require integrated or coordinated observations across multiple domains. Astronomy, geodesy, and space science often depend on shared infrastructure whose coordination is essential for precision science and space operations. This Focus Meeting will explore how shared global infrastructure and coordinated international projects, including ground- and space-based systems such as telescopes, missions, timing systems, geodetic networks, and computing platforms, can enable and advance multi-domain science at the interface of astronomy, space geodesy, and space science. Its distinctive contribution is to treat these elements in an explicitly integrated way, promoting genuine cross-disciplinary collaboration between communities while retaining a clear, focused scope in line with the IAU rules for Focus Meetings.
Today, observatories and data systems originally designed for specific scientific domains are increasingly utilised to support a diverse range of applications. Very Long Baseline Interferometry (VLBI), for example, underpins both the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF), as well as the determination of Earth Orientation Parameters (EOPs). These foundational geodetic products are crucial for astronomy and cosmology, Earth observation, spacecraft navigation, and the sustainability of modern space activities. At the same time, VLBI is a powerful astronomical technique, providing some of the highest angular resolution observations in astronomy, enabling the study of compact objects such as active galactic nuclei, relativistic jets, and masers.
Ongoing initiatives such as the Astro2Geo programme have demonstrated how VLBI infrastructure can be used strategically for multiple outputs, supporting ICRF realisation, geodetic monitoring, and AGN science, through coordinated scheduling and shared data processing. New mega-observatories such as the Square Kilometre Array (SKA) have the potential to serve multi-domain science. For example, ongoing work using MeerKAT and global VLBI networks to link planetary ephemerides to the ICRF through millisecond pulsar timing directly connects planetary science, astrometry, and geodesy.
In parallel, many optical observatories are now serving multiple scientific and strategic roles, including high-cadence transient surveys, satellite tracking, space-debris monitoring, and planetary defence through near-Earth-object observations and initiatives such as the UNESCO/GOTTA project. The next-generation International Celestial Reference Frame (ICRF4), planned for submission for adoption at the 33rd IAU General Assembly, will mark a major milestone in this multi-domain evolution by integrating Gaia-based optical positions with VLBI-derived radio data into a unified celestial reference frame. Space missions such as GENESIS, designed to link VLBI-based quasar observations with GNSS, SLR, and DORIS through precise orbit determination, will further strengthen the connection between the ICRF and ITRF.
Collectively, these overlapping use cases highlight the need for improved dialogue and alignment between the communities of astronomy, geodesy, and space science. Shared infrastructure also faces shared challenges: the rapid proliferation of satellite constellations and increasing unwanted electromagnetic radiation (UEMR) threaten data quality for both radio and optical observatories, as well as for geodetic observations. Coordinated international standards, conventions, and reference frameworks are essential to ensure consistency and compatibility across scientific domains.
Simultaneously, the promotion of outreach, awareness, and human capital development in multi-domain science is essential. Cultivating shared understanding, interdisciplinary skills, and collaborative capacity across astronomy, geodesy, and space science will be crucial for long-term impact, inclusivity, and sustainability, especially where infrastructure is hosted in remote or historically marginalised regions.
This meeting will bring together experts from astronomy, geodesy, and space science to address these intersecting issues, showcasing successful models, identifying opportunities for deeper collaboration, and developing a joint strategic agenda. It supports the IAU's mission to foster cross-disciplinary interaction, international coordination, and the sustainable use of global scientific infrastructure.
Expected outcomes
- Proceedings volume documenting invited reviews, contributed talks, and panel discussions
- Identification of priority areas for cross-disciplinary coordination across astronomy, geodesy, and space science
- Strengthened links between the IAU and geodesy/space-science communities and their official organisations
- A joint strategic agenda for multi-domain use of shared global infrastructure and for addressing shared challenges