ULTRASAT

ULTRASAT [WIS]

ULTRASAT (Ultraviolet Transient Astronomy Satellite) is an astronomical satellite designed to conduct the first wide-field survey of transient and variable ultraviolet (UV) sources. The satellite will carry a telescope with an unprecedentedly large field of view (204 square degrees), covering the UV band from 230 to 290 nm. ULTRASAT is a joint project managed and funded by the Israel Space Agency (ISA), the Weizmann Institute of Science (WIS), and DESY.

ULTRASAT will provide continuous UV light curves and early alerts, facilitating ground-based optical and infrared spectroscopy to capture the evolving signatures of transient events. Its combination of rapid response and high sensitivity in the UV spectrum will offer unique insights into the physics of the transient universe.

ULTRASAT’s ability to detect and monitor transient events across such a wide field in real-time represents a significant advancement in UV astronomy. The extra-Galactic volume accessible to ULTRASAT for discovering transient sources will be 300 times larger than that of the most sensitive UV satellite to date, GALEX. Its coverage will be comparable to that of the Large Synoptic Survey Telescope (LSST), a major ground-based optical survey expected to become fully operational in 2024.

ULTRASAT's primary scientific goals include:

• Gravitational Wave (GW) Counterparts: Detect electromagnetic counterparts of GW events involving neutron star mergers, providing insight into the origin of heavy elements and the expansion rate of the universe.
• Supernovae: Early detection and continuous monitoring of supernovae to understand their explosion mechanisms and light curves.
• Variable and Flare Stars: Study variability patterns and flaring activity in different stellar populations.
• Active Galactic Nuclei (AGN): Monitor AGN variability and explore accretion physics.
• Tidal Disruption Events: Capture the early UV emission from stars torn apart by supermassive black holes.
• Compact Objects and Galaxies: Investigate the UV properties and variability of compact objects and galaxies.

The satellite features a UV telescope built by Elbit/Elop, which features a 204-square-degree field of view, providing a wide-angle survey capability in the UV band. The UV camera, developed by DESY Zeuthen, operates in the 230–290 nm wavelength range, capturing transient UV sources with high sensitivity. All data will be transmitted to the ground in real-time, with transient alerts distributed to the scientific community within 15 minutes, enabling rapid follow-up by ground-based telescopes.

The spacecraft is being constructed by Israeli Aerospace Industry (IAI), while the telescope and UV camera are being developed by Elbit/Elop and DESY Zeuthen, respectively. Mission operations will be handled by IAI, with science operations — including data processing, transient alerts, and data products — managed by WIS.

Scheduled for launch in Q4 2027 as a secondary payload aboard a NASA-provided launch vehicle, ULTRASAT will operate in geostationary orbit (GEO) and is expected to revolutionize the study of the transient universe.

After launch and commissioning, ULTRASAT will begin a 3-year primary mission, with fuel reserves sufficient to extend operations up to 6 years. The satellite will have the capability to slew to more than 50% of the sky within minutes, allowing rapid follow-up of transient events detected by ground-based GW detectors starting in 2027.