ULTRASAT - The ULtraviolet TRansient Astronomy SATellite is an Israeli/US collaboration to design and launch a low-cost UV time-domain observatory with an unprecedented combination of sensitivity, extremely wide field-of-view, and continuous sky coverage. ULTRASAT will open a new observational window to study transient and variable phenomena on a range of timescales, from minutes to years.

ULTRASAT is a scientific mini-satellite carrying a telescope with an unprecedentedly large field of view (230 squared degrees) observing in the ultraviolet (220-280nm,UV) that is expected to be launched to near geostationary orbit in 2020/21. The wide field of view and the UV detectors will enable the discovery and monitoring of transient sources within a cosmic volume 300 times larger than that of the most powerful UV satellite to date, GALEX.

The main goals of the mission are investigating the explosions that end the lives of stars (Supernova) and exploring the processes in massive black holes at the centers of galaxies. In addition, the satellite will provide the astronomy community with real-time alerts on discovered transient events, and explore the rich world of UV transients, including stars being "swallowed" by massive black holes, identifying the sources of gravitational-waves and high-energy neutrinos as well as following variable stars and searching for planets around dwarf stars.

The ULTRASAT initiative was born in 2010, as an attempt by Weizmann Institute and Caltech scientists together with the Israel Space Agency (ISA) to answer the question: Can the Israeli space industry's proven capabilities of building small satellites enable building a scientific satellite that will provide a breakthrough by being significantly smaller (~1m3), lighter (~100kg) and cheaper (~100M$, including launch) than most space missions. The success of ULTRASAT will be a clear and positive answer to this question, and will lead the way to future similar missions.

The science mission is lead in tandem by a Weizmann Institute team (Waxman - principal investigator, Gal-Yam, Ofek, Sagiv, Aharonson, Lapid and Topaz), and a Caltech team (Kulkarni - US principal investigator, Harrison and Smith). The technological aspect of the mission is led by IAI-MBT (responsible for building the spacecraft, integrating the telescope and mission operations, and by JPL (responsible for building the telescope, contracting the launch opportunity and data archiving), under a joint oversight of ISA and NASA. A proposal for funding the US part of the mission has been submitted to NASA as part of the Astrophysics Explorer program. A decision on funding the detailed design phase, Phase A (where the alternative of an ELOP-Elbit provided telescope will also be considered) is expected around June 2015.