“It is a scientific breakthrough project that will place Israel at the forefront of astronomical research, position it as a rising force in the field of scientific satellites and provide excellent exposure to the Israeli industry,” says Professor Eli Waxman, astrophysicist at the Weizmann Institute of Science, principal investigator of the ULTRASAT mission and one of the fathers of the first Israeli space telescope, which is planned to be launched in 2025. “The beautiful thing about this mission is that it is led by science. We have set goals that are at the forefront of science, and to achieve them we have to be the first and the best.”
Transient Events, Radiation Flares
The idea of an Israeli space telescope was born more than a dozen years ago, during a conversation between Prof. Waxman, Weizmann Institute scientists and Zvi Kaplan, head of the Israeli Space Agency (ISA) at the time, who strove to advance groundbreaking science that would be based on Israeli satellites. The Israeli team began to discuss the matter with colleagues from Caltech (California Institute of Technology), and have reached the conclusion that the main existing gap in observational astronomy is in the ability of real-time detection of short-lived and fleeting cosmic events, such as supernovae and large star explosions, gamma-ray outbursts or neutron star mergers. The only way to study such events, which may last a few weeks or a few days, and sometimes even less, is by detecting them in real-time, and subsequently aim multiple telescopes of diverse capabilities, both ground and space-based, in the relevant direction. However, space is huge and the chances of detecting such an event in real-time through random observations are quite slim. Thus, the idea was to launch a wide-field space telescope, that is, a telescope that can, at any given moment, image a relatively large part of the sky, enabling its operators to detect such fleeting events, which astrophysicists term 'transient', in real-time.
The next stage consisted of selecting the type of radiation that the telescope would be able to detect. Stars emit electromagnetic radiation at all frequencies, from X-rays and gamma rays, through visible light to radio waves. The researchers eventually decided to choose a telescope that will detect ultraviolet (UV) radiation. “There are many wide-field sky surveys, but there are none in ultraviolet radiation”, explains Dr. Yossi Shvartzvald of the Weizmann Institute of Science, ULTRASAT Project Scientist. “This telescope is spearheading real-time astronomy. Thanks to the advanced technology and the instant communication, we can, within 15 minutes of identifying a transient event by the ULTRASAT telescope, determine the event’s location with high accuracy and aim more telescopes at it.”
“Ultraviolet radiation is emitted by ‘hot’ astronomical phenomena, such as collisions of supermassive bodies, such as black holes or neutron stars, explosions of stars as well as other phenomena” explains Dr. David Polishook of the Weizmann Institute of Science, coordinator of scientific communication of the ULTRASAT mission. “We cannot detect this radiation with telescopes on Earth, as it is filtered by the atmosphere, and we, therefore, have to use a telescope that is located in space.”
Weizmann Institute scientists, together with Caltech scientists, who were to build the satellite’s unique UV camera, later to be joined by NASA’s Jet Propulsion Laboratory (JPL), have submitted to NASA (National Aeronautics and Space Administration) several joint proposals for the development of the telescope. However, the proposals were not selected for development. Eventually, an agreement was reached with the German Electron Synchrotron, DESY (Deutsches Elektronen-Synchrotron) that it will provide a camera, which is one of the most expensive components in the telescope, in exchange for assignment of DESY scientists to the telescope’s research teams. The rest of the funding will come from the Weizmann Institute of Science (WIS) and from the Israel Space Agency (ISA), which operates under the auspices of the Ministry of Science and Technology.
Several cutting-edge companies from Israel’s technological sector have joined the complex project, the total cost of which is estimated to be around 100 million dollars. Among these companies are Elbit-owned ELOP (Elbit Systems Electro-Optics), in charge of building the telescope itself, Tower, together with AnalogValue, responsible for developing the camera's light detectors, which are set to effectively capture UV radiation, and IAI (Israel Aerospace Industries), in charge of the design and construction of the satellite itself and of its computer.
Innovation to Suit Every Pocket
A space telescope is a telescope mounted on a satellite orbiting the Earth, or in some cases the Sun, as in the case of the James Webb Space Telescope, launched in late 2021. Such telescopes have several important advantages: their activity is not limited to nighttime, they are unaffected by clouds and weather, and most importantly: the satellite is located above the atmosphere, which normally distorts the passage of certain forms of radiation and completely absorbs several types of radiation, such as ultraviolet radiation. “This filter is essential for the protection of life on Earth, but it is giving a hard time to astronomers,” says Polishook.
Alongside these advantages, space telescopes also have drawbacks. They are limited in size, can usually operate only for a few years before they begin to malfunction due to the rough environment, and the possibility of repair or maintenance in the case of malfunctions is nearly nonexistent. Another major drawback is their high cost, compared to ground-based telescopes. The cost of developing the James Webb Space Telescope, which also broke records in this field, has increased over the years to more than ten billion dollars. ULTRASAT’s budget is only about one percent of that.
"We are proving that it is possible to carry out missions with an achievable budget and be at the forefront of science, thanks to the precise and innovative design of the telescope” Eli Waxman emphasizes. “An example of this is the unique structure of the telescope constructed by ELOP as well as the UV sensors, developed in collaboration with Tower company. The appropriate technology required for building them did not even exist up until a few years ago”. The sensors, which are the heart of the telescope’s optical system, will enable it to detect ultraviolet light in the short range (at wavelengths of 230-290 nanometers), with much higher sensitivity compared to other UV telescopes. “There are very few substances that transmit UV light. Together with Tower, we developed several dedicated coatings for optimal filtering of the radiation, we have produced three such [UV transmitting] materials, and based on multiple experiments with them, we developed a light filter consisting of several layers of materials, each of a different thickness, tailored specifically for this purpose” Yossi Shvartzvald explains.
Collisions and Explosions
Another significant innovation in the telescope is the width of its field of view: 200 squared degrees. “For comparison, the diameter of the full moon in the sky is roughly half a degree”, notes David Polishook. “Such a wide field of view allows the telescope to capture a very large part of the sky at every shot.”
The main mission of ULTRASAT is to identify and study those short-lived or transient events that occur in the universe. These are events that occur rapidly by astronomical standards, from a few weeks to a few days, hours or minutes. Among these types of events are collisions of particularly heavy (supermassive) bodies, such as black holes and neutron stars.
Research into such phenomena has gained momentum in recent years thanks to the ability to identify them using gravitational wave detectors, albeit the many limitations of such detectors. “Thanks to ULTRASAT’s technology, which combines a wide field of view with depth sensitivity, it can determine, with an accuracy higher than that of those detectors, the location and distance of such events”, explains Schwarzvald. “We can turn the telescope towards the event within 15 minutes of receiving a gravitational wave detector alert. This allows us to both image the first stages of the event, which include increased emission of ultraviolet radiation, as well as to immediately notify the global astronomical community as to the event’s precise location, which will allow a wide range of telescopes and other measuring systems to be aimed at it. Our data collection and international collaboration will pave the way for a better understanding of the processes that occur during such collisions and of their impact.”
Other types of cosmic events that can be studied using the space telescope are the supernovae - explosions of large stars, occurring at the end of their lives. Once stars of certain sizes exhaust their nuclear fuel, their core collapses inwards rapidly, an event that results in a massive shockwave and a giant explosion of the star. These explosions have a substantial impact on life in the universe as we know it since they are the likely source of a large part of all heavy elements in the universe, including those elements, which constitute the building blocks of life.
One of the difficulties in studying supernovae is the ability to detect and study these explosions in real-time before their remains disappear. “Large quantities of UV radiation are emitted in these events, mainly during their first stage”, explains David Polishook. “Thanks to its wide field of view, ULTRASAT can detect many of these events, image them sequentially and instruct additional telescopes to be aimed at them. We expect to identify about 250 supernovae per year using ULTRASAT, and to be able to monitor the earliest stages of such events, thanks to sequential imaging. This research will finally allow us to understand the mechanisms of explosions of different types of supernovae and the energy regimes of these processes.”
Among its “housekeeping” day-to-day functions, between measurements of such events, the telescope will be used to survey the sky for objects that emit ultraviolet radiation. It will image the sky every five minutes and gather data regarding millions of stars and other celestial bodies. This will allow the researchers to gather massive amounts of data, and to create a basic map that will allow for comparison with newer images, and thus enable quick identification of newly occurring events. Thanks to the high-speed imaging and its high capabilities, the telescope is expected to increase the rate of detection of transient events 300 fold, and provide researchers with a goldmine of data for studying many phenomena.
The telescope’s extensive scientific team includes dozens of researchers from Israel and other countries, organized in 13 work teams, in order to take advantage of the telescope's many capabilities. One of these work teams, headed by Schvarzvald, will study other solar systems and their planets. “Observations in ultraviolet light will allow us to identify which solar systems may be suitable for life, in terms of the level of radiation emitted by their respective stars”, explains Schvarzvald. “Additionally, we will be able to try to identify new planets outside our solar system, and try to characterize the atmospheric composition of planets in other solar systems.”
Another group will make use of ULTRASAT’s observations to study the events that occur when a particularly large (‘supermassive’) black hole swallows stars, effectively tearing them up, in a process that also emits UV radiation that can be detected by the telescope, and through it better understand the mechanisms underlying the process. Another group will study quasars, celestial bodies that emit large amounts of energy. An additional group, led by David Polishook, will focus on using the telescope to study our solar system, mainly to distinguish between different types of asteroids by their pattern of reflection of ultraviolet radiation, which reflects their iron content.
The ULTRASAT telescope will be installed on a satellite that weighs roughly one ton. About half of the weight is fuel, which will allow it to enter orbit after it is launched, at an altitude of 36 thousand kilometers. Objects at this altitude complete a full circle around the Earth within 24 hours, which, naturally, is the time that takes Earth to revolve around itself. This means that such a satellite is constantly hovering above a specific location on Earth, and so it is called a geocentric orbit, meaning “stationary relative to Earth”. On such a trajectory we will usually find communication satellites since it allows for stable and continuous communication with ground stations. This is precisely the reason why ULTRASAT will be sent to such a location. From there it will be able to transfer data in real-time to the ground station, which will relay the data to the control room that is under construction at the Weizmann Institute of Science. Thus, upon any identification of a significant transient event, it will be possible to aim the telescope at it almost instantly.
The launch of the telescope is scheduled for early 2025. Once it enters orbit, the first months of the mission will be devoted to an initial sky survey, in order to compile a reference map that will allow it to identify future events. The satellite is expected to operate for 3-6 years overall, providing a wealth of rich scientific data, which will fill many gaps in our knowledge of the universe and its mysteries. At the end of the mission, the satellite will use the remainder of its fuel to launch itself into a higher orbit, which will ensure that it will not hit another object nor produce additional space debris in the future.
“It will be very exciting to see the images from this satellite. There were many steps along the way where we could have despaired and given up, for example, every time that our proposal was not approved, and it took a lot of determination and faith to keep all of our collaborators and carry on”, says Waxman. “It is a very gratifying feeling to have made it this far, and it is going to happen. Almost all of the astronomers in Israel are collaborators on this project, and all of Israel’s astronomy will change as a consequence of it.”
“The collaboration on this project is exceptional. It is the largest collaboration of its kind between industry and academia in Israel, and there is also a unique collaboration between the scientists themselves” adds Schwarzvald. “There is plenty of competition between scientists, but we are all trying to succeed together, with the common goal of better understanding the universe.”
In addition to the scientific mission of the space telescope, it also has an educational mission, led by the Davidson Institute for Science Education, the educational branch of the Weizmann Institute of Science. “I think that the telescope will have a meaningful educational impact”, says Waxman. “ The great exposure it generates will promote scientific and technological education, help encourage young girls and boys to study science and engineering, and will contribute to expanding the civic space community in Israel.”
Long before ULTRASAT is ready to set out on its historic path, and observe distant places in the universe, Waxman and colleagues are already looking much further. “We are aiming at having an Israeli space telescope in space at all times, and are already thinking of the next project, perhaps a wide-field X-ray telescope”’ concludes Waxman. “Israel has to launch such a satellite every five years. We will prove that it is possible to achieve this with a budget of this magnitude, and to march science forward.”
