Russia’s beleaguered space science program is hoping for a rare triumph this month. Spektr-RG, an x-ray satellite to be launched on 21 June from Kazakhstan, aims to map all of the estimated 100,000 galaxy clusters that can be seen across the universe. Containing as many as 1000 galaxies and the mass of 1 million billion suns, the clusters are the largest structures bound by gravity in the universe. Surveying them should shed light on the evolution of the universe and the nature of the dark energy that is accelerating its expansion.
First proposed more than 30 years ago as part of a Soviet plan for a series of ambitious “great observatories” along the lines of NASA’s Hubble Space Telescope, Spektr-RG fell victim to cost cutting in cash-strapped, post-Soviet Russia. But the roughly €500 million satellite, which will carry German and Russian x-ray telescopes, was reborn early last decade with a new mission. Its original goal was to scan the sky for interesting x-ray sources, such as supermassive black holes gorging on infalling material; now, by mapping galaxy clusters, it would find out what makes the universe tick. The new goal meant further delays. “There have been many ups and downs,” says Peter Predehl, leader of the team at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, that built one of the satellite’s two telescopes. “Whenever we thought we were out of the woods, a new one came along.”
Spektr-RG was born in the late 1980s. Glasnost was encouraging Soviet researchers to collaborate with Western colleagues, and studies of SN 1987A, the nearest supernova in modern times, had demonstrated the power of x-rays for tracing such violent events. Rashid Sunyaev of Moscow’s Space Research Institute (IKI) proposed an x-ray observatory to orbit above Earth’s atmosphere, which blocks x-rays. The 6-ton mission soon bristled with five telescopes and involved 20 institutes in 12 countries, including the United States. But after the collapse of the Soviet Union, Roscosmos, Russia’s space agency, struggled to keep its Mir space station aloft and contribute to the growing International Space Station (ISS). “They told us the spacecraft was too large for Russia, too ambitious,” says Sunyaev, now at the Max Planck Institute for Astrophysics in Garching. “It just died.”
Resurrection began in 2003 with plans for a smaller mission that would carry a U.K.-built all-sky x-ray monitor and MPE’s x-ray survey telescope, called ROSITA—which had been destined for the ISS but was grounded by the Challenger space shuttle disaster. The new impetus was cosmology. Studies of distant supernovae in the 1990s had revealed that the expansion of the universe is accelerating. Researchers wanted to know more about dark energy, the mysterious force that was causing it, and whether it varied in space or over time. Galaxy clusters are among the best indicators, says x-ray astronomer Andrew Fabian of the Institute of Astronomy (IoA) in Cambridge, U.K. “Clusters are the most massive objects in the universe, the pinnacle of galaxy formation, and are very sensitive to cosmological models.”
They are best seen in x-rays because the gaps between galaxies are filled with gas that is heated to millions of degrees as the galaxies jostle together in a cluster. By mapping the clusters, Spektr-RG “will study the evolution of the structure of the universe,” says Esra Bulbul, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who recently joined the MPE team.
The challenge was to boost the capabilities of the existing ROSITA telescope, which could only garner up to 10,000 galaxy clusters. Discussions led to a €90 million “extended” eROSITA, paid for by MPE and the German Aerospace Center, DLR. It is an array of seven identical telescopes with five times the effective collecting area of the original instrument. Russia and Germany signed an agreement in 2007 with launch penciled in for 2012.
But mission development was not smooth. The U.K. instrument failed to win funding and was replaced with a Russian telescope that will complement eROSITA by detecting scarcer “hard” x-rays. Though harder to collect, those higher energy photons are particularly useful for seeing the supermassive black holes at galactic centers, because they pierce the clouds of gas and dust that shroud them.
Making the mirrors for eROSITA posed another challenge. Because x-rays would penetrate a flat telescope mirror, focusing them requires cylindrical mirrors that gather the photons in glancing, low-angle reflections off inner surfaces. Each of eROSITA’s seven scopes contains 54 gold-plated cylindrical mirrors, nested inside one another, that must be shaped precisely to bring the photons to a focus. Making them proved so hard that the MPE team had to fire its main contractor part way through. “It almost killed us,” Predehl says.
A decision to site the telescope at a stable, gravitationally balanced point beyond the moon, outside the shelter of Earth’s magnetic field, meant electronics had to be hardened against solar radiation. Incompatibility between the German and Russian electronics delayed the launch, as did problems with the spacecraft’s communications system and a change in launch rocket.
Now that Spektr-RG is finally ready, expectations are high. “It’s going to be revolutionary in terms of numbers,” says IoA astronomer George Lansbury, taking x-ray studies into “the big data regime.”
It may also be a rare high point for Russia’s great observatories program. Previously, only one has made it into orbit: 2011’s Spektr-R, a radio astronomy mission that fell short of expectations and could not be revived after malfunctioning earlier this year (Science, 29 July 2011, p. 512).
Astronomers may face a long wait for Spektr-RG’s successors: the ultraviolet telescope Spektr-UV and Spektr-M, a millimeter-wave radio telescope. Spektr-UV has survived moments of near-death, most recently in 2014 when Russia’s annexation of Ukraine’s Crimean peninsula caused major Ukrainian partners to withdraw. The mission is now slated for a 2025 launch, but, Sunyaev says, some collaborators, including a German team supplying a spectrograph, have dropped out. Spektr-M, which would come next, is not yet fully funded, he says. And in the meantime, rival telescopes launched by other countries may scoop up the science the Russian missions aim to do.
“Russia is doing as much as possible with the budget available,” says Spektr-RG chief Mikhail Pavlinsky of IKI. He notes that Roscosmos’s lean budget, worth $20.5 billion over 10 years, faces multiple demands. Russia is building the landing system for the European ExoMars rover, due to launch next year, and like other countries it hopes to return to the moon, with the Luna 25 lander in 2021. For Russia’s astrophysicists, Pavlinksy says, “It means slow progress.”
Science 14 Jun 2019:
Vol. 364, Issue 6445, pp. 1020-1021
A German–Russian mission called SRG will detect millions of supermassive black holes, many new to science, and hundreds of thousands of stars.
“Have you seen your body in X-rays? It looks completely different,” says Rashid Sunyaev. “We will do the same with the Universe.” Sunyaev, an eminent Soviet-born cosmologist at the Max Planck Institute for Astrophysics in Garching, Germany, could be about to get his long-held wish.
On 21 June, a joint German–Russian mission called Spectrum-Roentgen-Gamma (SRG) will launch into space to chart an unprecedented map. It won’t be the first space telescope sensitive to high-energy ‘hard’ X-rays, which offer astrophysicists a window into otherwise faint objects in the Universe. But it will be the first able to create a full map of the sky in this part of the spectrum — one that will give researchers a new way to track the Universe’s expansion and acceleration over the aeons. “Within a half year, we will cover the whole sky,” says Peter Predehl, an X-ray astronomer at the Max Planck Institute for Extraterrestrial Physics, also in Garching, and a principal investigator for the mission.
SRG’s main scientific goal is cosmological: to create a 3D map of the cosmos that will reveal how the Universe accelerates under the mysterious repulsive force called dark energy. Cosmologists can probe this force through galactic clusters, whose distribution encodes the structure and history of the Universe. SRG will map a cosmic web of about 100,000 galactic clusters by detecting the X-ray glow from their intergalactic plasma and from the plasma filaments that join them. The mission will also detect up to three million supermassive black holes — many of which will be new to science — and X-rays from as many as 700,000 stars in the Milky Way.
“It’s going to be a great survey,” says X-ray astronomer Giuseppina Fabbiano of the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Its data will have a unique role in the field for a long time, she adds.
For Russia, SRG represents one of the most significant space-science missions for decades, and it aims to bolster the country’s astrophysics community, which has suffered decades of cuts and brain drain. The mission carries two independent X-ray telescopes: a German-built one called eROSITA (Extended Roentgen Survey with an Imaging Telescope Array) and a Russian-built one called ART-XC (Astronomical Roentgen Telescope — X-ray Concentrator), which is the first instrument of its kind in the history of Russian and Soviet space research, says Mikhail Pavlinsky, a high-energy astrophysicist at the Russian Academy of Sciences Space Research Institute in Moscow and principal investigator on ART-XC. “Now we have a new chance to return to world-class science,” he says.
The spacecraft will lift off on a Russian-built Proton-M rocket from the Baikonur Cosmodrome in Kazakhstan. X-ray sky surveys have been conducted by previous missions, including one from Germany in the 1990s, called ROSAT. But that mission was sensitive only to ‘soft’ X-rays, with energies of about 2 kiloelectronvolts (keV). Existing missions, such as NASA’s Chandra X-ray Observatory and NuSTAR, can see higher-energy radiation and resolve tiny details of cosmic structures, but they see only small parts of the sky.
SRG’s two instruments each cover X-ray bands that stretch to much higher energies: 0.2–10 keV for eROSITA, and 5–30 keV for ART-XC. (Despite its name — which was kept for historical reasons — SRG will not detect gamma radiation.) Each instrument is a bundle of seven X-ray telescopes that will frame the same swathe of sky simultaneously; their combined power means that they will collect more photons than a single telescope. X-ray photons from the sky are few and far between, so the telescopes’ semiconductor-based sensors — higher-energy versions of the sensors in ordinary digital cameras — will also be able to estimate the amount of energy contained in individual photons.
During its planned four-year mission, SRG will map the entire sky eight times, and researchers will compare the maps and look for changes. For instance, some of the supermassive black holes at galactic centres become extremely bright when they devour matter at a high rate, and then go back to relative quiescence. Although most soft X-rays from these black holes are likely to be absorbed by surrounding dust, harder X-rays should get through, says Pavlinsky. ART-XC might see the objects appearing and then disappearing again from one year to the next, providing information about how black holes consume matter. “We wish to observe several thousand of these events during these four years,” Sunyaev says.
SRG will also investigate the Universe’s distrubtion of ordinary matter and dark matter — the main engine of galaxy formation — and look for direct hints as to the nature of dark-matter particles. It will do this by trying to confirm previous signals that showed peaks in X-ray emissions from some galactic centres, which some researchers have suggested come from the decay of an unknown, heavier relative of the known subatomic particles called neutrinos. These neutrinos could be a major component of dark matter, they suggest — although this interpretation is controversial. “So far, the dark-matter explanation is still on the table” as a potential cause of the X-ray signal, says Esra Bulbul, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics and a lead scientist on the mission.
A long time coming
A hard-X-ray space mission has long been on the cards for Russian and German astrophysicists: SRG’s roots stretch back to the Soviet Union. In 1987, leading astrophysicists including Sunyaev — with his mentor Yakov Zeldovich and Andrei Sacharov — proposed a major mission using hard X-rays, but plans were cancelled after the Soviet Union fell in 1991.
The European and Russian space agencies revived the idea in 2004, but a proposal to send an X-ray telescope to the International Space Station was scrapped when NASA whittled down its space-shuttle programme, ultimately ending it in 2011. The German space agency and Roscosmos later approved a joint mission, and more ambitious design in 2009.
“There have been many, many ups and down until the whole thing really came out of the woods,” says Predehl.
Unusually, the mission has special data arrangement that aims to support Russia’s small astrophysics community. Instead of putting the data in one repository, as is typical for such missions, German researchers will store and analyse data on one half of the sky (the part west of the Galactic Centre) and Russian scientists will do the same with the other half, giving them dedicated time to work on the data, says Sunyaev. The mission will later open the data to other researchers.
В соответствии с установленным графиком работ, в монтажно-испытательном корпусе площадки 92А-50 специалисты предприятий Роскосмоса завершили сборку космической головной части (КГЧ) ракеты космического назначения «Протон-М». На аппарат «Спектр-РГ», установленный с помощью переходной системы на разгонный блок «ДМ-03», были установлены створки головного обтекателя, после чего специалисты приступили к стыковке электрических соединений КГЧ и их проверке.
В ближайшие несколько дней будет завершена общая сборка ракеты космического назначения (РКН) «Протон-М» и проведены электрические проверки её компонентов. Для обеспечения теплового режима аппарата «Спектр-РГ» на головной обтекатель установят защитный термочехол и РКН «Протон-М» подготовят к вывозу на техническую заправочную станцию для заправки баков низкого давления разгонного блока «ДМ-03». Пуск ракеты-носителя «Протон-М» с разгонным блоком «ДМ-03» и российской астрофизической обсерваторией «Спектр-РГ» запланирован 21 июня 2019 года в 15:17 мск с площадки № 81 космодрома Байконур.
Материал взят с youtube канала «Телестудия Роскосмоса»
Специалисты предприятий Роскосмоса на космодроме Байконур приступили к операциям по заправке космического аппарата «Спектр-РГ» компонентами топлива, они будут продолжаться несколько дней.
Затем космический аппарат будет транспортирован в монтажно-испытательный корпус для подготовки к сборке в составе космической головной части ракеты-носителя «Протон-М».
Запуск запланирован 21 июня 2019 года. «Спектр-РГ» – проект, нацеленный на создание орбитальной астрофизической обсерватории, предназначенной для изучения Вселенной в рентгеновском диапазоне длин волн. Аппарат будет выведен в окрестность точки Лагранжа L2 системы Солнце-Земля.