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Spektr-RG to expand horizons of X-ray astronomy
Conceived as one of three Soviet "great observatories" at the end of the 1980s, the Spektr-RG could become the main window on the Universe for the nation's astronomers. However, economic storms of the post-Soviet transition were continuously delaying and crippling the project.
Above: A Spektr-RG observatory. Copyright © 2010 Anatoly Zak
Previous chapter: Spektr-R observatory
A brainchild of the astronomical section of the Soviet Academy of Sciences, Spektr-RG (where RG stands for Roentgen-Gamma) was designed for astrophysics research. The project was proposed by Academician Rashid Syunyaev, who previously led a team of scientists working with astronomical payload of the Kvant module onboard the Mir space station. According to one of the project veterans, the concept of the spacecraft was first formulated at a scientific symposium in 1987, which was dedicated to the 30th anniversary of the First Artificial Satellite. Along with Syunyaev, Soviet scientists Yakov Zeldovich and Roald Sagdeev stood at the roots of the project.
By mid-1990s, the Spektr-RG program involved a wide international cooperation, including 20 organizations from Denmark, UK, Germany, Italy, US, Finland, Switzerland, Israel, Hungary, Kyrgyzstan, Canada and Turkey.
The 6,000-kilogram spacecraft would carry 2,750 kilograms of scientific instruments, including five telescopes: SODART, JET-X, MART-LIME, FUVITA, TAUVEX, as well as all-sky monitors MOXE in SPIN sensitive to X-ray and gamma radiation. The Proton rocket had to carry Spektr-RG into a highly elliptical orbit with an apogee of 200,000 kilometers above the Earth surface, a perigee of 500 kilometers and an inclination 51.6 degrees toward the Equator. There, the satellite could work up to 80 hours at a time, free of interference from the Earth's radiation belts. It would take the satellite four days to complete a single orbit. The spacecraft could be pointed at up to 10 different targets a day. (403)
Despite considerable political pressure from international partners, including the weight of the Gore-Chernomyrdin agreements on space cooperation between Russia and the United States, the cash-strapped Russian government ultimately failed to fund the project. With much of science instruments and other hardware manufactured and tested, its launch date kept slipping from 1996 to 1997, 1998, 1999, 2000, 2002 and 2003, before the project was finally declared dead in February 2002. As early as 1998, Western partners spent $300 million on their participation in three Spektr observatories, with most of these funds going to Spektr-RG. As a "compensation" for the losses by foreign partners, the Russian government offered a Proton rocket to launch a similar European space telescope, known as Integral. Even some of the Russian scientists, who participated in the Spektr-RG project decided to "jump the ship" and banked on the European observatory instead. ESA provided Russian partners 25 percent of available observation time onboard Integral. (402) Ironically, the European spacecraft was launched without problems or considerable delays in 2002.
Rebirth of Spektr-RG
Developers of sophisticated payloads for the original Spektr-RG had to find new carriers for their instruments or surrender them to museums. Yet, with the improvement of Russian financial situation in the first decade of the 21st century, Spektr-RG was reborn as a smaller, cheaper project. Once the highest priority for launch among Russian space observatories, Spektr-RG was moved behind the Spektr-R (Radioastron) project. Both satellites were redesigned to use NPO Lavochkin's new standard spacecraft bus, known as Navigator. It would play a role of the service module for Spektr-RG and other space observatories.
In 2005, Roskosmos and ESA started discussion about possible installation of a pair of European instruments on Spektr-RG. These included a German ROSITA (Roentgen Survey with an Imaging Telescope Array) and the British Lobster Eye, LE, an all-sky X-ray monitor. Both of these instrument were originally considered for installation on the European Columbus module of the International Space Station, ISS. However concerns over the contamination of sensitive optics in the polluted environment around the ISS coupled with the premature demise of the Space Shuttle program killed these plans. To resolve the problem, the International Working Group was formed, involving representatives from the Moscow-based Space Research Institute, Germany's Max Planck Institute, University of Leicester in England, as well as from the European, Russian and German space agencies. The group evaluated various ways to cluster available payloads and, at one point, considered incorporating a yet another telescope built by a US-Japanese-Dutch team. However, ultimately, even the LOBSTER instrument had to be dropped from the project, due to lack of funding on the British side.
Finally, a Memorandum of Understanding between Roskosmos and the German Space Agency, DLR, was signed in March 2007, followed by the "Detailed Agreement," finalized at the Moscow Air and Space Show, MAKS, in August 2009. Thus, Spektr-RG became a joint Russian-German project, with a projected launch date in 2012.
The original plan was to launch a 2,000-kilogram satellite in 2011, onboard the Soyuz-2/Fregat booster into a 500-580-kilometer circular orbit with an inclination 28 degrees toward the Equator, following a liftoff from Kourou, French Guiana. Later, a Baikonur-based launch into a 600-kilometer orbit with an inclination 30 degrees was considered. Yet by 2008, a Zenit rocket, also with Fregat was deemed affordable. (By the spring of 2012, the issue remained open whether a regular Fregat or Fregat-SB version of the upper stage would be used.)
According to initial plans, Zenit-2SLBF/Fregat-SB would carry the 2,400-kilogram Spektr-RG spacecraft into a highly elliptical orbit around the Earth with a perigee of 491 kilometers, an apogee of 411,490 kilometers and an inclination 51.4 degrees toward the Equator. From there, Spektr-RG would use its own propulsion system and a gravitational pull of the Moon to reach a "halo" orbit around the L2 (Lagrange) point. However by mid-2012, this scenario was reportedly dropped in favor of a direct flight to the L2 point. In the absence of a reliable X-band trajectory measurement system, which engineers never had a chance to test during the ill-fated Phobos-Grunt mission, planners preferred to spend more time and propellant on the direct flight. Such trajectory would give mission control more time to assess the actual path of the spacecraft after the launch and to calculate the amount of orbit correction necessary for reaching the final destination. Planners estimated that three or four orbit corrections would be required during the mission.
In any case, Spektr-RG would likely be the first Russian (or Soviet) spacecraft reaching any of the Lagrange points, which considered as carrying great potential for new-generation scientific missions and, lately, as a destination for manned space flight (at least those around the Moon) and even competing with such traditional goals of astronauts and cosmonauts as bases on the Moon and expeditions to Mars. According to sources at Keldysh Applied Mathematics Institute, IPM, which plans trajectories of Russian space missions, a favorable launch window conserving the most of the propellant on a direct flight for Spektr-RG would open on Dec. 30, 2014.
The L2 (Lagrange) libration point behind the Earth relative to the Sun would be an ideal spot for the Spektr-RG mission. This celestial "neighborhood" provides "quiet" gravitational and magnetic conditions for the spacecraft without many disturbances and no traces of thin air slowing down the spacecraft in the low Earth orbit. Only miniscule "pressure" of light particles is expected to require a monthly action of the attitude control system.
The spacecraft would need around three months (116 days) to reach its final destination, where it was expected to spend at least four years circling L2 in a 40,000-kilometer ellipse on a mission to conduct a global survey of the sky. Three following years would be spent observing particular objects. (589) This flight trajectory located 1.5 million kilometers from Earth would essentially make Spektr-RG a deep-space mission, along with the Spektr-R radio telescope launched in 2011.
A project presentation made at the end of 2013, indicated that Fregat-SB would use two firings within 1.6 hours after launch to send Spektr-RG into an orbit with a lowest point (perigee) at an altitude of 1,020 kilometers and a highest point extending all the way to 1,415,510 kilometers from Earth -- essentially near the target Lagrange point. An empty external tank would be jettisoned during an interval between two firings. The transfer to the L2 point would last between 70 and 80 days.
The scientific payload of Spektr-RG was ultimately limited to two instruments -- a 810-kilogram eRosita developed at Max Planck Institute for Extraterrestrial Physics in Munich, Germany, and a 350-kilogram Russian ART-XC telescope developed by the VNIIEF nuclear research center in the city of Sarov. NASA's Marshal Space Flight Center, MSFC, would provide mirrors for all instruments.
Despite its only two payloads, project scientists promised a revolutionary data in the field of so-called high-energy astrophysics. Unlike previous orbital X-ray telescopes, such as European XMM Newton and NASA's AXAF Chandra, which were equipped with instruments with narrow angles of view, Spektr-RG would enable a wide-angle survey of the sky. Germany's eRosita, (where "e" stood for "extended" denoting much larger and powerful instrument than the originally proposed version), promised a wide-angle view at the entire range of its sensitivity and ART-XC at low-energy levels. Thus, the spacecraft could be used to compile a global map of X-ray sources, such as black holes, neutron stars and white dwarfs. According to Mikhail Pavlinsky, Deputy Director of Moscow-based Space Research Institute, IKI, Spektr-RG's eRosita would deliver sensitivity and survey depth 30 times greater than it would be possible with previous instruments. Telescope eRosita will be sensitive to electromagnetic waves from 0.3 to 10 keV and ART-XC will be registering from 6 to 30 keV.
A resulting catalog of X-ray sources could include a comprehensive list of galaxy clusters, which had formed since the formation of the Universe. For example, the German team had established a goal for eRosita to detect mind-boggling 100,000 clusters of galaxies, which are the largest known astronomical entities in the Universe bound by gravity. Such a comprehensive survey would enable to assess an evolution of the Universe and to calculate key cosmological phenomena, such as the Dark Energy. In addition, the instrument would enable to detect as many as 700,000 stars and three million of super-massive Black Holes throughout the entire Universe.
Spektr-RG could also detect radiation emitted by hot gas from "Dark Matter" sources, enabling to map the distribution of this mysterious substance around the Universe. (441)
It was expected that the spacecraft would spend first four years of its mission conducting a global survey of the entire sky and following three years watching small remote targets such as individual galaxies.
Potential challenges to scientific priority of Spektr-RG
Despite unique capabilities of Spektr-RG's instruments, the Russian astrophysicist S. B. Popov noted that scientific results of the observatory's mission could be diminished by delays of its launch beyond 2014. For example, potential discoveries in the field of cosmological models and large-scale structures in the Universe could be achieved with alternative instruments operating in far-infrared or sub-millimeter range of spectrum. Such data could be obtained with the European Planck orbital observatory or even with some powerful ground-based telescopes, such as South Pole Telescope.
An improved funding of the Russian space program after 2005 finally gave some confidence to developers that Spektr-RG would eventually fly. Still, the overall poor state of the Russian space science program, particularly problems in the construction of the hardware and payloads, kept pushing the launch date for the "reborn" Spektr-RG years behind schedule. Some "unfeasible ideas" in the configuration of the spacecraft were also cited by project sources as reasons for delays.
In 2004, the launch was promised in 2006, then it was delayed to the end of 2007 and 2008. In 2008, the launch was set for Nov. 20, 2011.
As of August 2009, the earliest possible launch date for Spektr-RG was considered at the end of 2012, however by December 2010, despite , but it was likely to slip to the first quarter of 2013. (441) At the beginning of March 2011, the mission was promised to lift off in September 2013, however by December of the same year, the launch was set for Nov. 13, 2013. According to NPO Lavochkin, a three-day launch window would be available every three days.
Following the Phobos-Grunt launch fiasco, all planetary exploration and science projects in Russia faced uncertain future. The mission to Phobos was to test an X-band deep-space communications system for Spektr-RG. Following the loss of the spacecraft, NPO Lavochkin considered trials of the X-band package on a small-size MKA-FKI satellite (the second or third satellite in the MKA series). Combined with delays in the delivery of Spektr-RG's scientific instruments, the launch date for the observatory slipped to 2014.
In November 2012, a representative of IKI's high-energy astrophysics department Mikhail Pavlinsky told RIA Novosti that the radio-systems onboard Spektr-RG would be re-worked to make them compatible with Western ground stations, which could back up the Russian ground control.
In the meantime, ISS Reshetnev in Zheleznogorsk revealed its work on the contract with NPO Lavochkin on the development of a guiding mechanism for the high-gain antenna on Spektr-RG and Luna-Glob missions. The flight version of the guiding mechanism for the antenna on Spektr-RG was scheduled for delivery to Lavochkin in 2013, ISS Reshetnev said. The same company was also building solar panels for the spacecraft.
By the spring of 2012, the VNIIEF nuclear center in the town of Sarov manufactured and tested a full-scale mass and thermal prototype of the main telescope and was working on the second (engineering) prototype of the device. A representative of the center Dmitry Litvin promised to start the construction of a fully functional ground equivalent as well as the flight version of the instrument before the end of the year. (568)
At the end of May 2012, the schedule called for the vibration tests of the Spektr-RG engineering model equipped with development mockups of main instruments to start in June or July. At the same time, development versions of Russian and German telescopes for Spektr-RG were scheduled for delivery in June and September respectively to pave the way for integrated tests. Vibration trials would be followed by electrical tests also before the end of 2012. In the meantime, the shipment of the flight version of the German-built eRosita telescope to Russia was planned for June 2013, followed by the delivery of Russian-built ART-XC in October of the same year. This timeline would enable the launch of the mission in the fall of 2014.
In September 2012, NPO Lavochkin finally published its first press-release on the status of the Spektr-RG project, announcing that it had currently conducted testing of the antenna system on the prototype of the spacecraft. According to the company, a prototype of the spacecraft for testing of its structural strength and design was manufactured. Static and transportation tests had been completed and vibration tests had been underway, Lavochkin said. In parallel, testing of the thermal-control system had been completed on the flight prototype of the spacecraft, while the assembly of another "prototype for flight testing" had been underway, Lavochkin said. The company also announced that Space Research Institute, IKI, in Moscow had manufactured the technical version of the ART-XC telescope for the spacecraft and was preparing to ship it to NPO Lavochkin. The press-release was accompanied by an undated and uncaptioned photo apparently showing one of the prototypes of the Spektr-RG observatory.
Mechanical tests of the observatory were conducted from September to December 2012.
Speaking at a conference on astrophysics in December 2012, Mikhail Pavlinsky, Deputy Director for Science at Moscow-based Space Research Institute, IKI, and the head of high-energy astrophysics department, said that the project had been moving forward quite slowly and the launch date for the mission had moved to the third quarter of 2014. Final tests of the spacecraft were scheduled for April 2014. At the same conference, a leading engineer at NPO Lavochkin Ilya Lomakin promised the delivery of the spacecraft to the launch site in the third quarter of 2014 and the launch in the fourth quarter of the same year.
By the end of May 2013, new problems required to postpone the launch of Spektr-RG from the end of 2014 to 2015. On the Russian side the biggest obstacle was presented by an X-band radio communications system for the spacecraft. According to project sources, NPO Lavochkin was considering to switch from a movable High-Gain Antenna on the spacecraft to a less-capable Medium-Gain Antenna.
On July 16, NPO Lavochkin announced that the service module for the observatory had been fully assembled with all its hardware for the exception of the radio complex, which was represented by a test version. The systems went through radio and electric tests at the company's test and checkout station, KIS. The test version of the Russian ART-XC telescope and an electric prototype of the eRosita telescope were going through initial acceptance tests, the company said. NPO Lavochkin was also completing a clean room facility to handle flight version of scientific payloads for Spektr-RG.
In the meantime, in Germany, developers hit a major problem during the integration of around 60 circuit boards with up to 30,000 individual components on the eRosita telescope. The latest tests reportedly uncovered previously unknown incompatibility between programmable radiation-resistant electronics and regular circuit boards, requiring a major redesign of onboard electronics, which would take at least a year and a half. As a result by July of 2013, the German team made a decision to postpone the delivery of flight version of eRosita to NPO Lavochkin from December 2013 until June 2015. The head of NPO Lavochkin Viktor Khartov publicly confirmed the delay at the end of August.
As of October 2013, electrical interface tests on eRosita were yet to be performed. Nevertheless by November 11, the German team integrated last of 432 mirror shells, completing seven Flight Mirror Modules of eRosita and one Spare Module.
Specifications of science instruments onboard Spektr-RG (589):
Spektr-RG development team:
Expected total targets cataloged by Spektr-RG:
Writing and photography by Anatoly Zak
Last update: April 9, 2014
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The original architecture of the Spektr-RG spacecraft planned during 1990s. Credit: IKI
Spektr-RG's sophisticated JET-X telescope became a museum exhibit. Click to enlarge. Copyright © 2010 Anatoly Zak
A one-to-four model of the Spektr-RG satellite. Click to enlarge. Copyright © 2010 Anatoly Zak
A European-built eRosita telescope designed for the Spektr-RG mission. Click to enlarge. Copyright © 2009 Anatoly Zak
A general layout of the eRosita instrument. Credit: Max Planck Institute
A hexagon-shaped Navigator spacecraft bus was expected to serve as a base of the Spektr-RG mission. Credit: IKI
The Spektr-RG observatory is expected to watch the Universe from the L2 position located "behind" the Earth relative to the Sun as illustrated in this graphic. Credit: Credit: Max Planck Institute
A photo released on Sept. 18, 2012, apparently showed one of the full-scale prototypes of the Spektr-RG observatory. Credit: NPO Lavochkin
The assembly of eRosita telescope circa 2012. Credit: Max Planck Institute
The ART-XC telescope during testing circa 2012. Credit: Max Planck Institute