Russian Proton-M launches Spektr-RG observatory

[vostok]

Russia’s Proton-M rocket – after a lengthy standdown – finally launched the Spektr-RG observatory on Saturday at 12:30 UTC. Proton was expected to lift off from the Baikonur Cosmodrome last month before a delay was required to replace some faulty batteries on the spacecraft. With the aid of a Blok DM-03 upper stage, this mission deployed its payload two hours after launch.
The Spektr-RG satellite is an international collaboration led by the Russian Federal Space Agency, Roskosmos in partnership with the German Aerospace Centre, DLR, and universities and research institutes in both Russia and Germany. It is the second of three satellites in Roskosmos’ Spektr series, which aims to survey the cosmos across a wide range of electromagnetic frequencies. Spektr-RG covers the x-ray region of the spectrum.

Spektr-RG, whose name means Spectrum – Roentgen Gamma, follows the Spektr-R satellite that was launched in July 2011. Specializing in radio astronomy, the Spektr-R satellite exceeded its five-year design life but ceased operations in January 2019 after ground controllers unexpectedly lost contact with the satellite.

Attempts to restore communications continued until the end of May, at which point Spektr-R was declared lost. A third satellite, Spektr-UF, is slated to launch in 2025 and will be equipped for visible-light and ultraviolet observations.

The Spektr-RG mission will build on the research conducted by previous x-ray astronomy satellites, including the Granat observatory operated by the Soviet Union and later Russia from 1989 to 1998 and the German-led ROSAT mission that operated between 1990 and 1999.

Spektr-RG is designed to conduct a series of eight whole-sky x-ray surveys, each lasting six months, in the first four years of operation before beginning more detailed observations of specific targets of interest at high energies. The mission is expected to last at least six and three-quarter years from launch, including six and a half years of scientific observations.

Using its two x-ray telescopes, Spektr-RG’s primary mission is to find and map all massive galaxy clusters in the observable universe at x-ray wavelengths. By observing the universe at X-ray wavelengths, Spektr-RG will be able to see details that may be obscured at lower energies.
It will also look for active galactic nuclei – supermassive black holes at the heart of other galaxies – as well as regions of star formation, accreting white dwarf stars and stars with active coronas, and study x-ray emissions from the interstellar and intergalactic mediums.

Scientists hope that the satellite will help to give an increased understanding of the roles of dark matter and dark energy in establishing the structure of the universe, and of the lifecycles of supermassive black holes.

Spektr-RG was originally formulated as a Russian-led multinational research mission, slated to launch as early as 1995 with participation from the United States, Israel, Turkey and the European Space Agency. The program was canceled in 2002, but several of its instruments had already been built, including the JET-X telescope which now hangs in London’s Science Museum. Spektr-RG was reinstated in 2005 with the involvement of Germany, including a complete redesign of the satellite.

The redesigned Spektr-RG had been manifested to fly aboard a Zenit-3F rocket, however it was later moved to the Proton rocket that will carry it to orbit – the Zenit that had originally been built for the Spektr-RG mission was launched at the end of 2017 with Angola’s Angosat-1 satellite aboard instead.

NPO Lavochkin constructed the Spektr-RG spacecraft around its Navigator platform, which has previously been used for the Elektro-L series of weather satellites and the Spektr-R satellite. The bus incorporates fuel and propulsion systems and provides three-axis stabilization and control. It can generate 1,805 watts of power through twin deployable solar arrays, while the satellite communicates with the ground through an X-band antenna. Spektr-RG has a total mass at launch of 2,712.5 kilograms (5980.0 lb) including propellant.

Following launch, it will take Spektr-RG about three months to reach its operational orbit and complete initial testing and calibration. The satellite will be operated in a halo orbit around the L2 Lagrangian point between the Earth and the Sun, located 1.5 million kilometers (0.93 million miles, 0.81 million nautical miles) from the Earth in the opposite direction to the Sun.

At this point in space the interaction of the gravitational pull of the Sun and the Earth keeps a spacecraft at the same position relative to the latter. Spektr-RG will take about six months to complete an orbit around this point in space, and one year to complete a revolution around the Sun, along with the Earth.

Because it puts the Earth between the satellite and the Sun, the L2 point is ideal for spacecraft carrying sensitive instruments that must be kept at cold temperatures. For Spektr-RG this simplifies the cooling requirements for its X-ray detectors.

Spektr-RG carries two astronomy payloads: Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) and Extended Roentgen Survey with an Imaging Telescope Array (eROSITA).
The ART-XC telescope contains an optical bench with seven mirror modules, focusing incident radiation onto seven detectors at the other end of its carbon fiber structure. It was developed by the Russian Academy of Sciences’ Space Research Institute in cooperation with the Russian Federal Nuclear Centre.

ART-XC’s detectors, which use a Cadmium telluride semiconductor, measure 30 by 30 millimeters (1.2 by 1.2 inches) and are 1 mm (39 thou) thick. The mirror assemblies, each of which contains 28 individual mirror shells, were constructed by NASA’s Marshall Space Flight Center. The mirrors are comprised of a nickel/cobalt alloy with an iridium coating and arranged in a nested structure with increasing diameters to maximize the number of photons focused onto the detectors. The overall instrument has a mass of 350 kilograms (771 lb) and draws 300 watts of power from Spektr-RG.

A radiator is incorporated into the ART-XC instrument to keep the telescope’s detectors close to their design operating temperature of -20 degrees Celsius (-4 degrees Fahrenheit, 253 Kelvin), while a sunshield protects the optics. With a focal length of 2.7 meters (8.9 feet) ART-XC can observe high-energy x-rays between 5 and 30 kiloelectronvolts (wavelengths between 0.25 and 0.041 nanometres) with a 0.3-square-degree field of view and an angular resolution of 45 arcseconds.

As well as contributing to Spektr-RG’s sky survey, ART-XC will record transient x-ray events and attempt to identify their sources. It will also characterize the mass and physical properties of accreting white dwarf stars – binary systems where a white dwarf strips material from its companion star.

The eROSITA telescope is a German contribution to the mission, with the Max Planck Institute for Extraterrestrial Physics leading its investigation. Whereas ART-XC is designed to study high-energy or “hard” X-rays, eROSITA will observe lower-energy “soft” x-rays between 0.3 and 11 keV (4.1 to 0.12 nm wavelength).

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https://www.nasaspaceflight.com/2019/07/russian-proton-m-spektr-rg-observatory/