俄罗斯天基射电望远镜Spektr-M遮阳伞主体结构成型

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Russia embarks on a most complex space observatory project yet

Origin of Spektr-M project

After several decades of efforts, Russia launched a large orbital radio-telescope called Spektr-R Radioastron in 2011. It featured a 10-meter antenna designed to work in tandem with ground radio-telescopes in order to capture accurate radio "portraits" of remote objects in the Universe. From the outset of the project, Russian radio-astronomers hoped that Spektr-R would be followed by next-generation orbital radio-telescopes designated Spektr-M Millimetron and Spektr-S Submillimetron. As their names suggested, they would be sensitive to electromagnetic waves in the millimeter and sub-millimeter range -- which is shorter than radio waves registered by Spektr-R and thus could provide astrophysics data with higher sensitivity and angular resolution. (614) As many as 10 billion objects in the Universe could be discerned by such instruments. (615)

Additionally, thanks to its sensitivity to infrared light, the Spektr-M observatory would also pick up research where Europe's Herschel infrared telescope left off after it had stopped functioning. Developers of Spektr-M promised to bring the main mirror of their future observatory to a lower temperature and provide higher resolution than that of Herschel. (616)

Spektr-M overview

According to the plan formulated by 2008, the 6,420-kilogram, 17-meter tall Spektr-M observatory would be developed by NPO Lavochkin and managed by Lebedev Physics Institute in Moscow. The spacecraft would sport a main mirror with a diameter of 12 meters, developed by ISS Reshetnev, Russia's prime developer of communications satellites. The main mirror would have a four-meter solid center dish (later reduced to three meters (615)) and a deployable peripheral dish resembling a giant flower made of 24 petals. By 2012, the diameter of the mirror was reduced to 10 meters. (613)

On its back side, the mirror would be protected with a deployable shade, which would shield it from the infrared radiation of the Sun, the Earth and the Moon. The sunshade was expected to have a diameter of 15 meters, (615) even though several early depictions of the spacecraft showed a seemingly much larger structure.

The Spektr-M telescope was expected to be sensitive to sources radiating in the millimeter, submillimeter and far-infrared range of electromagnetic spectrum. Designed for a 7-10-year lifespan, the telescope's reflector and its sensors would be cooled to 269-270C degrees by helium during the first three years, providing maximum sensitivity for its detectors. After helium inevitably runs out, deployable shades would be used to retain some of the sensitivity of the observatory during its remaining lifetime. Spektr-M was designed to work on its own as an independent observatory as well as in conjunction with Earth-based telescopes to form a so-called interferometer, or a virtual mirror extending from the space observatory to its ground counterpart. Theoretically, a pair of such orbital telescopes could further increase the quality of observations, however, only a single vehicle was funded as of 2012.

The service module of Spektr-M would be based on the Navigator platform developed at NPO Lavochkin. The spacecraft would function for five years around the L2 Lagrangian point located some 1.5 million kilometers behind the Earth relative to the Sun. It would climb and descend up to 55 degrees relative to the ecliptic latitude. Spektr-M would spend following five years in a highly elliptical Earth orbit with an apogee of 400,000 kilometers. A later source promised three years of work with active cooling and four-seven years under a sole protection of a sunshade. (615)

Spektr-M would need a heavy Proton rocket to reach its orbit, however the next-generation Angara launcher could become available by the time the project would reach the launch pad in 2020s.

Development

The development of the Spektr-M observatory poses enormous engineering challenges. To make the telescope to be sensitive to this particular wavelength requires a super-efficient cooling system. Additionally, the main mirror would have to maintain its perfect shape with a precision of 0.01 millimeters for years, despite all stresses of space environment. Finally, the spacecraft would also need an advanced orbit measurement, orbit correction and the attitude control system providing an unprecedented guidance accuracy. To make it possible for the Russian industry to tackle these technical problems, the development of Spektr-M was planned to come on the heels of Spektr-R, Spektr-RG, Spektr-UF and Gamma-400 projects, which promised to give Russian scientists and engineers critically needed first-hand experience and know-how.

Early work on Spektr-M started in 2008 and by the end of 2010, Lebedev Physics Institute, FIAN, and ISS Reshetnev completed the preliminary design for the architecture and systems of the Spektr-M spacecraft. (458) The preliminary design for the overall project was to be defended at the end of 2010 (615), however the process was apparently delayed by around a year. (616) As of 2008, the mission was expected in 2014-2015. (299) In July 2011, a newly appointed head of the Russian space agency, Vladimir Popovkin, confirmed a previously quoted launch date for Spektr-M in 2017 or 2018. At the beginning of 2012, the head of NPO Lavochkin said that Spektr-M would follow Gamma-400 project, which itself was not expected to fly before 2018. At the same time, unofficial sources did not expect Spektr-M to lift off before 2020. On August 12, 2012, a presentation by NPO Lavochkin confirmed that Spektr-M had been expected to fly in 2020. Yet another source promised the launch in 2022.

By October 2012, ISS Reshetnev completed studies into the choice of structural materials, the design of the thermal control system, the telescope's components (all intended to work at temperatures near minus 269 degrees C) and ground test equipment for scientific payloads. ISS Reshetnev conducted this work in cooperation with Kirensky Physics Institute; Design and Technological Institute of Scientific Instrumentation of the Siberian Branch of the Academy of Sciences and Vekshinsky Vacuum Technology Institute. The results of these studies were then transferred to the Astronomy Center of the Lebedev Physics Institute, FIAN. According to ISS Reshetnev, it planned to manufacture and test components of the observatory during 2013-2015, based on the new agreement with FIAN expected to be signed within two months.

One of the challenges facing ISS Reshetnev was the choice of the material for the main mirror. Despite high strength and stability of beryllium, that NASA chose to manufacture the main mirror of James Webb Space Telescope, Russian developers found the metal too expensive and complex, given the fact that the only production facility in the former USSR capable of producing beryllium was located in Kazakhstan. Another material of choice for telescope mirrors -- silicon carbide -- was ruled out as too heavy for a space-based observatory. Instead, by 2010, FIAN proposed to manufacture the mirror out of a carbon-based plastic. At the time, ISS Reshetnev was yet to confirm that the material would remain stable at the temperatures as low as minus 270 C. (615)

In May 2013, ISS Reshetnev reported that it successfully tackled the technology necessary for the production of carbon-plastic petals for Spektr-M's reflector. The new technology would enable to double the strength and cut in half the mass of the structure, the company said.

During the summer of 2013, a group of astrophysics from FIAN visited ISS Reshetnev to draft a development roadmap for the Spektr-M project for the next three years. The scientists also toured the so-called Antennas and Feeders Facility, AFU, at Reshetnev that was expected to be used for the assembly the telescope's deployable mirror. (665)

In the first half of 2014, ISS Reshetnev started assembly of a full-scale mockup to demonstrate the deployable sunshade for Spektr-M.

International participation

As of 2011, Russian scientists working on Spektr-M reported contacts with NASA, German and Italian Space Agencies, as well as negotiations with Spanish institutions. (616)

(To be continued)