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The Russian Academy of Sciences and the Russian Federal Space Agency are planning to launch Radioastron in 2011, which is a unique space observatory with a 10-meter reflector antenna. In conjunction with the largest ground-based radio telescopes and tracking stations, it forms the first system that will be able to carry out studies with a resolution millions of times greater than that of eyesight.

The space interferometer Radioastron is working jointly with the largest radio telescopes of the world. Ground tracking stations provide for retrieving the information and determining the orbital parameters for data processing centers. The project is aimed at systematic studies of images of radio emitting regions, their coordinates, and time-dependent variations near super-massive black holes in galactic nuclei, stellarmass black holes, neutron and quark stars, regions of star and planet formation in our and other galaxies, the structure of interplanetary and interstellar plasma, and the Earth’s gravitational field.

The Russian Academy of Sciences and Federal Space Agency, together with the participation of many international organizations, worked toward the launch of the RadioAstron orbiting space observatory with its onboard 10-m reflector radio telescope from the Baikonur cosmodrome on July 18, 2011. Together with some of the largest ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna ground-space radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes, accretion disks, and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The results of ground-based and inflight tests of the space radio telescope carried out in both autonomous and ground-space interferometric regimes are reported. The derived characteristics are in agreement with the main requirements of the project. The astrophysical science program has begun., 54 pages, 11 figures; published by Astronomicheskij Zhurnal (in Russian) and Astronomy Reports (in English)

Three missions are now under consideration related to OVLBI technology: Radioastron, Millimetron and VOT. Radioastron consists of a 10-m diameter antenna and receiving complex for cm and dm ranges. This space radio telescope will operate with global network of all largest ground radio telescopes and realize angular resolution up to 30 microsecond of arc. Millimetron is the same type mission with more precise 10-m antenna for mm and cm ranges and angular resolution up to a nanosecond of arc for OVLBI mode. Second type of operation is a single dish mode for short millimeter and submillimeter observations with very high sensitivity. VOT is a VLBI optical system on a geostationary orbit for the synthesis of images in ultraviolet, optical and near infrared ranges with angular resolution up to a microsecond of arc. The array of identical freely flying satellites — telescopes with laser synchronyzation and information down-link will synthesize such images.

Large space antennas can solve some actual problems of fundamental and applied investigations. Mirror antennas of large diameters (up to tens or hundreds of meters) are designed using an automatically deployed truss frame as a base onto which the radioreflecting surface is pulled (long-wave version) or precisely controllable panels are mounted (shortwave version). The reasons are discussed why antennas of millimeter range can be promptly developed. The factors are considered that influence on the resultant precision of the reflecting surface of the space antenna: technological errors in the process of frame manufacturing; technological errors during manufacturing of the reflecting surface; deformations due to thermal or force effects. To operate in the millimeter wavelength range, it is required to design antennas with automatic control of the reflecting surface. The analysis of the mathematical model of a modular mirror leads to the conclusion about the basic possibility of its adjustment.

Great rewards for radio astronomy lie in increasing antenna collecting areas and the distance between them. Both these possibilities, which determine sensitivity and angular resolution, can be developed essentially without limit if radiotelescopes can be built in space. Radio interferometers, with base lines up to 10 AU, assembled from large reflectors 1 to 10 km in diameter, could operate in the 1 mm to 1 m range with a sensitivity of 3 × 10 −37 W m −2 Hz −1 and an angular resolution of 1.5 × 10 −10 sec of arc. These parameters are a million times better than those of modern radio astronomical systems. Such instruments could solve many urgent problems: the search for artificial radio signals and other evidence of extraterrestrial civilizations; detection and study, within the RF range, of solar-like stars and planets; and holography of astronomical sources and direct measurements of their distance. The maximum distances of objects which could be studied would be comparable with the radius of curvature of the Universe. A possible space radiotelescope (SRT) configuration, with a modular spherical reflector and feeds providing multibeam operation, is analyzed here. An extendable reflector capable of operating at any intermediate stage is assembled from 200-m modules. These consist of a three-dimensional spar framework on which flat hexagonal subreflectors of about 4 m are mounted. The precise geometry required of such a reflector is provided by automatic adjustment of subreflector position relative to the framework and by adjustment of connections between modules. In this way, radiotelescopes for the 1 mm to 1 m range may be built with diameters up to 10 km. The problems of system delivery and assembly in orbit are assessed. Preliminary estimates for developing and constructing an SRT that is more than 1 km in diameter are lower than for a similar collecting area on Earth. State-of-the-art technology already allows the development and construction of a 200-m space module.