535 ISSN 0038-0946, Solar System Research, 2017, Vol. 51, No. 7, pp. 535–554. © Pleiades Publishing, Inc., 2017. Original Russian Text © N.S. Kardashev, A.V. Alakoz, A.S. Andrianov, M.I. Artyukhov, W. Baan, V.E. Babyshkin, N. Bartel, O.S. Bayandina, I.E. Val’tts, P.A. Voitsik, A.Z. Vorobyov, C. Gwinn, J.L. Gomez, G. Giovannini, D. Jauncey, M. Johnson, H. Imai, Y.Y. Kovalev, S.E. Kurtz, M.M. Lisakov, A.P. Lobanov, V.A. Molodtsov, B.S. Novikov, A.V. Pogodin, M.V. Popov, A.S. Privesenzev, A.G. Rudnitski, G.M. Rudnitski, T. Savolainen, T.V. Smirnova, A.M. Sobolev, V.A. Soglasnov, K.V. Sokolovsky, E.N. Filippova, V.V. Khartov, M.E. Churikova, A.E. Shirshakov, V.I. Shishov, P. Edwards, 2016, published in Vestnik NPO imeni S.A. Lavochkina, 2016, No. 3, pp. 4–24. RadioAstron Science Program Five Years after Launch: Main Science Results N. S. Kardashev a, *, A. V. Alakoz a , A. S. Andrianov a , M. I. Artyukhov b , W. Baan c , V. E. Babyshkin b , N. Bartel d , O. S. Bayandina a , I. E. Val’tts a , P. A. Voitsik a , A. Z. Vorobyov b , C. Gwinn e , J. L. Gomez f , G. Giovannini g , D. Jauncey h , M. Johnson i , H. Imai j , Y. Y. Kovalev a , S. E. Kurtz k , M. M. Lisakov a , A.P. Lobanov l , V. A. Molodtsov b , B. S. Novikov a , A. V. Pogodin b , M. V. Popov a , A. S. Privesenzev b , A. G. Rudnitski a , G. M. Rudnitski m , T. Savolainen n , T. V. Smirnova o , A. M. Sobolev p , V. A. Soglasnov a , K. V. Sokolovsky a , E. N. Filippova b , V. V. Khartov b , M. E. Churikova b , A. E. Shirshakov b , V. I. Shishov o , and P. Edwards q a Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia b Lavochkin Scientific and Production Association, Khimki, Moscow oblast, Russia c ASTRON Netherlands Institute for Radio Astronomy, Dwingeloo, the Netherlands d Department of Physics and Astronomy, York University, Toronto, Canada e University of California at Santa Barbara, Santa Barbara, California, United States f Institute of Astrophysics of Andalusia, Granada, Andalusia, Spain g Department of Physics and Astronomy, University of Bologna, Bologna. Italy h Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australia i Harvard–Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States j Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan k Center for Radio Astronomy and Astrophysics, Nacional Autonomous University of Mexico, Morelia, Mexico l Max-Planck-Institute for Radio Astronomy, Bonn, Germany m Sternberg Astronomical Institute, Moscow State University, Moscow, Russia n Aalto University Metsähovi Radio Observatory, Aalto University Department of Radio Science and Engineering, Helsinki, Finland o Pushchino Radio Astronomy Observatory, Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Pushchino, Moscow oblast, Russia p Ural Federal University, Yekaterinburg, Russia q CSIRO Astronomy and Space Science, Epping, Australia *e-mail: nkardash@asc.rssi.ru Received June 30, 2016 Abstract⎯The RadioAstron ground-space interferometer provides the highest angular resolution achieved now in astronomy. The detection of interferometric fringes from quasars with this angular resolution on base- lines of 100–200 thousand km suggests the brightness temperatures which exceed the Compton limit by two orders of magnitude. Polarimetric measurements on ground-space baselines have revealed fine structure tes- tifying to recollimation shocks on scales of 100–250 μas and a helical magnetic field near the base of radio emission in BL Lacertae. Substructure within a the scattering disk of pulsar emission on interferometer base- lines (from 60000 to 250000 km) was discovered. This substructure is produced by action of the interstellar interferometer with an effective baseline of about 1 AU and the effective angular resolution of better than 1 μas. Diameters of scattering disks were measured for several pulsars, and distances to diffusing screens were evaluated. The ground-space observations of sources of the maser radiation in lines of water and hydroxyl have shown that the maser sources in star-forming regions remain unresolved on baselines, which consider- ably exceed the Earth diameter. These very compact and bright features with angular sizes of about 20–60 μas correspond to linear sizes of about 5–10 million km (several solar diameters). Keywords: ground-space interferometer, very long baseline interferometry (VLBI), active galactic nuclei (AGN), quasars, pulsars, cosmic masers, interstellar scattering DOI: 10.1134/S0038094617070085 INTRODUCTION The RadioAstron mission is a ground-space very- long-baseline interferometry (VLBI) system, designed for studying the structure of cosmic radio sources at ultrahigh resolution, ensured by large interferometer baselines reaching values on the order of 360000 km.