From the Spektr-R project to the Spektr-M project: milestones in space radio astronomy

The main technical solutions implemented in the Spektr-R observatory (RadioAstron) and the scientific results obtained during its orbital operation from 2011 through 2019 are reviewed. General characteristics and research objectives of the Millimetron (Spectrum-M) space observatory, a development of the Spectrum-R project in the submillimeter wavelength range, are outlined. The launch of Millimetron is scheduled for the early 2030s. Research programs of both projects are led by the Lebedev Physical Institute of the Russian Academy of Sciences.