Nikolai Semyonovich Kardashev, one of the most influential radio astronomers of the past 60 years, died on 3 August 2019 in Moscow. Born in Moscow on 25 April 1932, little “Kolya” lived with his parents only until age 5. At the peak of the Stalinist repressions in 1937, his father was executed and his mother imprisoned. Raised by his aunt, he was reunited with his mother only in 1956 after her return to Moscow from exile. Growing up, Nikolai developed a strong interest in natural sciences, especially in astronomy, and, from the age of 12, began attending a “circle of young astronomers” at the Moscow Planetarium. He would remain a devoted astronomer for his entire life.
Nikolai graduated from the Department of Astronomy of Moscow State University in 1955. He was at the first class to hear lectures on radio astronomy by the young and energetic Iosif Shklovsky. Nikolai was captivated by the beauty of this new science and, no less, by Shklovsky’s charisma and enthusiasm. For the next 30 years, until Shklovsky’s death in 1985, the teacher and his student remained close colleagues and friends.
In 1963, under Shklovsky’s supervision, Kardashev presented his “candidate of science” (PhD) dissertation composed of several topics. In one chapter he discussed the evolution of cosmic radio source spectra and demonstrated that the spectral shape of the synchrotron radiation depends on the age of the radio source. This analysis became the basis for radio astronomy studies around the world. In another chapter Kardashev described the radio recombination lines phenomenon. The discovery of those lines would be achieved several years later. Nikolai’s thesis was promoted to the higher level of doctoral thesis (“doctor of science”) in 1965, an analog of full professorship, and in 1988, Kardashev shared the USSR’s State Prize for the discovery of radio recombination lines.
In 1964 Kardashev published a paper discussing the behavior of a magnetic field of a collapsing star that results in the formation of a neutron star. Pulsars, de facto predicted in this paper, were discovered three years later.
Up until the 1960s, radio astronomy suffered from an inferior resolution compared with optical astronomy. In 1965, Leonid Matveenko, Nikolai, and Gennady Sholomitsky foreshadowed the development of very long baseline interferometry (VLBI), replacing conventional radio transmission lines with magnetic tape recordings. This technique, which ultimately surpassed the angular resolution of optical astronomy by three orders of magnitude, was demonstrated in Canada and the US two years later.
The 1960s saw the development of a new field of astronomy concerned with extraterrestrial life and civilizations. Shklovsky’s 1962 book, Universe, Life, Intelligence, marked the beginning of active theoretical and experimental SETI studies in the USSR. Nikolai’s 1964 paper presented the classification of civilizations based on their level of power consumption spanning 20 orders of magnitude and became known as the Kardashev scale.
In 1967 Shklovsky moved to the newly created Space Research Institute (IKI) of the USSR Academy of Sciences, together with Nikolai and other former students. Nikolai, who from 1977 was the deputy director of IKI, led several spaceborne radio astronomy projects, including the experiments with the radio telescope KRT-10 deployed on board the Soviet orbital space station Salyut-6.
In 1978 Kardashev initiated a project that would eventually become the Space VLBI mission RadioAstron. The implementation of this project spanned more than 30 years, which included the dissolution of the USSR and the enormous economic and social hurdles resulting from the transition from the socialist “planned” economy of the USSR to the free-market economy of modern Russia. This period also saw Nikolai become a director of the newly created Astro Space Center of the Lebedev Physical Institute. RadioAstron was finally launched in July 2011 and achieved a record-high angular resolution owing to its apogee almost reaching the Moon. The RadioAstron project, which unified virtually all the world’s VLBI radio astronomers and observatories, has become one of the highlights of modern observational astrophysics.
Kardashev was a Corresponding Member (from 1976) and a Full Member (from 1994) of the Russian Academy of Sciences. He served as the chair of the Russian Academy of Sciences Council on Astronomy (from 1999 until his last days) and vice president of both the International Committee for Space Research (COSPAR, 1982–86) and the International Astronomical Union (1997–2003). In 2012 he received the Grote Reber Gold Medal for innovative lifetime contributions to radio astronomy.
Kardashev once proclaimed his credo in the SETI context: “The concepts of morality and goodness are universal, like the Pythagorean theorem. Civilizations do not survive if they do not follow these concepts.” We still do not know whether any extraterrestrial civilization exists. But we are fortunate that Nikolai, a man who exemplified this simply formulated principle, was among us.