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After a mid-course correction on April 1, 1966, Luna 10, the second and backup model of two hastily prepared Soviet Ye-6S probes, successfully entered lunar orbit two days later at 18:44 UT, thus becoming the first human-made object to go into orbit around another planetary body.

A 546-pound (248.5-kilogram) instrument compartment separated from the main bus at 18:45:39 UT which was in a 217 x 631 mile (350 × 1,016-kilometer) orbit inclined at 71.9 degrees to the lunar equator.

The spacecraft carried a set of solid-state oscillators which had been programmed to reproduce the notes of the Internationale so that it could be broadcast live to the 23rd Communist Party Congress.

During a rehearsal on the night of April 3, 1966, the playback went well, but the following morning, controllers discovered a missing note and so played the previous night’s tape to the assembled gathering at the Congress, claiming it was a live broadcast from the Moon.

Luna 10 conducted extensive research in lunar orbit, gathering important data on the weakness of the Moon’s magnetic field, radiation belts, and micrometeoroid density. In 2012, a Soviet scientist made the claim that Luna 10’s achievements included “the first gamma-ray spectrometer used in the history of space research to first define the contents of natural radio nuclides in the lunar soil.”

Data from Luna 10 suggested that Moon rocks were comparable to terrestrial basalt rocks. Based on data collected by the probe, Efraim Akim (1929-2010) at the USSR Academy of Sciences identified the “noncentrality of the gravitational field of the Moon” which he argued was “the essential fact determining the evolution of the orbit of Luna 10,” as reported in an Academy journal in 1966.

Based on Akim’s claim, some sources incorrectly credit Luna 10 with discovery of mass concentrations (called mascons) -- areas of high density below the mare basins that distort lunar orbital trajectories. Their discovery, however, came much later, after the creation of a gravimetric map of the Moon (albeit at the time, only of the near side of the Moon).

Paul Muller and William Sjogren published their conclusions in 1968 based on data from the Lunar orbiters showing that very large positive gravity anomalies exist in all of the circular ringed sea basins on the Moon. The discovery of mascons thus should be credited to them.

Controllers made last contact with Luna 10 on May 30, 1966.

Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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