Goals: Luna 18 was to collect lunar samples and bring them to Earth.
Accomplishments: The spacecraft crashed while attempting to land on the lunar surface. Before its destruction, however, it transmitted data regarding the mean density of the lunar topsoil.
2 Sep 1971: Launch
7 Sep 1971: Lunar Orbit Insertion
11 Sep 1971: Crashed on the Moon
Mission Type: Sample Return
Launch Vehicle: 8K82K + Blok D (Proton-K no. 256-01)
Launch Site: Tyuratam (Baikonur Cosmodrome), USSR; NIIP-5 / launch site 81P
Spacecraft Mass: c. 5,750 kg
Spacecraft Instruments: 1) stereo imaging system; 2) remote arm for sample collection; 3) radiation detector; and;4) radio altimeter
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi
National Space Science Data Center, http://nssdc.gsfc.nasa.gov/
Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.
This mission was the seventh Soviet attempt to recover soil samples from the surface of the Moon and the first after the success of Luna 16.
After two midcourse corrections on 4 and 6 September 1971, Luna 18 entered a circular orbit around the Moon on 7 September at 100 kilometers altitude with an inclination of 35°. After several more orbital corrections, on 11 September, the vehicle began its descent to the lunar surface.
Unfortunately, contact with the spacecraft was abruptly lost at 07:48 UT at the previously determined point of lunar landing. Impact coordinates were 3°34' north latitude and 56°30' east longitude, near the edge of the Sea of Fertility. Officially, the Soviets announced that "the lunar landing in the complex mountainous conditions proved to be unfavorable." Later, in 1975, the Soviets published data from Luna 18's continuous-wave radio altimeter that determined the mean density of the lunar topsoil.