The Moon-18 automatic interplanetary station was launched from the Baikonur cosmodrome on September 2, 1971 with the help of a four-stage proton-K carrier missile. On the route of the flight to the Moon on September 4 and 6, trajectory corrections were performed.
When adjusting to the Moon, as a result of braking with the help of CTD, on September 7, 1971, the Luna-18 automatic station entered the orbit of the artificial satellite of the moon. However, due to the methodological error, the inclusion of the CTD has passed for 15 seconds before the estimated time, as a result of which the parameters of the near-the-ring orbit after the first braking were very different from the calculated.
To ensure the landing of the station to the settlement area of the Moon, two corrections were to be carried out, and after the second correction, the height of the orbit in the periolement was to be 16-17 km. In order to save fuel, it was decided to restrict ourselves to one correction of the orbit, which was carried out outside the radiochability zone. However, as a result of the engine inclusion, instead of the calculated H π 16.9 km and H α = 123.9 km, Hπ = 93.4 km and H were actually obtained. α = 180.3 km.
As a result of the analysis of telemetry information, it was found that the pitching angle is twice as fewer due to the effectiveness of one of the stabilization engines undertaken in ~ 40 times, which did not receive the oxidant, and the thrust was formed only by the expiration of fuel. In order to correct the trajectory in the radio abuse zone, additional correction was carried out.
On September 11, 1971, a moving unit was included for the removal of the orbit. However, as a result of the abnormal work of the same engine stabilization, a fuel is overrun, and when conducting a second braking, the efficiency of stabilization engines for all three channels fell. As a result, the angle of the roll turned out to be 10 ° less than the calculated value, which resulted in unroyed emergency conditions of descent to the surface of the moon.
Communication with the spacecraft stopped on September 11, 1971 at 10 hours 47 minutes 16.5 seconds. According to the calculations, the Moon-18 station reached the surface of the moon in the area of the mainland surrounding the sea of abundance, at a point with coordinates 3 ° 34 ‘p. NS. and 56 ° 30 ‘in. d.