Luna Ye-6

Ye-6 (Cruise)

Ye-6 (Surface)

The Ye-6 series was the first soviet attempt to perform a soft lunar landing. The 12th flight, Luna 9, finally achieved this goal with the first soft landing on an celestial body.

The Ye-6 probes consisted of a cruise stage, performing attitude control, mid-course correction and retro-fire manoeuveres and a small landing capsule.

The landing capsule had a weight of 99 kg and used cushioning air bags to soften the residual speed of about 22 km/h. The hermetical sealed capsule contained battery power sources, radio equipment, program timing device, heat control systems, a radiation detector and a television system. After landing, the capsule deployed four petals to put the probe in an upright position.

The probes were launched by Molniya launch vehicles into a highly elliptical geocentric orbit intersection with the lunar orbit.

Luna (4c) (Ye-6 №2) was launched on 4 January 1963, but the upper stage malfunctioned, which resulted in its ullage motors failing to ignite when the stage began its start-up sequence, sixty six minutes after launch. It remained in low Earth orbit until it decayed on 11 January 1963.

Luna (4d) (Ye-6 №3) was launched on 3 February 1963, but failed to achieve orbit.

Luna 4 (Ye-6 №4) was successfully launched on 2 April 1963, but failed to perform a course correction manoever and therefore missed the moon, remaining instead in Earth orbit.

Luna (5a) (Ye-6 №6) was launched on 21 March 1964 and failed to achieve orbit,

Luna (5b) (Ye-6 №5) launched on 20 April 1964, but the power system on the upper stage malfunctioned 340 seconds into the flight, causing the engine to cut off before reaching orbit.

Luna (5c) (Ye-6 №9) was launched on 12 March 1965, but failed to leave orbit for its journey to the Moon due to a failure of the power supply in the control system, and was designated Kosmos 60.

Luna (5d) (Ye-6 №8) was launched on 10 April 1965, but during third stage flight, a nitrogen pipeline in the oxidiser tank depressurised, which caused a loss of oxidiser flow to the engine and resulted in the engine cutting off. The spacecraft failed to achieve orbit,

Luna 5 (Ye-6 №10) was successfully launched on 9 May 1965. During a midcourse correction manoever, the spacecraft begun spinning. A subsequent attempt to fire the main engine failed because of ground control error, and the engine never fired. Luna 5 impacted hard on the lunar surface on 12 May 1965.

Luna 6 (Ye-6 №7) was sent successfully on trajectory to the moon on 8 June 1965. A day later during a mid-course correction, the S5.5A main engine ignited correctly, but failed to cut off and continued to fire until its propellant supply was exhausted. Luna 6 made a lunar fly-by on 11 June, with a closest approach of 159,612 km.

Luna 7 (Ye-6 №11) was also successfully launched on 4 October 1965. Immediately prior to planned retro-fire during the approach to the lunar surface, the Luna 7 suddenly lost attitude control and failed to regain it, preventing the main engine from firing. It impacted the lunar surface at a very high speed on 7 October 1965.

Luna 8 (Ye-6 №12), launched on 3 December 1965, nearly succeeded. Before the scheduled firing of its retrorocket, the cushioning air bags around the landing probe were to be inflated, but a plastic mounting bracket apparently pierced one of the two air bags, causing the ejection of the air, which put the spacecraft into a spin of about 12° per second. Luna 8 temprarily regained its proper attitude, long enough for a nine-second-long retrorocket firing, but then becoming unstable again. Without a retrorocket burn long enough to reduce its velocity sufficiently for a survivable landing, Luna 8 impacted the lunar surface 6 December 1965.

Luna 9 (Ye-6 №13), launched on 31 January 1966, finally succeeded and landed softly on the lunar surface on 3 February 1966. The spacecraft bounced several times before coming to rest in Oceanus Procellarum west of Reiner and Marius craters. Approximately 250 seconds after landing, the four petals which covered the top half of the spacecraft opened outward and stabilized it on the surface. Spring-controlled antennae were deployed, and the television camera rotating mirror system, which operated by revolving and tilting, began a photographic survey of the lunar surroundings. Seven radio sessions, totalling 8 hours and 5 minutes, were transmitted, as were three series of TV pictures. When assembled, the photographs provided a panoramic view of the nearby lunar surface. The radiation detector, measured a dosage of 30 millirads per day. The mission also determined that a spacecraft ground could support a lander. Last contact with the spacecraft was at 22:55 UT on 6 February 1966.