After the Soviet Luna 10 spacecraft became the first to enter orbit around the Moon on April 3, 1966 (see “Luna 10: The First Lunar Satellite”), there was only one more achievement that was needed to completely eclipse NASA’s upcoming Lunar Orbiter missions: return pictures from lunar orbit of prospective landing sites. That responsibility once again fell on the newly independent NPO Lavochkin design bureau which, under the leadership of Chief Designer Georgi Babakin, had also built the E-6S Luna 10 as well as the E-6M Luna 9 which became the first spacecraft to return data from the lunar surface on February 3, 1966 (see “Luna 9: The First Lunar Landing”).

Mapping the Moon

Work on the Soviet Union’s first lunar orbiter was initiated by the same establishment that was responsible for the E-6 lander as well as all of the earlier Soviet space successes: OKB-1 (Experimental Design Bureau 1) under the direction of the legendary Soviet aerospace engineer, Chief Designer Sergei Korolev. Like the E-6 lander, work on the E-7 lunar orbiter began around 1960. But unlike the E-6 lander, development of the E-7 orbiter never received official government sanction. As a result of this and the huge workload at OKB-1 for higher priority crewed and planetary missions, work on the E-7 lagged far behind that of the E-6. While little is still known even today about the E-7, its mission was to study the Moon from orbit using an array of instruments including an imaging system to scout out potential future landing sites.

With the limited resources at OKB-1 being committed to the development of the 7K Soyuz series of crewed spacecraft for missions to Earth orbit and other variants bound for the Moon, in April 1965 all unmanned lunar and planetary projects at OKB-1 were officially transferred to NPO Lavochkin under Babakin. This design bureau was well known for its intensive testing and quality control of the flight hardware it built – something that was sorely needed after a frustrating string of lunar and planetary mission failures. With resources initially focused on creating an improved E-6M lunar lander, a team of Babakin’s engineers also began looking at the E-7 lunar orbiter.

With development of the E-7 lagging far behind schedule, Babakin and his team quickly decided to use modified E-6 hardware to create a lunar orbiter borrowing instrumentation and other systems where possible which had been originally developed for the E-7. For the lunar orbiter missions, the E-6 bus would be employed with the lander replaced with an orbital payload. The bottom half of the E-6 bus held the propulsion system built around a KTDU-5A retrorocket developed by OKB-2 under Alexei Isayev. This propulsion system was topped with a toroidal aluminum alloy tank filled with an amine-based fuel and a 0.9 meter in diameter spherical oxidizer tank filled with nitric acid. The total propellant load for a landing mission was about 800 kilograms. Four outrigger vernier thrust chambers provided attitude control and thrust trimming during the firing of the main engine. The propulsion system generated up to 45.5 kilonewtons of thrust and was designed to fire twice: the first time was to provide a velocity change of up to 130 meters per second for a midcourse correction to ensure that the craft would come within about 150 kilometers of its intended target. For its original landing mission, the second firing was for the final 46-second braking burn to decrease the spacecraft’s velocity by about 2,600 meters per second for the vertical descent towards the lunar surface for landing. Because the orbiter mission required a much smaller velocity change, a lighter propellant load could be carried allowing the payload to grow in mass.

On top of the propulsion module was a cylindrical equipment section pressurized to 1.2 Earth atmospheres to provide a laboratory-like environment for the equipment inside. Although this resulted in a heavier spacecraft, this standard Soviet practice simplified design and testing of spacecraft systems as well as aided in thermal control. This section contained communications equipment, power supplies, batteries as well as the control and navigation system. This section also supported the Sun and Moon sensors needed for attitude reference during the coast to the Moon. Strapped to either side of the spacecraft bus were packages containing radar equipment to initiate retrorocket fire, additional batteries and the cruise attitude control system. This attitude control system consisted of sets of nitrogen gas jets mounted on three arms that fed off of three gas bottles. Unlike the Soviet Union’s planetary spacecraft of this era, the E-6 had no solar panels and relied solely on its batteries for power during its mission.

For the E-6S lunar orbiter mission, the original 100-kilogram lander capsule was replaced with a satellite with a mass of 248.5 kilogram. Similar in design to the small Earth-orbiting scientific satellites flown as part of the Soviet’s Kosmos series, this spin-stabilized satellite was roughly cylindrical with a diameter of 0.75 meters and a height of 1.5 meters. The battery-powered satellite separated from the bus after achieving orbit to perform its scientific mission. The E-6S satellite carried many of the proposed E-7 instruments including a magnetometer mounted on a 1.5-meter boom and radiation sensors to study the Moon’s magnetosphere, gamma ray and X-ray instruments to help gauge the composition of the lunar surface, micrometeoroid detectors and an infrared sensor to measure the Moon’s thermal emissions. Radio tracking of the satellite would allow the Moon’s gravitational field to be mapped while observations of the radio signals as the satellite moved behind the Moon would allow its atmosphere to be probed.

For the new lunar mapping mission, the E-6LF variant was developed. Unlike the E-6S whose payload separated from the main bus once in lunar orbit, the payload of the E-6LF remained attached and relied on the E-6 bus for attitude control, power, communications and other support functions. Most of the equipment to support the orbital science mission was housed in a conical instrument compartment mounted on top of the E-6 bus. Like its predecessors, the E-6LF would rely on batteries to power its systems.

In addition to a suite of instruments similar to those carried by the E-6S, the E-6LF carried a pair of phototelevision cameras mounted on the side of the spacecraft bus where the radar equipment would normally be carried during an E-6 landing mission. Similar in design to those successfully tested on the Zond 3 engineering test flight which photographed the Moon during a flyby in July 1965 (see “The Mission of Zond 3” ), these cameras would secure their images on 25 mm photographic film which would then be developed automatically on board. The developed negatives would then be scanned with up to 1,100 lines (comparable to today’s HD video format) and transmitted to Earth. Conceptually, this system was similar to that employed by NASA’s Lunar Orbiter series tasked with mapping the Moon. Television-based digital imaging was still in its infancy and a photographic system offered superior resolution and data storage capabilities. With one of the cameras employing a 500 mm telephoto lens, the E-6LF could take photographs covering an area about 25 kilometers on a side from an altitude of 100 to 340 kilometers revealing features as small at 15 to 20 meters on the lunar surface.

Like the earlier E-6-series missions, the E-6LF would use the 8K78M launch vehicle developed at OKB-1. Better known as the Molniya after the communication satellite series that also employed it, the first three stages of this rocket would eventually serve as the basis of what would become the Soyuz launch vehicle still in use today. The first two stages of the 8K78M consisted of the Blok A core surrounded by four tapered boosters designated Blok B, V, G, and D. The engines of the four boosters and core would ignite on the launch pad to generate 4,054 kilonewtons of thrust. After two minutes of flight, the four boosters would shut down and separate from the rising rocket. After another 175 seconds of flight, the Blok A core would exhaust its propellants leaving the Blok I third stage to take over. The Blok I would burn for four minutes to place the E-6 payload and its Blok L escape stage into a temporary Earth parking orbit. After a short coast in orbit, the Blok L escape stage would ignite to send the E-6 on its way to the Moon. The 8K78M was 42.1 meters tall and had a liftoff mass of about 306 metric tons. At the time, it was the most powerful operational rocket in the Soviet Union.

The E-6LF Missions

On August 14, 1966 NASA’s Lunar Orbiter 1 entered orbit around the Moon. Four days later, Lunar Orbiter started its photography mission and became the first spacecraft to return images of the lunar surface from orbit (see “Lunar Orbiter 1: America’s First Lunar Satellite”). Although it had been denied the honor of being the first photographic lunar orbiter, final preparations for the launch of the 1,640-kilogram E-6LF No. 101 proceeded in order to secure photographs of potential landing sites for Soviet cosmonauts.

At 11:03 Moscow Time (8:03 GMT) on August 24, the first E-6LF lifted off from the Baikonur Cosmodrome atop of 8K78M Molniya serial number N103-43. The first three stages of the Molniya rocket successfully placed the lunar orbiter and its Blok L escape stage into a temporary 193 by 201 km orbit with an inclination 51.8°. After a short coast, the Blok L successfully ignited and sent what was now called Luna 11 on its way to the Moon.

After a midcourse correction at 19:02 GMT on August 26, Luna 11 was on course for its target point above the lunar surface. The following day as the spacecraft was passing 8,000 kilometers from the Moon, it began to align itself to fire its KTDU-5A engine. At 21:49 GMT on August 27, Luna 11 fired its main engine and entered a 163.5 by 1193.6 kilometer lunar orbit with an inclination of 27° and a period of about three hours. For the first time in the history of the Space Age, the Moon had two active spacecraft in orbit – Luna 11 and Lunar Orbiter 1.

Once in orbit, Luna 11 began taking photographs of its target areas for immediate processing and transmission back to Earth. In order to avoid a repeat of the incident with Luna 9, the transmissions were encoded to prevent eavesdroppers in the West from intercepting useful images. Unfortunately, reports indicate that all that was returned by Luna 11 were pictures of black space. Apparently a foreign object had become lodged in one of the cold gas attitude control thrusters which prevented the E-6LF from pointing its cameras. Also lost by the attitude control system failure were data from an ultraviolet spectrometer carried to assess the surface structure. Luna 11 continued on in lunar orbit for a total of 277 revolutions and was last heard from at 2:03 GMT on October 1 when its batteries were finally exhausted during its 137th communications session.

Three weeks later, the 1,620-kilogram E-6LF No. 102 was ready to attempt the lunar photography mission for a second time. At 12:42 Moscow Time (8:42 GMT) on October 22, 1966, Molniya number N103-44 lifted off. The Molniya launch vehicle successfully placed what would become Luna 12 and its Blok L escape stage into a 199 by 212 kilometer parking orbit with an inclination of 51.9° and subsequently sent it on its way to the Moon. A burn of the KTDU-5A engine the following day refined the course of Luna 12.

Once again as the E-6LF passed an altitude of 8,000 kilometers from the Moon, it began to orient itself to enter lunar orbit. At 20:45 GMT on October 25 at an altitude of 1,290 kilometers, the KTDU-5A engine ignited for 28 seconds to cut the spacecraft’s velocity from 2,085 to 1,148 meters per second. Luna 12, which now had a mass of 1,136 kilograms after burning most of its propellant, had entered a 100 by 1,740 kilometer orbit with an inclination of 15° and an period of three hours and 25 minutes.

The day after NASA’s Lunar Orbiter 1 was deliberately crashed into the lunar surface on October 28 ending its successful mission, Luna 12 began its photography mission. Target areas included Oceanus Procellarum, Mare Imbrium as well as the craters Aristarchus and Alphonsus. While a handful of photographs were revealed on Soviet television and released to the press, their quality was disappointing compared to those returned by the more capable imaging system of NASA’s Lunar Orbiter 1 and 2 (the latter of which would join Luna 12 in orbit on November 10).

After completing its photography objective, Luna 12 was placed into a slow roll of once every 255 seconds and continued making fields and particles measurements from lunar orbit. Like Luna 10 and 11, the spacecraft’s orbit was also tracked to map out the Moon’s lumpy gravitational field – a prerequisite for the precision navigation required for a manned landing. Luna 12 also carried an engineering experiment to test the electric motors and gear train of the E-8 lunar rover then under development which would be later known as Lunokhod.

After 302 communication sessions over 602 revolutions, contact with Luna 12 was lost on January 19, 1967. No more E-6LF missions were launched and, presumably, Soviet mission planners would rely on high resolution photographs from NASA’s Ranger and Lunar Orbiters to supplement ground-based photography and Luna 12 images to perform their final landing site selections. In the mean time, one last batch of E-6 variants known as the E-6LS was being prepared by NPO Lavochkin to continue mapping the Moon’s gravitational field and perform vital communications tests in support of the planned Soviet manned lunar missions.

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Related Reading

“Luna 10: The First Lunar Satellite”, Drew Ex Machina, March 31, 2016 [Post]

“Lunar Orbiter 1: America’s First Lunar Satellite”, Drew Ex Machina, August 14, 2016 [Post]

General References

Brian Harvey, Soviet and Russian Lunar Exploration, Springer-Praxis, 2007

Wesley T. Huntress, Jr. and Mikail Ya. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer-Praxis, 2011

Nicholas L. Johnson, Handbook of Soviet Lunar and Planetary Exploration, Univelt, 1979

Asif Siddiqi, Bart Hendrickx and Timothy Varfolomeyev, “The Tough Road Travelled: A New Look at the Second Generation Luna Probes”, Journal of the British Interplanetary Society, Vol. 53, No. 9/10, pp 319-356, September/October 2000

Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 5: The First Planetary Probe Attempts, 1960-1964”, Spaceflight, Vol. 40, No. 3, pp. 85-88, March 1998