During the opening years of the Space Age, the Soviet Union managed to score a long string of space firsts taking an early lead in the quickly developing “space race” with the United States. Among these were an impressive set of firsts involving our nearest celestial neighbor, the Moon: the first lunar flyby (Luna 1 in January 1959), the first lunar impact (Luna 2 in September 1959) and the first probe to photograph the previously unseen far side of the Moon (Luna 3 in October 1959). But even after these achievements, there were other Moon-related space firsts that were within reach.

After three failed attempts by NASA to land the first scientific package on the lunar surface during 1962 as part of the Ranger program (see “NASA’s First Moon Lander”), the Soviet Union started launching their own series of spacecraft in 1963 designated E-6 meant to deliver a 100-kilogram lander to the Moon (see “50 Years Ago Today: The Launch of Luna 5”). After a series of 11 frustrating failures over three years, Luna 9 finally succeeded with a landing in Oceanus Procellarum on February 3, 1966 securing yet another space first for the Soviet Union (see “Luna 9: The First Lunar Landing”). With this success, the focus now turned towards the next Moon-related first: the first lunar orbiter.

A Lunar Orbiter

Ironically, the first spacecraft the US launched towards the Moon in 1958 were intended to be lunar orbiters. Originally part of a USAF program, these first three Pioneer missions attempted to send a simple 38-kilogram spacecraft close enough to the Moon so that they could fire a solid rocket motor to enter orbit. Unfortunately they all failed to reach the Moon due to problems with their Thor-Able launch vehicles (see “Pioneer 1: NASA’s First Space Mission“). A follow up program using a trio of much more advanced spin-stabilized Pioneer probes launched during 1959 and 1960 using the more capable Atlas-Able rocket likewise suffered from launch vehicle problems and were even less successful (see “NASA’s Forgotten Lunar Program”). Afterwards, NASA turned its attention towards developing a new series of lunar orbiters with the goal of mapping the Moon in support of it Apollo program.

As NASA worked on the development of what would eventually become known simply as “Lunar Orbiter” (see “Lunar Orbiter 1: America’s First Lunar Satellite“), their counterparts in the Soviet Union were busy doing likewise. Work on the Soviet’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 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 crewed spacecraft like Soyuz for missions to Earth orbit and the Moon, in April 1965 all unmanned lunar and planetary projects at OKB-1 were officially transferred to a new design bureau known as NPO Lavochkin run by Chief Designer Georgi Babakin. Recently spun off from OKB-52, this establishment 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. As the last E-6 flight hardware built by OKB-1 was being prepared for launch during the course of 1965, the engineers at Lavochkin, who eventually received partially completed E-6 and E-7 hardware, had to get up to speed quickly.

After the failure of the last E-6 built by OKB-1 during the Luna 8 mission, the first Lavochkin-built unit, a modified version designated E-6M No. 202/13, was launched on January 31, 1966. Known as Luna 9, it successfully landed on the lunar surface after a three-day flight. With this success under his belt, Babakin proposed launching a lunar orbiter as a space spectacular to coincide with the upcoming 23rd Congress of the Communist Party scheduled to start at the end of March. Being the first such Congress since Leonid Brezhnev came to power, a space spectacular was desired for its propaganda value. It had been planned to launch a long-duration Voskhod 3 manned mission to eclipse NASA’s record-setting two-week long Gemini 7 mission (see “Rendezvous in Space: The Launch of Gemini 7”), but this mission was postponed due to ongoing issues with its environmental control system and concerns about the reliability of its launch vehicle. Babakin’s lunar orbiter proposal offered a workable alternative which was ideal for propaganda purposes.

Developing the E-6S

With development of the E-7 lagging far behind schedule, Babakin and his team planned instead to use modified E-6 hardware to accomplish their feat. Known as the E-6S, the engineers at Lavochkin had already expended much effort looking into how to modify this proven hardware for an orbiter mission by retaining the spacecraft bus successfully employed by the lander mission. 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 relatively short 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 would separate from the bus after achieving orbit to perform its scientific mission. Although the imaging system was not yet available, 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.

Like the E-6, the E-6S would get underway using 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 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-6S Missions

With preparation of E-6S hardware already well underway, the construction of five flight units was officially authorized by the government’s Ministry of General Machine Building on February 11, 1966. The first E-6S, designated No. 204, lifted off from the Baikonur Cosmodrome at 11:03:49 GMT on March 1, 1966 atop of 8K78M serial number N103-41. The launch vehicle successfully placed the E-6S and its Blok L escape stage into a 191 by 226 kilometer parking orbit with an inclination of 51.9°. Unfortunately, the Blok L control system malfunctioned resulting in an inability to stabilize about its roll axis which prevented the escape stage from igniting its engine. Stranded in a quickly decaying orbit, the first Soviet lunar orbiter attempt was designated Kosmos 111 and reentered the atmosphere two days later.

Undaunted by the failure, a backup orbiter and rocket were prepared for the next launch window less than a month away. Anxiety about the success of the mission was heightened by the failure of 8K78M number N103-38 during a Molniya satellite launch attempt on March 27, 1966. But at 10:47:00 GMT on March 31, 8K78M number N103-42 successfully lifted off carrying the 1,582-kilogram E-6S No. 206 into orbit. After a short coast in its temporary 200 by 250 kilometer parking orbit, the Blok L stage ignited to send what was now designated Luna 10 on its way to the Moon.

The day after launch, a midcourse correction maneuver was performed setting the spacecraft on target to pass 1,000 kilometers from the lunar surface. On April 3 with Luna 10 still 8,000 kilometers from the Moon, the spacecraft dutifully aligned itself for its orbit insertion burn with began at 18:44 GMT. After its KTDU-5A engine shutdown cutting the approach speed from 2.1 to 1.25 kilometers per second, Luna 10 was in a 350 by 1,017 kilometer orbit inclined 71.9° to the lunar equator with a period of two hours and 58 minutes. The Soviet Union had secured another space first with the first artificial satellite placed into orbit around another world beating the American Lunar Orbiter 1 by four months.

After 20 minutes in lunar orbit, the E-6 bus released the Luna 10 satellite on ground command. Initial checks showed that all of the satellite’s systems were operating as planned and it was ready to begin its mission. One of the first tasks of that mission was a rehearsal of its propaganda function: the transmission of the Communist Party anthem, Internationale, which was scheduled to be broadcast live from Luna 10 during the session of the 23rd Congress on April 4. While the initial rehearsal went off without a hitch on the night of April 3, during the subsequent test the next morning it was discovered that one of the notes of the song was now missing. Fearful of the fallout if any further problems were encountered, the recording of Internationale made during the initial test was played during the session of the 23rd Congress contrary to the claims that were being publicly made to the Congress and the rest of the world that it was a live transmission from the Moon. Unwilling to admit to the subterfuge and wary of potential retaliation from party officials, this fact was kept secret until the 1990s – well after the Communist Party fell out of power and the Soviet Union had been dissolved.

With its propaganda objective met, Luna 10 then began to focus on its scientific mission. By April 15, Luna 10 had completed 96 orbits and 53 communication sessions with ground controllers. At this point it was already apparent from tracking data that the satellite’s orbit was changing because the lunar gravitational field was more irregular than expected. It was the first hint of the existence of what eventually became known as “mascons”. Data also indicated that there was no lunar magnetic field and that radiation was not a major hazard. The flux of micrometeoroids was found to be higher in lunar orbit than during the cruise to the Moon but it was not a major hazard as well. Further analysis of the data returned from Luna 10 showed that the lunar surface seemed to have a composition broadly similar to basalt and that the Moon has no detectable atmosphere.

The last of the 219 communication sessions with Luna 10 was held on May 30 when its batteries were finally exhausted. After 460 revolutions around the Moon, the satellite was in a 378 by 985 kilometer orbit with an inclination of 72.2°. The obvious changes in the orbit of Luna 10 after 56 days and the inability to predict accurately its evolution demonstrated the need to get more data to improve navigation to the level required for an eventual manned lunar mission. But Soviet scientists would not have long to wait as engineers at NPO Lavochkin were already busy preparing a new group of improved E-6LF lunar orbiters to study the Moon and start mapping its surface (see “Mapping the Moon: The Soviet Luna 11 & 12 Missions“).

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Related Reading

“Luna 9: The First Lunar Landing”, Drew Ex Machina, February 3, 2016 [Post]

“50 Years Ago Today: The Launch of Luna 5”, Drew Ex Machina, May 9, 2015 [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, The Soviet Space Race with Apollo, University Press of Florida, 2003

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