During the opening years of the Space Age, the Soviet Union managed to beat the United States to one Moon-related first after another: The first lunar flyby (Luna 1 in January 1959), the first lunar impact (Luna 2 in September 1959) and the first photographs of the previously unseen far side of the Moon (Luna 3 in October 1959). After numerous attempts using a variety of payloads and launch vehicles, the United States only managed to make a distant lunar flyby with their six-kilogram Pioneer 4 probe in March 1959 (see “Vintage Micro: The Pioneer 4 Lunar Probe”).

One of the next important “firsts” was to land a robotic spacecraft on the lunar surface and return data. Beyond scientific curiosity and national prestige, this was especially important after the commitment was made in 1961 to land a crew on the Moon. Engineers needed more information on the nature of the lunar surface to design hardware and ensure the survival of the crew. NASA had the opportunity to be first to land on the lunar surface using their new Ranger spacecraft a version of which was designed to hard land a simple instrument package. Unfortunately, all three attempts launched in 1962 failed (see “NASA’s First Lunar Lander”). As NASA pushed ahead with the development of the more advanced Surveyor robotic lunar lander, Soviet scientists and engineers had the chance to beat their American counterparts to a lunar landing using their new E-6 spacecraft.

The E-6 Spacecraft

Like the Soviet Union’s earlier Luna spacecraft, the E-6 was designed and built at OKB-1 (the Russian acronym for Experimental Design Bureau – 1) under the direction of the famed aerospace engineer, Chief Designer Sergei Korolev. While work on the E-6 lander began in 1960, it proceeded fairly slowly at first as the engineers at OKB-1 focused on the manned Vostok and related spacecraft (see “Vostok’s Legacy”), unmanned planetary spacecraft as well as the development of new launch vehicles.

The 2.7-meter tall E-6, initial versions of which had a launch mass of just over 1,400 kilograms, consisted of a two-part multi-mission bus and a lander package. The bottom half of the main bus held the propulsion system built around a KTDU-5 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 down within about 150 kilometers of its intended landing site. 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 of trajectory requirements and the need to approach the lunar surface nearly vertically, potential E-6 landing sites were restricted to just north of the equator in the western part of the lunar near side centered on Oceanus Procellarum.

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 I-100 control and navigation system built by Scientific Research Institute NII-885 under Nikolai Pilyugin. 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 300 kilograms of lightly constructed 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. Once the KTDU-5 engine had ignited for the final descent to the lunar surface, these items were no longer needed and were discarded to save weight. 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.

Mounted on top of this bus was the slightly egg-shaped lander with a diameter of 58 centimeters and originally with a mass of about 82 kilograms. It was protected from the impact of landing by an inflatable airbag system similar in principle to the one employed decades later by NASA’s Opportunity Mars rover and other American Mars landers. The airbags would be inflated just before the retrorocket started firing and the lander would be thrown clear of the main bus upon contact with the lunar surface. After the bottom-heavy lander rolled to a stop and the airbag deflated, four petals would open to stabilize the package. Inside were the lander’s transmitter, batteries, and other equipment including a simple facsimile-style camera which could return panoramic images of the lander’s surroundings. The E-6 lander was much more complex and certainly more capable than the 43-kilogram package NASA was trying to land on the Moon with Ranger.

The launch vehicle for the E-6 was a modified version of the four-stage 8K78 Molniya rocket which had been developed to launch the Soviet Union’s first planetary probes and Molniya communication satellites (see “The First Mars Mission Attempts”). 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 8K78 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 8K78 was 42.1 meters tall and had a liftoff mass of about 306 metric tons. Before the first orbital test flight of the American Block II Saturn I rocket on January 29, 1964, the 8K78 was the most powerful rocket in the world (see “The Coolest Rocket Ever”).

For the E-6 Luna flights, a special version of the 8K78 Molniya was initially employed designated the 8K78L. Unlike the original 8K78 and the 8K78M introduced in 1964 which had separate control systems for the Blok I and L stages, the 8K78L used the I-100 system of the E-6 to control the upper two stages. The elimination of the upper stage control systems decreased the total mass and improved the launch vehicle’s lunar payload performance. Unfortunately it also created another version of the failure-prone 8K78 with a unique control system that would require debugging.

First Flights of the E-6

After the failure of NASA’s three Block II Ranger missions to land on the Moon in 1962, the way was clear for the Soviet Union to attempt the first lunar landing. Unfortunately, Korolev and his team had as little luck as their American counterparts. The first E-6 lander launched on January 4, 1963 was stranded in Earth orbit while the second launched the following month never even made it to orbit. Both failures were traced back to the I-100 control system. Only Luna 4 launched on April 3 managed to make it beyond low Earth orbit but another failure of the I-100 left Soviet ground controllers unable to navigate the spacecraft which passed 8,336 kilometers from the Moon about 77 hours after launch.

Following these three failures, Luna launches were suspended for a year as the systems of the E-6 and its 8K78L launch vehicle were improved. The fourth E-6 launch on March 21, 1964 failed to reach orbit due to a LOX valve failure in the Blok I third stage. The next launch attempt on April 20 suffered another I-100 control system failure and also never reached orbit forcing another lengthy hiatus as continuing problems with the E-6 were ironed out.

After another stand down lasting almost eleven months, the sixth E-6 was launched on March 12, 1965. Yet another frustrating failure of the I-100 system resulted in the Blok L escape stage not firing stranding it and its payload in a quickly decaying parking orbit. Soviet authorities designated this spacecraft Kosmos 60 – the first in a string of failed lunar missions disguised under the generic “Kosmos” moniker. As another E-6 was prepared for launch, there were major changes unfolding behind the scenes in the Soviet aerospace industry. With so many of the resources at OKB-1 engaged in developing the Soyuz and other spacecraft for the Soviet’s manned lunar program, in April 1965 Korolev transferred responsibility for the automated lunar and planetary spacecraft to NPO Lavochkin under Chief Designer Georgi Babakin — a newly independent organization that was spun off of OKB-52 that was well known for its intensive testing and quality control of the flight hardware it built. But it would take time for the engineers at Lavochkin to get up to speed on the E-6 design and start producing their own flight units. In the mean time, there were still five more E-6 spacecraft in the production pipeline at OKB-1 to be launched.

Frustrated by the ongoing issues with the I-100 control system, engineers decided to install a separate control system for the launch vehicle upper stages like that already being employed in the standard 8K78M leaving he troublesome I-100 to concentrate just on controlling the spacecraft itself. The seventh E-6 launch on April 10, 1965 started off well but a pressurization issue in the LOX tank of the Blok I third stage prevented the rocket from reaching parking orbit. The next E-6 launched on May 9 fared much better and was sent successfully on its way to the Moon to become Luna 5. However, lack of in-flight experience with the I-100 system combined with ground controller errors meant that Luna 5 missed its opportunity to perform a needed course correction resulting in another failure (for a more detailed account of the Luna 5 flight and the earlier E-6 missions, see “50 Years Ago Today: The Launch of Luna 5”).

The Last of Korolev’s E-6 Missions

Korolev’s push to land an E-6 on the Moon continued with the launch of E-6 Number 7 at 10:40:00 Moscow Time on June 8, 1965 from the Baikonur Cosmodrome. The 8K78M launch vehicle serial number U103-31 successfully placed the Blok L escape stage and its 1,442-kilogram E-6 payload into a 167 by 246-kilometer parking orbit with an inclination of 64.8°. After a short coast, the Blok L stage ignited and sent what would become Luna 6 on its way to the Moon.

Initial checks showed that Luna 6 was operating as intended while tracking indicated that a midcourse correction would be required to land on target. After a total of 12 communication sessions since launch, Luna 6 was commanded to orient itself for its midcourse correction burn the day after launch. The upgraded KTDU-5A engine ignited as commanded but failed to shutdown as planned. Instead, the engine continued firing until its propellant supply was depleted pushing Luna 6 far off course. It was later determined that there was an error in the commands sent by ground controllers that set the shutdown time for the main engine. Luna 6 made a distant 160,935 kilometer flyby of the Moon on June 11 as it sailed into solar orbit. To make sure the mission was not a total loss, ground controllers performed a series of engineering tests on Luna 6. They successfully executed the landing sequence (save for the ignition of the main engine) including the inflation of the air bag and deployment of the lander.

As more changes were made to the E-6, a totally unrelated mission was launched towards the Moon on July 18, 1965. Zond 3 was an engineering test flight of the troublesome 3MV-series of interplanetary spacecraft also built by OKB-1. The primary objective of this mission was to exercise the spacecraft’s various systems including its highly advanced photo-television imaging system. Traveling along a faster trajectory than the heavier E-6, Zond 3 passed 9,219-kilometers from the Moon about 35 hours after launch and secured a spectacular set of images of the lunar surface including much of the far side that had been missed by the historic Luna 3 mission of 1959 (see “The mission of Zond 3”). Buoyed by the success of Zond 3, the scientists and engineers at OKB-1 pushed forward with the launch of E-6 No. 11 scheduled for September 4. Unfortunately, problems with the avionics in the core of the 8K78 serial number U103-27 rocket uncovered during prelaunch checkout could not be corrected in time forcing a postponement for a month.

With the problems with the launch vehicle corrected, what would become Luna 7 lifted off from the Baikonur Cosmodrome at 10:56:40 Moscow Time on October 4, 1965 – the seventh anniversary of the launch of Sputnik. The 1,506-kilogram Luna 7 and its Blok L escape stage were successfully placed into a temporary 129 by 286-kilometer parking orbit with an inclination of 64.8°. After a short coast, the Blok L ignited sending Luna 7 on its way to the Moon. This time the midcourse maneuver the day after launch was successful placing Luna 7 on target for a landing west of the crater Kepler.

About two hours before landing, Luna 7 turned to orient itself for the final firing of its KTDU-5A engine for landing. Unfortunately, the quickly descending spacecraft was unable to maintain its lock on the Earth and, without the required attitude reference, the automated system never ignited the main engine. Luna 7 crashed into Oceanus Procellarum at 9.8° N 47.8°W at 22:08:24 GMT on October 7, 1965. A subsequent investigation revealed that the Earth optical sensor on Luna 7 had been installed at the incorrect angle making it difficult for it to lock onto this required attitude reference. As Korolev tried to persuade Soviet leaders that the problems with the E-6 were under control, the last E-6 built by OKB-1 was modified and prepared for the design bureau’s last shot at landing on the Moon.

At 13:46:14 Moscow Time on December 3, 1965, 8K78 serial number U103-28 lifted off from the Baikonur Cosmodrome carrying the 1,552-kilogram E-6 No. 12. The payload and its escape stage were successfully placed into 181 by 221-kilometer parking orbit. Unlike earlier Soviet lunar and planetary missions, the parking orbit for this (and subsequent missions) had a lower inclination of 51.9° instead of about 65°. This parking orbit improved the performance of the 8K78 somewhat allowing the E-6 mass to grow well above 1,500 kilograms. After a short coast, the Blok L escape stage ignited and successfully propelled what was now called Luna 8 towards the Moon.

With the successful completion of a midcourse correction the day after launch, all was going well with the flight of Luna 8 up until the landing sequence. Unlike its predecessor, Luna 8 was able to align itself properly for the 46-second burn of the KTDU-5A main engine that would slow the spacecraft for landing. But when the lander’s airbag system inflated just before ignition of the engine, an incorrectly manufactured mounting bracket on the spacecraft apparently punctured the airbag. The escaping gas set the quickly descending Luna 8 spinning at a rate of twice per minute preventing the radar system from locking onto the lunar surface. The automated system briefly locked onto the lunar surface and fired the main engine for nine seconds before it shutdown. Luna 8 crashed into the lunar surface at 21:51:31 GMT on December 6 in Oceanus Procellarum at 9.1° N 61.3°W. The last of Korolev’s E-6 missions had failed like the previous ten attempts over the last three years.

Success at Last!

With the failure of the last of the E-6 spacecraft built by OKB-1, the spotlight now turned to NPO Lavochkin. Lavochkin started with two partially completed E-6 spacecraft they received from OKB-1 numbered 13 and 14. On the direction of Chief Designer Babakin, engineers at Lavochkin made improvements to the original E-6 hardware including a new independent guidance system and changes to the lander’s shock absorbers. In addition to new testing and quality control procedures, modifications were made to the spacecraft hardware to inflate the lander’s airbag after the KTDU-5A engine ignited when its outrigger-mounted vernier engines would provide attitude control instead of the less capable cold gas attitude thrusters. This would help avoid a repeat of the Luna 8 failure. The lander, whose mass now grew to 100 kilograms, was also modified and included a new panoramic camera design to take images from the lunar surface with higher resolution than the original. The lower power requirements of the new camera also meant that more images could be returned without shortening the lifetime of the battery-powered lander. With all these and other modifications, the version of the E-6 prepared by Lavochkin received the new designation E-6M.

The first E-6M, Number 202/13, lifted off at 14:41:37 Moscow Time on January 31, 1966. The 8K78M serial number U103-32 successfully placed the 1,583-kilogram E-6M and its escape stage into a temporary 167 by 219 kilometer orbit with an inclination of 51.9°. Before completing its first orbit, the Blok L stage ignited sending what was now called Luna 9 on its way to the Moon. The following day at 22:29 Moscow Time, while Luna 9 was still 233,000 kilometers from its target, the spacecraft used a 48-second burn of its KTDU-5A engine to change the spacecraft’s velocity by 71.2 meters per second and and set it on course for its designated lunar landing site.

About an hour before the scheduled landing on February 3 when it was still 8,300 kilometers from the Moon, Luna 9 reoriented itself to align its engines with the local lunar vertical. As the accelerating Luna 9 passed an altitude of 75 kilometers above the lunar surface at 18:44:42 GMT, the spacecraft jettisoned its unneeded equipment packages and ignited its KTDU-5A engine to decrease its 2.6 kilometer per second approach speed. At an altitude of 250 meters, the main chamber of the KTDU-5A shutdown with the four outrigger engines continuing to fire as the spacecraft continued to descend. When the spacecraft’s five-meter long probe made contact with the lunar surface, the lander with its inflated airbag was ejected and the remaining engines shutdown. As the main bus crashed into the lunar surface at 5.5 to 6.0 meters per second, the lander bounced across the surface and finally came to rest at 18:45:30 GMT on Oceanus Procellarum west of Renier crater at 7.08° N 64.37° W. Four minutes later, after the airbag system had been discarded, the Luna 9 landing capsule opened up and began transmitting back to Earth. After 11 failed attempts in three years, the Soviet Union became the first nation to land successfully on the Moon – and they did so on the first try using the new Lavochkin-built E-6M.

While the Soviet news media announced the success almost immediately, it would be another seven hours before Luna 9 was commanded to transmit its first full panorama from the lunar surface during the second communication session on February 4 starting at 1:50 GMT. The delay was required so that the Sun could rise to 7° above the horizon to improve the lighting conditions at the landing site. But because of bureaucratic rules imposed by the Kremlin, the first panorama transmitted by Luna 9 had to be reviewed and personally approved by Soviet leader Leonid Brezhnev himself before public release would be allowed. This delayed the official publication of the first image from the lunar surface by the Soviet press.

As they had done during earlier Luna flights, British radio astronomer Bernard Lovell and his team were independently monitoring the transmissions from Luna 9 using the 76-meter radiotelescope at the Jodrell Bank Observatory in England. Lovell soon realized that the 183 MHz radio transmissions from Luna 9 were not encoded and that images were being sent using the “Radiofax” transmission standard employed by the world’s news services to transmit images. The Manchester office of the Daily Express newspaper rushed a suitable receiver to Jodrell Bank and the pictures from Luna 9 were decoded and published worldwide before Soviet authorities had a chance to do so creating a minor diplomatic incident in the process.

The original and subsequent images from Luna 9 showed that the lander had come to rest near the rim of a 25-meter crater on a rolling landscape covered in dust and rocks of various sizes accentuated by long shadows created by the early lunar morning illumination. With the camera located about 0.6 meters above the ground, the images revealed details out to the horizon visible 1.4 kilometers from the lander. As result of the lander shifting slightly between the first and second panoramas acquired a couple of hours apart, stereo images were created of parts of the surface to reveal the true distances and sizes of various features. The fact that the 100-kilogram lander did not sink into a layer of lunar dust as some had feared indicated that the lunar surface could support the weight of astronauts and their spacecraft. The only other scientific data from Luna 9 was provided by a SBM-10 radiation sensor which indicated a daily dosage of 30 millirad – a level that would not be hazardous to humans.

The Luna 9 lander was last heard from on February 6, 1966 at about 22:55 GMT when its batteries were finally depleted. Over the course of seven communication sessions totaling eight hours and five minutes, Luna 9 transmitted four panoramas and other data. With the earlier failure of the three American Block II Ranger landing attempts and the first Surveyor flight still months away, the Soviet Union had secured another space first. Although the soundness of the basic E-6 design had been vindicated, Korolev did not live to see it having died on January 14, 1966 during an operation to remove intestinal tumors. No one realized it at the time but the triumph of Luna 9 would be among the last major space firsts for the Soviet Union. With the loss of Korolev and the continued struggle behind the scenes about the future direction of the Soviet lunar program, the United States was beginning to pull ahead in the Space Race.

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Related Video

Here is a Russian-language documentary about the Luna 9 mission filled with interesting footage of hardware and facilities.

Related Reading

“50 Years Ago Today: The Launch of Luna 5”, Drew Ex Machina, May 9, 2015 [Post]

“NASA’s First Moon Lander”, Drew Ex Machina, May 9, 2015 [Post]

“The mission of Zond 3”, The Space Review, July 27, 2015 [Article]

General References

Boris Chertok, Rockets and People Volume III: Hot Days of the Cold War, NASA SP-2009-4110, 2009

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