As the historic Apollo 11 mission was heading to the Moon, a bit of space drama was unfolding before the eyes of the world. Just three days before the launch of Apollo 11, the Soviet Union had launched a 5.7 metric ton robotic spacecraft called Luna 15 towards the Moon with only a vague announcement about its mission. Speculation swirled through the Western press and among space observers about the flight’s true intentions: Was it some last-minute Soviet space spectacular? Or maybe an attempt to spy on or even interfere with the American Apollo mission? It would be decades before it was confirmed that this was actually a lunar sample return attempt employing the new E-8-5 spacecraft launched in a last ditch effort to secure the first samples from the lunar surface before Apollo.

The New E-8 Lunar Spacecraft

The hardware that would be employed in the Soviet sample return missions can be traced back to the E-8 spacecraft family developed by the design bureau known as NPO Lavochkin. Run by Chief Designer Georgi Babakin until his death in 1971, NPO Lavochkin was given responsibility for the development and construction of unmanned lunar and planetary spacecraft in April 1965 so that OKB-1 (the ancestor of Russia’s RKK Energia, which previously had that task) could concentrate its resources on the development of the Soyuz spacecraft and the related hardware needed to send cosmonauts to the Moon in competition with Apollo. The design bureau’s very first successes included Luna 9, which became the first spacecraft to land a working payload on the Moon on February 3, 1966 (see “Luna 9: The First Lunar Landing”), and Luna 10, the first spacecraft to successfully enter orbit around the Moon two months later (see “Luna 10: The First Lunar Satellite”).

The E-8 program initially consisted of two components: The E-8 rover (which would eventually be known to the world as “Lunokhod”) and the E-8LS orbiter. Both versions of the E-8 used a standardized “correction and braking module” (known by the acronym “KT”) with a dry mass of about 1,100 kilograms which carried over 3,500 kilograms of hydrazine and nitric acid propellants internally and in four jettisonable outboard tanks. The KT carried all the consumables for its KTDU-417 main engine and attitude control thrusters. It also was equipped with an astro-orientation system and other sensors needed to support its payload in space. The rover would be brought to the surface from an intermediate lunar parking orbit by a version of the KT fitted with landing legs, a pair of ramps, and other equipment required for descent such as a radar altimeter. Originally, the mission of the rover was to perform an on-site survey of a proposed manned landing area to make sure it was safe. It would also carry a radio beacon to guide the Soviet’s manned lunar lander or “LK” (their version of the LM) towards a pinpoint landing. Later versions would be used to aid the cosmonaut’s exploration of the landing area.

With only small areas of potential lunar landing sites imaged in 1966 by the E-6LF Luna 12 mission (see “Mapping the Moon: The Soviet Luna 11 & 12 Missions”), the E-8LS orbiter’s mission was to perform a more thorough orbital survey of proposed landing sites. Its variant of the KT was loaded with less propellant than the lander version but it carried more consumables, such as for attitude control, needed for its planned yearlong mission in lunar orbit. The orbiter’s primary payload was a modified E-8 rover instrument compartment, minus its wheels and other drivetrain components, equipped with high resolution cameras and other instruments to study the lunar surface and surrounding environment.

Origins of the Sample Return Mission

As 1968 unfolded, it was becoming increasingly apparent to Soviet officials that the Apollo program was going to land men on the Moon long before the Soviet equivalent would be ready to fly. Babakin and his team at NPO Lavochkin had a potential means of at least partially upstaging Apollo: an automated lunar sample return mission. As early as 1966, engineers at Lavochkin had been working on design studies for lunar sample return missions. These engineers ultimately arrived at a simple means of doing so using the E-8 hardware then under development. The standard E-8 KT was modified to carry an 800 kilogram payload consisting of a toroidal shaped instrument compartment used to support surface operations and an ascent stage which was to return a small lunar sample.

A simple 0.9-meter sampling arm sporting a 13.6-kilogram drill mechanism could be swung over an arc of 100° in front of the lander to a sampling site selected using stereo images provided by a pair of imaging telephotometers. Once the drill mechanism at the end of the arm secured a 38-centimeter core sample with a mass of a couple of hundred grams, the arm would swing up and place the sample inside the spherical, 50-centimeter return capsule with a mass of 35 kilograms. The entire spacecraft, known as the E-8-5, stood 3.96 meters tall and had a launch mass of about 5,700 kilograms – right at the performance limit of its Proton-D launch vehicle (see “The Largest Launch Vehicles Through History”).

While in theory the KT could deliver its payload anywhere on the Moon’s surface from its intermediate parking orbit, the E-8-5 designers had to sacrifice some flexibility in order to limit the ascent stage to a mass of 520 kilograms and maintain the tight development schedule. Dmitry Okhotsimsky, a pioneer of space ballistics at the Soviet’s Institute of Applied Mathematics, had discovered a set of trajectories from the lunar surface which allowed a returning spacecraft to follow a simple ballistic path without the need for a midcourse correction or the mass penalty of a complex guidance system. This simplest of return strategies only required the ascent stage’s guidance system to maintain a vertical ascent profile while its KRD-61 engine accelerated the returning spacecraft to a velocity of about 2,700 meters per second. When properly timed, the return capsule would literally fall straight towards the Earth with any initial aiming errors minimized by the focusing effects of Earth’s gravity. Since this approach resulted in a large error ellipse at the Earth, a radio beacon on the ascent stage as well as optical tracking during its approach would allow the landing site to be determined precisely enough to ensure ground recovery crews could locate the return capsule after landing.

Such a simple ballistic return from the near side of the Moon was only possible for landing sites in a narrow band centered just north of the lunar equator near 56° east longitude in the general area of Mare Crisium and the highlands to the south. The exact location of the ten-kilometer wide landing zone varied over time depending on the time of year, the Moon’s position in orbit, the extent of lunar librations, and the location of the intended recovery site. Fortunately, much of this area of the Moon was relatively safe for landing and was scientifically interesting as well.

The First E-8 Launches

The successful conclusion of the Apollo 8 mission on December 27, 1968 (see “Apollo 8: Where No One Has Gone Before”) and NASA’s aggressive test flight schedule to follow meant that the first Apollo lunar landing attempt could come in the summer of 1969. With no hope of beating the American manned landing, Soviet officials shifted focus to automated lunar missions in hopes of casting some shade on NASA’s accomplishments. With the preparation of E-8-5 hardware in its advanced stages, the Soviet Military-Industrial Commission (VPK) approved the launch of the first sample return missions on December 30, 1968. This was followed on January 8, 1969 by a decree by the Council of Ministers which, in part, authorized launches of the E-8 missions.

The new E-8 rover, No. 201, was the first piece of hardware ready for flight. The rover was targeted to land on the flat floor of the 61-kilometer Le Monnier crater on the eastern edge of Mare Serenitatis. This would be the first time a lunar lander would make its final descent from lunar orbit (instead of a direct descent from a trans-lunar trajectory) and the northern-most lunar landing attempt made to date. As part of its propaganda function, the rover carried a tape recording of the Soviet national anthem which would be played after landing. The E-8 No. 201 rover lifted off at 9:48:15 AM Moscow Time (06:48:15 GMT) on February 19, 1969 on Proton No. 239-01 from Site 81/24 in the Baikonur Cosmodrome in Soviet Kazakhstan. As the ascending rocket was reaching maximum dynamic pressure, the newly designed launch shroud protecting the payload failed 51 seconds after launch. The launch vehicle exploded two seconds later raining debris 15 kilometers downrange. The first E-8 mission had failed.

With the completion of a second rover still many months away, attention turned towards the E-8-5 sample return missions. By June of 1969, five spacecraft were being prepared for a series of launches. The first ready was E-8-5 No. 402. With a launch date set for June 14, 1969, its planned 11-day sample return mission would be completed three weeks ahead of the scheduled launch of Apollo 11 now set to attempt the first manned lunar landing after the successful completion of the Apollo 10 rehearsal on May 26 (see “Apollo 10: The Adventure of Charlie Brown & Snoopy”). The first E-8-5 lifted off at 7:00:47 Moscow Time (04:00:47 GMT) on June 14 atop of Proton No. 238-01. This time the new shroud did its job as did the first three stages of the Proton rocket. Unfortunately, The Blok-D escape stage failed to ignite to place itself and the E-8-5 payload into a temporary parking orbit. Instead, the hardware was destroyed during reentry over the Pacific Ocean ending another attempt to upstage Apollo.

Preparing the Last Shot

The last chance to upstage the Apollo program came in July. Thankfully, celestial mechanics dictated that the next E-8-5, No. 401, would liftoff on July 13 about 3½ days before the scheduled launch of Apollo 11. Assuming a nominal 11-day mission, the E-8-5 return capsule would parachute back to Soviet territory on July 24. The plan was for the return capsule to be carried in an armored car through the streets of Moscow on July 26 or 27 as part of triumphant parade through Red Square as the sample was delivered to the Vernadsky Institute where it would be placed on display for the world press to see before detailed analysis would begin. Unfortunately, for this mission to succeed in its propaganda function, the Apollo 11 mission would need to stumble. If the Apollo 11 mission proceeded exactly as scheduled, it would return to Earth four hours ahead of the E-8-5. In order to beat the Americans, the Apollo 11 launch would need to be delayed by at least a day. Otherwise, Apollo 11 would either have to fail its lunar landing attempt or to return to Earth as scheduled for the Soviets to secure a lunar sample before the Americans.

With the pressure on to succeed, the hardware for the next E-8-5 flight was carefully assembled and tested for launch. During a detailed check of the mass of the spacecraft, it was found that the ascent stage for spacecraft No. 401 had a mass of 513.3 kilograms instead of the allotted 512.0 kilograms. With the Proton No. 242-01 launch vehicle already modified to squeeze every gram of payload capacity out of it, the excess mass had to be shed from somewhere. In the end it was decided to delete one of a pair of redundant 1.28-kilogram radio transmitters from the lander leaving only its primary unit with no back up. With all preparations completed, the 5,667-kilogram E-8-5 No. 401 lifted off from Site 81/24 at 5:54:41 AM Moscow Time (02:54:41 GMT) on July 13. Following a successful powered ascent culminating with the initial burn of the Blok D escape stage, the stage and payload were in a 182 by 247 kilometer parking orbit with an inclination of 51.6°. After a short coast, the Blok D reignited successfully sending its payload towards the Moon breaking a streak of five successive Proton launch failures during the first half of 1969.

The Luna 15 Mission

Upon the successful launch of E-8-5 No. 401, the spacecraft was officially designated as “Luna 15”. According to official Soviet press statements, the mission of Luna 15 was to study circumlunar space, the Moon’s gravitational field and the chemical composition of the lunar surface while performing surface photography. No mention was made about the sample return objective as rumors about the true nature of the mission swirled through the world press.

Because of the mass of the E-8-5, Luna 15 followed a slower trajectory to the Moon with a transit time of 103 hours – about a day longer than earlier Soviet lunar missions. Tracking showed the need for a course correction which Luna 15 executed the day after launch. Of greater concern was telemetry showing increasing temperatures in the propellant tanks of the ascent stage with the genuine fear that they might fail. In a desperate move against the advice of the more conservative engineers on the team, the attitude of Luna 15 was altered so that the tanks were placed into the shadow of the spacecraft. The solution worked and a potential mission ending failure was averted.

With Apollo 11, which was launched on schedule on July 16, just 82 hours behind Luna 15, the E-8-5 ignited its KTDU-417 main engine at 10:00 GMT on July 17 to enter an initial 100-kilometer orbit. After Luna 15 emerged from behind the Moon 20 minutes after orbit insertion, it was discovered that the lander was not in its intended orbit. A significant underburn with a delta-v of about 700 meters per second (instead of the planned 810 or so meters per second) left Luna 15 in a much higher 240 by 870 kilometer orbit with an inclination of 126°. As ground controllers worked to determine the orbit of Luna 15 and come up with a plan to get it into its proper orbit, concerns continued to mount that the Soviet mission might interfere with Apollo 11 in some way. NASA astronaut Frank Borman, who had just returned from a nine-day visit to the Soviet Union, made an appeal for more information. He was assured that there would be no interference with the Apollo 11 mission and the Soviet Academy of Sciences supplied orbit data.

At 13:00 GMT on July 18, Luna 15 made its first orbit adjustment during its tenth revolution to lower the orbit to 94 by 220 kilometers. The following day at about 13:08 GMT, Luna 15 made another trim maneuver to enter an 85 by 221 kilometer orbit. This maneuver also adjusted the longitude of the ascending node to set up Luna 15 to come down in its intending landing site in Mare Crisium. Apparently ground controllers were having more difficulty than expected with navigation due to the effects of the Moon’s lumpy gravitational field. There are also indications that Luna 15 was having attitude control issues as well. As ground controllers in the Soviet Union continued to track Luna 15 in its new orbit, Apollo 11 entered its initial 111 by 314 kilometer lunar orbit at 17:22 GMT. A subsequent planned maneuver 4⅓ hours later placed Apollo 11 into a more circular 101 by 122 kilometer orbit with an inclination of 178.8°.

The Landing Attempt

With the Apollo 11 mission still proceeding on schedule for a landing at 20:19 GMT on July 20, Soviet ground controllers commanded Luna 15 during its 39th revolution to perform another maneuver at 14:15 GMT lowering the orbit to 16 by 85 kilometers with an inclination of 127°. With the perilune of the orbit over the intended landing site, the plan was for Luna 15 to fire its KTDU-417 main engine at this low point to negate its orbital velocity and begin a freefall towards the lunar surface. When the onboard radar altimeter indicated an altitude of about 600 meters, the main engine would reignite to slow the 200 meter per second descent. The main engine would cut out at an altitude of 20 meters with vernier engines guiding the E-8-5 to a soft landing of just two meters per second six minutes after leaving orbit. For this method to work, the descent had to begin at an altitude of 16±3 kilometers. Any higher and the descent speed would be too high for the propulsion system to handle. Any lower and there was a risk of striking the side of a lunar mountain near perilune (a real concern given the uncertainties at the time about the shape of the Moon and the absolute heights of its surface topography).

When Luna 15 made its first perilune pass over Mare Crisium, it turned on its landing radar to test the unit and the nature of the lunar surface below. Instead of the fairly flat topography which had been expected, the radar data suggested a very uneven surface. With the landing of Luna 15 scheduled for 19:00 GMT, there was not enough time left to get a second set of readings to clarify the situation. Instead, the painful decision was made to delay the landing by 18 hours to get more radar readings and fine tune the navigation. The Apollo 11 LM, Eagle, undocked from the CSM, Columbia, at 17:44 GMT and successfully landed on Mare Tranquilitatis at 20:19 GMT after some last minute difficulties. Barring some tragedy during the remainder of the Apollo 11 mission, Luna 15 had lost the race to get the first lunar samples back to Earth.

During its 54th orbit of the Moon, Luna 15 jettisoned its nearly empty outboard propellant tanks and started its deorbit burn at 15:46 GMT on July 21. Neil Armstrong and Buzz Aldrin had already completed their historic first moonwalk 10½ hours earlier and were preparing Eagle for liftoff in two hours. At 15:50 GMT, contact with Luna 15 was lost just four minutes into its expected six-minute descent with a radar altimeter reading of three kilometers. According to the team at England’s Jodrell Bank, which had been monitoring the Luna 15 mission, the spacecraft had crashed into the lunar surface at a speed of about 130 meters per second. The crash site was at 12° N, 60° E about 800 kilometers east of the Apollo 11 landing site.

As engineers and scientists started investigating the causes of the disappointing failure of Luna 15, Soviet officials merely stated that the spacecraft had completed its research program and had reached the Moon in the preset area. There was no official mention of the actual mission and speculation about this flight would continue for the next couple of decades. Meanwhile, the Apollo 11 mission ended with a splashdown in the Pacific Ocean at 16:50 GMT on July 24. With the successful recovery of the crew and the 21.6 kilograms of lunar samples they had collected, the United States had won the race to the Moon.

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Related Reading

“The Last Lunar Sample Return Mission”, Drew Ex Machina, August 18, 2016 [Post]

General References

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

Wesley T. Huntress, Jr. and Mikhail 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 A. Siddiqi, The Soviet Space Race with Apollo, University Press of Florida, 2003