Every now and then, we have the opportunity to touch a piece of history. One of the more memorable of such moments for me came in the summer of 1990 when the Boston Museum of Science hosted an exhibition of Soviet space hardware (see “The Soviet Space Exhibit at the Boston Museum of Science – July 1990“). I visited the exhibit several times that summer along with friends similarly interested in the increasingly less secretive Soviet space program and got a chance to become acquainted with the Russian engineers accompanying the exhibit. With a wink for consent during one of those visits, I actually got to touch briefly the return capsule of the Luna 24 mission – the last lunar sample return mission flown by the Soviet Union 14 years earlier in 1976. While I have had the chance to see (and touch!) a lot of Russian space hardware in the decades which followed, this moment still sticks with me even after over a quarter of a century.

The Luna 24 mission was the culmination of decades of efforts by teams of Soviet scientists and engineers to build some of the most innovative space hardware of the era. With talk of new plans to return samples from the Moon, now is a good time to look back at this last lunar sample return mission four decades ago and the difficulties they encountered.

Origins of the Sample Return Mission

The hardware that would be employed in the Soviet sample return missions can be traced back to the E-8 program 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 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 Lunar Cabin (their version of the LM known as the LK) towards a pinpoint landing. Later versions would be used to aid the cosmonaut’s exploration of the landing area.

The E-8LS orbiter’s mission was to perform an 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 year long 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.

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 a simple ascent stage which was to return a small lunar sample secured by a sampling arm and placed inside a spherical 50 centimeter in diameter 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.

While in theory the KT could deliver its payload anywhere on the Moon’s surface from its 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 limited 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 the final 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 general 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-8-5 Missions

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. The first launch with E-8-5 No. 402 as the payload was made on June 14, 1969 – one month before the historic mission of Apollo 11 would liftoff. Unfortunately, the Blok D fourth stage of the Proton D launch vehicle failed to ignite and the payload reentered the atmosphere over the Pacific Ocean.

The second sample return attempt, using E-8-5 No. 401, successfully lifted off on July 13 just three days ahead of Apollo 11. Luna 15, as it was now called, entered lunar orbit on July 17 and spent the next four days carefully maneuvering in lunar orbit in preparation for landing. As astronauts Neil Armstrong and Edwin “Buzz” Aldrin were preparing for liftoff after a night’s sleep following their historic moonwalk, Luna 15 crashed on July 21 as it attempted a landing in southern Mare Crisium 800 kilometers to the east of “Tranquility Base” (see “Luna 15: The Soviet Union’s Last Lunar Gamble“).

Subsequent attempts to get an E-8-5 spacecraft to the Moon over the next several months were plagued by launch vehicle issues. The Blok D escape stage failed to reignite due to an oxidizer valve failure after placing itself and E-8-5 No. 403 into a parking orbit on September 23, 1969 stranding what became known as Kosmos 300. The next launch attempt on October 22 with E-8-5 No. 404 ended in failure when the Blok D misfired due to a programming error sending what became known as Kosmos 305 into Earth’s atmosphere during its first orbit. The fifth lunar sample return launch attempt on February 6, 1970 with E-8-5 No. 405 failed to even reach its parking orbit when the second stage shutdown prematurely due to a pressure sensor failure.

The next attempt with E-8-5 No. 406 was successfully launched on September 12, 1970. Luna 16, as it was called, placed itself into lunar orbit and landed in the northeast corner of Mare Fecunditatis eight days later as planned. The sampling arm on Luna 16 drilled 35 centimeters into the lunar soil before encountering an obstacle. The sampler arm was raised but some of the soil fell out as the sample was secured inside of the return capsule. After spending just over a day on the lunar surface, the ascent stage of Luna 16 lifted off using its KT as a launch pad and headed home. Following a flight of nearly 68 hours, the Luna 16 capsule returned to Earth on September 24 with 101 grams of lunar soil for study.

At this stage, the Soviet lunar exploration program settled into a fairly measured pace as part of a long-term program of lunar exploration which now included flights of the E-8 Lunokhod rovers (which would also make the first astronomical observations from the lunar surface – see “The Original Lunar Observatories”) and the E-8LS orbiters. The next sample return mission attempt was Luna 18 launched on September 2, 1971. Unfortunately, E-8-5 No. 407 crashed nine days later while attempting a landing in the rugged highlands between Maria Fecunditatis and Crisium. The Luna 20 mission, which was launched E-8-5 No. 408 to the Moon on February 14, 1972, successfully returned a sample from the Apollonius highland region north of Mare Fecunditatis eleven days later. Unfortunately, problems drilling into the lunar soil and the loss of sample material as it was being lifted to the return capsule resulted in only 55 grams of lunar material being returned to the Earth.

While the flights of Luna 16 and 20 were successful, issues with the sampling mechanism were limiting the sizes of the returned samples. Engineers at NPO Lavochkin, now managed by Sergei Kryukov, set about designing and building an improved spacecraft known as the E-8-5M. The most significant change in the appearance of the spacecraft was the addition of a frame on the side for the new drill mechanism designated LB-09 (a Russian acronym for “Lunar Drill-09”). LB-09 was designed by the Tashkent branch of KBOM (the Russian acronym for “General Construction Design Bureau” under Vladimir Barmin) known as TashKBM. It consisted of a rail-mounted rotary percussion drilling mechanism that would drill 2.5 meters into the lunar soil. Unlike the earlier E-8-5 sampling mechanism, the stratigraphy of the soil would be preserved as the 8 millimeter in diameter sample was slipped into a long flexible tube which would be coiled up and secured inside the return capsule. With all other instruments deleted to save mass, the new E-8-5M promised to return larger and better preserved samples of the lunar soil for study by scientists back on the Earth.

The E-8-5M Missions

The first flight of the new E-8-5M using spacecraft number 410 lifted off from the Baikonur Cosmodrome in Soviet Kazakhstan at 5:30:32 PM Moscow Time (14:30:32 GMT) on October 28, 1974. After a short coast in a 182 by 246 kilometer parking orbit with an inclination of 51.5°, the Proton’s Blok D escape stage reignited and placed what was now designated Luna 23 on trajectory towards the Moon. After a course correction on October 31, Luna 23 entered an initial 94 by 104 kilometer orbit around the Moon with an inclination of 138° at 21:50 GMT on November 2. Maneuvers on November 4 and 5 altered the spacecraft’s orbit to 17 by 105 kilometers in preparation for its descent to the southern part of Mare Crisium not far from the intended Luna 15 landing site.

On November 6, Luna 23 ignited its KTDU-417 engine during the 50th revolution and began its landing attempt. Luna 23 landed at 5:37 GMT at 12.68° north, 62.28° east. There are apparently conflicting accounts of what exactly happened as a result of its rather hard landing at a speed of 11 meters per second. Most stories published over the last four decades state that the drilling mechanism was damaged upon landing due to rough surface conditions rendering it unusable. A more recent account states that Luna 23 had actually tipped over upon landing but the drilling mechanism survived and was put through its paces as an engineering test – an account that appears to be supported by high-resolution images returned by NASA’s Lunar Reconnaissance Orbiter (LRO) in 2012. Either way, Luna 23 was unable to secure a sample and no attempt was made to launch the return stage. Contact with Luna 23 was maintained until November 9.

The next launch attempt came on October 16, 1975 using E-8-5M No. 412. Liftoff from the Baikonur Cosmodrome occurred at 7:04:56 AM Moscow Time (4:04:56 GMT) but the failure of Proton’s Blok D stage to ignite during ascent doomed the mission to failure. It would be ten months before the next attempt would be made, this time in the shadow of NASA’s highly publicized Viking mission which successfully landed its first spacecraft on Mars on July 20, 1976. At 6:04:12 PM Moscow Time (15:04:12 GMT) on August 9, the 5,795-kilogram E-8-5M No. 413 lifted off atop of Proton No. 288-02 and was successfully placed into a temporary 188 by 243 kilometer parking orbit with an inclination of 51.5°. The Blok D reignited as planned sending what was now called Luna 24 on its way.

Following a routine course correction on August 11, Luna 24 entered a circular 115-kilometer lunar orbit with an inclination of 120° at 23:11 GMT on August 13. As in previous E-8 landing missions, Luna 24 made a series of maneuvers on August 16 and 17 to enter a 12 by 120 kilometer orbit in preparation for a landing attempt. At 6:30 GMT on August 18, Luna 24 fired its KTDU-417 engine to begin its descent. Six minutes later, Luna 24 successfully landed in darkness near the rim of a 64-meter impact crater at 12.75° north, 62.20° east in Mare Crisium only 2.3 kilometers from the ill-fated Luna 23 (see the feature image at the top of this page for an LRO closeup of this site). Had Luna 24 come down about ten or more meters to the southeast, it would have landed in the boulder-filled crater and likely have failed like its predecessor.

Following the usual systems checks, Luna 24 set about drilling into the lunar surface 15 minutes after landing to secure its sample. Drilling down 2.35 meters at a slight angle, the drill was able to penetrate two meters below the lunar surface, extract the sample and place it into the return capsule. With its precious cargo secured, Luna 24 lifted off from the lunar surface at 5:25 GMT on August 19 while the craft was in view of the Soviet tracking station at Yevpatoria.

Unlike the earlier E-8-5 sample return missions which followed return trajectories which brought them back to Earth in 68 hours, Luna 24 followed a longer path that took 84 hours but brought the return capsule around to the far side of the Earth for a recovery in Soviet territory. The Luna 24 return capsule finally landed at 17:35 GMT on August 22 some 200 kilometers southeast of the Siberian city of Surgut. The initial inspection of the 170-gram sample at the Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKhI) in Moscow revealed gray brown soil with clearly visible layers which had been preserved as hoped by the new LB-09 drill.

The End of the E-8 Missions

As it turned out, Luna 24 would prove to be the last Soviet mission to the Moon before the USSR dissolved at the end of 1991 into the individual countries of today. With the end of the Apollo lunar missions in December 1972 and the cancellation of the Soviet manned lunar landing program in February 1976 by secret government decree, support for the lunar program disappeared. Efforts at NPO Lavochkin and its associated design bureaus shifted to supporting the ongoing 4V Venera missions to Venus (see “Venera 9 and 10 to Venus”) and development of the ambitious 5M Mars sample return mission as a follow on to NASA’s successful Viking missions. A third Lunokhod rover and another E-8-5M already prepared for flight along with an assortment other E-8 hardware in various states of preparation for flight or testing were consigned to museums. The highly successful KT hardware was adapted for use in the next generation planetary spacecraft such as the Phobos mission as well as the Fregat upper stage still in use today. It would be December 14, 2013 before the Chinese Chang’e 3 spacecraft, carrying the Yutu rover, would make the next soft landing on the Moon. And while there have been numerous plans announced over the last four decades, we are still waiting for the next lunar sample return mission.

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Related Reading

“Luna 15: The Soviet Union’s Last Lunar Gamble”, Drew Ex Machina, July 19, 2019 [Post]

“The Original Lunar Observatories”, Drew Ex Machina, August 21, 2014 [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

Jeff Plescia, “Mare Crisium: Failure Then Success”, LROC Web Site, March 16, 2013 [Post]

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

Andrew Wilson, Solar System Log, Janes Publishing, 1987