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Luna-24: Last Moon digger
The final Soviet mission to the Moon was launched on Aug. 9, 1976, under the official name Luna-24. In historical terms, it can be considered the last shot of the Moon Race between the US and the USSR. Unfortunately, it also marked the beginning of a long lull in the exploration of the Earth's natural satellite. For Russia, this dark age in its lunar program continues until this day.
The E8-5M spacecraft. Credit: NPO Lavochkin
Luna-24 mission at a glance:
Luna-24 (E8-5M) spacecraft
Luna-24 became the 11th Soviet attempt to return samples of the lunar soil back to Earth with a robotic probe and the third successful mission concluding the entire program.
Early on, Soviet sources disclosed that Luna-24 sported a re-designed drilling mechanism, which was different from the one used in the previous two successful sample-return missions. In fact, Luna-24 was the third spacecraft in a series designated E8-5M, which featured a number of upgrades from the original E8-5 sample-return vehicle.
In particular, the amount of water used in the thermal control system of the spacecraft's thorus-shaped instrument compartment was reduced by three. Also, the Kvant low-altitude altimeter was removed altogether. (788)
LB-09 drilling mechanism
Most importantly, E8-5M featured a new type of rotary percussion drill designated LB-09, where LB stands for Russian Lunny Bur ("lunar drill"). It was developed at TashKBM -- the Tashkent branch of the KBOM design bureau, on assignment from NPO Lavochkin. Unlike drills installed on the Luna-16 and Luna-20 probes, the new device was able to preserve the original relative position (stratigraphy) of regolith layers after they had been extracted. (71) The new drill also had the capability to adjust its drilling power depending on the density of the soil.
LB-09 included a drill head, a drilling shaft with a sample cartridge and a soil-retrieval mechanism, a drilling head driver, the sample transfer mechanism and the sample storage container.
During drilling, soil fills the internal cavity of the sample cartridge, containing a flexible soil tube with a diameter of 12 millimeters, along with a mechanism supporting the soil column during the entire drilling process. Once drilling stops, the flexible tube filled with soil is retrieved from the internal cavity of the cartridge and rolled up on a drum inside the storage container. The soil container is then transferred into the descent capsule of the lunar return vehicle. (788)
According to post-Soviet sources, Luna-24 carried no payloads besides the LB-09 drill.
The first attempt to fly the modified E8-5M spacecraft was made on Oct. 28, 1974, however, the mission, officially named Luna-23, ended prematurely when the spacecraft fell on its side on the lunar surface. Still, ground controllers were able to test the operation of the LB-09 drill, which functioned in nearly horizontal position and could not reach the surface.
The second attempt was made almost a year later, on Oct. 16, 1975, at 17:04:56 Moscow Time. However, the Proton-K's Block-D stage failed to place the payload into an initial parking orbit and, in accordance with the usual Soviet practice, the unsuccessful launch had never been announced. It took around 10 months to prepare another attempt. In the meantime, in February 1976, the Soviet government issued a secret decree, shutting down the N1-L3 lunar expeditionary effort.
To the Moon and back!
A Proton rocket with the E8-5M No. 413 spacecraft lifted off from Baikonur's Site 81, on Aug. 9, 1976, at 18:04:12 Moscow Time. (400) This time, the launch was successful and the mission was announced as Luna-24.
During the mission, the KIP-10 ground station in Simpheropol served as the main control center. Based on the data received from the vehicle, the main engine on the descent stage, known as the correction and braking module, KT, was commanded to fire on August 11, to adjust the lunar approach trajectory. (270) Three days later, on August 14, the spacecraft successfully entered its initial circular lunar orbit with an altitude of 115 kilometers, an inclination of 120 degrees toward the lunar Equator and an orbital period one hour 59 minutes.
On August 16 and 17, additional maneuvers with the engine of the KT module brought Luna-24 within 12 kilometers above the lunar surface at perigee (the apogee was still 120 kilometers high) during its final (elliptical) egg-shaped orbit around the Moon.
On Aug. 18, 1976, Luna-24 fired its engine one more time to conduct a braking maneuver and to initiate its final descent onto the lunar surface. Just six minutes later, at 09:36 Moscow Time, the spacecraft successfully touched down on the night-covered south-eastern region of Mare Crisium (Sea of Crisis), some 40 kilometers from the "shoreline" peaks rising between three and five kilometers above the "sea" surface. Shortly before touchdown, the main engine was cut off as planned and the final descent was conducted under the power of small vernier thrusters.
Operations on the Moon
As it transpired later, this landing area was primarily dictated by the propulsion capabilities of the launch vehicle. (397) The landing location was "traditional" for previous Soviet sample-return missions, concentrating in the Moon's equatorial areas on the eastern fringes of its visible side. (398) Deep underneath this region laid a large mascon -- a concentration of mass in the lunar interior, which affects the gravitational field of the Moon. (789)
Luna-24 apparently ended up just a few hundred meters (397) from its ill-fated predecessor -- Luna-23. It was also the same region, where another failed mission -- Luna 15 -- was heading to in 1969, in a last-ditch attempt to upstage Apollo-11 astronauts in bringing back lunar soil. Like other "sea" areas on the Moon, the slightly tilted plain where Luna-24 had landed was probably created by lava flows at least 1.4 billion years ago. In the following eons, meteoroid bombardment had peppered the landscape with numerous craters. A 1.5-kilometer deep, six-kilometer wide impact crater named after physicist Daniel Fahrenheit was located 18 kilometers to the west. The Luna-24 mission scientists believed that the probe's samples could contain blast debris ejected as a result of impacts that formed Fahrenheit and other nearby craters . (398)
Following the touchdown of Luna-24, it took the KIP-10 ground control station 15 minutes to check the health of the spacecraft and determine its location on the surface. (788) Then, ground controllers commanded the probe's soil-sampling mechanism to initiate drilling into the surface.
The LB-09 drill was using a rotating mode up to a depth of 120 centimeters, when it switched to percussion-rotating mode.
As in previous soil-return missions, telemetry relayed information to ground control on the performance of the drilling mechanism and the process of loading of the samples into the return vehicle. (393) Data showed that Luna-24's drill reached a depth of two meters under a 30-degree angle toward the local vertical, penetrating 225 centimeters deep into the soil. (398) As a result, a 260-centimeter flexible tube with a diameter of 12 millimeters was partially filled with lunar regolith. The tube was then coiled in a spiral-like fashion on a special drum with a diameter of 80 millimeters, which in turn, was sealed inside the metal storage container of the reentry capsule.
From the Moon to the Earth
After 22 hours 49 minutes on the Moon, the return craft containing the precious soil lifted off from the lunar surface on Aug. 19, 1976, at 08:25 Moscow Time, using its KT descent stage as a launch pad.
The ascent engine accelerated the vehicle to a speed of about 2.7 kilometers per second for a direct flight to Earth. At a predetermined distance from Earth, ground control sent a command for the separation of the reentry capsule from the return vehicle. Eight hours later, the capsule reentered the Earth's atmosphere. After initial deceleration, the capsule released a drogue parachute at an altitude of 15 kilometers, followed by a main parachute four kilometers lower. (185) The capsule successfully touched down 200 kilometers south-east of the city of Surgut in Western Siberia, on Aug. 22, 1976, after an 84-hour journey from the Moon to the Earth. According to official Soviet sources, the landing took place in the pre-determined area, however no other civilian missions are known to have concluded in this area either before or after Luna-24.
As with the Luna-23 mission, the descent stage functioned for several days on the lunar surface, during which ground controllers reportedly conducted a number of engineering tests, including additional operations of the drill. Those trials aimed to facilitate the development of yet another version of the sampling drill for Martian sample return missions.
Luna-24 brought back 170.1 grams of lunar soil from the "sea" region of the Moon packed in a 160-centimeter-long cylindrical column. The rest of the 260-centimeter plastic spiral was only partially filled. (398) Still, it was more than three times the amount delivered by the previous Soviet sample-return mission -- Luna-20 -- from the "continental" region of the Moon. (118)
After landing, the samples were delivered to the Vernadsky Institute of Geochemistry and Analytical Chemistry, GEOKhI, of the Russian Academy of Sciences in Moscow. Some portion of the soil from the Luna-24 mission was provided to the Geological Institute of the Czech Academy of Sciences, and 0.91 grams wee given to the British scientists. During his visit to Moscow three months after Luna-24's return to Earth, NASA scientist Dr. Michael Duke exchanged three grams of samples from Luna-24 for 0.5 grams of samples delivered by Apollo astronauts. Luna-24 samples were then studied at the lunar research institute in Houston and at a number of US academic institutions.
The wealth of scientific information resulting from the analysis of Luna-24's soil samples by an international team of scientists was summarized in a 1980 Soviet publication, comprising more than 30 scientific papers.
Soil samples showed multiple layers of diversely colored and structured material, which probably reflected the complex geological history of the region with multiple deposits of material over time.
Relatively large debris fragments were found within the sample, which mostly consisted of "sea"-type materials. No more than one or two percent of the soil represented the "continental" material and it was mostly found in the glass content of the sample.
A large portion of magma basalt in the soil was high in aluminum (up to 19 percent Al2 O3) and iron (16-20 percent FeO) with very low content of titanium (1 percent of TiO2).
The age of regolith was determined to be around 300 million years. (398)
Engineering legacy of E8-5M
Although Soviet scientists mulled follow-on lunar probes, Luna-24 turned out to be the last Soviet mission to the Moon and the last spacecraft to accomplish a soft landing on the Moon in the 20th century. Luna-24 can be considered the true conclusion of the first Moon race as just six months before its launch, the Soviet government canceled the nation's effort to land cosmonauts on the Moon.
With the conclusion of the lunar program, the Soviet engineers at KBOM design bureau, its Tashkent branch and NPO Lavochkin began a parallel effort to develop a new-generation drill for the 5M mission designed to return samples of soil from Mars. The new drill was expected to be capable of penetrating up to three meters into the Martian surface. KBOM had already begun testing components of the new-generation drill when the 5M project was also cancelled due to numerous technical and financial problems. (363)
Known specifications of the LB-09 drill on Luna-24:
Luna 24 mission chronology (1976):
Aug. 9, 18:04:12 Moscow Time (15:04 GMT): A Proton rocket carrying Luna-24 lifts off from the "Left" launch pad at Site 81 in Baikonur, entering an initial 188 by 243-kilometer Earth orbit with a 51.54-degree inclination toward the Equator. The Block DM upper stage then fires to send the spacecraft toward the Moon. Luna-24 then separates from the upper stage.
Aug. 11: Luna-24 conducts a trajectory correction.
Aug. 14 (Aug. 13, 23:11 GMT?): Luna-24 enters an initial lunar orbit with an altitude of 115 kilometers above its surface and a 120-degree inclination toward the lunar equator. The orbital period (the time to complete each orbit) is 1 hour 59 minutes.
Aug. 16: Luna-24 conducts a lunar orbit correction.
Aug. 17: Luna-24 conducts an orbit correction resulting in a 12 by 120-kilometer orbit above the Moon.
Aug. 18, 06:36 GMT: Luna-24 initiates a braking maneuver to descend onto the lunar surface.
Aug. 18, 06:36 GMT: Luna-24 touches down successfully on the lunar surface at 12 degrees 45 minutes North latitude, 62 degrees 12 minutes East longitude.
Aug. 19, 05:25 GMT: The return vehicle of Luna-24 lifts off from the Moon.
Aug. 23, 05:55 GMT: The reentry capsule of Luna-24 lands on Earth.
Luna 24 flight control team (GOGU):
Head - L. V. Onishenko; Deputy Head - V. M. Nikolsky; Members - I. L. Feodorov, N. M. Eremenko, V. M. Sapranov, G. G. Latypov, K. K. Davidovsky, E. G. Samal. (270)
Written by Anatoly Zak; last update: December 21, 2016
Page editor: Alain Chabot, Edits: June 22, 2010, August 9, 2016
All rights reserved
Artist renderings of the E8-5M spacecraft on the surface of the Moon. Credit: NPO Lavochkin
An artist rendering illustrates the liftoff of the return vehicle of the E8-5M spacecraft from the Moon. Click to enlarge. Credit: NPO Lavochkin
A full-scale prototype of the E8-5M lander. Credit: KBOM
The E8-5M spacecraft during pre-launch tests.
The ascent stage of the E8-5M spacecraft, the LB-09 drill and the instrument section of the descent stage, KT.
The E8-5M spacecraft during pre-launch processing. Credit: NPO Lavochkin
The LB-09 soil-sampling mechanism for the E8-5M probe (left) developed by Tashkent branch of KBOM (TashKBM) and capable of drilling up to a depth of 2.5 meters. A follow-on drill for the 5M Mars sample return mission is on the right. Click to enlarge. Copyright © 2002 Anatoly Zak
Opening of the Luna-24's sample container with a circular knife. Credit: (398)
Processing of soil samples inside a glove box chamber at Vernadsky GEOKhI institute in Moscow. After removal from the flight container, the flexible hose containing the lunar soil was placed on a special disk with a spiral groove for initial X-ray imaging. Click to enlarge. Credit: (398)
The sample-carrying spiral (top) known as a "slug" and its X-ray image. Credit: (398)
Lunar soil after removal from its container. Credit: Roskosmos
A fragment of agglutinate (a clump of soil particles) delivered from the Moon by Luna-24. Credit: GEOKhI
Lunar soil delivered by a Soviet sample-return spacecraft. Copyright © 2011 Anatoly Zak
A 1976 Soviet stamp dedicated to the Luna-24 mission. Anatoly Zak's collection
Pennants designed by G. M. Turgenev and carried on the Luna-24 mission. The bottom pennant (front and back) was probably attached to the edge of the return capsule, which brought it back to Earth after the trip to the Moon. Another probably remained on the lunar lander.
Luna-24's descent stage sits at the edge of the crater at the end of the first decade of the 21st century, as seen by the US Lunar Reconnaissance Orbiter. Click to enlarge. Credit: NASA