Luna-13: Charting the path for cosmonauts
Less than a week after the disastrous launch pad accident with the Soyuz spacecraft on Dec. 14, 1966, a team led by Georgy Babakin made up for the failure by successfully launching from a near-by pad the second Soviet robotic lander to the Moon. The E6 probe aimed to test the mechanical properties of the lunar soil, which would be crucial for the planned Soviet landing on the Moon. In fact, the spacecraft could be the final Soviet reconnaissance mission to the lunar surface before the arrival of the first cosmonaut.
The Luna-13 (E8M) lander.
Luna-13 mission at a glance:
Not new but improved lander
Belonging to the E6M series of Soviet landers, the Luna-13 closely resembled its predecessor, Luna-9, but had a number of major improvements in its scientific gear. First of all, the single Volga TV camera on the original lander was complemented with a second 1.3-kilogram optical-mechanical camera with a cylindrical window in order to produce stereo-imagery. Both camera turrets were mounted at the top of the lander. However the most visible addition to the lander design was a pair of 1.5-meter, five-section, spring-loaded deployable booms carrying a GR-1 soil-probing penetrator and a RP radiation density sensor. (788)
Probing ground for future spacecraft
The primary instrument of the Luna-13 mission was designed to study the mechanical strength of the soil for the first time. The GR-1 device, informally known in Russian as "gruntomer" (soil measurer) featured a 1.3 centimeter-long titanium cone with a diameter of 3.5 centimeters and an opening angle of 103 degrees. The size of the probe was chosen to ensure noticeable penetration into most soft and porous substances, with the exception of hardened lava.
The penetrator could extend up to five centimeters from a plastic body, which had a ring-like base with a diameter of 12 centimeters. The upper cylindrical section of the instrument contained a miniature solid rocket motor with its nozzle pointed upwards when on the surface. The nozzle was covered with an electrically operated pyrotechnic igniter, which was designed to be thrown out by the exhaust.
Simultaneously with the ignition of the motor, the instrument would unlock the penetrator, allowing its free movement downward. The cylindrical part of the penetrator had a pin, which could slide along the indentation of the instrument's casing and connected to a sensor measuring the motion of the penetrator. On a particular soft surface, such as dust-like material, the penetrator could extend to its maximum and then pull the ring base of the instrument into the ground, which could be documented by a TV camera.
A burst of the solid motor lasting from 0.6 to a second was designed to drive the cone into the soil with a force of from five to seven kilograms, while the instrument's sensors could record the position of the probe with an accuracy of 0.03 centimeters. (801)
The experiment was developed at the VNII-100 institute in St. Petersburg specialized in chassis for tanks and already involved into the Soviet lunar program designing future rovers. The developers used 14 different substances from dust-like materials to solid concrete and porous basalt to calibrate the instrument. Some tests were conducted in a vacuum chamber to simulate lunar conditions.
The second deployable instrument on the Luna-13 was designed to measure the composition of the surface layer by emitting gamma rays from a cesium-137 source and then recording their scattering. (118) Russian scientists dubbed it "plotnomer" or densitometer.
Three groups of five miniature SBM-10M gamma-ray counters protected from the direct radiation by a lead screen were used to calculate the scattering of the gamma rays by the surface. The distance from the center of each sensor group to the source of gamma rays varied. The entire sensor unit had a size of 258 by 48 by 10 millimeters.
The recording system for the instrument was housed inside the pressurized compartment of the lander and was connected with the counters by three cables. It had three channels for each group of sensors. The averaging of data from the three groups of sensors was required to reduce the probability of errors in measurements caused by uneven surface and resulting cavities between the sensor and the surface material.
The instrument was tested on the ground with many different types of materials. (801)
Yastreb dynamometer and other instruments
Inside its spherical pressurized compartment, the lander carried a DS-1 Yastreb dynamometer, measuring the level and timing of g-forces exerted onto the lander at touchdown with the help of three accelerometers installed at 90 degrees toward each other to provide three-axis measurements. The instrument was calibrated during drop tests of the spacecraft prototype onto various surfaces including dense sand.
Luna-13 also carried the ID-3 infrared radiometer with four sensors located on the circumference of the capsule to measure the thermal flow from the surface.
Finally, the KS-17MA radiation detector was also onboard, mounted near the TV camera at the top of the lander. (2)
Along with their importance for the fundamental studies of the Moon, practically all the experiments aimed to prepare the arrival of much more heavier lunar vehicles, and ultimately, human expeditions. (800)
Service systems upgrades
In addition to the new scientific instruments, the spacecraft bus also had a few upgrades. To prevent freezing of water in the vaporizer of the thermal control system, the floating controller was replaced with a new system using a bi-metalic controller. In addition, the Mayak-6 angle-measuring unit operating in the decimeter-range was replaced with the RKT-1 transmitter-receiver working in the same wavelength. (788)
Luna-13 heads to the Moon
The Molniya rocket carrying the E6 No. 205 spacecraft lifted off from Site 1 in Tyuratam on Dec. 21, 1966, at 13:17:08 Moscow Time. The first three stages of the rocket inserted the spacecraft into a 171 by 223-kilometer parking orbit around the Earth with an inclination of 51.8 degrees toward the Equator. (185)
After the Block-L upper stage successfully sent the spacecraft into its trans-lunar trajectory, Soviet media announced the mission as Luna-13. Following the measurement of its exact trajectory, the spacecraft was commanded to conduct an orbit correction on December 22, at 18:41 GMT.
The maneuver was successful, however soon thereafter, the RKT-1 transmitter failed to activate, complicating further estimates of the probe's trajectory. Also, onboard tests conducted during the trans-lunar flight revealed that one of the two TV cameras on the lander was inoperable.
Luna-13 lands on the Moon, begins its pioneering science
On the Christmas Eve of 1966, Luna-13 approached the Moon and began its braking maneuver at 20:57 Moscow Time (17:57 GMT) at an altitude of around 70 kilometers. The soft-landing bags were inflated around the lander and the avionics containers jettisoned from the main spacecraft.
Less than a second before the carrier vehicle made a low-speed collision with the Moon with a velocity of 30 kilometers per hour, the lander was successfully ejected upwards and then gently bounced on the surface inside its inflatable cocoon.
The successful landing was recorded at 21:01 Moscow Time (18:01 GMT) on December 24, on the night-covered Ocean of Storms, between craters Krafft and Seleucus. The landing site was determined to be around 440 kilometers from the final resting place of the Luna-13's predecessor, Luna-9. (2)
Ground controllers began receiving signals from Luna-13 at 21:05 Moscow Time (18:05:30 GMT) on December 24. The telemetry confirmed that the four petals of the lander had successfully opened, followed by the deployment of the newly designed instrument booms. The sensor of the penetrator at the end of one boom then marked the initial position of the instrument on the surface. Immediately, at 21:06 Moscow Time (18:06 GMT), the solid-propellant charge fired at the end of the boom, forcing the titanium rod of the penetrator 4.5 centimeters into the alien soil. (During future measurements, the depth of the penetrator varied from 4.17 to 4.33 centimeters, probably as a result of temperature deformation of the probe and the instrument boom. The extension of the probe was not enough to deepen its ring base into the surface.)
On the opposite side of the lander, the radiation-density experiment was also successfully activated, mostly confirming soil property data from its counterpart on another boom. The density of the lunar soil at the landing site was estimated at 0.8 grams per cubic centimeter, based on the data of the radiation densitometer and 1.52 grams per cubic meter based on the measurements of the dynamometer. In any case, it was lower than typical terrestrial materials and lower than the average density of the Moon itself. It was also possible to conclude that the surface material had low viscosity and had a depth of around five centimeters.
Looking at the data from Luna-13, Soviet scientists also concluded that the mineral composition of the material resembled basalt -- typical for "seas" of the Moon. Its statistical carrying capability at a depth of 3.2 centimeters was estimated to be 0.68 kilograms per square centimeter. (801)
Luna-13 takes another look at the surface of the Moon
On December 25, 1966, at 00:30 GMT, the Sun appeared over the horizon in the Ocean of Storms, right behind the probe's lenses and 11 hours 45 minutes later (at 12:15 GMT), the probe' one surviving stereo camera began scanning the surrounding landscape.
It took the camera 100 minutes to make a full circle with a focus from 1.5 meters to infinity. Five panoramas of the surface were obtained with the sun at the 6, 19 and 32 degrees of elevation. The transmission of the pictures was then conducted in stages during single communications sessions on December 25 and December 26 and during two sessions on December 27. For some reason, there was apparently a 4.7-minute gap in the total time of the transmission, which resulted in the loss of 16.6 degrees out of the 360-degree panoramic view.
Like during the Luna-9 mission, the Jodrell Bank observatory in England and the US intelligence posts listened to signals from the surface of the Moon along with the Soviet KIP-10 ground station near Simpheropol on the Crimean Peninsula. However this time, British scientists decided to wait for the Soviet authorities to release the photographs first, to avoid the repetition of a political scandal at the beginning of the year. The US government analysis of the intercepted data would not be released until 2003. (802)
The images from Luna-13 revealed details as small as 1.5 - 2 millimeters, when located around a meter and a half from the lander. The surrounding area was flatter than the landscape seen by Luna-9 and, as a result, the horizon extended farther away. The spacecraft was apparently sitting on the surface at an angle of 16 degrees, according to Soviet sources, (118) and 13 degrees 47 minutes, according to estimates made by US analysts. No changes in position were noticeable after four transmissions. Three separate objects originating from the spacecraft appeared in the images. (802)
Interestingly, the initial analysis of photos from Luna-13, as previously the imagery from Luna-9, seemingly convinced Soviet scientists of the absence of dust on the surface. They suggested that rocks visible in the pictures had been brought to the surface by the molten material rising from the interior of the Moon through cracks in the surface. (799) However, accounts published in the following years said that the images had revealed the presence of a powder layer on the surface. The first indication of that was the faint imprint of one of the petals visible on the photographs. Soviet scientists suggested that it had probably been formed during the opening of the petals after landing.
The radiation densitometer also left a visible print after it had gently fallen to the surface on its deployable boom from a height of a half a meter. Close-up images revealed that the device had apparently slid on the surface few millimeters forward and to the left, as a result of temperature changes and some movements of the spacecraft, leaving behind a trace of the flattened soil.
The scientists also calculated following distribution of rocks on the imaged area of 14.31 square meters:
More scientific experiments
The infrared radiometer recorded the climbing effective temperature of the lunar soil as the Sun was rising over the horizon, reaching a brutal 117 degrees C around noon. However, the radiation counter showed safe levels for human landings.
Luna-13 apparently conducted eight communications sessions with ground control and made its final contact between 04:05 and 06:13 GMT on December 28, 1966. However various sources disagree on when Luna-13's batteries were finally exhausted, ranging from December 28 to December 31, 1966. (185, 801)
What is known is that around 2 a.m. on December 31, the Luna-13 science team, carrying heavy boxes of telemetry tapes, finally boarded an Il-14 aircraft for a flight to Moscow, after being stranded for hours by bad weather at an airport in Simpheropol, Crimea. (771, 393)
Luna-13 ends the era of success
Luna-13 became the second Soviet probe and the world's third spacecraft to accomplish a soft-landing on the lunar surface, or on any other celestial body. At the conclusion of the Luna-13 mission, the Soviet space program was ready to enter the new 1967 with practically all the scientific knowledge about the Moon necessary to accomplish the landing of the first cosmonaut on the surface of our natural satellite. However, a long string of tragic events was to follow...
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Written by Anatoly Zak; last update: December 21, 2016
Page editor: Alain Chabot; last edit: December 21, 2016
All rights reserved
A museum replica of the Luna-13 lander. Credit: NPO Lavochkin
A Soviet-era painting depicts the E6M spacecraft starting braking maneuver on approach to the Moon.
An artist depiction of the Luna-13 lander on the surface of the Moon.
Luna-13 deploys its instrument booms.
Small solid-fuel charge firing to force density sensor deployed from Luna-13 into the lunar surface.
Soil-penetrating probe of the GR-1 experiment.
A close-up view of the radiation densitometer deployed from Luna–13.
Georgy Babakin (left) during transmission of data from Luna-13.
Parts of the Luna-13 spacecraft seen in its panoramas. Credit: NPO Lavochkin
Parts of the Luna-13 spacecraft seen in its panoramas.
Landing of E6M probes could be followed by the arrival of Soviet cosmonauts. Credit: Leonov, Sokolov.