On August 10, 2023, at 23:10 UTC, the Russian Luna 25 spacecraft launched to the Moon from Vostochny cosmodrome on top of a Soyuz-2.1b rocket with a Fregat-M upper stage. This is the first mission to explore the Earth satellite created by the Russian Federation: the previous spacecraft, Luna 24, was launched in 1976 by the Soviet Union. The entire future of the lunar program in Russia depends on whether this spacecraft will be able to make a soft landing near the south pole of the Moon.
The pause between Luna 24 and Luna 25 shouldn’t have been so long. Since the 1990s, the Luna-Globe program has been developed in Russia to study the internal structure of the Moon. At various times, it included penetrators (shock probes that had to be inserted into the lunar soil at three or four points at high speed), orbiters, landing stations, and lunar rovers, and the program was regularly changed. It was planned to prepare the mission for launch in 2013.
After the Russian Lunar Exploration Neutron Detector (LEND) onboard the American Lunar Reconnaissance Orbiter (LRO) showed the presence of water in the lunar soil, it was decided to focus on the study of the polar regions of the Moon. However, some researchers draw attention to the fact that the Luna-Globe project was revised after the Fobos-Grunt fail in 2011, since it was supposed to be manufactured on the same platform and contain some similar design solutions.
— Katya Pavlushchenko (@katlinegrey) August 2, 2023
The new concept was to launch a series of spacecraft, beginning with a small lander that will land near the south pole of the Moon and examine soil samples on the spot. Until recently, the leadership of Roscosmos and the developers of the spacecraft didn’t hesitate to admit that the main task of the mission would be to work out basic soft landing technologies, and, second of all, to explore the south pole of the Moon. In 2013, the mission received the name Luna 25, which made it look like a continuation of the Soviet lunar program.
NPO Lavochkin, which previously built Soviet lunar landers and orbiters, was selected as the developer of the new device, and the Space Research Institute became responsible for the scientific payload.
Luna 25 is a fairly simple spacecraft when compared with the achievements of the Soviet lunar program. With a mass of 615 kilograms without fuel, the mass of its scientific instruments is only 30 kilograms. The payload is concentrated in the upper part of the device. It is heated by a RITEG during the lunar night and consists of 9 science instruments, which tasks are:
- Estimation of the mass fraction of water in the lunar soil; determination of the elemental and isotopic composition of the upper layer of the polar regolith in the landing area at a depth of up to 40 centimeters.
- Measurement of the radiation background of neutrons and gamma rays on the lunar surface.
- Investigation of the composition of the circumpolar lunar exosphere and the physical processes occurring in it under conditions of a calm and active Sun, as well as during periods when the Moon passes through the tail of the Earth’s magnetosphere.
The bottom part of the spacecraft contains the propulsion system, fuel tanks, absorbing supports, as well as part of the communication system antennas, and scientific instruments — a manipulator to collect the soil samples, an active neutron spectrometer, and a lunar dust recorder.
Four solar panels will provide the onboard equipment with electricity. Their construction is somewhat unusual. On landers operating near the equator, the panels are usually fixed horizontally to catch the sunlight more easily. However, in the region where Luna 25 will land, the Sun isn’t rising above 20 degrees above the horizon, so the solar panels are installed vertically.
The spacecraft is equipped with eight cameras: four wide-angle cameras for panoramic shooting of the surrounding landscape, two narrow-angle stereo cameras on a common basis for shooting the working field of the manipulator and managing operations with the regolith, two cameras on the bracket of the spacecraft propulsion system for shooting the surface of the Moon during descent and landing.
Initially, it was planned that two foreign-made instruments would be installed on Luna 25, but both were canceled due to different reasons. A Swedish device LINA-XSAN to study the space plasma interaction with the lunar surface was planned to become one of the key instruments of the mission, but due to constant postponements, it flew on the Chinese Chang’e 4 in 2019. PILOT-D, a European navigation demonstration camera, was canceled due to Russia’s attack on Ukraine in 2022.
According to the original plan, Luna 25 was supposed to be launched in 2014. However, various reasons provoked delays one after another. The last big postponement (from 2021 to 2023) was caused by the malfunction detected in the Doppler speed and range meter (DISD-LR) during the tests. Being an important part of the soft landing system, this device couldn’t be ignored, and its insufficient accuracy may cost a mission. The repeated tests of DISD-LR and subsequent changes of the lander’s software caused a delay for almost two years.
As a result, Luna 25 is heading to the Moon only in August 2023, 47 years after Luna 24. For unknown reasons, Roscosmos kept the launch date a secret until August 7, although it made no sense due to multiple information leaks from different independent sources. Despite the fact that Vostochny Cosmodrome (as well as Baikonur) is located in a time zone different from Moscow, the official launch time in Russia is traditionally always considered to be Moscow time. It was 02:10:57 AM MSK on August 11, when Soyuz 2.1 cleared the tower and sent Luna 25 mounted on a Fregat upper stage to the Moon.
The rocket launched the spacecraft into a circular near-Earth orbit with an altitude of 200 kilometers. After about one hour, Fregat upper stage will fire its engine for the first time to send the lander to the trajectory to the Moon. After two burns, at a distance of about 3,000 kilometers from Earth, it will separate from Luna 25, and it will make the remaining journey to the Moon using its own engines.
— Katya Pavlushchenko (@katlinegrey) August 2, 2023
The first orbit correction is planned for a day and a half after launch, when the spacecraft will be at a distance of about 230,000 kilometers from Earth, with the help of Luna 25’s low-thrust engines firing for 20-30 seconds. The same engines will provide the second orbit correction around a day before entering the Moon’s orbit at a distance of 340,000 kilometers from Earth. The entire journey to reach the Moon’s orbit should take about four-and-a-half to five-and-a-half days. The main engine of the spacecraft will burn for the first time to slow Luna 25 down and enter the lunar transfer orbit.
The lander will spend the next three days in a circular 100-kilometer lunar orbit, making 36 orbits around the Moon, collecting data, while Mission Control will decide which landing site to choose. On the fourth day, MCC specialists will form a landing orbit for Luna 25. It will be elliptical, with a pedigree of 18 kilometers and an apogee of 100 kilometers.
The spacecraft will spend two more days in this orbit, having completed 24 orbits before the landing begins. Thus, according to the calculations of enthusiasts, the landing on the Earth satellite is scheduled for approximately August 21-23 (Roscosmos still has not confirmed the landing date and schedule).
Landing should occur with a vertical speed of 1.5 to 3 meters per second, a horizontal speed of no more than 1 meter per second, and the angle of deviation of the longitudinal axis from the gravitational vertical of no more than seven degrees. The planned landing accuracy is an ellipse measuring 30 by 15 kilometers.
There are three landing sites chosen for Luna 25. When choosing a landing site, the following parameters were taken into account: terrain (it is safe to land at a slope of no more than 15 degrees), the reliability of the lander’s radio communication, the length of daylight (this is important for the implementation of the scientific program), the abundance of signs of water, and sufficient geological diversity.
The main landing site is located in the area of 69.545 S 43.544 E, north of the Boguslavsky crater; two reserve sites are at 68.773 S 21.210 E southwest of the crater Mancini and 68.648 S 11.553 E south of the crater Pentland A.
Pavel Shubin, Russian space blogger and author of several books about the history of space exploration, calculated that the possible dates of #Luna25 landing are August 21, 23 and 24 by Moscow time (depending on the choosen landing site). So, we still have an intrigue! pic.twitter.com/uXsAuZBsFI
— Katya Pavlushchenko (@katlinegrey) July 14, 2023
If the Luna 25 mission is successful, Russia plans to launch the Luna 26 orbiter as the next step, which will study the Moon remotely and map the distribution of water ice on its surface. They say that NPO Lavochkin is already working on its design. After that, two more missions should take place.
The Luna 27 lander will again study the regolith and the ice contained in it near the south pole of the Moon, but with more instruments than Luna 25. And in the end, Luna 28 should deliver the regolith with ice to Earth. But the fate of all those missions depends on Luna 25 now; if the expensive mission fails, they can cut funding for the next missions, and in such circumstances, the cautious behavior of Roscosmos can be understood.
(Lead Image: Soyuz-2.1b on Vostochny Cosmodrome during launch. Credit: Roscosmos)