Last Sunday, the 12th, the Japanese space agency (JAXA) announced that its SLIM spacecraft, which has been in lunar orbit since December 25, had correctly positioned itself on its trajectory prior to the lunar landing attempt and added that “the current conditions of the ship are normal.” With this, it was confirmed that the descent maneuver would begin today, Friday, the 19th, starting at 4:00 p.m. (Spanish peninsular time).
SLIM is planned to descend to the Moon through a maneuver that ensures a maximum deviation of 100 meters from the planned location (on the edge of the Shioli crater), an unprecedented level of precision for a mission of this type. In the area chosen for the descent, there are rocks from the lunar mantle and, therefore, of great scientific interest.
In recent months, various missions have placed the Moon in the spotlight in a context of certain competition. If SLIM's moon landing is successfully completed, Japan will become the fifth country to do so, after the United States, the former Soviet Union, China and India.
SLIM left Earth in September last year, and successfully entered lunar orbit on Christmas Day. In its official statement, JAXA then explained that the ship followed the planned trajectory, consisting of an elliptical path that, passing over the poles of the Moon, reached 600 kilometers in height at its lowest point (called perilun). and that separated up to 1,200 kilometers in the furthest part of its orbit (the apolunium).
Since that first orbital insertion, JAXA engineers have been correcting the ship's route to end up placing it, last Sunday, on its optimal trajectory to prepare for the descent. It is a circular orbit 600 kilometers above the surface of the Moon.
Today SLIM will be maneuvered so that, once again, it begins to move in an elliptical orbit that, this time, places it at only 15 kilometers high in its perilunium and moving at a speed of 1,700 meters per second. The start of the final phase of the descent will take place around 4:00 p.m., with the expectation that it will touch the lunar surface twenty minutes later.
The location chosen for the lunar landing is located on one of the edges of Shioli, a crater located in the southeast of the visible side of the Moon and which is about 270 meters in diameter. This site is especially interesting from a scientific point of view, since, according to observations made in 2007 by the Japanese probe Selene, minerals from the lunar mantle would be found there, exposed on the surface. Materials that would allow us to obtain data that would complete the knowledge we have about the formation and subsequent evolution of our satellite.
Among other scientific equipment, SLIM is equipped with a camera capable of analyzing, through filters, sunlight reflected by rocks less than 30 meters away. With this information, researchers will be able to infer the detailed composition of these materials.
All scientific objectives of the mission must be completed before dark at the landing site (one lunar diurnal cycle is equivalent to about two weeks on Earth). The temperature difference between day and night on the Moon is extreme, with values dropping to –130C when sunlight is absent, and SLIM's instruments have not been designed to withstand the frigid and long lunar night. .
But for all this to be possible, the ship must land with great precision to be able to position itself as close as possible to the rocks of interest. To do this, SLIM will obtain images during the descent and continuously, and compare them with the cartography it has on board (data captured by the Selene mission), autonomously executing the necessary trajectory corrections. Engineers at the Japanese space agency have developed special algorithms so that the probe can perform these calculations with the required speed and fidelity.
In the most critical part of the maneuver, when there are only a few meters left to touch lunar soil, the spacecraft will use a laser fired at the surface to estimate, at every moment and with extreme accuracy, its height and be able to adjust the descent. The difficulty of the operation is even greater because the place where SLIM is planned to land has an inclination that can reach 15 degrees.
With all this, SLIM is expected to land with a maximum error of 100 meters above the planned point, an unprecedented level of precision since typical landing zones on lunar missions have a tolerance range that is measured in kilometers.
The fact that the maneuver must be carried out unattended and automatically adds tension to the team responsible for the mission. “Once the final phase of descent begins, there will be no point of return,” explained Masaki Fujimoto, deputy director general of the JAXA Institute of Space and Astronautical Sciences.
The manager added that all that remains is to contemplate the process, trusting that all the preparatory tasks have been carried out correctly.
Inside the ship, there are also two small robots that will explore the surroundings of the lunar landing site. SLIM will launch them to the surface at the final moment of descent, when there are only 1.8 meters left to touch the Moon.
The LEV-1 (Lunar Excursion Vehicle 1, in English) is a device that weighs just 2.1 kg and has the capacity for direct communication with Earth without dependence on the main ship. Its instruments can take images and collect data on the radiation level, temperature and slope of the terrain. But the most innovative thing about this robot is that it will move by jumping.
For its part, the LEV-2 has a spherical shape and is even smaller (250 grams in weight and a diameter of 8 centimeters). Once on the ground, the robot will open into two halves and use them, as wheels, to move. It is equipped with cameras and will send data to Earth via LEV-1. It is a design in which toy specialist companies, such as Tomy and Sony, have participated. The expected operating time for LEV-1 is about 40 minutes, and two hours for LEV-2.
In recent months, missions to the Moon have followed one after another, which shows the growing interest, both from governments and private companies, in the exploration of our natural satellite.
So far, only four countries have successfully landed on the moon. In addition to the United States, the former Soviet Union and China, India achieved it in August last year, when its Chandrayaan-3 spacecraft landed relatively close to the south pole of the Moon, a strategically interesting place due to the more than likely presence of water ice. The Asian country's milestone occurred a few days after the Russian Luna-25 mission, in its attempt to advance, crashed into the lunar surface.
With SLIM, Japan could enter this very exclusive list, as the fifth country on the Moon. Precisely, in April 2023 another Japanese ship (the Hakuto-R), owned by the ispace company, could have become the first mission financed by private capital to achieve this, but it ended in failure when it ran out of fuel in the last leg of the journey. decline.
But without a doubt, the news in recent days has been marked by the Peregrine mission, a project of the North American company Astrobotic. Its objective was to land on the Moon at the end of February carrying, inside, scientific instruments (some owned by NASA) and also human remains (ashes and DNA samples) from two companies specialized in funeral ceremonies in space. Although the ship has not been able to complete its objective due to a failure in the propulsion system, the mission has generated some debates about the extent to which it is necessary to regulate the use of space and celestial bodies.
For their part, the two great space powers, the United States and China, are advancing their ambitious lunar projects. Just a few days ago, NASA updated the dates of the Artemis program, which should mean the human return to the Moon. Specifically, it was announced that the Artemis II mission (which will send four astronauts into lunar orbit) will launch in September 2025 and that Artemis III (which will descend to the surface of the Moon) will do so in September 2026.
China's plans point towards 2030 for the arrival of its astronauts to our satellite, a destination in which the Asian giant has paid great interest in recent years. Currently, its Yutu-2 robot is still active on the far side of the Moon (China is the only country that can boast of having landed in the lunar hemisphere not observable from Earth), and at the end of 2020 the Chang'e 5 mission achieved return from the Moon with rock samples, an event that has not happened since 1976.
