With problems, Japanese probe lands on the Moon – 01/19/2024 – Science

This Friday (19), Japan became the fifth country to conduct a soft landing on the surface of the Moon — but now has a spacecraft languishing due to lack of electricity. The feat, which places him alongside a select group made up of Russia, the USA, China and India, was accomplished with the Slim landing module, a low-cost mission designed to demonstrate high-precision robotic landing.

With solar panels that are not generating electricity, the probe may be short-lived. Jaxa (Japanese space agency) does not yet know what the reason for the problem is — perhaps it was due to damage caused to the equipment at the time of landing, as they were working during the orbital phase of the mission, or it could be because they landed in such a position that sunlight is not shining on them.

In the first case, little could be done. In the second, the only solution is to wait. At this moment the landing region is in the morning light, but the Sun should advance across the sky over the next few days (much slower than on Earth, as lunar days and nights last 14 Earth days) and change position sufficiently to perhaps illuminate the panels and promote battery recharging.

The truth is that it is not even known whether the vehicle managed to land upright. Faced with uncertainty, engineers are prioritizing the collection of telemetry data and scientific observations on the Moon’s surface, with the remaining hours of battery life. The heating system was turned off to conserve energy.

How was the landing

The small spacecraft, just 2.7 meters long and weighing 200 kg (not counting fuel), began its final descent approach 20 minutes before landing (the famous “20 minutes of terror”, according to Kenji Kushiki, mission manager ), leaving a perilunium orbit (closest point to the lunar surface) of 15 km.

The procedure progressed within the strictest normality throughout the entire route, and Slim made two overflight stops, one at 500 meters and the other at 50 meters, assessing threats to the integrity of the probe on the ground, before descending — all automatically and living up to the name of the probe. Slim stands for Smart Lander for Investigating Moon.

Processing images produced by a camera pointed downwards and identifying craters previously mapped by the Japanese Kaguya orbital probe, which scanned the lunar surface between 2007 and 2009, the vehicle automatically headed to its landing site, close to the Shioli crater, where it descended punctually at 12:20 pm (Brasília time).

The telemetry data was broadcast live by Jaxa on the internet, but the moment after landing was followed by several minutes of “we are checking the status of the lander”. A press conference, held two hours later, revealed the problem with the solar cells, but highlighted the successful landing, a minimum goal for the project.

“Slim landed on the lunar surface, and communication was established after landing,” said Hiroshi Yamakawa, director of Jaxa, emphasizing that the two mini-rovers released shortly before the module touched down are also operating and transmitting data. One of them is a “jumper”, which propels itself across the surface with a spring, and the other is a “transformer”, spherical in shape, but which opens to form two wheels.

The entire objective of the technological mission, which cost US$120 million, was to demonstrate precision landing capability, within a radius of a maximum of 100 meters from the target, and in terrain that was not very hospitable, with an incline of around 15 degrees. The engineers emphasized that it will only be possible to confirm this after a detailed analysis of the data collected by the probe, but that all indications based on telemetry indicate success.

If this is the case, the level of accuracy will have surpassed any other unmanned lunar or planetary mission ever conducted (only on asteroids, with very low gravity, have there been high-precision unmanned landings). In general, the landing site of a spacecraft is designated by an ellipse (something like a stretched circle), several kilometers long, which can be larger or smaller according to uncertainties in the path from orbit to the surface.

To give an idea of ​​the ambition, the landing ellipse of Apollo 11, the mission that took humans to the lunar soil for the first time, in July 1969, was 20 km long by 5 km wide. In other words, the ship could land at any point in this vast area while still fulfilling its objective.

Things changed for Apollo 12, which descended just 200 meters from the Surveyor-3 probe — but then piloted by a human. For unmanned flights, uncertainty about the landing location hasn’t changed much since then. In 2021, NASA’s Perseverance rover descended to Jezero Crater, on the surface of Mars, aiming for a landing ellipse measuring 7.7 km by 6.6 km (the NASA vehicle ended up descending 1 km from the center of the ellipse , but just five meters from the exact place where they wanted to get off, in a great success, but still with great uncertainty).

For Slim, the goal was to reduce the width of the ellipse to a maximum of 200 meters. The process involves advanced algorithms to process surface images in real time and automatically calculate the exact landing trajectory. Interestingly, engineers adapted techniques from facial recognition systems so that the probe could recognize specific craters on the Moon and locate itself.

The Japanese are betting that this technology will be essential in the future of space exploration, going from a culture in which “you go down where it’s easy to land” to one in which you “go down where you want to land.” In fact, this will be an essential factor in the development of future lunar bases, which will require the landing of several manned and unmanned spacecraft in close proximity to each other.

The US and China are keeping an eye on this, each spearheading their own project and targeting the lunar south pole, where there are believed to be large amounts of water ice preserved at the bottom of craters where sunlight never hits.

Landing-tumble

To deal with the steepness of the region chosen for descent, the Japanese also developed a curious landing method, in which the spacecraft descends vertically and, only when its rear legs touch the ground, it tilts to a horizontal position, as if it were falling over the surface. It is not yet clear whether this method was completely successful, although the probe remained operational after descent.

In addition to the technological demonstration, the mission had the additional objective of conducting scientific research. To this end, the landing module was equipped with a spectroscopic camera capable of identifying the composition of lunar rocks. The objective is to find materials that once belonged to the lunar mantle, with the aim of elucidating the origin of the Moon. The main hypothesis put forward today is that it is the result of the collision of an object the size of Mars (called Theia) with the Earth, in the early days of the formation of the Solar System. By analyzing the composition of its interior, it is possible to corroborate or challenge this idea. But with the solar panels inoperative, the chance of completing this scientific part of the mission is greatly reduced.

Since 2013, when China conducted the first lunar landing mission of the 21st century, there have been ten attempts in total: three Chinese (all successful), two Indian (one successful), one Russian (failed), one Japanese ( partially successful) and three private companies (from the Israeli group SpaceIL, the Japanese company ispace and the American Astrobotic, all failed). It is a 50% utilization, treating Slim as a success. At least two other missions, one private (American) and one state-owned (Chinese), should take place in 2024.