Moon

SLIM: Japan Lands on the Moon

Published on 25 January 2024

The Smart Lander for Investigating Moon (SLIM) from the Japanese space agency JAXA, launched in September 2023, arrived on our natural satellite on January 19. Japan thus became the fifth nation to successfully land on the moon.

This is not the first time that the land of the rising sun has taken an interest in the Moon. In particular there was the small Hiten probe at the beginning of the 1990s and especially Kaguya, an ambitious 3-ton orbiter clad in scientific instruments which revolved around our celestial neighbour from 2007 to 2009. But this time, with SLIM, the Japanese space agency JAXA (Japan Aerospace eXploration Agency) is seeking to land on the surface of the Moon by testing a new technology.

The lunar surface seen by the MBC. This is the first image from the multispectral camera on board the SLIM lander .

@JAXA

SLIM RECHARGES ITS BATTERIES

UPDATE JANUARY 29, 2024

JAXA, the Japanese space agency, has announced that it has managed to reconnect with its lunar craft. “We managed to establish communication with SLIM last night and have resumed operations!” explained the SLIM teams on X (formerly Twitter). “We immediately began scientific observations with MBC,” the multispectral camera on board the Japanese lander. JAXA also published an image of the lunar surface. If SLIM is working again it is “probably because the energy production of its solar battery resumed while it was exposed to sunlight,” explained a JAXA spokesperson to Agence France Presse. “We are going to prioritise what we can do, which is observe and collect information, rather than adjusting Slim ‘s position, which could make the situation worse.”

AN IMAGE OF SLIM ON THE MOON

UPDATE JANUARY 25, 2024

On January 25 the Japanese agency JAXA published an astonishing image of its SLIM lander landed on the surface of our natural satellite. The image was acquired by the mini-rover Sora-Q (or LEV-2, see below), a sphere 8 cm in diameter weighing 250 grammes equipped with two cameras. The creation of this little robot called in particular on the know-how of toy manufacturer Takara Tomy (along with Sony and Dōshisha University).
The image confirms what the first data received seemed to indicate, namely that while SLIM succeeded in its moon landing, it did not land in the expected position and is resting on its “front” side (opposite the side housing the main thrusters, which we can see at the “top” of SLIM). This orientation explains why the solar panels are not correctly oriented upwards, which prevents the vehicle’s batteries from recharging.

SLIM on the Moon, an image acquired by the Sora-Q mini-rover. Note the nozzles of the main thrusters at the top of the lander, betraying the fact that SLIM is not in the expected arrival position.

Sora-Q only had two hours of battery life after being released by SLIM during the moon landing. The image was therefore acquired shortly after arrival on the Moon and relayed to Earth by LEV-1, equipped with its own communications capabilities.
© JAXA

AN ANOMALY DURING THE DESCENT

In parallel with the publication of this image, JAXA held a press conference broadcast on YouTube (in Japanese, opposite). We learned that during the final descent towards the Moon, SLIM experienced an anomaly with its main thruster only about fifty metres from ground level. Photos of the surface taken by the lander as it continued its descent even show a propellant nozzle that fell off onto the lunar surface! The reason for the anomaly has still to be determined.

On the other hand, and despite this major dysfunction, SLIM managed to land “gently” with a descent speed of 5 km/h (the upper tolerable range was 10 km/h). In addition, first observations point to a landing around fifty meters from the target point. The objective of 100 m of precision had been achieved. However, the loss of a motor resulted in residual lateral speed which explains why SLIM ended up on its side. Note that the mini-rovers LEV-1 and LEV-2 (Sora-Q) were released just before at an altitude of five metres.
These first findings confirm that Japan is the fifth nation to successfully make a soft landing on the Moon (after the Soviet Union, the United States, China and India.)

SLIM IS ON THE MOON

The SLIM robotic lander was sent to the Moon in September 2023, as a “secondary passenger” when the XRISM space telescope was put into orbit. A rather modest machine weighing 590 kg (fuel included), SLIM took a long trajectory towards our natural satellite.

UPDATE JANUARY 19 – 6:35 p.m.

JAXA had indicated that SLIM would land on Friday the 19th at 4:20 p.m. Metropolitan France time. The live broadcast certainly showed the arrival on the Moon of the machine (telemetry, no images), but the success of the mission was not announced formally. During a press conference broadcast a little more than two hours later, the Japanese agency indicated that SLIM had landed and was transmitting data (especially images).
On the other hand, the solar panels were not generating electricity. This meant that SLIM’s batteries would not recharge, which would limit the operational lifespan on the surface (an exact duration was not specified ). Apparently the LEV-1 and 2 mini-rovers (see below) had been released as planned and data analysis was underway.
As for the desired precision of the landing, they expressed optimism, while explaining that they needed to examine additional data before claiming success for this.

JAXA plans to provide additional information later.

The article continues below this YouTube window.

Direct de la JAXA pour suivre l’alunissage de SLIM le 19 janvier. La retransmission commencera à 15h heure française et deviendra un replay après.

SLIM: PRECISION OBJECTIVE

On this mission, JAXA tested new technology to allow arrival in automatic mode to a desired precision of 100 m. It has to be understood that a transmission (video images of the ground during descent, for example) takes a little more than a second to pass from the Moon to the Earth and the same, of course, for a command sent from a control centre. We cannot therefore effectively pilot from our planet to land a craft on our natural satellite. And if you also want to target an area with great precision, the only solution lies in an on-board computer capable of making the final trajectory adjustments depending on various data provided by one or more cameras and other instruments such as an approach radar.

An image of the Moon by SLIM taken in mid-January while the lander was in Lunar orbit.
© JAXA

Top: diagram of SLIM’s mode of arrival on the Moon.

Bottom: illustration of the Japanese machine once landed. Before its tilting phase shortly before landing, SLIM will release the LEV-1 and LEV-2 mini-rovers.
© Cité de l’espace after JAXA

FACIAL RECOGNITION APPLIED TO A MOON LANDING

With SLIM, JAXA is innovating by using the IT principles of facial recognition adapted to lunar reliefs (which explains the acronym Smart). The on-board computer will thus analyse images from its on-board camera, comparing them to a map of the region stored in memory in order to direct SLIM towards the target point while avoiding possible obstacles (large rocks, small unlisted craters, etc.).

The arrival area is on the slopes of the Shioli crater (270 m wide) located in a larger crater, Cyrillus, 98 km in diameter, on the edge of the Sea of Nectar (visible side). The descent profile is also quite original with an approach where SLIM is vertical from around 7 km altitude, using propulsion braking, then it tilts horizontally at around 3 m to fall to the ground, cushioned by short landing legs designed to withstand the residual speed. Just before, it will have released two mini-rovers (LEV-1 and LEV-2).
LEV-1 (Lunar Excursion Vehicle 1) has a mass of 2.1 kg and is 40 cm wide. It will be able to move by leaping. LEV-2 or Sora-Q is a sphere 8 cm in diameter weighing 250 g equipped with two cameras (lifespan limited to two hours by battery capacity).

LAND WHERE YOU WANT

With a target accuracy of 100 m, JAXA announced that it wants to move from “we land where we can” to “we land where we want!”

This is a challenge for scientific missions since very often the most interesting regions are located near potentially dangerous reliefs for a moon landing (slopes, rocks, craters , crevasses, etc.). It is also a very useful step forward for the new impetus towards our natural satellite, in particular the Artemis programme on which JAXA is a partner. Some future crewed flights to the surface will require cargo (experiments , rover, resources) transported by robotic vehicles and this precision will guarantee that the equipment brought in this way will not be too far from the site where the astronauts land.

JAXA illustration showing the release of LEV-1 and LEV-2 (Sora-Q) during the arrival of SLIM. LEV-1 has a direct communication capability with Earth and will relay images from Sora-Q.
© JAXA