The Smart Lander for Investigating Moon (SLIM), nicknamed the "Moon Sniper", was a lunar lander mission operated by the Japan Aerospace Exploration Agency (JAXA). Manufactured by Mitsubishi Electric, it was launched on September 6, 2023, aboard an H-IIA rocket from the Tanegashima Space Center, together with the X-Ray Imaging and Spectroscopy Mission (XRISM) space telescope. SLIM entered lunar orbit on December 25, 2023, and successfully soft-landed on the Moon on January 19, 2024, making Japan the fifth country to accomplish a soft landing on the Moon, after the Soviet Union, the United States, China, and India. SLIM's primary objective was to demonstrate precision lunar landing technology. Using facial recognition-derived image processing to identify lunar craters and data from the SELENE orbiter for navigation, it aimed to land within 100 m (330 ft) of its designated target near Shioli crater in the Sea of Nectar—a level of accuracy far exceeding that of earlier missions. Although the landing was successful, the spacecraft came to rest on its side, leaving its solar panels oriented away from the Sun and limiting initial power generation. After a brief period of battery-powered operation, SLIM was powered down on January 20, 2024 (JST), only to be revived nine days later when the sunlight shifted to its panels. SLIM carried two small lunar rovers: LEV-1, a hopping rover with direct-to-Earth communication capability, and LEV-2 (Sora-Q), a baseball-sized rover jointly developed with Tomy, Sony, and Doshisha University. Both were successfully deployed during descent. Although SLIM was not designed to survive the extreme cold of lunar night, it did so repeatedly, waking up for a total of four lunar days before going silent in late May 2024. JAXA officially declared the mission concluded on August 23, 2024. In doing so, SLIM set a world record for longevity among lunar surface spacecraft lacking a radioisotope thermoelectric generator (RTG).
Background The main purpose of Japan's first lunar surface mission was to demonstrate precision lunar landing. During its descent, the lander recognized lunar craters by applying technology from facial recognition systems, and determined its current location from observation data collected by the SELENE (Kaguya) lunar orbiter mission. SLIM aimed to perform a soft landing with an accuracy range of 100 m (330 ft). In comparison, the accuracy of the 1969 piloted Apollo 11 Lunar Module Eagle was an ellipse which was 20 km (12 mi) long in downrange and 5 km (3.1 mi) wide in crossrange. According to Yoshifumi Inatani, deputy director general of the JAXA Institute of Space and Astronautical Science (ISAS), succeeding in this extremely precise landing will lead to enhanced quality of space exploration. The expected cost for developing this project is 18 billion yen, or US$121.5 million.
History
The proposal came to be known as the Small Lunar Landing Experiment Satellite (小型月着陸実験衛星) (SLIM). On 27 December 2013, ISAS called for proposals for its next "Competitively-Chosen Medium-Sized Focused Mission", and SLIM was among the seven proposals submitted. In June 2014, SLIM passed the semi-final selection along with the DESTINY+ technology demonstration mission, and in February 2015, SLIM was ultimately selected. From April 2016, SLIM gained project status within JAXA. In May 2016, Mitsubishi Electric (MELCO) was awarded the contract for building the spacecraft. SLIM was not the first Japanese lunar lander built for operation on the Moon's surface; on 27 May 2016 NASA announced that the OMOTENASHI (Outstanding Moon exploration Technologies demonstrated by Nano Semi-Hard Impactor) CubeSat lander jointly developed by JAXA and the University of Tokyo was to be launched as a secondary payload on Space Launch System (SLS) Artemis 1. OMOTENASHI was meant to deploy a mini lunar lander weighing 1 kg (2.2 lb); however, on 21 November 2022, JAXA announced that attempts to communicate with the spacecraft had ceased, because the solar cells failed to generate power when facing away from the Sun. They did not face the Sun again until March 2023. In 2017, funding difficulties for developing XRISM led to SLIM's launch being switched from its own dedicated Epsilon flight to a rideshare H-IIA flight. The resulting cost savings will be transferred to develop other satellites that are behind schedule due to XRISM.
Rovers
Lunar Excursion Vehicle 1 Lunar Excursion Vehicle 1 (LEV-1) is a lunar rover which moves by hopping. It has its own direct-to-Earth communication equipment, two wide-angle visible light cameras, and electrical components and UHF band antennas courtesy of the MINERVA and OMOTENASHI projects. Science payloads:
Thermometer Radiation monitor Inclinometer
Lunar Excursion Vehicle 2
Lunar Excursion Vehicle 2 (LEV-2) or Sora-Q, is a tiny rover developed by JAXA in cooperation with the toy company Tomy, Sony, and Doshisha University. The baseball-sized rover has a mass of 250 g and is equipped with two small cameras. LEV-2 extends its shape to crawl on the lunar surface using two wheels at its sides, a method of locomotion inspired by frogs and sea turtles; it can "run" for approximately two hours. It is the second rover of its kind to attempt operations on the lunar surface; the first was on Hakuto-R Mission 1, which crashed before it could be deployed.
Mission SLIM was successfully launched together with the X-Ray Imaging and Spectroscopy Mission (XRISM) space telescope on 6 September 2023 at 23:42 UTC (7 September 08:42 Japan Standard Time) planning to land near Shioli crater (13.3°S, 25.2°E) via weak stability boundary-like trajectory. SLIM entered lunar orbit 25 December JST.
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