Japan's SLIM has triumphantly achieved lunar orbit insertion and is now poised for a meticulously planned lunar touchdown.

Japan's SLIM robotic spacecraft celebrated a significant achievement on December 25 as it smoothly entered lunar orbit, paving the way for an eagerly anticipated moon landing scheduled for January 19.

Credits: Japan Aerospace Exploration Agency (JAXA) 

The successful lunar orbit insertion burn, lasting approximately three minutes, occurred at 2:51 a.m. Eastern (0751 UTC), according to an announcement by the Japan Aerospace Exploration Agency (JAXA) on Christmas Day. Presently, SLIM is positioned in a polar lunar orbit with dimensions of 600 x 4,000 kilometers, aligning precisely with the mission plan. JAXA reported that the spacecraft is currently operating under normal conditions and is now poised to initiate a gradual descent, preparing for the imminent lunar landing.

Scheduled for January 19 at 10:00 a.m. Eastern (1500 UTC), the landing attempt is expected to conclude around 20 minutes later. The precision-focused mission aims to place the lander within a mere 100 meters of its designated target point on the slope of the mid-latitude Shioli crater.

The SLIM mission commenced on September 6 with a launch atop an H-2A rocket from Japan's Tanegashima Space Center, sharing its journey with the XRISM space telescope. Following its entry into low Earth orbit, SLIM undertook a series of orbit-raising maneuvers, embarking on a circuitous route to the moon. A translunar injection burn on September 30 facilitated a lunar flyby on October 4, setting the spacecraft on a propellant-efficient trajectory that ultimately led to lunar orbit insertion on Christmas Day.

In the upcoming phases of the mission, SLIM is set to gradually lower its apolune, reaching a circular orbit at an altitude of approximately 600 kilometers in mid-January. Subsequently, the perilune, or closest point to the moon, will be lowered to a 15-kilometer altitude orbit on January 19, Japan time, initiating the deceleration process from a speed of around 1,700 meters per second.

Credits: Japan Aerospace Exploration Agency (JAXA) 

To ensure a safe landing, SLIM is equipped with five crushable 3D-printed aluminum lattice landing legs, designed to absorb the impact and facilitate a gentle settlement on the sloped rim of the 300-meter-wide Shioli crater. Successfully achieving a lunar landing would position Japan as the fifth country to accomplish this feat, with India having achieved a similar milestone in August through its Chandrayaan-3 mission.

The primary goal of the SLIM mission is to demonstrate highly accurate lunar soft-landing capabilities with a lightweight architecture. Utilizing a vision-based navigation system and incorporating observational data from Japan's SELENE orbiter launched in 2007, SLIM will autonomously identify its landing zone during descent. Additionally, it carries a laser range finder for the final stages of descent.

Beyond the landing attempt, SLIM is designed for surface operations during the lunar day, conducting experiments that include the use of a Multi-Band Camera (MBC) to analyze the composition of the Shioli crater. Scientists are particularly interested in detecting the mineral olivine, potentially ejected from beneath the moon's crust.

Innovatively, SLIM is accompanied by two small rovers, Lunar Excursion Vehicle 1 (LEV-1) employing a hopping mechanism and LEV-2, a baseball-sized, spherical rover. Both rovers are equipped with cameras and scientific payloads.

JAXA envisions that the success of the SLIM mission could pave the way for more cost-effective lunar exploration efforts in the future. The precision of landings achieved by SLIM enhances accessibility to scientifically significant areas, moving beyond general, safer landing zones.

With a dry mass of 200 kilograms and a wet mass at launch ranging between 700 and 730 kilograms, the development cost for SLIM was estimated at 18 billion yen ($120 million). As SLIM approaches this historic lunar landing, the mission stands as a testament to Japan's advancements in space exploration, technology, and its contributions to expanding humanity's understanding of the Moon.