Chang'e 4 (Yutu-2)

Von Kármán crater — the landing site

Von Kármán is a large, ancient impact crater approximately 186 km in diameter on the Moon's far side, centred near 44.5°S, 176.2°E. It lies within the South Pole–Aitken basin — roughly 2,500 km across and about 13 km deep — one of the largest and oldest impact structures in the Solar System, and it is classified as Pre-Nectarian, meaning it formed more than 3.92 billion years ago.

The crater's interior floor was flooded by mare basalt lava flows after the original impact, particularly in its southern portion, producing a nearly flat, low-albedo surface. A central peak marks the crater's approximate centre; spectral studies show it bears an olivine-bearing noritic gabbro composition, interpreted as originating from depths of approximately 18–30 km and suggesting excavation of deep crustal or upper mantle material. Such deep material inside the SPA basin helps test models of crustal thickness, mantle composition, and the distribution of KREEP-rich material that is more typical of the nearside.

Lunar Penetrating Radar data from Chang'e 4 revealed a complex subsurface stack beneath the landing site, including multiple Imbrian-age lava flow units, several paleoregolith horizons preserved between those flows, an Eratosthenian mare unit, pyroclastic deposits, and crater ejecta. These findings imply intermittent volcanic activity with thin lava flows of 2–10 m, showing that far-side lava flow processes can be similar in scale to nearside mare volcanism.

Queqiao relay satellite

Because the Moon permanently occludes direct radio communication between Earth and any spacecraft on its far side, CNSA launched the Queqiao relay satellite in May 2018. Queqiao was inserted into a halo orbit around the Earth–Moon L2 point on 14 June 2018, approximately 65,000 km from the Moon. This location provides simultaneous visibility of both Earth and the far-side landing site, enabling uninterrupted relay of commands and science data.

The spacecraft has a mass of approximately 325–425 kg and is based on the earlier Chang'e 2 bus. Its primary communications architecture uses a 4.2 m parabolic antenna directed at the lunar surface via X-band links to the lander and rover, with reported data rates from the lander to Queqiao of up to 555 kbit/s depending on mode, and commands downlinked to the surface at 125 bit/s. The relay link to Earth uses S-band at a maximum of approximately 4 Mbit/s.

Beyond its relay role, Queqiao carries the Netherlands–China Low-Frequency Explorer (NCLE), jointly developed with Radboud University, which conducts low-frequency radio astronomy in the range 80 kHz to 80 MHz from the radio-quiet environment near L2. This instrument works in synergy with the low-frequency radio spectrometer on the Chang'e 4 lander.

Queqiao exceeded its designed lifespan and has since been supplemented by Queqiao-2, a more capable relay satellite launched by China to continue supporting Chang'e 4 and to serve future far-side and lunar south-pole missions including Chang'e 6.

Yutu-2 rover — design and performance

Yutu-2 (Jade Rabbit-2) is a six-wheeled, solar-powered lunar rover with a mass of approximately 135 kg. It features high-performance off-road suspension and four steering motors for enhanced maneuverability on the uneven floor of Von Kármán crater. Two deployable solar arrays power the rover during lunar day; during lunar night it enters a dormant state maintained by internal heating.

Designed for a nominal lifetime of approximately three lunar months, Yutu-2 vastly exceeded this figure. By 19 September 2024 it had traversed approximately 1.613 km across the far side over more than 71 lunar days of activity — making it the longest-lived lunar rover in history, surpassing the previous record held by Lunokhod-1. Movement appeared to cease after March 2024, though the rover's instruments and systems were reported as still functioning during 2024.