Chang'e 4

Chang'e 4 is a robotic spacecraft mission, part of the Chinese Lunar Exploration Program, that achieved the first-ever soft landing on the far side of the Moon. Launched by the China National Space Administration on 7 December 2018, it consists of a stationary lander and the Yutu-2 rover. The mission's landing in the Von Kármán crater within the South Pole–Aitken basin has enabled unprecedented scientific exploration of a previously unvisited region, relying on the Queqiao relay satellite for communications with Earth.

Overview

The mission represents a major milestone in lunar exploration, building directly on the technologies demonstrated by its predecessor, Chang'e 3. The primary challenge of operating on the lunar far side, which never faces Earth, was solved by first deploying the Queqiao relay satellite to the Earth–Moon L2 point in May 2018. This allowed the China National Space Administration to maintain constant communication with the spacecraft. The successful landing demonstrated advanced capabilities in autonomous hazard avoidance and soft-landing technology, cementing China's position as a leading space power alongside entities like NASA and Roscosmos.

Mission objectives

The core objectives of Chang'e 4 are multifaceted, encompassing technical demonstration, scientific investigation, and international cooperation. A primary goal was to prove the feasibility of soft landing and roving on the topographically complex lunar far side. Scientifically, the mission aims to conduct low-frequency radio astronomy observations free from Earth's ionospheric interference, characterize the surface composition and subsurface structure of the South Pole–Aitken basin, and study the interaction between the solar wind and the lunar surface. The mission also carries a student-designed biological experiment to study germination in a low-gravity environment.

Spacecraft and payloads

The Chang'e 4 spacecraft inherits its basic design from Chang'e 3 but features several upgraded instruments. The lander is equipped with a Landing Camera, Terrain Camera, and the Low Frequency Spectrometer for astronomical observations. It also carries the German-built Lunar Lander Neutrons and Dosimetry experiment and the Sweden-developed Advanced Small Analyzer for Neutrals. The Yutu-2 rover carries the Panoramic Camera, the Visible and Near-Infrared Imaging Spectrometer, the Ground-Penetrating Radar, and the Neutral Atom Detector. The biological experiment, containing seeds of potato and Arabidopsis, as well as silkworm eggs, was a collaboration with 28 Chinese universities.

Landing site and operations

The selected landing site was the floor of the Von Kármán crater, approximately 180 kilometers in diameter, located within the immense and ancient South Pole–Aitken basin. This basin is of great scientific interest as a potential probe into the Moon's mantle and deep history. After landing on 3 January 2019, the rover deployed and began traversing the surface. Operations are conducted in lunar day periods, with the spacecraft entering hibernation during the frigid lunar night. The mission has far exceeded its planned lifespan, with Yutu-2 becoming the longest-operating lunar rover in history, exploring diverse features like a small crater and unusual "gel-like" materials.

Scientific results

Data returned by Chang'e 4 has yielded significant discoveries. The Visible and Near-Infrared Imaging Spectrometer on Yutu-2 detected materials likely originating from the lunar mantle, specifically olivine and low-calcium pyroxene, providing the first direct evidence supporting models of the Moon's internal structure. The Ground-Penetrating Radar revealed a detailed subsurface stratigraphy of ejected material, suggesting a complex geological history of multiple impacts. Measurements from the Lunar Lander Neutrons and Dosimetry instrument have provided crucial data on the radiation environment, important for future crewed missions. The low-frequency radio observations from the far side, a unique quiet zone, offer new insights into the early universe and solar activity.

Category:Chinese Lunar Exploration Program Category:Spacecraft launched in 2018 Category:Missions to the Moon Category:2018 in spaceflight